Dr Tejas Joshi | BHAVNAGAR UNIVERSITY (original) (raw)

Papers by Dr Tejas Joshi

Research paper thumbnail of Physicochemical Properties of Cetrimonium Bromide in Electrolytes and Nonelectrolyte Environments

Current physical chemistry, Jul 20, 2023

Background: The physicochemical properties, including the thermodynamics of micellization studies... more Background: The physicochemical properties, including the thermodynamics of micellization studies, received much attention. Cationic surfactant cetrimonium bromide (C16TABr) in electrolytes (sodium chloride and sodium salicylate) and nonelectrolyte (Ethylene glycol) in an aqueous solution were examined, and interesting results were obtained. The present investigation aims to identify a suitable combination of cationic surfactant cetrimonium bromideelectrolytes and nonelectrolytes having the ability to alter the size or shape of the micellar system using available methods. Methods: Surface tension, conductivity, viscosity, ultrasonic velocity, and dynamic light scattering (DLS) methods at different temperatures (303-323K) were used during the experimental research work. Results: The experimental results pointed out that the incorporation of electrolytes and nonelectrolyte into the cationic surfactant affects the physicochemical properties such as critical micelle concentration (CMC), surface tension (ST), degree of ionization (α), degree of counterion binding (β), standard Gibbs free energy of micellization (ΔGom), standard entropy of micellization (ΔSom), standard heat of micellization (ΔHom), viscosities, and acoustic parameters. Dynamic light scattering (DLS) measurements reveal exciting facts related to the size and shape transformation of the mixed micellar assembly. Structure modification can be obtained by choosing the combination of cationic surfactant cetrimonium bromide + electrolytes (sodium chloride and sodium salicylate) and nonelectrolyte (Ethylene glycol) ratio. Conclusion: From this it is concluded that an electrolyte concentration such as NaCl above a threshold value leads to an increase in micelle size. The entropy of micellization goes down when a structure-breaker (EG) is added to the water phase, and this is because the structure of the water is changed near hydrophobic groups. The physicochemical features of cetrimonium bromide (C16TABr) show unique behaviour under the influence of micelle-driven and micelle-forbidden systems.

Research paper thumbnail of Cloud Point Phenomena of Mixed Block Copolymers

Journal of Dispersion Science and Technology, Jul 8, 2015

Cloud points data on solutions of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxid... more Cloud points data on solutions of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) abbreviated as EPE or Pluronics, such as P–65, P–84, P–85, P-105, L-64, and their mixtures at different salt (NaCl) concentrations in water are reported. The addition of NaCl to these mixed copolymers decreases cloud point, increases surface activity, and shifts micellization to lower concentration. In presence of NaCl, more surfactant is needed for demicellization of P105 micelles. GRAPHICAL ABSTRACT

Research paper thumbnail of Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates in Aqueous Solution

Journal of Dispersion Science and Technology, Oct 1, 2007

The aggregation behavior of metal dodecyl sulfates (MDS), [Na1+, Mg2+, Mn2+, Co2+, and Ni2+] in w... more The aggregation behavior of metal dodecyl sulfates (MDS), [Na1+, Mg2+, Mn2+, Co2+, and Ni2+] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion ...

Research paper thumbnail of Surfactant behavior in Environment

Surfactants form a unique class of chemical compounds. This review provides basics of surfactant,... more Surfactants form a unique class of chemical compounds. This review provides basics of surfactant, its types, applications and merit and demerit nature to environment. Surfactant has dual identity of either having environment friendly or polluting globe. Surfactants are discharged into sewage systems or into surface waters and mostly end up dispersed in diverse environmental compartments such as water, soil, etc. The toxic effects of surfactants on various marine organisms are well known. Most surfactants are willingly biodegradable and their proportion can be reduced with another suitable method. The release of wastewater polluted with enormous quantities of surfactants could have serious effects on the ecosystem. It is very important in future to focus on surfactant toxicities and biodegradation and vital to remove highly toxic and non-biodegradable compounds from commercial use and replace them with more environmentally friendly ones.

