Wetting, adhesion and droplet impact on face masks

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see https://doi.org/10.1021/acs.langmuir.0c03556.In the present pandemic time, face masks are found to be the most effective strategy against the spread of the virus within the community. As aerosol-based spreading of the virus is considered as the primary mode of transmission, the interaction of masks with incoming droplets needs to be understood thoroughly for an effective usage among the public. In the present work, we explore the interactions of the droplets over the most commonly used 3-ply surgical masks. A detailed study of the wetting signature, adhesion and impact dynamics of water droplets and microbe-laden droplets is carried out for both sides of the mask. We found that the interfacial characteristics of the incoming droplets with the mask are very similar for the front and the back side of the mask. Further, in an anticipated attempt to reduce the adhesion, we have tested masks with a superhydrophobic coating. It is found that a superhydrophobic coating may not be the best choice for a regular mask as it can give rise to a number of smaller daughter droplets and thus can linger in air for longer time and can contribute to the transmission of potential viral loads.NSERC Alliance Grant ALLRP 551068-20, Mitacs Accelerat

Friction and Adhesion of Microparticle Suspensions on Repellent Surfaces

This document is the Accepted Manuscript version of a Published Work that appeared in final form in LANGMUIR, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see https://doi.org/10.1021/acs.langmuir.0c02651.With the recent advancements in the development and application of repellent surfaces, both in air and under liquid medium, accurate characterization of repellence behavior is critical in understanding the mechanism behind many observed phenomena and to exploit them for novel applications. Conventionally, the repellence behavior of a surface is characterized by optical measurement of the dynamic contact angle of the target (to be repelled) liquid on the test surface. However, as already established in literature, optical measurements are prone to appreciable error, especially for repellent surfaces with high contact angle. Here, we present an alternative, more accurate force-based characterization method of both friction and adhesion forces of microparticle laden aqueous droplets over various repellent surfaces, where the force signature is captured by probing the surface with a droplet of the test liquid mounted at the tip of a flexible cantilever and then tracking the deflection of the tip of the cantilever as the probe droplet interacts with the surface. A systematic investigation of response of repellent surfaces towards droplets with different microparticle concentration revealed the dependency and sensitivity of measured adhesion and friction signature towards particle concentration. A comparison with theoretical estimate from optical goniometry highlights the deviation of the theoretical data from experimentally measured values and further substantiates the need of such a force-based approach for accurate characterization of repellence behavior.NSERC Alliance Grant ALLRP 551068 – 2

Microparticle suspensions and bacteria laden droplets: Are they the same in terms of wetting signature?

This document is the Accepted Manuscript version of a Published Work that appeared in final form in LANGMUIR, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see https://doi.org/10.1021/acs.langmuir.0c03365.Adhesion behavior of microbial pathogens on commonly encountered surfaces is one of the most pertinent questions now. We present the characterization of bacteria laden droplets and quantify the adhesion forces on highly repellent surfaces with the help of a simple experimental setup. Comparing the force signature measured directly using an in-house capillary deflection based droplet force apparatus, we report an anomalous adhesion behavior of live bacteria (E. coli) laden droplets on repellent surfaces, which stands in stark contrast to the observed adhesion signature when the doping agent is changed to inert microparticles or the same bacteria in an incapacitated state. We showed that the regular contact angle measurements using optical goniometry is unable to differentiate between the live bacteria and the dead ones (including microparticles) and thus delineate its limitations and the complementary nature of the adhesion measurements in understanding the fundamental interfacial interaction of living organisms on solid surfaces.NSERC Alliance Grant ALLRP 551068-2