The Formation of Ordered Nanoporous Structure with Controlled Micelle Size
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The Formation of Ordered Nanoporous Structure with Controlled Micelle Size
Jeongho Chang, Yongsoon Shin, Li-Qiong Wang, and Gregory J. Exarhos Materials Chemistry Research, Pacific Northwest National Laboratory, Richland, WA 99352, USA ABSTRACT
Selected MPEG-b-PDLLA block copolymers have been synthesized with systematic variation of the chain lengths of the resident hydrophilic and hydrophobic blocks. The size and shape of the micelles that spontaneously form in solution are then controlled by the characteristics of the copolymer template. Formation of nanoporous silica at room temperature with short-preparation time is demonstrated and silica-containing materials evolve with uniform pore shape and wall structure. The formation mechanism of these nanoporous structures obtained by controlling the micelle size has been confirmed using both liquid and solid state 13C and 29Si NMR techniques. INTRODUCTION The general route for preparation of the molecularly ordered inorganic materials involves an organic-templating technique based upon the electrostatic or sterically controlled assembly of commercial amphiphilic organic surfactants such as cetyltrimethyl ammonium bromide (CTAB) or non-ionic polyethylene oxide surfactants [1-3]. Many studies adopted these methods and demonstrated ordered materials with high surface area and uniform pore structures. The MCM-41 and SBA type materials are frequently studied among these porous materials because they exhibit well-ordered pore arrays, which can be modified by varying the alkane chain length of the ionic surfactants or by introducing a hydrophobic reagent such as trimethylbenzene (TMB) with a non-ionic surfactant [4]. However, ordered materials derived by this route are not prone to preparation in a short time because of lowered solubility and structural restriction. Consequently, control of their physicochemical properties becomes difficult. Although several key studies [5-7] have been reported on the formation of hybrid nanostructures based on models invoking charge density, layer puckering, and precursor organization into silica rod assemblies, the detailed formation mechanism is still unclear. These previous studies could not effectively explain the interaction between the silica precursor and the surfactant and how this interaction subsequently determines the observed ordering in the nanoporous materials derived using these techniques. The strategy in this work for using block copolymer templates as structure directing agents is that the overall morphology of the nanocomposite can be systematically controlled by varying the number of blocks, block lengths, and chemical composition associated with each block.
T3.1.1 Downloaded from https://www.cambridge.org/core. Karolinska Institutet University Library, on 28 Feb 2020 at 19:52:50, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/PROC-733-T3.1
EXPERIMENTAL DETAILS The polymerization of MPEG-b-PDLLA diblock copolymer was performed in dry toluene. Mono
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