Research paper thumbnail of A Concise Review on Surfactants and Its Significance

Surface active agents constitute an interesting class of substances with unique structural featur... more Surface active agents constitute an interesting class of substances with unique structural features. This review provides an introduction to the nature and physical properties of surfactants, its trade name, types, characteristics and their basic applications. Fundamental of critical micelle concentration (CMC), cloud point, kraft point are mentioned. Surfactant size and shape are vital characteristics and provide unique information during industrial formulation. Surfactant properties play significant roles in industrial and consumer products including detergents, paints, paper products, pharmaceuticals and cosmetics. The last few years show an increased interest in work involving the preparation and study of surfactants based on natural products.

Research paper thumbnail of Surface activity and antimicrobial performance of synthesized gemini surfactant and silver nanoparticles loaded gemini surfactants integrated with microscopy and scattering investigation

Research paper thumbnail of Significance of Amphiphilic Block Copolymer Micelles and its Characteristics

International Journal of Trend in Scientific Research and Development

Amphiphilic block copolymers (ABCs) have been used broadly in pharmaceutical applications. One of... more Amphiphilic block copolymers (ABCs) have been used broadly in pharmaceutical applications. One of the most widely used drug delivery systems is the self assembly of ABCs carriers in micelle forms in aqueous environment. Block copolymers have low toxicity and due to their nontoxic properties and surface-activity they have found application in the areas of biomaterials, protein separation, drug delivery and cardiovascular therapeutics and as industrially important surfactants. ABCs micelles have been the focus of research for the last many decades. Research in the field has been increasingly focused on achieving enhanced stability of the micellar assembly, prolonged circulation times and controlled release of the drug for optimal targeting.

Research paper thumbnail of Interaction of Bile Salts with Cetylpyridinium Chloride: Surface Tension and Viscosity Measurements

Current Physical Chemistry

Research paper thumbnail of Cloud point analysis: Influence of additives on polysorbate

Journal of Dispersion Science and Technology

Research paper thumbnail of Aggregation behavior of a PEO-PPO-PEO block copolymer+ ionic surfactants mixed systems in water and aqueous salt solutions

Colloids and Surfaces A: …, Jan 1, 2004

Cloud points, surface tension, viscosity and dynamic light scattering data on solutions of a poly... more Cloud points, surface tension, viscosity and dynamic light scattering data on solutions of a poly(ethylene oxide) poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO); Pluronic P105, in water and NaBr solutions and for the similar systems in the presence of two ionic surfactants, sodium dodecyl sulphate (NaDS) and dodecyltrimethylammonium bromide (DTABr) are reported. The addition of NaBr to copolymer decreases cloud point, increases surface activity, shifts micellization to lower concentration. The DLS results reveal that presence of ionic surfactant (below CMC) leads demicellization of copolymer P105. Furthermore, in the presence of NaBr more surfactant is needed for demicellization of P105 micelles. The surface tension study of P105-ionic surfactant indicates stronger interaction in case of NaDS as compared to DTABr. Also, the interaction seems to diminish in the presence of NaBr.

Research paper thumbnail of Effect of salt on the micelles of cetyl pyridinium chloride

Colloids and Surfaces A: …, Jan 1, 2005

Surface tension, conductance, viscosity, dynamic light scattering (DLS) and small angle neutron s... more Surface tension, conductance, viscosity, dynamic light scattering (DLS) and small angle neutron scattering (SANS) measurements were carried out in order to investigate the effect of added salt NaCl and NaBr on micellization and structure of cetylpyridinium chloride (CPyCl) micelles. Critical micelle concentration(CMC)of CPyCl decreases with increase in salts concentration, while CMC and counter ion dissociation (β) increases with increase in temperature. At a given CPyCl concentration, the micelle size increases with increasing salt concentration above a threshold value. Micellar growth in presence of salts is clearly reflected by an increase in viscosity, hydrodynamic diameter (d) from DLS and aggregation number from SANS measurements. The effect of NaBr on CPyCl micelles was more pronounced in comparison to NaCl. The difference in solution properties of Br− and Cl− is that Cl− counter ions being more hydrated are less effective to neutralize the charge on the micellar surface.

