A Quantitatively Accurate Theory to Predict Adsorbed Configurations of Asymmetric Surfactant Molecules on Polar Surfaces
A Quantitatively Accurate Theory to Predict Adsorbed Configurations of Asymmetric Surfactant Molecules on Polar Surfaces
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预测极性表面不对称表面活性剂分子吸附构型的定量准确理论
DOI：
10.1021/acs.jpcb.0c02681
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Sharma, Sumit
中科院分区：
文献类型：
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作者：
Ko, Xueying;Sharma, Sumit
我们引入了一个理论模型来预测不对称表面活性剂分子在极性表面上的吸附构型。这个模型扩展了我们以前工作中提出的预测线性表面活性剂分子在极性表面上的吸附构型的想法。表面活性剂分子有一个大的极性头基和一个线形的烷基尾巴。这些不对称分子在吸附状态下形成圆柱形/球状形态。我们的模型预测，分子的吸附要么与表面平行(平躺构型)，要么垂直于表面(站立构型)。立式构型和卧式构型的吸附形态明显不同。在立式构型中，吸附形态类似于满圆柱体，而在卧式构型中，吸附形态类似于部分球状。当极性头基团与表面的相互作用强度超过烷基尾基与表面的相互作用强度时，得到直立构型。当烷基尾部的相互作用占主导地位时，分子达到平卧构型。理论模型的预测结果与朗之万动力学模拟的结果定量吻合。该理论模型还解释了在极性表面吸附表面活性剂组织的实验研究中已报道的不同的动力学路径。
We introduce a theoretical model that predicts adsorbed configurations of asymmetric surfactant molecules on polar surfaces. This model extends the ideas developed in our previous work for predicting adsorbed configurations of linear surfactant molecules on polar surfaces. The surfactant molecules have a large polar headgroup and a linear alkyl tail. These asymmetric molecules form cylindrical/spherical morphologies in the adsorbed state. Our model predicts that the molecules adsorb either with their molecular axis parallel to the surface (lying-down configuration) or perpendicular to the surface (standing-up configuration). The standing-up and lying-down configurations result in significantly different adsorbed morphologies. In the standing-up configuration, the adsorbed morphology is like that of full cylinders, while, in the lying-down configuration, the adsorbed morphology resembles partial spheres. The standing-up configuration is obtained when the strength of interaction of the polar headgroup with the surface dominates over the interactions of the alkyl tail with the surface. When interactions of the alkyl tail are dominant, the molecules attain the lying-down configuration. Predictions from the theoretical model quantitatively match the results obtained from Langevin dynamics simulations. The theoretical model also explains the different kinetic pathways that have been reported in the experimental studies on the organization of adsorbed surfactants on polar surfaces.