Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Patent
1993-03-11
1996-06-25
Spear, Frank
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
21050035, 21050042, B01D 6900
Patent
active
055296904
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the formation of polymeric coatings on a support or carrier. The invention is especially concerned with the formation of coatings of porous material from self-assembled microstructured liquids suitable for use in microfiltration, ultrafiltration and reverse osmosis.
Hitherto, such porous materials have been prepared by either spinodal decomposition or phase inversion techniques. Membranes produced by these techniques suffer from a number of disadvantages in relation to structure and, moreover, these techniques can only be applied to a limited number of materials.
As the invention is particularly concerned with self assembled microstructured liquids, it is appropriate to discuss such liquids.
Although hydrophobic liquids such as oil and hydrophilic liquids such as water do not normally mix they can do in the presence of an amphiphilic substance such as surfactant. For the sake of convenience, the hydrophobic component will hereinafter be termed an oil and the hydrophilic component will be termed water. Depending on concentration-of components, an oil/water/surfactant mixture can form an emulsion. Such an emulsion may be a water-in-oil emulsion where usually water is the dispersed phase and oil is the continuous phase or an oil-in-water emulsion where oil is the dispersed phase and water is the continuous phase. These emulsions are opaque systems because the size of the droplets cause scattering of light at a wavelength of the same order of light itself.
A surfactant is characterised by a hydrophilic head group and a hydrophobic tail group. The tail group usually consists of a single paraffinic hydrocarbon type of chain but may be more complex. The present invention is particularly concerned with surfactants in which the tail group is a double chain which is usually sparingly soluble in both oil and water.
The amphiphilic nature of surfactant molecules leads to self-aggregation in solution as the surfactant molecules isolate hydrophobic regions from hydrophilic regions. For certain concentrations of oil, surfactant and water, the mixture surprisingly becomes clear and sometimes colourless which, on a scale of the wave length of light, indicates that the mixture is a homogeneous solution. The apparently homogeneous solution exhibits a fixed, quantifiable structure on the microscopic scale and this structure forms spontaneously.
In this specification, these thermodynamically stable clear solutions are called microemulsions. Although the invention will, in the main, be described in relation to ternary systems which form microemulsions, it is to be understood that the invention is not limited thereto as other systems and other microstructured liquids will be useful. For example, certain binary systems such as methyl methacrylate and hexadecane or polymerisable surfactant and water may be used to form porous material as may quaternary and other multi-component systems which can include salt, mixtures of oil, mixed surfactants as well as polymeric additives to an oil or water.
Such mixtures are said to exhibit a self-assembled microstructure and often consist of bicontinuous phases separated by a surfactant monolayer or bilayer (they may, however, consist of disconnected spheres of water-in-oil or vice versa). When the bicontinuous phases are separated by a surfactant monolayer, one phase (or sub-volume) is an oil phase and the other phase is an aqueous phase. When the bicontinuous phases are separated by a surfactant bilayer, both labyrinths are either both oily or both aqueous and the space between the surfactant bilayer may be swelled respectively by the inclusion of water or of an oil.
In self-assembled microstructures, the surface formed by the surfactant achieves a shape which complies with established thermodynamic laws and which represents a global or local minimum energy which fulfils both global and local packing constraints required for the surfactant molecules. The constraints on a particular surfactant depend on the nature of the oil or water. For example, a short chain alkan
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Hyde Stephen T.
Karaman Marilyn E.
Morris Richard A.
Ninham Barry W.
Pashley Richard M.
Memtec Ltd.
Spear Frank
The Australian National University
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