Tuning Structural Color Changes of Porous Thermo-sensitive Gels Through Quantitative Adjustment of The Cross-linker in Pre-gel Solutions Yukikazu Takeoka and Masayoshi Watanabe Department of Chemistry and Biotechnology, Yokohama National University, 156 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan. Tel & Fax: +81-45-339-3956 E-mail: ytakeoka@ynu.ac.jp Chemical gels, which are covalently cross-linked polymer networks swollen with solvent, freely swell and shrink in response to environmental changes. Much of the current research on chemical gels has focused on the use of templates or matrices for additional functions. So-called “smart” gels for molecular recognition, catalysis, and separation can be easily fabricated by a templating technique, because the spatial position and the three-dimensional shape of the templates used can be memorized by the permanent cross-links formation. Here we report the preparation of “Smart” porous gels with different optical behaviors by quantitative adjustment of the cross-linker in pre-gel solutions. A periodically ordered interconnecting porous structure could be created in the gels by using a closest-packing silica colloidal crystal as a template. The interconnecting porosity provides fast response to changes in temperature through the reversible swelling and shrinking of the gels, while the periodically ordered mesoscopic structure endows the porous gels with structural color, which can be tuned by simply changing the amount of the cross-linker in the pre-gel solutions. Acknowledgement We thank the Nippon Shokubai Co. for their free gifts of silica colloidal suspension. This work was supported by Shiseido Fund for Science and Technology and Grant-in-Aid for Scientific Research on Priority Areas (No. 413) from the Ministry of Education, Culture, Sports, Science, and Technology, Japan. References 1) Takeoka, Y. and Watanabe, Langmuir , 18, 5977-5980(2002). 2) Takeoka, Y. and Watanabe, M., Langmuir in press. 3) Takeoka, Y. and Watanabe, M., Adv. Mater , 15, 199-201(2003).