P.E. Vickers et al. Carbon 38(2000)675-689 contact angles of the reference liquids and therefore an cathodically oxidised fibres. The initial stages of the increased wettability upon treatment. oxidation appear to be the most active, supported by the Although IGC and DCAA provide information on the change in y P values recorded by DCAA. Certain nitrogen thermodynamics at two completely different scales they do containing organic species at the surface appear to be converge to show that acid-base are much more effective diminished after the initial stages of oxidation, consistent than the dispersive properties to minimise the solid-liquid with the removal of a chemically differing outer skin interfacial tension and thus improve the wettability of the present on untreated fibres carbon fibres upon treatment. DCAA appears to yield very subtle yet possibly very Another interesting aspect of th e surra powerful information within the fine structure of the namics properties of the carbon fibres is the consideration dvancing and receding plateaux of the spectrum. This of the adsorption of TMP as studied by IGC. The however, appears to be ambiguous in the sense that it is negligible deviation of TMP from the reference line(ABA, not clear whether this is related to chemical heterogeneity see Fig. 5 and Table 6) may indicate that the treatment or surface roughness. However, there was little difference does not yield a microporous structure at the surface. Such observed in RT In( n)values for TMP and n-heptane, micropores are known to yield negative deviations of bserved at this branched alkanes relative to the reference n-alkane line molecular scale, in good agreement with DCAA, where the [36] spectrum of water showed fine structure, in contrast I-bromonaphthalene and glycerol The increase in acidity and basicity of the fibre surface 5. Conclusion with oxidation is well correlated with the increase in surface concentration of heteroatom content. IGC and Untreated carbon fibres possess large y, values and XPS, therefore, provide good complementary data of the effect that oxic has on the surface properties of possess very little y character and are not wet particularly arbon fibres well even by moderately polar species. This is changed significantly during the first stages of electrochemical oxidation. At the molecular scale, y, decreases as a result Acknowledgements of surface treatment, but this is accompanied by a large increase in the acidity and a moderate increase in the PEV would like to acknowledge the epsrc for funding basicity of the surface. This increase is due to the this project, and Dr. L. Boniface for provision of carbon introduction of organic functional groups which result in fibres the capability of enhanced acid-base interactions which probably account for the increase in IFSS and ILSS with oxidation of carbon fibre surfaces previously observed References [1,447] Although XPS shows that the oxygen concentration o [1] Drzal LT, Rich M, Lloyd PF. J Adhesion 1982: 16: 1 the surface increases significantly as a result of electro- [2] Drzal LT, Rich MJ, Koenig MF, Lloyd PF. J Adhesion hemical oxidation, ToF-SIMS analysis indicates that there 1983;16:133 is significant oxygen present in the outer surface of the 3] Mahy J, Jenneskens Lw, Grabandt O, Venema A, van untreated fibres. and that this does not increase dramatical Houwelingen GDB. Surf Int Anal 1994- 21: 1 y as the oxidation progresses. This is somewhat in 14 Fitzer E, Geigl K-H, Huttner w, Weiss R. Carbon contrast to the data obtained by XPS, which shows a steady increase in oxygen content after the initial intro- 5] Zhdan PA, Bors M, Castle JE. Comp Sci and Technol 1998:58:559 duction of a relatively large amount of oxygen at 25% [6 Proctor A, Sherwood PMA. J Electron Spec and Rel Phen DCAA however, indicates that there is very little polar 1982;27:39 interaction from the untreated fibre, in agreement with the [7 Proctor A, Sherwood PMA Carbon 1983, 21: 53 data obtained from IGC. The y P increases significantly 8 Kozlowski C, Sherwood PMA. J Chem Soc, Fa the macroscopic scale as a result of electrochemical 1985;81:2745 treatment, allowing improved wettability of both moderate- [9] Weitzacker CL, Sherwood PMA Surf Int Anal 1995: 23: 55 ly polar (e.g. glycerol) and highly polar (e.g. water) [10 Kozlowski C, Sherwood PMA. J Chem Soc, Faraday Trans I 1984:80:2099 ToF-SIMS and XPs indicate that there is [11 Kozlowski C, Sherwood PMA Carbon 1986, 24: 357 introduction of inorganic ions such as Na, cl and ca [12 Nakao F, Takenaka Y, Asai H. Composites 1992: 23(5):365 [13] Bradley RH. Mech and Corr Prop A: Key Eng Mater the fibre surface with progressive oxidation. Positiv c出 1995;99-100:37 Na and Ca increase rapidly at low levels of oxidation, [14] Donnet JB, Park S],Balard H.Chromatographia which may be a result of them acting as counter ions to the 1991;31:434688 P.E. Vickers et al. / Carbon 38 (2000) 675 –689 contact angles of the reference liquids and therefore an cathodically