Plasmachemical Functionalization of Solid Surfaces with Low Surface

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Plasmachemical Functionalization of Solid Surfaces with Low Surface Energy Perfluorocarbon Chains S. R. Coulson, I. S. Woodward, and J. P. S. Badyal* Department of Chemistry, Science Laboratories, Durham University, Durham DH1 3LE, U.K.

S. A. Brewer and C. Willis DERA, Porton Down, Salisbury SP4 OJQ, U.K. Received February 7, 2000. In Final Form: April 17, 2000 Pulsed plasma polymerization of precursors containing long perfluoroalkyl chains can lead to the formation of structurally well-defined low surface energy films. Greater chemical selectivity and faster deposition rates are found for monomers containing carbon-carbon double bonds compared to their saturated analogues. Critical surface tension values (γc) as low as 1.5 mN m-1 have been achieved, which corresponds to exceptional hydrophobic and oleophobic liquid repellency behavior.

1. Introduction Low surface energy finishes are important for many everyday applications, 1-4, e.g., protective coatings, biocompatible layers, and stain-resistant textiles. In the past, these have been prepared using solution and dispersedphase polymerization, and then applied by spraying, padding, or solvent-casting techniques.5-8 Here, we describe an approach based on plasma polymerization, which offers a number of benefits: control of film thickness and composition regardless of substrate geometry,9 good adhesion, minimal energy consumption, and negligible waste. Plasma polymerization comprises of electromagnetic excitation of a precursor in the vapor phase to produce ions (both positive and negative), neutrals, secondary electrons, and photons. Under favorable conditions, this can lead to film deposition. Recently, it has been demonstrated that highly specific polymerization mechanisms can be instigated by modulating the electrical discharge on the millisecond-microsecond time scale.10,11 Since longterminal perfluoroalkyl chains are renowned for their propensity to confer liquid repellency (oleophobicity as well as hydrophobicity),12,13 fluorinated alkenes of the type CnF2n+1CHdCH2 (a typical example being 1H,1H,2Hperfluoro-1-dodecene (C10F21CHdCH2)) have been sub* Corresponding author. (1) Boutevin, B.; Pietrasanta, Y. Les Acrylates et Polyacrylates Fluore´ s: De´ rive´ s et Applicatios; EREC: Paris, 1988. (2) Klinger, L.; Griffith, J. R.; Rall, C. J. N. Org. Coat. Appl. Polym. Sci. Proc. 1983, 48, 407. (3) Bonardi, C. Eur. Patent 426530, 1991. (4) DeMarco. C. G.; Macquade, A. J.; Kennedy, S. J. J. Mod. Text. Mag. 1960, 2, 50. (5) Park, I. J.; Lee, S. B.; Choi. C. K.; Kim. K. J. J. Colloid Interface Sci. 1996, 181, 284. (6) Tamura, M.; Funaki, H. Jpn. Pat. 1997, 302, 335. (7) Thunemann, A. F.; Lieske, A.; Paulke, B. R. Adv. Mater. 1999, 11, 321. (8) Morita, M.; Ogisu, H.; Kubo, M. J. Appl. Polym. Sci. 1999, 73, 1741. (9) Chan, C.-M.; Ko, T.-M.; Hiraoka, H. Surf. Sci. Rep. 1996, 24, 1. (10) Savage, C. R.; Timmons, R. B. Chem. Mater. 1991, 3, 575. (11) Ryan, M. E.; Hynes, A. M.; Badyal, J. P. S. Chem. Mater. 1996, 8, 37. (12) Kissa, E. Handbook of Fibre Science and Technology; Lewin, M., Sello, S. B., Eds.; Marcel Dekker: New York, 1984; p 143. (13) Mino, N.; Ogawa, K.; Minoda, T.; Takatsuka, M.; Sha, S.; Moriizumi, T. Thin Solid Films 1993, 230, 209.

