Addition Of AOT Research Articles

Silver nanoparticles stabilized by AOT and Tergitol NP-4 mixture: Influence of composition on electrophoretic concentration, properties of concentrated organosols and conductivity of films

A comparative analysis of the main physico-chemical characteristics of silver nanoparticles produced in mixed reverse micelles of nonionic surfactant Tergitol NP-4 with addition of anionic AOT was carried out. The nanoparticles are shown to have a positive electrokinetic potential. The only exception is nanoparticles synthesized in Tergitol NP-4 reverse micelles without addition of AOT, which have a zero electrokinetic potential. An increase in AOT concentration in the mixture leads to a decrease in the size of particles produced and an increase in the electrokineticpotential. It was shown that silver nanoparticles with close to quantitative extraction rates can be concentrated by non-aqueous electrophoresis with AOT content in mixture equaled 5 mol% and more. For mixture with content of AOT more than 50 mol%, no concentration is observed for surfactants. In the systems with high content of Tergitol NP-4 an increase in the concentration of surfactants is observed compared to the starting organosol. A decrease in AOT concentration leads to a decrease in the stability of the nanoparticles that results in a reversible change in the surface plasmon resonance spectra of nanoparticles under drying and irreversible agglomeration of nanoparticles with a decrease in the surfactant concentration. The presence of reversible agglomeration of the nanoparticles is likely due to the strong negative effect of Tergitol NP-4 on the stability as well as the conductivity and adhesion of coatings produced by thermolysis of the nanoparticle concentrate.

Probing interactions of neurotransmitters with twin tailed anionic surfactant: A detailed physicochemical study

Keeping in view the role of neurotransmitters (NTs) in central nervous system diseases and in controlling various physiological processes, present study is aimed to study the binding of neurotransmitters (NTs) such as norepinephrine hydrochloride (NE) and serotonin hydrochloride (5-HT) with twin tailed surfactant sodium bis(2-ethylhexyl)sulfosuccinate (AOT). Spectroscopic and electrochemical measurements combined with microcalorimetric measurements were used to characterize the interactions between AOT and NTs. Meteoric modifications to emission profile and absorption spectra of NTs upon addition of AOT are indicative of the binding of NTs with AOT. Distinct interactional states such as formation of ion-pairs, induced and regular micelles with adsorbed NTs molecules have been observed in different concentration regimes of AOT. The formation of ion-pairs from oppositely charged NTs and AOT is confirmed by the reduced absorbance, quenched fluorescence intensity and decrease in peak current (ipa) as well as shifts in peak potential (Epa) values. The stoichiometry and formation of the NTs–AOT complexes has been judged and the extent of interactions is quantitatively discussed in terms of binding constant (K) and free energy of binding (ΔG°). The enthalpy (ΔH°mic) and free energy of micellization (ΔG°mic) for AOT in presence and absence of NTs are determined from the enthalpy curves.

Rod-shaped Hydroxyapatite Nanoparticle Formation by Maturation with AOT

Abstract Amorphous calcium phosphate nanoparticles were synthesized by mixing aqueous solutions of Ca(NO3)2 and (NH4)2HPO4. Then the particles were matured with sodium bis(2-ethylhexyl) sulfosuccinate (AOT) at various temperatures. Rod-shaped hydroxyapatite (HAp) nanoparticles were formed at maturation temperature ≥40 °C. These results indicate that addition of AOT not during the particles synthesis but during the maturation at more equal critical temperature is a key to form the rod-shaped HAp nanoparticles using AOT.

Properties and thermal decomposition of polypyrrole prepared in the presence of sodium bis(2-ethylhexyl) sulfosuccinate

Polypyrrole (PPy) was synthesized by chemical oxidative polymerization of pyrrole in aqueous solution containing an oxidant, ferric sulfate, or potassium peroxydisulfate and an anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT). The addition of AOT to the polymerization mixture leads to the incorporation of the anionic surfactant into the structure of the polymer, as well as to its improved conductivity. Non-isothermal thermogravimetry runs revealed that the decomposition of PPy into volatiles is influenced by the presence of AOT, the latter having the stepwise decomposition into volatiles much more pronounced than it corresponds to original ratio of both AOT and PPy in a composite. Non-isothermal thermogravimetry records were analyzed as being composed from 3 independent processes from which the degradation products are formed. They involve AOT and PPy decomposition and ultimately the formation of carbon and inorganic residue.

Adsorption of aerosol OT on alumina from mixtures of water and cyclohexane

The adsorption of sodium bis(2-ethylhexyl)sulfosuccinate (AOT) on alumina from mixtures of water and cyclohexane was studied. Although the adsorption isotherms were Langmuir-type from water or cyclohexane alone, the adsorbed amount of AOT from the mixtures of water and cyclohexane increased sharply at low AOT concentration, then showed a minimum, and then gradually increased again with increasing AOT concentration for all mixed systems. In addition, ESR spectra from methyl 12-doxylstearate adsorbing on the alumina suggested that the order parameters increased with the addition of AOT, particularly at low AOT concentration for lower mixed ratios of water/cyclohexane systems. The adsorption mechanisms of AOT are also discussed.

Conformational studies of the oligomers of L-lysine in reversed micelles

The effect of the chain length on the conformation of oligo-L-lysines (Lys-n, n= 9, 12 and 15) was examined in the reversed micelles of bis(2-ethylhexyl)sodium sulfosuccinate (AOT) in octane by the circular dichroism (CD) measurements. These oligomers seem to take aβ-structure in these systems. The structure-inducing effect of the reversed micelles is enhanced as the molar ratio of water to AOT (w0=[H2O]/[AOT]) becomes smaller. On the other hand, in the aqueous solutions the oligomers having 12 and 15 residues show the conformational transition from random coil toα-helical structure by the addition of AOT, but the short oligomer of 9 residues does not show such a conformational transition.

Conformational studies of basic poly (α-amino acid)s in reversed micelles

The conformation of various basic poly (α-amino acid)s was investigated by CD measurements in aqueous solutions containing bis (2-ethylhexyl)sodium sulfosuccinate (AOT) as well as in the AOT reversed micelles. The addition of AOT into an aqueous solution of poly(L-lysine) induces the conformational transition from coil to ordered structure, followed by aggregation. On the other hand, poly(L-lysine) assumesΒ-structure in the reversed micelles at low wovalue (wo=[H2O]/[AOT]). Similarly to poly(L-lysine), poly(L-ornithine) takes an ordered structure in the aqueous solution containing AOT andΒ-structure in the reversed micelles. In this case, however, these ordered structures are not so stable, compared with that of poly(L-lysine). Poly(L-arginine) undergoes the conformational transition from coil to helix by addition of AOT into the aqueous solution. Further addition of AOT allows transformation intoΒ-structure. Copoly(L-lysyl-L-leucine) with 63% leucine residue was shown to take a stable helical conformation even in pure water. In the reversed micelles, however, this ordered structure is significantly changed probably because the hydrophobic interaction among the leucyl residues is lowered in the reversed micelles.