软物质非平衡体系的挑战和机遇

总结了国家自然科学基金委员会化学科学部组织召开的“软物质非平衡体系的挑战和机遇”学科发展战略高层论坛学术交流内容.首先概述了软物质非平衡体系的主要物理化学特点,随后阐述了其在国际学术前沿所面临的重要挑战,最后介绍了当前我国在化学、物理和数学等基础研究领域所取得的相关研究进展及一些创新性交叉研究成果,探讨了如何面向生命科学和材料科学未来的发展方向,更好地发挥化学、物理和数学等基础学科交叉集成的引领作用.同时,为了满足我国国民经济发展所面临的重大技术需求,凝练了软物质非平衡体系研究领域未来5~10年的关键科学问题,提出了加强科学基金资助的战略性建议.

Special Issue:Theory and Simulation of Macromolecules

We are pleased to announce the special issue on Theory and Simulation of Macromolecules published in the Chinese Journal of Polymer Science.In recent years,a vibrant research community in the theory and simulation of macromolecules has been established in China[Hu,W.B.Computer simulation of polymers:bridging the gap between theory and experiment,Chinese J.Polym.Sci.2022,40,709-710].

中国改革开放以来的高分子物理和表征研究

本综述介绍了改革开放四十多年来中国大陆学者在高分子物理和表征领域所取得的部分成就.按照时间顺序,分别从概念的突破、理论的发展和技术的创新三个方面选取具有代表性研究成果进行简短的介绍,以期展示当代中国学者在这一基础研究领域所表现出来的拼搏意志和创新精神,激励新一代学者共同努力,勇攀科学高峰,为国民经济和社会发展作出更大的贡献.

Computer Simulation of Polymers:Bridging the Gap between Theory and Experiment

In the early history of polymer science, theory and experiment achieved all the milestones. At that time, scientific research was commonly activated by human curiosity or demand to solve a problem. It started with a hypothesis of theory and ended up with the verification of experiment. With the fast expansion of research frontiers,specifically in the typically multi-disciplinary field as polymer science.

The Effect of Self-nucleation on Isothermal Crystallization Kinetics of Poly(butylene succinate)(PBS) Investigated by Differential Fast Scanning Calorimetry

Differential fast scanning calorimetry（DFSC） was employed on the study of self-nucleation behavior of poly（butylene succinate）（PBS）.The ultra-fast cooling ability of DFSC allows investigating the effect of self-nucleation on the isothermal crystallization kinetics over a wide temperature range.Crystallization half-time,instead of crystallization peak temperature,was used to describe the self-nucleation behavior,and the self-nucleation domain for the samples crystallized at different temperatures was determined.Due to the competition between homogenous nucleation and self-nuclei,the effect of self-nucleation was less pronounced at high supercooling than that for the sample isothermally crystallized at higher temperature.An efficiency scale to judge the efficiency of nucleating agents from the crystallization half-time was also introduced in this work.

Local Transient Jamming in Stress Relaxation of Bulk Amorphous Polymers

Bulk amorphous polymers become stretched and parallel-aligned under loading stress,and their intermolecular cooperation slows down the subsequent stress relaxation process.By means of dynamic Monte Carlo simulations,we employed the linear viscoelastic Maxwell model for stress relaxation of single polymers and investigated their intermolecular cooperation in the stress relaxation process of stretched and parallel-aligned bulk amorphous polymers.We carried out thermal fluctuation analysis on the reproduced Debye relaxation and Arrhenius fluid behaviors of bulk polymers.We found a transient state with stretch-coil coexistence among polymers in the stress relaxation process.Further structure analysis revealed a scenario of local jamming at the transient state,resulting in an entropy barrier for stretch-coil transition of partial polymers.The microscopic mechanism of intermolecular cooperation appears as unique to polymer stress relaxation,which interprets the hydrodynamic interactions as one of essential factors raising a high viscosity in bulk amorphous polymers.Our simulations set up a platform of molecular modeling in the study of polymer stress relaxation,which brought new insights into polymer dynamics and the related mechanical/rheological properties.

PREFACE

Crystalline polymers exhibit their strong connections to our practical world. In synthetic polymer materials, crystallization brings fiber orientation-strengthening, rubber strain-hardening and plastic neck-toughening Important properties such as hardness, thermal stability, anisotropic structures, etc. are endowed to the polymeric materials. In natural polymer materials, crystallization provides proteins of skins, hairs, wools and silks as well as carbohydrates like celluloses, starches and chitins with the necessary strength to support versatile living activities. On the other hand,

Kinetic Monte Carlo Simulations of Polymer Cold Crystallization

We performed kinetic Monte Carlo simulations of a lattice polymer model holding intramolecular and intermolecular activation barriers for polymer diffusion, on the basis of the previous dynamic Monte Carlo simulations of polymer crystallization. We explored the effective parameter sets for two barriers to freeze the amorphous polymers at low temperatures. The subsequent heating process of the frozen amorphous polymers exhibits clear cold crystallization behaviors. We made preliminary investigation on the crystallinity and the morphology of polymer crystallites yielded during the cold crystallization, which appear in consistence with our common experimental observations. Our present work paves the way for molecular simulations of hot and cold polymer crystallization in the whole temperature range between the glass transition temperature and the melting temperature.

Polymer Features in Crystallization

This review firstly gives an overview on the importance of crystallization in natural and synthetic polymers/macromolecules.Then it introduces the typical features that have been raised by chain-like macromolecules in crystallization,including anisotropic interactions in the thermodynamic driving forces,chain folding in the crystal morphologies,chemical confinement in the copolymer crystallization,and mechanical enhancement in the stretching processes.Four features separately cover the thermodynamics and the kinetics of polymer crystallization,as well as the crystallinity and the mechanical properties of semicrystalline polymers.The review ends up with how these features enhance specific functions of crystalline polymers,which demonstrates polymer crystallization as a challenging yet promising field in the future.

Nonlinear Viscoelasticity Raised at Low Temperatures by Intermolecular Cooperation of Bulk Amorphous Polymers

We performed dynamic Monte Carlo simulations of stress relaxation in parallel-aligned and uniaxially stretched bulk amorphous polymers at low temperatures.We observed an extra-slowing down in the early stage of stress relaxation,which causes nonlinear viscoelasticity as deviated from Debye relaxation and Arrhenius-fluid behaviors observed previously at high temperatures.Meanwhile,fluctuation analysis of stress relaxation revealed a substantial increase in the stretch fractions of polymers at the transient periods of high-temperature Debye relaxation.Structural analysis of free volume further revealed the scenario that,at low temperatures,the modulus of polymer entropy elasticity decreases with temperature and eventually loses its competition to the imposed modulus(Deborah number becomes larger than one),and hence upon stress relaxation under constant strains,monomers are firstly accumulated nearby two stretching ends of polymers,resulting in tentative global jamming like physical cross-linking there,and thus retarding the coming transient state of stress relaxation.We concluded that intermolecular cooperation raises physical crosslinking for nonlinear viscoelasticity of polymer stress relaxation as well as the rubbery states unique to bulk amorphous polymers.The new microscopic mechanism of the fluid-rubbery transition of polymers may bring insights into the intermolecular cooperation mechanism of glass transition of small molecules,if the fluid-rubbery transition is regarded as an extrapolation of glass transition from low to high molecular weights.