Enthalpy Of Micellization Research Articles

Comparative Thermodynamic Studies of the Micellization of Amphiphilic Block Copolymers before and after Cyclization.

The enthalpy and entropy of micellization in water, ΔHmic and ΔSmic, respectively, of three linear amphiphilic BAB block copolymers consisting of either poly(methyl acrylate) (Mn ∼ 1200 and 700 Da) or poly(ethyl acrylate) (Mn ∼ 800 Da) as hydrophobic (B) segments and poly(ethylene oxide) (PEO) as the hydrophilic (A, Mn ∼ 3000 Da) segment were determined by isothermal titration calorimetry (ITC). The ΔHmic and ΔSmic of the cyclic AB block copolymers obtained by cyclization of the linear triblock copolymers were determined under the same conditions. The ΔHmic value of the cyclic copolymers was smaller than that of their linear precursors. The ΔSmic value showed the same trend, but the relative difference between the cyclized and linear copolymers was less pronounced. The hydrodynamic diameter (Dh), critical micelle concentration (CMC), molecular weight (Mw-mic), and second virial coefficient (A2) of the micelles were determined. The Dh value of the cyclic copolymer micelles was smaller than the linear counterpart. On the other hand, the CMC value became larger, whereas the A2 value was comparable or increased by cyclization. Overall, the results suggest that, in the unimer state, the hydrophobic segments of the cyclized copolymers form a tightly coiled structure to minimize contact with water, resulting in the smaller ΔHmic value. Contrary to the linear copolymer micelles, the cyclic copolymer micelles have no "dangling chains", which may explain the topology-driven slight difference in the ΔSmic value.

Transition from antagonistic to synergistic interaction in mixed micellar system by increase in alkyl chain length of alkyl trimethylammonium bromide

Herein, the electrical conductivity technique used to measure the critical micelle concentration (cmc) for pure cationic surfactants (Dodecyl/cetyltrimethylammonium bromides) and phenothiazine drug (Promethazine hydrochloride), as well as their different mole fractions in 10−3 ​mol/kg 1-methyl-3-octylimidazolium chloride (C8mim.Cl) at different temperatures. By using the cmc values the regular solution theory used to evaluate the micellar mole fraction for DTAB/CTAB-PMT mixed systems. The clint's model used to calculate the ideal critical micelle concentration (cmc∗) that helps to evaluate the ideal micellar mole fraction for studied mixed systems, both explain the deviation from ideality. In addition, interaction parameter βm helps to confirm the nature of interaction (either antagonistic or synergistic) for the studied systems. The calculated parameters confirm a transition in the binding nature from antagonistic to synergistic with the increase in alkyl chain length of cationic surfactant i.e., component of the binary mixed system. The ease of micellization for the studied systems discussed by the standard Gibb's energy of micellization (ΔGm0), as well as the standard enthalpy and standard entropy of micellization were (ΔHm0) and (ΔSm0), respectively to discuss the stability of the studied systems.

Encapsulation of ethyl violet by anionic-cationic mixed micellar solution: Spectroscopic and conductometric studies

Organic dyes are extensively used in various industries i.e. textile. Their hydrophobicity is the main bottleneck in their applications, where the dispersion medium is water. The poor solubility of such colorants is addressed by the addition of different surfactants, but none of the single surfactants proved fully satisfactory so far. Herein, different formulations of anionic and cationic surfactants (SDS, SDBS, CTAB, and TTAB) have been employed to enhance the solubility and stability of a cationic dye, ethyl violet (EV). Spectrophotometric data helped to calculate the values of the partition coefficient (K x ), binding constant (K b ), and Gibbs energies of respective processes. The said parameters are indicators of the degree of solubilization which were calculated at 298.15 K. The data of specific conductance was utilized to estimate critical micelle concentration (CMC) and to calculate thermodynamic parameters; Gibbs energy (ΔG m ), entropy (ΔS m ), and enthalpy (ΔH m ) of micellization for surfactants in the presence of dye at different temperatures (303.15–318.15 K). The obtained results from both techniques revealed the spontaneous nature of micellization and solubilization. Furthermore, the binding and partitioning ability of mixed micellar media came out to be significantly different than that of the solo surfactant system due to the synergistic effect of cationics on micellar media of anionics. It shows how dye is lying inside the SDS and SDBS micelle. • Locus of incorporated dye is near water-micelle interface. • Charge density of a micelle governs its solubilizing efficacy. • Mixing of different surfactants has a synergistic effect on solubilizing power.

