Force-extension curve of a polymer in a high-frequency electric field

We study theoretically the conformation and force-extension curve of a semiflexible polymer in a spatially uniform ac electric field. The polymer backbone minimizes its energy by aligning along one of two orientations parallel to the field. In a strong ac field, hairpin kinks develop between regions of opposite alignment. These kinks are mathematically described as sine-Gordon solitons. We calculate the equation of state of the one-dimensional kink gas, which yields the force-extension curve of the polymer. A sufficiently strong ac field causes the polymer to extend spontaneously to almost its full contour length. The theory is applied to recent experiments on dielectrophoretic stretching of DNA.     

Molecular-dynamics simulations with explicit hydrodynamics I: On the friction coefficients of deformed polymers

We implement large-scale Molecular-Dynamics (MD) simulations which incorporate hydrodynamic interactions via the inclusion of explicit Lennard-Jones solvent to examine the behaviour of polymer chains in sieving media. We begin by examining the friction coefficients of polymers in long-lived states responsible for inducing length-dependent mobility, i.e., allowing separation of polymers (or polyelectrolytes) by molecular weight. In particular, the conformations we examine occur in devices which utilize arrays of molecular obstacles or dilute solutions of polymers. We compare the results from our MD simulations with expressions from macroscopic hydrodynamics for four specific cases: i) a random coil excluded-volume Zimm polymer, ii) a rigid polymer moving perpendicular to its major axis iii) a rigid polymer moving parallel to its major axis and iv) a rigid polymer, folded at different points along its contour. We also examine the behaviour of the friction coefficient of a fully flexible molecule pulled by its middle monomer as a function of an applied force F and show that there are several distinct frictional regimes.PACS: 83.10.Mj Molecular dynamics, Brownian dynamics - 61.41. + e Polymers, elastomers, and plastics - 82.20.Wt Computational modeling; simulation     

Hierarchic Structure Formation in Binary and Ternary Polymer Blends

The phase morphology of multi-component polymer blends is governed by the interfacial interactions of its components. We discuss here the domain morphology in thin films of model binary and ternary polymer blends containing polystyrene, poly(methyl metacrylate), and poly(2-vinylpyridine) (PS, PMMA, PVP). When sandwiched between two non-polar surfaces, characteristic lateral phase morphologies are observed after the film formation by spin-coating. We discuss here two techniques, by which hierarchical lateral structures in polymer films can be made. The first method makes use of two simultaneously occurring interfacial instabilities. The second technique employs the effect of a variation of the enthalpic interaction parameters in a ternary polymer mixture on its lateral polymer phase morphology.     

Single long-polymer translocation through a long pore

This paper theoretically studies the free energy and conformational entropy of a long polymer threading a long nanopore (n₀/N \ge 0.1) on external electric field. The polymer expanded model is built in this paper, that is, a single long polymer chain with N monomers (each of size a) threading a pore with n₀ monomers can be regarded as polymer with N+n_{0} monomers translocating a 2-dimension hole embedded in membrane. A theoretical approach is presented which explicitly takes into account the nucleation theory. Our calculations imply that, the structure of polymer changes more acutely than other situation, while its leading monomer reaches the second vacuum and its end monomer escapes the first vacuum. And it is also shown that the length scale of polymer and pore play a very important role for polymer translocation dynamics. The present model predicts that the translocation time depends on the chemical potential gradient and the property of the solvent on sides of pore to some extent.     

光折变聚合物材料在光电子技术中的应用

光折变聚合物材料与光折变晶体相比，其非线性光学系数大，响应时间快，成本低廉，制备灵活，有可能成为制作光子学集成器件的材料。简要介绍了光折变聚合物材料在图像识别、光信息存储及光学相干层析技术等方面的应用情况，指出光折变聚合物材料中存在光子带隙。最后预测了光折变聚合物材料作为光子晶体在光子学器件中的应用前景。     

Contraction and reswelling of a polymer chain near the critical point of a binary liquid mixture

We have studied the conformation change of a flexible linear polymer chain near the critical point of a binary liquid mixture using fluorescence correlation spectroscopy, which measured the hydrodynamic radius of the chains. Our results indicate that as the critical temperature (Tc) is approached, the chain size decreases. The polymer attains its most compact conformation when the correlation length of the critical fluctuations becomes comparable to the coil size. At very close to Tc, the polymer reexpands dramatically. To our knowledge, this is the first experimental evidence supporting the prediction of Brochard and de Gennes that a polymer chain will collapse and subsequently reswell on approaching Tc.     

