https://web.iitd.ac.in/~arunku/files/CEL311_Y13/Adsorption%20Theory%20to%20practice_Dabrowski.pdf

Adsorption — from theory to practice

Thin films of surfactant-templated mesoporous materials1,2 could find applications in membrane-based separations, selective catalysis and sensors. Above the critical micelle concentration of a bulk silica–surfactant solution, films of mesophases with hexagonally packed one-dimensional channels can be formed at solid–liquid and liquid–vapour interfaces3,4,5. But this process is slow and the supported films3,5 are granular and with the pore channels oriented parallel to the substrate surface, so that transport across the films is not facilitated by the pores. Ogawa6,7 has reported a rapid spin-coating procedure for making transparent mesoporous films, but their formation mechanism, microstructure and pore accessibility have not been elucidated. Here we report a sol–gel-based dip-coating method for the rapid synthesis of continuous mesoporous thin films on a solid substrate. The influence of the substrate generates film mesostructures that have no bulk counterparts, such as composites with incipient liquid-crystalline order of the surfactant–silica phase. We are also able to form mesoporous films of the cubic phase, in which the pores are connected in a three-dimensional network that guarantees their accessibility from the film surface. We demonstrate and quantify this accessibility using a surface-acoustic-wave nitrogen-adsorption technique. We use fluorescence depolarization to monitor the evolution of the mesophase in situ, and see a progression through a sequence of lamellar to cubic to hexagonal structures that has not previously been reported.

Continuous formation of supported cubic and hexagonal mesoporous films by sol–gel dip-coating

Today cross-cutting approaches, where molecular engineering and clever processing are synergistically coupled, allow the chemist to tailor complex hybrid systems of various shapes with perfect mastery at different size scales, composition, functionality, and morphology. Hybrid materials with organic–inorganic or bio–inorganic character represent not only a new field of basic research but also, via their remarkable new properties and multifunctional nature, hybrids offer prospects for many new applications in extremely diverse fields. The description and discussion of the major applications of hybrid inorganic–organic (or biologic) materials are the major topic of this critical review. Indeed, today the very large set of accessible hybrid materials span a wide spectrum of properties which yield the emergence of innovative industrial applications in various domains such as optics, micro-electronics, transportation, health, energy, housing, and the environment among others (526 references).

Applications of advanced hybrid organic–inorganic nanomaterials: from laboratory to market

Sol–gel coatings on metals for corrosion protection

Zeolite membranes – state of their development and perspective

Fundamentals of sol-gel dip coating

Sol-gel thin films are formed by gravitational or centrifugal draining accompanied by vigorous drying. Drying largely establishes the shape of the fluid profile, the timescale of the deposition process, and the magnitude of the forces exerted on the solid phase. The combination of coating theory and experiment should define coating protocols to tailor the deposition process to specific applications.

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Review of sol-gel thin film formation

The overlap between the drying stage and the aggregation/gelation and aging stages of sol-gel film formation establishes a brief time for further condensation reactions to occur. For this reason, the structures of films are often considerably more compact than those of the corresponding bulk gels or xerogels prepared from identical precursors. Experimental techniques to study film formation and the structure of the deposited film in situ have been developed. These techniques include imaging ellipsometry, infrared microscopy and gas sorption on surface acoustic wave substrates.

Sol-gel thin film formation

During sol-gel dip-coating, inorganic precursors are rapidly concentrated on the substrate surface by gravitational draining with concurrent evaporation and condensation reactions. We have presented examples of several factors that influence the structure of the deposited films: (1) size and opacity of fractal precursors; (2) relative rates of condensation and evaporation; (3) capillary pressure; (4) shear resulting from surface-tension-gradient-driven-flows; and (5) substrate withdrawal speed. By control of these factors it is possible to tailor the pore size, surface area, pore volume and refractive index of the deposited film for applications ranging from dense protective or passivation layers to films with precisely controlled pore sizes for sensor surfaces and separation membranes.

G.C. Frye

Papers

Fundamentals of sol-gel dip coating

Review of sol-gel thin film formation

Sol-gel thin film formation

Sol-gel thin film formation

Section 4. Physical and chemical properties of shaped materials: (c) Thin films and coating SOL-GEL THIN FILM FORMATION