Crystalline polymorphism in poly(vinylidenefluoride) membranes
Zhaoliang Cui, Naser Tavajohi Hassankiadeh, Yongbing Zhuang, Enrico Drioli*, Young Moo Lee*
Abstract
PVDF is widely employed in membrane processes. Its crystals have five different polymorphs, α, β, γ, δ, and ɛ forms. In the past decades, research has been focused on the properties and performances of PVDF membranes. However, the formation mechanisms of the various polymorphs and their different effects on membrane performance are still not clear. Therefore, overall clarification of, conclusions about, and outlook on the effects of PVDF polymorphism on membrane properties and performance are important topics for further research. This manuscript systematically summarizes the structures and properties of PVDF crystals with different polymorphs, discusses the mechanisms of formation and transformation methods, reviews the crystallization and applications of different PVDF polymorphs in membrane separation, and presents the outlook for applications in membrane operations.
Keywords
PVDF
Polymorphism
Membranes
Crystallization
Abbreviations
Keywords
1. Introduction
2. PVDF polymorphs
2.1. Structures of PVDF crystals with different polymorphs
2.2. Properties of PVDF crystals with different polymorphs
2.3. Identification and characterization of PVDF polymorphs
2.3.1. Qualification
2.3.2. Quantification
2.4. Formation of different polymorphs
3. PVDF membrane preparations with different polymorphs
3.1. Polymorphism during PVDF membrane fabrication via solvent evaporation (solution casting)
3.2. Polymorphism during PVDF membrane fabrication via electro-spinning
3.3. Polymorphism during PVDF membrane fabrication via NIPS and VIPS processes
3.4. Polymorphism during PVDF fabrication via TIPS process
4. Polymorph promotions during PVDF membrane preparation
4.1. Using substrates or epitaxy
4.2. Using PVDF copolymers
4.3. Blending with polymers
4.4. Adding inorganic fillers
5. Polymorph transformations of PVDF membranes in the solid state
6. Applications of PVDF membranes with different polymorphs
6.1. For biomaterials and tissue engineering
6.2. For controlling membrane fouling and cleaning
6.3. Perspectives on research on PVDF polymorphs in membrane separation
7. Conclusions and outlook
Acknowledgments
References
