Phase Separation Casting
Microstructures can be formed by phase separation casting. A homogeneous fluid is poured into a mold, a conditions altered to induce phase separation or precipitation.
“1. Vapour-induced phase separation (VIP), also called "dry casting" or "air casting". Evaporation of the liquid (solvent) will result in a dense or porous product depending on the material and the used solvent/solute mixtures. (e.g. acetone /polysulfone solutions)
2. Liquid-induced phase separation (LIPS), mostly referred to as "immersion casting" or "wet casting". This process normally yields dense or porous products depending on the material and the used solvents and non-solvent mixtures. This technique may be combined with 1) for polymer solutions with e.g. two solvents with different boiling points.
3. Thermally induced phase separation (TIPS), frequently called "melt casting"; The material may solidify to a dense or porous product of a material-solvent-additive mixture by varying the temperature of the material-solvent during the casting process.
4. Colloidal induced phase separation (CIPS). A phase separated colloidal solution is used to perform structure arrestment on the micro fabricated mould. For example, a polymerizable bicontinuous microemulsion can be applied onto the mould, or a sol/gel mixture of a ceramic material. The pore morphology can be tuned by the addition of a co-solvent resulting generally into smaller pores.
5. Pressure induced phase separation (PIPS), "pressure casting"; The casting solution may contain for example a saturated dissolved gas. Reduction of the pressure (or increase of temperature) will induce growth of gas cells in the casting solution with a closed cell or open cell morphologies and a typical size of 0.01-1000 micron.
6. Reaction-induced phase separation (RIPS), a casting solution containing monomers start to react and initiate phase separation due to for instance increase in molecular weight or production of a non-solvent
Most common phase separation processes are based on phase separation of a polymer solution. by bringing the casting solution into contact with a non-solvent, which is normally a gas (vapour) or a liquid not well miscible with the solvent of the casting solution. “
Recent US Patents
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5/12/2009
7,531,120
Method of making a product with a micro or nano sized structure and product
Rjin et al of Aquamarijn Holding formed a polysulfone microsieve by casting a polysulfone/acetone solution onto a surface with protruding rods and removing the acetone by evaporation. 13 other structures were formed using different casting strategies.
10/28/2008
7,442,336
Capillary imprinting technique
Choi of Molecular Imprints has developed a method for form micropatterns by casting a liquid which fills the micromold structure by capillary action and, then, solidifying the material. The casting material is a acrylic solution in ethylene glyhcol diacrylate isobornyl acrylate.