Sachin Krishnan T V, Okamoto Ryuichi, Komura Shigeyuki
Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Tokyo 192-0397, Japan.
Department of Physics, Indian Institute of Technology Madras, Chennai 600036, India.
Phys Rev E. 2016 Dec;94(6-1):062414. doi: 10.1103/PhysRevE.94.062414. Epub 2016 Dec 30.
We study the relaxation dynamics of a compressible bilayer vesicle with an asymmetry in the viscosity of the inner and outer fluid medium. First we explore the stability of the vesicle free energy which includes a coupling between the membrane curvature and the local density difference between the two monolayers. Two types of instabilities are identified: a small wavelength instability and a larger wavelength instability. Considering the bulk fluid viscosity and the inter-monolayer friction as the dissipation sources, we next employ Onsager's variational principle to derive the coupled equations both for the membrane and the bulk fluid. The three relaxation modes are coupled to each other due to the bilayer and the spherical structure of the vesicle. Most importantly, a higher fluid viscosity inside the vesicle shifts the crossover mode between the bending and the slipping to a larger value. As the vesicle parameters approach the unstable regions, the relaxation dynamics is dramatically slowed down, and the corresponding mode structure changes significantly. In some limiting cases, our general result reduces to the previously obtained relaxation rates.
我们研究了一种可压缩双层囊泡的弛豫动力学，该囊泡的内外流体介质粘度存在不对称性。首先，我们探讨了囊泡自由能的稳定性，其中包括膜曲率与两个单层之间局部密度差的耦合。识别出了两种不稳定性：小波长不稳定性和较大波长不稳定性。将体相流体粘度和层间摩擦力视为耗散源，接下来我们运用昂萨格变分原理推导膜和体相流体的耦合方程。由于囊泡的双层结构和球形结构，三种弛豫模式相互耦合。最重要的是，囊泡内部较高的流体粘度会将弯曲和滑动之间的交叉模式转移到更大的值。当囊泡参数接近不稳定区域时，弛豫动力学显著减慢，相应的模式结构也发生显著变化。在某些极限情况下，我们的一般结果简化为先前得到的弛豫率。
