arXiv subjects

Alexander Chertovich

Publications and source records attributed to Alexander Chertovich.

6 recordsLinked to original sources

arXiv2022

Optimal Entanglement of Polymers Promotes Formation of Highly Oriented Fibers

Polymer fibers consist of macromolecules oriented along the fiber axis. Better alignment of chains leads to an increased strength of the fiber. It is believed that the key factor preventing formation of a perfectly oriented fiber is entanglement of polymers. We performed large-scale computer simulations of uniaxial stretching of semicrystalline ultrahigh molecular weight polyethylene. We discovered that there is an optimal number of entanglements per macromolecule necessary to maximize chain orientation in a fiber. Polymers that were entangled too strongly formed less oriented fibers. On the other hand, when polymers had too few entanglements per chain, they disentangled during stretching, and the strong fiber was not formed. We constructed a microscopic analytical theory describing both the fiber formation and disentanglement processes. Our work presents a novel view on the role of entanglements during fiber production and predicts the existence of a single universal optimal number of entanglements per chain maximizing the fiber quality: approximately $10^2$ entanglements.

cond-mat.soft↗

arXiv2020

A novel heterogeneous structure formed by a single multiblock copolymer chain

We studied structures formed by a single $(AB)_k$ multiblock copolymer chain, in which interaction between A-type beads was purely repulsive, and B-type beads tended to aggregate. We studied how attraction between A-type beads and B-type beads affected the structure of the chain. We discovered formation of an equilibrium globular structure, which had unique heterogeneous checkerboard-like distribution of contact density. Unlike the structures usually formed by a single $(AB)_k$ multiblock copolymer chain, this structure had contact enrichment at the boundaries of A and B blocks. This structure was formed by a multiblock copolymer chain, in which B-type beads could form maximum two reversible bonds either with A-type or B-type beads, A-type beads could form maximum one reversible bond with a B-type bead, and interactions between A-type beads were purely repulsive. Multiblock copolymer chains with this type of intrachain interactions can model structure of chromatin in various organisms.

cond-mat.soft↗

arXiv2020

Low-entangled UHMWPE melt: analytical model and computer simulations

In this work we developed a theoretical model to describe the polymerization of very long macromolecules with simultaneous precipitation. As a reference system for our model we consider UHMWPE polymerization process, via homogeneous catalysis and with molecular weight above $10^6$ monomers. We derived time dependency of the entanglement length in the system, and assessed how polymerization rate and fraction of initiators affects this dependency. We show that decrease of the fraction of initiators leads to increase of the average entanglement length in the melt after complete polymerization. The results are supported by computer simulations and in principle could be applied to the wide set of polymerized materials, both crystallized and amorphous.

cond-mat.soft↗

arXiv2019

Kinetic mechanisms of crumpled globule formation

Homopolymer chain with beads forming pairwise reversible bonds is a well-known model in polymer physics. We studied kinetics of homopolymer chain collapse, which was induced by pairwise reversible bonds formation. We compared kinetic mechanism of this coil-globule transition with the mechanism of collapse in a poor solvent. We discovered, that coil-globule transition occurs sufficiently more homogeneously on different scales, if collapse is induced by pairwise reversible bonds formation. This effect leads to formation of transient structures, which are not similar to the classical pearl-necklace conformations formed during collapse in a poor solvent. However, both types of collapse lead to formation of a metastable state of crumpled globule, which is one of the well-known models of interphase chromatin structure in different organisms. Moreover, we found out that stability and dynamics of this state can be controlled by fraction of reversible bonds and bond lifetime.

cond-mat.soft↗

arXiv2019

Modelling Polymerization-Induced Self Assembly (PISA)

In this work we studied polymerization-induced self-assembly by means of computer simulations. Using this model, phase diagrams of the micelle states were constructed depending on the polymer concentration and the asymmetry of the composition for various reaction conditions. We found that if the reaction is ideal controlled radical polymerization (the initiation speed is much larger than the propagation speed and there are no side reactions such as termination or chain transfer), the phase diagram is no different from that obtained for pre-synthesized monodisperse diblock-copolymers with one insoluble block. Next, we studied two cases of slow initiation. We found that the phase diagram change dramatically: upon decreasing the initiation speed, the regions of spherical and cylindrical micelles shrink, while the region of vesicles/lamellae expands. This happens because at small initiation speed there is a significant amount of chains with a very short non-soluble block (and even without such block altogether), which do not participate in the formation of micelles. Therefore, decreasing the initiation speed essentially remaps the phase diagram coordinates by making the effective concentration lower (by decreasing the number of active chains) and the effective block length ratio higher (again, because the number of active chains gets higher, while the number of monomers remains the same).

cond-mat.soft↗

arXiv2017

Electrode/electrolyte Interface in the Li-O2 Battery: Insight from Molecular Dynamics Study

In this paper for the first time we report the results of molecular dynamics simulation of electrode/electrolyte interface of Li-O2 cathode under potential close to experimental values in 1M dimethyl sulfoxide (DMSO) solution of LiPF6 salt. Electric potential profiles, solvent structuring near the electrode surface and salt ions distributions are presented and discussed here as well as potentials of mean force (PMF) of oxygen and its reduction products. The latter would be of a great use for the future theoretical studies of reaction kinetics as PMF being essentially the work term is a required input for the reaction rate constant estimations. Electrode/electrolyte interface under the realistic potential effectively push oxygen anions out of the reaction layer that makes second reduction of superoxide anion hardly probable. Thus the main cause of the passivation should be the lithium superoxide presence near the electrode surface. The way to suppress the passivation is the shifting of equilibrium O_2^- + Li_+ <-> LiO_2 to the side of separately solvated ions, for example by using solvents resulting in lower free energy of the ions. This conclusion is in agreement with the hypothesis stating that high donor number solvents lead to dominantly solution Li2O2 growth and significantly higher cell discharge capacities.

physics.chem-ph↗