Enthalpy Of Micellization Research Articles

Fast and Robust Quantification of Detergent Micellization Thermodynamics from Isothermal Titration Calorimetry.

Detergents are widely used in modern in vitro biochemistry and biophysics, in particular to aid the characterization of integral membrane proteins. An important characteristic of these chemicals in aqueous solutions is the concentration above which their molecular monomers self-associate to form micelles, termed the critical micellar concentration (CMC). Micelles are supramolecular assemblies arranged with the hydrophobic portions oriented inward and the hydrophilic head groups positioned outward to interact with the aqueous solvent. Knowledge of the CMC is not only of practical relevance but also of theoretical interest because it provides thermodynamic insights. Isothermal titration calorimetry (ITC) is a powerful method to determine CMCs, as it furnishes additional information on the enthalpy and entropy of micellization. Here we describe our extension of previous methods to determine CMCs and other thermodynamic parameters from ITC demicellization curves. The new algorithm, incorporated into the stand-alone software package D/STAIN, analyzes ITC demicellization curves by taking advantage of state-of-the-art thermogram-integration techniques and automatically providing rigorous confidence intervals on the refined parameters. As a demonstration of the software's capabilities, we undertook ITC experiments to determine the respective CMCs of n-octyl β-d-glucopyranoside (OG), n-dodecyl β-d-maltopyranoside (DDM), and lauryldimethylamine N-oxide (LDAO). Motivated by the fact that in vitro membrane protein studies often require additives such as precipitants (e.g., polyethylene glycol (PEG)), we also carried out ITC demicellization studies in the presence of PEG3350, finding in all cases that PEG had significant effects on the thermodynamics of detergent micellization.

Synthesis, aggregation and adsorption behavior of benzyldimethylhexadecylammonium based double-chained metallosurfactants

Benzyldimethylhexadecylammonium (BDHA) based double-chained metallosurfactants, BDHA2[MCl4] (M = Mn, Co, Ni, Cu, Zn) were synthesized and characterized by elemental analysis, NMR (1H, 13C) and FT–IR spectroscopy. Thermal gravimetric analysis showed more stability of synthesized metallosurfactants as compared to the precursor benzyldimethylhexadecylammonium chloride. Their critical micelle concentration (cmc) values were determined in aqueous medium by using surface tension, conductivity and fluorescence spectrophotometric methods. The cmc values follow the order: Mn > Co ≈ Cu ≈ Zn > Ni. The thermodynamic parameters of micellization were computed from the temperature dependence of the cmc. These metallosurfactants have surprisingly low counterion binding constant values (0.25 to 0.31) compared to benzyldimethylhexadecylammonium chloride and other ionic surfactants. Compensation of enthalpy and entropy of micellization of BDHA2[MCl4] metallosurfactants is observed in the aqueous medium. Adsorption behavior of BDHA2[MCl4] metallosurfactants was assessed by calculating surface excess and area per molecule at the air/water interface. Dynamic light scattering and zeta potential measurements revealed the small average hydrodynamic diameter of highly stable micelles of the metallosurfactants in aqueous solutions (hydrodynamic diameter = 4–6 nm with polydispersity index <0.13 and zeta potential >+45 mV). Transmission electron microscope measurements also showed the presence of small spherical micelles.

Conductometric Study of Influence of Urea on Interactions of Sodium Dodecyl Sulfate with Cefradine

Interaction of anionic surfactant, sodium dodecyl sulfate (SDS) with antibiotic drug cefradine monohydrate (CFD) were carried out in H2O/low concentration urea medium through conductivity measurement. The variation of critical micelle concentration (CMC) of SDS with the addition of drug (CFD) discloses the presence of interaction between SDS and CFD. The CMC of SDS were attained to dwindle in the presence of CFD. The attained values of CMC show U-shaped behavior as a function of temperature. The effect of urea on the CMC values was observed to be reduced as compared to aqueous medium which is different from the most of the reports mentioned in the literature. The estimated negative values of Gibbs free energy of micellization (∆$$G_{{\text{m}}}^{^\circ }$$) express that micellization is thermodynamically spontaneous within the entire systems investigated. The magnitudes of CFD mediated enthalpy of micellization (Δ$$H_{{\text{m}}}^{^\circ }$$) as well as entropy of micellization (Δ$$S_{{\text{m}}}^{^\circ }$$) for SDS were achieved and clarified in details.

