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0897-J06-06.1

High-Porosity Nanoporous Silica by Nanocasting using Hydrogel Takanori Nakamura, Ken-ichi Kurumada, Atsushi Suzuki, Naoki Umeda1, Naoki Kishimoto1 Graduate School of Environment & Information Sciences, Yokohama National University, Yokohama 240-8501, Japan 1 National Institute of Materials Sciences, Sakura, Tsukuba 305-0044, Japan ABSTRACT High-porosity nanoporous silica was prepared by nanocasting method using N-isopropylacrylamide (NIPAm) cross-linked by N, N’-methelenbisacrylamide (BIS) as the templating agent. The obtained silica was a bulk silica with good transparency indicating that the characteristic length-scale of the obtained silica is in the nanoscopic scale being much smaller than that of the wave length of visible light. Nitrogen adsorption/desorption measurements revealed that the nano porosity increases up to 80% with the weight ratio of NIPAm to silica. The mean pore size (radius) also increased with the weight ratio in the region smaller than 10nm. TEM observation revealed that the nanoscopic network structure was replicated into tube-like nanopores randomly distributed in the silica matrix. The whole nanoscopic morphology of these tube-like nanopores was much like as the predicted for the cross-linked polymer.

INTRODUCTION There had been studies using organic polymeric species for silica nano-casting method [1-4], obtaining nanoporous bulk solids had been a practical aim. We studied the precise replication of NIPAm gel cross-linked by N, N’-methelenbisacrylamide (BIS). In the present paper, the effect of the amount of the template polymer was mainly focused on. The replication mechanism was discussed based on the obtained results.

EXPERIMENTAL DETAILS [Materials] NIPAm monomer was provided by Kojin Chemical. BIS, N, N, N’, N’-tetramethylethylenediamine (TEMED), ammonium persulfate (APS) and hydrochloric acid (HCl) were purchased from Wako Pure Chemical and used as provided. Water for the sample preparation was purified by ion-exchange followed by distillation.

0897-J06-06.2

[Sample Preparation] For preparation of samples used in the present work, two precursory solutions (silica sol and NIPAm/BIS pregel solution) were necessary. Silica sol was prepared by hydrolyzing 20.8 g (0.1 mol) of TEOS with 7.2 g (0.4 mol) of H2O catalysed by addition of 0.1 g of 1 M HCl. The hydrolysis was completed in a couple of hours. These amounts of chemicals for preparing the silica sol were common to all the samples. On the other hand, the amount of NIPAm gel moiety was varied at ε = 0.67, 1.00, 1.33, 1.67, and 2.33, where ε denotes the weight ratio of used NIPAm to silica, 6.0 g (0.1 mol). The molar ratio of NIPAm to BIS was fixed at 81. (This is a typical value in preparing standard NIPAm hydrogels cross-linked by BIS in the present preparation.) It should be noted that the amounts of NIPAm monomer and BIS dissolved in water were four times more than NIPAm in weight used in the well established recipe [1,2]. At room temperature, 2 hours were necessary for completion of the dissolution with 200rp