Research paper thumbnail of Micellization and Interaction of Anionic and Nonionic Mixed Surfactant Systems In Water

Colloids and Surfaces A: Physicochemical …, Jan 1, 2005

Interaction between binary surfactant mixtures containing anionic surfactants viz. sodium dodecyl... more Interaction between binary surfactant mixtures containing anionic surfactants viz. sodium dodecyl sulphates (NaDS) and magnesium dodecyl sulphates (Mg(DS)2) and a nonionic surfactants viz. dodecyl dodecapolyethylene glycol ether (C12E12) and dodecyl pentadecapolyethylene glycol ether (C12E15) in water at different mole fractions (0–1) were studied by surface tension, viscometry and dynamic light scattering (DLS) methods. The composition of mixed micelles and the interaction parameter, β evaluated from the CMC data obtained by surface tension for different systems using Rubingh’s theory were discussed. Activity coefficient (f1 and f2) of metal dodecyl sulphates (MDS)/C12Em (m= 12, 15)
mixed surfactant systems were evaluated, which shows extent of ideality of individual surfactant in mixed system. The estimated interaction parameter indicates an overall attractive interaction in the mixed micelles, which is predominant for NaDS as compared to Mg(DS)2. Counter ion valency has specific effect on the mixed micelles, as Mg(DS)2 has less interaction with nonionic surfactants in comparison to NaDS due to strong condensation of counter ion. The stability factors for mixed micelles were also discussed by Maeda’s approach, which was justified on the basis of steric factor due to difference in head group of nonionic surfactant. DLS measurements and viscosity data reveals the synergism in mixed micelles, showing typical viscosity trends and linearity in sizes were observed.

Research paper thumbnail of Micellar behavior of mixtures of sodium dodecyl sulfate and dodecyldimethylamine oxide in aqueous solutions

Colloids and Surfaces A: …, Jan 1, 2005

Studies on adsorption characteristics and micellization of mixtures containing cationic/nonionic ... more Studies on adsorption characteristics and micellization of mixtures containing cationic/nonionic surfactant dodecyldimethylamine oxide
(DMDAO) and anionic surfactant sodium dodecyl sulfate (SDS) with and without NaCl as studied by surface tension, viscosity, dynamic light scattering (DLS) and small angle neutron scattering (SANS) showed strong synergisms and micellar growth. A large negative interaction parameter, β, using Rubing’s theory for above mixed system was estimated. Sphere-to-rod transition driven by ion–dipole interactions between the dissimilar head groups in mixtures of the two surfactants (total concentration 25–100 mM) was well reflected in DLS and SANS measurements. These results are consistent with the concept that nonidealities of mixing in micelles of oppositely charged mixed surfactant
systems are primarily of electrostatic origin with specific interactions.

Research paper thumbnail of Micellization and Interaction Properties of Aqueous Solutions of Mixed Cationic and Nonionic Surfactants

Journal of Dispersion Science …, Jan 1, 2008

The micellization process of binary surfactant mixtures containing cationic surfactants viz.dodec... more The micellization process of binary surfactant mixtures containing cationic surfactants viz.dodecyl pyridinium halide (C12PyX; X 5 Cl, Br, I), tetradecyl pyridium bromide (C14PyBr),and hexadecyl pyridium halide (C16PyX; X 5 Cl, Br) and a nonionic surfactants viz.dodecyl nonapolyethylene glycol ether (C12E9), dodecyl decapolyethylene glycol ether (C12E10), dodecyl dodecapolyethylene glycol ether (C12E12), and dodecyl pentadecapolyethylene glycol ether (C12E15) in water at different mole fractions (0–1) were studied by surface tension and viscosity methods. The composition of mixed micelles and the interaction parameter 'b' evaluated from the CMC data obtained by surface tension for different systems using Rubingh’s theory were discussed. Activity coefficient (f1 and f2) of cationic surfactant (CnPyBr)/C12Em (n 5 12, 14, 16 and m 5 10, 12, 15) mixed surfactant systems were evaluated, which shows extent of ideality of individual surfactant in mixed system. The stability factors for mixed micelles were also discussed by Maeda’s approach, which was justified on the basis of steric factor due to difference in head group of nonionic surfactant.

