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Phase inversion in stimulable and reversible emulsions
We studied transitional phase inversion of water/toluene emulsions stabilized by amphiphilic diblock copolymers with one polystyrene (PS) block and a second block consisting of either (dimethylamino)ethyl methacrylate (DMAEMA) unit or DMAEMA and styrene units. Atom transfer radical polymerization was used to synthesize several copolymers with different molar mass, block length ratio and composition of the hydrophilic block.
Because of the presence of DMAEMA, pH and/or temperature were used as stimuli to control the properties of adsorbed copolymer chains at the water/toluene interface. More specifically, we exactly control emulsions stability and the sweep of the transitional sequence “direct emulsions (O/W) - multiple emulsions or coexistence of O/W and W/O unstable emulsions - inverse emulsions (W/O)”. Our work is original by several aspects. It shows for the first time that stable but stimulable multiple emulsions can be prepared within the transitional phase inversion domain separating the domains of inverse and direct emulsions. The results are indeed promising in the domain of encapsulation/release of active species.
From a fundamental viewpoint, we explain how the sequence of formed emulsions depends on the copolymer type and pH. We performed a multiscale approach to establish correlations between emulsion kind, microemulsions and type of copolymer adsorbed at interface. To probe the various scales, we used rising and spinning tensiometry, confocal microscopy, UV spectroscopy, cryo-TEM and small angle neutrons scattering.
We also presents original results of neutron reflectivity to probe the conformation of chain adsorbed at toluene/water interface. Measurements are achieved in a specially designed cell.