The emulsion is thermodynamically stable. However, if I dilute the emulsion with water, and mix it using high speed mixer, the emulsion destabilize and the wax particles sediment at the top of water surface.
Dear Saud Khalid, I think the applied shear of mixing is too high and forced the dispersed phase towards coalescence and floculation. It is known that the stability is up to critical values of shear (mixing and centrifuging), temperature, and other factors. In the following document, stability was maintained after dilution, but with gentle mixing. My Regards
https://www.researchgate.net/publication/301303453_Phase_behaviour_and_droplet_size_of_oil-in-water_Pickering_emulsions_stabilised_with_plant-derived_nanocellulosic_materials
Saud Khalid
By diluting and increasing the mixing speed you have
1. The concentration of cellulose stabilizer decreases.
2. the molar mass of cellulose decreases
3. The specific surface area of oil droplets increases.
To improve stabilization, it is necessary to add cellulose and reduce the mixing speed.
Thank you so much for sharing your insights~ Yuri Mirgorod and Abdelkader BOUAZIZ
Besides slowing down the mixing speed and adding more cellulose to stabilize emulsion (before diluting with water). In your opinion, does ionic strength or polarity of water play any role in keeping emulsion stable?
Saud Khalid
When using cellulose as a stabilizer, a steric stabilization mechanism is observed. The adsorbed layer of cellulose prevents the nanoparticles from "sticking together". Water dissociates weakly and a small amount of protons has almost no effect on stabilization. The ionic strength can influence the stabilization, but not by adsorption of ions, but by "salting out" of cellulose nanoparticles. Inorganic ions are better hydrated than the hydroxyl groups of cellulose.
Dear Saud Khalid, the following documents deal with the different influencing factors on pickering emulsions stability. My Regards
DOI: 10.5772/intechopen.75308
https://doi.org/10.1021/acs.langmuir.5b01857
https://doi.org/10.3389/fchem.2018.00409
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6835308/
DOI: 10.5772/intechopen.99139
Yuri Mirgorod
Thanks for your useful recommendation. Following your suggestion, I mixed 10-100 mM of CaCl2 in water, and used this water to dilute emulsion. I found the emulsion to be relatively stable under diluted conditions. However, it could not withstand high shear mixing (>1000 rpm).
Abdelkader BOUAZIZ
My ultimate objective is to develop a stable emulsion that can withstand pumping and filling under high shear. Thanks for sharing this interesting article. I now have better understanding of the problem.
I realized that the problem in my emulsion is of flocculation (process where droplets in emulsion are attracted to each other and form flocs without the rupture of stabilizing layer at the interface) not coalescence (process where droplets come into contact and merge, creating larger droplets).
Plus, I have found few good additive and processing recommendations (e.g., polysaccharide-protein complex and mixed-emulsion methodology) from the article that I will test to further stabilize the emulsion.
Saud Khalid
I introduce you to a simple theory of your task, see paragraph 2.
Potential curves - the dependence of the energy of electrostatic repulsion, the energy of molecular attraction and the total energy of interaction of particles on distance. There are three types of curves corresponding to certain states of stability of dispersed systems:
1. At any distance between particles, the energy of attraction prevails over the energy of repulsion. The thermal motion of particles does not change this ratio either. In this state of the dispersed system, rapid coagulation with the formation of aggregates is observed;
2. There is a sufficiently high potential barrier and a secondary minimum of the total energy. There is a rapid flocculation of particles at distances corresponding to the secondary minimum. Due to the presence of a potential barrier, the particles in the floccules do not have direct contact and are separated by interlayers of the medium. This state corresponds to the reversibility of coagulation. Peptization is possible after elimination of the secondary minimum or its reduction to a value less than kT;
3. There is a high potential barrier in the absence of a secondary minimum or when its depth is less than the thermal energy (kT). The probability of formation of particle aggregates under such conditions is low, and dispersed systems have a high aggregative stability.
- Badges
- Science topic
- Similar topics
- Phytochemistry
- Extracts