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membranes from a given material. Among them, phase inversion is the most extensively applied method due to its simplicity and flexibility (Han and
Bhattacharyya 1994).
6.2.1 Phase Inversion
Phase inversion by immersion and precipitation method, a generic name of
nonsolvent- induced phase separation relies on the variation in the stability of the
casting solution during mass exchange of solvent and nonsolvent, occurred at the
polymer water interface (Luccio et al. 2002). Depending on the mass exchange rate,
an asymmetric structure consisting of a dense and a thin top layer, a porous sublayer
with finger-like structure, and a sponge-like bottom layer can be accomplished at
the end of the nonsolvent-induced phase separation. Obtaining an asymmetric structure is important since it provides less resistance to flow and hence high water flux.
The important aspects in this process include solvent–nonsolvent system selection,
polymer and coagulation bath composition, and casting conditions. Early history of
the method relies on ternary phase diagrams that can be used to analyze thermodynamic aspects of the three components in the system and demixing which affects the
structure of the resulting membrane (Fig. 6.2) (Guillen et al. 2011). The three components in the system (polymer, solvent, and nonsolvent) are represented in the
corners of the triangle and indicate a different composition made of a mixture of the
components at any point on the diagram. In the diagram, the system is composed of
a single-phase and a two-phase region. The former contains miscibility of three
components, while the solution is segregated to two phases, i.e., polymer-rich and
polymer-poor phases in the two-phase region. Tie lines represent equilibrium compositions and the binodal line represents liquid–liquid phase boundary. The solution
within the binodal curve segregates to two phases with different composition but in
equilibrium with each other whose compositions are represented by a tie line. After
submerging the casting solution into a nonsolvent bath (t < 1 s), the composition
Fig. 6.2 Illustration of the mechanisms of the membrane formation immediately after immersion
(t < 1 s): (a) fast and (b) slow demixing; T and B refer to top and bottom of the film, respectively
Y. Yurekli
membranes from a given material. Among them, phase inversion is the most extensively applied method due to its simplicity and flexibility (Han and
Bhattacharyya 1994).
6.2.1 Phase Inversion
Phase inversion by immersion and precipitation method, a generic name of
nonsolvent- induced phase separation relies on the variation in the stability of the
casting solution during mass exchange of solvent and nonsolvent, occurred at the
polymer water interface (Luccio et al. 2002). Depending on the mass exchange rate,
an asymmetric structure consisting of a dense and a thin top layer, a porous sublayer
with finger-like structure, and a sponge-like bottom layer can be accomplished at
the end of the nonsolvent-induced phase separation. Obtaining an asymmetric structure is important since it provides less resistance to flow and hence high water flux.
The important aspects in this process include solvent–nonsolvent system selection,
polymer and coagulation bath composition, and casting conditions. Early history of
the method relies on ternary phase diagrams that can be used to analyze thermodynamic aspects of the three components in the system and demixing which affects the
structure of the resulting membrane (Fig. 6.2) (Guillen et al. 2011). The three components in the system (polymer, solvent, and nonsolvent) are represented in the
corners of the triangle and indicate a different composition made of a mixture of the
components at any point on the diagram. In the diagram, the system is composed of
a single-phase and a two-phase region. The former contains miscibility of three
components, while the solution is segregated to two phases, i.e., polymer-rich and
polymer-poor phases in the two-phase region. Tie lines represent equilibrium compositions and the binodal line represents liquid–liquid phase boundary. The solution
within the binodal curve segregates to two phases with different composition but in
equilibrium with each other whose compositions are represented by a tie line. After
submerging the casting solution into a nonsolvent bath (t < 1 s), the composition
Fig. 6.2 Illustration of the mechanisms of the membrane formation immediately after immersion
(t < 1 s): (a) fast and (b) slow demixing; T and B refer to top and bottom of the film, respectively
Y. Yurekli