Effect of surface roughness and softness on water capillary adhesion in apolar media
Banerjee, S. ; Mulder, P. ; Kleijn, J.M. ; Cohen Stuart, M.A. - \ 2012
The Journal of Physical Chemistry Part A: Molecules, Spectroscopy, Kinetics, Environment, & General Theory 116 (2012)25. - ISSN 1089-5639 - p. 6481 - 6488.
atomic-force microscope - lamellae formation - phase-separation - mica surfaces - thin-film - condensation - kinetics - liquid - alkanes - pore
The roughness and softness of interacting surfaces are both important parameters affecting the capillary condensation of water in apolar media, yet are poorly understood at present. We studied the water capillary adhesion between a cellulose surface and a silica colloidal probe in hexane by AFM force measurements. Nanomechanical measurements show that the Young’s modulus of the cellulose layer in water is significantly less (7 MPa) than in hexane (7 GPa). In addition, the cellulose surface in both water and hexane is rather rough (6–10 nm) and the silica probe has a comparable roughness. The adhesion force between cellulose and silica in water-saturated hexane shows a time-dependent increase up to a waiting time of 200 s and is much (2 orders of magnitude) lower than that expected for a capillary bridge spanning the whole silica probe surface. This suggests the formation of one or more smaller bridges between asperities on both surfaces, which is confirmed by a theoretical analysis. The overall growth rate of the condensate cannot be explained from diffusion mediated capillary condensation alone; thin film flow due to the presence of a wetting layer of water at both the surfaces seems to be the dominant contribution. The logarithmic time dependence of the force can also be explained from the model of the formation of multiple capillary bridges with a distribution of activation times. Finally, the force–distance curves upon retraction show oscillations. Capillary condensation between an atomically smooth mica surface and the silica particle show less significant oscillations and the adhesion force is independent of waiting time. The oscillations in the force–distance curves between cellulose and silica may stem from multiple bridge formation between the asperities present on both surfaces. The softness of the cellulose surface can bring in additional complexities during retraction of the silica particle, also resulting in oscillations in the force–distance curves.
Transmission and fractionation of micro-sized particle suspensions
Brans, G.B.P.W. ; Dinther, A.M.C. van; Odum, B. ; Schroën, C.G.P.H. ; Boom, R.M. - \ 2007
Journal of Membrane Science 290 (2007)1-2. - ISSN 0376-7388 - p. 230 - 240.
cross-flow microfiltration - colloidal particles - pore
In processes aimed at the fractionation of a multi-component feed stream, transmission of particles through the membrane is at least as important as retention of larger particles. In this paper, we describe the mechanisms of transmission of mono-disperse latex particles through a polymer membrane. The effects of process parameters, such as transmembrane pressure, cross flow velocity and feed concentration were investigated. In dead end filtration mode, we found that, depending on the transmembrane pressure, four particle transmission regimes could be distinguished. Particle deposition on polymer membranes and polymer microsieves was investigated in-line with confocal scanning laser microscopy (CSLM). It was observed that with the polymer membrane random depth deposition took place, while the microsieve exhibited in-pore fouling. In addition, bi-disperse particle suspensions were fractionated with dead end and cross flow membrane filtration, and various effects were charted. Based on the phenomena observed, it is concluded that the design of a fractionation process starts with defining a stable transmission regime for small particles, and subsequently choosing the process conditions for minimal deposition of the larger particles
Status of cross-flow membrane emulsification and outlook for industrial application
Gijsbertsen-Abrahamse, A.J. ; Padt, A. van der; Boom, R.M. - \ 2004
Journal of Membrane Science 230 (2004)1-2. - ISSN 0376-7388 - p. 149 - 159.
shirasu-porous-glass - in-water emulsions - microchannel emulsification - droplet formation - ceramic membranes - microspheres - size - pore
Cross-flow membrane emulsification has great potential to produce monodisperse emulsions and emulsions with shear sensitive components. However, until now, only low disperse phase fluxes were obtained. A low flux maybe a limiting factor for emulsion production on a commercial scale. Therefore, the effects of membrane parameters on the disperse phase flux are estimated. Besides, the effects of these parameters on the droplet size and droplet size distribution are qualitatively described. Wetting properties, pore size and porosity mainly determine the droplet size (distribution). Membrane morphology largely determines the disperse phase flux. As an example, industrial-scale production of culinary cream was chosen to evaluate the required membrane area of different types of membranes: an SPG membrane, an alpha-Al2O3 membrane and a microsieve. Due to the totally different morphologies of these membranes, the fraction of active pores is I for a microsieve and is very low for the other membranes. The choice of the optimal membrane did not depend on the production strategy: either to produce large quantities or to produce monodisperse emulsions, the best suitable was a microsieve with an area requirement of around I m(2). In general, the total membrane resistance should be low to obtain a large disperse phase flux. In contrast, the membrane resistance should be high to obtain monodisperse emulsions when using membranes with a high porosity. (C) 2003 Elsevier B.V. All rights reserved.