Imbibition in mesoporous silica: rheological concepts and experiments on water and a liquid crystal

Abstract

We present, along with some fundamental concepts regarding imbibition of liquids in porous hosts, an experimental, gravimetric study on the capillarity-driven invasion dynamics of water and of the rod-like liquid crystal octyloxycyanobiphenyl (8OCB) in networks of pores a few nanometers across in monolithic silica glass (Vycor). We observe, in agreement with theoretical predictions, square root of time invasion dynamics and a sticky velocity boundary condition for both liquids investigated. Temperature-dependent spontaneous imbibition experiments on 8OCB reveal the existence of a paranematic phase due to the molecular alignment induced by the pore walls even at temperatures well beyond the clearing point. The ever present velocity gradient in the pores is likely to further enhance this ordering phenomenon and prevent any layering in molecular stacks, eventually resulting in a suppression of the smectic phase in favor of the nematic phase.

18 pages, 8 figures

References in corpus (5)

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• Rate-dependent slip boundary conditions for simple fluids
• Spontaneous Imbibition Dynamics of an n-Alkane in Nanopores: Evidence of Meniscus Freezing and Monolayer Sticking
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• Thermotropic nematic order upon nano-capillary filling
• Conflicting Effects of Extreme Nanoconfinement on the Translational and Segmental Motion of Entangled Polymers
• Capillary Condensation, Freezing, and Melting in Silica Nanopores: A Sorption Isotherm and Scanning Calorimetry Study on Nitrogen in Mesoporous SBA-15
• High-resolution dielectric study reveals pore size-dependent orientational order of a discotic liquid crystal confined in tubular nanopores