Stimuli-responsive gel emulsions stabilized by microgel particles

Using pH- and thermo-responsive poly(N-isopropylacrylamide-co-methacrylic acid) (PNIPAM-co-MAA) microgels as an solely emulsifier, we have prepared a series of oil-in-water (o/w) highly concentrated emulsions with an internal phase ranging from 65% up to 80%. The resultant emulsions are gel-like and exhibit elastic properties due to the formation of a viscoelastic three-dimensional network of interconnected microgels and emulsion droplets. The dynamical rheology measurements show that elastic modulus (G') of the emulsion increases as the internal phase volume increases. For a fixed internal phase volume, microgels are shown to stabilize emulsion with a high elasticity at room temperature above a solution pH of 6, but below this threshold, G' decreases gradually with pH. This indicates that a stronger transient gel network is formed between the interconnected microgels and emulsions droplets at the high pH solutions. On the other hand, for emulsions prepared at pH 4.2, gel-to-fluid transition occurs when the temperature is raised to 37 A degrees C, whereas the emulsions produced above pH 6 are stable even when heat at 60 A degrees C for 12 h. Therefore, the formulated gel emulsion stabilized by the microgels shows their twofold responsiveness to pH and temperature.