Stimuli-responsive brushes with active minority components: Monte Carlo study and analytical theory

Abstract

Using a combination of analytical theory, Monte Carlo simulations, and three dimensional self-consistent field calculations, we study the equilibrium properties and the switching behavior of adsorption-active polymer chains included in a homopolymer brush. The switching transition is driven by a conformational change of a small fraction of minority chains, which are attracted by the substrate. Depending on the strength of the attractive interaction, the minority chains assume one of two states: An exposed state characterized by a stem-crown-like conformation, and an adsorbed state characterized by a flat two-dimensional structure. Comparing the Monte Carlo simulations, which use an Edwards-type Hamiltonian with density dependent interactions, with the predictions from self-consistent-field theory based on the same Hamiltonian, we find that thermal density fluctuations affect the system in two different ways. First, they renormalize the excluded volume interaction parameter $v_{\mathrm{bare}}$ inside the brush. The properties of the brushes can be reproduced by self-consistent field theory if one replaces $v_{\mathrm{bare}}$ by an effective parameter $v_{\mathrm{eff}}$, where the ratio of second virial coefficients $B_{\mathrm{eff}}/B_{\mathrm{bare}}$ depends on the range of monomer interactions, but not on the grafting density, the chain length, and $v_{\mathrm{bare}}$. Second, density fluctuations affect the conformations of chains at the brush surface and have a favorable effect on the characteristics of the switching transition: In the interesting regime where the transition is sharp, they reduce the free energy barrier between the two states significantly. The scaling behavior of various quantities is also analyzed and compared with analytical predictions.

15 pages, 14 figures

References in corpus (4)

• Renormalization of the one-loop theory of fluctuations in polymer blends and diblock copolymer melts
• Nano-scale brushes: How to build a smart surface coating
• Sharp and fast: Sensors and switches based on polymer brushes with adsorption-active minority chains
• Using field theory to construct hybrid particle-continuum simulation schemes with adaptive resolution for soft matter systems

Cited by in corpus (7)

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• Bottom-up construction of dynamic density functional theories for inhomogeneous polymer systems from microscopic simulations
• Anomalous Critical Slowdown at a First Order Phase Transition in Single Polymer Chains
• A hybrid particle-continuum resolution method and its application to a homopolymer solution
• Phase transitions in single macromolecules: loop-stretch transition versus loop adsorption transition in end-grafted polymer chains
• Polymer brushes with reversibly tunable grafting density