I was trying to hydrophobically modfiy a couple of polymeric surfaces using silane treatment. While they do show a higher contact angle for water after the treatment, they continue showing affinity for alcohol mixtures. Is this an expected phenomenon? I presume they continue liking alcohol due to its organic nature.
I was looking for information about surfaces/ surface modifications that can repel water and alcohol (ethanol or propanol) but not other organic compounds. Can someone please share some information about the same?
Hi
The silane treatment is really ? Have you used NMR spectra 29SI & 1H ?
The extraction of the polymer after this treatment with aprotic solvent (chloroforme....)
Are you sur , the silane is telechelic (on the final extrmemities? of the polymer chain)
Regards
M.Belbachir
Your assumption is correct. Treatment with fluorocarbon compounds helps to achieve in addition to hydrophobic and oleophobic yet. This will reduce the wettability of organic substances containing many C-H bonds, including alcohols.
How high is the water contact angle? Maybe the degree of silylation is still too low to repel long chain alcohols, but good enough to repel methanol.
Hydrophobe= Little contact angle= degree of silylation
Regards
M.B
Thanks for the replies.
At present I have only confirmed surface modificatoin using contact angle. Water shows a contact angle of around 82 degrees for this case. This is higher than the base pmma that I used. This indicates some amount of silylation, although I am not sure what you mean exactly by the degree of silylation?
As your contact angle for water has increased this definitely implies some kind of modification has occurred though not sufficient to repel the alcohol mixtures.
It is a simplification but in order for your surface to repel alcohols you need the surface energy of the polymer to be below that of the alcohol mix.
If you are measuring a surface energy ~80 degrees with water this would imply your surface probably has a surface energy of between 30 & 40 mN/m (use Owens-Wendt analysis with 2 or more test liquids if you want a more accurate SE value).
However, alcohols often have very low surface tensions (20-30 mN/m) compared with water (72 mN/m) so they will still wet the surface - you are most likely to succeed using fluoro-modified silanes or polymer coatings - as suggested above. In particular, long alkyl-chain fluoro-modified silanes often have very low surface energy values. A problem with fluoro modified polymers is that they are by nature Teflon-like (i.e. non-stick) and will not adhere well to your polymer without bridging groups, etc.
You do not get more hydrophobic surface than already have by silylation. A alcohols such surface well wetted. To create a surface without wetting alcohol, you need organofluorine compounds: fluoroakrilat, fluororganosilikon compounds etc.
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