An investigation into the effect of surfactants on iron oxide powder suspension formulations for fingermark development

Iron oxide powder suspension (FePS) is a fingermark development technique that can be used on adhesive and non-porous surfaces, the efficacy of which is known to be influenced by the surfactant used in the formulation. Despite previous work optimising surfactants for use in FePS, there is limited understanding of the interactions between surfactants, powders and fingermark residue which aid the successful development of fingermarks. To better understand the effect of surfactant on development quality produced by FePS, this research assessed a wide range of surfactants of different ionic natures and evaluated their ability to develop fingermarks based on the quality of ridge detail, contrast and background development produced. It was found that surfactants play a critical role in the selective deposition of powder on fingermark residue, as formulations made with only water (no surfactant) produced heavy background deposition. The efficacy of each surfactant depended on the quality parameter considered, and the addition of some surfactants hindered fingermark development. Effective surfactants such as T20, KP and TX100 prevented background development and produced well contrasted developed marks. Poor contrast was produced by LN, SP80/T80 and T80 due to indiscriminate powder deposition either across the entire sample or preventing any powder to deposit on the surface, demonstrating the role surfactants play in allowing powder deposition in this technique. The effectiveness of a surfactant in PS was not directly dependent on its ionic nature, and most surfactants were more effective when diluted from stock concentrations. This research has provided a robust base for future work improving fundamental understanding of FePS, which will greatly aid the efficacy of future optimisation efforts.