Many-chain effects on the co-nonsolvency of polymer brushes in a good solvent mixture

Abstract

The polymer brush normally swells in a good solvent, while it collapses in a poor solvent. An abnormal response of polymer brush, so-called co-nonsolvency, is a phenomenon where the brush collapses counter-intuitively in a good solvent mixture. In this work, the structural properties of the co-nonsolvency in the grafted polymers are investigated using molecular dynamics simulation. We consider the brushes at three different grafting densities to study the effect of topologically excluded volumes on the co-nonsolvency. Preferential adsorption of solvent molecules on the polymers leads to the formation of a bridging structure between them, which causes the polymer brush to collapse significantly. We find that the intermolecular bridging structure is predominant in the overlapping brush regime, while the intramolecular bridging is only formed in the mushroom brush regime. Topological constraints also affect the degree of collapse as well as the orientation of the polymer substantially. Based on these observations, we construct a phase diagram of the polymer brush system using the average thickness and orientation as structural order parameters when both the grafting density and the fraction of the solvent mixture are varied, respectively. Going beyond previous works 1 arXiv:1905.13478v1 [cond-mat.soft] 31 May 2019 on the co-nonsolvency in the single polymer model and adsorption-attraction model, this work provides a microscopic insight into many-chain effects on the co-nonsolvency behavior in a systematic way. Furthermore, the phase diagrams presented in this work can provide useful theoretical guidelines for controlling co-nonsolvency behavior in various polymer brush systems such as bio-interface, drug-delivery, and sensor devices.

Regulating the Translocation of DNA through Poly(N-isopropylacrylamide)-Decorated Switchable Nanopores by Cononsolvency Effect

“…The reason behind this observation is that the grafting-to synthetic approach leads to much lower grafting densities for the high-molecular-weight polymers, see the second column of Table . This in turn leads to particular morphologies in the collapsed state such as octopus-shape micelles or collapsed globules, − see the last column of Table . In turn, the hydrodynamic thickness variation of such sparsely grafted polymer layers displays only weak variation as compared with the dense brush regime.…”

Polymer Brushes and Gels in Competing Solvents: The Role of Different Interactions and Quantitative Predictions for Poly(N-isopropylacrylamide) in Alcohol–Water Mixtures

“…Parameter γ represents the bridging efficiency of the molecular matching between the monomer and cosolvent; for convenience but without losing generality, in this study, γ can be treated as a constant with a value of γ = 1 for the PNiPAAm/alcohol/water system. Direct evidences supporting this central assumption from molecular dynamic simulations ,, showed that a single chain can form loops because of preferential attraction between the polymer and cosolvent. In addition, experimental evidences supporting this central assumption come from a Raman spectroscopic study which investigated cononsolvency behaviors of linear poly­( N -isopropylacrylamide) polymers in methanol–water mixtures, in which methanol molecules aggregate into clusters and behave like temporal bridges between the polymer segments…”

PMMA-b-PNIPAM Thin Films Display Cononsolvency-Driven Response in Mixed Water/Methanol Vapors

“…Starting from solutions of linear homopolymers, the research on cononsolvency has been extended toward increasingly complex systems, such as cross-linked microgels, , diblock copolymer micelles, and grafted polymer brushes. − This resulted in a number of applications of the effect across different fields of science. To name a few examples, the cononsolvency effect can be used for the capture and release of nanoparticles, , selective precipitation of DNA, force actuation, friction tuning, and the detection of volatile organic compounds .…”