P.E. Vickers et al./ Carbon 38(2000)675-689 Table I 3. Results Physico-chemical properties of probes used for IGC abbreviation bp"C-1 3.1. Surface chemical composition 8.4 3.1.I. Electron spectroscopy Survey spectra of fibres that had received treatments of n-Nonane 0, 25 and 200% are presented in Fig. 1(a-c). There is very TMP little difference observed between any of the spectra Tert-butyl alcohol t-BuOH recorded, save for the increase in magnitude of theo Is Carbon tetrachloride fiac, peak observed at =530 eV and the O KLL X-ray induced Auger peak at 980 ev. The surface chemical com- positions present within the fibre as measured by xPs are Tetrahydrofuran shown in Table 3. It is assumed that the surface com- Isooctane is 2, 2, 4-trimethyl pentane position does not vary significantly along the tow of fibres, and that fibre heterogeneity is present but at a much smaller scale than the analysis area probed by the X-ray beam. It can be seen that the oxygen content gradually speed of 19.8 um s, giving the greatest number of mass increases at the expense of carbon as the oxidation eadings per unit length of fibre, because mass readings are procedure progresses. The residual nitrogen content fuc- taken at a rate of 1 Hz, irrespective of the speed of th tuates slightly around 3%, and there are traces of Na, Cl motor. Samples were conditioned in an air oven at 160C and Ca. These latter three elements appear to be slightly overnight to remove adsorbed water from the surface of increasing with treatment and are probably introduced to the fibres. A single fibre, approximately 10 mm in length, the surface as a direct result of electrochemical oxidation. was attached to a small piece of adhesive tape, approxi their origin most probably the wash water used in the mately 2X2 mm, that had already been attached to a piece dustrial process, and possibly, in the case of sodium(and of nichrome wire, approximately 60 mm in length, and less likely, chlorine), the electrolyte. The high-resolution a hook at the far end. This was hooked onto the spectra (not shown), show little difference in the C Is sample pan of the microbalance. The hook, tape and fibre envelope for all types of fibre, and the o Is peak reveals ssessed a mass in the range of 4-6 mg, and this was an overall increase in intensity, possibly indicating an balanced to within +2 mg by adding tare weights to the introduction of more carbonyl groups at the fibre surface. other side of the microbalance. Once these were in position The N Is spectra have poor counting statistics, and are the liquid surface was brought to within 5 mm of the fibre centred at approximately 401 ev. Genera ally, the xP end by raising a platform situated underneath the microbal- spectra obtained do not possess sufficient resolution to ance. The fibres were then subjected to one cycle of determine the relative amounts of hydroxyl-ester, car- immersion, i.e. lowered and raised by 10 mm, taking a bonyl-carboxyl, and acid sites on the fibre surface total analysis time of 1020 s. Cyclohexane was used to determine the average fibre perimeter of each type of fibre, 3.1.2. Mass spectrometry and the dispersive and polar contributions to the surface ToF-SIMS has greater surface specificity and better free energies of the fibres were estimated by conducting detection limits than those possible by XPS, and should DCAA experiments using the contact media listed in Table show differences in spectra for different treated fibres 2. 1-Bromonaphthalene(98%), n-hexadecane(99%)and owing to its sensitivity to changes in chemical structure glycerol(99.5%), supplied by Aldrich, were used in the occurring at the surface. Surprisingly though, the spectra DCA analyses obtained were remarkably similar for 0, 25 and 100% treated fibres. However, the spectra revealed a significant increase in inorganic ions with surface treatment. SIMS is very sensitive to inorganic ions which possess low ionia tion energies such as Na, cl and Ca. The increase in these Surface free energy contributions of contact media used for elements is illustrated in Fig. 2, which shows the variation DCAA of the intensity of ions normalised to the total ion signal ontact medium y(kJ mol )y(]J mol)yP(]J mol -) with oxidation treatment. As would be expected from the XPS results, the oxygen content gradually increases and the relative intensity of the CH ions decrease slightly Both Na and Ca show a marked increase at early stages of 26.4 treatment and the Cl content increases steadily. It is interesting to note that there is very little change in the678 P.E. Vickers et al. / Carbon 38 (2000) 675 –689 Table 1 3. Results Physico-chemical properties of probes used for IGC Probe Abbreviation bp 8C21 