I'm trying to observe how micro bubbles behave in hydrophilic steel micro channels, however, since the bubbles need to be visible, I'm replacing one of the micro channels' sides with a PMMA substrate.
The solution flowing through the micro channels will be a 1-2 M aqueous solution of methanol, and preferably, will flow for a potentially unlimited time...
I rather foolishly tried grafting PVA, both pure and cross linked with borax, onto the PMMA, but both dissolved in water quite quickly (even at room temperature).
I also briefly tried to oxidise the surface with 3 M Nitric acid, but to no avail.
I've been considering oxygen plasma treatment and LbL TiO2 nanoparticle coatings, but I'm worried about the durability when immersed and the visibility, respectively...
If anyone can comment on the longevity of an oxygen plasma hydrophilic surface treatment when immersed in water or suggest an alternative surface treatment I'd appreciate it greatly
Dear Michael-James,
You might check the work of Whitesides or Dave Weitz at Harvard. For instance
https://arxiv.org/ftp/arxiv/papers/0805/0805.0885.pdf
shows conditions Whitesides used for plasma treating and for sulfuric acid treating to make pMMA hydrophilic for his microfluidic devices in that paper. They report air corona treatment as most effective in their particular situation.
Best regards,
Mike Bender
Thank you Michael and Mike (Incidentally, you all have great names),
Michael, I did think about using glass as my transparent substrate, however, some of my flow feeder channels and reservoirs (which are larger than the micro channels) need to be machined into the substrate. But, if the surface modification on the PMMA doesn't work, I suppose I'll have to find a way to use glass.
I read the photografting article and it seems like it is worth a try. Do you think that I could just leave the PMMA at the aminated stage? Or will the amine groups only support hydrogen bonding in their protonated state (acidic media)?
Also, for the saponification, I'm guessing just a concentrated aqueous solution of NaOH work? I'll give it a try, doesn't seem too tricky unless I'm missing something.
Mike, I had a read of the Whitesides and Dave Weitz publication, by eye their results for the sulphuric acid treatment matched up very closely with my nitric acid treatment results, but I didn't take any formal CA measurements because the decrease in hydrophobicity was too small for my application.
I think that I'm going to try the Air Plasma treatment/saponification first and if that doesn't work I'll give amination a go...
Hi,
You can try to use this simple method, which gives very good results. The PMMA surface is very simple to modify due to its simple chemistry, when compared to Polystyrene, which is reasonably hard to modify because if the phenyl group.
1 M NaOH at 55 deg C for 30 min. This modifies the hydrophobic surface group of polymer to give a hydrophilic surface.
@Rohan Aggrawal. I am facing similar problem. Will treatment with NaOH make the PMMA surface permanently hydrophilic?
Acid or base treatment will bring down the contact angle from >60 deg to around 30 deg. The problem is that the PMMA chains desorb from PMMA surface when extent hydrolysis crosses a certain threshold. So one cannot increase hydrophilicity of PMMA to a large extent just by hydrolysis. So the solution would be to perform a second step of coating based on hydrogen bonding/van der waals interactions using block-co-polymer melts/protein
Electrophoresis 2007, 28, 3308–3314
Journal of Colloid and Interface Science, Vol. 126, No. 1, November 1988
Biomaterials 1992, 13:682-92 and https://www.rug.nl/research/portal/files/2647173/c2.pdf
These are some good examples to get started. Similar coatings of molecules discussed here should help bring down the contact angle from 30 deg to < 10 (permanently)
Note: The block-co-polymers will adsorb as micelles if used at conc >CMC, in which case the properties of coating will change upon storage, because of rearrangement of surfactant molecules upon exposure to air/vacuum.
Hello all,
May I know which one of the techniques discussed here (air corona treatment, sulphuric acid, nitric acid, PVA coating, etc) is more stable, i.e. which technique will retain the hydrophilicity longer (for hours and days). Or is it not possible to retain hydrophilicity, and surface modification will have to be conducted routinely prior to experiments? Or will keeping the PMMA device immersed in DI water will help to preserve hydrophilicity?
Just in case, somebody is curious to know the answer (atleast in part) to my question posted above.
I see that in the paper mentioned below,
Yu, H., Chong, Z. Z., Tor, S. B., Liu, E., & Loh, N. H. (2015). Low temperature and deformation-free bonding of PMMA microfluidic devices with stable hydrophilicity via oxygen plasma treatment and PVA coating. RSC Advances, 5(11), 8377-8388.
it is has been demonstrated that the hydrophilicity of PMMA substrates treated with oxygen plasma, coated with PVA and treated again with oxygen plasma prior to thermal bonding remains stable for up to 30 days under both dry (in air) and wet (in DI water) storage conditions.
Hello everyone, I do not have an answer but I have a similar question. I want to plasma treat PMMA surface and make it hydrophilic. But as it is not a permanent solution, I want to modify it further to make the change long-lasting. can anyone suggest some chemical modification of the plasma-treated PMMA surface?
Hi Humayra Bushra,
Please check if the Fig. 2B in the paper below would be helpful.
Ko, J., Cho, K., Han, S. W., Sung, H. K., Baek, S. W., Koh, W. G., & Yoon, J. S. (2017). Hydrophilic surface modification of poly (methyl methacrylate)-based ocular prostheses using poly (ethylene glycol) grafting. Colloids and Surfaces B: Biointerfaces, 158, 287-294.
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