Measuring the effective viscosity of polymeric liquids under strong confinement

CENCHA, LUISA G.; URTEAGA, RAÚL; BERLI, CLAUDIO L. A.

Santa Fe

Congreso; 104a Reunión de la Asociación Física Argentina; 2019

Asociación Física Argentina

The behavior of complex fluids in nanoscale confinement is currently of high interest in fundamental and applied sciences. In this work, we report an investigation of the capillary-driven flow of poly-dimethylsiloxane (PDMS) through nanoporous silicon membranes by a dynamic spectroscopy technique based on interferometry [1]. We have found that, after a slower first stage, the fluid front velocity is higher than the expected for the bulk fluid viscosity. This effect may be due to a decrease of the effective fluid viscosity, as the polymer becomes strongly confined in the nanopore space; a result previously reported in literature for similar systems [2-4]. Nowadays it is clear that, when forced to flow through nanometer scale pores, polymeric fluids exhibit properties different from those measured in bulk flow [5], however the explanation of this fact is still one of the major concerns in the field of soft matter. In order to gain some insights about the underlying mechanisms affecting the capillary flow of polymers under confinement, we have compared our experimental results with a two fluid model, which considers a shell and a core flow having different viscosities. The analysis showed that the decrease in effective viscosity can be also understood in terms of a slippage of the polymer in the pore walls. These approaches allow one to infer some experimental responses, however further modeling with deeper insights at the nanoscale is still required.