Micellization, anti-proliferative activity and binding study of cationic gemini surfactants with calf thymus DNA

Aggregation behaviour of two cation gemini surfactants i.e., 1,3-bis (1-decylbenzimidazolium) propane bromide BG10 and 1,3-bis (1-octylbenzimidazolium) propane bromide BG8 was studied using conductivity and dynamic light scattering (DLS). The enthalpy (∆Hmо), entropy (∆Smо) and Gibbs free energy of micellization (∆Gmо) have been observed from the conductivity method at various temperatures. The anti-proliferative potential of these novel gemini surfactants against human non-small lung cancer cell line-H1299 has been investigated. Both gemini surfactants, BG8 and BG10 showed a considerable inhibition in cancer cell proliferation and IC50 values are observed to reduce with chain length. The ctDNA binding was also observed by UV–visible, transmission electron microscopy (TEM), ethidium bromide (EtBr) exclusion experiments, agarose gel electrophoresis, circular dichroism (CD) and viscometry techniques. These results were further validated by in-silico studies. The binding capability of BG surfactants to ctDNA can be observed from their ability to remove EtBr from the intercalating complex of DNA resulting in fluorescence quenching.

On the Thermodynamics of Micellizationof Oppositely Charged Surfactants in the Presence of Organic Additives in the Aqueous Medium

Abstract To investigate the effect of additives urea and thiourea, on the micellization behavior of sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB), detailed conductance measurements were carried out in aqueous media at different temperatures. The critical micelle concentration (CMC), determined from the discontinuity in the plots of molar conductance versus square root of concentration, indicated an inhibitory effect of urea and thiourea on micelle forming ability of the surfactants SDS and CTAB in the range of composition studied. The demicellizing effect of urea has been found to be more pronounced in SDS than CTAB. These observations are further augmented by the evaluation of thermodynamic parameters of micellization. A negative change in enthalpy of micellization ( Δ H m ∘ $\Delta{\text{H}}_{\text{m}}^{\circ}$ ) indicates a strong interaction between water and the additives and a positive change observed in entropy of micellization ( Δ S m ∘ $\Delta{\text{S}}_{\text{m}}^{\circ}$ ) manifest, that the micellization is an entropy-driven process. Further Δ H m ∘ $\Delta{\text{H}}_{\text{m}}^{\circ}$ and Δ S m ∘ $\Delta{\text{S}}_{\text{m}}^{\circ}$ change in mutually compensating manner, so that Δ G m ∘ &lt; 0 $\Delta{\text{G}}_{\text{m}}^{\circ} &lt; 0$ is not significantly affected. Finally, the counterion binding values (β) obtained for SDS and CTAB remain practically constant from 0.6 to 0.8 between 25 °C and 45 °C indicate that the size and shape of micelle remain essentially constant. Moreover, the increase in Δ G II ∘ $\Delta{\text{G}}_{{\text{II}}}^{\circ}$ values, which represent the effect of co-solvent or additive on micellization, substantiates the above observations. Many early works has investigated the micellization behavior of surfactants using a fixed additive composition. However, in this study, variable aqueous compositions of urea (0.30–1.78 wt%) and thiourea (0.24–1.41 wt%) have been considered.

Effects of nonionic surfactant (TX-100) on solubilizing power of cationic surfactants (CTAB and CPC) for Direct Red 13

In present study, the solubility of anionic dye, Direct Red 13, has been, spectroscopically and conductometrically, investigated in micellar media of cationic surfactants; Cetylpyridinium chloride (CPC), Cetyltrimethylammonium bromide (CTAB) and mixed micellar media of each with nonionic surfactant, Tritron X-100. The spectral behavior of dye in presence of surfactants was regularly monitored from pre- to post-micellar region of concentration. The UV–vis spectroscopy was applied for estimation of extent of solubilization in terms of partition coefficient (Kx), binding constant (Kb) and Gibbs free energy of corresponding processes. The addition of nonionic surfactant in ternary solution of dye was made to elucidate the role of mixed micelles on solubility of dye. The electrical conductivity data, measured at different temperatures, was used for detection of CMC and calculation of different thermodynamic parameters like; entropy (ΔSm), enthalpy (ΔHm) and Gibbs free energy change (ΔGm) of micellization of selected surfactants. Results reveal the spontaneity of binding and partitioning of dye in aqueous and micellar phase for all the used surfactant systems.

