Complex coacervation for two-in-one formulations
Paul Whitaker of Colonial Chemical shares some results of how some of its products can help with coacervate formation
Traditionally , hair cleansers are based on high-foam , high-clarity combinations of surfactants – typically an anionic primary surfactant and an amphoteric secondary surfactant – together with a foam stabiliser and a salt response modifier to stabilise the salt-thickening process , such as an alkanolamide . Formulators frequently add conditioning aids to cleansers in order to refat the hair skeins , smooth the cuticles and add extra shine . These are most commonly quaternary or polymeric quaternary additives ( quats ), which are known to deposit onto anionic surfaces like skin and hair . The conditioning aids selected typically have a low charge density relative to the anionic surfactant and often have large hydrophilic heads , such as PQ-10 , guar quats , starch quats , etc . Anionic surfactants and conditioning aids form water-soluble or ‘ soft ’
A complexes . The latter are watersoluble but do not give optimum conditioning benefit . As a result , formulators often use higher concentrations of quats than might otherwise be expected to deliver the performance required . This raises problems , because a high quat loading can increase cost , degrade foaming performance and / or generate instability in the formulation .
Improved conditioning
Dilution deposition or the ‘ Lochhead effect ’ can be employed to improve the substantivity of cationic polymers . This effect depends on the formation of a coacervate . The term ‘ coacervation ’ refers to the generation and separation of an insoluble complex within a solution upon dilution . In the case of anionic cleansers , it is most effective at below the critical micelle concentration of the surfactant . The complex itself , which includes the quats and
B other water-insoluble materials , will thus be more readily deposited to the substrate Coacervate formation can be demonstrated by an increase in the opacity of the solution as a clear product is diluted . Its efficacy can be proven by comb testing or other means of analysis for the target molecules . The formation of a coacervate can be quite a complex issue , as it is influenced by a variety of factors :
• Molecular weight ( MW ) of the cationic polymer
• Charge density of the cationic polymer
• Ionic strength
• pH of the solution
• Characteristics of the surfactants used ( MW , relative sizes of head and tail groups )
• Relative proportions of surfactant ( s ) and polymer ( s ) in the solution
• Width of dilution range over which the coacervate is formed
Mean corneometer value
Mean visual dryness value
Figure 1 - ColaMoist 200 skin moisturisation study , rinse-off : Corneometer ( a ) & visual ( b )
44 SPECIALITY CHEMICALS MAGAZINE ESTABLISHED 1981