Hydrophilic and hydrophobic materials and their applications

Abstract

Wettability of a material’s surface plays a significant role in how fluids interact with such surfaces. Wetting behaviour is universal but can vary depending on the chemical nature of the solid and liquid phases. Plants and animals adapt to their environment through having evolved special properties. These properties are such as hydrophilic and hydrophobic. Hydrophilic surface has a strong affinity to water and spreading of water on such surface is preferred. The degree of hydrophilicity of the substance can be measured by measuring the contact angle between the liquid and solid phases. Hydrophobic materials are known as non-polar materials with a low affinity to water, which makes them water repelling. A contact angle of less than 90° indicates hydrophilic interaction where as an angle greater than 90° indicates a hydrophobic interaction. More recently, superwetting such as superhydrophilicity has been receiving an increased focus in literature due to its potential significance. Superhydrophilic surface has a contact angle of less than 5°. The fabrication of hydrophilic materials can be carried out in two main ways: depositing molecules on surfaces or modification of surface chemistry. Both methods have been successful historically in achieving their intended purposes. Hydrophobic and superhydrophobic materials can be produced with many fabrication methods such as layer-by-layer assembly, laser process, the solution-immersion method, sol-gen techniques, chemical etching and Hummer’s method. The applications of such an important property are significant. For example, hydrophilic surfaces can be used in anti-fogging applications, biomedical, filtration, heat pipes, and many others. Hydrophobic and superhydrophobic materials have been successfully applied in many sectors, such as: (I) the removal of petroleum from aqueous solutions, (II) applied to plastic, ceramics and mesh to contribute to the oil removal from aqueous solutions, (III) hydrophobic layers have a strong self-cleaning effect on plastics, heat pipes, metals, textiles, glass, paints and electronics, (IV) hydrophobic layers improve the anti-freezing behaviour of heat pipes which prevents unwanted build-up and (V) they function as a water and dust protecting coat on electronics The presence of this property is historic but there is still a huge potential for development for its applications in many sectors such as water treatment, heat transfer applications, biomedical devices, and many more.