Non-aqueous retention measurements: ultrafiltration behaviour of polystyrene solutions and colloidal silver particles

Abstract

The retention behaviour of polyimide ultrafiltration membranes was investigated using dilute solutions of polystyrene in ethyl acetate as test solutions. It is shown that flow-induced deformation of the polystyrene chains highly affects the membrane retention. This coil-stretch transition is not instantaneous, but gradual. The concept of a deformation resistance has been introduced to explain this behaviour. This concept can be applied to describe the flux behaviour of the membranes during the tests as well. Solute deformation allows comparison of the pore size distributions of the membranes qualitatively. Retention measurements were also performed with silver sol particles that were prepared in mixtures of ethanol and water; these sols remain stable as long as the ethanol concentration does not exceed 57 vol%. The sols were completely retained by the membranes, which is probably caused by the fact that the effective diameter of the particles is much larger than that observed by transmission electron microscopy.

How does a polymer chain pass through a cylindrical pore under an elongational flow field?

“…4B. Such an experiment may explain why most of previously observed ultrafiltration transitions [24,31,34,35] were smooth, instead of sharp. In contrast, a continuously 3-dimentional networklike membrane is highly not recommended for the quantitative ultrafiltration-related study because of its poorly defined pore geometry.…”

“…However, most of studies [24,31,33,34] reported a smooth transition from total retention to forced penetration, except for us [26,28]. Namely, Beerlage et al [31] investigated the retention behavior of linear polystyrenes in ethyl acetate. It was shown that the "coil-stretch" transition is not precipitous, but gradual; and the critical volumetric flow rate is chain length and polymer concentration independent in dilute solution.…”

“…Though the existing experimental results [24,26,28,31,33,34] (Fig. 6A) and an abundant of computer simulation work [15,20,22,24] (Fig.…”

“…Usually, most of the experimental results reported in literatures have been essentially performed in pressure driven ultrafiltration devices and basically consist of measuring the relative retention concentration [(C 0 e C)/C 0 ] of the studied polymers, where C 0 and C are the concentrations of polymer retentate and permeate [24,26,28,31,33,34]. However, most of studies [24,31,33,34] reported a smooth transition from total retention to forced penetration, except for us [26,28]. Namely, Beerlage et al [31] investigated the retention behavior of linear polystyrenes in ethyl acetate.…”

Properties of a Filter Cake Formed in Dead-End Microfiltration of Colloidal Particles Suspended in Aqueous Organic Solvents

“…There have been numerous studies (de Rooy et al, 1980;Kandori et al, 1984;Kosmulski and Matijevic, 1992;Kage et al, 1993;Ketelson et al, 1996;Chadwick et al, 2002) on the colloidal stability and electrokinetic properties of dispersions in the aqueous organic solvent. However, related filtration study is rather scarce (Gupta et al, 1995;Lencki and Williams, 1995;Beerlage et al, 1996) since, until now, most studies have been done with aqueous colloidal suspensions, thus little understanding currently exists regarding the effect of aqueous organic solvents on filtration behavior of colloidal solutions.…”