(213b) Snips Membranes-How It Came about

A SNIPS membrane is made by a non-solvent-induced phase separation of a block copolymer solution. Self-assembly of the block copolymer and phase separation happen nearly simultaneously. The very first isoporous SNIPS membrane was manufactured at the former GKSS (Germany) in 2006. I prepared this membrane myself, and I would describe this discovery as a pseudo-serendipitous event^*. A concentrated polymer solution with two or more solvents was cast into a film and plunged into water. In less than 30 seconds, an asymmetric membrane was formed with a spongy substructure covered by a thin, highly porous skin with pores all of the same size in the low nm range¹. This was done with a lab-synthesized block copolymer, and it was spectacular. However, it turned out that I could not reproduce this process with commercially available block copolymers, and this could have been the sad end of a story that had an exciting start. This was the right time to join forces with Suzana. However, we could not continue this work at GKSS^** in Germany, and we searched for a new workplace. Luckily, we both received an offer from the King Abdullah University for Science and Technology (KAUST) in Saudi Arabia), where we started our work as founding members in the fall of 2009. I think we were the first researchers doing chemical experiments in the new KAUST labs. We were a special team because we had complementary talents.

As a hands-on experimenter, I loved to smell the mixture of solvents, and I liked to dive my fingers into the precipitation bath. On the other hand, Suzana dived deep into the mechanism of phase separation and the theory of morphology formation in block copolymer systems. She used the whole armada of characterization techniques available for us, including Cryo- FESEM, Cryo-TEM, Small and wide-angle X-ray scattering, focused ion beam microscopy and more. Suzana could show that micelle evolution and micelle self-assembly was vital for the membrane’s morphology formation. Only ten months after our arrival at KAUST, we submitted a paper to Macromolecules which was pivotal for the further development of SNIPS membranes.² Suzana pushed hard, and soon afterward, we could publish more details on membrane formation by block copolymer micelle assembly^3,4; the term SNIPS was not even coined at this time. In the Langmuir paper, a convincing correlation is shown between the micelle formation and self-assembly in solution and the final morphology of the solid membrane.

Thanks, Suzana! Without you, I would have given up this work at an early stage; with you, it developed into a fascinating project.

1.K.-V. Peinemann et al., Asymmetric superstructure formed in a block copolymer via phase separation, Nature Materials 2007, 6, 992, DOI: 10.1038/nmat2038

2.S. P. Nunes et al., Ultraporous films with uniform nanochannels by block copolymer micelles assembly, Macromolecules 2010, 43, 8079. DOI: 10.1021/ma101531k

3.S. P. Nunes et al., Switchable pH-responsive polymeric membranes prepared via block copolymer micelle assembly, ACS Nano 2011, 5, 3516. DOI: 10.1021/nn200484v

4.S. P. Nunes et al., From micelle supramolecular assemblies in selective solvents to isoporous membranes, Langmuir 2011, 27, 10184. DOI: 10.1021/la201439p

^* Pseudo serendipity means discovering something one was looking for in a surprising way (Diaz de Chumaceiro, The Journal of Creative Behavior 29, 143–147 (1995))

^** see also my blog at https://peinemann-lifetwists.blogspot.com