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1.
Discontinuous molecular dynamics simulations are performed on a system containing 32 hard chains of length 192 at a volume fraction of phi = 0.45 to explore the idea that localized entanglements have a significant effect on the dynamics of the individual chains within an entangled polymer melt. Anomalous behavior can still be observed when studying the dynamics of the individual chains, although increased time averaging causes the anomalous relaxation-memory-release behavior that was observed previously in the system to smooth out. First, the individual chain mean squared displacements and apparent diffusion coefficients are calculated, and a wide distribution of diffusive behavior is found. Although the apparent diffusion coefficient curve averaged over all chains displays the predicted long-time diffusive behavior, the curves for the individual chains differ both qualitatively and quantitatively. They display superdiffusive, diffusive, and subdiffusive behavior, with the largest percentage of chains exhibiting superdiffusive behavior and the smallest percentage exhibiting the predicted diffusive behavior. Next, the individual chain end-to-end vector autocorrelation functions and relaxation times are determined, and a wide distribution of stress relaxation behavior is found. The times when the end-to-end vector autocorrelation functions relax completely span almost an order of magnitude in reduced time. For some chains, the end-to-end vector autocorrelation function relaxes smoothly toward zero similar to the system average; however, for other chains the relaxation is slowed greatly, indicating the presence of additional entanglements. Almost half of the chains exhibit the anomalous behavior in the end-to-end vector autocorrelation function. Finally, the dynamic properties are displayed for a single chain exhibiting anomalous relaxation-memory-release behavior, supporting the idea that the relaxation-memory-release behavior is a single-chain property. 相似文献
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We investigated the uniaxial deformation behavior of crosslinked low‐density polyethylene in partially and substantially molten states using a real‐time true stress–strain birefringence system. The stress–birefringence behavior exhibits a multiregime behavior during stretching and holding process. The details of this regime behavior are primarily governed by the degree of unmelted crystallinity as it has a dominant role in the long‐range structural connectivity. When the long‐range physical connectivity is present, a three‐regime nonlinear stress–optical behavior was observed. When the long‐range connectivity is substantially eliminated at higher temperatures, the regime I behavior disappears. Structural studies including cooling process reveal that the lower the proportion of molten material during stretching, the higher the concentration of fibrillar structure and the shorter are the lengths of the kebabs that exhibit twisted lamellae after solidification. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1825–1841, 2005 相似文献
4.
对水+3-甲基吡啶+溴化钠三元电解质溶液的临界跨接行为的认识存在着争议. 部分研究认为由于三甲基吡啶的聚集, 体系存在从非经典的3D-Ising(三维伊辛)行为向经典的平均场行为的非单调跨接; 另一部分研究发现该体系符合3D-Ising临界行为, 并不存在跨接. 采用动-静态光散射研究了溴化钠, 3-甲基吡啶和水三元溶液的临界性质, 得到动态关联长度和静态关联长度, 发现动态关联长度和静态关联长度一致, 且在实验温度范围内(离临界温度0.01~25 K), 体系不违背3D-Ising行为, 也观测不到显著的临界跨接现象. 相似文献
5.
In the phase behavior of binary polymer/solvent mixtures, a lower critical solution temperature (LCST) and hour-glass shaped and closed miscibility loop phase behavior are encountered. The closed miscibility loop phase behavior may be mainly due to highly oriented interactions such as hydrogen bonding. The purpose of this study is to describe closed miscibility loop phase behavior in the liquid-liquid equilibria of polymer solutions. To consider highly oriented interactions (or specific interactions), we employed a secondary lattice concept as a perturbation term. 相似文献
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Jopp J Grüll H Yerushalmi-Rozen R 《Langmuir : the ACS journal of surfaces and colloids》2004,20(23):10015-10019
The wetting behavior of water droplets on periodically structured hydrophobic surfaces was investigated. The effect of structure geometry, roughness, and relative pore fraction on the contact angles was investigated experimentally for droplets of size comparable to the size of the structures. It was found that surface geometry may induce a transition from groove-filling and Wenzel-like behavior to nonfilling of surface grooves and consequential Cassie-Baxter behavior. Numerical calculations of the free energy of these systems suggest that the equilibrium behavior is in line with the experimental observations. The observations may serve as guidelines for the design of surfaces with the desired wetting behavior. 相似文献
8.
Y. -K. Leong 《Colloid and polymer science》1997,275(9):869-875
The effect of pH on the flow behavior of ZrO2 suspensions containing polyacrylic and octanoic acids was evaluated. In the flocculated pH regime, the flow behavior is highly
shearthinning and can be described by a power-law model. The shear-thinning behavior increases with increasing degree of flocculation.
Maximum shearthinning was observed at the zero zeta potential condition. Hydrophobic interaction arising from adsorbed octanoic
acid was found to enhance the shear-thinning behavior. No such enhancement was observed for adsorbed polyacrylic acid. It
was also illustrated that the viscosity–pH behavior is a mirror image of the yield stress–pH behavior. A quantitative particle-pair
interactions model incorporating steric and hydrophobic interactions was proposed to explain the effects of polyacrylic and
octanoic acids on the maximum yield stress.
