P.E. Vickers et al. Carbon 38(2000)675-689 22 86420 86420 8E32 86420 86420 110 Fig. 5. Plot of RT In(N)vs. T, for:(a)0%; and (b)200% carbon fibres +, n-CE-9: D, CHCI,, O, THF; +CCl4: A, EtAc, -1-BuOH; X TME Chloroform has its marker above but close to the I-BuoH(38%)*THF(27%)> EtAc(18%)> CHCI, (2%) us indicating a weakly basic character of the T treated fibres. CCla is a weak acid and usually The trend observed in the probes relevant to this study is interacts mainly via dispersive interactions. For this reason shown above. where the numbers in brackets refer to the its corresponding marker is very close to the reference line degree of self-association. CCl, may undergo some repul As far as TmP is concerned retention data are almost sive interactions with the surfaces as AGa invariably identical to those of n-heptane since both alkanes have takes positive values(negative deviation from the disper- very close boiling points. For this apolar probe we define a △ BA parameter as[36 Table 6 △BA=RTin(N(TMP)/Ne Free energy of adsorption per methylene group(-AG4 ), ABA for isooctane and acid-base contribution to the free energy of where Ba stands for branched alkane. Since TMP and C7 adsorption(aGa )of polar probes adsorbed onto untreated and have comparable boiling points, VN.ref for TMP is almost treated carbon fibres at 50C that of c7 Table 6 reports △ ba and ag values for ethylene groups Kanes, TMP and the specific -△GH4.3053.9763864 3.718 probes, respectively results reported in Table 6 0.565-0.1810.052 0.304 0.005 oxidised fibres than with the untreated fibres. One can also 9 9cT quantitatively indicate that there is a significantly greater interaction between the acidic and basic probes with the CHO 1.14 2.35 1.67 139 145 note that the strength of acid-base interactions roughly 1-BuOH 3.78 11.13 10.1612.49 increase with the degree of self-association reported in the EtAc 9.24 1145 728 10.99 THF literature 37, 38 3.3510.721249 1.73 11.76P.E. Vickers et al. / Carbon 38 (2000) 675 –689 683 Fig. 5. Plot of RT ln(V ) vs. T for: (a) 0%; and (b) 200% carbon fibres. ♦, n-C ; h, CHCl ; d, THF; 1CCl ; m, EtAc; 2 t-BuOH; 3, N b 6–9 3 4 TMP. character. Chloroform has its marker above but close to the t-BuOH(38%) | THF(27%) . EtAc(18%) . CHCl (2%) 3 n-alkane thus indicating a weakly basic character of the 200% DFT treated fibres. CCl is a weak acid and usually 4 The trend observed in the probes relevant to this study is interacts mainly via dispersive interactions. For this reason shown above, where the numbers in brackets refer to the its corresponding marker is very close to the reference line. degree of self-association. CCl may undergo some repul- 4 AB As far as TMP is concerned, retention data are almost sive interactions with the surfaces as DGa invariably identical to those of n-heptane since both alkanes have takes positive values (negative deviation from the disper￾very close boiling points. For this apolar probe we define a DBA parameter as [36]: Table 6 CH2 DBA 5 RT ln(V (TMP)/V ) (5) Free energy of adsorption per methylene group (2DGa ), DBA N N,ref for isooctane and acid–base contribution to the free energy of AB where BA stands for branched alkane. Since TMP and C7 adsorption (2DGa ) of polar probes adsorbed onto untreated and have comparable boiling points, V for TMP is almost treated carbon fibres at 508C N,ref that of C7. 0 25 50 100 200 CH2 AB Table 6 reports DG , DBA and DG values for a a CH2 methylene groups in 2DGa 4.305 3.976 3.864 3.887 3.718 n-alkanes, TMP and the specific DBA 20.565 20.181 0.052 20.304 0.005 probes, respectively. The results reported in Table 6 AB quantitatively indicate that there is a significantly greater — DGa interaction between the acidic and basic probes with the CHCl3 20.22 1.14 2.35 1.67 2.55 oxidised fibres than with the untreated fibres. One can also CCl4 22.07 21.92 21.39 21.45 21.12 t-BuOH 3.78 11.13 – 10.16 12.49 note that the strength of acid–base interactions roughly EtAc 1.52 9.24 11.45 7.28 10.99 increase with the degree of self-association reported in the THF 3.35 10.72 12.49 11.73 11.76 literature [37,38]: