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Interaction between the anionic double tail AOT (sodium bis (ethylhexyl) sulfosuccinate) and the zwitterionic single tail TPS ( N -tetradecyl- N , N -dimethyl-3-ammoino-1-propane sulfonate) in water and at the air/water interface has been studied. The surfactants synergistically interact with the solution as well as at the air/water interface forming mixed assemblies. The physicochemical properties of the free amphiphile monomers up to the point of their critical micelle concentration (CMC) have been evaluated and discussed. The interactions between the two amphiphiles in the mixed micelles in the bulk, and the adsorbed mixed assemblies at the air/solution interface have been analyzed using Rubingh and Rosen formalisms. The mixed systems have been found to undergo composition dependent salt induced micelle → vesicle → micelle forming transitions (MVMT). This has been supported by the fluorescence anisotropy measurements of the DPH probe, and the hydrodynamic diameter determined by the DLS method. Stable vesicle formation has been confirmed from the calcein dye encapsulation experiments, and the high resolution transmission electron microscopy (HRTEM) measurements. Nano-structured gold particles (GNPs) have been synthesized in the pure and mixed micelles of the AOT and TPS by the reduction of the HAuCl 4 by NaBH 4 . The morphology of the nano-structured materials was characterized from the UV and HRTEM measurements.

Entrapping of a fluorogenic material comprising prospective therapeutic activity in microhetrogeneous environments and modulating important photophysical properties is highly desirable as far as potential applications of such systems are concerned. The present work demonstrates the interesting photobehavior of a newly synthesized antioxidative naphthalimide (isoquinolinedione) derivative (ANAP) in micellar solutions of anionic sodium dodecyl sulphate (SDS), cationic cetyl trimethylammonium bromide (CTAB) and nonionic p-tert-octylphenoxy polyoxyethanol (TX-100) surfactants using steady-state, time-resolved fluorescence and fluorescence anisotropy techniques. The remarkable sensitivity of the fluorescence properties of ANAP to the polarity of the media is attributed to the existence of a fluorescent intramolecular charge transfer (ICT) state. ANAP is found to be an excellent fluorescence sensor for following the micellar aggregation process. Fluorometric studies suggest that the probe resides at the micelle–water interface in all these systems. The present effort endeavors the degree of accessibility of the fluorophore toward the metal ion quencher in the presence of micelles of different surface charge characteristics. The enhancements in the steady-state anisotropy and rotational relaxation time in the micellar media compared to that in pure aqueous solution reflect that the fluorophore resides in a motionally restricted environment introduced by the micelles.

Fluorescence resonance energy transfer (FRET) between anionic probe 1-anthracene sulphonate (1-AS) and transport proteins, bovine serum albumin (BSA) and human serum albumin (HSA) solubilized in reverse micelles of sodium 1,4-bis (2-ethylhexyl) sulphosucccinate (AOT) in heptane was studied where the donor and acceptor pair comes in close proximity within the smaller water pools. The mechanism of fluorescence quenching of transport proteins by 1-AS in reverse micelles has been ascribed to the non-radiative energy transfer process. The probable binding site of the probe with proteins has been ascertained from FRET study. Circular dichroism study suggests that the number of folding of the protein increases markedly due to binding of the proteins with 1-AS.

The aggregation of surfactant of polyoxyethylene-p-(1,1,3,3-tetramethylbutyl)phenyl ether (Triton X) series in chloroform has been studied. The critical micellar concentration (cmc) of the reverse micelles formed has been determined by four different techniques. The determined cmc values by various techniques are close to each other and facilitate determination of the free energy change (Δ G ) values associated with the micellization. From the correlation of cmc with hydrophile–lipophile balance (HLB) it was found that cmc decreases with decrease in HLB values. The association constant of the reverse micelle with fluorescent probe 1-anthracene sulphonate (1-AS) and micellar aggregation number has been evaluated. The location of the fluorophore in the reverse micelle and the polarity of the micelle solubilized sites have been determined from the E T (30), Kosower Z , and dielectric constant values. The pH of the aqueous region of reverse micelles has been estimated by comparison method.

The absorption and steady-state fluorescence of a non-amphiphilic derivative of pyrene, Pyrene-1-Carboxaldehyde (1-PyCHO) is sensitive to the probe’s environment. Association of the surfactants in aqueous medium as micelles and mixed micelles has been studied from the photophysical changes of 1-PyCHO in these media. The physicochemical characteristics of the micelles, i.e. CMC, aggregation number have been determined. The obtained CMC values from different methods are close to each other. The association constants of the 1-PyCHO molecules with the non-ionic micelle of Igepal and location of the fluorophore in the micellar environment have been determined. Micropolarity of Igepal micelle and Igepal/Igepal mixed micelle surrounding 1-PyCHO has been ascertained comparing the shift in fluorescence maximum with ET(30) values of standard solutions. © 2007 Elsevier B.V. All rights reserved.

Growth of colloidal ZnS nanoparticles in aqueous solution has been extensively investigated in presence of two water-soluble thiols, cysteine and mercaptoethanol. In addition to controlling the particle size by duration of heating, an effective control over growth rate (dr/dt) was also obtained just by altering the functional groups of thiol-surfactants, even without changing heating rate or temperature. The growth rate was found to vary linearly with the average radius of growing nanoparticles. Higher growth rate for cysteine-capped ZnS NPs was observed which could be attributed to greater specific surface energy at the solvent–NP interface as compared to mercaptoethanol capped ones. Photoluminescence of these nanoparticles was found to be influenced by the concentration and nature of the surfactant molecules. Maximum PLQY of 2.3% and 2.0% was obtained for mercaptpethanol and cysteine capped NPs, respectively at an optimum Zn2+:surfactant molar ratio, 1:1.5. For given particle size, mercaptoethanol-capped ZnS NPs show greater PLQY as compared to cysteine-capped ones. The lower PLQY of cysteine-capped ZnS NPs is attributed to the sulfur vacancy defects, which was not found in case of mercaptoethanol-capped ZnS nanoparticles.

Visible spectra of Safranine T (ST) in anionic reverse micelle (AOT/cyclohexane/water), non-ionic reverse micelle (Igepal CO720/cyclohexane/water) and mixed reverse micelles of AOT/Igepal CO720/cyclohexane/water at different compositions and different ω (=[water]/[surfactant]) have been studied. Charge transfer band of Safranine T in reverse micellar and mixed reverse micellar medium has been isolated both in ground and excited state. Iodide ion induced dynamic quenching at low quencher concentration becomes a combination of both the dynamic and static quenching at high quencher concentration. Iodide ion induced quenching study has been used as a tool to identify the altered interface of AOT/Igepal CO720/cyclohexane/water mixed reverse micelle compared to AOT/cyclohexane/water reverse micelle. Absorption and fluorescence spectra of ST in polyethylene glycol coated interface of AOT reverse micelle has been observed to identify the role of poly(oxyethylene) group of Igepal CO720 on spectral behavior of ST in mixed reverse micelle.

A steady-state fluorescence quenching study has been undertaken to estimate aggregation numbers, N, and the average occupancy number ( n ¯ ) of quencher per micelle and the water pool size, rw, of nonionic surfactant Igepal (polyoxyethylene nonyl phenol), carbon tetrachloride and water reverse micelles at a different [water]/[Igepal] ratio. For the purpose, Safranine T (3,7-diamino-2,8-dimethyl-5-phenyl phenazinium chloride) has been employed as fluorescent probe and iodide, bromide and azide ions as static quencher. The fluorescence quenching data has been exploited to determine the nature and properties of water in the core of reverse micelles (RM), size of the water pool, association of quencher molecule with the RM, the localization of the probe and the distribution of quencher molecule in the quenching sphere. The demarcation of reverse micelles and microemulsion has also been determined.

The fluorescence characteristics of Safranine T (ST) (3,6-diamino-2,7-dimethyl-5 phenyl phenazinium chloride) in presence of thiourea have been studied in reverse micelles of Aerosol–O–T in heptane and in presence of alkanols. From the results of the fluorescence quenching of ST by thiourea the occupancy number of the quencher in the reverse micelle (RM), and the binding constant of the quencher with the RM have been determined using Encinas–Lissi equation. The alkanols added are found to affect the quenching process.