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2020 Volume 36 Issue 6
2020, 36(6): 190402
doi: 10.3866/PKU.WHXB201904027
Abstract:
Energy components used in solid rocket propellants are beneficial for improving the energy performance, and their thermal decomposition characteristics significantly affect the combustion properties of the propellants. As a kind of energetic material with both high energy and low sensitivity (impact and friction), 5, 5'-bistetrazole-1, 1'-diolate (TKX-50) can effectively improve the energy and safety characteristics of solid propellants. Burning catalyst is another important component of solid propellants, which can significantly improve the burning rate of the propellant and reduce the pressure exponent. Among various burning catalysts, nanoscale transition metal oxides can promote the thermal decomposition of the energetic component, thus enhancing the combustion properties of the solid propellant. However, the catalytic effects of nanoscale transition metal oxides with different morphologies on the thermal decomposition of TKX-50 have rarely been studied. Based on the excellent catalytic activity of Fe2O3 for TKX-50 thermal decomposition, nano-Fe2O3 particles with spherical and tubular microstructures were used for TKX-50 thermal decomposition. The Fe2O3 nanoparticles were successfully fabricated via the solvothermal method and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses. The XRD, FT-IR, and XPS results confirmed the successful fabrication of spherical and tubular Fe2O3 samples. The SEM and TEM images showed that the spherical Fe2O3 samples are composed of agglomerated Fe2O3 nanoparticles with an average particle size of 110 nm. In addition, the average diameter and length of hollow tubular Fe2O3 nanoparticles are 120 nm and 200 nm, respectively. The catalytic activities of spherical and tubular Fe2O3 for TKX-50 decomposition were studied by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) methods. The DSC and TG-DTG curves showed that both tubular and spherical Fe2O3 could effectively promote TKX-50 thermal decomposition. The first thermal decomposition peak temperature (TFDP) of TKX-50 was reduced by 36.5 K and 26.3 K in the presence of tubular and spherical Fe2O3, respectively, at 10 K·min−1. The activation energy (Ea) of TKX-50, determined by the iso-conversional method, was significantly reduced in the presence of both tubular and spherical Fe2O3. The results indicated that the microstructure of the catalyst has a significant effect on its catalytic performance for TKX-50 thermal decomposition, and that tubular Fe2O3 with hollow microstructure possesses better catalytic activity than spherical Fe2O3. The excellent catalytic activity of tubular Fe2O3 can be attributed to the hollow microstructure, which has more active sites for TKX-50 thermal decomposition. ![]()
Energy components used in solid rocket propellants are beneficial for improving the energy performance, and their thermal decomposition characteristics significantly affect the combustion properties of the propellants. As a kind of energetic material with both high energy and low sensitivity (impact and friction), 5, 5'-bistetrazole-1, 1'-diolate (TKX-50) can effectively improve the energy and safety characteristics of solid propellants. Burning catalyst is another important component of solid propellants, which can significantly improve the burning rate of the propellant and reduce the pressure exponent. Among various burning catalysts, nanoscale transition metal oxides can promote the thermal decomposition of the energetic component, thus enhancing the combustion properties of the solid propellant. However, the catalytic effects of nanoscale transition metal oxides with different morphologies on the thermal decomposition of TKX-50 have rarely been studied. Based on the excellent catalytic activity of Fe2O3 for TKX-50 thermal decomposition, nano-Fe2O3 particles with spherical and tubular microstructures were used for TKX-50 thermal decomposition. The Fe2O3 nanoparticles were successfully fabricated via the solvothermal method and characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and X-ray photoelectron spectroscopy (XPS) analyses. The XRD, FT-IR, and XPS results confirmed the successful fabrication of spherical and tubular Fe2O3 samples. The SEM and TEM images showed that the spherical Fe2O3 samples are composed of agglomerated Fe2O3 nanoparticles with an average particle size of 110 nm. In addition, the average diameter and length of hollow tubular Fe2O3 nanoparticles are 120 nm and 200 nm, respectively. The catalytic activities of spherical and tubular Fe2O3 for TKX-50 decomposition were studied by thermogravimetric analysis (TG) and differential scanning calorimetry (DSC) methods. The DSC and TG-DTG curves showed that both tubular and spherical Fe2O3 could effectively promote TKX-50 thermal decomposition. The first thermal decomposition peak temperature (TFDP) of TKX-50 was reduced by 36.5 K and 26.3 K in the presence of tubular and spherical Fe2O3, respectively, at 10 K·min−1. The activation energy (Ea) of TKX-50, determined by the iso-conversional method, was significantly reduced in the presence of both tubular and spherical Fe2O3. The results indicated that the microstructure of the catalyst has a significant effect on its catalytic performance for TKX-50 thermal decomposition, and that tubular Fe2O3 with hollow microstructure possesses better catalytic activity than spherical Fe2O3. The excellent catalytic activity of tubular Fe2O3 can be attributed to the hollow microstructure, which has more active sites for TKX-50 thermal decomposition.
