Thermodynamics of micellization at charged interphases within the framework of the phase-separation model

Abstract

8453that give rise to the model, are not predicted to be especially important in the overall energy transfer (in the same way that individual solvent molecule/particle collisions in macroscopic Brownian motion do not contribute much to the overall diffusive motion): indeed, in the most primitive version of the model, the average energy transfer is Seen to be completely independent of the highest-frequency modes of the substrate.1° ConclusionsTrajectory calculations and the BRW model agree with experiments on related systems: that there should be only a small isotope effect in the energy transfer between highly excited azulene and monatomic bath gases. This suggests that the low-frequency modes have an important role to play in determining the amount of energy transfer. In particular, the lack of any strong effect with helium suggests that classical calculations can provide an adequate representation, and the poor accord between experiment and trajectory results for light bath gas= is due to the poor description of the interaction potential. The results also predict that isotopic substitution should not have a strong effect on the fraction or the magnitude of supercollisions. Acknowledgment.An application of classical thermodynamics is made in the case of surface phase transitions occurring throughout a charged interphase. This kind of surface phase transitions characterizes the aggregation of micelle-forming surfactants within the interphase formed between electrolyte solutions and an ideally polarized electrode, at least at concentrations higher than the critical micelle concentration. On the basis of a multilayer model for the electrical double layer, the thermodynamic conditions for its stability and the reversibility of a pbseparation proc~ss which extends along the double layer are established. It is further shown that a rigorous but sufficient thermodynamic criterion for a surface micellization to take place across a charged interphase is the existence of two deformed peaks in the differential capacity versus applied potential curves on both sides of the adsorption maximum. The peaks may have comers and/or abrupt vertical segments and they may be split into two or more parts. Moreover, due to hysterisis phenomena their shape may depend on the potential scan rate and scan direction. Some expected deviations from the above criterion are also discussed.

Study of Oleate Adsorption at the Mercury/Electrolyte Solution Interface as a Function of Electrode Potential and Time

“…Second, although the width of the capacitance pit increases with increasing concentration at negative potentials, as expected for a compact layer, the opposite trend is observed at the positive end of the capacitance pit (a trend confirmed for all concentrations studied in the 1 × 10 -5 to 1 × 10 -4 M range). As described in refs and , the transformation of an adsorbed layer which consists of close-packed patches of associated adsorbate molecules (surface aggregates or micelles) rather than a continuous single-entity layer is expected to give rise to bell-shaped peaks of finite height as the ones shown in Figure . At a molecular level, one could speculate that the oleate molecules have a vertical orientation with the hydrocarbon tails in contact with the mercury surface and their charged carboxylate tail in contact with the aqueous solution.…”

“…The variation of the C vs E curves with time is even more pronounced at extreme polarizations where the shape, height, and position of the capacitance peaks are seen to be critically dependent on time. This suggests once again that if the characteristics of these peaks are to be correlated to the oleate bulk cmc according to the empirical criteria developed by Volldhart, Dörfler, and Müller − or interpreted according to the theory of phase transitions involving surface aggregates developed by Nikitas 24 and Nikitas et al, then only the long-time curves can safely be considered as near-equilibrium ones. This makes the use of a dropping mercury electrode (DME) whose mercury drop lifetime rarely exceeds 10 s and is usually never longer than 5 s, completely inadequate for the study of slowly proceeding adsorption/phase transition phenomena.…”

“…The aim of the present work is dual. First of all, by the near-equilibrium C vs E curves we intend to deduce the surface state of the adsorbed oleate on Hg based on the thermodynamic criteria described in refs and and to investigate whether there is any correlation (apparent or other) between the bulk cmc value and the adsorption behavior of oleate. Second, by studying the C vs t curves, i.e., the evolution of the phenomenon with time, we seek to gain information about the mechanism of the adsorption/phase changes and investigate whether simple diffusion or adsorption kinetics or the Avrami formalism for phase transitions are followed.…”

Synthesis and electrochemical behaviour of new electroreducible amphiphilic saccharide derivatives

“…20 For disaccharidic compounds, a split of the capacity peak is observed at c \ 1 ] 10~3 M for MALTACO8 and c \ 5 ] 10~4 M for MALTACS8. As proposed by Nikitas et al,30,31 this splitting, which appears above the CMC, is related to the formation of multilayers of micelles on the electrode surface. According to our previous observations with non-reducible disaccharidic surfactants,20 these concentrations should approach the value of the CMC of MALTACO8 and MALTACS8.…”

Complex voltammetric and fractal study of adsorbed layer’s structure of pure Triton-X-100 and in mixture with o- or p-nitrophenol

“…Also, chronoamperometric measurements had not provided any evidence of nucleation processes [22]. Such behavior is usually associated with the transformation of an adsorbed layer that consists of close-packed patches of associated adsorbate molecules, rather than continuos single entity layer [23,24].…”