Anomalous diffusion of a polymer chain in an unentangled melt

Contrary to common belief, hydrodynamic interactions in polymer melts are not screened beyond the monomer length and are important in transient regimes. We show that viscoelastic hydrodynamic interactions (VHIs) lead to anomalous dynamics of a tagged chain in an unentangled melt at t相似文献   

Quantum diffusion in bilateral doped chains

In this paper,we quantitatively study the quantum diffusion in a bilateral doped chain,which is randomly doped on both sides.A tight binding approximation and quantum dynamics are used to calculate the three electronic characteristics:autocorrelation function C(t),the mean square displacement d(t) and the participation number P (E) in different doping situations.The results show that the quantum diffusion is more sensitive to the small ratio of doping than to the big one,there exists a critical doping ratio q 0,and C(t),d(t) and P (E) have different variation trends on different sides of q 0.For the self-doped chain,the doped atoms have tremendous influence on the central states of P (E),which causes the electronic states distributed in other energy bands to aggregate to the central band (E=0) and form quasi-mobility edges there.All of the doped systems experience an incomplete transition of metal-semiconductor-metal.     

GDP/D-GDP化学结构与力学性能的研究

利用低压等离子体增强化学气相沉积技术制备碳氢辉光放电聚合物(GDP)和全氘代辉光放电聚合物(D-GDP)薄膜。利用表面轮廓仪、傅里叶红外光谱仪和纳米压痕技术对制备的样品进行表征,讨论了GDP/D-GDP薄膜的沉积速率、化学结构和力学性能在ICF物理实验用靶应用中的优缺点。结果表明：GDP/D-GDP薄膜的沉积速率都随反应气体流量比例近线性增加,GDP的沉积速率达到2.6 m,D-GDP的沉积速率达到1 m,GDP的沉积速率远大于D-GDP的沉积速率;D-GDP薄膜内部的交联化程度较弱,D-GDP更有利于靶丸内燃料的红外均化;GDP的力学性能明显优于D-GDP,更有利于ICF物理实验用靶的燃料填充与装配操作。     

GDP/D-GDP化学结构与力学性能的研究

利用低压等离子体增强化学气相沉积技术制备碳氢辉光放电聚合物(GDP)和全氘代辉光放电聚合物(D-GDP)薄膜。利用表面轮廓仪、傅里叶红外光谱仪和纳米压痕技术对制备的样品进行表征,讨论了GDP/D-GDP薄膜的沉积速率、化学结构和力学性能在ICF物理实验用靶应用中的优缺点。结果表明:GDP/D-GDP薄膜的沉积速率都随反应气体流量比例近线性增加,GDP的沉积速率达到2.6μm,D-GDP的沉积速率达到1μm,GDP的沉积速率远大于D-GDP的沉积速率;D-GDP薄膜内部的交联化程度较弱,D-GDP更有利于靶丸内燃料的红外均化;GDP的力学性能明显优于D-GDP,更有利于ICF物理实验用靶的燃料填充与装配操作。     

Simultaneous imaging for surface and internal structure of polymer blend thin films

A novel experimental technique for three-dimensional (3D) visualization of phase-separated structure of polymer blend thin film was proposed. Polystyrene/poly(methyl methacrylate) (PS/PMMA) blend thin films with the thickness of approximately 100 nm were cut at extremely low angle by utilizing surface and interface cutting analysis system (SAICAS), and the cross-section was exposed as gradient surface with the width of approximately 2.5 μm. SFM investigation for the grazing cross-section imaged the detailed internal and surface phase separated structure of the (PS/PMMA) blend thin films on one image.     

Chemical diffusion in CoO

Equilibration kinetics of CoO have been studied over the range 1–10^?5 atm oxygen pressure and 900–1300°C by both thermogravimetric and electrical conductivity techniques. The former technique gives excellent agreement with theory based on bulk diffusion and results in a chemical diffusion coefficient given by, $\text{D}\text{?}\text{= 4.8×10}{}^{\mathrm{?3}}\text{exp (?22,500/RT)}$ cm${}^2\text{sec}$. The defect diffusion coefficient (Dinvinco) is equal to $\text{i}\text{?}\text{tD}\text{2}$. No dependence of ?tD on defect concentration was observed. The electrical conductivity technique qualitatively supports these results.     

Simulations of single polymer chains in the dense limit

We present simulation results for single α-thermal chain polymers in finite volumes. For this we use a recently proposed recursive implementation of the enrichment method. In 3 dimensions it allows the simulation of extremely long chains (up to N = 300000). It is much less efficient for d = 2, but we can also there extend considerably the previously accessible range of chain lengths and densities. We verify most tested scaling laws, and we point out similarities with complex optimization problems.     