2020, 36(6): 190504
doi: 10.3866/PKU.WHXB201905048
Abstract:
High-performance solid propellants are very important for the development of modern weapons. Aside from their high energy and high burning rate, safety performance is regarded as the most important factor that should be considered whenever a new solid propellant recipe is formulated. Therefore, exploring a new type of combustion catalyst that can improve both catalytic activity and reduce the sensitivity of the energetic component is significant. Traditionally, transition metals or metal oxides are used as a combustion catalyst for accelerating the thermal decomposition of energetic components. However, the existing problem of these catalysts is the aggregation of particles accompanied by poor surface area. Coupling metal oxides with graphene is a promising approach to obtain a binary composite with stable structure and large specific surface area. In this work, rod-like and granular Fe2O3 nanoparticles were synthesized using a hydrothermal method. Then, the two as-prepared Fe2O3 nanoparticles were coupled with graphene sheets using an interfacial self-assembly method, which can effectively prevent the aggregation of Fe2O3 particles and simultaneously increase the active sites that participate in the reaction. X-ray diffraction and X-ray photoelectron spectroscopy were used to identify the phase states and chemical compositions of the prepared samples. The morphology and internal structures were further demonstrated through scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption tests. Both phase analysis and structure identification indicate that the prepared Fe2O3/G has high purity and high surface area. The catalytic performance of the prepared Fe2O3 and Fe2O3/G in the thermal decomposition of hexanitrohexaazaisowurtzitane (CL-20) was evaluated based on thermal gravimetric analysis-infrared spectroscopy (TGA-IR) and differential scanning calorimetry (DSC) tests. The non-isothermal decomposition kinetics of CL-20, Fe2O3/CL-20, and Fe2O3/G/CL-20 were further studied by DSC. The results reveal the excellent catalytic activity of Fe2O3/G in the thermal decomposition of CL-20, which is attributed to the presence of abundant pore structure and large surface area. The reaction mechanisms of the exothermic decomposition process of CL-20, Fe2O3/CL-20, and Fe2O3/G/CL-20 were obtained by the logical choice method, and the composites all followed same mechanism function model as CL-20. Through comparison, the rod-like Fe2O3 coupled with graphene was found to have the best catalytic activity in the thermal decomposition of CL-20. Thus, the rod-like Fe2O3 and its Fe2O3/G composite were used to investigate their influence on the impact sensitivity of CL-20 by fall hammer apparatus. The results show that rFe2O3/G can effectively decrease the impact sensitivity of CL-20 compared with pure CL-20 and rFe2O3/CL-20. Therefore, rFe2O3 coupled with graphene not only promotes the thermal decomposition but also improves the safety performance of CL-20. ![]()
High-performance solid propellants are very important for the development of modern weapons. Aside from their high energy and high burning rate, safety performance is regarded as the most important factor that should be considered whenever a new solid propellant recipe is formulated. Therefore, exploring a new type of combustion catalyst that can improve both catalytic activity and reduce the sensitivity of the energetic component is significant. Traditionally, transition metals or metal oxides are used as a combustion catalyst for accelerating the thermal decomposition of energetic components. However, the existing problem of these catalysts is the aggregation of particles accompanied by poor surface area. Coupling metal oxides with graphene is a promising approach to obtain a binary composite with stable structure and large specific surface area. In this work, rod-like and granular Fe2O3 nanoparticles were synthesized using a hydrothermal method. Then, the two as-prepared Fe2O3 nanoparticles were coupled with graphene sheets using an interfacial self-assembly method, which can effectively prevent the aggregation of Fe2O3 particles and simultaneously increase the active sites that participate in the reaction. X-ray diffraction and X-ray photoelectron spectroscopy were used to identify the phase states and chemical compositions of the prepared samples. The morphology and internal structures were further demonstrated through scanning electron microscopy, transmission electron microscopy and nitrogen adsorption-desorption tests. Both phase analysis and structure identification indicate that the prepared Fe2O3/G has high purity and high surface area. The catalytic performance of the prepared Fe2O3 and Fe2O3/G in the thermal decomposition of hexanitrohexaazaisowurtzitane (CL-20) was evaluated based on thermal gravimetric analysis-infrared spectroscopy (TGA-IR) and differential scanning calorimetry (DSC) tests. The non-isothermal decomposition kinetics of CL-20, Fe2O3/CL-20, and Fe2O3/G/CL-20 were further studied by DSC. The results reveal the excellent catalytic activity of Fe2O3/G in the thermal decomposition of CL-20, which is attributed to the presence of abundant pore structure and large surface area. The reaction mechanisms of the exothermic decomposition process of CL-20, Fe2O3/CL-20, and Fe2O3/G/CL-20 were obtained by the logical choice method, and the composites all followed same mechanism function model as CL-20. Through comparison, the rod-like Fe2O3 coupled with graphene was found to have the best catalytic activity in the thermal decomposition of CL-20. Thus, the rod-like Fe2O3 and its Fe2O3/G composite were used to investigate their influence on the impact sensitivity of CL-20 by fall hammer apparatus. The results show that rFe2O3/G can effectively decrease the impact sensitivity of CL-20 compared with pure CL-20 and rFe2O3/CL-20. Therefore, rFe2O3 coupled with graphene not only promotes the thermal decomposition but also improves the safety performance of CL-20.
2020, 36(6): 190505
doi: 10.3866/PKU.WHXB201905052
Abstract:
Borate is considered one of the most important additives for improving the fire-resistance of combustible polymers because of its smoke suppression, low toxicity, and good thermal stability. However, the size of prepared borate is usually in the micrometer range, which makes it difficult to disperse in a polymer matrix, thus hindering its use as fire-retardant material. The preparation and application of borate nanomaterial as flame retardant is considered an effective method. However, the preparation of barium borate nanomaterials as flame retardant has not been reported. In this paper, nanosheets and nanoribbons with different sizes for a new barium borate BaO·4B2O3·5H2O are prepared by hydrothermal method, and characterized by X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), thermogravimetric analysis-differential scanning calorimetry (TG-DSC), and scanning electron microscope (SEM). The flame-retardant properties of polypropylene (PP)/BaO·4B2O3·5H2O composites are investigated by thermogravimetric analysis (TG), differential scanning calorimetry (DSC) thermal analysis methods and limited oxygen index (LOI) method. Considering the near TG mass losses and the near LOI values for PP with 10% prepared BaO·4B2O3·5H2O nanosheet and nanoribbon, their flame-retardant properties need to be further evaluated by non-isothermal decomposition kinetic method. The apparent activation energy for this decomposition reaction was obtained from the slope by plotting ln(β/Tp2) against 1/Tp according to Kissinger's model. With the reduction of TG mass loss, increased heat absorption in DSC under N2 atmosphere, increased apparent activation energy Ea for the thermal decomposition of PP/BaO·4B2O3·5H2O composite as well as increased LOI value, the flame-retardant performance of prepared BaO·4B2O3·5H2O samples with PP gradually improved from bulk to nanoribbon to nanosheet. This can be attributed to the decrease in the size of BaO·4B2O3·5H2O samples because the smaller sample size leads to improved dispersion and increased contact area with the polymer. The flame-retardant mechanism is discussed by analyzing the after-flame chars of the PP/BaO·4B2O3·5H2O composite in SEM images, which show that the char layer is more compact and continuous for the PP/BaO·4B2O3·5H2O nanosheet composite. The influence of loading BaO·4B2O3·5H2O nanomaterials on the mechanical properties of PP is also tested using a universal material testing machine, in which the PP/BaO·4B2O3·5H2O nanosheet composite has higher tensile strength. The PP/BaO·4B2O3·5H2O nanosheet composite has the best flame-retardant and mechanical properties, which is promising to be developed for the application as flame-retardant material.
