Two-Particle Interfacial Microrheology at Polymer-Polymer Interfaces

We continue to develop two-particle interfacial microrheology and have applied it to study the interfacial viscoelastic properties of immiscible polydimethylsiloxane (PDMS) – polyethylene glycol (PEG) interfaces. The interfacial storage and loss moduli are measured over a wide frequency range; at low frequencies, the interfaces are dominated by viscous responses. The interfacial viscosity, estimated based on the Cox-Merz rule, falls between the bulk viscosities of two individual polymers. Surprisingly, the interfacial relaxation time, calculated from the crossover of the storage and loss moduli, is found to be an order of magnitude larger than that of the PDMS bulk polymers. The effects of tracer particle size (40 nm to 1.0 um) and surface chemistry (hydrophilic vs. hydrophobic) have also been studied and shown minimum influences on two-particle interfacial microrheology.