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P. S. Goyal - One of the best experts on this subject based on the ideXlab platform.
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role of different counterions and size of micelle in concentration dependence Micellar Structure of ionic surfactants
Chemical Physics Letters, 2003Co-Authors: V K Aswal, P. S. GoyalAbstract:Abstract Small-angle neutron scattering experiments have been carried out on aqueous Micellar solutions of cationic surfactants cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl) and dodecyltrimethylammoinum bromide (DTABr) as a function of varying surfactant concentration. It is found that while CTABr shows sphere-to-rodlike transition of micelles with the increase in the surfactant concentration, the micelles of CTACl and DTABr remain more or less spherical even at very high surfactant concentrations. We explain the propensity of the above surfactants to form different Structures in terms of the counterion condensation. The counterion condensation on the micelle decreases as the hydrated size of the counterion increases or the size of the micelle decreases.
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Micellar Structure of silicone surfactants in water from surface activity sans and viscosity studies
Journal of Physical Chemistry B, 2002Co-Authors: Saurabh S Soni, V K Aswal, N V Sastry, P. S. GoyalAbstract:The aqueous solutions of two nonionic silicone surfactants based on polyether modified poly(dimethylsiloxane)s have been analyzed by cloud point, surface tension, small angle neutron scattering (SANS), and viscosity measurements. These surfactants have a comb-like Structure with a linear poly(dimethylsiloxane) backbone chain and a grid containing block oligomers of ethylene oxide and/or propylene oxide as branches. The critical micelle concentrations (CMCs) were obtained from break points in surface tension vs log concentration plots and, as expected, decreased systematically with the increase in the hydrophobicity. Small angle neutron scattering (SANS) measurements have been made in aqueous solutions of silicone surfactants at different concentrations (1, 2, and 5 % w/v) and temperatures (30, 45, and 60 °C) to elucidate the structural information on micelles. The analysis of the SANS curves revealed the presence of oblate ellipsoidal micelles in three selected concentrations and temperatures. The size of...
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role of counterion of the surfactant molecule on the Micellar Structure in aqueous solution
Current Science, 2002Co-Authors: J V Joshi, V K Aswal, Pratap Bahadur, P. S. GoyalAbstract:This article reports the sizes and shapes of micelles of anionic surfactants of LiDS, NaDS, KDS, RbDS and CsDS in aqueous solutions as studied by the technique of small-angle neutron scattering. The micelles of these surfactants are made up of negatively charged DS - ions, while the positively charged ions such as Na + (referred to as counterions) tend to stay near the Micellar surface. The present study shows that the distribution of counterions around the micelle depends on hydrophilicity of the counterions, and this in turn decides the Micellar Structure.
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Micellar Structure and inter micelle interactions in Micellar solutions results of small angle neutron scattering studies
2001Co-Authors: P. S. Goyal, V K AswalAbstract:Micelles are aggregates of surfactant molecules suspended in water. The Structure (shape and size) of a micelle depends both on the architecture of the constituent surfactant molecule and the solution conditions such as temperature, presence of impur ities, etc. The inter-particle interaction between micelles also depends on several different parameters. It is of interest to study the Structure and interMicellar interactions in Micellar solutions both from the point of view of basic research and the applic ations. It has been found that the technique of Small Angle Neutron Scattering (SANS) is ideally suited for the above studies. This paper gives an introdu ction to the technique of SANS and discusses the results of typical SANS studies dealing with the mice llar Structure and the inter-Micellar interactions.
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Micellar Structure of an ethylene oxide propylene oxide block copolymer a small angle neutron scattering study
Journal of Physical Chemistry B, 1998Co-Authors: Nirmesh Jain, P. S. Goyal, V K Aswal, Pratap BahadurAbstract:Micellar solutions of a highly hydrophilic ethylene oxide−propylene oxide triblock copolymer, pluronic F88 (EO103PO39EO103), in aqueous solution are examined by small-angle neutron scattering (SANS) at different concentrations and temperatures and in the presence of different salts. At temperature less than 30 °C, F88 solution in water (5 wt %) showed unimers which are fully dissolved Gaussian chains. The unimer-to-micelle transition takes place when the temperature or concentration is increased. Added neutral salt favors micellization of the copolymer at lower concentration/temperature. At temperature close to ambient, block copolymer forms micelles that consist of a central core, presumably dominated by the propylene oxide blocks, surrounded by a corona of highly hydrated ethylene oxide subchains. SANS analysis shows that the size of hydrophobic core increases as a part of PEO adjacent to the PPO core loses water with increasing temperature or salt (KCl) concentration. The Micellar volume fraction incre...
V K Aswal - One of the best experts on this subject based on the ideXlab platform.
