Collision of a droplet onto a still spherical particle was experimentally investigated. The effect of droplet impact velocity and wettability of the particle surface on collision outcomes was studied (0.05 < V₀ < 5.0 and θ = 70°, 90°, 118°). Compared to the literature, the range of Weber number variations was significantly extended (0.1 < We < 1146), and while focus of the previous works was on impacts in which particle is larger than the droplet (D_r < 1), the drop to particle diameter ratio in this work was larger than one. Therefore, formation of a thin liquid film, i.e., lamella, was observed due to impact of a relatively high velocity droplet onto a hydrophobic particle. Temporal variations of various geometrical parameters of collision outcomes including lamella length and lamella base diameter were investigated during the impact. It was also shown that for hydrophobic targets, the extent of hydrophobicity of the particle does not affect the lamella geometry. A comprehensive map of all the available works in drop impact on a spherical target was also provided.

Chronic wounds are among the major healthcare issues affecting millions of people worldwide with high rates of morbidity, losses of limbs and mortality. Microbial infection in wounds is a severe problem that can impede healing of chronic wounds. Accurate, timely and early detection of infections, and real time monitoring of various wound healing biomarkers related to infection can be significantly helpful in the treatment and care of chronic wounds. However, clinical methodologies of periodic assessment and care of wounds require physical visit to wound care clinics or hospitals and time-consuming frequent replacement of wound dressing patches, which also often adversely affect the healing process. Besides, frequent replacements of wound dressings are highly expensive, causing a huge amount of burden on the national health care systems. Smart bandages have emerged to provide in situ physiochemical surveillance in real time at the wound site. These bandages integrate smart sensors to detect the condition of wound infection based on various parameters, such as pH, temperature and oxygen level in the wound which reduces the frequency of changing the wound dressings and its associated complications. These devices can continually monitor the healing process, paving the way for tailored therapy and improved quality of patient's life. In this review, we present an overview of recent advances in biosensors for real time monitoring of pH, temperature, and oxygen in chronic wounds in order to assess infection status. We have elaborated the recent progress in quantitative monitoring of several biomarkers important for assessing wounds infection status and its detection using smart biosensors. The review shows that real-time monitoring of wound status by quantifying specific biomarkers, such as pH, temperature and tissue oxygenation to significantly aid the treatment and care of chronic infected wounds.

In this study, a smartphone-based contact angle measurement instrument was developed. Compared with the traditional measurement instruments, this instrument has the advantage of simplicity, compact size, and portability. An automatic contact point detection algorithm was developed to allow the instrument to correctly detect the drop contact points. Two different contact angle calculation methods, Young-Laplace and polynomial fitting methods, were implemented in this instrument. The performance of this instrument was tested first with ideal synthetic drop profiles. It was shown that the accuracy of the new system with ideal synthetic drop profiles can reach 0.01% with both Young-Laplace and polynomial fitting methods. Conducting experiments to measure both static and dynamic (advancing and receding) contact angles with the developed instrument, we found that the smartphone-based instrument can provide accurate and practical measurement results as the traditional commercial instruments. The successful demonstration of use of a smartphone (mobile phone) to conduct contact angle measurement is a significant advancement in the field as it breaks the dominate mold of use of a computer and a bench bound setup for such systems since their appearance in 1980s.

In this paper, a systematic study was performed to understand the drop impact on hydrophilic and hydrophobic surfaces that were moving in the horizontal direction. Drops (D₀ = 2.5 mm) of liquids with three different viscosities were used. Wide ranges of drop normal velocity (0.5 to 3.4 m s⁻¹) and surface velocity (0 to 17 m s⁻¹) were studied. High speed imaging from the top and side was used to capture the impact phenomena. It was found that drop impact behavior on a moving surface significantly differs from that on a stationary surface at both the lamella extension stage (i.e. t ≤ t_max) and the retraction stage (t > t_max). Starting with the lamella extension stage, it was observed that the drop spreads asymmetrically over a moving surface. It was also found that the splashing behavior of the drop upon impact on a moving surface, unlike the understanding in the literature, is azimuthally different along the lamella contact line. In the case of the drop spreading over a moving surface, the surface movement stretches the expanded lamella in the direction of the surface motion. For hydrophilic surfaces, the stretched lamella pins to the surface and moves with the surface velocity; however, for hydrophobic surfaces, the lamella recoils during such stretching. A new model was developed to determine the splashing threshold of the drop impact on a moving surface. The model is capable of describing the azimuthally different behavior of the splashing which is a function of normal capillary and Weber numbers, surface velocity, and surface wettability. It was also found that the increase of the viscosity decreases the splashing threshold. Finally, comprehensive regime maps of the drop impact outcome on a moving surface were provided for both t ≤ t_max and t > t_max stages.

A superhydrophobic coating endows pristine hydrophilic wood with excellent water/moisture repellency and thus prolongs its service life. Generally, the superhydrophobic coating on wood is fabricated by a two-step process in which the nanoparticles are first introduced onto the surface and then modified by low-surface-energy molecules. Herein, for the first time, we have fabricated the superhydrophobic wood via a one-step process free of nanoparticles by immersing the pristine hydrophilic wood, such as pine, balsawood, and basswood, into a composite silane solution of hexadecyltrimethoxysilane and methyltrimethoxysilane. The wood remains superhydrophobic or highly hydrophobic after long-term exposure to mechanical damage (such as abrading, knife-cutting, and tape-peeling), chemical damage (such as immersion in acid, alkali, or ethanol), and environmental impacting (such as UV irradiation and low/high-temperature exposure).