Multiscale entanglement in ring polymers under spherical confinement

The interplay of geometrical and topological entanglement in semiflexible knotted polymer rings confined inside a spherical cavity is investigated by using advanced numerical methods. By using stringent and robust algorithms for locating knots, we characterize how the knot length l(k) depends on the ring contour length L(c) and the radius of the confining sphere R(c). In the no- and strong-confinement cases, we observe weak knot localization and complete knot delocalization, respectively. We show that the complex interplay of l(k), L(c), and R(c) that seamlessly bridges these two limits can be encompassed by a simple scaling argument based on deflection theory. The same argument is used to rationalize the multiscale character of the entanglement that emerges with increasing confinement.     

Stress relaxation in entangled melts of unlinked ring polymers

Stress relaxation in unlinked ring polymer melts poses an important challenge to our theoretical understanding of entangled polymer dynamics. Recent experiments on entangled unlinked ring melts show power-law stress relaxation with no hint of a rubbery plateau, usually the hallmark of entangled polymers. Here we present a theory for stress relaxation in rings analogous to the successful approach for star polymers. We augment our theory with mesoscale Monte Carlo dynamics simulations of equivalent "lattice animal" configurations. We find a stress relaxation function G(t)～t(-α) with α≈1/2 consistent with experiment, emerging ultimately from the disparate relaxation times of more- and less-central portions of ring conformations.     

The dynamic scattering factor for linear and ring polymers using renomalization group techniques

The dynamic scattering factorS(k,t) for simple ring polymers and linear chains in the presence of hydrodynamic interactions is calculated toO() (4–d, d being the spatial dimensionality) and toO(k ⁴) (k being the external momentum). Results are presented in universal functional form toO().     

Knots in polymers

Knots and topological entanglements play an important role in the statistical mechanics of polymers. While topological entanglement is a global property, it is possible to study the size of a knotted region both numerically and analytically. It can be shown that long-range repulsive interactions, as well as entropy favor small knots in dilute systems. However, in dense systems and at the Θ-point in two dimensions the uncontracted knot configuration is the most likely.     

Piezoelectricity in polymers

In the last few years it has been shown that polyvinylidene fluoride, a polymer which can.readily be formed into very thin, flexible, and transparent films, is a ferroelectric material. The availability of a ferroelectric material in this unusual form has led to a large number of possible new applications, and the Japanese company, Pioneer Electronic Corporation, has already developed a commercial product.¹ They are producing headphones in which the active element is an 8-pm-thick film of polyvinylidene fluoride. Indicative of the kind of creativity this new material permits, the headphones do not use the change in thickness of the film at all. The polymer film is stretched over a flexible polyurethane foam and application of a voltage causes a change in the area of the film so that the foam, functioning like a spring, is either compressed or allowed to expand, depending on the polarity of the applied voltage.     

超导π环零环混合阵列的自发磁化

研究了超导π环零环的混合规则阵列，计算了阵列的自由能.结果表明，两个π环通过中间零环间接耦合使得两π环反向自发磁化能量较低.规则阵列中，相邻π环倾向于反向自发磁化.这一现象起因于超导波函数的量子相干效应. 关键词： 超导结 π环 零环 自发磁化     

Melting kinetics in polymers

In polymers, it is possible to obtain single chain forming single crystals. It is feasible to melt these crystals by simple consecutive detachment of chain segments from the crystalline substrate and its diffusion into the melt. However, complication in the melting process occurs when the chain in the process of detachment from the surface is shared between different crystals. Experimentally, a clear distinction in different melting processes is observed, by the differences in the activation energies required for the consecutive detachment of chain segments or of segments having topological constraints. The consecutive detachment of free chain segments starts at the melting temperature predicted from the Gibbs-Thomson equation, whereas higher temperature or time is required if the chain has to overcome the constraints.     

