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...

We describe the entropy of liquids in the context of kinetic theory of dense gases. In the equilibrium regime the statistical entropy has an explicit dependence of the pair correlation function. In order to test the entropy functional, we use the Morse potential to reproduce experimental pair correlation functions of liquid sodium, using the molecular dynamics technique. With this information, we can compare the theoretical entropy with experimental thermodynamic data. On the other hand, from the nonequilibrium point of view, we discuss the entropy-increase-law analyzing the entropy balance equation. The entropy production due to the molecular diffusion processes displays an upper bound which is proportional to the so-called Fisher information. In the regime at which the one-particle distribution function only depends on particles momentum and time, we show that the factor of proportionality which appears in the upper bound is essentially the time integral of the force autocorrelation function between particles. Besides the parameters of the interparticle potential found through molecular dynamics simulations, we find the time scale of particles’ thermalization and therefore the approach to equilibrium for the system.

The explicit dependence of the thermal diffusion factor with respect to composition and interaction parameters for the van der Waals binary mixture is obtained in the framework of the mean-field kinetic variational theory and in the scheme of Scott and van Konynenburg. Here, we present a numerical study where the global behavior of the thermal diffusion factor is described in terms of molecular masses, sizes, and interaction parameters, along the phase diagram of this model mixture. This numerical study allows us to understand what molecular parameters modify the sign of the thermal diffusion factor. In addition, a comparison is made between the thermal diffusion factor coming from the van der Waals mixture and from the hard-sphere mixture.

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Cordia globosa is used to treat gastrointestinal diseases in San Rafael Coxcatlan, Puebla, Mexico; however, its medicinal properties have not been investigated. This study reports the chemical composition and the antimicrobial effect of C. globosa essential oil. The essential oil of aerial parts was obtained by steam distillation and 25 compounds were identified by gas chromatography-mass spectrometry (GC-MS). The major constituent was α-pinene (38.4%). Antimicrobial activities were tested on 6 bacterial and 9 fungi strains. The most sensitive strain was Vibrio cholera (minimum inhibitory concentration [MIC], 0.060 mg/ml). These results show the chemical composition and biological properties of essential oil of C. globosa. The results validate the medicinal use of C. globosa.