MEASURING THE EFFECTIVE VISCOSITY OF POLYMERIC LIQUIDS UNDER STRONG CONFINEMENT

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

Santa Fe

Congreso; 104 Reunión de la Asociación Física Argentina; 2019

The behavior of complex fluids in nanoscale confinement is currently of high interest in fundamental and applied sciences. In this work, we report an investigationof the capillary-driven flow of poly-dimethylsiloxane (PDMS) through nanoporoussilicon membranes by a dynamic spectroscopy technique based on interferometry[1]. We have found that, after a slower first stage, the fluid front velocity is higherthan the expected for the bulk fluid viscosity. This effect may be due to a decreaseof the effective fluid viscosity, as the polymer becomes strongly confined in thenanopore 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 fieldof soft matter. In order to gain some insights about the underlying mechanismsaffecting the capillary flow of polymers under confinement, we have compared ourexperimental results with a two fluid model, which consider a shell and a core flowhaving 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 porewalls. These approaches allow one to infer some experimental responses, howeverfurther modeling with deeper insights at the nanoscale is still required.[1] Cencha, L. G., Urt eaga, R. and Berli, C. L. A. Interferometric technique to determine the dyna mics of polymeric fluids un der stro ng confinement. Macromolecules2018, 51, 21, 8721- 8728.[2] Shin, K., Obukhov, S., Chen, J.-T., Huh, J., Hwang, Y., Mok, S., Dobriyal,P., Thiya garajan, P., Russel l, T. P. Enhanced mobility of confin ed polymers. Nat.Mater. 2007, 6, 961.[3] Cuenca, A., Bodiguel, H. Submicron flow o f polym er solutions: slippage reduction due to confinement. Phys. Rev. Lett. 2013, 110, 108304.[4] Yao, Y., Alexandris, S., Hen rich , F., Auernha mmer, G., Steinhart, M., Butt,H.-J., Floudas, G. Complex dynamics of capil lary imbibition of poly(ethylene oxide)melts in nanoporous alumina. J. Chem. Phys. 2017, 146, 203320.[5] Huber, P. Soft m atter in hard confinement: phase transition thermodynamics,structure, texture, diffusion and flow in nanoporous media. J. Phys.: Condens.Matter 2015, 27, 103102.