Soft Matter Laboratory Research

Complex Fluids Inside Microfluidic Devices

Nanoporous Synthesis

BioMimetics

Bioenergy

Energy Storage

Granular Materials

Nanoporous Synthesis:

As evaporation induced self-assembly (EISA) mesoporous films possess large surface areas, adjustable pore sizes and compositions , they have become increasingly important in applications such as photonics, sensing, quantum electronics, and catalysis.

The synthesis of EISA porous films relies on the cooperative assembly of organic structural directing agents (i.e., surfactants or block copolymers) with inorganic building clusters (i.e., silicate clusters) that forms ordered lytropic liquid crystalline mesostructured phases. A major technique to prepare such films is sol-gel coating.

The sol solution normally starts with a mixture of ethanol, water, silica based solution, and surfactants. As the coating process proceeds, the ethanol evaporates, causing an increase in the surfactant concentration, which triggers micelle formation. The micellar aggregates interact with a silica inorganic precursor, further self-assemble, and eventually form a well-ordered mesostructured film on the substrate.

A good understanding of the coating dynamics during the sol-gel processing is critical to control and manipulate the mesostructure of these films. In this paper, we perform systematic experiments to measure the meniscus shape and film thickness with varying coating speed and fluid properties to gain insight of the hydrodynamics during sol-gel coating. In particular, we investigate evaporation induced changes of the rheology of the entrained sol solution, and its subsequent impact on the steady state film thickness. We also compare the experimental results with a lubrication approximation based evaporation model. Our results show that during sol-gel coating, evaporation induced self-assembly leads to rheological variations in the entrained film and, consequently, alters the film thickness. The steady state film thickness from sol-gel coating is much smaller compared to the Landau--Levich--Derjaguin (LLD) prediction.