Lateral Drying in Thick Films of Waterborne Colloidal Particles

Abstract

The first systematic and quantitative experimental study of the influences on lateral drying in colloidal films is reported. The time until water recedes from the edge of a drying thick film of a waterborne colloidal dispersion, called the open time, was measured as a function of several controllable parameters. Magnetic resonance microscopy, using a specially designed probe, noninvasively provides a direct and quantitative measurement of the concentration of water as a function of vertical and lateral position. Images were obtained from drying films of latices with known values of thickness, particle size, and surface tension, which are neatly encapsulated in an expression for the reduced capillary pressure, p c. A strong increase in the open time was found over a relatively narrow range of p c values. Larger particles, slower evaporation rates, and thinner films encourage more uniform lateral drying with a delay in drying from the edges. This observation is consistent with a recent model (Routh, A. F.; Russel, W. B. AIChE J. 1998, 44, 2088) based on the lubrication approximation. The experiments and the modeling point to a way of achieving control over the lateral drying processes of waterborne colloids.

An experimental test of the scaling prediction for the spatial distribution of water during the drying of colloidal films

“…Some research has considered the drying process laterally in the film (i.e. parallel to the substrate) [13,14]. Drying in the direction perpendicular to the substrate (i.e.…”

Heterogeneous Drying of Colloidal Polymer Films: Dependence on Added Salt

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Watching paint dry: Magnetic resonance imaging of soft condensed matter

“…The analysis predicts a normalised time for drying of a film's edge as a function of reduced capillary pressure pc. Using MRI data, such as that just presented, the Surrey group provided the first experimental test ofRouth and Russel's predictions [6]. The data shown in figure 4, obtained from MR experiments, shows an encouraging agreement with the theory.…”

“…Fig. 3: Three images extracted from a series showing the drying of a latex film from the edges towards the centre [6]. From top to bottom are images of the initial wet film and after drying for three and six hours.…”

“…Studies of thin layers, low water concentrations and non-aqueous phases all require much greater magnetic field gradients than can normally be achieved using switched current-windings. To that end Paul Glover (now at the University of Nottingham) and colleagues designed a small portable permanent magnet with a uniform (magnitude) magnetic field in the horizontal plane and with a very strong field gradient in the orthogonal vertical direction [6]. This field profile is carefully tailored to provide best achievable spatial resolution across planar samples.…”