Received: 23 May 1997 Accepted: 4 June 1997 相似文献
9.
Ren B Ruditskiy A Song JH Kretzschmar I 《Langmuir : the ACS journal of surfaces and colloids》2012,28(2):1149-1156
Three types of iron oxide Janus particles are obtained by varying the deposition rate of iron in a 3:1 Ar/O(2) atmosphere during physical vapor deposition. Each type of iron oxide Janus particle shows a distinct assembly behavior when an external magnetic field is applied, i.e., formation of staggered chains, double chains, or no assembly. A detailed deposition rate diagram is obtained to identify the relationship between deposition rate and assembly behavior. The extent of iron oxidation is identified as the key parameter in determining the assembly behavior. In addition, the effects of particle volume fraction, thickness of the iron oxide cap, and assembly time on the final assembly behavior are studied. Cap thickness is shown not to influence the assembly behavior, while particle volume fraction and assembly time affect the chain growth rate and the chain length, but not the overall assembly behavior. The samples are characterized by optical, scanning electron, and atomic force microscopies. 相似文献
10.
In this article, we analyze different factors that affect the diffusion behavior of small tracer particles (as they are used, e.g., in fluorescence correlation spectroscopy (FCS)) in the polymer network of a hydrogel and perform simulations of various simplified models. We observe, that under certain circumstances the attraction of a tracer particle to the polymer network strands might cause subdiffusive behavior on intermediate time scales. In theory, this behavior could be employed to examine the network structure and swelling behavior of weakly crosslinked hydrogels with the help of FCS. 相似文献
11.
In this paper, we study how information transmission delays affect the spiking behavior of electrically coupled stochastic Hodgkin-Huxley (HH) neurons on Newman-Watts networks. It is found that the spiking behavior becomes the most regular at an optimal time delay, indicating the occurrence of delay-induced coherence resonance-like (CR-like) behavior. Interestingly, there are different CR-like types, depending on the membrane patch size of the neuron. For a smaller patch size, only single CR-like behavior occurs; while for a larger patch size, coherence bi-resonance-like (CBR) behavior appears. These findings show that the delay-induced CR-like behavior is closely related to the channel noise strength, and the coupled neurons may exhibit different spiking behaviors under the interplay of the channel noise and time delay. Therefore, the channel noise should be taken into account in the study of time delay-related spiking activity in stochastic HH neurons. This work provides new insight into the role of channel noise and information transmission delays in realistic neural systems. 相似文献
12.
Salomé Machado A. A. Martins V. C. A. Plepis A. M. G. 《Journal of Thermal Analysis and Calorimetry》2002,67(2):491-498
Collagen:chitosan blends in 1:1 ratio were prepared and characterized by Fourier transform infrared spectroscopy, thermal
(DSC, TG) and rheological studies. Apparently each material maintains its behavior and addition of chitosan does not denature
collagen fibers. The rheological behavior showed that adding chitosan to collagen causes a decrease of storage modulus (G’),viscous
loss modulus (G”) and apparent viscosity when measured as a function of frequency. Both anionic and native collagen presented
more solid-like behavior than fluid-like viscoelastic behavior. Collagen:chitosan blends exhibits a more fluid-like viscoelastic
behavior.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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R. Kirchner M. Rodriguez de Rivera J. Seidel V. Torra 《Journal of Thermal Analysis and Calorimetry》2005,82(1):179-184
Summary Using an RC model, the behavior of a TAM high-performance calorimeter (Thermometric AB, Sweden) equipped with a flow-mixing
insertion vessel using independent pumps for each reactant is studied. The model shows a reliable sensitivity behavior for
mixtures realized inside the cell. The model behavior is compared with experimental measurements.</o:p> 相似文献
14.
Previous studies on the dilute-solution behavior of sulfonated ionomers have shown these polymers to exhibit unusual viscosity behavior in mixed solvents of low polarity. These results have been interpreted as arising from specific solvation effects by the solvents with the metal sulfonate groups which persist as ion pairs. The consequences of ion pair interactions and their solvation are exceptional thickening behavior at low polymer levels as compared to unfunctionalized polymers, and anomolous solution viscosities with varying temperature. These studies have now been extended to single-component solvents which traverse a range of polarities. Using the sodium salt of lightly sulfonated polystyrene (S-PS) as a model system, the authors found the solution behavior in low-polarity solvents (tetrahydrofuran) to be consistent with that observed previously for mixed solvents; ion pair interactions predominated. However, in polar solvents such as dimethyl sulfoxide or dimethyl formamide, these polymers behave as classic polyelectrolytes even at sulfonate levels below 2 mol %. The behavior of the S-PS acids is similar to that observed for the metal salts. To a first approximation these two behaviors, ion pair association and polyelectrolyte behavior, are dependent on solvent polarity. In some cases it is possible to induce polyelectrolyte behavior in a S-PS/solvent combination exhibiting ion pair interactions by the addition of very low levels of a polar cosolvent, such as water. These results again demonstrate the selectivity of the solvent-sulfonate interactions. 相似文献
15.
