Publications: #78

78. "QCM Studies of Gel Spreading: Kraton Gels on Polystyrene Surfaces" Nunalee, F.N.; Shull, K.R., Langmuir, 22, 431 (2006).

Contact of a polymer gel made from a styrene/ethylene-butene/styrene triblock copolymer in mineral oil is investigated by bringing the gel into contact with the coated surface of a quartz crystal microbalance (QCM). The experimental apparatus enables simultaneous measurement of the load, displacement and contact area, in addition to the resonant frequency and dissipation of the oscillating quartz crystal. The QCM response is determined by the linear viscoelastic properties of the gel at the frequency of oscillation. A geometric correction factor involving the contact area provides a means for quantitatively determining these viscoelastic parameters as the gel spreads over the QCM surface. When the gel is removed from the surface, a thin solvent layer is left behind. The thickness of this solvent layer was determined from the QCM response, and was compared to predictions from a simple model involving the disjoining pressure of the film and the osmotic pressure of the gel. Qualitative agreement with the model required that tensile, adhesive forces at the perimeter of the gel/QCM contact area be taken into account when calculating the film thickness.

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