Thermodynamics and micellization behavior of ethanolammonium carboxylate surface active ionic liquids in aqueous media

A systematic experimental study of the micellization of ethanolammonium carboxylate surface active ionic liquids (SAILs) in aqueous solutions was performed. The effect of two separate anions having different alkyl chain length, laurate and palmitate on the micellization behavior was studied. The effect of different cationic head groups, n-butyl, tertiary butyl as well as phenyl group on the micellization parameters was also investigated. The critical micelle concentration (cmc) values and the surface active parameters were evaluated from tensiometric methods. The values of cmc are observed to be lower for palmitate anion SAILs in comparison to the laurate anions. The values of surface tension reduction (πcmc) and surface excess (Γmax) show considerable variation as the anion chain length and the cationic head groups changed. The thermodynamics of the micellization parameters, standard Gibbs free energy of micellization (∆Gm°), enthalpy of micellization (∆Hm°) and entropy of micellization (∆Sm°) were evaluated by conductometric measurements. Using pyrene as a probe molecule, the cmc values were evaluated by steady state fluorescence. The values of critical micelle concentration obtained from three different methods for all the studied SAILs are found to be in good match with each other. The order of cmc for the synthesized SAILs were as follows: [NPEA][PAL] < [TBEA][PAL] < [NBEA][PAL] < [NPEA][LAU] < [TBEA][LAU] < [NBEA][LAU].

Deciphering aggregation behavior and thermodynamic properties of anionic surfactant sodium hexadecyl sulfate in aqueous solutions of ionic liquids [C5mim][Br] and [C6mim][Br

The present work aims to study the interactions of cationic imidazolium based ionic liquids i.e. 1-alkyl-3-methylimidazolium bromide ([Cnmim][Br], where n = 5 &6) with anionic surfactant sodium hexadecyl sulfate (SHS) in aqueous media employing the various techniques such as conductivity measurement, fluorescence spectroscopy, UV–visible spectroscopy and FT-IR spectroscopy. The temperature dependence of critical micelle concentration (CMC) determined using conductivity measurements at temperatures (298.15, 303.15 and 308.15) K at different concentrations (0.02, 0.05 and 0.1) wt. %, of ionic liquids (ILs) in aqueous medium was used to calculate the various thermodynamic parameters of micellization such as, standard free energy of micellization (ΔGm0), standard enthalpy of micellization (ΔHm0), and standard entropy of micellization (ΔSm0). Further, fluorescence and UV–Visible spectroscopy have been utilized to confirm the CMC values obtained from conductivity measurements, which were found to be in good agreement. A continuous increment in CMC value was observed with the increase in concentration of ILs as well as in temperature. Further FT-IR Spectroscopic studies have been done to demonstrate the structural alterations occurring in the respective mixtures.

Effect of Spironolactone on the Micellar Properties of Non-Ionic Surfactant: Assessment by Conductivity and Surface Tension Methods

An interaction of spironolactone (SPI) with octyl phenol ethoxylate (Triton-X-100 or TX-100) has been investigated by using conductometric and tensiometric measurement. The value of critical micellar concentration (CMC), degree of ionization (a) and thermodynamic parameters like standard enthalpy of micellization (?H°m), standard entropy of micellization (?S°m) and standard Gibb’s free energy (?G°m) were determined by conductivity data. The negative value of ?G°m shows spontaneity in the solubilization of drug. Various interfacial parameters such as maximum surface excess concentration (Gmax) and minimum area per molecule (Amin) was determined by surface tension measurement. All these parameters have been discussed in terms of drug-surfactant interactions. Based on the result it was found that variation in the presence of spironolactone in micellar properties of TX-100 increases with increase in concentration of drug. This study will help the pharmaceutical industries in the discovery of new drug and enhancement of their bioavailability.

