Delivered by Ingenta to: Purdue University Libraries IP: 195.34.78.39 On: Thu, 23 Jun 2016 14:05:51 Copyright: American Scientific Publishers RESEARCH ARTICLE Copyright © 2011 American Scientific Publishers All rights reserved Printed in the United States of America Journal of Nanoscience and Nanotechnology Vol. 11, 5358–5364, 2011 Surface Modification of Anodised Aluminium Using a Femtosecond Laser I. A. Ansari 1 * , K. G. Watkins 1 , M. C. Sharp 2 , R. A. Hutchinson 3 , and R. M. Potts 4 1 Lairdside Laser Engineering Centre, Department of Engineering, University of Liverpool, Birkenhead, CH41 9HP, UK 2 General Engineering Research Institute, Liverpool John Moores University, Liverpool, L3 3AF, UK 3 Derwent Technology, Whitewynn, Aughton Ruddings, Ellerton, York, YO42 4PN, UK 4 J. P. Imaging Ltd., Lairdside Laser Engineering Centre, Birkenhead, CH41 9HP, UK Femtosecond laser pulses at 775 nm, combined with a scanning galvonometer system, have allowed the micro scale structuring of an aluminium plate coated with a 2 micron thick anodised aluminium layer for potential industrial applications. The micro-scale structuring of aluminium was investigated using ultrafast pulses of 180 fs duration at a repetition rate of 1 kHz. Under suitably optimised conditions, the interaction of the laser pulses with the substrate created a hydrophilic surface with a contact angle of less than 10 degrees. These surfaces revealed a ‘lotus-leaf’ like morphology when examined under a Scanning Electron Microscope (SEM). It has been found that these laser processed hydrophilic surfaces revert with time and they undergo this cycle of alternate hydrophilic/hydrophobic behaviour several times upon exposure to the laser pulses. Their potential application in the printing industries is strong due to their reusability and sustainability; initial trials on printing confirm this. This technology would offer extra advantages as a non-chemical process without the need for developer, thereby reducing the overall cost and time of printing. Keywords: Anodised Aluminium, Hydrophilic, Hydrophobic, Morphology, Ultrafast Laser. 1. INTRODUCTION The wettability of materials is an important surface prop- erty. It depends not only on the surface free energy of the given chemical composition but also on the geomet- rical structure of the solid surface. 1 2 The understanding and fabrication of surfaces with superhydrophobicity or superhydrophilicity are of great interest for fundamental research and practical applications. 3–6 It has been shown that surfaces which respond to external stimuli such as light allow various interfacial properties such as wetting, dispersability etc. to be controlled. 7 A considerable amount of research has been reported on creating reversible wet- tability of different materials, mainly TiO 2 , by employ- ing various forms of light source and dark storage to switch from a hydrophilic to a hydrophobic state and vice- versa. 3 7–15 Two excellent review articles on photorespon- sive surfaces and controlled switchable surfaces have been written by Jiang et al. and Kong et al. 16 17 Use of an ultra- violet (UV) and a green laser to bring about change in surface wettability in polymers has been recently reported by Athanassiou et al. 18 19 To the best of author’s knowl- edge, no work has been reported on the use of ultra short * Author to whom correspondence should be addressed. Femtosecond Infra-Red (IR) laser pulses to create super- hydrophilicity on aluminium and aluminium oxide. In the present study, Al is chosen because it is a material of choice in the printing industry as a well established uni- versal substrate that is cheap and readily available. Accord- ing to one estimate, the worldwide value of the printing and publishing market is ∼£200 billion, while the UK market is worth in excess of £10 billion. A significant pro- portion of this value is associated with aluminium litho- graphic plates. In 2006, the worldwide sales value of Al lithographic plates was of the order of £2 billion, equiv- alent to ∼500 million m 2 . The market is dominated by Agfa, Kodak and Fuji, sharing 75% of the market. Historically, lithographic plates have been produced in ‘analogue’ format. In brief, the plate is exposed to UV light through a film negative (or positive) and ‘developed’ to give the image. From the early 1990’s lasers have been used to directly expose plates from digital data; the expos- ing unit being known as a ‘platesetter’. There are different methods of digitally printing; basically, with three main options: computer to film, computer to plate (Ct-P) and computer to press. It is beyond the scope of this article to describe these processes in detail, readers are advised to refer to a well written book on these by Kipphan. 20 5358 J. Nanosci. Nanotechnol. 2011, Vol. 11, No. 6 1533-4880/2011/11/5358/007 doi:10.1166/jnn.2011.3796