Temperature/pH dual-responsive reversible morphology evolution of block copolymer microparticles under three-dimensional confinement
Development of block copolymer (BCP) microparticles with switchable morphology in response to external stimuli is important for exploiting new intelligent materials. In this work, thermo/pH dual-responsive nanoparticles (NPs) were employed as a co-surfactant to modulate the self-assembly morphology of polystyrene- b -poly(2-vinylpyridine) (PS- b -P2VP) microparticles within confined emulsion droplets. The co-surfactant was synthesized by grafting poly(acrylic acid)- b -poly( N -isopropylacrylamide) onto the surface of Fe 3 O 4 NP. The introduction of the dual-responsive co-surfactant enabled thermo/pH dual-responsive reversible morphology transition of the PS- b -P2VP microparticles by tailoring the hydrophobicity and interfacial affinity of the co-surfactant. By using this strategy, the thermo-inert PS- b -P2VP self-assembled into pupa-like microparticles at T = 10 °C and pH 7.5, which could transform into tulip-like microparticles when T was increased to 50 °C. When the pH value was increased to 11, the pupa-like particles turned into onion-like microparticles although the PS- b -P2VP was inert to alkali. However, the pupa-like microparticles remained unchanged when both T and pH were simultaneously increased. The PAA- b -PNIPAM-grafted Fe 3 O 4 NP surfactants showed obvious advantages over the linear PAA- b -PNIPAM surfactants in modulating the morphology transition, since the linear PAA- b -PNIPAM could not induce the reversible shape transition of microparticles. Our work provides an efficient strategy to achieve reversible shape transformation of BCP microparticles while the internal phase structure is preserved, which may be utilized to switch the structural color properties of BCP microparticles.
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