During our particle size measurement using Malvern Mastersizer 3000, we measured both solid and in liquid and found liquid shows smaller particles and results are significantly different from each other. Can someone comment on the issue?
Mr. Naik you are talking about theory. You can follow our research on the area for last few years. My question has been addressed to researchers who have tremendous experiences on the subject. It does not mean to describe the theory what we already know for may years.
Hi Jasim,
Thank you for your question.
Could you confirm the particle size range you are working in for your materials? This may help in understanding what is happening.
The most important issues to consider in any particle sizing experiment are sampling and dispersion. Sampling is most important for large particles - if the sample measured for wet dispersion is much smaller than for dry dispersion and you are measuring large particles then this could explain the differences seen. Dispersion is most important for small particles (in the colloidal range below 20 microns). Here, it may be that wetting of the particles in liquid dispersion enables the dispersion of strongly bound agglomerates which cannot be dispersed using aerodyanmic (dry) dispersion.
All the best,
Paul
the answer which is best depends. The one method will be more suitable which is the closer to application where you need info. If it is about powder handling than dry method gives you related info, if you want to know e.g. how well is the powder dispersible in the liquid then of course wet dispersion gives you more insight.
Dear Jasim Sir,
Particle size measurement in dispersion forms might helps in understanding the consumptions process of food products. In that case dispersion preparation using enzymatic solution will be useful protocols, in order to understand the biochemical degradations path ways.
Paul: We are working 0.15 to 1000 micrometer and you are right. As far as small particles are concerned, the differences are not significant whereas the large size particles are observed through dispersion not the powder form and the differences are highly significant. Therefore, I am taking the measurement in dispersion. We are using water dispersion. however, in literature I found people are using propyl alcohol as dispersing medium. Do you feel any difference in solvent used? We may work out on the issue soon. Thank you.
It is obvious that if particles find suitable dispersion medium and if the agglomerates are soft in nature it will disperse and you find the average size smaller. Difference between alcohol and water is that latter is more polar.
Hi Jasim,
As Patrick suggests, powders in the size range you suggest are likely to be cohesive. The differences could therefore be due to dispersion, with liquid dispersion being more effective than dry dispersion due to the wetting of the particle surfaces by the liquid (provides a gentle but effective method of dispersion).
For liquid dispersion, one of the most important parameters is the liquid surface tension. A high surface tension will yeild a high contact angle, which in turn will mean that the particles are less likely to be fully wetted. Water has a high surface tension, so you may need to add surfactants to reduce the surfrace tension in order to improve particle wetting (be careful to not add too much, otherwise you'll create bubbles!). Alternatively, you could move to using an organic dispersant (e.g. alcohols or alkanes) as these have a lower surfrace tension and may wet the sample more readily.
Other considerations are:
1) You may need to apply ultrasound or another means of agglomerate break-up to open up agglomerates so that the particle surfaces can be wetted. This will help you achieve full dispersion.
2) If you are measuring in an aqueous dispersant then you should consider if the conductivity and pH need to be adjusted to aid stability of the sample. This is particularly true where particle charge (zeta potential) provides an means of achieving dispersion stability.
Note that the requirement to control the zeta potential is one reason why it is not a good idea to measure samples in tap water (tap water can contain a high concentration of dissolved electrolytes, yeilding a conductivity which may eliminate the positive effect of having a high zeta potential). Measuring in DI water is generally preferable.
All the best,
Paul
Thank you Patrick and Paul for nice discussion. I appreciate both of you for the excellent input.
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