Effect of chain length and counter-ion on interaction study of mixed micellar system of isoquinoline-based surface active ionic liquid and cationic surfactants in aqueous medium

In the present study, we have investigated the effect of nature of surfactant, chain length and counter-ion on the mixed micellization behaviour ofvarious cationic surfactants, tetradecyltrimethylammonium bromide (TTAB), dodecyltrimethylammonium chloride (DTAC) and cationic gemini surfactant, bis(tetradecyldimethylammonium)hexane dibromide(C14-6-C14,2Br) with surface active ionic liquid (SAIL) tetradecylisoquinolinium bromide [C14iQuin][Br]. The interactions and mixed micellar behaviour of cationic surfactants and SAIL in aqueous medium have been studied by employing conductometry measurements and 1H NMR technique. The critical micelle concentration (cmc) and various thermodynamic parameters like standard Gibbs free energy of micellization (ΔGm0), change in standard enthalpy (ΔHm0) and entropy of micellization (ΔSm0) have been calculated from conductometry measurements. Mixed micellar parameters such as ideal cmc (cmc*), micellar mole fraction (X1m), micellar interaction parameter (βm) and activity coefficients, (f1 and f2) have been evaluated by applying Clint, Rubingh and Motomura theoretical models. Synergistic and non-ideal interactions have been found between SAIL and surfactants.

Self‐Assembly of Polyethylene Glycol Ether Surfactants in Aqueous Solutions: The Effect of Linker between Alkyl and Ethoxylate

AbstractThe aqueous self‐assembly behavior of two homologous series of poly(ethylene oxide) (PEO)‐containing nonionic surfactants based on a C10‐Guerbet hydrophobe is reported. The two families of surfactants, alkyl ethoxylates and alkyl alkoxylates, are commercially available from BASF under the trade name Lutensol® XP‐series and XL‐series, respectively. The latter incorporate propylene oxide (PO) units in the surfactant chain. Dye solubilization was used to determine the critical micellization concentration (CMC) of each surfactant at 22 and 50 °C. The PO‐containing alkyl alkoxylates displayed lower CMC values, which were also more sensitive to temperature. The Gibbs free energy, enthalpy, and entropy of micellization were computed from the CMC data and used to identify the contribution of each surfactant moiety (alkyl chain, PO unit, and PEO block) in controlling the CMC. The micellization properties are compared with compositionally similar surfactants with linear alkyl chains, yielding information about the effects of the Guerbet alkyl chain on micellization. Isothermal titration calorimetry was also used to characterize the CMC and enthalpy of micellization which generally compare well with the dye solubilization results. Cloud point data reveal nonmonotonic relationships for the Lutensol® surfactants with respect to composition, unlike linear alkyl chain surfactants. Finally, dilute solution viscosity measurements performed on some Lutensol® surfactants show a change in the slope, suggesting a structural change that tends to be more pronounced for surfactants with longer PEO blocks. The data presented herein enhance the understanding of surfactant structure–property relationships required for industrial formulation.

Thermodynamic and solution properties of sodium valporate in aqueous solution and its interaction with cetyl trimethylammonium bromide (CTAB)

This manuscript reports the volumetric, viscometric and aggregation properties of sodium valporate in aqueous solution. The interaction of drug with cationic surfactant (CTAB) was also studied. From volumetric study, partial molar volume, Hepler's constant, partial molar expansivity and isobaric thermal expansion coefficient were calculated while from viscometric study, the constants of Jones-Dole equation and thermodynamic parameters of viscous flow like free energy change, entropy change and enthalpy change were calculated. Critical micelle concentration of drug at four different temperatures was measured by surface tension and electrical conductivity measurements. The data was used to calculate surface excess concentration and thermodynamic parameters for the micellization process i.e. free energy of adsorption, free energy, entropy and enthalpy of micellization. Spectroscopic study of the drug/surfactant interaction was helpful to calculate partition coefficient, free energy of partition, binding constant and free energy of binding.

