Thermally induced phase separation and electrospinning methods for emerging membrane applications: A review

Abstract

In this review, thermally induced phase separation (TIPS) and electrospinning methods for preparation of fluoropolymer membranes are assessed, particularly for the polyvinylidene fluoride (PVDF) and polyethylene chlorotrifluoroethylene membranes. This review focuses on controlling the membrane morphology from the thermodynamic and kinetic perspectives to understand the relationship between the membrane morphology and fabrication parameters. In addition, the current status of the nonsolvent induced phase separation (NIPS) method and the combined NIPS-TIPS (N-TIPS) method, which is a new emerging fabrication method, are discussed. The past literature data are compiled and an upperbound curve (permeability vs. tensile strength) is proposed for the TIPS-prepared PVDF membranes. Furthermore, the key parameters that control and determine the membrane morphology when using the electrospinning method are reviewed. Exploiting the unique advantages of the electrospinning method, our current understanding in controlling and finetuning the PVDF crystal polymorphism (i.e., b-phase) is critically assessed. V C 2015 American Institute of Chemical Engineers AIChE J, 62: 461-490, 2016 Figure 15. Cross section of 40 wt % PVDF/GBL hollow fiber membranes: (left) with LiCl additive, (middle) with glycerol additive, (right) with LiCl and glycerol additives.Formation of such fine pores nearly doubled the flux without losing mechanical strength. 28 481 TEM images of 4 wt % PVP nanofibers from different compositions of EtOH/DMF: (b) 65/35, (c) 50/50, (d) 35/65, and (e) SEM image of 4 wt % PVP nanofibers using EtOH/DMF (50/50). 146 482

Understanding the non-solvent induced phase separation (NIPS) effect during the fabrication of microporous PVDF membranes via thermally induced phase separation (TIPS)

“…Morphological study of the solvent/nonsolvent diffusion rate in PVDF/PolarClean s membranes A significant limitation of the phase diagram is that it only reflects the thermodynamic stability and neglects kinetic factors such as the solvent/nonsolvent diffusion rate and polymer crystallization rate, which are considered to be more important parameters in membrane fabrication [12]. Since the NIPS process is driven by the solvent/nonsolvent exchange, one of the effective ways to control the NIPS effect is to slow the exchange rate by changing the coagulation bath concentration [24].…”

“…Indeed, most TIPS solvents usually have poor interactions with the polymer and follow the phase diagrams shown in Fig. 1e and f. In such cases, the dope composition and cooling kinetic determines whether the system will undergo liquid-liquid separation (L-L separation) or simultaneous solid-liquid (S-L)/liquid-liquid separations [12]. On the other hand, if the TIPS solvent has a good interaction with the polymer, i.e.…”

“…Such phenomenon is referred to as the combined NIPS and TIPS (N-TIPS) method [12] and has been gaining interest as an attractive candidate for controlling the morphology and performance [12]. For instance, combining the advantages of NIPS and TIPS could yield highly permeable membranes with strong mechanical properties [12]. Since Matsuyama et al first pioneered the N-TIPS method in 2002 [26], there have been many studies to understand this new emerging method by employing a co-solvent [27] or by controlling the system temperature [28].…”

“…Notably, as the TIPS method is composed of only two components (polymer and solvent), membranes fabricated by the TIPS method are inherently more reproducible and less prone to defects [12]. In addition, the elevated working temperatures in the TIPS method allow a wider selection of solvents and polymers, albeit with higher energy consumption [12].…”

“…Therefore, when a water-soluble TIPS solvent is used, both the NIPS and TIPS effects can co-exist. Such phenomenon is referred to as the combined NIPS and TIPS (N-TIPS) method [12] and has been gaining interest as an attractive candidate for controlling the morphology and performance [12]. For instance, combining the advantages of NIPS and TIPS could yield highly permeable membranes with strong mechanical properties [12].…”