By: D.G. Waugh¹, J. Lawrence¹ and D.J. Morgan²

¹ Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University, Leicestershire, LE11 3TU, UK

² Cardiff Catalysis Institute, School of Chemistry, Cardiff University, Cardiff, CF10 3AT, UK

It has been shown that the surface topography and surface chemistry on both the micro- and nano- scales can have major effects on the wettability characteristics of a material. The term wettability is given to the study of how a liquid interacts with the surface of a material incorporating surface topography, surface chemistry, surface energy and contact angle. The contact angle, θ, shown in Figure 1 is determined by the liquid-vapour (γ_lv) solid-vapour (γ_sv) and solid-liquid (γ_sl) tangential lines.

Wettability can be seen as a potential driving force in numerous applications such as biomedical and adhesion. For each of these applications it can be seen that, in general, the researcher employs the wettability characteristics to predict how a surface is going to react after treatment in relation to the anticipated application. From work such as this, one can extrapolate that it would be more commercially viable to have the ability to know how a process is going to modify a surface and ultimately be able to predict how that modified surface will perform during it’s intended use.

In order to induce surface modifications for numerous material types a large number of techniques have been demonstrated such as employing plasma surface modification, coating technologies, lithography, and radiation grafting. Another is that of laser technology, which offers numerous benefits such as clean non-contact processing, flexibility and the ability to accurately modify the surface properties of a material without modifying the bulk properties.

Modification of the wettability of polymers has been demonstrated previously; however, it is known that the wettability modifications of these materials can degrade or vary over time. But at the same time, atmospheric parameters may affect the contact angle and must therefore be accounted for as a control variable in any long-term study of wettability. This can be seen to be crucial from a commercial point of view as this would indicate that a shelf-life has to be established. As a result, a unique study has been undertaken by analysing how the wettability varies over time and how atmospheric parameters effect the contact angle of four CO₂ laser patterned nylon 6,6 samples with differing topographical patterns and one as-received sample.

This study has confirmed the fact that a relatively inexpensive, low power CO₂ laser holds the ability to significantly modify the surface topography and oxygen content of nylon 6,6. Furthermore, it has also been shown that through these surface modifications the wettability of  nylon 6,6 can be modified. It is evident through the results obtained that atmospheric pressure may be a main driving force for the observed contact angle indicating that considerably more research is required to determine the main driving forces for the characteristic contact angle.

The above brief overview was extracted from its original abstract and paper presented at The International Congress on Applications of Lasers & Electro-Optics (ICALEO) in Orlando, FL. To order a copy of the complete proceedings from this conference click here

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