Effects of Molecular Structure and Temperature on Micellization of Cationic Ammonium Gemini Surfactants in Aqueous Solution

AbstractMicellization of four cationic quaternary ammonium gemini surfactants, having a diethyl ether or hexyl spacer with the alkyl chain lengths of 12 and 16 carbon atoms, was studied using isothermal titration microcalorimetry (ITC) and electrical conductivity measurements in the temperature range from 298.15 to 313.15 K. In this temperature range, where surfactants are normally applied, the temperature almost does not influence the critical micelle concentration (CMC) and the degree of micelle ionization (α) values of the gemini surfactants, and the replacement of a hexyl spacer by a diethyl ether spacer leads to a slight decrease in the CMC and α values. However, as the alkyl chain length increases from 12 to 16 carbon atoms, the CMC values significantly decrease from 0.99–1.19 mM to 0.020–0.057 mM. In particular, the enthalpy of micellization (ΔHmic) and the associated thermodynamic parameters show obvious changes with varying temperature and molecular structure. ΔHmic becomes much more exothermic at higher temperature or for the surfactants with a more hydrophilic spacer. Moreover, the heat capacity change of micellization (ΔC P, mic) is less exothermic for the surfactants with a more hydrophilic spacer or a longer alkyl chain. The enthalpy–entropy compensation data show that the surfactants with longer alkyl chains have a more stable micellar structure.

Effect of Molecular Composition of Head Group and Temperature on Micellar Properties of Ionic Surfactants with C12 Alkyl Chain

The paper analyses influences of the temperature and hydrophilic groups on micellar properties of ionic surfactants with 12-carbonic hydrophobic chains. The aim is to assess the impact of hydrophilic groups and temperature on thermodynamic parameters and micellization. This knowledge is indispensable for the formulation of new dosage forms. The method uses conductometric measurements. The following hydrophilic groups are analyzed: trimethylammonium bromide, trimethylammonium chloride, ethyldimethylammonium bromide, didodecyldimethylammonium bromide, pyridinium chloride, benzyldimethyl-ammonium chloride, methylephedrinium bromide, cis and trans-[(2-benzyloxy)-cyclohexyl-methyl]-N, N-dimethylammonium bromide, sodium sulphate and lithium sulphate. Except for a few cases, there is a good agreement between values of critical micellar concentrations (CMC) and critical vesicle concentration (CVC) obtained here and those which were obtained by other authors and/or by other physicochemical methods. Values of the CMC are compared with respect to the molar masses of hydrophilic groups. It was found that CMC values increased non-linearly with increasing system temperature. The degrees of counterion binding and thermodynamic parameters, like the standard molar Gibbs energy, enthalpy and entropy of micellization are determined and discussed in detail. The results obtained will be incorporated into in silico processes of modeling and design of optimal dosage forms, a current interdisciplinary research focus of the team.

Mixed micellization of a trisubstituted surface active ionic liquid 1-dodecyl-2,3-dimethylimidazolium chloride [C12bmim][Cl] with an amphiphilic drug amitriptyline hydrochloride AMT: A detailed insights from conductance and surface tension measurements

The thermodynamics and interfacial behavior of the mixed micellization of a trisubstituted imidazolium based surface active ionic liquid (SAIL), 1-dodecyl-2,3-dimethylimidazolium chloride [C12bmim][Cl], with an antidepressant amphiphilic drug amitriptyline hydrochloride (AMT) have been studied by employing surface tension measurements at 298.15 K and from conductance at 288.15, 298.15 and 308.15 K. Critical micelle concentration (cmc), degree of ionization (α), and other thermodynamic parameters like Gibbs free energy of micellization (∆Gmic.°), standard enthalpy of micellization (∆Hmic.°) and standard entropy of micellization (∆Smic.°) were derived from conductivity measurements. The respective surface active parameters like surface tension at cmc (γcmc), minimum surface area per ionic liquid molecule (Amin), adsorption efficiency (pC20), maximum surface excess concentration (Гmax), effectiveness of surface tension reduction (Πcmc), and cmc of the mixed systems of SAIL and AMT have been cognized using surface tension measurements. The negative values of ∆Gmic.° and the standard Gibbs free energy of adsorption at the air/water interface (∆Gad.°) indicate the feasibility of the micellization behavior of the mixed systems and confirm the feasibility of drug-SAIL interactions. The micellar interaction parameter (βm) have also been analyzed to get detailed insights of the interactions between the amphiphilic drug and the SAIL by applying theoretical model introduced by Rubingh and Motomura. The negative value of this parameter indicates the presence of synergistic interactions of SAIL-AMT binary mixtures. A comparative study has been done between disubstituted and trisubstituted SAILs and it has been found that the surface activity of trisubstituted SAIL is better than their disubstituted analogue due to the high hydrophobicity and hydrophilicity of trisubstituted SAIL.