Borate is considered one of the most important additives for improving the fire-resistance of combustible polymers because of its smoke suppression, low toxicity, and good thermal stability. However, the size of prepared borate is usually in the micrometer range, which makes it difficult to disperse in a polymer matrix, thus hindering its use as fire-retardant material. The preparation and application of borate nanomaterial as flame retardant is considered an effective method. However, the preparation of barium borate nanomaterials as flame retardant has not been reported. In this paper, nanosheets and nanoribbons with different sizes for a new barium borate BaO·4B2O3·5H2O are prepared by hydrothermal method, and characterized by X-ray diffraction (XRD), Fourier transform infrared spectrum (FT-IR), thermogravimetric analysis-differential scanning calorimetry (TG-DSC), and scanning electron microscope (SEM). The flame-retardant properties of polypropylene (PP)/BaO·4B2O3·5H2O composites are investigated by thermogravimetric analysis (TG), differential scanning calorimetry (DSC) thermal analysis methods and limited oxygen index (LOI) method. Considering the near TG mass losses and the near LOI values for PP with 10% prepared BaO·4B2O3·5H2O nanosheet and nanoribbon, their flame-retardant properties need to be further evaluated by non-isothermal decomposition kinetic method. The apparent activation energy for this decomposition reaction was obtained from the slope by plotting ln(β/Tp2) against 1/Tp according to Kissinger's model. With the reduction of TG mass loss, increased heat absorption in DSC under N2 atmosphere, increased apparent activation energy Ea for the thermal decomposition of PP/BaO·4B2O3·5H2O composite as well as increased LOI value, the flame-retardant performance of prepared BaO·4B2O3·5H2O samples with PP gradually improved from bulk to nanoribbon to nanosheet. This can be attributed to the decrease in the size of BaO·4B2O3·5H2O samples because the smaller sample size leads to improved dispersion and increased contact area with the polymer. The flame-retardant mechanism is discussed by analyzing the after-flame chars of the PP/BaO·4B2O3·5H2O composite in SEM images, which show that the char layer is more compact and continuous for the PP/BaO·4B2O3·5H2O nanosheet composite. The influence of loading BaO·4B2O3·5H2O nanomaterials on the mechanical properties of PP is also tested using a universal material testing machine, in which the PP/BaO·4B2O3·5H2O nanosheet composite has higher tensile strength. The PP/BaO·4B2O3·5H2O nanosheet composite has the best flame-retardant and mechanical properties, which is promising to be developed for the application as flame-retardant material.
2020, 36(6): 190508
doi: 10.3866/PKU.WHXB201905085
Abstract:
Solvent molecules can significantly reduce the heat of detonation and stability of energetic metal-organic framework (EMOF) materials, and the development of solvent-free EMOFs has become an effective strategy to prepare high-energy density materials. In this study, a solvent-free EMOF, [Ag2(DTPZ)]n (1) (N% = 32.58%), was synthesized by reacting a high-energy ligand, 2, 3-di(1H-tetrazol-5-yl)pyrazine (H2DTPZ), with silver ions under hydrothermal conditions, and it was structurally characterized by elemental analysis, infrared spectroscopy, X-ray diffraction, and thermal analysis. In 1, the DTPZ2− ligands that adopted a highly torsional configuration bridged the Ag+ ions in an octadentate coordination mode to form a three-dimensional framework (ρ = 2.812 g∙cm−3). The large steric effect and strong coordination ability of DTPZ2− effectively prevented the solvent molecules from binding with the metal centers or occupying the voids of 1. Moreover, the strong π-π stacking interactions [centroid-centroid distance = 0.34461(1) nm] between the tetrazole rings in different DTPZ2− ligands provided a high thermal stability to the framework (Te = 619.1 K, Tp = 658.7 K). Thermal analysis showed that a one-step rapid weight loss with intense heat release primarily occurred during the decomposition of 1, suggesting potential energetic characteristics. Non-isothermal thermokinetic analyses (based on the Kissinger and Ozawa-Doyle methods) were performed using differential scanning calorimetry to obtain the thermoanalysis kinetic parameters of the thermodecomposition of 1 (Ea = 272.1 kJ·mol−1, Eo = 268.9 kJ·mol−1; lgA =19.67 s−1). The related thermodynamic parameters [enthalpy of activation (ΔH≠ = 266.9 kJ·mol−1), entropy of activation (ΔS≠ = 125.4 J·mol−1·K−1), free energy of activation (ΔG≠ = 188.3 kJ·mol−1)], critical temperature of thermal explosion (Tb = 607.1 K), and self-accelerating decomposition temperature (TSADT = 595.8 K) of the decomposition reaction were also calculated based on the decomposition peak temperature and extrapolated onset temperature when the heating rate approached zero. The results revealed that 1 featured good thermal safety, and its decomposition was a non-spontaneous entropy-driven process. The standard molar enthalpy for the formation of 1 was calculated to be (2165.99 ± 0.81) kJ·mol−1 based on its constant volume combustion energy determined using a precise rotating oxygen bomb calorimeter. Detonation and safety performance tests revealed that 1 was insensitive to impact and friction, and its heat of detonation (10.15 kJ·g−1) was higher than that of common ammonium nitrate explosives, such as octogen (HMX), hexogene (RDX), and 2, 4, 6-trinitrotoluene (TNT), indicating that 1 is a promising high-energy and insensitive material. ![]()
Solvent molecules can significantly reduce the heat of detonation and stability of energetic metal-organic framework (EMOF) materials, and the development of solvent-free EMOFs has become an effective strategy to prepare high-energy density materials. In this study, a solvent-free EMOF, [Ag2(DTPZ)]n (1) (N% = 32.58%), was synthesized by reacting a high-energy ligand, 2, 3-di(1H-tetrazol-5-yl)pyrazine (H2DTPZ), with silver ions under hydrothermal conditions, and it was structurally characterized by elemental analysis, infrared spectroscopy, X-ray diffraction, and thermal analysis. In 1, the DTPZ2− ligands that adopted a highly torsional configuration bridged the Ag+ ions in an octadentate coordination mode to form a three-dimensional framework (ρ = 2.812 g∙cm−3). The large steric effect and strong coordination ability of DTPZ2− effectively prevented the solvent molecules from binding with the metal centers or occupying the voids of 1. Moreover, the strong π-π stacking interactions [centroid-centroid distance = 0.34461(1) nm] between the tetrazole rings in different DTPZ2− ligands provided a high thermal stability to the framework (Te = 619.1 K, Tp = 658.7 K). Thermal analysis showed that a one-step rapid weight loss with intense heat release primarily occurred during the decomposition of 1, suggesting potential energetic characteristics. Non-isothermal thermokinetic analyses (based on the Kissinger and Ozawa-Doyle methods) were performed using differential scanning calorimetry to obtain