Impact of ethanol and NaCl on the acid yellow dye mediated self-aggregation of sodium dodecyl sulfate: A combined investigation by conductivity and molecular dynamics simulation

Herein, we report the micellization behavior of the mixture of sodium dodecyl sulfate (SDS), and acid yellow (AY) dye in water, water + ethanol, and water + NaCl media. The degree of interaction between SDS and AY has been assessed quantitatively from the estimated values of critical micelle concentration (cmc). Three cmc values were observed for the AY + SDS systems at each temperature and solvents utilized, which exhibit a reversed U-shaped variation with respect to the change of temperature in aqueous/NaCl solution while increased monotonically in ethanolic medium almost in all cases. The extent of micellization was found to be disfavored in presence of AY dye. The micellization was also found to be disfavored up to 15% ethanol and favored in the addition of electrolyte species. The values of counterion binding were found to be temperature dependent. The Gibbs free energy (ΔGmo), which was found negative, reveal a spontaneous micellization of AY + SDS system. The other thermodynamic parameters, like enthalpy (ΔHmo) and entropy (ΔSmo) of micellization along with different transfer energies, were also assessed to have an insight on the mode of interaction of surfactant and dye assemblies. The molecular level interaction between SDS and AY has been unveiled by Molecular Dynamics (MD) simulation and exhibits good agreement with experimental results.

Interaction of crystal violet dye with dodecyltrimethylammonium bromide in aqueous and electrolyte medium at different temperatures

Dyeing is one of the most important processes in the textile industries which require optimum binding of dye with the fabrics. In the binding phenomenon of dye with the fabrics, surfactants play a significant role. The presence of different auxiliaries modifies the dye-surfactant interaction which can influence the binding of dye with the fabrics. Herein, we studied the interaction of crystal violet (CV) dye with a cationic surfactant, dodecyltrimethylammonium bromide (DTAB) conductometrically in absence and presence of electrolytes (NaBr, Na2SO4, and Na3PO4). The critical micelle concentration (cmc) of DTAB was found to dwindle with the boost of concentration of CV. The cmc of CV + DTAB mixtures were monotonically increased with the increase of temperature. The presence of electrolytes facilitates the micellization of CV + DTAB mixture. The values of counterion binding were found to be augmented with the augmentation of temperature in aqueous and NaBr media while the opposite trend was observed in Na2SO4 and Na3PO4 media. The Gibbs free energy of micellization (ΔGm0) were found to be negative in all cases. The enthalpy (ΔHm0) and entropy (ΔSm0) of micellization were negative and positive in aqueous, NaBr, and Na2SO4 media while both values were positive in Na3PO4 medium. The enthalpy–entropy compensation parameters suggest that the most stable micelle of CV + DTAB is formed in Na2SO4 medium.

The effect of erythrosine-B on the structuration of poloxamer 407 and cellulose derivative blends: In silico modelling supporting experimental studies

