Impact of conjugated polymer addition on the properties of paraffin-asphaltene blends for heat storage applications: Insight from computer modeling and experiment.

Adding carbon nanoparticles into organic phase change materials (PCMs) such as paraffin is a common way to enhance their thermal conductivity and to improve the efficiency of heat storage devices. However, the sedimentation stability of such blends can be low due to aggregation of aromatic carbon nanoparticles in the aliphatic paraffin environment. In this paper, we explore whether this important issue can be resolved by the introduction of a polymer agent such as poly(3-hexylthiophene) (P3HT) into the paraffin-nanoparticle blends: P3HT could ensure the compatibility of aromatic carbon nanoparticles with aliphatic paraffin chains. We employed a combination of experimental and computational approaches to determine the impact of P3HT addition on the properties of organic PCMs composed of paraffin and carbon nanoparticles (asphaltenes). Our findings clearly show an increase in the sedimentation stability of paraffin-asphaltene blends, when P3HT is added, through a decrease in average size of asphaltene aggregates as well as in an increase of the blends' viscosity. We also witness the appearance of the yield strength and gel-like behavior of the mixtures. At the same time, the presence of P3HT in the blends has almost no effect on their thermophysical properties. This implies that all properties of the blends, which are critical for heat storage applications, are well preserved. Thus, we demonstrated that adding polyalkylthiophenes to paraffin-asphaltene mixtures led to significant improvement in the performance characteristics of these systems. Therefore, the polymer additives can serve as promising compatibilizers for organic PCMs composed of paraffins and asphaltenes and other types of carbon nanoparticles.

[Surgical treatment results of metastatic spine disease with using minimally invasive technologies, including 3D video endoscopic technologies]. / Rezul'taty khirurgicheskogo lecheniya metastaticheskikh porazhenii pozvonochnika s primeneniem maloinvazivnykh metodov lecheniya, v tom chisle 3D-videoendoskopicheskikh tekhnologii.

THE AIM OF THE STUDY: Was to evaluate the results of surgical treatment of patients with metastatic lesions of the spine using 3-D video endoscopic technologies. MATERIAL AND METHODS: We analysed the results of surgical treatment of 33 patients with metastatic lesions of the thoracic spine using a 3D video-assisted thoracoscopic intervention that was performed from November 2017 to December 2019. When examining patients, the following were used: X-ray of the spine, spiral computed tomography (CT), magnetic resonance imaging (MRI), as well as the SINS, Bilsky, Karnovsky, Tokuhashi, Frankel, SF-36 and VAS scales. RESULTS: The actual life expectancy of the patients completely coincided with the predicted one according to the Tokuhashi scale. Regression of neurological disorders in the early postoperative period (before discharge from the hospital) was observed in 6% of patients (complete in 3%, partial in 3%). When evaluating the results of treatment 12 months after surgery, regression of neurological symptoms was observed in 19% of patients. At the same time, complete regression of neurological disorders occurred in 10%, partial in 9% of patients. When assessing the quality of life on the SF-36 scale, improvement was observed according to the most of the criteria. Also, in the postoperative period, there was a persistent decrease in the intensity of pain syndrome according to VAS compared with the preoperative level. CONCLUSION: The use of 3-D video endoscopic technologies in the surgical treatment of patients with metastatic lesions of the spine made it possible to improve the quality of life of patients and reduce the number of complications.

Molecular dynamics simulations of oligoester brushes: the origin of unusual conformations.

We present results from all-atom molecular dynamics simulations for the structural properties of oligomeric lactic acid chains (OLA) grafted to the surface of cellulose nanocrystals (CNCs) and immersed in the melt of polylactic acid (PLA). Earlier, we have found that the distribution of free ends of OLA molecules is bimodal [Glova et al., Polym. Int., 2016, 65(8), 892]. The results cannot be explained within the standard picture of uncharged polymer brushes exposed to the melt of a chemically identical polymer. Although the oligomeric brushes of the OLA chains are uncharged, they have partial polarization charges producing a non-zero dipole moment of the monomeric chain unit. We study the influence of partial charges on the structure of the layer of OLA chains grafted to the CNC surface. A detailed analysis of the conformations of the grafted chains shows that interaction of partial charges in the models causes bending of the OLA molecules toward the cellulose surface, forming a hairpin structure. The observed separation of the grafted chains into two populations increases with grafting density. We demonstrate that hydrogen bonds can be formed between the free ends of the grafted chains and the CNC surface, but they do not affect the brush structure significantly. Thus, dipole-dipole interactions turn out to be the key factor governing the unusual conformations of grafts.

