A Method of Immobilizing Colloids in Polymer Gels Used in the "Colloidal Clusters" Space Experiment Project

Abstract

This paper reports on a method to immobilize aqueous colloidal dispersions using polymer gels, which was used in the space experiment "Colloidal Clusters" project. The association structure of colloidal particles formed under microgravity conditions on the International Space Station was successfully immobilized by the gel, even after a long storage period of more than 8 months. Gelation was performed through radical polymerization under ultraviolet irradiation. The gelation technique had already been used in the JAXA 3D Photonic Crystal Project on colloidal crystallization, and we found that gelation was possible on the ISS about one month after the sample preparation. On the other hand, since the Colloidal Clusters Project assumed a long waiting time of several months or more, it was necessary to develop a gelation method that could be used over a longer period of time. Thus, we used a gel monomer (N,N-dimethylacrylamide) that is more resistant to aging. In addition, the reaction initiator and gel monomer were injected into separate bags and mixed in space. The colloidal samples could be fixed in the gel successfully and returned to the ground for analysis. We expect the present gelation technique to be useful for space experiments on various soft matter systems.