Interfacial Confinement in Semi-Crystalline Shape Memory Polymer Towards Sequentially Dynamic Relaxations

Sequential glass and melting transitions in semi-crystalline shape memory polymers (SMPs) provide great opportunities to design and generate multiple shape-memory effects (SMEs) for practical applications. However, the complexly dynamic confinements of coexisting amorphous and crystalline phases within the semi-crystalline SMPs are yet fully understood. In this study, an interfacial confinement model is formulated to describe dynamic relaxation and shape memory behavior in the semi-crystalline SMPs undergoing sequential phase/state transitions. A confinement entropy model is first established to describe the glass transition behavior of amorphous phase within the SMPs based on the free volume theory, where the free volume is critically confined by the crystalline phase. An extended Avrami model is then formulated using the frozen volume theory to characterize the melting and crystallization transitions of the crystalline phase in the SMPs, whose interfacial confinement with the amorphous phase has been identified as the driving force for the supercooled regime. Furthermore, an extended Maxwell model is formulated to describe the effect of dynamic confinement of two phases on the multiple SMEs and shape recovery behaviors in the semi-crystalline SMPs. Finally, the effectiveness of the newly proposed model is verified using the experimental data reported in the literature. This study aims to provide a new methodology for the dynamic confinements and cooperative principles in the semi-crystalline SMP towards multiple SMEs.

Viscosity model of deep eutectic solvents from group contribution method

In this work, based on mathematical model inspired by transition state theory, the group contribution (GC) method is used to predict the viscosity of DESs. The model is constrained by Eyring rate theory and hard sphere free volume theory. A dataset of 2229 experimental measurements of the viscosity of 183 DESs from literature is used for determining the model parameters and subsequent verification of the model. The rules introduced by this model are simple and easy to understand. The results show that the proposed model is able to predict the DESs viscosity with very high accuracy, i.e., with an average absolute relative deviation of 8.12% over the training set and 8.64% over the test set, using only temperature and composition as inputs. The maximum absolute relative deviation is 34.63%. Therefore, the as-proposed model can be considered a highly reliable tool for predicting DESs viscosity when experimental data are absent.

Design of Composites by Infiltration Process: A Case Study of Liquid Ir-Si Alloy/SiC Systems

The design of processing routes involving the presence of the liquid phase is mainly associated with the knowledge of its surface and transport properties. Despite this need, due to experimental difficulties related to high temperature measurements of metallic melts, for many alloy systems neither thermodynamic nor thermophysical properties data are available. A good example of a system lacking these datasets is the Ir-Si system, although over the last fifty years, the structures and properties of its solid phases have been widely investigated. To compensate the missing data, the Gibbs free energy of mixing of the Ir-Si liquid phase was calculated combining the model predicted values for the enthalpy and entropy of mixing using Miedema’s model and the free volume theory, respectively. Subsequently, in the framework of statistical mechanics and thermodynamics, the surface properties were calculated using the quasi-chemical approximation (QCA) for the regular solution, while to obtain the viscosity, the Moelwyn-Hughes (MH) and Terzieff models were applied. Subsequently, the predicted values of the abovementioned thermophysical properties were used to model the non-reactive infiltration isotherm of Ir-Si (eutectic)/SiC system.

Design of Composites by Infiltration Process: A Case Study of Liquid Ir-Si Alloy/SiC Systems

The design of processing routes involving the presence of the liquid phase is mainly associated with the knowledge of its surface and transport properties. Despite this need, due to experimental difficulties related to high temperature measurements of metallic melts, for many alloy systems neither thermodynamic nor thermophysical properties data are available. A good example lacking these datasets represents the Ir-Si system, although over the last fifty years, the structures and properties of its solid phases have been widely investigated. To compensate the missing data, the Gibbs free energy of mixing of the Ir-Si liquid phase was calculated combining the model predicted values for the enthalpy and entropy of mixing using Miedema’s model and Free Volume Theory, respectively. Subsequently, in the framework of statistical mechanics and thermodynamics, the surface properties were calculated using the Quasi Chemical Approximation (QCA) for the regular solution, while to obtain the viscosity, the Moelwyn-Hughes (MH) and Terzieff models were applied. Subsequently, the predicted values of the abovementioned thermophysical properties were used to model the non-reactive infiltration isotherm of Ir-Si (eutectic) / SiC system.

