Electromagnetic response from composite carbon-containing structures with technological inhomogeneities at EHF

The results of studies of the electromagnetic response from composite structures made of a carbon-containing polymer with the inclusion of spherical pores in the bulk of the material and with pyramidal corrugation on the surface of the material are presented. The results of modeling the frequency dependences of the transmission, reflection and absorption coefficients in the EHF range are shown. Samples of composite carbon-containing structures with technological inhomogeneities have been fabricated by 3D printing. Measurements of the electromagnetic response from experimental samples were carried out in the frequency range from 100 to 1000 GHz. At frequencies up to 250 GHz, the inclusion of air pores in the polymer volume reduces the transmission coefficient, practically does not affect the reflection, and increases the absorption. Pyramid corrugated material absorbs more than 99% of radiation in the frequency range from 200 to 635 GHz.

Polymer-Assisted Condensation: A Mechanism for Hetero-Chromatin Formation and Epigenetic Memory

We consider the formation of droplets from a 2-component liquid mixture induced by a large polymer chain that has preferential solubility with one of the components. We assume that the liquid mixture is in a fully miscible state, but far above the critical interaction limit of the two species. We show that the polymer coil acts as a chemical potential trap, which can shift the mixture inside the polymer volume into the partially miscible state and thus triggers the formation of a polymer-bound droplet of the preferred solvent phase which we denote as polymer-assisted condensation (PAC). We propose a simple mean-field model which can predict the essential feature of PAC and perform molecular-dynamics simulations to show that the predicted phase behavior is robust against fluctuation effects. Our model aims to understand the formation of macromolecular condensates inside the cell nucleus, such as those formed by heterochromatin 1 (HP1). We propose that such droplets organize the spatial structure of chromatin into hetero- and euchromatin and ensure the propagation of epigenetic information through the cell generations.

ЕFFECT OF IRON AND NICKEL DITHIOCARBAMATES ON THE PROPERTIES OF MODIFIED POLYURETHANES

The effect of modifiers - nickel bis(N,N-dimethyldithiocarbamate) (DTC-Ni) and iron tris(N, N-dimethyldithiocarbamate) (DTC-Fe) depending on their content on the structural peculiarities of polyurethane matrix based on polyoxytetramethylene glycol-1000 4,4’-diphenylmethane diisocyanate and 1,4-butanediol has been studied. The method of IR spectroscopy according to the results of NH groups’, C = O- and COC fragments’ association has shown the structuring effect of modifiers due to the PU matrix coordination. The processes of photolysis occurred as a result of exposure of PU under the conditions of the climate chamber have been also studied by IR spectroscopy method. The influence of modifiers and their content on the modified polyurethanes density has been investigated. The planar structure of DTC-Ni has shown to contribute to the density increase of modified PU as the result of polymer chain coordination, while the spherical structure of DTC-Fe - causes a density decrease due to steric hindrances in the implementation of H-bonds. Modification of polyurethanes with both nickel bis (N, N-dimethyldithiocarbamate) and iron tris (N, N-dimethyldithiocarbamate) as well as UV irradiation and moisture under the conditions of the climatic chamber contribute to the increase of water absorption. Studies of the strength properties of modified polyurethanes in comparison with the matrix under the conditions of the climate chamber have established the photosensitizing effect of nickel and iron dithiocarbamates. By studying the mass of samples of PU-DTС-Fe/Ni after extraction with dimethylformamide in the Soxhlet apparatus it has been found an increase in the level of gel fraction (0.29 - 1.58%) with increasing the modifier content, which confirms the presence of a network structure of modified PU due to radical processes taking place during destruction with the modifier participation. The influence of alkaline and acidic media on the destruction level of both modified polyurethanes and their analogues depending on the modifier content under the influence of climatic chamber conditions has been studied. Comparative derivatographic studies in air of weight loss of modified polyurethanes have confirmed the structuring and thermostabilizing effect of DTC-Ni on the PU matrix due to the probable difficulty of oxygen diffusion to the polymer volume, while the spatial structure of PU-DTC-Fe reduces the thermal stability.

Phase Diagram for Ideal Diblock-Copolymer Micelles Compared to Polymerization-Induced Self Assembly

In this work we constructed a detailed phase diagram for the solutions of ideal diblock-copolymers and compared such diagram with that obtained during polymerization-induced self-assembly (PISA); a wide range of polymer concentrations as well as chain compositions was studied. As the length of the solvophobic block nB increases (the length of the solvophilic block nA was fixed), the transition from spherical micelles to cylinders and further to vesicles (lamellae) occurs. We observed a rather wide transition region between the spherical and cylindrical morphology in which the system contains a mixture of spheres and short cylinders, which appear to be in dynamic equilibrium; the transition between the cylinders and vesicles was found to be rather sharp. Next, upon increasing the polymer concentration in the system, the transition region between the spheres and cylinders shifts towards lower nB/nA values; a similar shift but with less magnitude was observed for the transition between the cylinders and vesicles. Such behavior was attributed to the increased number of contacts between the micelles at higher polymer volume concentrations. We also found that the width of the stability region of the cylindrical micelles for small polymer volume concentrations is in good quantitative agreement with the predictions of analytical theory. The obtained phase diagram for PISA was similar to the case of presynthesized diblock copolymer; however, the positions of the transition lines for PISA are slightly shifted towards higher nB/nA values in comparison to the presynthesized diblock copolymers, which is more pronounced for the case of the cylinders-to-vesicles transition. We believe that the reason for such behavior is the polydispersity of the core-forming blocks: The presence of the short and long blocks being located at the micelle interface and in its center, respectively, helps to reduce the entropy losses due to the insoluble block stretching, which leads to the increased stability of more curved micelles.

