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We reconsider a recently proposed design for smart responsive brushes, which is based on a conformational transition in very dilutely embedded block copolymers with a surface active block (Qi et al., Macromolecules 53, 5326, 2020). Under certain conditions, the transition acquires an unusual character: it remains very sharp, but the barrier separating the adsorbed and desorbed states disappears completely. We show that these features are very robust with respect to changing almost all system parameters: the lengths of the inert and active blocks of the minority chain, the brush length, its density, and its polydispersity. The only relevant condition is that the inert block of the minority chain is long enough to extend outside the brush density profile. We develop an analytical theory that predicts the relevant characteristics of the transition and verify it with Monte Carlo simulations. We also show that the surprising universality of the transition properties is rooted in an underlying connection to the force-induced desorption transition, which is known to combine the features of the first- and second-order transitions with a pretransition fluctuation growth accompanied by phase coexistence.

Recently, a new design for switch sensors has been proposed that exploits a conformational transition of end-grafted minority adsorption-active homopolymers in a monodisperse polymer brush [Klushin...

We study the effect of polydispersity on the compression and interpenetration properties of two opposing polymer brushes by numerical self-consistent field approach and by analytical theory. Polydispersity is represented by an experimentally relevant Schulz–Zimm chain-length distribution. We focus on three different polydispersities representing sharp, moderate, and extremely wide chain length distributions and derive approximate analytical expressions for the pressure–separation curves, Π(D). We study the brush interpenetration and quantify it in terms of the overlap integral, Γ, representing the number of interbrush contacts, and interpenetration length, δ. For the case of moderate densities where the equation of state is dominated by the second virial term with coefficient υ, we demonstrate that the pressure, the overlap integral, and the interpenetration length are related by a simple equation, Π/kBT = υΓ/δ, where kBT represents the thermal energy. We propose a scaling form for δ(D) for the three poly...

We present a scaling theory and Monte Carlo (MC) simulation results for a flexible polymer chain slowly dragged by one end into a nanotube. We also describe the situation when the completely confined chain is released and gradually leaves the tube. MC simulations were performed for a self-avoiding lattice model with a biased chain growth algorithm, the pruned-enriched Rosenbluth method. The nanotube is a long channel opened at one end and its diameter $D$ is much smaller than the size of the polymer coil in solution. We analyze the following characteristics as functions of the chain end position $x$ inside the tube: the free energy of confinement, the average end-to-end distance, the average number of imprisoned monomers, and the average stretching of the confined part of the chain for various values of $D$ and for the number of monomers in the chain, $N$. We show that when the chain end is dragged by a certain critical distance $x^*$ into the tube, the polymer undergoes a first-order phase transition whereby the remaining free tail is abruptly sucked into the tube. This is accompanied by jumps in the average size, the number of imprisoned segments, and in the average stretching parameter. The critical distance scales as $x^*\sim ND^{1-1/\nu}$. The transition takes place when approximately 3/4 of the chain units are dragged into the tube. The theory presented is based on constructing the Landau free energy as a function of an order parameter that provides a complete description of equilibrium and metastable states. We argue that if the trapped chain is released with all monomers allowed to fluctuate, the reverse process in which the chain leaves the confinement occurs smoothly without any jumps. Finally, we apply the theory to estimate the lifetime of confined DNA in metastable states in nanotubes., Comment: 13pages, 14figures