Stress-induced textures in polymers

The effect of an applied stress on the annealing texture of polyethylene is demonstrated by means of stress annealing experiments. Cold-drawn polyethylene specimens were annealed for various times at 126°C with and without a compression stress of 0.4 kg/mm² normal to the drawing direction. The observed change in the annealing texture resulting from the compression stress indicates that stress-induced alignment of the crystalline regions in the polyethylene occurs (stress-induced texture). The alignment may be understood in terms of the elastic energy stored in the material during annealing. The stored elastic energy is minimized by aligning the crystallites such that the crystallographic direction of lowest modulus is parallel to the direction of the applied stress. The importance of this observation for the interpretation of the high-temperature deformation textures of polymers is discussed.     

激光陀螺中背向散射的研究

为了研究谐振腔形状变化对激光陀螺中背向散射的影响,基于矢量叠加理论,分析了激光陀螺背向散射源及其对总的背向散射的影响.根据背向散射对顺逆时针光的耦合作用,推导出了总的背向散射系数与顺逆时针旋转光光强的关系式.基于这一关系,设计实验,通过施加电压使谐振腔反射镜到不同位置来改变光腔形状变化,同时测量光强交流量的振幅,得到了总的背向散射系数的变化曲线.通过与仿真结果对比,验证了背向散射的矢量叠加理论.     

Solitons in a ring superlattice

We consider the propagation of electromagnetic solitons in a ring superlattice formed by the successive deposition of coaxial ring-shaped layers lying in parallel planes. In contrast to a rectilinear (infinite) superlattice, in which either one soliton (a single solution) or an infinite number of solitons (fluxon solution), any finite number of equidistant solitons is possible in a ring superlattice. We calculate the constant component of the electric field along the axis of the superlattice and the density of the current of electron drag by solitons (solitonelectric current).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 79–81, November, 1990.     

Amphiphilic polymers in photodynamic therapy

It is shown that some amphiphilic polymers (AP), including, polyvinylpyrrolidone (PVP), which exhibit no their own photochemical activity, can increase the activity of porphyrin photosensitizers (PPS), the most effective and nontoxic types of dyes for photodynamic action on tumor cells. It is also shown that, under the model conditions of tryptophan photooxidation, addition of amphiphilic polymers increases the activity of carborane-substituted tetra(fluorophenyl)porphyrins, Photoditazine, and dimegin. According to NMR and fluorescence spectroscopy data, this phenomenon, known as polymer effect, is probably associated with the formation of AP-PPS complexes, a factor that prevents the aggregation of PPS, normally occurring in aqueous solutions, thereby enhancing the photosensitizing activity of PPS.     

Polarons in organic conjugated polymers

An unified treatment of the electronic structure of organic conjugated polymers based on a renormalization approach is presented. The changes in the electronic structures of trans-polyacetylene, poly-(p-phenylene), polypyrrole and polythiophene, brought about by the presence of polarons in these systems, are studied. For all systems, two localized states, which can be interpreted as the symmetric and antisymmetric combinations of soliton wavefunctions, are created at the central gap.     

Electrocaloric effect in ferroelectric polymers

The electrocaloric effect (ECE) of poly (vinyledene fluoride?Ctrifluoroethylene) (P(VDF?CTrFE)) 55/45?mol% copolymers was directly measured, which confirms the results deduced from Maxwell relation. The adiabatic temperature change ??T under a given electric field peaks at the ferroelectric?Cparaelectric (FE?CPE) transition. Away from it, ECE becomes small. ??T versus applied electric field can be described well by a modified Belov?CGoryaga equation. The ECE in ferroelectric polymers, especially near FE?CPE transition where larger ECE is observed, are analyzed under different boundary conditions employing phenomenological theory and constitutive equations. The secondary pyroelectricity is found to play a significant role which enhances ECE in ferroelectric polymers.     

Delocalized radiation damage in polymers

We present and discuss measurements of electron-irradiation damage in polystyrene and other polymers, based on fading of the 7-eV energy-loss peak. These measurements suggest a large increase in characteristic dose as the electron-beam diameter is reduced from 1 μm to below 1 nm. This finding is discussed in terms of secondary-electron production and delocalization of the inelastic scattering, both as it affects the volume of specimen in which the energy is deposited and the volume giving rise to the inelastic signal used to assess the damage.