奎尼丁分子印迹聚合物的制备及其吸附性能

以奎尼丁(Quinidine)为模板分子,合成奎尼丁分子印迹聚合物(MIP)。通过封管聚合法研究不同功能单体对奎尼丁分子印迹聚合物的影响,并运用Scatchard方程研究奎尼丁分子印迹聚合物选择吸附特性。以甲基丙烯酸(MAA)为功能单体合成的分子聚合物具有较高的选择吸附性,并且印迹聚合物大于非印迹聚合物的吸附量。奎尼丁印迹聚合物用于临床对奎尼丁的富集与检测有应用前景。     

Tunneling through a Metal/Polymer Interface Containing a Thin Oxide Layer: Discussion of the Consequences of Oxide Presence on Charge Injection

The charge injection from oxidized metal electrodes into conjugated polymer thin films is calculated and compared with ideal metal/polymer interfaces. The presence of the oxide layer has a major influence on the magnitude of the tunneling current as well as on its behavior with applied voltage. It was also found that the fitting of the simple Fowler-Nordheim model for triangular barriers to the obtained current-voltage data from the oxidized interfaces leads to incorrect values of the potential barrier height at the metal/polymer interface. Prediction and its consequences on charge injection control in organic devices are discussed.     

Efficiency of polymer inhibitors upon methylmethacrylate polymerization in frontal mode

It is shown that methylmethacrylate polymerization in frontal mode in the presence of a polymer inhibitor is realized in the lower part of the conversion profile. This region is depleted of polymer inhibitors due to its diffusion into upper layers of the sample. The remaining unreacted polymer inhibitor is contained as an “immured” microphase which is inaccessible for active sites.     

Measurement of shear elasticity and viscosity of rubberlike materials

The method and results of measuring the shear elastic modulus of a rubberlike polymer by the deformation of a plane elastic layer are described. For shear deformations not exceeding 0.5 of the layer thickness, the shear modulus is constant and its value is in agreement with the value determined by pressing a rigid ball against the polymer layer. For deformations exceeding 0.5 of the layer thickness, the stress-strain dependence becomes nonlinear. The coefficient of shear viscosity is determined from the shear wave form generated by focused ultrasound in a homogeneous polymer sample.     

Dynamic instability of strongly confined thin polymer films in spinodal dewetting

We present a general criterion for determining the dynamic instability of a thin polymer film that is strongly confined to a substrate. When such a polymer film is heated above its glass transition temperature, it dewets from the substrate by a spinodal dewetting scenario, in which the onset of the instability is governed by dispersion force and residual thermal stress. It turns out that the thermal stress plays an important role when there is a special interaction between a polymer and a substrate.     

The influence of solar radiations to the physical and structural properties of CR-39

Long chain polymers owe many of their properties to the structural arrangements of their molecules and are extensively used for many industrial and applied sciences. One of such application is their perspective use in the field of solid-state nuclear track detectors. However they are profoundly influenced by low LET radiations exposure and new structural arrangements may emerge. CR-39 is one of the most popular polymeric track detectors, however its aliphatic nature restricts its applications. Thus in the present investigations the damage densities produced by solar radiations to the polymer have been estimated by analyzing the structural, physical and etching properties of the polymer. The polymer is found to be highly sensitive towards solar radiations and great changes in physical and structural properties of polymer have been observed. The sensitivity of the polymer has been found to decrease by 83.40% during eight months.      

分子印迹材料选择性截留卷烟烟气中芳胺的研究

采用分子印迹技术合成了一种对1-萘胺有高度选择性的分子印迹聚合物材料。应用固相萃取吸附试验研究了该聚合物对1-萘胺及其结构类似物的选择特性,表明印迹聚合物材料对4种芳胺类物质表现出良好的选择性结合能力。将所制备的印迹聚合物按不同剂量添加到卷烟嘴棒中,考察其对卷烟烟气中芳胺的截留效果。结果显示,该分子印迹材料能选择性截留卷烟烟气中的1-萘胺、2-萘胺、3-氨基联苯和4-氨基联苯等烟气有害成分;当印迹聚合物添加量为50mg时,卷烟烟气中芳胺的降低率达到30%。     

Chains at interfaces

Simha, together with Frisch and Eirich, was among the first to realize that in energetic interaction with a surface a flexible polymer chain would be under a major conformational constraint which could be analyzed by solving a random walk (diffusional) problem near a barrier. These results stimulated more work, and today we have a fairly good knowledge of the factors which determine polymer adsorption from very dilute solution. Conformational problems arise also when more concentrated systems are used and it has become apparent that as concentration increases the surface phase will, more and more, be scaled by the root mean square diameter of the undeformed macromolecule. One can view the presence of an energetically attractive interface as creating a sink for macromolecules. The closer a polymer solution is to its Θ point, the more easily the polymer in solution can enter the sink and the stronger will be the extent of adsorption. The presence of an interface can thus be seen as a means to produce a phase separation in a polymer system which would otherwise be stable. Coatings of adsorbed polymers over colloidal particles create “macromolecular” solutions, where the “macromolecule” is the colloid particle with its adsorbed coat. This causes polymer segment/polymer segment contacts to dominate the encounter energetically. Hence, the solution behavior of the coated colloid becomes reminiscent of the solution behavior of the polymer in the coat. Stabilization by adsorbed polymer layers derives from converting the original solubility characteristics of the colloid, from what they were, essentially to those of the polymer being used.     

