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

HK Qi and X Yang and QH Yang and C Wang and MB Luo, MACROMOLECULES, 56, 9983-9993 (2023).

DOI: 10.1021/acs.macromol.3c01606

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* proportional to N(R)(3)f(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.

Return to Publications page