Movement of air bubbles under various liquids using bioinspired conical surfaces

Gas bubbles are of interest in various applications. The study of their movement is of importance. Gas bubbles are typically formed under liquids. Movement of liquid droplets on bioinspired conical surfaces is known to be facilitated by the Laplace pressure gradient. These conical surfaces, with various wettabilities and shapes, can also be used to move gas bubbles. In this study, effect of various liquids on movement of air bubble under liquid was studied. It was found that liquids with high surface tension and high density are more efficient in moving air bubbles. High surface tension and higher density increases the Laplace pressure gradient force and the buoyancy force, respectively, which drive under liquid air bubbles.

Contact angles and movement of air bubbles on bioinspired conical surfaces

Air bubbles are of interest in various applications. The study of their formation, interaction with underlying surfaces, and their movement is of importance. Bioinspired conical surfaces have been known to exhibit Laplace pressure gradient which facilitates the movement of liquid droplets. These conical surfaces, with various geometries and wettabilities, can be used to regulate gas bubble movement. In this study, contact angles of air bubbles and their movement on various conical surfaces were investigated. The effect of parameters including cone orientation, air bubble volume, tip angle, and wettability on air bubble movement were studied. A smaller tip angle cone with high wettability was found to be most efficient for an air bubble movement.

Passive water harvesting by desert plants and animals: lessons from nature

Fresh water sustains human life and is vital for human health. For some of the poorest countries, 1 in 10 people do not have access to safe and easily accessible water sources. Water consumption by man continues to grow with an increasing population. The current supply of fresh water needs to be supplemented to meet future needs. Living nature provides many lessons for water harvesting. It has evolved species which can survive in the most arid regions of the world by passively collecting water from fog and condensation of water vapour in the night. Before the collected water evaporates, species have mechanisms to transport water for storage or consumption. These species possess unique chemistry and structures on or within the body for collection and transport of water. Among the high diversity of species surviving in deserts, only a handful of species have been studied. Based on lessons from nature, bioinspired water harvesters can be designed. In this paper, an overview of various desert plants and animals is given and known water harvesting mechanisms of some are presented. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 3)'.

Multistep Wettability Gradient on Bioinspired Conical Surfaces for Water Collection from Fog

Water scarcity is on the rise globally. In severely arid deserts, nature has developed different mechanisms to transport water collected from fog and condensation before it is evaporated. This water is either stored or consumed. Some of the studied mechanisms are Laplace pressure gradient, grooves, and gravity. Another way to transport water is through heterogeneity in wettability, in which a droplet moves from a water repelling (hydrophobic) region to a water loving (hydrophilic) region. A combination of multistep heterogeneity on a bioinspired conical surface is studied to provide fast movement of water droplets. A representative cone was selected, and its water collection rates at different wettabilities were measured.

Designing bioinspired conical surfaces for water collection from condensation

In arid deserts, water supply is supplemented by water from fog and condensation. Once the droplets are collected, they are transported to a location where they are consumed or stored before they evaporate. Conical geometries or triangular patterns are known to create Laplace pressure gradient inside droplets which facilitates droplet transport. Water collection by fog on conical and triangular patterns have been studied. The research on the water collection by condensation exist only on flat triangular patterns. These flat surfaces have limitations for practical purposes, such as the Laplace pressure gradient does not act of droplets unless they touch the border. That is not the case in cones, which makes them superior for practical water collection. In this study, for the first time, water collection from condensation on cones have been studied. Cones of different tip angle, cone length, and surface area were used. Effect of inclination angle and array was also characterized. The results are compared to water collection by fog.

Bioinspired conical design for efficient water collection from fog

Nature is known for using conical shapes to transport the collected water from fog for consumption or storage. The curvature gradient of the conical shape creates a Laplace pressure gradient in the water droplets which drives them towards the region of lower curvature. Linear cones with linearly increasing radii have been studied extensively. A smaller tip angle cone transports water droplets farther because of higher Laplace pressure gradient. Whereas a larger tip angle with a larger surface slope transports water droplets because of higher gravitational forces. In this study, for the first time, a nonlinear cone with a concave profile has been designed with small tip angle and nonlinearly increasing radius to maximize water collection. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 2)'.

Fabrication of bioinspired, self-cleaning, anti-icing, superliquiphilic/phobic titanium using different pathways

Titanium is an important material having a high tensile strength-to-density ratio and high corrosion resistance. It has found applications in the aerospace, marine, automotive and biomedical industries. In some of the applications, it is important to have it as a highly liquid repellent, anti-icing and self-cleaning. There have been several attempts to make titanium superliquiphobic. The common pathways include chemical etching and anodizing. However, important characteristics such as self-cleaning, anti-icing and durability have not been investigated. If any durability data were reported, it was poor. In the current study, various superliquiphilic/phobic surfaces were fabricated using three pathways which include chemical etching, anodizing and nanoparticle-binder coating. Each surface was characterized for wettability, self-cleaning, anti-icing, self-cleaning properties and durability. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology'.

Designing bioinspired surfaces for water collection from fog

A systematic study is presented on various water collectors, bioinspired by desert beetles, desert grass and cacti. Three water collecting mechanisms including heterogeneous wettability, grooved surfaces, and Laplace pressure gradient, were investigated on flat, cylindrical, conical surfaces, and conical array. It is found that higher water repellency in flat surfaces results in higher water collection rate and inclination angle (with respect to the vertical axis) has little effect. Surfaces with heterogeneous wettability have higher water collection rate than surfaces with homogeneous wettability. Both cylindrical and conical surfaces resulted in comparable water collection rate. However, only the cone transported the water droplets to its base. Heterogeneity, higher inclination and grooves increased the water collection rate. A cone has a higher collection rate per unit area than a flat surface with the same wettability. An array of cones has higher collection rate per unit area than a single cone, because droplets in a conical array coalesce, leading to higher frequency of droplets falling. Adding heterogeneity further increases the difference. Based on the findings, scaled-up designs of beetle-, grass- and cactus-inspired surfaces and nets are presented. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology'.

Lessons from mosquitoes' painless piercing

Arthropods are the largest group of the living organisms. They attack other organisms by biting, stinging, or piercing and sucking. Among various medically important arthropods, which feed on living hosts, mosquitoes' piercing spread viruses which have been reported to cause the highest number of deaths annually. The primary cause of the deaths is malaria, which is spread by infected mosquitoes' piercing. This study aims at elucidating lessons from mosquitoes' painless piercing. Mosquitoes pierce using their fascicle, which is a bundle of coherently functioning six stylets. Based on experiments and available literature, it is presented that mosquitoes painlessly pierce using a combination of the numbing, the fascicle's serrated design, the vibratory actuation, and the graded and frequency-dependent mechanical properties of the labrum. Based on this understanding, a mosquito-inspired microneedle design has also been proposed.