Principles of Hierarchical Meso- and Macropore Architectures by Liquid Crystalline and Polymer Colloid Templating

Abstract

The generation of porous silica with hierarchically organized bimodal mesoporosity of adjustable size and well-defined shape was investigated by using surfactant mixtures and the nanocasting procedure (liquid crystalline templating). A systematic study of combinations of various block copolymers (Pluronics F127, KLE (poly(omega-hydroxypoly(ethylene-co-butylene)-co-poly(ethylene oxide))) and SE (PS-co-PEO)) with smaller surfactants (Pluronics P123, C16mimCl, and CTAB) revealed that hierarchical bimodal mesopore architectures could only be obtained by the usage of block copolymers with a strong hydrophilic-hydrophobic contrast, such as KLE and SE, giving rise to pores between 6 and 22 nm. Furthermore, the ionic liquid (IL) C16mimCl appeared to have advantageous templating properties, resulting in 2-3-nm pores being located between the block copolymer mesopores, whereas phase separation was observed for Pluronics and CTAB as small templates. Thereby, the study provided also general insights into the mixing and co-self-assembly behavior of block copolymers and ionic surfactants in water and confirmed the special templating properties of ILs, as recently proposed. In addition to the bimodal mesoporosity, additional tunable macroporosity was created by the presence of poly(styrene) or poly(methyl methacrylate) spheres, leading to well-defined trimodal hierarchical pore architectures with the small pores being located in the walls of the respective larger pores. As a major improvement, due to the pore hierarchy, these large-pore materials showed relatively large surface areas and pore volumes, and the size of densely packed macropores could even be decreased down to 90 nm. The materials were characterized by electron microscopy, small-angle X-ray scattering, and nitrogen sorption using a proper NLDFT (nonlocal density functional theory) approach for calculations of the pore size distribution in the entire range of micro- and mesopores.

Fabrication of Hierarchically Ordered Porous Films Composed of Imogolite via Colloidal Templating

“…18 -20 However, multiple use of surfactants have been known to have some problems of complex interactions among templates. 20 Therefore, the use of building blocks, having nanopores within the structures, as the pore wall components can circumvent such a problem.…”

Hierarchical Meso‐Mesoporous and Macro‐Mesoporous Silica Templated by Mixtures of Polyoxyethylene ­Fluoroalkyl Ether and Triblock Copolymer

“…Indeed, it was reported that a hierarchical combination of mesopores reduces transport limitations in catalysis, resulting in higher activities and better controlled selectivity [27] . Therefore, over the past few years the development of these hierarchically ordered structures at multiple length scales has attracted much attention and materials with a micro-macroporous or a meso-macroporous structure have been synthesized using multiple templates through either soft or hard templating methods [28][29][30][31][32][33][34] .…”

One-Step Introduction of Broad-Band Mesoporosity in Silica Particles Using a Stimuli-Responsive Bioderived Glycolipid

“…Hierarchy in size and pore interconnection have been judged to be equally, if not more, important in terms of final application because of the much easier control that one can establish on the diffusion properties inside the pores. 4,5,6 Typically, organic templates are currently used to obtain micro-or meso-scale porosity such as in zeolites (use of quaternary ammonium salts) or in MCM-41 or SBA-15 materials (use of surfactant micelles). 7,8 Ordered macroporosity is easily achieved using micrometer-sized colloidal packing.…”