The biocide molecules are widely used both in disinfectant formulations and in all-purpose cleaners. The cleaning process should ensure a complete soil removal from the cleaned surface and the long-time biocidal action is controlled by a deposition of the biocidal molecules on the surfaces. The deposited layer must be invisible to the naked eye otherwise, the customers would decide that residues seen on the surfaces are rather soils than something useful. Recently, we have investigated the cleaning properties of biocidal formulations by a new simplified laboratory method for hard surface cleaning [1]. We have paid a special attention to the surface haze as a measure of residues visibility.
The present study aims to investigate the structure of the deposited layers of biocidal molecules composed of di-octyl or di-decyl hydrocarbon chain lengths and different hydrophilic groups. Layers deposited on smooth silicon wafer were characterized by imaging ellipsometry and contact angle measurements. We observed that the evolution of the surface pattern and the hydrophobicity with the biocide concentration follow the stages of surfactant adsorption on solid surfaces from bulk solutions (from hemimicelles at low concentration to dense layers well above the CMC). The obtained results showed less homogeneous layers from octyl chain biocides than from decyl ones. The addition of a nonionic surfactant significantly improve the surface hydrophilicity and does not change the homogeneity of the deposited layer.

[1] Yavrukova, V., Cooban, E., Blanco, I., Pambou, E., Marinova, K., Petkov, J. Investigation of the detergency properties of mixtures of biocides and nonionic surfactants using a new simplified hard surface cleaning method. Journal of Surfactants and Detergents.
The authors are grateful for the financial support from the Project # KP-06-М89/2 – 04.12. 2024, with the National science fund of Bulgaria (abbreviated as BG FNI – MON).