Emulsion stabilization using polyelectrolytes
Polyelectrolytes are charged polymers capable of stabilizing (or destabilizing) colloidal emulsions through electrostatic interactions.
Their effectiveness can be dependent on molecular weight, pH, solvent polarity, ionic strength, and the hydrophilic-lipophilic balance (HLB).
Stabilized emulsions are useful in many industrial processes, including deflocculation, drug delivery, petroleum waste treatment, and food technology.
In turn, the charge of the polymer classifies the polyelectrolyte, which can be positive (cationic) or negative (anionic).
In addition to surfactants, nanoparticles can also help stabilize the emulsion by also providing a charged interface for the polyelectrolyte to adsorb on.
[11] The effect of pH on the stability of polyelectrolytes is based upon the functional group on the polymer backbone that is bearing the charge.
Polyelectrolytes will be much more soluble in polar solvents due to the charge on the polymer backbone and will spread out more.
[14] Electrostatic repulsive forces dominate in polyelectrolyte stabilized emulsions.,[1][15] Although there are steric interactions, they are negligible in comparison.
1): where In addition, pH and ionic strength have a great influence on electrostatic interactions because these affect the "magnitude of electrical charge" in solution.
From the equation for the Debye length, it is demonstrated how ionic strength can ultimately affect the electrostatic interactions in a solution.
The Bjerrum length is the distance at which the electrostatic interaction between two charges is comparable to the thermal energy,
The repelling forces in a deflocculation increase the zeta potential, which in turn reduces the viscosity of the suspension.
Deflocculants are used as thinning agents in molding plastics, making glassware, and creating clay ceramics.
[20] Polyelectrolytes can also act as flocculants, separating solids (flakes) and liquids in industrial processes such as solubilization and oil recovery and they usually have a large cationic charge density.
Using organic materials to refine petroleum instead of iron or aluminum coagulated would greatly decrease that amount of inorganic waste produced.
The addition of various polyelectrolytes to petroleum waste can cause the oil to coagulate, which will make it easier to remove and dispose of, and does not significantly decrease the stability of the solution.
Polyelectrolytes such as dextran sulfate (DSS), protamine (PRM) or poly-L-arginine all fulfill these requirements and may be used as a capsule with an emulsion inside.
For example, the ester bonds of the polyelectrolyte poly(HPMA-DMAE) can undergo hydrolysis in the human body and VERO cells envelope DSS and use poly-L-arginine to break them down.
Several studies have focused on using polyelectrolytes to induce mixing of proteins and polysaccharides in oil-in-water emulsions.
[25] Other studies have focused on stabilizing oil-in-water emulsions using β-lactoglobulin (β-Lg), a globular protein, and pectin, an anionic polysaccharide.
