Macromolecular Theory and Simulations最新文献

Front Cover: A continuous transition function that approximates the macroscopic-phenomenological behavior of amorphous polymers at glass transition is obtained from an exactly-solvable Riccati equation. This ordinary differential equation is derived within thermodynamics with internal state variables. More details can be found in article 2400052 by Claudio Corbisieri.

Theoretical analysis of the kinetic scheme describing formation and randomization of a binary copolymer due to end-group interchange reactions is presented. Compact analytical expressions are obtained for the transient and equilibrium values of the copolymer degree of blockiness and fractions of active end-groups of different types. The resulting copolymer is described by the first-order Markov statistics, which can be rather far from the Bernoullian one. Its structure is determined by the composition of the system and a single combination of the rate constants of four elementary reactions. The kinetics includes fast and slow stages with characteristic time periods independent of and proportional to the average polymerization degree, respectively. During the fast stage, the initial polymers disappear, whereas the copolymer degree of blockiness is still very low. The distribution of units in the copolymer is Markovian, only if the initial polymers possess the most probable molar mass distributions. At the slow stage copolymer randomization gradually progresses, whereas the distribution of end groups may change in the opposite direction compared to the fast stage. The results can be used to analyze the experimental data on the chain structure of condensation, metathesis, and dynamic covalent polymers, where interchange reactions play a significant role.

The role of the sulfur analog of cyclic ketene acetals in the synthesis of polyvinyl chloride is examined in this study. In this context, whether 2-methylene-1,3-dithiolane (S-CKA5), 2-methylene-1,3-dithione (S-CKA6), and 2-methylene-1,3-dithiepane (S-CKA7) monomers are involved in the radical polymerization of vinyl chloride through the ring opening reaction is examined by quantum chemical methods. In light of calculations at the M06-2X/6-31+G(d) level, it is concluded that, in general, S-CKAs undergo little or no ring-opening and form block copolymers, mainly with the homopolymerization of S-CKAs and their ring-retaining step. It is determined that S-CKA7 is the most prone to ring-opening reaction and inserting dithioate links to the polymer backbone. However, the radical ring-opening of S-CKA7 is strongly reversible, as in other S-CKAs.

Studying the macroscopic-phenomenological behavior of amorphous polymers at glass transition is often subject to limitations because the ordinary differential equations that describe the material behavior require numerical solution. To avoid these limitations, ad-hoc-formulated models of the glass transition have been proposed. However, their scope of application is expected to be limited due to insufficient theoretical foundation. This work establishes a theoretical framework for models that use the logistic function to approximate the macroscopic-phenomenological behavior of amorphous polymers at glass transition. For this purpose, an exactly-solvable Riccati equation is derived within thermodynamics with internal state variables. A closed-form expression in terms of mathematical functions for the temperature derivative of a single internal state variable is the result. This closed-form expression contains the logistic function thus featuring a continuous transition region centered around a pressure and cooling-rate dependent transition temperature. Based on comparison of existing models with the exact solution derived from the Riccati equation, generalized models that approximate the thermal expansion coefficient and heat capacity at glass transition are proposed. This work thus demonstrates the validity of the logistic function in glass transition models of amorphous polymers and provides suggestions as to how existing models can be extended in their applicability.

Front Cover: The rheological parameters are important factors influencing mixing of polymer blends. The tracer particle method is used to represent the mixing effect of the melt, the flow of virtual material/thermoplastic polyurethanes with high and low viscosities in dynamic mixers are simulated. The patterns of zero shear viscosity ratio, relaxation time ratio and non-Newtonian index ratio influencing the mixing are discovered. More details can be found in article 2400031 by Jiankang Wang and co-workers.

Blade coating is a process that applies a fluid to a surface using a fixed blade. Among various coating technologies, blade coating offers significant economic advantages. It is commonly employed in the production of paper, information preservation, the application of coloring agents, and the manufacture of photographic films and magnetic storage devices. The novelty of this work lies in the investigation of the blade coating process for an electrically conducting Oldroyd 4-constant liquid, incorporating velocity slippage at the blade surface in an area previously underexplored. The mathematical equations are modeled with the use of Lubrication Approximation Theory (LAT) and the normalized equations of the Oldroyd 4-constant fluid are numerically solved by the Matlab built-in function bvp4c using Regula-Falsi Method. The impact of sundry parameters on physical quantities is examined through graphical representation. It is noted from the theoretical results that for the fixed value of the MHD parameter (M = 2.5), the coating thickness and blade load increased by 31% and 1648% respectively, for plane coater. For the exponential coater, these values increased by 29% and 1618% from their Newtonian value. These findings offer new insights into optimizing the blade coating process for complex fluid systems.

This study introduces a rheological equivalent circuit model inspired by electrochemical impedance spectroscopy (EIS) to analyze complex viscosity data. By exploiting the similarity between the Cole–Cole plot in rheology and the Nyquist plot in EIS, the study adopts circuit fitting methodologies to interpret rheological behavior of various polymers. The model employs redefined electrochemical elements, including dashpots, springs, rheological constant phase elements, and Warburg elements, to capture both linear and non-linear responses. This approach offers both analytical and predictive capabilities, providing new insights into material composition.

Polymer flooding, using hydrolyzed polyacrylamide (HPAM), is crucial in enhanced oil recovery technology. The effect of the HPAM and NaCl concentration on the stability of the simulated emulsions was assessed through multiple light scattering experiments. The results demonstrated that HPAM significantly enhanced the stability of both oil-in-water (O/W) and water-in-oil (W/O) emulsions. The HPAM concentration escalated from 200 mg L⁻¹ to 1000 mg L⁻¹, increasing from 1.24% to 1.31% at 60 minute in the average backscattering of W/O emulsions. The average transmittance of O/W emulsions exhibited a significant decline from 2.54% to 0.12%. The NaCl concentration had a small effect on the stability of the emulsions. Molecular dynamics simulations revealed that HPAM adsorbed at the oil water interface by the point-like nature, with stronger interaction between its amide group and the oil molecule than its carboxyl group. The hydrogen bond number and the hydrogen bond lifetime of HPAM-H₂O and HPAM-HPAM increase with increasing the number of HPAM molecules at the oil-water interface, slowing diffusion coefficient of water molecules and increasing the interface thickness. Increasing salinity can weaken the HPAM-water interaction, reducing the emulsification stability. This work provides insights into the emulsification characteristics and mechanisms of HPAM.