the thermoanalysis kinetic parameters of the thermodecomposition of 1 (Ea = 272.1 kJ·mol−1, Eo = 268.9 kJ·mol−1; lgA =19.67 s−1). The related thermodynamic parameters [enthalpy of activation (ΔH≠ = 266.9 kJ·mol−1), entropy of activation (ΔS≠ = 125.4 J·mol−1·K−1), free energy of activation (ΔG≠ = 188.3 kJ·mol−1)], critical temperature of thermal explosion (Tb = 607.1 K), and self-accelerating decomposition temperature (TSADT = 595.8 K) of the decomposition reaction were also calculated based on the decomposition peak temperature and extrapolated onset temperature when the heating rate approached zero. The results revealed that 1 featured good thermal safety, and its decomposition was a non-spontaneous entropy-driven process. The standard molar enthalpy for the formation of 1 was calculated to be (2165.99 ± 0.81) kJ·mol−1 based on its constant volume combustion energy determined using a precise rotating oxygen bomb calorimeter. Detonation and safety performance tests revealed that 1 was insensitive to impact and friction, and its heat of detonation (10.15 kJ·g−1) was higher than that of common ammonium nitrate explosives, such as octogen (HMX), hexogene (RDX), and 2, 4, 6-trinitrotoluene (TNT), indicating that 1 is a promising high-energy and insensitive material.
2020, 36(6): 190505
doi: 10.3866/PKU.WHXB201905051
Abstract:
Biological systems can be regarded as complex and open thermodynamic systems. All processes involved in biological growth and metabolism are accompanied by material and energy exchange. During metabolism, energy in the organisms is released in the form of heat, i.e., metabolic heat, which is the basis for development in the field of biothermochemistry. The calorimetric method considers the thermal effects produced by the various forms of action as the research object, to reveal the law of energy change and quantitative energy conversion. Studying the thermodynamic processes of complex biological systems and related reactions through microcalorimetry and thermodynamic methods reflects the intrinsic laws of life-related processes macroscopically and intrinsically. With the tremendous development and progress in microcalorimetry in terms of the temperature measurement accuracy, stability of temperature control, automation, and multi-functionalization, calorimetry has been widely used in life sciences. It can be used to describe macroscopic processes such as ecosystems and biological evolution, observe organismal and cell growth, examine mitochondrial metabolism, and study problems at the molecular level, including enzymatic reactions and interactions between small molecules and biomacromolecules. Herein, the application of biomass calorimetry in the life sciences is reviewed. The status and progress of biomass calorimetry at different biological and structural levels, such as the ecosystem, biological, organ, cellular, subcellular, and molecular levels are introduced. For example, soil microbial metabolic activity is a universal index for evaluating soil quality. The growth and metabolism of organisms as well as the physical and chemical processes of substances in soil are often accompanied by heat release, which is usually a nonselective signal. The use of isothermal microcalorimetry to nonspecifically monitor and record soil microbial metabolic characteristics has promoted the study of microbial metabolism in complex soil systems. The application of calorimetry to the study of tissues and organs mainly involves the calorimetric study of isolated animal and plant tissues and organs. Calorimetry of animal and microbial cells is considered the most common application of calorimetry in life sciences research. It mainly involves the classification and identification of bacteria, their growth and metabolism, inhibition mechanisms of drugs on microbial growth, principles of kinetics, and the thermodynamic characteristics of microbial growth and metabolism. However, owing to the lack of specificity of biomass calorimetry and the lack of direct access to information at the molecular level, more applications of calorimetry combined with other analytical techniques (especially in biology, medicine, and pharmacy) are needed in the future. ![]()
Biological systems can be regarded as complex and open thermodynamic systems. All processes involved in biological growth and metabolism are accompanied by material and energy exchange. During metabolism, energy in the organisms is released in the form of heat, i.e., metabolic heat, which is the basis for development in the field of biothermochemistry. The calorimetric method considers the thermal effects produced by the various forms of action as the research object, to reveal the law of energy change and quantitative energy conversion. Studying the thermodynamic processes of complex biological systems and related reactions through microcalorimetry and thermodynamic methods reflects the intrinsic laws of life-related processes macroscopically and intrinsically. With the tremendous development and progress in microcalorimetry in terms of the temperature measurement accuracy, stability of temperature control, automation, and multi-functionalization, calorimetry has been widely used in life sciences. It can be used to describe macroscopic processes such as ecosystems and biological evolution, observe organismal and cell growth, examine mitochondrial metabolism, and study problems at the molecular level, including enzymatic reactions and interactions between small molecules and biomacromolecules. Herein, the application of biomass calorimetry in the life sciences is reviewed. The status and progress of biomass calorimetry at different biological and structural levels, such as the ecosystem, biological, organ, cellular, subcellular, and molecular levels are introduced. For example, soil microbial metabolic activity is a universal index for evaluating soil quality. The growth and metabolism of organisms as well as the physical and chemical processes of substances in soil are often accompanied by heat release, which is usually a nonselective signal. The use of isothermal microcalorimetry to nonspecifically monitor and record soil microbial metabolic characteristics has promoted the study of microbial metabolism in complex soil systems. The application of calorimetry to the study of tissues and organs mainly involves the calorimetric study of isolated animal and plant tissues and organs. Calorimetry of animal and microbial cells is considered the most common application of calorimetry in life sciences research. It mainly involves the classification and identification of bacteria, their growth and metabolism, inhibition mechanisms of drugs on microbial growth, principles of kinetics, and the thermodynamic characteristics of microbial growth and metabolism. However, owing to the lack of specificity of biomass calorimetry and the lack of direct access to information at the molecular level, more applications of calorimetry combined with other analytical techniques (especially in biology, medicine, and pharmacy) are needed in the future.
