Compatibilizing A/B blends with AB diblock copolymers: Effect of copolymer molecular weight

Abstract

We use numerical self-consistent field (SCF) calculations to determine the interfacial behavior of AB diblocks in a blend of immiscible homopolymers, A and B. In particular, we compare the compatibilizing effect of relatively short and long AB copolymers. In the calculations, we explicitly take into account the formation of micellar or multilamellar phases. The results show that the interfacial tension can be reduced to zero only if the blocks in the diblock are longer than the corresponding homopolymer. Our two-dimensional SCF calculations reveal that short diblocks form multilamellar structures in the blend, whereas a microemulsion is formed when relatively long copolymers are added to the A/B mixture. These observations are compared with experiments on blends of polystyrene (PS), polymethyl methacrylate (PMMA), and PS-PMMA symmetric diblock copolymers. By measuring the contact angle of PS droplets on the PMMA layer, we can obtain a direct estimate for the interfacial tension at the PS/PMMA interface. The experiments also reveal that negligible interfacial tensions and emulsionlike structures are only obtained with relatively long diblocks.

Field-Driven Translocation of Regular Block Copolymers through a Selective Liquid−Liquid Interface

“…for compatilizers, thickeners or emulsifiers. Not surprisingly, during the last two decades the problem has gained a lot of attention also from theory [9][10][11][12][13] as well as from computer experiment [14][15][16][17][18]. While in earlier studies attention has been mostly focused on diblock copolymers [6,8] due to their relatively simple structure, the scientific interest shifted later 1 to random HP-copolymers at penetrable interfaces [10][11][12][13]18].…”

Diblock Copolymers at a Homopolymer−Homopolymer Interface: A Monte Carlo Simulation

“…The amphiphilic strength of a copolymer, i.e., the maximum reduction of the interfacial tension it can achieve, increases with the length of the A and B blocks relative to the size of the homopolymers. Mean field theories predict that the interfacial tension can be driven to zero for long copolymers, which implies that the copolymer rich lamellar phase evolves into the two-phase region via a continuous unbinding transition [13,14]. Fluctuations push the transition to first order in real systems [15].…”

Monte Carlo simulations of copolymers at homopolymer interfaces: Interfacial structure as a function of the copolymer density

“…First, they reduce the number of direct contacts between homopolymers, thereby reducing the interfacial tension [10][11][12][13][14][15][16][17]. Second, they significantly enlarge the interfacial region, where polymers bridging the interface between the coexisting phases can entangle, thereby increasing the fracture toughness [18,19].…”