Erythrosine is a dye approved for medical use that has shown promising photodynamic activity, allowing for the inactivation of microorganisms and activity against malignant cells. Despite the great photodynamic potential, erythrosine exhibits hydrophilicity, negatively impacting its action in biological membranes. Therefore, the incorporation of erythrosine in micellar polymeric systems, such as poloxamers, may overcome this limitation. Moreover, using bioadhesive and thermoresponsive polymers to combine in situ gelation and bioadhesion may enhance retention of this topically applied drug. In this work, mucoadhesive and thermoresponsive micellar systems were prepared containing erythrosine in two states: the native form (ERI) and the disodium salt (ERIs). The systems were evaluated based on the effect of ERI/ERIs on the micellar structure of the binary polymer mixtures. Optimised combinations of poloxamer 407 (polox407) and mucoadhesive sodium carboxymethylcellulose (NaCMC) or hydroxypropyl methylcellulose (HPMC) were used as micellar systems for ERI or ERIs delivery. The systems were studied with respect to theoretical interactions, qualitative composition, morphology, and micellar properties. In silico modelling indicated a higher interaction of the drug with poly(ethylene oxide) (PEO) than poly(propylene oxide) (PPO) fragments of polox407. Systems containing NaCMC displayed a repulsive effect in the presence of erythrosine, due to the polymer's charge density. Both systems could convert the photosensitizer in its monomeric form, ensuring photodynamic activity. In these mixtures, crystallinity, critical micellar temperature and enthalpy of polox407 micellisation were reduced, and micellar size, evaluated by transmission electron microscopy (TEM), showed low impact of ERI/ERIs in HPMC preparations. Aiming toward photodynamic applications, the findings showed how ERI or ERIs can affect the micellar formation of gels composed of 17.5% (w/w) polox407 and 3% (w/w) HPMC or 1% (w/w) NaCMC, important for understating their behaviour and future utilisation as erythrosine delivery systems.

Interactions of tricyclic antidepressant drug chlomipramine hydrochloride with imidazolium based surface active ionic liquid in aqueous solution

Tricyclic antidepressant drug, Chlomipramine hydrochloride (CLP) with surface active ionic liquid (SAIL), 1-octyl-3-methylimidazolium chloride, was investigated using electrical conductivity. Various theoretical models were employed to calculate various interaction parameters and thermodynamic parameters. Different mole fractions of CLP with SAIL were studied to evaluate the critical micelle concentration (CMC) using electrical conductivity measurements. The change in Gibbs free energy of micellization, change in enthalpy of micellization, change in entropy of micellization, micellar mole fraction, χ1, of the CLP, and the interaction parameter, β, activity coefficients ƒ1 and ƒ2were calculated. The χIdeal and χ1 values were observed to increase on increasing the mole fraction of CLP from 0.4 to 0.6. This may be an indication of drug molecules being adsorbed on the micellar surface. As a result the mixed system (CLP and SAIL) were found to form stable mixed micelles.

Micellization, acoustic and thermodynamic study of procaine in aqueous solution at different temperatures

Critical micelle concentrations (CMC) of procaine hydrochloride (PHCl) in aqueous solution has been determined from conductivity (κ), density (ρ) and speed of sound (u) measurements using Williams and Philips methods at the temperature range 298.15–318.15 K intervals of 5 K.The CMC values found by these two methods using the speed of sound, density and conductivity data were in good agreement at all temperature. As the applied temperature increases, the CMC increases, owing to the lower probability of hydrogen bond formation at higher temperatures.The obtained values of the standard Gibbs energy of micellization (ΔGmo) and the standard enthalpy of micellization (ΔHmo) are negative at all investigated temperatures. Thus, one can say that the micellization process and the relationship between drug-water interactions and solute-solute interactions occur at different temperatures. Negative ΔGmo values were recorded when the systems become more hydrophobic. The negative increase in ΔHmo by the increased temperatures can be explained by the exothermic nature of the micellization process. The obtained values of the entropy for micellization (ΔSmo) are positive at all temperatures. The ΔSmo values decrease with temperature increase, this result interpreted as micellazation tend to be energy driven at higher temperatures.Apparent molar volume (V∅), apparent molal volumes at ınfinite dilution (V∅0), micellar apparent molal volumes (V∅mic), changes in apparent molal volumes upon aggregation (ΔVm), apparent molar isentropic compressibilities (K∅(S)), isentropic apparent molal adiabatic compressibilities at infinite dilution (K∅(S)0), micellar ısentropic apparent molal adiabatic compressibilities (K∅(S)m) and changes in isentropic apparent molal adiabatic compressibilities (ΔK∅(S)) of procaine in aqueous solution have been calculated by combining the speed of sound and density measurements. ΔVm are estimated and found to be negative except for 0.43 m3mol−1 (maximum value) at 318.15 K. The variations in these parameters were discussed for micellization process and drug-water interactions and solute-solute interactions at different temperatures.

