pH-mediated control over the mesostructure of ordered mesoporous materials templated by polyion complex micelles

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.

Synthesis of Hierarchical Porous Silica by Sol‐Gel of Sodium Silicate and Nanoemulsion Templating: Effective Combination Conditions

“…Thus, when the ammonia is added to start the condensation of the silicate, a silica framework is formed, in which the oil droplets are homogeneously distributed over long‐range arrangement as shown in Figure 5 (b). Figures 5 (c) clearly shows the mesoporous structure of the silica matrix, which results from the selection of conditions conducive to the formation of the sol‐gel [20] …”

Integrated Process for Structuring and Functionalizing Ordered Mesoporous Silica to Achieve Superprotonic Conductivity

“…The strategy relies on the use of a novel structure-directing agent, namely, polyion complex (PIC) assemblies, which incorporate desired functionalities that are masked during the sol–gel process, preventing disruption of the mesostructuring process. As reported, − PIC micelles formed with a weak polyacid-based double-hydrophilic block copolymer (DHBC) and an oppositely charged polyelectrolyte direct the structure of PIC-silica materials with tunable textural and structural properties (2D hexagonal, lamellar, cubic), called MesoPIC materials. In most subsequent studies, the PIC assembly has been completely removed from the organic–inorganic hybrid material.…”

“…Moreover, this strategy could be adapted to design Li- or Na-ion conducting materials. Furthermore, the versatility of the process can be easily exploited to control the ordered silica structure and to tune the pore properties of functionalized hybrid materials through the reactivity of PIC micelles to pH, concentration, or ionic strength. , Overall, our synthesis strategy paves the way for the large-scale sustainable development of well-defined polymer-functionalized mesoporous materials.…”

Weak Polyelectrolytes as Nanoarchitectonic Design Tools for Functional Materials: A Review of Recent Achievements

“…In contrast, when BCPs combine weak polyion blocks with hydrophobic blocks, they can micellize on complexation of their polyelectrolyte block with oppositely charged partners (polycations, drugs, multivalent cations) as reported for poly(ethylene glycol-b-2-(dimethylamino)ethylmethacrylate) (PEG- b -PDMAEMA), poly(acrylic acid- b -ethylene oxide) (PAA- b -PEO) and PNIPAM- b -PAA [ 230 , 231 ]. Such micelles recently found applications as drug vectors and sol-gel structure directing agents with pH-triggered stability [ 232 ].…”