I am doing research in producing hydrophobic coating. but my problem here is that the hydrophobic agent which is the heptadecafluorodecyltrimethoxysilane (HFTMS) did not dissolve in my sol-gel solution. my solution is consist of 5.0g TEOS, 0.5g HFTMS, 5.0g ethanol, and 2.0g of water. I already sonicate the solution for 5 hours and still some left undissolved.
A patent in this field (Process for producing article coated with water-repellent film article coated with water-repellent film and liquid composition for water-repellent film, article coated-US 6511753 B1) indicates
"Regarding solvent, organic solvents can be used including hydrocarbons such as hexane, toluene and cyclohexane; ketones such as acetone and methyl ethyl ketone; nitrogen-containing compounds such as diethylamine; esters such as ethyl acetate Among them, alcoholic solvents are preferably used which can easily dissolve acid. Examples include methanol, ethanol, 1-propanol, 2-propanol, butyl alcohol, amyl alcohol and the like. Amongst them, preferred are saturated chain monovalent alcohols having 3 or less carbon atoms, such as methanol, ethanol, 1-propanol and 2-propanol, because they have a high evaporating velocity at ordinary temperatures."
Taking into consideration that you already have in system ethanol, I would try firstly methanol or 1-propanol and from my personal experience I would recommend THF.
THF leave your sol-gel process to continue properly, even if you add 10 mL to your actual solution.
In your composition HFTMS plays the role of surfactants. Hydrophilic siloxane core will be covered with a hydrophobic layer. You will receive a solution of nanoparticles with a hydrophobic coating with an alcohol as solvent. It's not too bad, the coating from a thin layer of nanoparticles are also used for water-repellency.
To obtain a homogeneous solution, the solvent should be replaced by THF, as advised Eugenia.
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