Solution and Surface Properties of Metformin Hydrochloride in Aqueous Solution and Its Interaction with Amino Acids and Anionic Surfactant, Sodium Dodecyl Sulphate

This manuscript reports critical micelle concentration of metformin hydrochloride in aqueous solution which was determined by electrical conductivity, surface tension and refractive index measurements. From conductometric and surface tension data, different parameters were calculated which include surface excess concentration, area per molecule, dissociation constant and free energy of adsorption. Thermodynamic parameters like free energy of micellization, enthalpy of micellization and entropy of micellization were also calculated. The effect of change in pH on the CMC of drug was studied in pH range of 2–9. Three amino acids, i.e. glycine, tyrosine and tryptophane, were used to study their effect on CMC of drug. The interaction of this drug with two common surfactants, i.e. sodium dodecyl sulphate (SDS) and cetyl trimethylammonium bromide, was also studied with the help of UV–visible spectroscopy and conductivity measurements. Viscometric study was carried out to find the constants of Jones–Dole equation which are helpful to find the different types of interactions in solution. The results showed the spontaneous nature of adsorption of drug at air solution interface and spontaneous nature of micellization, becoming more spontaneous at elevated temperature. Strong interaction of drug with anionic surfactant SDS was observed. The increase in pH decreased CMC of drug, but higher CMC was found at pH of 7. The amino acids affect the CMC of the drug in different ways. Viscometric study showed the hydrophobic interaction of drugs with the solvent molecules.

Interactions of Some Hofmeister Cations with Sodium Dodecyl Sulfate in Aqueous Solution

AbstractIn this work, we have investigated the influence of some alkali metal ions on the Krafft temperature (TK) and critical micelle concentration (CMC) of a classical ionic surfactant, sodium dodecyl sulfate (SDS), over a wide range of temperature. The alkali metal cations such as Li+, Na+, Cs+, and K+ are found to affect the solubility and hence the TK of the surfactant. It was observed that kosmotropic Li+ lowers the TK of the surfactant. Due to the common ion effect, the solubility of SDS decreases in the presence of Na+, resulting in an increase in the TK. On the other hand, chaotropic K+ and Cs+, capable of forming contact ion pairs with the chaotropic dodecyl sulfate ion, lower the solubility and hence elevate the TK. In terms of decreasing the TK, the ions follow the trend: Li+ &gt; Na+ &gt; Cs+ &gt; K+ except for 0.0025 M CsCl. The added cations screen the charge of the micelle surface and facilitate closer packing of the surfactant with a consequent decrease in the CMC. In terms of the effectiveness in lowering the CMC, the ions follow the order: Cs+ &gt; K+ &gt; Na+ &gt; Li+. In the presence of added electrolytes, the γCMC values are found to be lower than the corresponding values in pure water. The thermodynamic parameters (Gibbs free energy, enthalpy, and entropy changes) of micellization were calculated to gain insights into the mechanism of the process.

