[Adityax26]

Hi all,

I am in high school/university (it's a course in between the two) conducting an experiment on the effect of the surface tension of straight-chain alcohols and their wettability (measured by the contact angle formed with glass, SiO2).

Essentially, I am dropping 1 drop of different alcohols (methanol, ethanol, propanol, butanol, etc.) and measuring their contact angle. I have hypothesized that as I increase the surface tension (by dropping alcohols with larger carbon chain lengths on glass), the angle formed between the glass will become larger, since the intermolecular forces between the alcohol will be larger than the adhesive forces between the alcohol and the glass (SiO2). I have conducted an experiment, and my results DO confirm this.

However, in my background information (which I haven't yet written), I plan on including the chemistry of surface tension & intermolecular forces between the individual alcohol molecules (using this website: http://divverethanol.blogspot.com/2011/03/intermolecular-forces-in-ethanol.html , although I'm not sure if the chemistry there is correct..?), along with the attraction of the OH group of the alcohol and the glass (SiO2).

My question is, I am very confused to as how that would work. CAN SiO2 actually form some type of bond with alcohols?

I would very much appreciate it if you could answer this question, along with explain to me how each alcohol molecule is bonded to each other! This is a very important essay for me, and thought I could get some valuable advice here. Thanks!

[Enthalpy]

[...] increase the surface tension by dropping alcohols with larger carbon chain lengths on glass [...]

Do longer chains increase the surface tension? They mean fewer alcohol functions per volume unit.
https://en.wikipedia.org/wiki/Surface-tension_values
check methanol and ethanol.

[...] Can SiO2 actually form some type of bond with alcohols?[...]

Yes. About any pair of compounds builds intermolecular forces. But in some cases, molecules have a much larger attraction to their siblings than to the molecule of other type, and then wetting is bad.

As a ceramic, SiO₂ has polar bonds and deformed oxygen orbitals. What kind of intermolecular bonds do you expect then, especially with alcohols?

Bonds between alcohols: check a list of intermolecular bonds, several could apply but one is stronger.
https://en.wikipedia.org/wiki/Intermolecular_force

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More generally, and for my personal information: have the forum members here made experiments that confirm or refute the theory that claims to predict wetting and contact angle just by comparing surface tensions? I'd find more logical that wetting follows a subtle behaviour similar to solubility, where "like likes like", hence not characterized by a single number.

[Adityax26]

Hello! Thanks for replying !

I am actually studying carbon chain lengths varying between 3-10 (propanol to decanol), and some of my figures/sources show that higher chain lenghts have higher surface tensions, indicating greater intermolecular forces between the corresponding alcohols (i.e., I found that hexanol for instance has a greater surface tension than pentanol). I have attached a picture of my values. And also, that's a good point you raised about the ethanol/methanol surface tensions, and I find it quite strange that methanol has a greater S.T. than ethanol, any ideas...? And do you by any chance know why increasing carbon chain lengths lead to a larger S.T., and so more intermolecular forces? (excluding methanol and ethanol?) They all have the same number of hydrogen bonds with each other, as there is only 1 OH group, right..?

I did some research and found that the intermolecular forces present between alcohol molecules are hydrogen bonds (primarily), along with dipole-dipole attraction, both pertaining to the O in the OH group and a hydrogen on the terminal end of another alcohol molecule.

Since SiO2 is a giant network covalent structure, I would assume that it would form hydrogen bonds with the H atom of the alcohols' OH groups? Since I know that a hydrogen bond may be formed when H is anywhere near O, F, etc. I have also attached another picture partaining to this, do you think I could use this in my essay? It is the picture on the left "before O2 Plasma treatment", which I think in their project they mean without adding OH groups to the SiO2 and placing the alcohol on the film directly, producing a greater angle = less wetting.

I appreciate the *delete me* :')

[Adityax26]

Update: Just saw that the IPA means isopropyl alcohol which means that the OH group is on the 2nd carbon atom. However, the diagra, would still be roughly the same, right? Only a slightly different structure?

[Enthalpy]

And the hydrogen bond is much stronger than what hydrocarbons build. That's why methanol and ethanol are liquids. The first additional -CH₂- only dilute this hydrogen bond.