由有吸引力的聚合物链的塌陷转变引起的混合聚合物刷的高度切换,Macromolecules

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由有吸引力的聚合物链的塌陷转变引起的混合聚合物刷的高度切换
Macromolecules ( IF 5.1 ) Pub Date : 2023-12-04 , DOI: 10.1021/acs.macromol.3c01606
Hang-Kai Qi ₁ , Xiao Yang ₂ , Qing-Hui Yang ₃ , Chao Wang ₂ , Meng-Bo Luo ₁

Affiliation

使用朗之万动力学模拟研究了混合聚合物刷中有吸引力的聚合物链的塌陷转变。接枝密度为f的混合聚合物刷由长度为N _R的排斥聚合物和长度较长的吸引聚合物组成N _A > N _R。当有吸引力的较长聚合物稀疏接枝时，我们在中间f区域观察到花球转变，随着f的增加，转变温度T _c降低，塌陷转变变得更加尖锐。在接枝密度略高于临界接枝密度f _{c时，通过将体系淬火至低于}T _{c 的}低温，我们发现整个有吸引力的聚合物同时从暴露状态塌陷为浸没的小球。当N _A低于上限长度N _A * ∝ N _R³f _R时，花球转变会引发高度切换现象，其中f _R是排斥聚合物的接枝密度。然而，在相对较高的f下，观察到两步花-球转变，即小簇形成并在排斥聚合物层上方生长，然后这些簇向下移动并形成球。当有吸引力的聚合物相对密集地接枝时，在低温下观察到有吸引力的聚合物的聚集和随后的高度转换。我们的模拟研究提出了一种温度敏感、高度可调的混合聚合物刷，具有更长、更有吸引力的聚合物链。

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Height-Switching in a Mixed Polymer Brush Induced by the Collapse Transition of Attractive Polymer Chains

The collapse transition of attractive polymer chains in a mixed polymer brush is studied using Langevin dynamics simulations. The mixed polymer brush of grafting density f consists of repulsive polymers with length N_R and attractive polymers with a longer length N_A > N_R. When the attractive longer polymers are sparsely grafted, we observe a flower-globule transition in the intermediate f region, with the transition temperature T_c decreasing and the collapse transition becoming sharper with increasing f. At the grafting density slightly above the critical grafting density f_c, by quenching the system to a low temperature below T_c, we find that the entire attractive polymer collapses simultaneously from the exposed state to an immersed globule. The flower-globule transition can induce a height-switching phenomenon when N_A is below the upper threshold length N_A* ∝ N_R³f_R, with f_R being the grafting density of the repulsive polymers. Whereas, at a relatively high f, a two-step flower-globule transition is observed, i.e., small clusters form and grow above the repulsive polymer layer, and then these clusters move downward and form a globule. When the attractive polymers are relatively densely grafted, the aggregation of attractive polymers and subsequent height-switching are observed at low temperatures. Our simulation study suggests a temperature-sensitive, height-tunable mixed polymer brush with longer, attractive polymer chains.

更新日期：2023-12-04

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