Comprehensive Analysis on Anomalous Phenomenon of Ethanol-Soluble PVB Membrane for Ethanol Recovery via Pervaporation

Poly(vinyl butyral) is selected as a promising ethanol-permselective membrane based the solubility parameter theory, however it exhibits anomalous water perm-selectivity in practical pervaporation process. Comprehensive analysis based on experimental and theoretical methods were carried out to explore the inherent mechanism of the anomalous performance. Firstly, sum frequency generation vibrational spectra and contact angle were developed to quantify the surface reconstruction of membrane in air and ethanol, which indicated that hydrophilic hydroxyl tended to expose on membrane surface with ethanol thus improved the membrane affinity to water. Meanwhile, swelling behaviors proved more water would accumulate in the ethanol swollen membrane. Furthermore, theoretical analysis in terms of sorption and diffusion process, based on the UNIFAC-FV model and Fujita free volume theory, confirmed the mechanism of anomalous phenomenon of poly(vinyl butyral) membrane. The comprehensive investigation was expected to provide insights into the basic separation mechanism of pervaporation process.

Modeling Of Infrared Drying Of Polymer Solutions

This thesis presents the development of dynamic models for drying a coating polymer layer placed on fixed and moving substrate in a dryer using infrared (IR) heat source. The IR drying model is a set of coupled nonlinear partial differential equations (PDEs) arising from simultaneous mass and heat balances and they describe variations of the solvent concentration and the polymer system temperature during the drying process. The model was numerically solved in MATLAB environment and then validated using data from literature. Using polyvinyl acetate (in toluene) as a coating material on a polyester substrate, the simulation revealed that the model agrees with data and describes adequately well the drying kinetics. The modeling approach was also extended to simulate the drying of a polymer solution in a container. Since solvent and polymer molecular sizes are quite different, the diffusion coefficient was better described with free volume theory.

Modeling Of Infrared Drying Of Polymer Solutions

This thesis presents the development of dynamic models for drying a coating polymer layer placed on fixed and moving substrate in a dryer using infrared (IR) heat source. The IR drying model is a set of coupled nonlinear partial differential equations (PDEs) arising from simultaneous mass and heat balances and they describe variations of the solvent concentration and the polymer system temperature during the drying process. The model was numerically solved in MATLAB environment and then validated using data from literature. Using polyvinyl acetate (in toluene) as a coating material on a polyester substrate, the simulation revealed that the model agrees with data and describes adequately well the drying kinetics. The modeling approach was also extended to simulate the drying of a polymer solution in a container. Since solvent and polymer molecular sizes are quite different, the diffusion coefficient was better described with free volume theory.

Using the group contribution method and molecular dynamics to predict the glass transition temperatures and mechanical properties of poly-(p-phenylenediamine-alt-2, 6-diformyl multiphenyl)

This article reports the glass transition temperatures of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) predicted by both the group contribution method and the molecular dynamics simulations. The related modeling method and the degree of polymerization, density, specific volume, radius of volume, radius of rotation, and non-bonding energy terms with temperature are analyzed in depth. The bulk modulus, shear modulus, compressibility, Young’s modulus, and Poisson’s ratio of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) at room temperature are simulated by molecular dynamics. The results show that the simulated glass transition temperatures of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) are greater than 480 K, which indicates that poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) can be expected to be used as a high-temperature-resistant material. As the number of rigid benzene rings on the molecular side chain increases, the glass transition temperature decreases, with an average decrease of 10 K for each additional benzene ring. The free volume theory can explain the glass transitions of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl). The modulus and density of poly-( p-phenylenediamine-alt-2,6-diformyl multiphenyl) change accordingly with an increase of rigid benzene rings on the side chain, probably due to the fact that the flexibility of the polymers changes accordingly as the number of benzene rings on the side chain increases.