Stimulus-responsive liquid marbles.

Millimeter-sized "liquid marbles" are usually prepared using highly hydrophobic particles such as fluorosilane-treated lycopodium powder or alkylated silica sols. In the present work it is shown that "liquid marbles" can be prepared using sterically stabilized polystyrene latex; remarkably, such latex particles can be readily prepared by aqueous emulsion polymerization using a well-defined styrene-functionalized poly(2-(diethylamino)ethyl methacrylate) macromonomer as a reactive steric stabilizer. The macromonomer stabilizer chains are water-soluble when partially protonated below their pK(a) of approximately 7.0 but become sufficiently hydrophobic in their deprotonated form to allow formation of robust "liquid marbles" that remain stable when placed at the air/water interface. Moreover, the stabilizer chains confer pH-responsive behavior on the "liquid marbles"; addition of acid to the aqueous subphase causes immediate destruction of the "liquid marble".