Complex Micellization Behavior of the Polysorbates Tween 20 and Tween 80.

Polysorbates (PSs, Tweens) are widely used surfactant products consisting of a sorbitan ring connecting up to four ethylene oxide (EO) chains of variable lengths, one or more of which are esterified with fatty acids of variable lengths and saturation degrees. Pharmaceutical applications include the stabilization of biologicals in solutions and the solubilization of poorly water soluble, active ingredients. This study characterizes the complex association behavior of compendial PSs PS20 and PS80, which is fundamentally different from that of single-component surfactants. To this end, a series of demicellization experiments of isothermal titration calorimetry with different PS concentrations are evaluated. Their experiment-dependent heats of titration are converted into a common function of the state of a sample, the micellar enthalpy Qm(c). These functions demonstrate that initial micelles are already present at the lowest concentrations investigated, 2 μM for PS20 and 10 μM for PS80. Initial micelles consist primarily of the surfactant species with the lowest individual critical micelle concentration (cmc). With increasing concentration, the other PS species gradually enter these micelles in the sequence of increasing individual cmc's and hydrophilic-lipophilic balance. Concentration ranges with pronounced slopes of Qm(c) can be tentatively assigned to the uptake of the major components of the PS products. Micellization and the variation of the micelle properties progress up to at least 10 mM PS. That means the published cmc values or ranges of PS20 and PS80 may be related to certain, major components being incorporated into and forming specific micelles but must not be interpreted in terms of an absence of micelles below and constant properties, e.g., the surface activity, of the micelles above these ranges. The micellization enthalpy curves differ quite substantially between PS20 and PS80 and, in a subtler fashion, between individual quality grades such as high purity, pure lauric acid/pure oleic acid, super-refined, and China grade.

Thermodynamics of Micellization of Ionized Surfactants: The Equivalence of Enthalpies of Micellization from Calorimetry and the Variation of Critical Micelle Points with Temperature as Exemplified for Aqueous Solutions of an Aliphatic Cationic Surfactant

There is considerable confusion on experimental and thermodynamic aspects of the formation of ionized surfactant micelles. Recent claims that the van't Hoff and calorimetric enthalpies of micellization of ionized surfactants represent different aspects of micellization are shown to be incorrect. New conductance and surface tension measurements on n-dodecyltrimethylammonium bromide (DTAB) in water and in cosolution with 0.1 M KBr over a range of temperatures are used to provide a set of critical micelle concentrations (cmc's). The molar enthalpies of micellization derived from these cmc's are compared with calorimetric enthalpies of micellization obtained from a critical survey of the literature and shown to be equivalent. This signifies that both enthalpies capture the contributions from all aspects of micellization of charged micelles. The apparent discrepancies arise from experimental problems, incorrect use of the van't Hoff equation, and failure to recognize the constraints of the Phase Rule and electroneutrality. Deficiencies in the application of the two major models of micellization, namely, the "mass-action" model and the "phase" model, are exposed. Neither model is generally valid. The van't Hoff enthalpies of micellization of DTAB in water are similar in the presence and absence of 0.1 M KBr, confirming a similar correspondence found with calorimetric enthalpies for DTAB in water and NaBr.

Effect of caffeine on the micellization and related thermodynamic parameters of sodium dodecyl sulphate, hexadecyltrimethylammonium bromide and triton x-100: a physicochemical study

ABSTRACT Effect of caffeine on the micellization of anionic surfactant (SDS), cationic surfactant (HTAB) and non-ionic surfactant (Tx-100) was investigated using the conductometric and tensiometric techniques. The thermodynamic parameters such as change in Gibbs-free energy, , change in enthalpy of micellization, , change in entropy of micellization, , change in Gibbs-free energy of transfer, , surface excess concentration, , minimum area per surfactant molecule, , surface pressure, , change in Gibbs-free energy of adsorption, and other related parameters were calculated to gain insights into the interactions of caffeine with different surfactants at different temperatures. The CMC in mole fraction units, , values of SDS in caffeine are low, while that of HTAB are large in comparison with the values reported in water. The negative values of and and the positive values of are indicative of SDS-caffeine and HTAB-caffeine interactions.