Micellization behavior of anionic surface active ionic liquid 1-butyl-3-methylimidazolium dodecylbenzenesulfonate in aqueous solutions of nonionic polymer polyethylene glycol: Insights into competing mechanisms

In this study, an understanding of interactions among the anionic surface active ionic liquid (SAIL) 1-butyl-3-methylimidazolium dodecylbenzenesulfonate [C4mim][DBS] and non-ionic low molecular weight polymer polyethylene glycol 400 (PEG 400) in aqueous solution has been developed systematically. Various techniques such as tensiometry, conductivity, dynamic light scattering (DLS), nephelometric turbidity and rheology have been employed to understand the exquisite interplay of different competing mechanisms prevailing between these unlike molecules in bulk as well as in the interfacial region. Surface activity of the current systems at air-aqueous interface have been evaluated using by deriving various important surface parameters, such as surface excess concentration (Гmax), surface pressure at interface (Πcmc), minimum area occupied by one molecule of SAIL at air-solvent interface (Αmin), adsorption efficiency (pC20) and surface tension at critical micelle concentration (cmc) (γcmc). Also, the thermodynamic parameters such as standard free energy of micellization (ΔGm°), standard enthalpy of micellization (ΔHm°) and standard entropy of micellization (ΔSm°) have been evaluated from conductivity measurements. The process of micellization has been found to be exothermic and spontaneous thermodynamically in presence of PEG supported by gain in entropy. The values of critical micelle concentration (cmc) decrease with increase in concentration of PEG which signals towards the predominance of ion-dipole interactions as well as hydrophobic interactions. However, at the higher concentration (0.045 g/L PEG), the cmc has been found to increase due to modification in surface and bulk structure of system. These results have been confirmed by the electrical conductivity measurements. The aggregate formation has also been tracked with the help of dynamic light scattering and nephelometric turbidimetry which provides useful information regarding the complexation dynamics. The rheological measurements have been carried out with the intent of understanding the complex behavior of these SAIL-polymer systems.

The Role of Non-Ionic Surfactants in Solubilization and Delivery of Sparingly Soluble Drug Naproxen Sodium (NS): A Case Study

Abstract Nonsteroidal anti-inflammatory hydrophobic drugs (NSAIDs) are amongst the most commonly given categories of drugs worldwide in the treatment of pain, irritation and some of them even fever in many conditions. Critical micelle concentration of NSAIDs with Naproxen sodium (NS) and its mixture with non-ionic surfactants i.e. Tween 20, Tween 40 and Tween 60 was investigated at 293 K, 303 K, 313 K and 323 K at different concentrations using surface tension and dynamic laser light scattering (DLS) techniques. Due to amphiphilic behaviour in aqueous solution NS form aggregates at sufficiently high concentration. Thermodynamic/adsorption properties like free energy of micellization (ΔGmic), enthalpy of micellization (ΔHmic), entropy of micellization (ΔSmic), Γmic and area per molecule (A2) of NS in the presence of surfactants were also measured at different temperatures. The results showed that the presence of surfactants favoured the ΔGmic and become more enhanced with increase in temperature. Further the solubility of drug is more favourable with increase in polyethylene chain in basic surfactant molecules i.e. 20–60, which indicates that Tween-60 enhanced the solubility of NS more comparatively to Tween-40 and Tween-20 and may be applied as best additive for solubilisation of NS.

Structural Characterization of Pluronic Micelles Swollen with Perfume Molecules.

The insertion in nonionic polymer micelles (Pluronics F127) of seven essential oils and some of the pure compounds that compose them was investigated by complementary differential scanning calorimetry, small-angle X-ray, and neutron scattering (SAXS and SANS). The study revealed various insertion and swelling behaviors for the different oil molecules, an evidence of different interaction mechanisms involved between oils and Pluronic monomers. Thermodynamically, the addition of oil increased the micellization enthalpy due to an enhanced release of water molecules, leading subsequently to a decrease of the critical micellar temperature (CMT). Structurally, with oil, SANS revealed the presence of large aggregates at lower temperature than the CMT for which their size is maximal. Above the CMT, the size decreased and the equilibrium was reached a few degrees after the temperature corresponding to the maximum of the endothermic peak. At 37 °C, the detailed combined SANS and SAXS analysis demonstrated a partial phase separation between the oil and the poly(propylene oxide) core. The hydrophilic stabilizing poly(ethylene oxide) shell remains unchanged.