Mutual diffusion coefficients in the water-rich region of water/phenol mixtures and their relation to aggregate formation

Abstract

1475repulsions between the charged carboxylic groups and results in the formation of mixed micro domain^.'^^ Effect I11 should bring about a decrease of 11/13 but would occur only in PSX solutions with X 2 4.Obviously, for PS1 and PS2 the changes of 11/13 are essentially due to effect I. The decreases of 11/13 in the presence of PS1 or PS2 are only slightly less steep than in pure water. A partial recoiling of the copolymer (effect 111) would have no impact on the change of 11/13, as pyrene is not bound by PS1 or PS2 in the whole a! range (see Figures 7 and 9 at very low Cs).On the contrary, PS16 appears to correspond to a situation where partition is unimportant. Indeed the value of 11/13 in the absence of DTAB in Figure 18, at C, = 2 X lo4 M, is close to that found at C, = 10-* M.29 This indicates that pyrene is nearly completely solubilized in the microdomains and that effect I is negligible. The increase of 11/13 with Cs reflects the progressive enrichment of the microdomains in DTAB (effect 11). Recall that in PS16 most repeat units appear to be forming micro domain^.^^ Thus effect I11 discussed above is negligible. Note that the 11/13 vs C , plot for PS16 extends to a Cs value slightly below that where a DTAB-PS16 complex precipitates out.PS4, PS6, and PSlO correspond to intermediate situations. A minimum is expected to result from the superimposition of effects I and I1 in the variation of 11/13 with Cs at high Cs where effect I1 becomes predominant. This minimum is observed for the three copolymers. Evidence for the contribution of effect I11 can be found in the results for PS10. Microdomains are known to exist in PSlO solutions, but at LY = 1.00 "sin formation involves only 15% repeat units.30 Nevertheless as for PS16 the Z1/I3 value at Cs = 0 indicates that pyrene is nearly completely solubilized within these domains. Thus effect I contributes only little to the change of 11/13 at low Cs. This is borne out by the increase of 11/13 with Cs at very low Cs. One would therefore expect a monotonous increase of I'll3 from the value of 1.10 in the absence of DTAB to 1.45 at very high Cs. The leveling off of 11/13 and its subsequent decrease in Figure 18 reveal that a new effect sets in where additional repeat units become involved in microdomains, together with the added DTAB. These additional repeat units can only be those not involved in microdomains at low C,. Their involvement corresponds to a miling of PSlO (effect 111). When most of the free repeat units have been used up by this process, 11/13 is expected to increase again with Cs, as observed.A similar process is likely to occur in PS4 and PS6 solutions. In the latter, 11/13 slowly decreases up to Cs = 3 X M then decreases faster up to 2 X lo4 M DTAB. These two concentrations probably determine the range where PS6 recoils. ConclusionsThe above study of the binding of DTAB to a series of homologous but increasingly hydrophobic copolymers has clearly shown that the cooperativity in the binding is modulated by the hydrophobicity of the copolymer. As one g...

Factors affecting microporous membrane liquid‐liquid extraction

“…With sequential injections the average diffusion coefficient obtained was 9.34610 -10 (RSD 0.71%). The obtained diffusion coefficients were repeatable and they agreed well with the values reported in the literature (reference D: 9.4610 -10 m 2 /s) [30]. In the study of the effect of the sample concentration on the measured diffusion coefficients it was found that, at lower concentrations (1 lg/ mL), the peak shapes were poor owing to poor signal to noise ratio.…”

Computer simulation of the structure and dynamics of phenol in sodium montmorillonite hydrates

“…We note first that our simulated data for phenol in the bulk solution are in good agreement with the experimental data of Castillo et al (1992). At infinite dilution, they obtained values of 9.4 × 10 −10 m 2 s −1 and 1.88 × 10 −9 m 2 s −1 at 296 and 342 K, respectively.…”

“…This structural picture is consistent with the interpretation of computer simulations (Jorgensen & Nguyen, 1993; Jorgensen et al , 1993). The diffusion coefficients of phenol in the water‐rich regime have been measured with the Taylor dispersion technique (Castillo et al , 1992). At infinite dilution, values of 0.94 × 10 −9 m 2 s −1 and 1.88 × 10 −9 m 2 s −1 are recorded at 296 and 342 K, respectively.…”

Facilitated transport of phenol through supported liquid membrane containing bis(2-ethylhexyl) sulfoxide (BESO) as the carrier

“…The diffusivity of PhOH in water is calculated as D aq = 9.4 Â 10 À10 m 2 s À1 using the Wilke-Chang equation [50]. Therefore, the thickness of the aqueous boundary layer is calculated as d aq = D aq D aq = 7.74 Â 10 À5 m.…”