Two-particle interfacial microrheology at polymer-polymer interfaces.

We continue to develop two-particle interfacial microrheology and have applied the technique to study the interfacial viscoelastic properties of immiscible poly(dimethylsiloxane) (PDMS)-poly(ethylene 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 whereas elasticity dominates at high frequencies. The zero-shear interfacial viscosity, estimated following the Cox-Merz rule and Cross model, falls between the bulk viscosities of the two individual polymers. Surprisingly, the interfacial relaxation time, calculated from the crossover of the storage and loss moduli, is observed to be an order of magnitude larger than that of the PDMS bulk polymers. The effects of tracer particle surface chemistry and size have also been investigated and show minimum influences on two-particle interfacial microrheology.