Influence of specific intermolecular interactions on the thermal and dielectric properties of bulk polymers: atomistic molecular dynamics simulations of Nylon 6.

Specific intermolecular interactions, in particular H-bonding, have a strong influence on the structural, thermal and relaxation characteristics of polymers. We report here the results of molecular dynamics simulations of Nylon 6 which provides an excellent example for the investigation of such an influence. To demonstrate the effect of proper accounting for H-bonding on bulk polymer properties, the AMBER99sb force field is used with two different parametrization approaches leading to two different sets of partial atomic charges. The simulations allowed the study of the thermal and dielectric properties in a wide range of temperatures and cooling rates. The feasibility of the use of the three methods for the estimation of the glass transition temperature not only from the temperature dependence of structural characteristics such as density, but also by using the electrostatic energy and dielectric constant is demonstrated. The values of glass transition temperatures obtained at different cooling rates are practically the same for the three methods. By proper accounting for partial charges in the simulations, a reasonable agreement between the results of our simulations and experimental data for the density, thermal expansion coefficient, static dielectric constant and activation energy of γ and ß relaxations is obtained demonstrating the validity of the modeling approach reported.

Molecular dynamics simulations of uniaxial deformation of thermoplastic polyimides.

The results of atomistic molecular-dynamics simulations of mechanical properties of heterocyclic polymer subjected to uniaxial deformation are reported. A new amorphous thermoplastic polyimide R-BAPO with a repeat unit consisting of dianhydride 1,3-bis-(3',4,-dicarboxyphenoxy)diphenyl (dianhydride R) and diamine 4,4'-bis-(4''-aminophenoxy)diphenyloxide (diamine BAPO) was chosen for the simulations. Our primary goal was to establish the impact of various factors (sample preparation method, molecular mass, and cooling and deformation rates) on the elasticity modulus. In particular, we found that the elasticity modulus was only slightly affected by the degree of equilibration, the molecular mass and the size of the simulation box. This is most likely due to the fact that the main contribution to the elasticity modulus is from processes on scales smaller than the entanglement length. Essentially, our simulations reproduce the logarithmic dependence of the elasticity modulus on cooling and deformation rates, which is normally observed in experiments. With the use of the temperature dependence analysis of the elasticity modulus we determined the flow temperature of R-BAPO to be 580 K in line with the experimental data available. Furthermore, we found that the application of high external pressure to the polymer sample during uniaxial deformation can improve the mechanical properties of the polyimide. Overall, the results of our simulations clearly demonstrate that atomistic molecular-dynamics simulations represent a powerful and accurate tool for studying the mechanical properties of heterocyclic polymers and can therefore be useful for the virtual design of new materials, thereby supporting cost-effective synthesis and experimental research.

Shear-induced effects in hyperbranched-linear polyelectrolyte complexes.

Static and dynamic properties of complexes formed by hyperbranched polymers with linear polyelectrolytes are studied under the influence of steady shear flow by means of Brownian dynamics simulations. Models of peripherally charged hyperbranched molecules bearing two extreme topological structures and different molecular weights complexed with linear neutralizing chains are subjected to a range of shear rates starting from a low-shear regime toward the complex-breaking point. Examination of the stability limit, shape and mass distribution parameters, and dynamics in different lengths and timescales is performed as a function of the applied shear. The results described illustrate features of the generic behavior that should be expected from such systems under conditions of steady shear flow.

Effects of topology and size on statics and dynamics of complexes of hyperbranched polymers with linear polyelectrolytes.

Brownian dynamics simulations with explicit hydrodynamic interactions have been employed to study generic effects of size and topology in noncovalent (Coulombic-driven) complexes formed by irregular-shaped hyperbranched polymers and linear polyelectrolytes. The behavior of the complexes was explored in detail in terms of static and dynamic properties, both in local and in the entire complex scale. The results were compared to previous studies on perfect dendrimers and other hyperbranched molecules where available. It was found that both molecular weight and structure may impart significant changes to key factors known to be associated with the ability of these systems to take part in relevant nanoscale applications.