Alterations induced in the micellization behavior of dioctyl sodium sulfosuccinate in the presence of imidazolium-based surface-active ionic liquids in aqueous medium

The present work describes the effect of 1-nonyl-3-methylimidazolium bromide [C9mim][Br] and 1-dodecyl-3-methylimidazolium bromide [C12mim][Br] on aggregation behavior of anionic surfactant dioctyl sodium sulfosuccinate (NaAOT) in aqueous medium by employing different techniques such as conductivity measurement, UV–Visible spectroscopy and FT-IR spectroscopy. The conductivity data of anionic surfactant in the aqueous solution of surface-active ionic liquids is taken experimentally in the temperature range from 293.15 to 308.15 K with the interval of 5 K at various concentrations that is, (0.04, 0.08, 0.12, and 0.16) wt.% of both the SAILs. The critical micelle concentration (CMC) of NaAOT is detected to alter in the presence of both the SAILs. Temperature dependence of CMC obtained from conductivity measurements is utilized to evaluate various thermodynamic parameters of micellization such as, standard free energy of micellization (), standard enthalpy of micellization (), and standard entropy of micellization (). The UV–Visible spectroscopic study is utilized to confirm CMC values obtained from conductivity measurements, which are found to be in good agreement. FT-IR Spectra are recorded to analyze the structural changes that prevailed in both systems.

Influence of sodium bis(2-ethylhexyl) sulfosuccinate on the self-assembly of AOT based surface-active ionic liquids having different pharmacologically active cations in the aqueous medium

The aggregation behavior of three AOT based ionic liquids have been investigated in aqueous medium in the presence of different concentrations i.e. (0.04, 0.08, 0.12, 0.16) mM of sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) at different temperatures (298.15, 308.15, 318.15) K. The AOT based ionic liquids have been successfully synthesized by replacing the cation of sodium bis(2-ethylhexyl) sulfosuccinate (NaAOT) with various pharmacologically active cations such as cholinium [Cho]+, tetraethylammonium [TEA]+, and tetrabutylammonium [TBA]+. The conductivity and surface tension measurements have been employed to understand their aggregation behavior by evaluating various thermodynamic and surface-active parameters such as standard free energy of micellization (ΔGm0), standard enthalpy of micellization (ΔHm0), standard entropy of micellization (ΔSm0), surface pressure at cmc(á́¨cmc), maximum surface excess concentration (Γmax), the minimum area of surfactant monomer at the air/water interface (Amin), the standard Gibbs free energy of adsorption (ΔGad0) and the free energy of a surface at equilibrium (Gmins).

Scrutinizing the Micellization Behaviour of 14-2-14 Gemini Surfactant and Tetradecyltrimethylammonium Bromide in Aqueous Solutions of Betaine Hydrochloride Drug

In the present work, we investigated the effect of drug Betaine Hydrochloride (Betaine HCl) on the aggregation behavior of ethylene-1, 2-bis (N, N-dimethyl-N-tetradecylammonium bromide) (14-2-14) and tetradecyltrimethylammonium bromide (TTAB) by employing electrical conductivity and FT-IR spectroscopic techniques. Initially, synthesis of 14-2-14 is carried out in laboratory followed by determination of critical micelle concentration (CMC) through electrical conductivity measurements at temperatures 293.15 K, 298.15 K, 303.15 K, 308.15 K in absence and presence of Betaine HCl at concentrations 0.10 mmol/kg, 0.15 mmol/kg and 0.25 mmol/kg. The decrement in CMC value is observed with increasing concentrations of Betaine HCl as well as with decreasing temperatures. Several thermodynamic parameters such as the standard enthalpy of micellization (ΔH0m), the standard entropy of micellization (ΔS0m) and the standard Gibbs energy of micellization (ΔG0m), etc. have been evaluated using values of CMC for various concentrations of Betaine HCl at different temperatures. The alterations instigated in respective have been recognized by FT-IR spectroscopic analysis, which signifies the variations produced by the drug on the aggregation of the surfactants (14-2-14 and TTAB) in aqueous media.