2020, 36(6): 190506
doi: 10.3866/PKU.WHXB201905062
Abstract:
Thermal analysis (TA) is a technology that can be applied to evaluate the relationship between the physical properties of substances and temperature changes under programmed temperature control. It has been widely used in many fields and is particularly useful for determining the thermal stability and service life of polymers and other materials, the stability of drugs, and the danger of flammable and explosive materials. Simultaneously, the mechanism of dehydration, decomposition, and degradation of inorganic materials or dissociation of complexes can be studied and the decomposition rates of environmental pollutants can be estimated. Recently, TA kinetics has become the most extensively studied topic in TA research. The main purpose of kinetic analysis is to obtain the three kinetic triplets of a reaction process, namely, activation energy Ea, pre-exponential factors A, and and mechanism function f(a). For a solid-state reaction, many mathematical models and corresponding data processing methods can be used for the study of TA kinetics. These methods can be classified as either isothermal or non-isothermal methods and further divided into integral and differential methods in the form of the kinetic equation. These equations can be divided into a single scanning rate and multiple scanning rate methods (isoconversion method) by the operation method. The isoconversion method can calculate activation energies without the mechanism function, and the complexity of the reaction can be determined by the change in activation energy as a function of conversion rate. Therefore, the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommends the isoconversion method for processing TA data. Because of the limitation of traditional isoconversion methods, novel isoconversion methods have been proposed over the past 10 years. The relationship among the existing dynamic analysis methods must be complementary, instead of competitive, because the reliability of the analysis results can be improved only through complementarity. Further efforts to popularize modern integral and differential methods with equal conversion rates are essential. Herein, the progress in isoconversion method development is briefly introduced. A novel kinetic equation and seven new isoconversion methods are reviewed, and the characteristics and limitations of these methods are discussed. In addition, the development trends and prospects of TA kinetics research methods are highlighted. We suggest that the Arrhenius formula should be modified on the basis of the relationship between the rate constant and temperature. The rate equation that is more suitable for non-isothermal and heterogeneous reactions should be used. The mechanism of multi-step solid-state reactions should be studied in depth, and unified standards must be adopted for the study of thermal decomposition kinetics. This represents imminent and important progress in the study of TA kinetics. ![]()
Thermal analysis (TA) is a technology that can be applied to evaluate the relationship between the physical properties of substances and temperature changes under programmed temperature control. It has been widely used in many fields and is particularly useful for determining the thermal stability and service life of polymers and other materials, the stability of drugs, and the danger of flammable and explosive materials. Simultaneously, the mechanism of dehydration, decomposition, and degradation of inorganic materials or dissociation of complexes can be studied and the decomposition rates of environmental pollutants can be estimated. Recently, TA kinetics has become the most extensively studied topic in TA research. The main purpose of kinetic analysis is to obtain the three kinetic triplets of a reaction process, namely, activation energy Ea, pre-exponential factors A, and and mechanism function f(a). For a solid-state reaction, many mathematical models and corresponding data processing methods can be used for the study of TA kinetics. These methods can be classified as either isothermal or non-isothermal methods and further divided into integral and differential methods in the form of the kinetic equation. These equations can be divided into a single scanning rate and multiple scanning rate methods (isoconversion method) by the operation method. The isoconversion method can calculate activation energies without the mechanism function, and the complexity of the reaction can be determined by the change in activation energy as a function of conversion rate. Therefore, the International Confederation for Thermal Analysis and Calorimetry (ICTAC) recommends the isoconversion method for processing TA data. Because of the limitation of traditional isoconversion methods, novel isoconversion methods have been proposed over the past 10 years. The relationship among the existing dynamic analysis methods must be complementary, instead of competitive, because the reliability of the analysis results can be improved only through complementarity. Further efforts to popularize modern integral and differential methods with equal conversion rates are essential. Herein, the progress in isoconversion method development is briefly introduced. A novel kinetic equation and seven new isoconversion methods are reviewed, and the characteristics and limitations of these methods are discussed. In addition, the development trends and prospects of TA kinetics research methods are highlighted. We suggest that the Arrhenius formula should be modified on the basis of the relationship between the rate constant and temperature. The rate equation that is more suitable for non-isothermal and heterogeneous reactions should be used. The mechanism of multi-step solid-state reactions should be studied in depth, and unified standards must be adopted for the study of thermal decomposition kinetics. This represents imminent and important progress in the study of TA kinetics.