3.1. Surface chemical composition n-Hexane C 69 6 3.1.1. Electron spectroscopy n-Heptane C 98.4 7 Survey spectra of fibres that had received treatments of n-Octane C 125.7 8 0, 25 and 200% are presented in Fig. 1(a–c). There is very n-Nonane C 150.8 9 a little difference observed between any of the spectra Isooctane TMP 99.2 Tert-butyl alcohol t-BuOH 83.0 recorded, save for the increase in magnitude of the O 1s Carbon tetrachloride CCl 76.8 4 peak observed at ¯530 eV and the O KLL X-ray induced Chloroform CHCl 61.2 3 Auger peak at ¯980 eV. The surface chemical com￾Ethyl acetate EtAc 77.1 positions present within the fibre as measured by XPS are Tetrahydrofuran THF 66.0 shown in Table 3. It is assumed that the surface com- a Isooctane is 2,2,4-trimethyl pentane. position does not vary significantly along the tow of fibres, and that fibre heterogeneity is present but at a much smaller scale than the analysis area probed by the X-ray beam. It can be seen that the oxygen content gradually 21 speed of 19.8 mm s , giving the greatest number of mass increases at the expense of carbon as the oxidation readings per unit length of fibre, because mass readings are procedure progresses. The residual nitrogen content fluc￾taken at a rate of 1 Hz, irrespective of the speed of the tuates slightly around 3%, and there are traces of Na, Cl motor. Samples were conditioned in an air oven at 1608C and Ca. These latter three elements appear to be slightly overnight to remove adsorbed water from the surface of increasing with treatment and are probably introduced to the fibres. A single fibre, approximately 10 mm in length, the surface as a direct result of electrochemical oxidation, was attached to a small piece of adhesive tape, approxi- their origin most probably the wash water used in the mately 232 mm, that had already been attached to a piece industrial process, and possibly, in the case of sodium (and of nichrome wire, approximately 60 mm in length, and less likely, chlorine), the electrolyte. The high-resolution possessing a hook at the far end. This was hooked onto the spectra (not shown), show little difference in the C 1s sample pan of the microbalance. The hook, tape and fibre envelope for all types of fibre, and the O 1s peak reveals possessed a mass in the range of 4–6 mg, and this was an overall increase in intensity, possibly indicating an balanced to within 62 mg by adding tare weights to the introduction of more carbonyl groups at the fibre surface. other side of the microbalance. Once these were in position The N 1s spectra have poor counting statistics, and are the liquid surface was brought to within 5 mm of the fibre centred at approximately 401 eV. Generally, the XPS end by raising a platform situated underneath the microbal- spectra obtained do not possess sufficient resolution to ance. The fibres were then subjected to one cycle of determine the relative amounts of hydroxyl–ester, car￾immersion, i.e. lowered and raised by 10 mm, taking a bonyl–carboxyl, and acid sites on the fibre surface. total analysis time of 1020 s. Cyclohexane was used to determine the average fibre perimeter of each type of fibre, 3.1.2. Mass spectrometry and the dispersive and polar contributions to the surface ToF-SIMS has greater surface specificity and better free energies of the fibres were estimated by conducting detection limits than those possible by XPS, and should DCAA experiments using the contact media listed in Table show differences in spectra for different treated fibres 2. 1-Bromonaphthalene (98%), n-hexadecane (99%) and owing to its sensitivity to changes in chemical structure glycerol (99.5%), supplied by Aldrich, were used in the occurring at the surface. Surprisingly though, the spectra DCA analyses. obtained were remarkably similar for 0, 25 and 100% treated fibres. However, the spectra revealed a significant increase in inorganic ions with surface treatment. SIMS is very sensitive to inorganic ions which possess low ionisa￾tion energies such as Na, Cl and Ca. The increase in these Table 2 Surface free energy contributions of contact media used for elements is illustrated in Fig. 2, which shows the variation DCAA of the intensity of ions normalised to the total ion signal 21 d 21 p 21 with oxidation treatment. As would be expected from the Contact medium g (kJ mol ) g (kJ mol ) g (kJ mol ) sss XPS results, the oxygen content gradually increases and C H 27.6 27.6 0 2 16 34 the relative intensity of the CH ions decrease slightly. C H Br 44.6 44.6 0 10 7 Both Na and Ca show a marked increase at early stages of Glycerol 63.4 37.0 26.4 treatment and the Cl content increases steadily. It is H O 72.8 21.8 51.0 2 interesting to note that there is very little change in the