I would like to obtain the PMMA microspheres by solvent evaporation method. I am using two types of emulsions:
1. PMMA dissolved in acetone and dispersed in paraffin oil (both phases cooled to 5-10'C)
2. PMMA dissolved in DCM and dispersed in water (at room temp.)
In both cases emulsification is going well. During the evapration (just stirring without heating), practically at the end of it, microspheres start to aggregate, resulting in one big amorphous piece of polymer sticked to the stirring bar.
I have tried to use a Span80 or BRIJ35 as a surfactant in different concentration. The effect was the same. Is it possible that the surfactant was chosen wrong? I also thought about stirring rate during the evaporation. I keep it at the high rate as when emulsifing. Lowering did not change anything.
Or maybe the evaporation is going too fast...?
My ideas are over, and PMMA does not want to cooperate...
I will be very grateful for any advices.
Larger the particles more it tends to aggregate easily due to gravity..
1) Do not try first method to prepare
2) In second method, increase the viscosity of aqueous phase using PVA, sodium CMC, PVP..
There's a competition between attractive van der Waals forces (small sizes) and inertial forces (larger sizes). See:
November 3rd, 2015 Adhesion and cohesion http://tinyurl.com/zwb2wlh
You have a stabilization issue - not a wetting one = so surfactant will not work. You need to stabilize the system either ionically (in water) or sterically (in solvent). Take a look at:
Nov 11th, 2008. Dispersion and nanotechnology http://tinyurl.com/hpywsge
surfactants not only act as wetting agent but can also act as stabilizer. One would expect that Span 80 would provide steric stabilization in paraffin oil and Brij 35 for water (maybe - or not - an anionic surfactant could be more efficient for the latter by adding electrostatic repulsion).
My guess is that surfactant concentration is too high leading either to too high adsorption (re-destabilization) or depletion flocculation.
- Badges
- Science topic