Phase Inversion Formulations
When people tell me that "HLD can't do PIT formulations" I tend to get agitated. HLD describes Phase Inversion Temperature formulations precisely (in a way that leaves HLB in the dust) and then goes on to show that you can do a PIC (Cc), PIE (EACN), PIS (Salinity) formulation, or any combination of them. In short HLD allows PIFs, Phase Inversion Formulations.
Once this fact finally penetrates the formulation industry it will be truly revolutionary. To those who love PIT I have one question: "How do you do a PIT formulation with an APG surfactant?" Because APGs have no temperature sensitivey, they can't. But with PIF you can.
Everyone has heard of the PIT technique - Phase Inversion Temperature. By heating an ethoxylated system to the PIT the interfacial energy approaches zero (HLD~0) so it is very easy to obtain a fine emulsion dispersion with very little stirring energy. Rapid cooling returns the system to a Type I domain, so PIT is good for creating o/w ethoxylate emulsions. However, there are drawbacks.
- The emulsion is, by definition, unstable to increasing temperature during transport and storage.
- The technique applies only to ethoxylates where the HLD decreases with increasing temperature.
- It cannot be used for ionics (except for making w/o emulsions) or for surfactants such as APGs which have no temperature coefficient.
- It wastes a lot of energy to heat a large formulation batch and to cool it again.
PIFs via the Fishtail Diagram
With the fishtail diagram we can work out how to get PIFs (Phase Inversion Formulations) via salinity, Cc or EACN in addition to T. Thus we can for example start a formulation at a low interfacial energy zone (HLD~0) at room temperature using the right combination of Cc, S and EACN. We can then create the fine emulsion drops and, finally, adjust the Cc, S or EACN through rapid addition of an extra component to bring us to the desired Type I (for o/w) or Type II (for w/o) zone for a stable macroemulsion.
Of course people have been doing things like this for many years - but often by luck or intuition. With the fishtail plot it is now possible to work out the various tradeoffs in advance and get to an appropriate formulation with much less work.