arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 1503.02818cond-mat.softcond-mat.stat-mechphysics.bio-ph
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负表面张力下的小膜

Small membranes under negative surface tension

Yotam Y. Avital, Oded Farago

摘要:

我们使用计算机模拟和一个简单的自由能模型来研究双层膜的负(压缩)机械张力的应用程序的响应。这种张力使巨囊泡的长波长波动模式不稳定,但当考虑小膜和囊泡时,它可以持续。我们的负张力模拟结果揭示了两个制度-(i)一个弱的负张力制度,其特征在于拉伸为主的弹性,和(ii)一个强的负张力制度,其特征在于弯曲为主的弹性行为。这类似于在巨大单层囊泡(GUV)中的经典Evans和Rawicz微量移液管抽吸实验的发现[Phys,Rev. Lett. { \bf 64},2094(1990)]。然而,在GUV中,两种弹性状态之间的交叉发生在小的正表面张力下,而在较小的膜中,它发生在中等的负张力下。关于小膜对负表面张力的响应的另一个有趣的观察与机械张力和波动张力之间的关系有关,对于非负值,机械张力和波动张力彼此相等。当张力减小到负值时,波动张力$γ$在小的负张力区域中比$τ$下降得稍微快一些,然后在大的负张力下饱和(并且变得大于$τ$)。弯曲模量呈现“相反”的趋势。它几乎保持不变,在拉伸为主的弹性制度,并减少在弯曲为主的制度。热高度波动和投影面积变化的振幅在机械不稳定性开始时发散。

英文摘要:

We use computer simulations and a simple free energy model to study the response of a bilayer membrane to the application of a negative (compressive) mechanical tension. Such a tension destabilizes the long wavelength undulation modes of giant vesicles, but it can be sustained when small membranes and vesicles are considered. Our negative tension simulation results reveal two regimes - (i) a weak negative tension regime characterized by stretching-dominated elasticity, and (ii) a strong negative tension regime featuring bending-dominated elastic behavior. This resembles the findings of the classic Evans and Rawicz micropipette aspiration experiment in giant unilamellar vesicles (GUVs) [Phys, Rev. Lett. {\bf 64}, 2094 (1990)]. However, while in GUVs the crossover between the two elasticity regimes occurs at a small positive surface tension, in smaller membranes it takes place at a moderate negative tension. Another interesting observation concerning the response of a small membrane to negative surface tension is related to the relationship between the mechanical and fluctuation tensions, which are equal to each other for non-negative values. When the tension decreases to negative values, the fluctuation tension $γ$ drops somewhat faster than $τ$ in the small negative tension regime, before it saturates (and becomes larger than $τ$) for large negative tensions. The bending modulus exhibit an "opposite" trend. It remains almost unchanged in the stretching-dominated elastic regime, and decreases in the bending-dominated regime. Both the amplitudes of the thermal height undulations and the projected area variations diverge at the onset of mechanical instability.

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