This study introduced a robust and promising approach to fabricate highly stable phase change material (PCM) emulsions consisting of n-tetradecane as a dispersed phase and a mixture of meso-2,3-butanediol (m-BDO) and water as a continuous phase. We showed that amphiphilic poly(ethylene oxide)-b-poly(ε-caprolactone) block copolymers assembled to form a flexible but tough polymer membrane at the interface during phase inversion from water-in-oil emulsion to oil-in-water emulsion, thus remarkably improving the emulsion stability. Although the incorporation of m-BDO into the emulsion lowered the phase changing enthalpy, it provided a useful means to elevate the melting temperature of the emulsions near to 15 °C. Interestingly, supercooling was commonly observed in our PCM emulsions. We attributed this to the fact that the PCM molecules confined in submicron-scale droplets could not effectively nucleate to grow molecular crystals. Moreover, the presence of m-BDO in the continuous phase rather dominated the heat emission of the emulsion system during freezing, which made the supercooling more favorable.
This study introduces a robust approach for the fabrication of extremely stable oil-in-water nanoemulsions in which the interface is stabilized by assembly of amphiphilic poly(ethylene oxide)-block-poly(3caprolactone) (PEO-b-PCL) copolymers. Phase inversion emulsification, induced by variation of the water volume fraction, facilitated effective assembly of the block copolymers at the oil-water interface.Subsequent application of simple probe-type sonication reduced the droplet size of the precursor emulsions to approximately 200 nm. The prepared nanoemulsions were surprisingly stable against drop coalescence and aggregation, as confirmed by analysis of changes in the droplet size after repeated freeze-thaw cycling and by monitoring the creaming kinetics under conditions of high ionic strength and density mismatch. The results highlight that good structural assembly of the PEO-b-PCL block copolymers at the oil-water interface generated a mechanically flexible but tough polymer film, thereby remarkably improving the emulsion stability.
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