Wetting imperfections are omnipresent on surfaces. They cause contact angle hysteresis and determine the wetting dynamics. Still, existing techniques (e.g., contact angle goniometry) are not sufficient to localize inhomogeneities and image wetting variations. We overcome these limitations through scanning drop friction force microscopy (sDoFFI). In sDoFFI, a 15 μL drop of Milli-Q water is raster-scanned over a surface. The friction force (lateral adhesion force) acting on the moving contact line is plotted against the drop position. Using sDoFFI, we obtained 2D wetting maps of the samples having sizes in the order of several square centimeters. We mapped areas with distinct wetting properties such as those present on a natural surface (e.g., a rose petal), a technically relevant superhydrophobic surface (e.g., Glaco paint), and an in-house prepared model of inhomogeneous surfaces featuring defined areas with low and high contact angle hysteresis. sDoFFI detects features that are smaller than 0.5 mm in size. Furthermore, we quantified the sliding behavior of drops across the boundary separating areas with different contact angles on the model sample. The sliding of a drop across this transition line follows a characteristic stick−slip motion. We use the variation in force signals, advancing and receding contact line velocities, and advancing and receding contact angles to identify zones of stick and slip. When scanning the drop from low to high contact angle hysteresis, the drop undergoes a stick−slip−stick−slip motion at the interline. Sliding from high to low contact angle hysteresis is characterized by the slip−stick−slip motion. The sDoFFI is a new tool for 2D characterization of wetting properties, which is applicable to laboratory-based samples but also characterizes biological and commercial surfaces.
Background Basal and squamous cell carcinomas represent the most common cancers in North America. Their management is an important issue. Objectives The evaluation of cure rates of minimally invasive cutaneous carcinomas with curettage-cryosurgery compared to curettage-electrodesiccation, as well as the assessment of the aesthetic appearance of scars. Methods This prospective trial randomized 117 patients 1:1 to treatments of curettage-cryosurgery or curettage-electrodesiccation. They were then followed at 6, 12, 18, and 24 months. Results At 12-month follow-up, only one (1/49) patient had a recurrence of cutaneous carcinoma in the curettage-cryosurgery group and none (0/43) in the curettage-electrodesiccation group. Farrington-Manning analysis with a 5% margin of error showed the non-inferiority of the first method ( P = .04). For the aesthetic appearance of scars after 12 months, better results with curettage-cryosurgery procedure has been observed, but this was not statistically significant ( P = .80 and P = .27 for evaluations of patients and clinicians respectively). Limitations This study was mainly limited by its small sample size. Conclusion We have demonstrated that curettage-cryosurgery compared to curettage-electrodesiccation for the treatment of minimally invasive carcinomas is noninferior (comparable) with regards to cure rates at 12-month follow-up. No significant difference has been demonstrated for the appearance of scars.
The friction force opposing the onset of motion of a drop on a solid surface is typically considered to be a material property for a fixed drop volume on a given surface. However, here we show that even for a fixed drop volume, the static friction force can be tuned by over 30% by preshaping the drop. The static friction usually exceeds the kinetic friction that the drop experiences when moving in a steady state.Both forces converge when the drop is prestretched in the direction of motion or when the drop shows low contact angle hysteresis. In contrast to static friction, kinetic friction is independent of preshaping the drop, that is, the drop history.Kinetic friction forces reflect the material properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.