Unusual Nature of Fingerprints and the Implications for Easy-to-Clean Coatings.

Irrespective of the technology, we now rely on touch to interact with devices such as smart phones, tablet computers, and control panels. As a result, touch screen technologies are frequently in contact with body grease. Hence, surface deposition arises from localized inhomogeneous finger-derived contaminants adhering to a surface, impairing the visual/optical experience of the user. In this study, we examined the contamination itself in order to understand its static and dynamic behavior with respect to deposition and cleaning. A process for standardized deposition of fingerprints was developed. Artificial sebum was used in this process to enable reproducibility for quantitative analysis. Fingerprint contamination was shown to be hygroscopic and to possess temperature- and shear-dependent properties. These results have implications for the design of easily cleanable surfaces.

Cleaning Dirty Surfaces: A Three-Body Problem.

Human interaction with touch screens requires physical touch and hence results in contamination of these surfaces, resulting in the necessity of cleaning. In this study we discuss the three bodies of this problem and how each component contributes and can be controlled. Utilizing a standard fingerprint machine and a standard cleanability test, this study examines the influence of parameters such as the wiping speed and pressure, the material and surface area of the cloths, and the surface energy of the contaminated surfaces. It was shown that fingerprint contamination undergoes shear banding and hence is not easily removed. The degree of material removal depends on the position of the shear plane, which is influenced by surface energies and shear rates.