Engineering Thermoresponsive Emulsions with Branched Copolymer Surfactants

Abstract

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Polymer architecture dictates thermoreversible gelation in engineered emulsions stabilised with branched copolymer surfactants

“…This T gel is believed to correspond to the establishment of an inter-droplet percolating gel-network, as hypothesised in prior studies on responsive emulsions. 13,14,17 As aggregation progresses, both G ′ and G ′′ increased up to 55 °C, which coincided with a minima for tan δ , indicating a point of maximum relative elasticity (Fig. S13†).…”

“…The materials exhibit a sol–gel transition upon warming across a range of concentrations and architectures, generating materials up to ten-times stronger than the previously reported thermoresponsive engineered emulsions. 17 Variation of cross-linker density proves for the first time that a branched structure is required for an effective thermal transition to the gel state, as the phenomenon is “turned off” when non-branched polymers are used to stabilize the emulsions. Increasing the molecular weight of the BCS improves the gel strength (as assessed by the elastic modulus G ′) and shifts the onset of thickening into a physiologically relevant temperature range ( ca.…”

“…30 Pa). 17 Furthermore, the onset of thickening for these two constructs was ca. 35 °C, such that hardening could be triggered upon exposure to the body's heat, which is advantageous for drug delivery.…”

“…30 Pa) and existed over a narrow temperature range. 17 The study found that polymer exists at the O/W interface and as nanoscale aggregates in the bulk, with rising temperature inducing changes to nanostructure which triggers gelation. There is a need to generate thermoresponsive engineered emulsions of higher performance, which requires an understanding of how polymer architecture links to rheology.…”

Branched copolymer surfactants impart thermoreversible gelation to LAPONITE® gels

“…23,24 The synthetic approach allows control of many factors in the thermoresponsive BCS, which is composed of an LCST-imparting monomer, poly(ethylene glycol)methacrylate (PEGMA); ethylene glycol dimethacrylate (EGDMA), as a cross-linker to induce branching, and dodecanethiol (DDT), as a chain transfer agent to impart C12 terminal groups. 19,24 Resultant BCS structures impart varied and controllable thermoresponsive behaviours to oil-in-water emulsions, 21 including the induction of gelation upon heating, however their utility for alternative dispersions, such as clays, has not been explored. Considering the structural similarity of the PEGMA component to poly(ethylene oxide), the potential that BCS will interact with clays was considered as a positive attribute in their selection for composite materials.…”