oxidised fibres. The initial stages of the increased wettability upon treatment. oxidation appear to be the most active, supported by the p Although IGC and DCAA provide information on the change in g s values recorded by DCAA. Certain nitrogen thermodynamics at two completely different scales they do containing organic species at the surface appear to be converge to show that acid–base are much more effective diminished after the initial stages of oxidation, consistent than the dispersive properties to minimise the solid–liquid with the removal of a chemically differing outer skin interfacial tension and thus improve the wettability of the present on untreated fibres. carbon fibres upon treatment. DCAA appears to yield very subtle yet possibly very Another interesting aspect of the surface thermody- powerful information within the fine structure of the namics properties of the carbon fibres is the consideration advancing and receding plateaux of the spectrum. This of the adsorption of TMP as studied by IGC. The however, appears to be ambiguous in the sense that it is negligible deviation of TMP from the reference line (DBA, not clear whether this is related to chemical heterogeneity see Fig. 5 and Table 6) may indicate that the treatment or surface roughness. However, there was little difference does not yield a microporous structure at the surface. Such observed in RT ln(V ) values for TMP and n-heptane, N micropores are known to yield negative deviations of indicating that there is little or no porosity observed at this branched alkanes relative to the reference n-alkane line molecular scale, in good agreement with DCAA, where the [36]. spectrum of water showed fine structure, in contrast to 1-bromonaphthalene and glycerol. The increase in acidity and basicity of the fibre surface 5. Conclusion with oxidation is well correlated with the increase in surface concentration of heteroatom content. IGC and d Untreated carbon fibres possess large g values and XPS, therefore, provide good complementary data of the s therefore have relatively energetic surfaces. However, they effect that oxidation has on the surface properties of p possess very little g character and are not wet particularly carbon fibres. s well even by moderately polar species. This is changed significantly during the first stages of electrochemical d oxidation. At the molecular scale, g decreases as a result Acknowledgements s of surface treatment, but this is accompanied by a large increase in the acidity and a moderate increase in the PEV would like to acknowledge the EPSRC for funding basicity of the surface. This increase is due to the this project, and Dr. L. Boniface for provision of carbon introduction of organic functional groups which result in fibres. the capability of enhanced acid–base interactions which probably account for the increase in IFSS and ILSS with oxidation of carbon fibre surfaces previously observed References [1,4,47]. Although XPS shows that the oxygen concentration of [1] Drzal LT, Rich MJ, Lloyd PF. J Adhesion 1982;16:1. the surface increases significantly as a result of electro- [2] Drzal LT, Rich MJ, Koenig MF, Lloyd PF. J Adhesion 1983;16:133. chemical oxidation, ToF-SIMS analysis indicates that there [3] Mahy J, Jenneskens LW, Grabandt O, Venema A, van is significant oxygen present in the outer surface of the Houwelingen GDB. Surf Int Anal 1994;21:1. untreated fibres, and that this does not increase dramatical- [4] Fitzer E, Geigl K-H, Huttner W, Weiss R. Carbon ly as the oxidation progresses. This is somewhat in 1980;18:389. contrast to the data obtained by XPS, which shows a [5] Zhdan PA, Bors M, Castle JE. Comp Sci and Technol steady increase in oxygen content after the initial intro- 1998;58:559. duction of a relatively large amount of oxygen at 25%. [6] Proctor A, Sherwood PMA. J Electron Spec and Rel Phen DCAA however, indicates that there is very little polar 1982;27:39. interaction from the untreated fibre, in agreement with the [7] Proctor A, Sherwood PMA. Carbon 1983;21:53. p data obtained from IGC. The g increases significantly at [8] Kozlowski C, Sherwood PMA. J Chem Soc, Faraday Trans I s 1985;81:2745. the macroscopic scale as a result of electrochemical [9] Weitzacker CL, Sherwood PMA. Surf Int Anal 1995;23:551. treatment, allowing improved wettability of both moderate- [10] Kozlowski C, Sherwood PMA. J Chem Soc, Faraday Trans I ly polar (e.g. glycerol) and highly polar (e.g. water) 1984;80:2099. species. [11] Kozlowski C, Sherwood PMA. Carbon 1986;24:357. ToF-SIMS and XPS indicate that there is a steady [12] Nakao F, Takenaka Y, Asai H. Composites 1992;23(5):365. introduction of inorganic ions such as Na, Cl and Ca into [13] Bradley RH. Mech and Corr Prop A: Key Eng Mater the fibre surface with progressive oxidation. Positive ions 1995;99–100:37. Na and Ca increase rapidly at low levels of oxidation, [14] Donnet JB, Park SJ, Balard H. Chromatographia which may be a result of them acting as counter ions to the 1991;31:434