Research paper thumbnail of Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates In Aqueous Solution

Journal of Dispersion Science and …, Jan 1, 2007

The aggregation behavior of metal dodecyl sulfates (MDS), [Na1+, Mg2+, Mn2+, Co2+, and Ni2+] in w... more The aggregation behavior of metal dodecyl sulfates (MDS), [Na1+, Mg2+, Mn2+, Co2+, and
Ni2+] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion
dissociation (b) evaluated from conductivity data. Using law of mass action model, the thermodynamic parameters viz. Gibbs energy (DGm 0 ), enthalpy (DHm 0 ), and entropy (DSm 0 ) were
evaluated. The enthalpy of micellization decreases strongly with increasing temperature. DG is always negative (thermodynamically favored process) and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of the counterion. The plots of differential conductivity, (dk/dc)T,P, versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. Surfactants with strong condense counterion are adapted to rodlike micelle better
than to a spherical micelle. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counterion.

Research paper thumbnail of Mixed Micellization of Dodecyldimethylamine Oxide With Bile Salts In Aqueous Solutions

Journal of Dispersion Science and …, Jan 1, 2009

Micellar behavior of dodecyldimethylamine oxide (DMDAO) with bile salts [sodium deoxycholate (NaD... more Micellar behavior of dodecyldimethylamine oxide (DMDAO) with bile salts [sodium deoxycholate (NaDC) and sodium cholate (NaC)] with and without NaCl was studied by surface tension. Interaction parameters of the mixed micelles were estimated using Rubingh’s theory. Strong synergism observed for each mixed system, which is a common feature shown by anionic-cationic mixtures. The mixed solutions remained clear even at equimolar ratio. Different behavior of the two bile salts is explained on the basis of their orientation in cationic micelles.

Research paper thumbnail of Physicochemical Properties of Cetrimonium Bromide in Electrolytes and Nonelectrolyte Environments

Current physical chemistry, Jul 20, 2023

Background: The physicochemical properties, including the thermodynamics of micellization studies... more Background: The physicochemical properties, including the thermodynamics of micellization studies, received much attention. Cationic surfactant cetrimonium bromide (C16TABr) in electrolytes (sodium chloride and sodium salicylate) and nonelectrolyte (Ethylene glycol) in an aqueous solution were examined, and interesting results were obtained. The present investigation aims to identify a suitable combination of cationic surfactant cetrimonium bromideelectrolytes and nonelectrolytes having the ability to alter the size or shape of the micellar system using available methods. Methods: Surface tension, conductivity, viscosity, ultrasonic velocity, and dynamic light scattering (DLS) methods at different temperatures (303-323K) were used during the experimental research work. Results: The experimental results pointed out that the incorporation of electrolytes and nonelectrolyte into the cationic surfactant affects the physicochemical properties such as critical micelle concentration (CMC), surface tension (ST), degree of ionization (α), degree of counterion binding (β), standard Gibbs free energy of micellization (ΔGom), standard entropy of micellization (ΔSom), standard heat of micellization (ΔHom), viscosities, and acoustic parameters. Dynamic light scattering (DLS) measurements reveal exciting facts related to the size and shape transformation of the mixed micellar assembly. Structure modification can be obtained by choosing the combination of cationic surfactant cetrimonium bromide + electrolytes (sodium chloride and sodium salicylate) and nonelectrolyte (Ethylene glycol) ratio. Conclusion: From this it is concluded that an electrolyte concentration such as NaCl above a threshold value leads to an increase in micelle size. The entropy of micellization goes down when a structure-breaker (EG) is added to the water phase, and this is because the structure of the water is changed near hydrophobic groups. The physicochemical features of cetrimonium bromide (C16TABr) show unique behaviour under the influence of micelle-driven and micelle-forbidden systems.

