Fast Multiresponsive Micellar Gels from a Smart ABC Triblock Copolymer

Abstract

Self-assembly of block copolymers in a solvent selective for one block is at the origin of unique behaviors of micellar particles, such as stimuli responsiveness. [1][2][3][4] ABC triblock copolymers are very versatile precursors of micelles, whose internal structure is dictated by the constitutive blocks and their sequential arrangement. Accordingly, smart materials can be contemplated, including multiresponsive ones. Herein, we report on pH-and temperature-sensitive gels formed by an amphiphilic ABC triblock copolymer, polystyrene-bpoly(2-vinylpyridine)-b-poly(ethylene oxide). The selfassembly of this copolymer into core-shell-corona (CSC) micelles [5,6] is observed in N,N-dimethylformamide upon addition of water. The micellar solution forms a soft gel at a lower threshold copolymer concentration (8 wt %) than other systems. [7][8][9] This soft gel is reversibly converted into an optically clear hard gel by merely decreasing the pH value or increasing the temperature. The ordered packing of the CSC micelles and the fast response to pH value were investigated by small-angle neutron scattering (SANS) and rheological measurements.Block copolymers consist of two or more chemically different polymer chains covalently bonded at their chain ends to form one single linear macromolecule.[10] The freeenergy-driven micellization of these copolymers takes place in a selective solvent, that is, a nonsolvent for one block and a good solvent for another. This self-association phenomenon is based on the phase separation of the insoluble blocks, which is, however, restricted to the nanometric scale by a surrounding shell of soluble blocks. Depending on the nature, length, and number of constitutive blocks and their interaction with the solvent, a variety of nanoobjects can be formed in dilute solutions, ranging from typical core-shell nanospheres [11][12][13] to cylinders, [12,14] vesicles, [12,15,16] and tubules, [16] as well as multilayered (onion), [5,17] non-centrosymmetric ("Janus"), and segregated structures. [18,19] Quite importantly, although less extensively studied, higher levels of organization can be observed, that is, assembly into clusters, networks, and gels. Stimulus-triggered aggregation of micelles has been reported for ABA triblock copolymers in a solvent selective for the B block, [9,[20][21][22][23][24] with special attention paid to the well-known polyoxyalkylene-type ABA copolymers (mainly Pluronics). [9,20,21] Among other responsive systems, Armes and coworkers synthesized biocompatible ABA triblocks, where A is poly(N-isopropylacrylamide) and B is poly(2-methacryloyloxyethyl phosphorylcholine).[24] Because of the thermosensitivity of the outer A blocks, micellization and ultimately gelation occurred above a lower critical solution temperature (LCST) of 37 8C. In recent years, increasing attention was paid to sol-to-gel transitions exhibited by multitalented ABC terpolymers. In addition to the synthesis of several isomers of a triblock terpolymer (ABC, BAC, and ACB) by Patrickios and co-workers that were...

Structure of Metallo‐Supramolecular Micellar Gels

“…[ 28 ] At higher concentrations, the contribution of the structure factor becomes signifi cant, which is particularly interesting since the short-range organization of the micellar network or gel can then be monitored. [29][30][31][32][33][34] In the present contribution, a detailed SANS analysis of metallo-supramolecular micellar gels from polystyrene-block -poly( tert -butylacrylate) PS-b -PtBA-tpy diblock copolymers is presented and the results are correlated with previous rheology experiments. [ 24 , 25 ] To that end, a two-level hierarchical self-assembly is performed.…”

Bio‐Inspired, Smart, Multiscale Interfacial Materials

“…[5,6] These bioinspired, smart materials are attracting more and more interest because of their unique properties, which have paved the way to many real-world applications, e.g., biomimetic fins, [7] actively moving polymers, [8] neural memory devices, [9] smart micro-/nanocontainers for drug delivery, [10] various biosensors, [11][12][13] dual/multi-responsive materials. [14,15] Also, many of these smart materials have surfaces that dynamically alter their physicochemical properties in response to changes in their environmental conditions and a triggered control of interfacial properties at the solid/water interface can be found in ion channels, [13] directional surface motions, [16] and bioinspired, smart surfaces with controllable wettability and adhesion. [17,18] The self-cleaning effect of lotus leaves, [19] the anisotropic de-wetting behavior of rice leaves, [20] the superhydrophobic forces exerted by a water strider's leg, [21] the attachment mechanism of geckos, [22] and many other natural phenomena are all related to unique micro-and nanostructures on surfaces.…”

Recent Progresses in Polymeric Smart Materials

“…In the last decade, a wide range of novel polymeric smart materials have been developed in biomaterials, bioinspired materials, functional nanomaterials [4] , sensors, actuators [5,6] , etc. The applications cover aerospace, automobile, telecommunications, such as actively moving polymers, neural memory devices, smart micro-/nanocontainers for drug delivery, various biosensors, dual/multi-responsive materials, biomimetic fins [1,7,8] .…”