We continue to develop two-particle interfacial microrheology and haveapplied the technique to study the interfacial viscoelastic properties of immisciblepolydimethylsiloxane (PDMS) – polyethylene glycol (PEG) interfaces. Theinterfacial storage and loss moduli are measured over a wide frequency range: atlow frequencies, the interfaces are dominated by viscous responses whereaselasticity dominates at high frequencies. The zero-shear interfacial viscosity,estimated from the Cross model, falls between the bulk viscosities of twoindividual polymers. Surprisingly, the interfacial relaxation time, estimated fromthe crossover of the storage and loss moduli, is observed to be an order ofmagnitude larger than that of the PDMS bulk polymers. The effects of tracerparticle surface chemistry and size have also been investigated and show minimuminfluences on two-particle interfacial microrheology.
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