BEHAVIOR OF ANIONIC SURFACTANT MICELLES IN THE PRESENCE OF Al3+ AND Ca2+

The estimation of the C-potential of ionic surfactant micelles may be useful for the study of adsorption of solutes onto the micellar surface, which causes a reduction of the net electrostatic charge. This work presents results on the variation of ζ-potential of alkylsulfate and fatty carboxylate micelles with the bulk concentrations of Al³⁺ and Ca²⁺ cations. Combined with results from the literature about the effect of micellar surfactant concentration on reducing surfactant precipitation in the presence of polyvalent cations, these allow to conclude that micelles of anionic surfactants will have a higher chance of electroneutralization of their surface charge by adsorbing cations if the end functional group of the surfactant is smaller.     

Effect of pH on the Flocculation of SDS Micelles by Al3+

SDS micelles flocculate in the presence of Al³⁺, creating an aggregate with pollutant-removing properties. The fraction of SDS micelles flocculating depends on the concentrations of SDS and Al³⁺. This paper describes how this fraction also changes with pH. There are two reasons for this dependence: a change in pH has a strong effect in the solution chemistry of Al³⁺, converting it into the compound [Al₁₃O₄(OH)₂₄]⁷⁺, a strong flocculant, or precipitating it as Al(OH)₃; and at low pH protons may compete with Al³⁺ as binding counter-ions for micelles. An increase in pH allows flocculation of SDS at high concentrations of Al³⁺, which under unmodified pH does not occur. Micelle flocculates are reported in this work to exist between pH 5 and pH 8, suggesting the potential use of Adsorptive Micellar Flocculation for the removal of anionic pollutants from waste waters not necessarily limited to acidic solutions. Received: 18 August 2000 Accepted: 5 October 2000     

STUDY OF THE MECHANISM OF 12C（d,d）12C AND 12C（d,p）13C* REACTIONS

A formalism for studying the interference between the direct reaction and the compound resonance processes is presented by the S-matrix theory; The mechanism of ¹²C（d, d） ¹²C, ¹²C（d, p₁） ¹³C* and ¹²C（d, p₂） ¹³C* reactions in the energy range E_d=1.63 MeV to 2.05 MeV is analysed.Te results show that: the interference between these two processes exists; and the quantitative relation between them is given. While the parameters of direct reactions and compound resonance processes, particularly for four resonance states with E_d=1.726, 1.767, 1.792 and 1.86 MeV are determined.     

Combining rule for interaction energies of the (CO)2, (N2)2 and CO-N2 complexes

The relationship between interaction energies of the most stable structures of the (CO)₂, (N₂)₂ and CO-N₂ complexes is investigated using the supermolecule CCSD(T) and MP4 methods and aug-cc-pVXZ (X = D,T,Q) basis sets extended by a set of midbond functions centred in the middle of the intermolecular bond. A simple combining rule for interaction energies of this triad of clusters is proposed.     

Flocculation of anionic surfactant micelles in the presence of hydrocarbons

Adsorptive micellar flocculation (AMF) is a surfactant-based separation process based on the flocculation of micelles of suitable anionic surfactants by Al³⁺. The micelles form large amorphous flocs which can be removed by filtration, which is attractive because soluble pollutants are captured by the floc, thus providing a simple separation method. As the primary aim of AMF is the removal of anionic pollutants from aqueous streams, it is important to investigate the influence of the various substances which may affect it. This article discusses the influence of the presence of insoluble hydrocarbons on the flocculation of micelles of the anionic surfactant dodecyl sulfate by Al³⁺. The ratio between surfactant remaining in solution and total surfactant and the ratio between Al³⁺ and surfactant in the flocculate are determined in systems composed of an aqueous solution containing a constant dodecyl sulfate concentration of 0.05 M and a variable Al³⁺ concentration and an organic phase (decane) with phase volume ratios of decane/water ranging from 0 (no decane) to 0.15. The flocculation is only slightly affected by the presence of decane for decane/solution ratios below 0.05, while the effect (lower flocculated fraction) is more marked above this ratio. Received: 25 October 1999/Accepted: 7 February 2000     

ADSORPTION DYNAMICS OF MACROPOROUS POLYMERIC ADSORBENT Ⅱ. The Studies on the Film Diffusion Mass-Transfer Process

1 INTRODUCTIONAt present time, most of the studies for the adsorption dynamics of macroporous adsorbent,.especially for the film diffusion mass-transfer process, were based on the conclusions for theBoyd ion-exchange dynamics equationl'l. The structure of gel-type ion-exchange resin andmacroporous polystyrene resin is different. Because of having the hydrophilic group, both of theirmer and outer of the ion-exchange resin can swell to the reticulation struCture in the aqueous.Based on the…     

On the concept of critical surface excess of micellization

The critical surface excess of micellization (CSEM) should be regarded as the critical condition for micellization of ionic surfactants instead of the critical micelle concentration (CMC). There is a correspondence between the surface excesses Γ of anionic, cationic, and zwitterionic surfactants at their CMCs, which would be the CSEM values, and the critical association distance for ionic pair association calculated using Bjerrum's correlation. Further support to this concept is given by an accurate method for the prediction of the relative binding of alkali cations onto dodecylsulfate (NaDS) micelles. This method uses a relative binding strength parameter calculated from the values of surface excess Γ at the CMC of the alkali dodecylsulfates. This links both the binding of a given cation onto micelles and the onset for micellization of its surfactant salt. The CSEM concept implies that micelles form at the air-water interface unless another surface with greater affinity for micelles exists. The process would start when surfactant monomers are close enough to each other for ionic pairing with counterions and the subsequent assembly of these pairs becomes unavoidable. This would explain why the surface excess Γ values of different surfactants are more similar than their CMCs: the latter are just the bulk phase concentrations in equilibrium with chemicals with different hydrophobicity. An intriguing implication is that CSEM values may be used to calculate the actual critical distances of ionic pair formation for different cations, replacing Bjerrum's estimates, which only discriminate by the magnitude of the charge.