I am trying to dissolve the PS beads in MS media as a treatment to plants. I can not make a suspension. I also require to measure Zeta potential of the PS beads, but the DLS analysis needs a suspension or atleast in a colloid in water. Please help.
The zeta potential will need to be measured in the medium. Any measurement you do of the beads in water will be meaningless.
Also, the concentration of salts in the medium will be sufficiently high that any measurements you do make will be subject to problems with electrolysis of the electrodes.
As far dispersing (not dissolving) the particles, are they dried or already in concentrated suspension? If dry, you will have a hard time getting them to disperse well in an aqueous medium. In addition, the high salt concentration will affect the stability of the particles.
So, this raises a couple of questions:
1. Why are you wanting to do this?
2. What concentration of particles are you trying to achieve?
3. What are the details of the PS particles you plan to use?
Thank you so much for the response John Francis Miller Sir. We have synthesized the PS particles from Polystyrene sheets. So they are in dry powdered form. But in order to use these particles as treatments we need to disperse them in a medium. Also to characterize we need to measure the zeta potential. How can I do that? Please help. Can these particles be made to form a colloid in the medium?
Ekta Bhattacharya How was your sheet made and powdered?
If your particles are in dry form then you have no free, discrete, independent particles < 100 nm. Your size measurement should be laser diffraction, and not DLS, as you'll have material in the post-micron size. The density of polystyrene (1.2 g/cm3) should work for you though in terms of zeta potential measurement. As John Francis Miller correctly points out, you can't have zeta potential of a material per se. It's a holistic property of the system (material + liquid) where factors such as pH (especially) play a major role. I suspect you'll have great difficulty in reducing this material down to nano dimensions. You could (completely) dissolve the PS in a medium (such as styrene monomer or perhaps hexane and precipitate down with another medium e.g. an alcohol. However, ZP is normally an aqueous based measurement and you may have interpretation (and measurement) difficulties. If you get your dry material into suspension (say with a surfactant) then you'll need a lot of energy to reduce the size. Sonication will simply disturb agglomerates and not the primary particles or aggregates. For further exploration of this topic, this webinar may be useful (free registration required):
Dispersion and nanotechnology
https://www.malvernpanalytical.com/en/learn/events-and-training/webinars/W190528DispNanoMat
Good luck with your research.
thank you so much Alan F Rawle Sir. It is very informative to me. In case if I can prepare a suspension using a surfactant, will that effect my Zeta potential measurement?
Ekta Bhattacharya Why do you require or desire zeta potential measurement? What will it tell you? Why not buy PS beads in water? There are many types available...
I actually need to characterize the PS particles because we are going to use those as treatments to organisms. In order to do that I need to know the electrokinetic properties in while in suspension, as it will be useful in case it interacts with the cells and membranes.
Ekta Bhattacharya You can buy PS materials with known mobility/derived ZP values. For example, the Malvern Panalytical secondary (transfer) standard for instrument verification:
https://www.malvernpanalytical.com/en/products/category/calibration-standards/particlesizeanalysis/zetatransferstandard
Ekta Bhattacharya If you're wanting to test your materials and their interaction with living organisms, then this rules out the use of organic solvents and thus rules out my first suggestion of dissolving up your comminuted (?) polystyrene sheet.
Yes Alan F Rawle Sir, I am trying a surfactant that is helping to make a suspension. I am open to any other feasible suggestions for my problem. Thank you so much for the responses.
Ekta Bhattacharya If you use a non-ionic surfactant such as Nonidet P40 or 42 then you should not affect the charges in the system. An anionic surfactant will. There are very few cationic surfactants on the market, BTW...
Ekta Bhattacharya You may also look at Tween and Span as these are permitted in drugs, foods, and formulations.