Photochemical modification of polytetrafluoroethylene into oleophilic property using an ArF excimer laser
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K. Toyoda Riken, Institute of Physical and Chemical Research, 2-1 Hirosawa, Wako, Saitama 351-01, Japan (Received 28 November 1991; accepted 19 December 1991)
Photochemical modification of the polytetrafluoroethylene (PTFE) with incorporation of the CH 3 radical released from the B(CH 3 ) 3 molecule excited by an ArF excimer laser has been demonstrated. The incorporation of CH 3 radicals and the depletion of fluorine atoms of the polymer surface were studied by XPS analysis and infrared ATR spectrum measurement. In these photochemical reactions, the photoirradiated surface changed into oleophilic. The properties were studied by contact angle measurement. The stability of the oleophilic surface was examined at the elevated temperature of 200 °C for 6 h in O2 or N2 ambient and also by immersing in alkaline or acid water solutions.
I. INTRODUCTION Recently, various interesting processes of surface modification of polymers such as direct laser ablation1 to form highly periodic structures and selective area electroless plating2 of metal deposition have been demonstrated. The 70 nm lines were produced in polyimide using the interference of the two beams of a KrF excimer laser. Electroless plating was carried out on a polyimide or polyethyleneterephthalate surface irradiated by excimer lasers. These studies are based on the laser ablations of polymer surfaces using excimer lasers at high laser fluence. Unlike these methods of surface processing to produce the microstructures and to change the electrochemical property, attention has been directed toward the control of the physical properties of the polymer surface. The oleophobic surface of PTFE changes into oleophilic by photochemical reactions using an excimer laser. In the process, the laser fluence was kept relatively low so as not to ablate the polymers.3 Some radicals such as alkyl and phenyl radicals are known to show affinity to liquid benzene and paraffin oil. Therefore, by introducing the alkyl (CH3) radical to the oleophobic surface, new photochemical processes to obtain the oleophilic property might be developed. Adhesion W of the liquid of surface tension j A is given by W =
(1)
where 9 is the contact angle. The zero contact angle (0 = 0) gives the maximum adhesion to the solid surface. Investigation to obtain the conditions that give rise to the minimum contact angle has been carried out.3 The oleophilic property of the surface is evaluated by measuring the contact angle with benzene. The mea1912 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 7, Jul 1992 Downloaded: 13 Mar 2015
surements were carried out by the shape measurement of a liquid drop of benzene. The shape was photographed by the illumination of 633 nm He-Ne laser. Variations of the contact angle with the laser fluence dependence are discussed. The chemical composition of the photomodified surface was analyzed by x-ray photoelectron spectroscopy (XPS) and infrared ATR spectrum measurement. The thermal and chemical stabilities of the sample were also examined. No significant change
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