Solidification Behavior of Polymer Solution during Membrane Preparation by Thermally Induced Phase Separation

• Main Authors: Toru Ishigami, Yoko Nii, Yoshikage Ohmukai, Saeid Rajabzadeh, Hideto Matsuyama
• Format: Article
• Language: English
• Published: MDPI AG 2014-02-01
• Series: Membranes
• Subjects: solidification rate; membrane preparation process; thermally induced phase separation; poly(vinylidene fluoride)
• Online Access: http://www.mdpi.com/2077-0375/4/1/113

The solidification behavior of poly(vinylidene fluoride) (PVDF) solution during membrane preparation by thermally induced phase separation (TIPS) was investigated. Apparatus newly developed in our laboratory was used to quantitatively measure membrane stiffness during phase separation. In this apparatus, a cooling polymer solution, placed on a stage, is moved upwards and the surface of the polymer solution contacts a sphere attached to the tip of a needle. The displacement of a blade spring attached to the needle is then measured by a laser displacement sensor. Different phase separation modes, such as liquid-liquid (L-L) phase separation and solid-liquid (S-L) phase separation (polymer crystallization) were investigated. In the case of S-L phase separation, the stiffness of the solution surface began to increase significantly just before termination of crystallization. In contrast, L-L phase separation delayed solidification of the solution. This was because mutual contact of the spherulites was obstructed by droplets of polymer-lean phase formed during L-L phase separation. Thus, the solidification rate was slower for the L-L phase separation system than for the S-L phase separation system.