Dual mechanical braiding experiments provide a useful tool with which investigate the nature of interactions between rod-like molecules, for instance actin and DNA. In conditions close to molecular condensation, one would expect an appearance of a local minimum in the interaction potential between the two molecules. We investigate this situation, introducing an attractive component into the interaction potential, using a model developed for describing such experiments. We consider attraction that does not depend on molecular structure, as well that which depends on a DNA-like helix structure. In braiding experiments, an attractive term may lead to certain effects. A local minimum may cause molecules to collapse from a loosely braided configuration into a tight one, occurring at a critical value of the moment applied about the axis of the braid. For a fixed number of braid pitches, this may lead to coexistence between the two braiding states, tight and loose. Coexistence implies certain proportions of the braid are in each state, their relative size depending on the number of braid pitches. This manifests itself as linear dependence in numerically calculated quantities as functions of the number of braid pitches. Also, in the collapsed state, the braid radius stays roughly constant. Furthermore, if the attractive interaction is helix dependent, the left-right handed braid symmetry is broken. For a DNA like charge distribution, using the Kornyshev-Leikin interaction model, our results suggest that significant braid collapse and coexistence only occurs for left handed braids. Regardless of the interaction model, the study highlights the possible qualitative physics of braid collapse and coexistence; and the role helix specific forces might play, if important. The model could be used to connect other microscopic theories of interaction with braiding experiments.
Experiments with polymer latex solutions show the coexistence of order-disorder structures of macroions. Because of the large macroions' sizes, this order-disorder phase coexistence imply the existence of very long-range attractive and repulsive forces, which can not be explained in terms of conventional direct interaction potentials, which are short-range. Here we apply an integral equations theory to a simple model for colloidal dispersions, at finite concentrations, calculate the particles distribution functions and the involved effective forces. We find very long-range attractive and repul…
Generalization of the van der Waals equation for anisotropic fluids in porous media
多孔介质中各向异性液体的广义van der Waals状态方程由两项组成。一项是基于标度粒子理论得到的无规多孔介质中硬球柱的状态方程。另一项是用分子间吸引力的平均值表示的。所得方程用于研究气液两相流动。分子系统的相变行为取决于分子形状的各向异性，分子间吸引力的各向异性，研究表明，各向异性相是由分子间相互吸引作用的各向异性和分子形状的各向异性共同作用形成的，分子形状的各向异性使多孔介质的孔隙率和孔隙率发生变化，从而使多孔介质的孔隙率和孔隙率发生变化。相图的温度和密度。吸引相互作用的各向异性使各向同性相和各向异性相之间的共存区域明显变宽，并将其移到低密度和高温度的区域。结果表明，对于足够长的球柱，液-气相变完全局限在相变区域内。对于所有考虑的情况，孔隙率的降低使相图移动到较低密度和较低温度的区域。
