Spontaneous Imbibition of Liquids into Nanopores
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Spontaneous Imbibition of Liquids into Nanopores Patrick Huber1, Klaus Knorr1 and Andriy Kityk2 Technische Physik, Universität des Saarlandes, D-66041 Saarbrücken (Germany) 2 Institute for Computer Science, Technical University of Czestochowa, PL-42200 Czestochowa, (Poland) 1
ABSTRACT We present measurements on the spontaneous imbibition of water, a linear hydrocarbon (nC16H34) and a liquid crystal (8OCB) into the pore space of monolithic, nanoporous Vycor glass (mean pore radius 5nm). Measurements of the mass uptake as a function of time, m(t), are in good agreement with the Lucas-Washburn t -prediction typical of imbibition of liquids into porous hosts. The relative capillary rise velocities scale as expected from the bulk fluid parameters. INTRODUCTION Spontaneous imbibition, the capillary rise of a wetting liquid in a tube or more generally a porous host, plays a crucial role in such different areas as oil recovery, printing, cooking and fluid transport in living organisms [1]. It is governed by a balance of capillary action versus viscous drag forces. Therefore, the details of the imbibition process, e.g. the morphology and speed of the advancing imbibition front depend sensitively on fluid parameters (viscosities η of displacing and displaced fluid and interfacial or surface tensions σ) and on the structure of the porous host. Here, we shall present experiments on spontaneous imbibition of liquids into nanoporous, monolithic silica glass. We will demonstrate that such experiments shed light on the flow properties of liquids in restricted geometry. A topic which is of importance for lubrication, transport of liquids through biomembranes and folding of proteins - not to mention the growing, technological and scientific interest concerning the physics of liquids in nanodevices, e.g. carbon nanotubes [2, 3]. As porous host we have chosen “thirsty” Vycor glass, a nanoporous silica glass which is permeated by a 3D network of interconnected, randomly oriented pores [4]. In order to play with the complexity of the imbibing fluids we have chosen three different liquids: Water, a chain-like, linear hydrocarbon (n-C16H34) and a rod-like liquid crystal (4-Cyano-4’-n-octyloxybiphenyl, 8OCB). EXPERIMENTAL A cuboid (0.4 x 0.43 x 2.65cm3) was cut from a Vycor rod (Corning, code 7930) with a diamond saw. Prior to using the Vycor sample and after each imbibition experiment we subjected the host to a cleaning procedure with hydrogen peroxide and sulphuric acid followed by rinsing in Millipore water and drying at 70°C in vacuum. The cleaned glass was colorless. In
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agreement with former results on the pore structure of samples from this Vycor batch [5], the mean volume porosity, Φ and mean pore diameter, rm was determined to Φ=30% and rm =5nm, resp. Water cleaned by a Millipore filtering setup was used for the water imbibition experiment. Nhexadecane (99.5% purity) was purchased from Aldrich and the 80CB sample (99% purity) from Synthon Chemicals (Germany). The capillary rise experiments were perfo
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