jected to pulsed plasma deposition. The purpose of this investigation is to show that preferential activation and reaction occurs at the polymerizable carbon-carbon double bond, while the low surface energy perfluoroalkyl chains remain structurally intact. Plasmachemically deposited fluorocarbon films have been characterized by X-ray photoelectron spectroscopy (XPS), infrared spectroscopy, atomic force microscopy (AFM), and surface energy measurements. 2. Experimental Section Plasma polymerization experiments were carried out in an inductively coupled cylindrical reactor (diameter of 5 cm, volume of 470 cm3, base pressure of 3 × 10-3 mbar, and a leak rate14 of better than 6 × 10-9 mol/s). This was connected to a two-stage Edwards rotary pump via a liquid nitrogen cold trap, a thermocouple pressure gauge, and a glass tube containing a fluoromonomer (either 1H,1H,2H-perfluoro-1-dodecene or (perfluoro-n-decyl)ethane, Fluorochem, 98%+ purity following multiple freeze-thaw cycles). All connections were grease-free. An L-C matching unit was used to minimize the standing wave ratio (SWR) of the transmitted power from a 13.56 MHz radio frequency (rf) generator to the electrical discharge. For the pulsed plasma deposition experiments, the rf source was triggered by a signal generator, and a cathode ray oscilloscope was used to monitor the pulse width and amplitude. The average power 〈P〉 delivered to the system during electrical pulsing was calculated using the following formula:15

〈P〉 ) Pp[ton/(ton + toff)] where ton/(ton + toff) is defined as the duty cycle and Pp is the continuous wave power. A typical experiment comprised initially scrubbing the reactor with detergent and rinsing with isopropyl alcohol, followed by oven drying. The system was then reassembled and cleaned further with a 50 W air plasma for 30 min. Next, the chamber was vented to air, and the substrate to be coated was placed in the center of the reactor; then the chamber was evacuated down to base pressure. Fluorochemical vapor was subsequently introduced at a constant pressure of ∼0.2 mbar and allowed to purge for 5 min, followed by ignition of the glow discharge. The pressure on the reactor outlet was found to be steady, which is consistent with a sufficient monomer flow rate. Deposition was terminated after 5 min, and monomer vapor was (14) Enrlich, C. D.; Basford, J. A. J. Vac. Sci. Technol. 1992, A10, 1. (15) Nakajima, K.; Bell, A. T.; Shen, M. J. Appl. Polym. Sci. 1979, 23, 2627.

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allowed to pass over the substrate for another 5 min; finally the plasma chamber was evacuated down to base pressure and then vented to atmosphere. Deposition rate measurements were carried out using a goldcoated quartz crystal monitor (Inficon XTM/2) located in the center of the reaction chamber.16 A control experiment was undertaken where monomer vapor was allowed to pass over the substrate for 15 min in the absence of the electrical discharge. This confirmed no film deposition. A VG ESCALAB MKII electron spectrometer, fitted with a nonmonochromated Mg KR X-ray source (1253.6 eV) and a hemispherical analyzer operating in the CAE mode (20 eV pass energy), was used for XPS analysis of the deposited plasma polymer coatings. The photoemitted atomic core level electrons were collected at a take-off angle of 30° from the substrate normal, which corresponds to an escape depth of approximately 10-15 Å for the C(1s) envelope. XPS peaks were referenced to the C(1s) CxHy environment at 285.0 eV and fitted using a Marquardt minimization computer program in conjunction with linear background subtraction.17 From the instrument sensitivity factors obtained using chemical standards, elemental concentration ratios were calculated to be 1.00:0.36:0.23 C(1s)/O(1s)/F(1s). X-ray beam damage caused less than 1% variation in the F/C ratio during a typical XPS scan. This was sufficiently small so that no discernible change was observed in the C(1s) envelope. Complete plasma polymer coverage was confirmed by the absence of any Si(2p) XPS signal from the underlying glass substrate. A FTIR Mattson Polaris instrument fitted with a Golden Gate single reflection diamond attenuated total reflectance (ATR) apparatus (Graseby Specac) was used for infrared analysis. Plasma polymerization depositions were carried out onto sodium chloride plates and analyzed using 128 scans at a resolution of 4 cm-1. The physical structure of the plasma polymer coatings was examined using a Digital Instruments Nanoscope III atomic force microscope. The microscope was operated in Tapping Mode, where changes in the oscillation amplitude of the cantilever tip serve as a feedback signal for measuring topographic variations across a surface.18 Phase-modulation AFM was also used: this process measures the phase of oscillation with respect to the piezoelectric driver.16 All of the AFM images were acquired in air and are presented as unfiltered data. Root mean square (RMS) roughness values were obtained from 10 µm × 10 µm images.19 Sessile drop contact angle measurements were carried out at 20 °C with a video capture apparatus (A.S.T. Products VCA2500XE). The Wilhelmy plate technique (Cahn microbalance, model DCA322) was used for dynamic contact angle analysis.20 This comprised suspending a glass slide coated on both sides from the microbalance while a motorized stage moved a beaker containing the probe liquid upward and over the substrate at a speed of 154 µm/s. The advancing contact angle, θ, corresponds to the tangent at the three-phase solid/liquid/vapor interface formed during the initial immersion of the plate; this was calculated from the modified Young equation:21

