Liquid repellent surfaces

Abstract

The work in this thesis is primarily aimed at supporting the NBe (Nuclear, Biological and Chemical) aspect of Crusader 21, the military clothing programme for the early 21st Century. This aims to produce a multi-purpose, systems-orientated combat ensemble for the UK Armed Services. Conventional "wet" techniques for chemically modifying fabrics have certain disadvantages, however employing plasma technology may provide a route for many novel "multi-functional effects" fabrics such as repellency against toxic chemical agents. In order to produce repellent coatings the surface must have a low surface energy. To obtain this, inert chemical groups need to be attached to the solid substrate. In addition to chemistry, surface roughness plays an important role in repellency. Liquid repellent surfaces have been produced by the pulsed plasma polymerisation of I H, 1 H,2H,2H -heptadecafluorodecyl acrylate. These films have chemical functionalities indicative of polymerisation occurring through the acrylate double bond, as shown by Infrared Spectroscopy analysis. Structural retention was optimised using experimental design techniques and resulted in a critical surface tension of wetting as low as 4.3 mN m-I (c.f. Teflon 18.5 mN m-I). Plasma deposition of a functionalised surface followed by reaction with a fluorinated alcohol proved less affective. Enhanced deposition rates for 1 H, 1 H,2H-perfluorododec-I-ene, over the saturated analogue, have indicated that polymerisation can occur during the off-time of the pulsed plasma period, via free radical polymerisation pathways. X-ray Photoelectron Spectroscopy (XPS) has indicated greater structural group retention for monomers containing double bonds. In order to obtain super liquid repellency the effect of surface roughness was investigated, where both commercially available rough surfaces and plasma roughened substrates were utilised. Once optimised, the rough surfaces were coated with 1 H, 1 H,2H,2H-heptadecafluorodecyl acrylate and produced super repellent films.