Solubilization of multicomponent solubilizers
Solubilization of multi-component solubilizers: when there are multiple components in the formulation, the solubilization effect on the main drug depends on the interaction between the components and the surfactant; multiple components compete with the main drug for the same solubilization position, the solubilization of the main drug decreases; a component adsorbs or binds to the surfactant molecules, the solubilization of the main drug decreases; certain components can also expand the volume of micelles to increase the solubilization of the main drug.
Stability after solubilization: it may be related to the surface properties of the micelles, the structure and reactivity of the micellar aggregates, the degradation pathway of the drug itself, the pH of the environment, ionic strength and other factors.
The effect of temperature on solubilization: ① affects the formation of micelles ② affects the solubilization of solubilizing substances ③ affects the solubility of surfactants; for ionic surfactants, the rise in temperature mainly increases the solubility of solubilizing substances in micelles as well as increases the solubility of surfactants.
Krafft point: the solubility of ionic surfactant in water increases with temperature, and when it reaches a certain temperature, its solubility increases sharply, the temperature is called the krafft point, and the corresponding solubility is the critical micellar concentration (CMC) of the ionic surfactant; the krafft point is the characteristic value of the ionic surfactant, and the higher the krafft point is, the smaller the CMC is. The krafft point is also the lower limit of the application temperature of ionic surfactants, i.e., only higher than the krafft point, the surfactant can work to a greater extent.
Blip and blip point: polyoxyethylene nonionic surfactant, the temperature rises to a certain temperature, its solubility decreases sharply and precipitation, the solution appears turbid, this phenomenon is called blip, the temperature is called blip point (or turbidity point). In the same polyoxyethylene chain, the longer the hydrocarbon chain, the lower the turbidity point; in the hydrocarbon chain length at the same time, the longer the polyoxyethylene chain is the higher the turbidity point.
Toxicity of surfactants: generally cationic > anionic > nonionic.
Compounding of surfactants
Appropriate compounding system is better than single surfactant system in solubilization, emulsification, foaming, etc. Inappropriate compounding will destroy the surface active effect.
Positive and negative ion surfactant compounding
In all surfactant mixing systems, positive and negative ionic surfactants have the strongest synergistic effect. It is generally believed that cationic surfactants and anionic surfactants can not be mixed in aqueous solution, the interaction between the two in aqueous solution will produce precipitation or flocculent complexes, resulting in a negative effect or even make the surfactant lose surface activity. And it is found that due to the strong electrostatic effect between anionic and cationic surfactant ions, under certain conditions, the positive and negative ionic surfactant compounding system has high surface activity and shows great synergistic effect.
