School of Chemical and Physical Sciences, MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington, New Zealand.
Langmuir. 2012 Jul 10;28(27):10256-65. doi: 10.1021/la300903w. Epub 2012 Jun 25.
We study capillary absorption of small polymer droplets into nonwettable capillaries using coarse-grained molecular dynamics simulations and a simple analytical model. Studies of droplets of simple fluids have revealed that the capillary process depends on the ratio of tube-to-droplet radii [Willmott Faraday Discuss., 2010, 146, 233; Marmur J. Colloid Interface Sci. 1988, 122, 209]. Here we consider the absorption of droplets of polymers and study the effect of polymer chain length on the capillary absorption process. Our simulations reveal that for droplets of the same size (radius), the critical tube radius, below which there is no absorption, increases with the length of the polymer chains that constitute the droplets. We propose a model to explain this effect, which incorporates an entropic penalty for polymer confinement and find that this model agrees quantitatively with the simulations. We also find that the absorption dynamics is sensitive to the polymer chain length. In some cases during the capillary uptake transient partial absorption states, where the droplet is partially in and partially out of the tube, were observed. Such dynamics cannot be explained by a generalized Lucas-Washburn approach.
我们使用粗粒化分子动力学模拟和一个简单的分析模型研究了小聚合物液滴通过非润湿毛细管的毛细吸收。对简单流体液滴的研究表明，毛细过程取决于管-液滴半径比[Willmott Faraday Discuss.，2010，146，233；Marmur J. Colloid Interface Sci. 1988，122，209]。在这里，我们考虑了聚合物液滴的吸收，并研究了聚合物链长对毛细吸收过程的影响。我们的模拟表明，对于相同尺寸（半径）的液滴，没有吸收的临界管半径随着构成液滴的聚合物链的长度而增加。我们提出了一个模型来解释这种效应，该模型包含了对聚合物限制的熵惩罚，并且发现该模型与模拟结果定量一致。我们还发现吸收动力学对聚合物链长敏感。在某些情况下，在毛细吸收瞬态中观察到部分吸收状态，其中液滴部分在管内，部分在管外。这种动力学不能用广义 Lucas-Washburn 方法来解释。
