Center for Condensed Matter Theory, Department of Physics, Indian Institute of Science, Bangalore 560012, India.
Department of Chemistry, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, United States.
Langmuir. 2020 May 26;36(20):5492-5501. doi: 10.1021/acs.langmuir.0c00208. Epub 2020 May 13.
Physical confinement of polymers not only affects their structure but also modifies their effective interaction profiles. In this article, we investigate the nature of graphene-adsorbed poly(amidoamine) (PAMAM) dendrimers' interactions using fully atomistic molecular dynamics simulations. Using the umbrella sampling technique, we calculate the potential of mean force (PMF) profiles for the interaction between two graphene-adsorbed PAMAM dendrimers of generations 3 and 4 as a function of their protonation levels. We find that the attractive PMF profile observed for the interaction between two nonprotonated (high pH) PAMAM dendrimers in bulk becomes repulsive upon adsorption. Also, the repulsive interdendrimer interactions known in bulk for the protonated dendrimers become enhanced for the adsorbed case. We further explain these weakened interactions by explicitly showing that the dendrimer-graphene interaction is an order of magnitude larger than the dendrimer-dendrimer bulk interaction. Using the force integration method, we obtain the contributions from various subinteractions present in the system, that is, dendrimer-water, dendrimer-ions, dendrimer-graphene, and dendrimer-dendrimer to the total PMF. From these contributions, we conclude that the reduced dendrimer-dendrimer interactions in the adsorbed case, as compared to those in bulk, lead to the enhanced repulsive effective interdendrimer interactions. Our PMF profiles fit well with the sum of exponential and Gaussian functions, proposed in the bulk interdendrimer interaction study. We hope the current results provide the microscopic origin of how adsorption weakens the interpolymer interactions in general.
聚合物的物理限制不仅会影响其结构，还会改变其有效相互作用的分布。在本文中，我们使用全原子分子动力学模拟研究了石墨烯吸附的聚（酰胺-胺）（PAMAM）树枝状大分子相互作用的性质。我们使用伞状采样技术，计算了两个石墨烯吸附的第三代和第四代 PAMAM 树枝状大分子之间相互作用的平均力势（PMF）分布作为它们质子化水平的函数。我们发现，在本体中观察到的两个未质子化（高 pH）PAMAM 树枝状大分子之间相互作用的吸引力 PMF 分布在吸附后变为排斥。此外，对于吸附情况，在本体中已知的质子化树枝状大分子之间的排斥相互作用得到了增强。我们通过明确表明树枝状大分子-石墨烯相互作用比树枝状大分子本体相互作用大一个数量级，进一步解释了这些减弱的相互作用。我们使用力积分方法，获得了系统中存在的各种子相互作用的贡献，即树枝状大分子-水、树枝状大分子-离子、树枝状大分子-石墨烯和树枝状大分子-树枝状大分子对总 PMF 的贡献。从这些贡献中，我们得出结论，与本体相比，吸附情况下的树枝状大分子-树枝状大分子相互作用减弱导致有效排斥相互作用增强。我们的 PMF 分布与在本体中研究的树枝状大分子相互作用中提出的指数和高斯函数的和拟合得很好。我们希望当前的结果为吸附如何普遍减弱聚合物间相互作用提供微观起源。
