Interfacial Properties of Miktoarm Star Polymers with a Poly(divinylbenzene) Core

The interfacial properties of miktoarm star polymers composed of poly(divinylbenzene) (PDVB) cores with poly(ethylene oxide) (PEO) hydrophilic arms and poly(n-butyl acrylate) (PBA) or poly(lauryl acrylate) (PLA) hydrophobic arms at the oil/water interface are reported. The kinetics of miktoarm star polymer adsorption from the oil phase depended on the polymer concentration. This suggested that the rate-determining step was the adsorption and penetration of the polymer onto and through the interface. This was attributed to the desolvation of the polymer arms from the oil phase being less facile than that of similar star polymers with PEO arms alone from the aqueous phase. PEO star polymers showed diffusion-controlled kinetics, and as such, the adsorption and so forth were facile and rapid compared to the rate of diffusion to the interface. The interfacial oscillatory dilatational rheology of the polymers adsorbed at the interface was dependent on the relative molecular weights or lengths of the arms. In the case where both arms showed similar contour lengths, the interfacial rheological response was strongly frequency dependent, suggesting that the polymer adsorption/desorption was relatively facile on the time scale of the oscillation. Polymers in which the hydrophilic arms were longer than the hydrophobic arms showed a relatively frequency-independent response. This was attributed to the hydrophobic arms effectively increasing the size of the hydrophobic core in conjunction with the penetration of the hydrophilic arms through the interface into the aqueous phase, thus pinning the polymer at the interface.