Stimuli-ResponsiveBrushes with Active Minority Components:Monte Carlo Study and Analytical Theory.

Using a combination of analyticaltheory, Monte Carlo simulations,and three-dimensional self-consistent field calculations, we studythe equilibrium properties and the switching behavior of adsorption-activepolymer chains included in a homopolymer brush. The switching transitionis driven by a conformational change of a small fraction of minoritychains, which are attracted by the substrate. Depending on the strengthof the attractive interaction, the minority chains assume one of twostates: an exposed state characterized by a stem-crown-like conformationand an adsorbed state characterized by a flat two-dimensional structure.Comparing the Monte Carlo simulations, which use an Edwards-type Hamiltonianwith density-dependent interactions, with the predictions from self-consistent-fieldtheory based on the same Hamiltonian, we find that thermal densityfluctuations affect the system in two different ways. First, theyrenormalize the excluded volume interaction parameter vbareinside the brush. The properties of the brushes canbe reproduced by self-consistent field theory if one replaces vbareby an effective parameter veff, where the ratio of second virial coefficients Beff/Bbaredependson the range of monomer interactions but not on the grafting density,the chain length, and vbare. Second, densityfluctuations affect the conformations of chains at the brush surfaceand have a favorable effect on the characteristics of the switchingtransition: 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 comparedwith analytical predictions. [ABSTRACT FROM AUTHOR]