Tuning Pore Dimensions of Mesoporous Inorganic Films by Homopolymer Swelling

Abstract

The functionality and applications of mesoporous inorganic films are closely linked to their mesopore dimensions. For material architectures derived from block copolymer (BCP) micelle co-assembly, the pore size is typically manipulated by changing the molecular weight corresponding to the pore-forming block. However, bespoke BCP synthesis is often a costly and time-consuming process. An alternative method for pore size tuning involves the use of swelling agents, such as homopolymers (HPs), which selectively interact with the core-forming block to increase the micelle size in solution. In this work, poly(isobutylene)-block-poly(ethylene oxide) (PIB-b-PEO) micelles were swollen with poly(isobutylene) HP in solution and co-assembled with aluminosilicate sol with the aim of increasing the resulting pore dimensions. An analytical approach implementing spectroscopic ellipsometry (SE) and ellipsometric porosimetry (EP) alongside the more commonly used atomic force microscopy (AFM) and small angle x-ray scattering in transmission (SAXS) and grazing-incidence (GISAXS) modes enabled to study the material evolution from solution processing through to the manifestation of the mesoporous inorganic film after BCP removal. In-depth SE/EP analysis evidenced an increase of over 40% in mesopore diameter with HP swelling and a consistent scaling of the overall void volume and number of pores. Importantly, our analytical tool-box enabled us to study the effect of swelling on the connecting necks between adjacent pores, with observed increases as high as ≈35%, knowledge of which is crucial to sensing, electrochemical and other mass transfer-dependent applications.

Controlled Porosity in Ferroelectric BaTiO3 Photoanodes

“…This is in line with previous studies, where controllable porous materials were synthesized using BCPs as sacrificial structure-directing agents. Indeed, following this approach, the pore size can be tuned by controlling the BCP molecular weight 41 or by the addition of swelling agents to the hybrid solution, 42 while the total sample porosity directly relies on the final organic/inorganic ratio. 43 SEM top-view images confirm the porous structure of pBTO thin films (Figure 2a).…”

Solvent Vapor Annealing for Controlled Pore Expansion of Block Copolymer-Assembled Inorganic Mesoporous Films

“…28 Alternative methods based on pore expansion by supramolecular coassembly of swelling agents, carefully chosen to selectively interact with the pore-forming block, have been successfully implemented. To this end, benzene derivatives, 29,30 homopolymers, 31,32 carboxylic acids, 33,34 or solvents such as toluene or xylene 35,36 can be used for tuning structural dimensions of the final inorganic mesoporous thin film. However, following this approach, and contrary to the size exclusion chromatography, a negative impact in pore size dispersity and long-range order of the structure has been identified.…”

Enhanced Structural Control of Soft-Templated Mesoporous Inorganic Thin Films by Inert Processing Conditions

“…Hybrid thin films were fabricated following a protocol reported elsewhere. 14,15 In brief, a previously hydrolyzed aluminosilicate sol from aluminum tri-sec-butoxide and (3-glycidyloxypropyl)-trimethoxysilane (GLYMO) were mixed with the structure-directing agent PI-b-PEO prior to thin film deposition by spin-coating. The hybrid films were subsequently annealed in argon at a temperature of 450 °C.…”