Hydrodynamic and viscoelastic effects in polymer diffusion

We develop a fluctuating hydrodynamics approach to study the impact of the hydrodynamic and viscoelastic interactions on the motion of the center of mass of a polymer as well as on the relaxation of Rouse modes, either in a Θ solvent or in a melt of identical unentangled chains. We show that this method allows us to describe the effect of hydrodynamic interactions beyond the Zimm (for a single chain in a Θ solvent) or the Rouse models (for an unentangled melt). In the latter case, we recover the same important effect of the viscoelastic hydrodynamic interactions on the center-of-mass diffusion, first described in Farago et?al (2011 Phys. Rev. Lett. 107 178301).     

Quantum fluctuations and lattice dimerization in coupled polymer chains

Effects of quantum lattice fluctuations on the Peierls dimerization are considered for two neighboring polymer chains, which are modeled individually by the Su, Schrieffer, and Heeger Hamiltonian and coupled by an interchain electron-transfer term. By a functional-integral approach, an equation for the dimerization order parameter is obtained within a one-loop approximation. It is found that the quantum fluctuations are partly suppressed by the interchain coupling and then the system is dimerized for an arbitrary coupling constant and phonon frequency even for the spinless fermion system.     

Cooperative diffusion in concentrated polymer solutions

Summary Concentrated solutions of polystyrene in dioctylphthalate have been examined as a function of temperature over the concentration range 0.2 to 0.9 g/ml. The static screening length and the hydrodynamic screening length evaluated from the cooperative-diffusion coefficient are compared with the predictions of current models. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Nature of the interaction between benzaldehyde links in polymer chains

Journal of Applied Spectroscopy -     

Unusual thermal diffusion in polymer solutions

Thermal diffusion forced Rayleigh scattering results on thermal diffusion of poly(ethylene oxide) (PEO) in ethanol/water mixtures are presented. In water-rich solvent mixtures, PEO is found to migrate towards regions of lower temperature. This is typical for polymer solutions and corresponds to a positive Soret coefficient of PEO. In solvent mixtures with low water content, however, the polymer is found to migrate towards higher temperatures, corresponding to a negative Soret coefficient of PEO in ethanol-rich solutions. To our knowledge, this is the first observed sign change of the Soret coefficient of a polymer in solution. We also present a simple lattice model for the polymer solvent system and calculate Soret coefficients with statistical mechanics methods. The calculated values agree qualitatively with the experimental results.     

Metal and polymer melt jet formation by the high-power laser ablation

The laser-induced metal and polymer melt jets are studied experimentally. Two classes of physical phenomena of interest are: first, the process of explosive phase change of laser induced surface ablation and second, the hydrodynamic jetting of liquid melts ejected from a beamed spot. We focus on the dynamic link between these two distinct physical phenomena in a framework of forming and patterning of metallic and polymer jets using a high-power Nd:YAG laser. The microexplosion of ablative spot on a target first forms a pocket of hot liquid melt and then it is followed by a sudden volume change of gas-liquid mixture leading to a pressure-induced spray jet ejection into surrounding medium.     

Chemical diffusion in molybdenum disulphide

Ceramic molybdenum disulphide (MoS₂) was equilibrated at an ambient sulphur vapour partial pressure p(S₂), 10 Pa<p(S₂)<1000 Pa. After the step change of p(S₂) to a new value, the equilibration kinetics was monitored by measuring electrical conductivity. The application of the solution of Fick's second law (with the initial condition: no concentration gradient in specimen and the boundary condition: surface concentration constant) to the kinetic data gave the chemical diffusion coefficient. The chemical diffusion coefficient, D_chem, determined at 1273 K, was D_chem=(3.20±0.32)*10⁻⁷ cm² s⁻¹ and was found to be independent of sulphur vapour partial pressure. The usefulness of transient electrical conductivity method for determining real values of diffusion data was discussed in terms of defect structure of the studied material.     

Elasticity transition and loop formation in vibrated bead chains: A simulation of polymer chains

By measuring the distribution function of the end-to-end distance, we find that strongly shaken bead chains exhibit many properties, such as the rigid-rod-to-Gaussian chain transition, scaling, fast drop of loop formation probability in the short-chain regime, and enhancement of loop formation probability for kinked chains, of long-chain polymers. Though there is difference in local details between our chains and the worm-like chains, our results are consistent with recent calculations based on the worm-like chain model in many respects.     

Chemical diffusion in calcium titanate

This work reports the gas/solid equilibration kinetics for the O₂/CaTiO₃ system. The electrical conductivity measurement was applied for monitoring the kinetics in the ranges of temperature 973-1323 K and oxygen partial pressure 10 Pa-72 kPa. It was found that the gas/solid equilibration kinetics for the polycrystalline CaTiO₃ specimen in the above experimental conditions is determined by bulk diffusion rather than by grain boundary conditions. The obtained data of the electrical conductivity vs. time were used for the determination of the chemical diffusion coefficient as a function of temperature at low and high p(O₂), respectively:

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