Interfacial behavior of pH responsive ampholytic heteroarm star block terpolymers

We report the pH-controlled surface behavior of amphiphilic PSn(P2VP-b-PAA)(n) heteroarm star block terpolymers, (n = number of arms, 9 and 22), bearing amphoteric diblock arms with varying polyvalent ionic charges (i.e. negative, positive, and zwitterionic) at the air water and air solid interfaces. We investigated the assembly of these pH-sensitive star terpolymers in Langmuir and Langmuir-Blodgett monolayers under different pH conditions of the subphase. The pi-A isotherms acquired at variable pH conditions revealed a distinct aggregation behavior of surface micelles which is dependent on the ionization of the polyelectrolyte blocks and the number of arms. The star block copolymer with a small number of arms (n = 9) was found to exhibit a strong pH-dependent phase transformation under compression. The pH responsive (zwitterionic) behavior results in changes in surface morphologies from circular micelles to complex labyrinth structures. In contrast, star polymers with a larger number of arms (22) and a crowded branched architecture show stable circular domain morphology without the internal reorganization under variable conditions. The observed variety of surface behaviors is attributed to the fine balance of intra molecular interactions caused by the highly branched chain architecture composed of both acidic and basic blocks. This study proposes a novel strategy for pH induced tunable surface assembly of responsive ultrathin films with multicompartments. We indeed demonstrated that the enhanced responsiveness of star polymers to wide pH range and their diverse morphology at the interface is enabled by coupling amphoteric concept and tailored molecular architecture. (C) 2013 Elsevier Ltd. All rights reserved.