cos θ ) F/(γ × p)

(1)

where F is the wetting force at the meniscus measured by the microbalance, γ is the surface tension of the probe liquid, and p is the perimeter of the meniscus formed at the three-phase interface. The value of θ was then used to calculate the surface energy (also referred to as surface tension, with the units mJ m-2 and mN m-1 being dimensionally equivalent) using two (16) Brice, J. C. Rev. Mod. Phys. 1985, 57, 105. (17) Evans, J. F.; Gibson, J. H.; Moulder, J. F.; Hammond, J. S.; Goretzki, H. Fresenius’ J. Anal. Chem. 1984, 319, 841. (18) Zhong, Q.; Inniss, D.; Kjoller, K.; Elings, V. B. Surf. Sci. 1993, 290, L688. (19) ASTM E-42.14 STM/AFM subcommittee recommendation for analysing and reporting surface roughness. (20) Andrade, J. D. Surface and Interfacial Aspects of Biomedical Polymers; Andrade, J. D., Ed.; Plenum Press: New York, 1985; Vol. 1, Chapter 7. (21) Young, T. Philos. Trans. R. Soc. London, Ser. A 1805, 95, 82.

Figure 1. XPS C(1s) envelope for pulsed plasma polymerization of 1H,1H,2H-perfluoro-1-dodecene (ton ) 20 µs, toff ) 20 000 µs, and Pp ) 70 W). Table 1. Probe Liquid Surface Energy Values surface energy/ mN m-1 (at 20 °C) repellency

liquid

literature24

hydrophobicity

water isopropyl alcohol hexadecane tetradecane dodecane decane octane heptane hexane pentane

72.8 21.3 27.5 26.6 25.4 23.8 21.6 20.1 18.4 16.1

oleophobicity

different methods. First was the geometric mean equation:22,23

(1 + cos θ)γi ) 2[(γdi γds )1/2 + (γpi γps )1/2]

(2)