2020, 36(6): 190508
doi: 10.3866/PKU.WHXB201905081
Abstract:
Biological systems can be regarded as complex and open thermodynamic systems. All processes involved in biological growth and metabolism are accompanied by material and energy exchange. During metabolism, energy in the organisms is released in the form of heat, i.e., metabolic heat, which is the basis for development in the field of biothermochemistry. The calorimetric method considers the thermal effects produced by the various forms of action as the research object, to reveal the law of energy change and quantitative energy conversion. Studying the thermodynamic processes of complex biological systems and related reactions through microcalorimetry and thermodynamic methods reflects the intrinsic laws of life-related processes macroscopically and intrinsically. With the tremendous development and progress in microcalorimetry in terms of the temperature measurement accuracy, stability of temperature control, automation, and multi-functionalization, calorimetry has been widely used in life sciences. It can be used to describe macroscopic processes such as ecosystems and biological evolution, observe organismal and cell growth, examine mitochondrial metabolism, and study problems at the molecular level, including enzymatic reactions and interactions between small molecules and biomacromolecules. Herein, the application of biomass calorimetry in the life sciences is reviewed. The status and progress of biomass calorimetry at different biological and structural levels, such as the ecosystem, biological, organ, cellular, subcellular, and molecular levels are introduced. For example, soil microbial metabolic activity is a universal index for evaluating soil quality. The growth and metabolism of organisms as well as the physical and chemical processes of substances in soil are often accompanied by heat release, which is usually a non-selective signal. The use of isothermal microcalorimetry to nonspecifically monitor and record soil microbial metabolic characteristics has promoted the study of microbial metabolism in complex soil systems. The application of calorimetry to the study of tissues and organs mainly involves the calorimetric study of isolated animal and plant tissues and organs. Calorimetry of animal and microbial cells is considered the most common application of calorimetry in life sciences research. It mainly involves the classification and identification of bacteria, their growth and metabolism, inhibition mechanisms of drugs on microbial growth, principles of kinetics, and the thermodynamic characteristics of microbial growth and metabolism. However, owing to the lack of specificity of biomass calorimetry and the lack of direct access to information at the molecular level, more applications of calorimetry combined with other analytical techniques (especially in biology, medicine, and pharmacy) are needed in the future. ![]()
Biological systems can be regarded as complex and open thermodynamic systems. All processes involved in biological growth and metabolism are accompanied by material and energy exchange. During metabolism, energy in the organisms is released in the form of heat, i.e., metabolic heat, which is the basis for development in the field of biothermochemistry. The calorimetric method considers the thermal effects produced by the various forms of action as the research object, to reveal the law of energy change and quantitative energy conversion. Studying the thermodynamic processes of complex biological systems and related reactions through microcalorimetry and thermodynamic methods reflects the intrinsic laws of life-related processes macroscopically and intrinsically. With the tremendous development and progress in microcalorimetry in terms of the temperature measurement accuracy, stability of temperature control, automation, and multi-functionalization, calorimetry has been widely used in life sciences. It can be used to describe macroscopic processes such as ecosystems and biological evolution, observe organismal and cell growth, examine mitochondrial metabolism, and study problems at the molecular level, including enzymatic reactions and interactions between small molecules and biomacromolecules. Herein, the application of biomass calorimetry in the life sciences is reviewed. The status and progress of biomass calorimetry at different biological and structural levels, such as the ecosystem, biological, organ, cellular, subcellular, and molecular levels are introduced. For example, soil microbial metabolic activity is a universal index for evaluating soil quality. The growth and metabolism of organisms as well as the physical and chemical processes of substances in soil are often accompanied by heat release, which is usually a non-selective signal. The use of isothermal microcalorimetry to nonspecifically monitor and record soil microbial metabolic characteristics has promoted the study of microbial metabolism in complex soil systems. The application of calorimetry to the study of tissues and organs mainly involves the calorimetric study of isolated animal and plant tissues and organs. Calorimetry of animal and microbial cells is considered the most common application of calorimetry in life sciences research. It mainly involves the classification and identification of bacteria, their growth and metabolism, inhibition mechanisms of drugs on microbial growth, principles of kinetics, and the thermodynamic characteristics of microbial growth and metabolism. However, owing to the lack of specificity of biomass calorimetry and the lack of direct access to information at the molecular level, more applications of calorimetry combined with other analytical techniques (especially in biology, medicine, and pharmacy) are needed in the future.
2020, 36(6): 190508
doi: 10.3866/PKU.WHXB201905087
Abstract:
The thermodynamics and kinetics of photocatalytic processes provide the scientific foundation for the optimization of reaction conditions and establishment of reaction mechanisms. Because of the limited availability of techniques that can provide in situ thermodynamics coupled with spectral information during photo-driven processes, research regarding the thermodynamics of the photo-driven processes is rare and in-depth studies on their kinetics remain inadequate. Herein, a novel photocalorimetry-fluorescence spectroscopy system composed of a photocalorimeter and laser-induced fluorescence spectrometer based on a 405 nm laser was developed. This system could simultaneously monitor the thermal and spectral information during photocatalytic processes, providing a correlation between nonspecific thermodynamic and specific molecular fluorescence spectral results. A highly efficient, bionic Z-type g-C3N4@Ag@Ag3PO4 nano-composite photocatalyst was developed and characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In situ thermodynamic and spectral kinetic information for Rhodamine B (RhB) degradation on g-C3N4@Ag@Ag3PO4 was obtained at five temperatures by synchronously monitoring the calorimetric and spectrometric results using the newly developed photocalorimetry-fluorescence spectroscopy system and the effects of temperature on various parameters were investigated. The catalytic decomposition comprised three stages at different temperatures: (ⅰ) photoresponse of RhB and photocatalyst, (ⅱ) competition between the endothermic photoresponse and exothermic RhB photodegradation, and (ⅲ) stable exothermic period of RhB photodegradation. The in situ heat flux and fluorescence spectra could be combined to estimate the concentration characteristics of the different photocatalytic reactions: (1) the spectral information suggested that the competitive endothermic and exothermic reactions followed first order kinetics, and the reaction rate constants (k) at five temperatures were calculated. The results also indicated that the degradation rate increased with increasing temperature. The activation energy at each temperature interval was determined, and yielded an average value of 23.82 kJ·mol−1. (2) The calorimetric results revealed that the subsequent stable exothermic period was a pseudo-zero-order process. The exothermic rates at 283.15, 288.15, 293.15, 298.15, and 303.15 K were determined to be 0.4668 ± 0.3875, 0.5314 ± 0.3379, 0.5064 ± 0.3234, 0.5328 ± 0.3377, and 0.5762 ± 0.3452 μJ·s−1, respectively. The novel photocalorimetry-fluorescence spectroscopy technique could concurrently obtain thermodynamic, thermo-kinetic, and molecular spectral information, allowing for the direct correlation of the thermodynamics, thermo-kinetics, and spectrokinetics with the underlying mechanisms of the reaction. This in situ technique integrated the thermal information with spectral information for improved understanding of the microscopic mechanisms of photo-driven processes, providing scientific support for the establishment of photothermal spectroscopy. ![]()
