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ESRI Scientists Develop New Class of Nanomaterials with Tunable Wettability

Scientists in the Energy Safety Research Institute (ESRI) at Swansea University have developed new materials that are economical, nontoxic and that show promise to replace more dangerous and expensive materials used for fogging/antifouling and waterproofing.

Schematic of the functionalization of the nanoparticles along with photographic images of the water droplets on spray-coated microscope slides. An environmentally friendly superhydrophobic coating to superhydrophilic coating for antifogging and antifouling according to scientists at Swansea University. Credit: Shirin Alexander/University of Swansea

A new series of nanomaterials with tunable wettability have found significant applications ranging from antifouling to water proofing surfaces. Materials developed by the Swansea University Scientists are nontoxic, cost-effective and applicable to a wide range of surfaces through spray or spin-coating.

The Researchers headed by Dr. Shirin Alexander and Professor Andrew Barron reported their work in the American Chemical Society open access journal ACS Omega.

The spray coated nanomaterials are capable of providing a texture to the surfaces, despite the substrate and they also provide the chemical functionality that can modify the surface from superhydrophilic (water wetting) to superhydrophobic (water repelling) based on the customized functionality that is selected.

Wafaa Al-Shatty, a Masters Student at the Energy Safety Research Institute at the Swansea University Bay Campus, performed the fabrication and testing of low surface energy to high surface energy materials.

Wafaa Al-Shatty synthesized aluminum oxide nanoparticles by using hydrocarbon linear and branched carboxylic acids (with varied surface energies) in order to demonstrate the possibility of readily tuning hydrophobicity based on the nature of the chemical functionality. The research explains that slight changes in the organic chain will enable the control of surface wettability, surface energy, roughness and the capability of the nanoparticles to act as surface active agents.

Both hydrophilicity and hydrophobicity are reinforced by roughness. Nanoparticles with the methoxy (-OCH3) functionality display high surface energy and thus superhydrophilicity properties. In contrast, branched hydrocarbons reduce the surface energy. Spiky (branched) chains are considered to be the first line of defense against water alongside surface roughness, which is brought about by nanoparticles in both cases. This minimizes contact between the water droplets and surface, which indeed permits them to slide off.

A material can be superhydrophobic if it has a water contact angle greater than 150 degrees, while superhydrophilic surfaces are materials whose surfaces display water contact angles lower than 10 degrees. Contact angle refers to the angle at which the surface of the water comes in contact with the surface of the material.

The hydrocarbon-based superhydrophobic material could be a "green" replacement for expensive, dangerous fluorocarbons commonly used for superhydrophobic applications.

They also are able to reduce the interfacial tension of various oils-water emulsions by behaving as surface active agents (surfactants).

Dr. Shirin Alexander, Head of the Research

The understanding of the relationships between the superhydrophilic and superhydrophobic nanoparticles and the resulting emulsion properties, oil stability and interfacial tension at the water/oil boundary is greatly instructive yielding insights that could majorly benefit the futuristic development of higher efficiency in the recovery of oil via enhanced oil recovery (EOR) methods.

The Researchers are currently working to enhance the material's durability on different substrates and they are also focusing on large-scale application to surfaces.

Co-authors of the papers include Alex Lord, a Research Fellow at the Swansea University Center for Nanohealth. Barron is the Charles W. Duncan Jr.–Welch Professor of Chemistry and a Professor of Materials Science and Nanoengineering at Rice and the Sêr Cymru Chair of Low Carbon Energy and Environment at Swansea. Alexander is the Sêr Cymru Research Fellow at Swansea University.

The research was supported by the Robert A. Welch Foundation and the Welsh Government Sêr Cymru II Fellowship Program.

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