How to Formulate Biobased Surfactants Through the HLD-NAC Model

Abstract This chapter tackles the question of formulation with biobased surfactants (including biosurfactants). This question is explored through a workflow that starts with the formulation objectives, followed by the required formulation properties (solubilization capacity, interfacial tension, etc.). At this point in the workflow, the formulator asks what surfactant or surfactant mixture one should use. To connect surfactant selection with the required formulation properties, two frameworks are introduced, the hydrophilic- lipophilic difference (HLD) and the net-average curvature (NAC). The HLD answers the question, “does the surfactant mixture partitions in oil (positive HLD) or in water (negative HLD), at a given set of conditions (salinity, oil phase, and temperature)?” At the point of surfactant phase inversion, HLD = 0, many properties of the formulation vary in a highly nonlinear fashion. The NAC comes to connect formulation properties (solubilization capacity, interfacial tension, phase diagrams, emulsion formation and emulsion stability, etc.) with the value of HLD. As it will be shown, any given value of desired HLD can be obtained through an almost infinite number of combinations of surfactants. One just needs to know the necessary empirical HLD parameters for the surfactant candidates. The value of these HLD parameters for various biobased surfactants are listed and discussed. Example uses of these parameters in the workflow for the formulation of drug delivery systems, oil spill dispersants, and latex formulations are discussed.