Research paper thumbnail of Cloud Point Phenomena of Mixed Block Copolymers

Journal of Dispersion Science and Technology, Jul 8, 2015

Cloud points data on solutions of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxid... more Cloud points data on solutions of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) abbreviated as EPE or Pluronics, such as P–65, P–84, P–85, P-105, L-64, and their mixtures at different salt (NaCl) concentrations in water are reported. The addition of NaCl to these mixed copolymers decreases cloud point, increases surface activity, and shifts micellization to lower concentration. In presence of NaCl, more surfactant is needed for demicellization of P105 micelles. GRAPHICAL ABSTRACT

Research paper thumbnail of Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates in Aqueous Solution

Journal of Dispersion Science and Technology, Oct 1, 2007

The aggregation behavior of metal dodecyl sulfates (MDS), [Na1+, Mg2+, Mn2+, Co2+, and Ni2+] in w... more The aggregation behavior of metal dodecyl sulfates (MDS), [Na1+, Mg2+, Mn2+, Co2+, and Ni2+] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion ...

Research paper thumbnail of Surfactant behavior in Environment

Surfactants form a unique class of chemical compounds. This review provides basics of surfactant,... more Surfactants form a unique class of chemical compounds. This review provides basics of surfactant, its types, applications and merit and demerit nature to environment. Surfactant has dual identity of either having environment friendly or polluting globe. Surfactants are discharged into sewage systems or into surface waters and mostly end up dispersed in diverse environmental compartments such as water, soil, etc. The toxic effects of surfactants on various marine organisms are well known. Most surfactants are willingly biodegradable and their proportion can be reduced with another suitable method. The release of wastewater polluted with enormous quantities of surfactants could have serious effects on the ecosystem. It is very important in future to focus on surfactant toxicities and biodegradation and vital to remove highly toxic and non-biodegradable compounds from commercial use and replace them with more environmentally friendly ones.

Research paper thumbnail of A Concise Review on Surfactants and Its Significance

Surface active agents constitute an interesting class of substances with unique structural featur... more Surface active agents constitute an interesting class of substances with unique structural features. This review provides an introduction to the nature and physical properties of surfactants, its trade name, types, characteristics and their basic applications. Fundamental of critical micelle concentration (CMC), cloud point, kraft point are mentioned. Surfactant size and shape are vital characteristics and provide unique information during industrial formulation. Surfactant properties play significant roles in industrial and consumer products including detergents, paints, paper products, pharmaceuticals and cosmetics. The last few years show an increased interest in work involving the preparation and study of surfactants based on natural products.

Research paper thumbnail of Surface activity and antimicrobial performance of synthesized gemini surfactant and silver nanoparticles loaded gemini surfactants integrated with microscopy and scattering investigation

Research paper thumbnail of Significance of Amphiphilic Block Copolymer Micelles and its Characteristics

International Journal of Trend in Scientific Research and Development

Amphiphilic block copolymers (ABCs) have been used broadly in pharmaceutical applications. One of... more Amphiphilic block copolymers (ABCs) have been used broadly in pharmaceutical applications. One of the most widely used drug delivery systems is the self assembly of ABCs carriers in micelle forms in aqueous environment. Block copolymers have low toxicity and due to their nontoxic properties and surface-activity they have found application in the areas of biomaterials, protein separation, drug delivery and cardiovascular therapeutics and as industrially important surfactants. ABCs micelles have been the focus of research for the last many decades. Research in the field has been increasingly focused on achieving enhanced stability of the micellar assembly, prolonged circulation times and controlled release of the drug for optimal targeting.

Research paper thumbnail of Interaction of Bile Salts with Cetylpyridinium Chloride: Surface Tension and Viscosity Measurements

Current Physical Chemistry

Research paper thumbnail of Cloud point analysis: Influence of additives on polysorbate

Journal of Dispersion Science and Technology

Research paper thumbnail of Aggregation behavior of a PEO-PPO-PEO block copolymer+ ionic surfactants mixed systems in water and aqueous salt solutions

Colloids and Surfaces A: …, Jan 1, 2004

Cloud points, surface tension, viscosity and dynamic light scattering data on solutions of a poly... more Cloud points, surface tension, viscosity and dynamic light scattering data on solutions of a poly(ethylene oxide) poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO); Pluronic P105, in water and NaBr solutions and for the similar systems in the presence of two ionic surfactants, sodium dodecyl sulphate (NaDS) and dodecyltrimethylammonium bromide (DTABr) are reported. The addition of NaBr to copolymer decreases cloud point, increases surface activity, shifts micellization to lower concentration. The DLS results reveal that presence of ionic surfactant (below CMC) leads demicellization of copolymer P105. Furthermore, in the presence of NaBr more surfactant is needed for demicellization of P105 micelles. The surface tension study of P105-ionic surfactant indicates stronger interaction in case of NaDS as compared to DTABr. Also, the interaction seems to diminish in the presence of NaBr.

