An integrated study of dropwise condensation heat transfer on self-assembled organic surfaces through Fourier transform infra-red spectroscopy and ellipsometry

Abstract Self-assembled monolayers (SAMs) formed by adsorption of 1-octadecanethiol [CH 3 (CH 2 ) 17 SH] and 16-mercaptohexadecanoic acid [CO 2 H(CH 2 ) 15 SH] onto gold-coated-copper substrates were applied to investigate the enhancement of dropwise condensation (DWC) heat transfer of steam at atmosphere pressure. A durability test was also conducted. Although hydrophobic SAMs increase the heat transfer coefficient by nearly an order of magnitude from that of filmwise condensation, it was found that DWC using octadecanethiol SAM as a promoter is a dynamic process in that the heat transfer coefficient decreases with time over 2 h. These results were reconfirmed by an integrated study using Fourier transform infra-red spectroscopy (FT-IR) and Spectroscopic Ellipsometry. We found that the monolayer of octadecanethiol becomes less crystalline with time, causing the film thickness and heat transfer coefficient to decrease. There was also some indications that, as SAMs were partly removed (leaving patches of the bare metal), contaminant from steam spontaneous adsorbed onto these high energy sites, resulting in a slightly higher heat transfer coefficient at a later stage of condensation.

[1]  Xuehu Ma,et al.  Influence of processing conditions of polymer film on dropwise condensation heat transfer , 2002 .

[2]  Ralph G. Nuzzo,et al.  Fundamental studies of microscopic wetting on organic surfaces. 1. Formation and structural characterization of a self-consistent series of polyfunctional organic monolayers , 1990 .

[3]  Jingyu Huang,et al.  Characterization of thiol self-assembled films by laser desorption Fourier transform mass spectrometry , 1992 .

[4]  I. Rubinstein,et al.  Self-Assembled Monolayers on Oxidized Metals. 2. Gold Surface Oxidative Pretreatment, Monolayer Properties, and Depression Formation , 1998 .

[5]  Q. Zhao,et al.  Dropwise condensation on L-B film surface , 1996 .

[6]  Y. Jaluria,et al.  An Introduction to Heat Transfer , 1950 .

[7]  Self-Assembled n-Alkanethiolate Monolayers on Underpotentially Deposited Adlayers of Silver and Copper on Gold , 1997 .

[8]  P. J. Marto,et al.  Evaluation of organic coatings for the promotion of dropwise condensation of steam , 1986 .

[9]  Y. Mori,et al.  Effectiveness of composite copper/graphite fluoride platings for promoting dropwise condensation of steam: A preliminary study , 1994 .

[10]  Gerry B. Andeen,et al.  The Use of an Organic Self-Assembled Monolayer Coating to Promote Dropwise Condensation of Steam on Horizontal Tubes , 2000 .

[11]  D. W. Tanner,et al.  Heat transfer in dropwise condensation—Part I The effects of heat flux, steam velocity and non-condensable gas concentration , 1965 .

[12]  G. Kane Jennings,et al.  Effect of Chain Length on the Protection of Copper by n-Alkanethiols , 1998 .

[13]  J. Westwater,et al.  Steam Condensation on Various Gold Surfaces , 1981 .

[14]  Gerry B. Andeen,et al.  Dropwise Condensation of Steam on Horizontal Corrugated Tubes Using an Organic Self-Assembled Monolayer Coating , 2000 .

[15]  E. Schmidt,et al.  Versuche über die Kondensation von Wasserdampf in Film- und Tropfenform , 1930 .

[16]  George M. Whitesides,et al.  Comparison of the Structures and Wetting Properties of Self-Assembled Monolayers of n- Alkanethiols on the Coinage Metal Surfaces, Cu, Ag, Au' , 1991 .

[17]  G. Whitesides,et al.  Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto gold , 1989 .

[18]  L. A. Bromley,et al.  Dropwise and filmwise condensation of water vapor on gold , 1973 .

[19]  J. W. Westwater,et al.  Dropwise condensation of steam on electroplated silver surfaces , 1984 .

[20]  P. J. Marto,et al.  The Use of Organic Coatings to Promote Dropwise Condensation of Steam , 1987 .

[21]  W. Zisman,et al.  Confirmation of spontaneous spreading by water on pure gold , 1970 .

[22]  B. Wang,et al.  Lifetime test of dropwise condensation on polymer-coated surfaces , 1999 .

[23]  J. W. Westwater,et al.  Steam condensation on electroplated gold: Effect of plating thickness , 1979 .