where γi is the surface tension of the probe liquid and γdi and γpi are the respective dispersive and polar components (as reported in the literature).24 When eq 2 is substituted with the values for water (representative polar liquid, γdi ) 22.1 mN m-1 and γpi ) 50.7 mN m-1) and octane (representative nonpolar liquid, γdi ) 21.6 mN m-1 and γpi ) 0.0 mN m-1),24 the dispersive (γds ) and polar (γps ) surface energy components for the coating could be determined by solving the corresponding set of simultaneous equations. Summation of γds and γps yielded the total surface energy, γ. The alternative approach was to construct a Zisman plot.25 This comprised choosing a set of probe liquids from the same homologous series (pentane, hexane, heptane, octane, and dodecane were employed for the plasma polymer surfaces, which displayed virtually no polar contribution)26,27 and measuring their advancing contact angles using the Wilhelmy plate apparatus. A plot of the cosine of the advancing contact angle versus the liquid surface tension (γi) approximates to a linear relationship, (22) Mittal, K. L. Ed.; Contact Angle, Wettability and Adhesion; VSP BV: Zeist, Netherlands, 1993; p 28. (23) Park, J.-M.; Kim. H. K. J. Colloid Interface Sci. 1994, 168, 103. (24) Jasper, J. J. J. Phys. Chem. Ref. Data 1972, 1, 841. (25) Bernett, M. K.; Zisman, W. A. J. Phys. Chem. 1960, 64, 1292. Shafrin, E. G.; Zisman, W. A. J. Phys. Chem. 1960, 64, 519. (26) Dalal, E. N. Langmuir 1987, 3, 1009. (27) Cherry, B. W. In Cambridge Solid State Series: Polymer Surfaces; Cambridge University Press: Cambridge, 1981; p 28.

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Figure 2. XPS C(1s) spectra of continuous-wave plasma polymerization of 1H,1H,2H-perfluoro-1-dodecene at various powers. often referred to as the Zisman plot.25 The critical surface tension of spreading for the solid surface, γc, is obtained by extending the line of best fit to cos θ ) 1. Any liquid with a surface tension lower than this value will form a zero contact angle with the coating. The Wilhelmy plate apparatus was also used to check if the surface tension of each probe liquid was consistent with previously reported literature values (see Table 1).

3. Results (a) 1H,1H,2H-Perfluoro-1-dodecene (CH2dCHC10F21). The C(1s) XPS envelope for each deposited plasma polymer coating was fitted to six Gaussian Mg KR1,2 components28 with equal full-widths-at-half-maximum (fwhm):17 CxHy at 285.0 eV, C-CFn at 286.6 eV, CFn at 287.8 eV, CF-CFn at 289.3 eV, CF2 at 291.2 eV, and CF3 at 293.3 eV (this relatively high value can be attributed to the electron-withdrawing nature of the attached perfluoroalkyl backbone; see Figure 1). Additional Mg KR3,4 X-ray satellite peaks, shifted by ∼9 eV toward lower binding energy,29 were also taken into consideration. Continuous-wave (CW) plasma polymerization experiments indicated rising perfluoroalkyl chain incorporation (i.e., the relative proportion of -CF2- groups) with decreasing electrical discharge power (Figure 2). Even better structural retention was achieved by pulsing the system on the millisecond-microsecond time scale (Figure 3). The optimum parameters were found to be ton ) 20 µs, toff ) 20 000 µs, and Pp ) 70 W, which is equivalent to an average power, 〈P〉, of 0.07 W. A good correlation was found between the elemental composition of these deposited films and the structure of the 1H,1H,2H-perfluoro-1-dodecene monomer unit (Table 2). No oxygen was detected. The concentration of CF3 functionalities in the C(1s) envelope for the pulsed plasma polymer layer was higher than predicted, and can be attributed to the surface sensitivity of the XPS technique detecting a greater signal from the (28) Beamson, G.; Briggs, D. High Resolution XPS of Organic Polymers. The Scienta ESCA300 Database; John Wiley and Sons: New York, 1992. (29) Briggs D.; Seah M. P. Practical Surface Analysis by Auger and X-Ray Photoelectron Spectroscopy; John Wiley and Sons: Chichester, England, 1983.

Figure 3. Plot of CF2 group incorporation as a function of (a) ton (at fixed toff ) 20 000 µs and Pp ) 70 W), (b) toff (at fixed ton ) 20 µs and Pp ) 70 W), and (c) average power.