Supercritical fluid chromatography (SFC) sometimes exhibits GC-like behavior and sometimes LC-like behavior, depending on conditions. However, it is not always clear whether one of these types of behavior, or a combination, operates for a particular set of conditions for every solute in a mixture. For example, some components may be partitioned mostly by their vapor pressures, while others, in the same mixture, are partitioned predominantly by solvent-like properties of the mobile phase. Plots of retetion (as log of the capacity factor) vs. reciprocal temperature at constant pressure reveal a clear change in the character of the separation of well-behaved solutes. A thermodynamic explanation of the observed behavior is given, based on the assumption that partitioning is controlled by the heats of solution of solute in the mobile and stationary phases. A model of SFC retention as it deviates from pure-GC behavior on the same column is presented. 相似文献
16.
微波场下非贵金属氧化物的升温行为和烹饪油烟的催化净化性能研究 总被引:3,自引:0,他引:3
在考察了多种金属氧化物在微波场下升温性能的基础上,制备了用于烹饪油烟催化净化的非贵金属催化剂.实验表明,VB族、V族、B族和B族元素氧化物在微波中升温效果明显,其中Co、Ni和V三种元素氧化物的升温效果最好.涂覆氧化铝的蜂窝堇青石负载V2O5的催化剂具有较稳定的吸波升温性和高油烟催化净化活性.添加La2O3后负载型V2O5催化剂活性明显增加,在微波条件下,含有1%La2O3的负载型V2O5催化剂在150℃可使油烟净化率达到88%以上. 相似文献
17.
Dr. Rabih Makki Dr. Alberto P. Muñuzuri Dr. Juan Perez‐Mercader 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(44):14213-14217
It is well known that a large number of catalyst‐carrying beads immersed in an oscillatory chemical medium (Belousov–Zhabotinsky reaction) display collective oscillatory behavior. Using a light sensitive version of BZ, we show that this collective behavior can be entrained to an external light source with an oscillatory intensity. Thus, the emerging collective behavior can be controlled by an external perturbation. 相似文献
18.
The rheological properties of Pluronic L64 in aqueous solutions at various temperatures and concentrations have been investigated. Changes in temperature and concentration cause structural and rheological modifications in Pluronic L64 in aqueous solutions as well as the appearance of a micellization process. For concentrations between 10 and 20 mg/mL, the Pluronic L64 showed a Newtonian or liquid-like behavior at various temperatures. However, for concentrations ranging between 30 and 40 mg/mL, the solutions showed a Newtonian behavior for temperatures below 55°C and a non-Newtonian behavior at 60°C. In p-xylene solutions, the solution exhibits a Newtonian behavior for all the concentrations and temperatures studied. It is believed that the Newtonian behavior of the binary Pluronic L64/p-xylene is due to the nonformation of complex conformations as direct or reverse micelles. 相似文献
19.
Zeynep Mutlu Mayank Jain Sung Ho Yook Mukerrem Cakmak 《Journal of polymer science. Part A, Polymer chemistry》2021,59(18):2045-2056
Mechano-optical behavior and related structural evolution during uniaxial stretching of melt miscible poly (ethylene terephthalate) (PET)/poly (ether imide) (PEI) blends were studied near their glass transition temperature using an instrumented machine that measures true stress, true strain and spectral birefringence simultaneously. Stretching from amorphous state, two distinct stress-optical regimes were observed at temperatures between Tg and Tcc (cold crystallization). Near Tg, a typical photoelastic behavior persists until a critical temperature above which temperature independent initial stress optical behavior is observed. At those temperatures above Tg, where glassy behavior is observed, decreasing stretching rate was also found to eliminate this glassy photo elastic regime leading to the observation of a linear initial stress optical behavior that becomes temperature independent as expected from linear stress optical rule. Increasing PEI concentration in the blends suppresses crystallizability and increases temperature at which initial elastic region disappears giving way to pure liquid behavior where linear stress optical behavior is observed. This is attributed to the increase and broadening of the glass transition temperature with the addition of noncrystallizable PEI. In PET/PEI blends, the stress-optical coefficient (SOC), determined in a linear stress optical regime, was found to increase linearly with the increase in PEI concentration. 相似文献
20.
外显子周期三行为特征的研究 总被引:2,自引:0,他引:2
基因中蛋白质的编码区具有周期三行为这一规律已成为目前基因预测的理论基础, 采用功率谱对外显子的周期三行为特征进行了研究, 结果表明: 大多数外显子独立存在于基因中时并不具有周期三行为, 而当基因被剪切后外显子连在一起编码蛋白质的时候才具有周期三行为. 并且这种行为特征与外显子的长度、碱基在密码子三个位置上的分布以及氨基酸密码子的使用偏好均有密切关系, 同时符合蛋白质翻译次序的外显子也具有对密码子使用的偏好性, 这一研究结果对于提高基因预测的准确率以及内含子功能的研究具有重要意义. 相似文献