The insertion of spherical, nonadsorbing colloidal particles into a swollen planar polymer brush is characterized using Monte Carlo simulations with umbrella sampling focusing on small particles whose radius R p is smaller than the unperturbed brush thickness, h 0. This process plays a key role in the modeling antifouling poly(ethylene glycol) brushes that repress protein adsorption. Two properties are studied as a function of R p and the altitude within the brush z: (i) The particle induced perturbation of the monomer concentration profile and (ii) The insertion free energy penalty, F ins . The perturbation of the concentration profile is short ranged involving pure depletion at high z and depletion followed by a maximum at low z. When the particle does not experience the surface depletion layer F ins grows with the monomer volume fraction ϕ and R p . F ins ∼ R p 3 for the larger R p reflects an osmotic insertion penalty at the high ϕ range of the brush. At the lower ϕ range a surface tension correction plays a role. In the range explored there is no evidence for F ins ∼ R p 4/3 as was suggested for small particles.

For simulating hydrophobic−amphiphilic (HA) copolymers, we have developed a “side-chain” HA model in which hydrophilic (P) interaction sites are attached to hydrophobic (H) main chain, thereby forming amphiphilic (A) monomer units, each with dualistic (hydrophobic/hydrophilic) properties. Using this coarse-grained model, we performed molecular dynamics simulations of the hydrophobically driven self-assembly in a selective solvent, for both single-chain and multichain systems. The focus is on the regime in which H and P interaction sites are strongly segregated. Single-chain simulations are performed for copolymers with the same HA composition but with different distribution of H and A monomer units along the hydrophobic backbone, including regular copolymers comprising H and A units in alternating sequence, (HA) x , regular multiblock copolymers (H L A L ) x composed of H and A blocks of equal lengths L = 3, and quasi-random proteinlike copolymers having quenched primary structure. In a solvent selectively poor for H sites, the proteinlike polyamphiphiles can readily adopt spherical-shaped compact conformations with the hydrophobic chain sections clustered at the globular core and the hydrophilic groups forming the envelope of this core and buffering it from solvent. Because of the fact that these globules are size- and shape-persistent objects, they maintain their morphological integrity even in rather concentrated solutions where no large-scale aggregation is observed. Moreover, we find that the population of aggregates generally decreases with worsening solvent quality. The compact conformations of long regular copolymers tend to be strongly elongated in one direction.

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