Combining a Fluoroalkylsiloxane and Ion Implantation for Hydrophilic/Hydrophobic Patterning

M.J. Cook, J.H. Johnston, J. Leveneur
Victoria University of Wellington,
New Zealand

Keywords: hydrophilic, hydrophobic, patterning, fluoroalkylsiloxane, ion implantation

Summary:

We present a novel method of producing hydrophilic/hydrophobic patterning on several different substrates using a novel two-step process. The developed process involves a simple surface functionalization with a fluoroalkylsiloxane (FAS), followed by masked ion implantation. This method allows for the patterning of many different substrates, with only two facile steps, producing the same degree of hydrophilicity and hydrophobicity irrespective of the wettability of the initial substrate. The way in which water interacts with surfaces has an impact on many different industries and so the ability to control this interaction and determine the wetting behavior of a surface allows for the development of intelligent interfaces to overcome challenges and improve efficiency in many areas. Compared to uniform surface properties, the design of a surface with particular areas of hydrophilicity and areas of hydrophobicity allows for a greater control of the wetting behavior and flow of water across the surface. This has well-known applications in microfluidics,1–4 but can be of use in many different industries where benefits can be gained through controlling behaviours at the interface between water and a surface, such as heating and air conditioning,5,6 and water harvesting,7,8 in particular. As there is a wide range of potential applications for hydrophilic/hydrophobic patterning, there is a similarly large variety of substrate materials that may be used in these applications. As some applications require other material characteristics, it is not always possible to utilise different materials to achieve hydrophobic/hydrophilic patterning, without producing a less efficient surface due to a loss in other properties. Hence, it is desirable to have a method of hydrophilic/hydrophobic patterning that can be applied to different substrate materials, without significantly affecting the other physical properties of the surface. Existing methods of hydrophilic/hydrophobic patterning generally utilize lithography/etching techniques and chemical deposition.9–12 These methods involve numerous steps, many of which are often delicate and require many resources. These existing methods also often require specific substrates or rely on relatively thick surface coatings, which can alter other properties of the surface. Conversely, we have developed a novel system that allows facile hydrophilic/hydrophobic patterning of a surface with only a two-step process. The FAS functionalization and ion implantation can be applied to a number of substrates and the resulting hydrophobicity and hydrophilicity is dependent on the chemistry of the FAS and products resulting from the ion implantation, hence this system can be applied to a number of different substrate materials, while achieving the same hydrophilic/hydrophobic pattern with similar wetting properties. We are progressing applications on polymers, metals and glass. To date, aluminium panels for heat exchangers have been treated and also showed improved heat transfer properties after the patterning treatment. Hence, this treatment process shows great promise for commercial applications.