The thermodynamics and kinetics of photocatalytic processes provide the scientific foundation for the optimization of reaction conditions and establishment of reaction mechanisms. Because of the limited availability of techniques that can provide in situ thermodynamics coupled with spectral information during photo-driven processes, research regarding the thermodynamics of the photo-driven processes is rare and in-depth studies on their kinetics remain inadequate. Herein, a novel photocalorimetry-fluorescence spectroscopy system composed of a photocalorimeter and laser-induced fluorescence spectrometer based on a 405 nm laser was developed. This system could simultaneously monitor the thermal and spectral information during photocatalytic processes, providing a correlation between nonspecific thermodynamic and specific molecular fluorescence spectral results. A highly efficient, bionic Z-type g-C3N4@Ag@Ag3PO4 nano-composite photocatalyst was developed and characterized by field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In situ thermodynamic and spectral kinetic information for Rhodamine B (RhB) degradation on g-C3N4@Ag@Ag3PO4 was obtained at five temperatures by synchronously monitoring the calorimetric and spectrometric results using the newly developed photocalorimetry-fluorescence spectroscopy system and the effects of temperature on various parameters were investigated. The catalytic decomposition comprised three stages at different temperatures: (ⅰ) photoresponse of RhB and photocatalyst, (ⅱ) competition between the endothermic photoresponse and exothermic RhB photodegradation, and (ⅲ) stable exothermic period of RhB photodegradation. The in situ heat flux and fluorescence spectra could be combined to estimate the concentration characteristics of the different photocatalytic reactions: (1) the spectral information suggested that the competitive endothermic and exothermic reactions followed first order kinetics, and the reaction rate constants (k) at five temperatures were calculated. The results also indicated that the degradation rate increased with increasing temperature. The activation energy at each temperature interval was determined, and yielded an average value of 23.82 kJ·mol−1. (2) The calorimetric results revealed that the subsequent stable exothermic period was a pseudo-zero-order process. The exothermic rates at 283.15, 288.15, 293.15, 298.15, and 303.15 K were determined to be 0.4668 ± 0.3875, 0.5314 ± 0.3379, 0.5064 ± 0.3234, 0.5328 ± 0.3377, and 0.5762 ± 0.3452 μJ·s−1, respectively. The novel photocalorimetry-fluorescence spectroscopy technique could concurrently obtain thermodynamic, thermo-kinetic, and molecular spectral information, allowing for the direct correlation of the thermodynamics, thermo-kinetics, and spectrokinetics with the underlying mechanisms of the reaction. This in situ technique integrated the thermal information with spectral information for improved understanding of the microscopic mechanisms of photo-driven processes, providing scientific support for the establishment of photothermal spectroscopy.
2020, 36(6): 190509
doi: 10.3866/PKU.WHXB201905090
Abstract:
Resveratrol is a natural polyphenol and phytoalexin with anti-inflammatory, anti-oxidant, anti-cancer, and neuroprotective effects. However, resveratrol exhibits low solubility, light sensitivity, poor absorption by oral administration, and short cycle time, which greatly limit its applications in medicine and the food industry. To overcome these limitations, a nano-resveratrol liposome (RES-Lip) was prepared. As a drug carrier, liposomes have many advantages such as good targeting properties, low toxicity, biocompatibility, and long-term sustained release. In liposomal studies, the oil-water (n-octanol-water) partition coefficient (Po/w) is often used to predict the encapsulation and drug loading efficiencies. This method focuses on the lipophilicity of the drug, reflecting its hydrophobic action while ignoring the biological properties of the biofilm. The liposome-water partition coefficient (Plip/w) reflects the structure of the biofilms and its interaction with drugs governed by factors including hydrophobicity, electrostatic forces, and hydrogen bonding. Herein, RES-Lip was successfully prepared using a rotary-evaporated film-ultrasonication method and subsequent characterization by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The effects of the membrane to material ratio (lecithin to cholesterol mass ratio mPC : mChol = 5 : 1, 8 : 1, 10 : 1, and 12 : 1) and drug to lipid ratio (drug to lecithin mass ratio mRES : mPC = 1 : 25, 1 : 40, 1 : 50, and 1 : 60) of nano-resveratrol liposomes on the liposome-water partition coefficient (Plip/w) were determined. Changes in the oil-water partition coefficient (lgPo/w) and liposome-water partition coefficient (lgPlip/w) as a function of pH were also determined. In addition, the Gibbs free energy between the drug and phospholipid bilayer membrane in RES-Lip was calculated. The results showed that RES-Lip adopted a spherical vesicle structure with a particle size of approximately 100 nm. When the membrane to material ratio was 10 : 1 and the drug to lipid ratio was 1 : 40, lgPlip/w was maximized, indicating that the combined forces between RES and the phospholipid membrane were the highest at these ratios. The trends of lgPo/w and lgPlip/w as a function of pH were the same, indicating that the main interaction force between RES and the phospholipid membrane was the hydrophobic effect with secondary interaction forces of hydrogen bonding and electrostatic interaction. The Gibbs free energy between the RES and liposome membrane in RES-Lip was determined to be −17.07 kJ·mol−1. ![]()
Resveratrol is a natural polyphenol and phytoalexin with anti-inflammatory, anti-oxidant, anti-cancer, and neuroprotective effects. However, resveratrol exhibits low solubility, light sensitivity, poor absorption by oral administration, and short cycle time, which greatly limit its applications in medicine and the food industry. To overcome these limitations, a nano-resveratrol liposome (RES-Lip) was prepared. As a drug carrier, liposomes have many advantages such as good targeting properties, low toxicity, biocompatibility, and long-term sustained release. In liposomal studies, the oil-water (n-octanol-water) partition coefficient (Po/w) is often used to predict the encapsulation and drug loading efficiencies. This method focuses on the lipophilicity of the drug, reflecting its hydrophobic action while ignoring the biological properties of the biofilm. The liposome-water partition coefficient (Plip/w) reflects the structure of the biofilms and its interaction with drugs governed by factors including hydrophobicity, electrostatic forces, and hydrogen bonding. Herein, RES-Lip was successfully prepared using a rotary-evaporated film-ultrasonication method and subsequent characterization by transmission electron microscopy (TEM) and dynamic light scattering (DLS). The effects of the membrane to material ratio (lecithin to cholesterol mass ratio mPC : mChol = 5 : 1, 8 : 1, 10 : 1, and 12 : 1) and drug to lipid ratio (drug to lecithin mass ratio mRES : mPC = 1 : 25, 1 : 40, 1 : 50, and 1 : 60) of nano-resveratrol liposomes on the liposome-water partition coefficient (Plip/w) were determined. Changes in the oil-water partition coefficient (lgPo/w) and liposome-water partition coefficient (lgPlip/w) as a function of pH were also determined. In addition, the Gibbs free energy between the drug and phospholipid bilayer membrane in RES-Lip was calculated. The results showed that RES-Lip adopted a spherical vesicle structure with a particle size of approximately 100 nm. When the membrane to material ratio was 10 : 1 and the drug to lipid ratio was 1 : 40, lgPlip/w was maximized, indicating that the combined forces between RES and the phospholipid membrane were the highest at these ratios. The trends of lgPo/w and lgPlip/w as a function of pH were the same, indicating that the main interaction force between RES and the phospholipid membrane was the hydrophobic effect with secondary interaction forces of hydrogen bonding and electrostatic interaction. The Gibbs free energy between the RES and liposome membrane in RES-Lip was determined to be −17.07 kJ·mol−1.
