Origins of solidification when a simple molecular fluid is confined between two plates

A simple globular-shaped liquid (octamethylcyclotetrasiloxane, OMCTS) was p laced between two rigid mica plates at variable spacings comparable to the size of this molecule and the linear shear viscoelasticity of the confined interfacial film was measured. Strong monotonic increase of the shear relax ation time, elastic modulus, and effective viscosity were observed as the s pacing was decreased below about 10 molecular dimensions. The frequency dep endence of the viscoelastic spectra measured at different film thicknesses appeared to scale with reduced variables. The data are inconsistent with th e abrupt first-order transition, from bulk fluid to solid with decreasing f ilm thickness, whose possibility has been hypothesized, and suggest a glass like transition instead. (C) 2001 American Institute of Physics.