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Figure 4. Infrared spectra of (a) the 1H,1H,2H-perfluoro-1dodecene monomer, (b) optimum pulsed plasma polymerization conditions (ton ) 20 µs, toff ) 20,000 µs, and Pp ) 70 W), and (c) a 5 W continuous wave. Table 2. Compilation of the Theoretical (corresponding monomer structure, CH2)CHC10F21), and Actual Chemical Environments Measured by XPS for 1H,1H,2H-Perfluoro-1-dodecene treatment theoretical optimum pulsed continuous wave

average power (〈P〉) (in W) F:C ratio %CF2 %CF3 0.07 5

1.75 1.56 1.26

75.0 64.8 32.9

8.3 15.1 20.5

terminal CF3 groups as a consequence of perfluoroalkyl chain alignment away from the surface. Similar behavior has been previously observed for solution-phase polymerized perfluoroalkyl monomers.30 XPS was also used to

check the quality of the coating on the different types of substrates used in this study. Identical chemical compositions were found in each case. Thus, the nature of the substrate was not found to influence the quality of the coating. Preferential loss of the following characteristic alkene infrared absorption features was observed upon plasma polymerization of 1H,1H,2H-perfluoro-1-dodecene:31 1424 cm-1 (alkene in-plane deformation) and 710-1067 cm-1 (CH2 out-of-plane deformation, wagging, and twisting vibrations, as well as CH in- and out-of-plane deformations, see Figure 4). Pulsed plasma polymerization gave rise to significantly less broadening of the perfluoroalkyl chain absorption bands31 at 1120-1280 cm-1 (CF2) and 1120-1350 cm-1 (CF3). This is consistent with the greater structural retention compared to continuous wave conditions (i.e., less rearrangement, fragmentation, and crosslinking reactions). The maximum deposition rate was found to be close to 1 W average power, with the pulsed discharge being more effective than its continuous wave counterpart (Figure 5). The most likely explanation for this is that the plasma sheath potential and vacuum ultraviolet (VUV) flux are significantly smaller for the former case;32 and therefore, ion-assisted ablation and VUV damage of the growing film will be less favored. The low deposition rate observed at very short pulse duty cycles can be attributed to insufficient monomer activation. AFM analysis gave RMS roughness values of 0.7 nm for the flat glass substrate and 11 nm for the 1H,1H,2H-perfluoro-1-dodecene pulsed plasma polymer coating (Figure 6). Surface roughness on the sub-micrometer scale was clearly discernible in the corresponding AFM phase image. Water contact angle measurements taken on plasma polymer coated flat glass substrates indicated a good correlation between liquid repellency and the extent of perfluoroalkyl chain retention (Figure 7). The droplet contact angle value was found to be stable with respect to time. For optimum structural retention, the combined geometric mean-Young’s equation gave surface energy values as low as γ ) 8.3 ( 0.3 mN m-1 (where γds ) 8.2 mN m-1 and γps ) 0.1 mN m-1). The extremely low polar contribution to the total surface energy under these

Figure 5. Deposition studies for 1H,1H,2H-perfluoro-1-dodecene: (a) deposition rate; (b) deposition efficiency.

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Figure 6. AFM micrographs of pulsed plasma polymer of 1H,1H,2H-perfluoro-1-dodecene (ton ) 20 µs, toff ) 20 000 µs, and Pp ) 70 W): height image shown on left-hand side (z ) 100 nm) and corresponding phase image on right-hand side.