姜黄素在丙烯酰胺聚合物中的发光特性研究

以丙烯酰胺为功能单体、乙二醇二甲基丙烯酸酯为交联剂 ,在聚合之前的溶液体系中均匀混入荧光分子姜黄素 ,制备了具有光致发光性能的块状聚合物 ,并将此聚合物粉碎为 4 0～ 75 μm直径的粉末。姜黄素在此聚合物中与其在乙醇溶液中相比 ,其荧光发射光谱有明显的蓝移现象。用同样方法制备的含有罗丹明 6G、四碘荧光素、荧光桃红的丙烯酰胺聚合物也有类似的现象 ,初步认为此蓝移现象的机理可能是聚合物的三维空间网状结构对于荧光分子的隔离效应导致其接近于单分子发光所致     

Hydrodynamic screening of star polymers in shear flow

The mutual effects of the conformations of a star polymer in simple shear flow and the deformation of the solvent flow field are investigated by a hybrid mesoscale simulation technique. We characterize the flow field near the star polymer as a function of its functionality (arm number) f . A strong screening of the imposed flow is found inside the star polymer, which increases with increasing f . To elucidate the importance of hydrodynamic screening, we compare results for hydrodynamic and random solvents. The dependence of the polymer orientation angle on the Weissenberg number shows a power law behavior with super-universal exponent --independent of hydrodynamic and excluded-volume interactions. In contrast, the polymer rotation frequency changes qualitatively when hydrodynamic interactions are switched on.     

Luminescence kinetics of linear polymer molecules with chromophores randomly distributed along the chain

Luminescence kinetics of chromophores randomly attached to an isolated flexible polymer chain is studied. In the static case, when the polymer chain does not change its conformation during the donor excited-state lifetime, analytical equations are derived for the luminescence kinetics of both ideal and nonideal polymer chains. The conditions are formulated when the inhomogeneous broadening should be taken into account. For the dynamic case, the diffusion and hopping mechanisms of the polymer motion are studied.     

电子辐照下聚合物介质深层充电现象研究

空间辐射环境中,聚合物介质的深层充放电效应是威胁航天器安全的重要因素之一.文中在Chudleigh和von Berlepsch所发展的电位衰减模型基础上引入传输电流项,考虑了电子入射引起的感应电导率和感应电场的影响,提出了新的分析研究介质材料深层充电规律和特征的模型.通过该模型,分析了不同辐射条件下介质的表面电位、内部电荷与电场分布的变化,并设计实验及援引其他实验数据对模型分析结果进行验证.分析和实验结果表明,聚合物介质在深层充电过程中的平衡电位随着入射电子束流强度和介质电阻率的增加而增大,决定深层充电平 关键词： 深层充电 电荷传输模型 电子束 聚合物     

Dewetting as an investigative tool for studying properties of thin polymer films

Employing mass conservation, time-resolved dewetting experiments of thin polymer films allow to determine in real time the dynamic contact angle and the slippage length. Moreover, based on a systematic variation of interfacial properties of a polymer brush, dewetting makes it possible to calculate the force it needs to extract a single polymer chain from its own melt. In the visco-elastic regime close to the glass transition, the temperature and molecular weight dependence of the relaxation time of residual stresses resulting from film preparation by spin-coating can be obtained from the evolution of the shape of the dewetting rim. The presented examples demonstrate that dewetting represents a powerful approach for a sensitive characterization of rheological, frictional and interfacial properties of thin polymer films.     

Effect of deformation of a polymer matrix on the optical properties of CdS nanocrystals incorporated into it

A study is made of the photodegradation kinetics of luminescence and absorption of cadmium sulfide nanocrystals incorporated into a plastic polymer matrix. The reversibility effect of photodegradation under mechanical deformation (stretching) of a polymer film is revealed. It is suggested that the photodegradation reversibility is related to the extraction of electrons, photoexcited in nanocrystals, from deep-lying traps in the surrounding polymer matrix during its deformation. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 101–104, January–February, 2000.