Polydimethylsiloxane flow defined for experiments in fluid dynamics

Linear polydimethylsiloxanes (PDMS's) are liquid polymers between 200 and 550 K and are well suited for experimental studies in fluid mechanics because (1) they are commercially available in a wide range of molecular lengths, (2) they are transparent and colorless, and (3) their flow behavior can be predicted from their molecular length. A particular PDMS can flow either as a viscous or strain rate softening fluid, depending upon its molecular length and the applied strain rate. Six different flow regimes are defined here to aid the selection of the appropriate PDMS for any particular experiment in fluid dynamics. Diffusion is sufficiently slow in PDMS's of long molecular length so that finite strains can be visualized by the deformation of strain markers within it. This allows laboratory modeling of three-dimensional strain histories in fluids which previously could only be approached by two-dimensional numerical modeling.