Structured Liquids with pH-Triggered Reconfigurability

The ability to manipulate the shape of liquids in an external field and trapping these non-equilibrium shapes holds significant promise for the development of bicontinuous fluids, novel encapsulants for delivery systems, or all-liquid separations media. We find that the complementary electrostatic interactions of amine-terminated polydimethylsiloxane (PDMS-NH2) dissolved in a hydrophobic fluid (oil) and carboxlic acid functionalized nanoparticles (NPs) dispersed in water results in the formation of NP-surfactants (NPs with a well-defined number of ligands dynamically attached). The NP-surfactant assemblies are disordered yet dynamic, similar to those seen with NPs, and when the fluids are deformed, more NP-surfactants form at the interface such that, upon release of the deformation field, the NP-surfactants jam at the interface locking-in highly non-equilibrium shapes of the fluids. Such structured liquids can be reconfigured back into their equilibrium spherical shapes remotely using a water-soluble photoacid generator, which is triggered by light to disrupt the dynamic complementarity between the polymers and NPs in their jammed state. We present a detailed analysis of NP-surfactant dynamics as a function of pH.