hydrophobicity and oleophobicity toward a range of liquids with varying surface tensions35 (Table 1). This comprised placing three drops of each test liquid onto plasma polymer coated cotton fabric. The surface was considered to repel each liquid if, after 30 s, the drops remained spherical/ hemispherical, i.e., absence of any penetration or wicking into the fabric at the liquid-fabric interface. Repellency was observed for water/isopropyl alcohol (IPA) mixtures of up to 90% IPA (hydrophobicity) and for alkane chains as short as dodecane (oleophobicity) (Figure 8). (b) Role of the Polymerizable End Group. The pulsed plasma polymerization of 1H,1H,2H-perfluoro-1dodecene (CH2dCHC10F21) was compared with its saturated analogue (perfluoro-n-decyl)ethane (CH3-CH2C10F21) as a function of pulse frequency at a fixed duty cycle and peak power. XPS analysis revealed greater structural retention of the perfluoroalkyl chain for the alkene monomer, which improved at shorter on-times (Figure 9). Furthermore, deposition rate measurements at the duty cycle pulse frequency corresponding to greatest structural retention showed that the alkene underwent polymerization at a faster rate (Table 3). Figure 7. Sessile drop water contact angle values versus (% CF2 + % CF3) incorporation into the plasma polymer films.

conditions meant that it was valid to use a homologous series of alkane probe liquids to construct a Zisman plot; this yielded a critical surface tension value of γc ) 1.5 ( 0.4 mN m-1, which is significantly better than that for PTFE (γc ) 18.5 mN m-1).33,3433 The optimum pulsed plasma deposition conditions were subsequently used to coat pieces of cotton fabric to test for (30) Coulson, S. R.; Brewer, S.; Willis, C.; Badyal, J. P. S. Chem. Mater. 2000, in press. (31) Lin-Vien, D.; Colthup, N. B.; Fateley, W. G.; Grasselli, J. G. The Handbook of Infrared and Raman Characteristic Frequencies of Organic Molecules; Academic Press: New York, 1991. (32) Panchalingam, V.; Chen, X.; Huo, H.; Savage, C. R.; Timmons, R. B.; Eberhart, R. C. ASAIO J. 1993, 39, M305. (33) Fox, H. W.; Zisman, W. A. J. Colloid. Sci. 1950, 5, 514. (34) Owens, D. K.; Wendt, R. C. J. Appl. Polym. Sci. 1969, 13, 1741.

4. Discussion The observed improvement in >CF2 group retention during electrically pulsed plasma polymerization of 1H,1H,2H-perfluoro-1-dodecene compared to continuous wave conditions is consistent with less fragmentation and damage of the perfluoroalkyl chain during deposition (Table 2). This can be attributed to the lower plasma sheath potential leading to milder ion bombardment of the growing film,36 as well as less VUV surface damage37 during the plasma on-period. Intermediate pulse duty (35) 3M water repellency test II water/alcohol drop test, 3M Test Methods 1988. 3M oil repellency test I, 3M Test Methods 1988. (36) Panchalingam, V.; Chen, X.; Huo, H.; Savage, C. R.; Timmons, R. B.; Eberhart, R. C. ASAIO J. 1993, 39, M305. (37) Yasuda, H.; Hsu, T. J. Polym. Sci., Polym. Chem. Ed. 1977, 15, 81.

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Figure 9. Comparison of pulsed plasma polymerization of 1H,1H,2H-perfluoro-1-dodecene versus (perfluoro-n-decyl)ethane as a function of pulse frequency (1/(ton+toff), where duty cycle ) 0.07 and Pp ) 70 W). Table 3. Comparison of Deposition Rates (ton ) 20 µs, toff ) 20 000 µs, and Pp ) 70 W)

Figure 8. Optical images illustrating liquid repellency (droplet volume, 2 µL) for the 1H,1H,2H-perfluoro-1-dodecene pulsed plasma polymer layer deposited onto cotton fabric (ton ) 20 µs, toff ) 20 000 µs, Pp ) 70 W): (top) water (hydrophobicity); (bottom) dodecane (oleophobicity).