Research paper thumbnail of Effect of salt on the micelles of cetyl pyridinium chloride

Colloids and Surfaces A: …, Jan 1, 2005

Surface tension, conductance, viscosity, dynamic light scattering (DLS) and small angle neutron s... more Surface tension, conductance, viscosity, dynamic light scattering (DLS) and small angle neutron scattering (SANS) measurements were carried out in order to investigate the effect of added salt NaCl and NaBr on micellization and structure of cetylpyridinium chloride (CPyCl) micelles. Critical micelle concentration(CMC)of CPyCl decreases with increase in salts concentration, while CMC and counter ion dissociation (β) increases with increase in temperature. At a given CPyCl concentration, the micelle size increases with increasing salt concentration above a threshold value. Micellar growth in presence of salts is clearly reflected by an increase in viscosity, hydrodynamic diameter (d) from DLS and aggregation number from SANS measurements. The effect of NaBr on CPyCl micelles was more pronounced in comparison to NaCl. The difference in solution properties of Br− and Cl− is that Cl− counter ions being more hydrated are less effective to neutralize the charge on the micellar surface.

Research paper thumbnail of Micellization and Interaction of Anionic and Nonionic Mixed Surfactant Systems In Water

Colloids and Surfaces A: Physicochemical …, Jan 1, 2005

Interaction between binary surfactant mixtures containing anionic surfactants viz. sodium dodecyl... more Interaction between binary surfactant mixtures containing anionic surfactants viz. sodium dodecyl sulphates (NaDS) and magnesium dodecyl sulphates (Mg(DS)2) and a nonionic surfactants viz. dodecyl dodecapolyethylene glycol ether (C12E12) and dodecyl pentadecapolyethylene glycol ether (C12E15) in water at different mole fractions (0–1) were studied by surface tension, viscometry and dynamic light scattering (DLS) methods. The composition of mixed micelles and the interaction parameter, β evaluated from the CMC data obtained by surface tension for different systems using Rubingh’s theory were discussed. Activity coefficient (f1 and f2) of metal dodecyl sulphates (MDS)/C12Em (m= 12, 15)
mixed surfactant systems were evaluated, which shows extent of ideality of individual surfactant in mixed system. The estimated interaction parameter indicates an overall attractive interaction in the mixed micelles, which is predominant for NaDS as compared to Mg(DS)2. Counter ion valency has specific effect on the mixed micelles, as Mg(DS)2 has less interaction with nonionic surfactants in comparison to NaDS due to strong condensation of counter ion. The stability factors for mixed micelles were also discussed by Maeda’s approach, which was justified on the basis of steric factor due to difference in head group of nonionic surfactant. DLS measurements and viscosity data reveals the synergism in mixed micelles, showing typical viscosity trends and linearity in sizes were observed.

Research paper thumbnail of Micellar behavior of mixtures of sodium dodecyl sulfate and dodecyldimethylamine oxide in aqueous solutions

Colloids and Surfaces A: …, Jan 1, 2005

Studies on adsorption characteristics and micellization of mixtures containing cationic/nonionic ... more Studies on adsorption characteristics and micellization of mixtures containing cationic/nonionic surfactant dodecyldimethylamine oxide
(DMDAO) and anionic surfactant sodium dodecyl sulfate (SDS) with and without NaCl as studied by surface tension, viscosity, dynamic light scattering (DLS) and small angle neutron scattering (SANS) showed strong synergisms and micellar growth. A large negative interaction parameter, β, using Rubing’s theory for above mixed system was estimated. Sphere-to-rod transition driven by ion–dipole interactions between the dissimilar head groups in mixtures of the two surfactants (total concentration 25–100 mM) was well reflected in DLS and SANS measurements. These results are consistent with the concept that nonidealities of mixing in micelles of oppositely charged mixed surfactant
systems are primarily of electrostatic origin with specific interactions.

