Vapor-induced phase separation

Asymmetric membranes are usually produced by phase inversion techniques. In these techniques, an initially homogeneous polymer solution becomes thermodynamically unstable due to different external effects and the phase separates into polymer-lean and polymer-rich phases. The polymer-rich phase forms the matrix of the membrane, while the polymer-lean phase, rich in solvents and nonsolvents, fills the pores. Four main techniques exist to induce phase inversion and thus to prepare asymmetric porous membranes [85] (a) thermally induced phase separation (TIPS), (b) immersion precipitation (wet casting), (c) vapor-induced phase separation (VIPS), and (d) dry (air) casting. 

Vapor-Induced Phase Separation During the VIPS process, phase separation is induced by penetration of nonsolvent vapor, into the homogeneous polymer solution consisting of polymer and solvent(s). Mass transfer is usually much slower than that in the wet casting process thus, the VIPS process has been used to obtain membranes with symmetric, cellular, and interconnected pores [86,87],... 

Tsai J, Sn Y, Wang D, Kuo J, Lai J, Deratani A. Retainment of pore connectivity in membranes prepared with vapor-induced phase separation. JMembr Sci. 2010 362(l-2) 360-373. 

Caquineau H, Menut P, Deratani A, Dupny C. Influence of the relative hnmidity on film formation by vapor induced phase separation. Polym Eng Sci. 2003 43(4) 798-808. 

Khare V, Greenberg A, Krantz W. Vapor-induced phase separation—Effect of the humid air exposure step on membrane morphology Part I. Insights from mathematical modeling. J Membr Sci. 2005 258(1-2) 140-156. 

Phase inversion is known to be an effective way to create porous structures in membranes, where a competitive mutual diffusion between solvent and nonsolvent occurs to yield the porous structure. Phase inversion can be described as a demixing process whereby the initially homogeneous polymer solution is transformed in a controlled manner from a liquid to a solid state [24]. Apart from immersion in a nonsolvent bath, or immersion precipitation (IP), a variety of related techniques, such as precipitation by solvent evaporation, precipitation by absorption of water Irom the vapor phase, and precipitation by air cooling, corresponding to thermally induced phase separation (TIPS), vapor-induced phase separation (VIPS), and air-casting phase separation... 

Zhao N, Xie QD, Weng LH, Wang SQ, Zhang XY, Xu J. (2005) Superhydrophobic surface from vapor-induced phase separation of copolymer micellar solution. Macro-... 

Menut, R, Bohatier, C. R, Deratani, A., Dupuy, C., and Guilbert, S. (2002). Structure formation of poly(ether-imide) films using nonsolvent vapor induced phase separation Relationship between mass transfer and relative humidity. Desalination 145, 11. 

Section 33.6 reviewed the work of Kools et al. (1998) who published the only study to date of the use of UTDR to characterize membrane formation processes. This powerful appUcation of UTDR should be used to smdy other membrane formation processes such as wet-casting, thermally induced phase separation, vapor-induced phase separation, and interfacial polymerization. Indeed, UTDR characterization can provide invaluable insight into precisely how membranes acquire their unique permselective properties during the fabrication process. This knowledge in turn will help develop improved and new membranes. 

An innovative idea for inexpensive large area SERS substrate fabrication was proposed by Akil-Jradi et al. (2012). A solution was prepared by dissolving AgN03 in ethanol and mixing it with PMMA dissolved in acetone. The manufacture of substrates was based on the vapor-induced phase separation and chemical reduction of a metal precursor-doped... 

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