2020, 36(6): 190600
doi: 10.3866/PKU.WHXB201906006
Abstract:
The micelles of zwitterionic betaine surfactant, SB3-12, have good biocompatibility and smaller negative charge density on the surface due to the electrostatic neutralization on the polar head that consists of two opposite charges. However, the available charge density on the micellar surface is essential for its application as a drug carrier owing to either the increased binding to cells or its favorable delivery into some specific organs under physiological conditions. This also facilitates the selective solubilization of drug molecules, depending on the interaction between the surfactant headgroup and drug molecule. When an anionic sodium dodecyl sulfate (SDS) is incorporated into SB3-12 micelles, the negative charge density of the micellar surface (from the sulfonic groups) can be continuously adjusted with a negative-positive order of the zwitterionic headgroup, where the electrostatic interaction occurs with the positively charged quaternary ammonium in the inner layer of the micellar polar region. Accordingly, positive micelles with adjustable charge density could be obtained if a cationic surfactant is incorporated into the micelles of the zwitterionic surfactant with a positive-negative headgroup. Using isothermal titration calorimetry, it is determined that a strong synergistic interaction occurs between SB3-12 and SDS, followed by a significant decrease in the mixed critical micelle concentration (CMC) and micellization enthalpy, which is mainly caused by weak electrostatic interaction. The synergistic effect is similar to that in the case of oppositely charged surfactant mixtures; however, the mixtures of zwitterionic and ionic surfactants do not form catanionic precipitates even at an equimolar ratio. When rutin, a model drug, is added to the SB3-12/SDS solution mixture, both SDS and the negatively charged rutin, obtained from the dissociation of the hydrogen of 7-hydroxyl group of rutin, can together interact with SB3-12 forming mixed micelles. The dissolved rutin molecules do not change the mixed CMC and the solubility of rutin is approximately constant when the composition of the mixed surfactants is in the range of 0.5 < xSB3-12 < 1; however, these can significantly enhance the electrostatic interaction between the mixed micelle and rutin molecule as xSB3-12 decreases. This can possibly allow the controlled release of rutin. UV-visible absorption spectroscopy and 1H NMR spectroscopy reveal that in SB3-12 micelles, the A ring of rutin is located near the positively charged quaternary ammonium group of SB3-12, and the B ring is located between the oppositely charged headgroups of SB3-12. In SDS micelles, the B ring is located on the palisade layer and the A ring and disaccharide are exposed to the aqueous phase. For the mixed SB3-12/SDS micelles, as the molar fraction of SDS increases, the electrostatic attraction toward the A ring weakens. The role of ionic surfactant in adjusting the surface charge density of the zwitterionic surfactant micelles allows the fine-tuning of the physical and chemical properties of polar micellar region, thereby exhibiting the potential for selective solubilization and controlled release of drugs. ![]()
The micelles of zwitterionic betaine surfactant, SB3-12, have good biocompatibility and smaller negative charge density on the surface due to the electrostatic neutralization on the polar head that consists of two opposite charges. However, the available charge density on the micellar surface is essential for its application as a drug carrier owing to either the increased binding to cells or its favorable delivery into some specific organs under physiological conditions. This also facilitates the selective solubilization of drug molecules, depending on the interaction between the surfactant headgroup and drug molecule. When an anionic sodium dodecyl sulfate (SDS) is incorporated into SB3-12 micelles, the negative charge density of the micellar surface (from the sulfonic groups) can be continuously adjusted with a negative-positive order of the zwitterionic headgroup, where the electrostatic interaction occurs with the positively charged quaternary ammonium in the inner layer of the micellar polar region. Accordingly, positive micelles with adjustable charge density could be obtained if a cationic surfactant is incorporated into the micelles of the zwitterionic surfactant with a positive-negative headgroup. Using isothermal titration calorimetry, it is determined that a strong synergistic interaction occurs between SB3-12 and SDS, followed by a significant decrease in the mixed critical micelle concentration (CMC) and micellization enthalpy, which is mainly caused by weak electrostatic interaction. The synergistic effect is similar to that in the case of oppositely charged surfactant mixtures; however, the mixtures of zwitterionic and ionic surfactants do not form catanionic precipitates even at an equimolar ratio. When rutin, a model drug, is added to the SB3-12/SDS solution mixture, both SDS and the negatively charged rutin, obtained from the dissociation of the hydrogen of 7-hydroxyl group of rutin, can together interact with SB3-12 forming mixed micelles. The dissolved rutin molecules do not change the mixed CMC and the solubility of rutin is approximately constant when the composition of the mixed surfactants is in the range of 0.5 < xSB3-12 < 1; however, these can significantly enhance the electrostatic interaction between the mixed micelle and rutin molecule as xSB3-12 decreases. This can possibly allow the controlled release of rutin. UV-visible absorption spectroscopy and 1H NMR spectroscopy reveal that in SB3-12 micelles, the A ring of rutin is located near the positively charged quaternary ammonium group of SB3-12, and the B ring is located between the oppositely charged headgroups of SB3-12. In SDS micelles, the B ring is located on the palisade layer and the A ring and disaccharide are exposed to the aqueous phase. For the mixed SB3-12/SDS micelles, as the molar fraction of SDS increases, the electrostatic attraction toward the A ring weakens. The role of ionic surfactant in adjusting the surface charge density of the zwitterionic surfactant micelles allows the fine-tuning of the physical and chemical properties of polar micellar region, thereby exhibiting the potential for selective solubilization and controlled release of drugs.
2020, 36(6): 190702
doi: 10.3866/PKU.WHXB201907020
Abstract:
2020, 36(6): 190704
doi: 10.3866/PKU.WHXB201907048
Abstract:
2020, 36(6): 190902
doi: 10.3866/PKU.WHXB201909020
Abstract:
