Adsorption of the Dyes (Methylene Blue and Acridine Orange and Their Mixtures) from Aqueous Solutions on Cholesterol Surface

The adsorption of the dyes, methylene blue and acridine orange, from their aqueous solutions individually as well as in mixtures were investigated with respect to the variation of temperature and concentration of the KCl and the bile salt, sodium cholate. The features of different isotherms were presented and discussed. The isotherms obtained differ from those described by the Langmuir equation. The adsorption process was controlled by the ion-dipole and hydrophobic interactions. While KCl retarded the adsorption, the bile salt enhanced the process due to synergistic effect.     

Interaction of acridine orange monohydrochloride dye with sodiumdodecylsulfate, (SDS) cetyltrimethylammoniumbromide (CTAB) and p-tert-octylphenoxypolyoxy ethanol (Triton X 100) surfactants

Summary Results of spectrophotometric, conductometric and dialysis studies on the interaction of acridine orange monohydrochloride dye with sodiumdodecylsulfate (anionic), cetyltrimethylammoniumbromide (cationic) and Triton X 100 (nonionic) surfactants have been reported. The anionic surfactant, SDS has been observed to undergo both electrostatic and hydrophobic interactions with the dye cation. Aggregation of the dye molecules can be destroyed when the surfactant is in large excess, whereas, excess dye can check micellization of SD S. At a ratio of AO:SDS=1:7 and above, dye embedded mixed micelles are formed. These remain in a separate phase, probably as coacervates. At lower ratios than 1:7, aggregation of dye molecules is induced, which being complexed with SDS become stabilized as colloids. The colloid and the coacervate have been observed to be thermally stable, negatively charged materials that can be broken by salts, and cations of higher valency are more effective in this regard. An 1:3 = AO:SDS colloid has beeen found to be sufficiently large like the coacervates to pass through a membrane having cut off permeability for molecular weights 12,000 and above. All the above features of AO-SDS interaction have been observed to be absent for AO-CTAB and AO-TX 100 systems, Even hydrophobic interaction has played an insignificant role in these cases. Thus, the dye cation, the cationic and the nonionic surfactants have almost retained their self physicochemical identities in solution in the presence of each other. Electrostatic interaction is thus the primary requirement for acridine orange-surfactant (anionic) system; the hydrophobic effect is secondary and may become co-operative.With 9 figures and 2 tables     

Physicochemical Investigations on the Interaction of Surfactants and Salts with Polyvinylpyrrolidone in Aqueous Medium

Microcalorimetric investigations have been carried out onthe interaction of the surfactants sodium cholate, sodium deoxycholate, tetradecyltrimethylammonium bromide, cetyl(hexadecyl)trimethylammonium bromide, and p-tert-octylphenoxy polyoxy-ethylene ether (Triton X-100) and the salts potassium iodide, sodium benzoate, sodium bromide, and sodium salicylate with the neutral polymer polyvinylpyrrolidone (PVP). The enthalpy of dilution of the surfactants has been measured in the absence and presence of the polymer and the results are compared to determine the effect of PVP on the micellization of the surfactants and the energetics of the process. As well, the micellization activity of the surfactants in the presence of the polymer has been studied by conductometric and fluorimetric methods. The enthalpy of dilution of the salts has been measured to provide an understanding of the nature and magnitude of their interaction with PVP. Copyright 2001 Academic Press.     

Counterion binding behaviour of micelles of sodium dodecyl sulphate and bile salts in the pure state,in mutually mixed states and mixed with a nonionic surfactant

The counterion binding behaviour of micelles of sodium dodecyl sulphate (SDS) and several bile salts in the pure state have been studied, as well as in mutually mixed states, and in a mixed state with polyoxyethylene sorbitan monolaurate (PSML) as a nonionic surfactant. Electrochemical measurements have shown no counterion binding by the pure bile salt micelles and their mixtures with PSML; they can bind counterions when mixed with SDS, whereas the surfactant anions of SDS micelles bind counterions in the pure state and/or in mixed states with PSML. In the SDS-PSML and SDS-bile salts combinations, the counterion association is decreased by the increased proportions of the second component. The extent of counterion binding by the different systems is presented.     

Interaction between sodium dodecyl sulfate (SDS) and polyvinylpyrrolidone (PVP) investigated with forward and reverse component addition protocols employing tensiometric, conductometric, microcalorimetric, electrokinetic, and DLS techniques

The interaction between polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate (SDS) after the procedure of addition of the surfactant to polymer and the reverse procedure of addition of polymer to SDS micelles has been studied by tensiometric, conductometric, and microcalorimetric methods. The results have been analyzed and correlated with reference to SDS interfacial adsorption, association, and binding to PVP. Two aggregation states of SDS in presence of PVP have been found. The enthalpies of formation of SDS aggregates/micelles and their binding to the polymer have been evaluated. The interaction of PVP with SDS at concentrations below its critical micellar concentration (CMC) and above have evidenced distinctions. The forward addition protocol (FAP, SDS addition to PVP) and reverse addition protocol (RAP, PVP addition to SDS) have shown similarities and differences. Electrokinetic measurements have evidenced the interacted (SDS–PVP) colloidal products to possess negative zeta potential in the range of −39 to −65 mV. The hydrodynamic diameters of the PVP–SDS dispersion obtained from DLS measurements have ranged between 60 and 160 nm. Both zeta potential and hydrodynamic diameter have depended on [SDS] showing a maximum for the former at twice the critical micellar concentration of SDS.     

The k-essence scalar field in the context of Supernova Ia observations

We study a framework where the hypothesis of a minimum length in space-time is complemented with the notion of reference frame invariance. It turns out natural to interpret the action of the obtained reference frame transformations in the context of doubly special relativity. As a consequence of this formalism we find interesting connections between the minimum length properties and the modified velocity-energy relation for ultra-relativistic particles. For example, we can predict the ratio between the minimum lengths in space and time using the results from OPERA on superluminal neutrinos.     

Interfacial Behavior,Structure, and Thermodynamics of Water in Oil Microemulsion Formation in Relation to the Variation of Surfactant Head Group and Cosurfactant

Interfacial behavior, structural, and thermodynamic parameters in relation to the formation of water-in-oil (w/o) microemulsion (μE) with varied surfactant head groups and cosurfactants have been evaluated through dilution technique at different temperature and [water]/[surfactant] mole ratio. Dodecyltrimethylammonium bromide (DTAB), sodium dodecylsulphate (SDS), and polyoxyethylene sorbitan monolaurate (Tween-20) were used as surfactants and n-butanol and n-pentanol were used as cosurfactants. Distribution of cosurfactants between bulk oil and the interface using fixed amount of surfactant at varied [water]/[surfactant] mole ratio and temperature has been studied to evaluate thermodynamic parameters. Associated structural parameters, such as droplet dimension and aggregation number of surfactant and cosurfactant at the droplet interface, have also been evaluated. Spontaneity of the μE formation followed the order DTAB>SDS>Tween-20 for both butanol and pentanol in the studied range of temperature. Correlations of the results in terms of the evaluated physicochemical parameters have been attempted.     

JR 400–NaAOT interaction: a detailed thermodynamic study of polymer–surfactant interaction bearing opposite charges

The present study entails interaction between the cationic polymer N,N-dimethylhydroxyethyl cellulose (JR 400) and the double-tailed anionic surfactant Na-bis-2-ethyhexylsulphosuccinate (NaAOT). This oppositely charged polymer and surfactant are expected to cause coacervation and precipitation; hence, we have observed formation of thick solution similar to diluted gel at [JR 400]?~?0.01 and 0.10 %?w/v in aqueous solution. Viscometry, conductometry, tensiometry, and microcalorimetry techniques are used to monitor the interaction process. The results are explained in the light of both intrachain and interchain linking by way of NaAOT reverse micelle formation. Adsorption of NaAOT monomers onto the charged side chains of the polymer shields interchain electrostatic repulsion, leading to the formation of hydrophobic microdomains and microscopic heterogeneity in the solution. The morphologies of the domains depend on the level of addition of NaAOT in the system. The different stages of physiochemical changes that arise in solution have been identified by the use of different techniques, and correlations of the results have been attempted in terms of pragmatic models.     

Dye sensitization of a large band gap semiconductor by an iron(III) complex

The Fe(III) complex, [Fe^III(HQS)₃] (HQS = 8-hydroxyquinoline-5-sulfonic acid), is found to effect sensitization of the large band gap semiconductor, TiO₂. The role of interfacial electron transfer in sensitization of TiO₂ nanoparticles by surface adsorbed [Fe^III(HQS)₃] was studied using femtosecond time scale transient absorption spectroscopy. Electron injection has been confirmed by direct detection of the electron in the conduction band. A TiO₂-based dye-sensitized solar cell (DSSC) was fabricated using [Fe^III(HQS)₃] as a sensitizer, and the resulting DSSC exhibited an open-circuit voltage value of 425 mV. The value of the short-circuit photocurrent was found to be 2.5 mA/cm². The solar to electric power conversion efficiency of the [Fe^III(HQS)₃] sensitized TiO₂-based DSSC device was 0.75 %. The results are discussed in the context of sensitization of TiO₂ by other Fe(II)-dye complexes.     

Scheduling control for Markov-modulated single-server multiclass queueing systems in heavy traffic

This paper studies a scheduling control problem for a single-server multiclass queueing network in heavy traffic, operating in a changing environment. The changing environment is modeled as a finite-state Markov process that modulates the arrival and service rates in the system. Various cases are considered: fast changing environment, fixed environment, and slowly changing environment. In all cases, the arrival rates are environment dependent, whereas the service rates are environment dependent when the environment Markov process is changing fast, and are assumed to be constant in the other two cases. In each of the cases, using weak convergence analysis, in particular functional limit theorems for Poisson processes and ergodic Markov processes, it is shown that an appropriate “averaged” version of the classical \(c\mu \) -policy (the priority policy that favors classes with higher values of the product of holding cost \(c\) and service rate \(\mu \) ) is asymptotically optimal for an infinite horizon discounted cost criterion.