A Thin Film Analog of the Corneal Mucus Layer of the Tear Film: An Enigmatic Long Range Non-Classical DLVO Interaction in the Breakup of Thin Polymer Films

Abstract

We present experimental results on the instability and dewetting of thin liquid polydimethylsiloxane (PDMS) films intercalated between an aqueous medium and a silicon wafer grafted with PDMS 'brushes'. This is a thin film analog of the precorneal thin mucus coating sandwiched between the aqueous tear film and the glycocalyx carrying corneal epithelial surface. Lowering of the PDMS-water interfacial tension by a surfactant results in dewetting even of micrometer thick films within a few minutes. The instability appears to be induced by a long range non-classical DLVO force which has the same decay behavior as the nonretarded van der Waals force, but a magnitude which is about 2-3 orders higher. Implications for the breakup of the precorneal mucus layer and the tear film are discussed.