Physicochemical studies on the interfacial and aggregation behavior of immidazolium- and pyrrolinidium-dodecyl sulfate in aqueous medium

Salt free surface active ionic liquids (SAILs), 1-butyl-3-methylimidazolium dodecyl sulfate ([bmim]DS) and N-butyl-N-methylpyrrolidinium dodecyl sulfate ([bmp]DS) were synthesised by stoichiometric mixing of ionic liquid (IL) and sodium dodecyl sulfate (SDS). SAILs were characterised by FTIR, 1H NMR, 13C NMR and thermogravimetric analysis and differential thermal analysis (TGA-DTA). Interfacial and aggregation behavior of the SAILs were investigated by surface tension, conductance, UV–visible absorption, emission spectroscopy, dynamic light scattering and isothermal titration calorimetric studies. Results were compared with the precursor surfactant SDS. Critical micelle concentration (CMC) of the surfactants followed the sequence: SDS > [bmp]DS > [bmim]DS. Lower surface excess values of SAILs were due to electrostatic interaction between IL cation and DS-, besides the higher aqueous solubility of DS-, induced by the IL cations. Negative Gibbs free energy of micellization and higher fraction of counter ion binding values further support the proposition. Aggregation number (n) and size (dh) of the micelles were determined by fluorescence quenching and dynamic light scattering studies respectively; both ‘n’ and ‘dh’ values were higher for SAILs than SDS ([bmim]DS > [bmp]DS > SDS). SAIL aggregates, although larger in size with higher aggregation number, were more compact than SDS micelles. Enthalpies of micellization, being exothermic in nature, were higher for SAILs although the micellization processes were entropically controlled. SAILs are considered to have dual advantages of surfactant and IL with substantial decrease in toxicity level.

Investigation of intermolecular interactions of anionic surfactant SDS and rutin: A physico-chemical approach for pharmaceutical application

The thermodynamic, acoustic and 1H NMR studies between rutin trihydrate and sodium dodecyl sulfate (SDS) were carried out to investigate the flavonoid-surfactant interactions. Four different hydro-ethanolic concentrations (aqueous, 30% v/v, 70% v/v and absolute ethanol) at five different temperatures (20–40 °C with a difference of 5 °C) were selected for the study. The critical micelle concentration (CMC) values were calculated using conductivity (κ) parameter to further compute the change in standard enthalpy (△Hom), standard entropy (△Som) and standard Gibbs free energy (△Gom) of micellization. Other thermo-acoustic parameters, i.e., apparent molar volume (ϕv) and apparent molar compressibility (ϕk) were calculated employing the density (ρ) and ultrasonic sound velocity (μ) studies. In addition to these, the relative viscosity (ηr) for all the concentrations was also determined to understand the flow properties. The introduction of surfactant into the system increased the diffusion properties of rutin trihydrate. The acoustic studies highlighted the existence of hydrophobic and electrostatic interactions within the system. The intermolecular interactions between SDS and rutin trihydrate were also established from the chemical shifts observed for 1H NMR spectra in DMSO‑d6. The obtained parameters play a vital role in optimizing the thermo-physically stable concentration which might prove useful in formulation development.

Micellization Behaviour of Cationic Surfactants in the Presence of Food Additives: Conductance and Spectroscopic Investigations

