单层膜界面上亚微米颗粒的阻力系数及扩散行为

The friction coefficient and diffusion of sub-micro particles straddling a monolayer

  • 摘要: 微纳米颗粒作为生物膜的流变测量探针以及药物疏运载体,研究颗粒于膜上的流体力学阻力与扩散行为具有重要科学意义。已有研究主要侧重于嵌入在膜内且与膜厚度相同的圆柱体(比拟单个磷脂/蛋白质分子)的阻力系数,是一个二维流体力学问题。球形颗粒穿透膜伸入水相中,受力更加复杂。近几年有研究发现当微米颗粒在纯水—空气界面上做布朗扩散时,阻力系数有分子热运动引起的界面扰动对颗粒施加的表面张力的贡献。本论文在亚微米颗粒—单层生物膜界面实验中发现了类似现象,考虑到生物膜与纯水界面的不同力学特性以及亚微米颗粒尺度,本文对表面张力进行了修正:一是加入膜的Maxwell黏弹性项;二是加入热力学毛细波波数项,进而区分微观分子纳米尺度与宏观尺度下表面张力的不同。实验结果发现:由阻力系数拟合得到的热力学毛细波波长恰好等于膜内磷脂分子间的平均间距,符合界面热力学扰动理论的描述;此外,当颗粒与膜内微米磷脂凝聚区域粘连时,粘连体整体所受的阻力几乎全部源自于凝聚区域,水相及膜内对颗粒施加的阻力贡献极小。

     

    Abstract: As the rheological measurement probe of bio-membrane and drug delivery carrier, it is of great scientific significance to study the fluid mechanics resistance and diffusion behavior of particles straddling a monolayer. Existing research focuses primarily on the friction of a disk-like cylinder embedded in a monolayer to simulate a singe lipid or protein molecule, which is a two-dimensional problem. Spherical particles protrude through the monolayer and reach the water subphase, resulting in more complex forces. According to resent research, when micro-sized particles diffuse on the air-water interface, the friction coefficient includes an extra component of the surface tension force induced by interface fluctuations resulting from the molecular thermal motion. This study discovered a similar phenomenon in the diffusion of sub-micro particles across the bio-monolayer interface. We modify the surface tension in the calculation of the friction coefficient by taking into account the different mechanical properties between the monolayer and the water interface, as well as the sub-micro scale. First, the surface tension includes a Maxwell term to account monolayer's viscoelasticity. Second, the surface tension includes the wave number term of thermal capillary waves to distinguish it from the macroscopic surface tension. It is discovered that the wave length fitted using the experimental friction coefficient is nearly equal to the average distance between the lipid molecules in the monolayer, confirming the theoretical descriptions of the interfacial thermal fluctuations. Furthermore, when the particles adhere to the condensed lipid domains within the monolayer, the resistance of the entire assembly is almost entirely derived from the condensed domains. The resistance force induced by water on the protruding particle or the force induced by the monolayer on the contact line are both negligible.

     

/

返回文章
返回