Abstract
Ordered mesoporous silica materials were prepared under different pH conditions by using a silicon alkoxide as a silica source and polyion complex (PIC) micelles as the structure-directing agents. PIC micelles were formed by complexation between a weak polyacid-containing double-hydrophilic block copolymer, poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA), and a weak polybase, oligochitosan-type polyamine. As both the micellization process and the rate of silica condensation are highly dependent on pH, the properties of silica mesostructures can be modulated by changing the pH of the reaction medium. Varying the materials synthesis pH from 4.5 to 7.9 led to 2D-hexagonal, wormlike or lamellar mesostructures, with a varying degree of order. The chemical composition of the as-synthesized hybrid organic/inorganic materials was also found to vary with pH. The structure variations were discussed based on the extent of electrostatic complexing bonds between acrylate and amino functions and on the silica condensation rate as a function of pH.
Highlights
Due to their unique physicochemical properties originating from their uniform pore size and periodically arranged network at the mesoscale, silica-based ordered mesoporous materials (OMMs) have attracted considerable attention in various fields such as adsorption, separation and catalysis
We reported that double hydrophilic block copolymer (DHBC) such as poly(ethylene oxide)-b-poly(acrylic acid) (PEO-b-PAA) or poly(ethylene oxide)-b-poly(methacrylic acid) (PEO-b-PMAA) copolymers, are able to form polyion complex (PIC) micelles upon interaction with weak polybases such as oligochitosan (OC) [25], poly-L-lysine (PLL) [26,27] and aminoglycoside antibiotics [28]
We investigate how a simple synthesis parameter, such as the pH of the reaction medium, which governs the extent of the polyion electrostatic complexation and the silica condensation rate, influences the macrophase separation of the hybrid material and the nature of the mesostructures which are obtained
Summary
Due to their unique physicochemical properties originating from their uniform pore size and periodically arranged network at the mesoscale, silica-based ordered mesoporous materials (OMMs) have attracted considerable attention in various fields such as adsorption, separation and catalysis. We investigate how a simple synthesis parameter, such as the pH of the reaction medium, which governs the extent of the polyion electrostatic complexation and the silica condensation rate, influences the macrophase separation of the hybrid material and the nature of the mesostructures which are obtained.
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