Research paper thumbnail of Micellization and Interaction Properties of Aqueous Solutions of Mixed Cationic and Nonionic Surfactants

Journal of Dispersion Science …, Jan 1, 2008

The micellization process of binary surfactant mixtures containing cationic surfactants viz.dodec... more The micellization process of binary surfactant mixtures containing cationic surfactants viz.dodecyl pyridinium halide (C12PyX; X 5 Cl, Br, I), tetradecyl pyridium bromide (C14PyBr),and hexadecyl pyridium halide (C16PyX; X 5 Cl, Br) and a nonionic surfactants viz.dodecyl nonapolyethylene glycol ether (C12E9), dodecyl decapolyethylene glycol ether (C12E10), dodecyl dodecapolyethylene glycol ether (C12E12), and dodecyl pentadecapolyethylene glycol ether (C12E15) in water at different mole fractions (0–1) were studied by surface tension and viscosity methods. The composition of mixed micelles and the interaction parameter 'b' evaluated from the CMC data obtained by surface tension for different systems using Rubingh’s theory were discussed. Activity coefficient (f1 and f2) of cationic surfactant (CnPyBr)/C12Em (n 5 12, 14, 16 and m 5 10, 12, 15) mixed surfactant systems were evaluated, which shows extent of ideality of individual surfactant in mixed system. The stability factors for mixed micelles were also discussed by Maeda’s approach, which was justified on the basis of steric factor due to difference in head group of nonionic surfactant.

Research paper thumbnail of Conductometry and Thermodynamics Study of Metal Dodecyl Sulfates In Aqueous Solution

Journal of Dispersion Science and …, Jan 1, 2007

The aggregation behavior of metal dodecyl sulfates (MDS), [Na1+, Mg2+, Mn2+, Co2+, and Ni2+] in w... more The aggregation behavior of metal dodecyl sulfates (MDS), [Na1+, Mg2+, Mn2+, Co2+, and
Ni2+] in water has been studied by electrical conductivity (at 293.15–333.15 K) and surface tension methods (at 303.15 K). Critical micelle concentrations (CMCs), degree of counterion
dissociation (b) evaluated from conductivity data. Using law of mass action model, the thermodynamic parameters viz. Gibbs energy (DGm 0 ), enthalpy (DHm 0 ), and entropy (DSm 0 ) were
evaluated. The enthalpy of micellization decreases strongly with increasing temperature. DG is always negative (thermodynamically favored process) and slightly temperature and counterion dependent. Gibbs energy and entropy exploit micellization as thermodynamic favorable process. The electrostatic repulsions between ionic head groups, which prevent the aggregation, are progressively screened as the ionic character decreases with the size of the counterion. The plots of differential conductivity, (dk/dc)T,P, versus the total surfactant concentration enables us to determine the CMC values more precisely than the conventional method. Surfactants with strong condense counterion are adapted to rodlike micelle better
than to a spherical micelle. The data are explained in terms of molecular characteristics of surfactants viz. degree of dissociation, polar head group size and counterion.

Research paper thumbnail of Mixed Micellization of Dodecyldimethylamine Oxide With Bile Salts In Aqueous Solutions

Journal of Dispersion Science and …, Jan 1, 2009

Micellar behavior of dodecyldimethylamine oxide (DMDAO) with bile salts [sodium deoxycholate (NaD... more Micellar behavior of dodecyldimethylamine oxide (DMDAO) with bile salts [sodium deoxycholate (NaDC) and sodium cholate (NaC)] with and without NaCl was studied by surface tension. Interaction parameters of the mixed micelles were estimated using Rubingh’s theory. Strong synergism observed for each mixed system, which is a common feature shown by anionic-cationic mixtures. The mixed solutions remained clear even at equimolar ratio. Different behavior of the two bile salts is explained on the basis of their orientation in cationic micelles.