Aim: The micellization behavior of cationic surfactants has been studied in the presence of food additives. Objectives: Micellization behaviour of cationic surfactants, Cetyltrimethylammonium Bromide (CTAB) and Tetradecyltrimethylammonium Bromide (TTAB) has been studied in water and in various concentrations of salts (food additives) L-glutamic acid, sodium propionate, sodium citrate tribasic dihydrate and disodium tartrate dihydrate at (298.15, 308.15 and 318.15) K. Methods: Two methods used in the present study are specific conductance measurements and spectroscopy (NMR) studies. Results: From the specific conductance(κ), various parameters such as Critical Micelle Concentration (CMC), degree of ionization of micelle (α), standard Gibbs free energy (ΔG°m), enthalpy (ΔH°m), and entropy (ΔS°m) of micellization have also been calculated. Thermodynamic parameters related to the micellization process were also analyzed through NMR studies. Conclusion: The CMC values are influenced by the presence of food additive. The magnitude of CMC values increases with an increase in the concentration of food additive. In all the cases, enthalpy of micellization, ΔH°m values are found to be negative, whereas entropy of micellization, ΔS°m values are positive, which indicates that hydrophobic interactions play a major role in the micellization process. Moreover, NMR studies reveal that tartrate and citrate are more hydrated than glutamic acid and propionate, resulting in a more downfield shift.

A Source of Systematic Errors in the Determination of Critical Micelle Concentration and Micellization Enthalpy by Graphical Methods in Isothermal Titration Calorimetry.

Isothermal titration calorimetry is frequently employed to determine the critical micelle concentration and the micellization enthalpy of surfactants in terms of geometrical characteristics of the titration curves. Previously we have shown theoretically that even for an infinitesimal injection, the heat per titrant mol depends on the stock solution concentration. In this work, we explore experimentally the influence of the stock solution concentration on the geometrical characteristics of the titration curve and its effect in determining the critical micelle concentration and the micellization enthalpy of surfactants. The systematic study of this phenomenology involves a great number of measurements at different temperatures with several repetitions carried out using a robotic calorimeter. As surfactant hexadecyltrimethylamonium bromide was used. The magnitude and shape of the heat titration depend on the stock solution concentration. As a consequence, the inflexion-point, break-point, and step-height decrease until a limiting value. A qualitative analysis suggests that the limiting value depends only on substance. This work shows that graphical methods could not be suitable for the calculation of the critical micelle concentration and micellization enthalpy because the magnitude and shape of the titration curve depend on the stock solution concentration. Micellar properties should be calculated by the application of theoretical models as in the ligand-binding studies.

Thermodynamic analysis of micelles formation of anionic surfactant SDS in the presence of aqueous and aqueous solution of ionic liquid 1‐butyl‐3‐methylimidazolium chloride

AbstractIn this study, the experimental conductivity, fluorescence, and UV spectroscopy study have been done for aqueous solutions of sodium dodecyl sulfate (SDS) and in aqueous ionic liquid (IL) 1‐butyl‐3‐methylimidazolium chloride [C4mim][Cl] solutions at a temperature of 298.15 K. Experimental conductivity measurement has been done at different temperatures from 298.15 to 308.15 K. Moreover, the critical micelle concentrations (CMCs) of the mentioned systems were determined by different methods; furthermore, the CMC values have been utilized to originate the values of thermodynamical parameters of micellization like standard enthalpy of micellization ( ), the standard free energy of micellization ( ), and standard entropy of micellization ( ). Fourier transform‐infrared (FT‐IR) spectra have been recorded to investigate the interactions and structural changes that occurred in the mixed system. Work has been discussed in terms of the effect of the aqueous IL solution on the micellization process of the SDS.

Volumetric and aggregation properties of metformin hydrochloride in methanol in temperature range of (288.15–318.15) K

This manuscript is related to the study of volumetric and micellar properties of metformin hydrochloride (Met-HCl) in methanol in temperature range of (288.15–318.15) K. Conductometric and refractive index data was used to find CMC of drug. From conductometric data various thermodynamic variables were calculated which include free energy of micellization, entropy of micellization and enthalpy of micellization. Density measurements of different drug solutions at specified temperatures were utilized for the calculation of apparent molar volume, partial molar volume, Hepler's constant and partial molar expansivity. These parameters are important for getting an understanding about different types of interaction of drug in solution. Met-HCl showed strong solvophobic than electrostatic interaction with methanol and had a structure promoting effect on it which was apparent from positive value of partial molar volume, Hepler's constant and partial molar expansivity. Micellization process was spontaneous, endothermic and resulted in increase in entropy of system because Gibbs energy change was negative, enthalpy change and entropy changes were positive.