Coacervation
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Coacervation is the phase separation into two liquid phases in colloidal systems. The phase more concentrated in colloid component is the coacervate, and the other phase is the equilibrium solution [1]
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[edit] Complex coacervation
Complex coacervation refers to the phase separation of a liquid precipitate, or phase, when solutions of two hydrophilic colloids are mixed under suitable conditions. The general outline of the processes consists of three steps carried under continuous agitation [2]:
[edit] Step 1: Formation of three immiscible chemical phases:
The immiscible chemical phases are (i) a liquid manufacturing vehicle phase (ii) a core material phase and (iii) a coating material phase. To form the three phases, the core material is dispersed in a solution of the coating polymer, the solvent for the polymer being the liquid manufacturing vehicle phase. The coating material phase, an immiscible polymer in a liquid state, is formed by utilizing one of the methods of phase separation coacervation, that is,
- By changing the temperature of the polymer solution
- By adding a salt
- By adding a non-solvent
- By adding incompatible polymer to the polymer solution
- By inducing a polymer-polymer interaction.
[edit] Step 2: Depositing the liquid polymer coating upon the core material:
This is accomplished by controlled, physical mixing of the coating material (while liquid) and the core material in the manufacturing vehicle. Deposition of the liquid polymer coating around the core material occurs if the polymer is adsorbed at the interface formed between the core material and the liquid vehicle phase, and this adsorption phenomenon is a prerequisite to effective coating. The continued deposition of the coating material is promoted by a reduction in the total free interfacial energy of the system, brought about by the decrease of the coating material surface area during coalescence of the liquid polymer droplets.
[edit] Step 3: Rigidizing the coating:
This is usually done by thermal, cross linking or desolvation techniques, to form a self sustaining microcapsule.