Tracer Diffusion in Tightly-Meshed Homogeneous Polymer Networks: A Brownian Dynamics Simulation Study

We report Brownian dynamics simulations of tracer diffusion in regularly crosslinked polymer networks in order to elucidate the transport of a tracer particle in polymer networks. The average mesh size of homogeneous polymer networks is varied by assuming different degrees of crosslinking or swelling, and the size of a tracer particle is comparable to the average mesh size. Simulation results show subdiffusion of a tracer particle at intermediate time scales and normal diffusion at long times. In particular, the duration of subdiffusion is significantly prolonged as the average mesh size decreases with increasing degree of crosslinking, for which long-time diffusion occurs via the hopping processes of a tracer particle after undergoing rattling motions within a cage of the network mesh for an extended period of time. On the other hand, the cage dynamics and hopping process are less pronounced as the mesh size decreases with increasing polymer volume fractions. The interpretation is provided in terms of fluctuations in network mesh size: at higher polymer volume fractions, the network fluctuations are large enough to allow for collective, structural changes of network meshes, so that a tracer particle can escape from the cage, whereas, at lower volume fractions, the fluctuations are so small that a tracer particle remains trapped within the cage for a significant period of time before making infrequent jumps out of the cage. This work suggests that fluctuation in mesh size, as well as average mesh size itself, plays an important role in determining the dynamics of molecules and nanoparticles that are embedded in tightly meshed polymer networks.

Decoupling Salt- and Polymer-Dependent Dynamics in Polyelectrolyte Complex Coacervates via Salt Addition

In polyelectrolyte complex coacervates, changes in salt concentration and changes in polymer concentration are typically strongly coupled, complicating interpretation of the salt- and polymer concentration-dependent dynamics of these materials. To address this problem, we developed a “salt addition” method for preparation of complex coacervates that allows the salt concentration of a coacervate sample to be varied without changing its polymer concentration. This method was used to prepare coacervates of poly(styrene sulfonate) (PSS) with poly(diallyldimethylammonium chloride) (PDADMAC) with salt concentrations between 1.2 and 2 M and volume fractions of polymer between 0.1 and 0.25. Characterization of these samples by small-amplitude oscillatory shear rheology revealed that the relaxation times scale significantly more strongly with polymer volume fraction than has been previously assumed, highlighting the need to account for both salt and polymer-dependent contributions to the dynamics of these complex materials.

Theory of Flexible Polymer Networks: Elasticity and Heterogeneities

A review of the main elasticity models of flexible polymer networks is presented. Classical models of phantom networks suggest that the networks have a tree-like structure. The conformations of their strands are described by the model of a combined chain, which consists of the network strand and two virtual chains attached to its ends. The distribution of lengths of virtual chains in real polydisperse networks is calculated using the results of the presented replica model of polymer networks. This model describes actual networks having strongly overlapping and interconnected loops of finite sizes. The conformations of their strands are characterized by the generalized combined chain model. The model of a sliding tube is represented, which describes the general anisotropic deformations of an entangled network in the melt. I propose a generalization of this model to describe the crossover between the entangled and phantom regimes of a swollen network. The obtained dependence of the Mooney-Rivlin parameters C 1 and C 2 on the polymer volume fraction is in agreement with experiments. The main results of the theory of heterogeneities in polymer networks are also discussed.

Compatibility study of plasticizing additives based on recycled raw materials in the petrochemical with elastomer matrix

The compatibility of SRI-3 polyisoprene rubber with plasticizing additives based on recycled petrochemical raw materials (DVCH, DVCH with modifying additive (MA) in the amount of 0.5; 1.0; 2.5; 5.0 and 10.0% mas.) in comparison with industrial petroleum oils (PO-6 and I-20). The compatibility of polymer with a plasticizer additive was evaluated by of experimental data using the equilibrium swelling method. As a result, the polimer-plasticizer interaction parameter (Huggins parameter) and the diffusion coefficient of plasticizing components in the polymer volume were determined. Analysis of the experimental data showed that the plasticizer component based on recycled petrochemical raw materials DVCH has better compatibility with the elastomer matrix SRI-3 compared to industrial oils PO-6 and I-20. Was established that the use of modifying additives in the amount of 0.5 and 1.0% mas. leads to an increase in the diffusion coefficient and a decrease in the Huggins parameter in comparison with DVCH in individual form It indicates their better compatibility with rubber SRI-3. Was shown that a further increase in the content of modifying additive (more than 1.0% mas.) in the volume of plasticizing component DVCH is impractical. This leads to a deterioration of the parameters, and, as a result, to a worse compatibility with the elastomer.