The aim is to improve understanding of solution properties and aggregation of hydrotropes and alkyl¿hydrotropes, and the relationship with common surfactants. Although they are interesting colloidal systems in their own right, there is only limited scientific literature concerning hydrotrope association structures. (Surprisingly, an extensive literature search revealed only five papers [1-5], but no systematic studies from which clear conclusions can be drawn). Hydrotropes are of great industrial interest, boosting detergency efficiencies in both aqueous and oily phases. The molecular origins of these properties are not yet fully understood, and this proposal is part of a joint university-industry collaboration to shed new light on these systems. MH is a PhD, part-funded by Infineum, who has attended the ISIS training course and is gaining much experience in the technique.