Volume 65, Nº 1 (2023)

Theoretical results of the authors in the field of the capillary thinning of polymer solution threads are reviewed. The dynamics of threads of both concentrated solutions without entanglements and dilute solutions, where hydrodynamic interactions play an important role, is considered. A molecular approach, in which macromolecules are simulated by a semiflexible chain, is used as a basis. This makes it possible to describe, from common positions, the nonlinear elasticity of solution and interactions taking into account the orientation of the chains. Particular attention is given to thread thinning in the region of the elastic behavior of solution where macromolecules unfold along the axis of stretching. The results of analysis of the capillary stability of a thread and conditions for solvent droplets emergence on its surface are presented, and the dynamics of formation of the hierarchical structure of beads-on-string droplets is viewed. Mechanisms behind the subsequent merging of droplets related to solvent overflow and droplets diffusion along the polymer string are discussed. The polymer string breakup occurs at time scales higher than the Rouse relaxation time of the polymer chain. String hardening and fiber formation may be an alternative.

We utilize the self-consistent field theory to explore the mechanical and electrical properties of charged surfaces immersed in polyelectrolyte solutions that could be potentially useful for electrochemical applications. Our research focuses on how the dielectric heterogeneity of the solution could affect the disjoining pressure and differential capacitance of the electric double layer. Relying on the developed theoretical framework, based on the Noether’s theorem, we calculate the stress tensor, containing the term, arising from the conformational entropy of the polymer chains. With its help we compute the disjoining pressure in polyelectrolyte solution confined between two parallel charged surfaces and analyze its behavior as a function of separation between the surfaces for different values of dielectric mismatch parameter. We also calculate the differential capacitance of the electric double layer and discuss how dielectric heterogeneity of the polyelectrolyte solution influences its values.

The adsorption of a single random copolymer chain containing correlations in a sequence on the chemically heterogeneous periodic surface with the alternating striped texture is studied theoretically. The problem is solved within the framework of a partially directed walk polymer model in three dimensions using the generating functions approach and the annealed disorder approximation for averaging over the ensemble of random sequences of units in the copolymer. Dependences of the adsorption transition point on the composition of the random copolymer and the degree of correlation in the random sequence of units for various periodic surfaces are presented. It is shown that for compositionally symmetric and weakly symmetric surfaces there is the optimal composition of the random copolymer and the degree of correlation in the sequence of units, at which the inverse temperature corresponding to the adsorption transition point has a local minimum. In the case of the compositionally symmetric surface, the “optimal” random copolymer is also symmetric in composition. For surfaces with a pronounced composition asymmetry the best adsorbent is a homopolymer complementary to sites that prevail on the surface. The degree of asymmetry range, in which the dependence of the inverse transition temperature on the copolymer composition and the correlation parameter exhibits the local minimum, is fairly narrow.

Представлены история и перспективы развития потенциалов межатомного взаимодействия для моделирования молекулярных систем и, в частности, полисахаридов. Рассмотрены популярные семейства потенциалов, такие как CHARMM, GROMOS, AMBER и OPLS. Обозначены проблемы применимости данных моделей для мономеров сахаров: плохая воспроизводимость экспериментальных свойств и гиперагрегация при малых концентрациях. Также рассмотрены векторы развития данной области: модификация невалентных взаимодействий в потенциале и использование поляризуемых потенциалов. Продемонстрированы примеры применения атомистического моделирования полисахаридов в актуальных фундаментальных и промышленных задачах на примере целлюлозы. Приведены важные вычислительные работы, внесшие существенный вклад в понимание структуры и процессов, происходящих в кристалле целлюлозы. Кроме того, дан обзор доступных на сегодня масштабов времен и характерных размеров систем для моделирования в пакетах GROMACS, LAMMPS, OpenMM и AMBER для модели раствора сахарозы.

Solutions based on polymer-like micelles of ionic surfactants attract the attention of scientists as stimuli-responsive systems that can transform from a low-viscosity Newtonian fluid to a viscoelastic solution having a viscosity of up to 10 kPa s and an elastic response. The shape of micelles and their length are determined by the balance of hydrophobic and electrostatic interactions; therefore, the use of various low molecular weight substances or functional nanoparticles as additives can significantly change the rheological properties of such solutions and impart new stimuli-responsive properties to them. This review presents the most commonly used methods for controlling the properties of multicomponent solutions of wormlike surfactant micelles, including nanocomposite systems. Modern areas of practical application of such systems and prospects for their development are described.