cycles produce the highest ratio of polymerizable species to nonpolymerizable/ablative species in the plasma. The

monomer

deposition rate / ng s-1 cm-2

1H,1H,2H-perfluoro-1-dodecene (perfluoro-n-decyl)ethane

15.7 ( 2.4 8.4 ( 0.4

fall in deposition rate toward continuous wave conditions is a manifestation of ablation becoming a competing process as a consequence of more energetic species in the plasma. For the influence of average power to be factored out, the deposition rate efficiency (defined as deposition rate divided by average power) was considered38 (Figure 5). This shows that the deposition rate per joule of energy increases with decreasing average power, which is consistent with the active sites created during the on-period (via UV irradiation or ion or electron bombardment, etc.) participating in conventional polymerization reaction pathways either in the gas phase or at the plasmasubstrate interface during the off-time.11 Eventually for very short duty cycles, there is insufficient monomer activation to effectively sustain polymerization, and hence, a drop-off in deposition efficiency is observed. Supporting evidence is provided by the fact that greater structural retention and deposition rate is observed for the 1H,1H,2H-perfluoro-1-dodecene monomer than for its saturated counterpart, (perfluoro-n-decyl)ethane, which is consistent with the alkene bond undergoing conventional polymerization during the off-period. Compared to the existing solvent-based liquid-repellent coatings, the described plasma polymerization method benefits from not requiring additional nonfluorochemical reagents (e.g., catalysts, cross-linking agents, surfactants, etc).11,39 This is reflected in the exceedingly low critical surface tension value, γc, of 1.5 mN m-1 measured for the 1H,1H,2H-perfluoro-1-dodecene pulsed plasma polymer film. Electron density withdrawal by the (-CF2-)n backbone away from the terminal CF3 group in the (38) Chen, X.; Rajeshwar, K.; Timmons, R. B.; Chen, J. J.; Chyan, M. R. Chem. Mater. 1996, 8, 1067. (39) Shimizu, T. Modern Fluoropolymers; Scheirs, J., Ed.; John Wiley and Sons: New York, 1997; p 513.

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perfluoroalkyl chains will hinder hydrogen bonding and dispersion interactions with polar and nonpolar liquids, respectively.40 Any distortion in γc to an abnormally low value as a consequence of surface roughness is unlikely.41 Since the series of alkane probe liquids chosen for the Zisman plot all exhibit contact angles less than 90° and Wenzel’s law42 predicts lower liquid contact angles (contact angle decreases with roughness for liquids exhibiting contact angles less than 90° on flat surfaces), therefore cos θ should have been greater for these probe liquids on the Zisman plot leading to an artificially high value of γc. Porosity in the film leading to a composite interface containing trapped air can also be ruled out due to the absence of the low contact angle hysteresis normally associated with a composite interface43-45 (the pulsed (40) Smart, B. E. In Organofluorine Chemistry: Principles and Commercial Applications; Banks, R. E., Ed.; Plenum Press: New York, 1994. (41) Coulson, S. R.; Brewer, S.; Willis, C.; Badyal, J. P. S. Br. Patent 9712338.4, 1997. (42) Wenzel, R. N. J. Phys. Chem. 1949, 53, 1466. (43) Garbassi, F.; Morra, M.; Occhiello, E. In Polymer Surfaces: From Physics to Technology; John Wiley and Sons: New York, 1994; p 183.

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plasma 1H,1H,2H-perfluoro-1-dodecene film exhibited advancing and receding contact angle values, θadv/θrec, of 127°/86° and 74°/35° for water and octane, respectively). 5. Conclusions Pulsed plasma polymerization of 1H,1H,2H-perfluoro1-dodecene gives rise to the formation of very low surface energy films containing perfluoroalkyl chains. A comparison with the saturated analogue of this monomer, (perfluoro-n-decyl)ethane, indicates that the alkene bond must participate in conventional polymerization reaction pathways during the off-period in order to account for the observed improvement in structural retention and deposition rate. Acknowledgment. S.R.C. thanks DERA for a Ph.D. studentship. LA0001676 (44) Johnson, R. E., Jr.; Dettre, R. H. Adv. Chem. Ser. 1963, No. 43, 112. (45) Johnson, R. E., Jr.; Dettre, R. H. J. Phys. Chem. 1964, No. 68, 1744.