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phenyl ring bearing cationic surfactants effect of ring location on the Micellar Structure
Langmuir, 2010Co-Authors: V K Aswal, S RamakrishnanAbstract:A series of isomeric cationic surfactants (S1-S5) bearing a long alkyl chain that carries a 1,4-phenylene unit and a trimethyl ammonium headgroup was synthesized; the location of the phenyl ring within the alkyl tail was varied in an effort to understand its influence on the amphiphilic properties of the surfactants. The cmc's of the surfactants were estimated using ionic conductivity measurements and isothermal calorimetric titrations (ITC); the values obtained by the two methods were found to be in excellent agreement. The ITC measurements provided additional insight into the various thermodynamic parameters associated with the micellization process. Although all five surfactants have exactly the same molecular formula, their Micellar properties were seen to vary dramatically depending on the location of the phenyl ring; the cmc was seen to decrease by almost an order of magnitude when the phenyl ring was moved from the tail end (cmc of S1 is 23 mM) to the headgroup region (cmc of S5 is 3 mM). In all cases, the enthalpy of micellization was negative but the entropy of micellization was positive, suggesting that in all of these systems the formation of micelles is both enthalpically and entropically favored. As expected, the decrease in cmc values upon moving the phenyl ring from the tail end to he headgroup region is accompanied by an increase in the thermodynamic driving force (Delta G) for micellization. To understand further the differences in the Micellar Structure of these surfactants, small-angle neutron scattering (SANS) measurements were carried out; these measurements reveal that the aggregation number of the micelles increases as the cmc decreases. This increase in the aggregation number is also accompanied by an increase in the asphericity of the Micellar aggregate and a decrease in the fractional charge. Geometric packing arguments are presented to account for these changes in aggregation behavior as a function of phenyl ring location.
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role of different counterions and size of micelle in concentration dependence Micellar Structure of ionic surfactants
Chemical Physics Letters, 2003Co-Authors: V K Aswal, P. S. GoyalAbstract:Abstract Small-angle neutron scattering experiments have been carried out on aqueous Micellar solutions of cationic surfactants cetyltrimethylammonium bromide (CTABr), cetyltrimethylammonium chloride (CTACl) and dodecyltrimethylammoinum bromide (DTABr) as a function of varying surfactant concentration. It is found that while CTABr shows sphere-to-rodlike transition of micelles with the increase in the surfactant concentration, the micelles of CTACl and DTABr remain more or less spherical even at very high surfactant concentrations. We explain the propensity of the above surfactants to form different Structures in terms of the counterion condensation. The counterion condensation on the micelle decreases as the hydrated size of the counterion increases or the size of the micelle decreases.
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Micellar Structure of silicone surfactants in water from surface activity sans and viscosity studies
Journal of Physical Chemistry B, 2002Co-Authors: Saurabh S Soni, V K Aswal, N V Sastry, P. S. GoyalAbstract:The aqueous solutions of two nonionic silicone surfactants based on polyether modified poly(dimethylsiloxane)s have been analyzed by cloud point, surface tension, small angle neutron scattering (SANS), and viscosity measurements. These surfactants have a comb-like Structure with a linear poly(dimethylsiloxane) backbone chain and a grid containing block oligomers of ethylene oxide and/or propylene oxide as branches. The critical micelle concentrations (CMCs) were obtained from break points in surface tension vs log concentration plots and, as expected, decreased systematically with the increase in the hydrophobicity. Small angle neutron scattering (SANS) measurements have been made in aqueous solutions of silicone surfactants at different concentrations (1, 2, and 5 % w/v) and temperatures (30, 45, and 60 °C) to elucidate the structural information on micelles. The analysis of the SANS curves revealed the presence of oblate ellipsoidal micelles in three selected concentrations and temperatures. The size of...
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role of counterion of the surfactant molecule on the Micellar Structure in aqueous solution
Current Science, 2002Co-Authors: J V Joshi, V K Aswal, Pratap Bahadur, P. S. GoyalAbstract:This article reports the sizes and shapes of micelles of anionic surfactants of LiDS, NaDS, KDS, RbDS and CsDS in aqueous solutions as studied by the technique of small-angle neutron scattering. The micelles of these surfactants are made up of negatively charged DS - ions, while the positively charged ions such as Na + (referred to as counterions) tend to stay near the Micellar surface. The present study shows that the distribution of counterions around the micelle depends on hydrophilicity of the counterions, and this in turn decides the Micellar Structure.
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Micellar Structure and inter micelle interactions in Micellar solutions results of small angle neutron scattering studies
2001Co-Authors: P. S. Goyal, V K AswalAbstract:Micelles are aggregates of surfactant molecules suspended in water. The Structure (shape and size) of a micelle depends both on the architecture of the constituent surfactant molecule and the solution conditions such as temperature, presence of impur ities, etc. The inter-particle interaction between micelles also depends on several different parameters. It is of interest to study the Structure and interMicellar interactions in Micellar solutions both from the point of view of basic research and the applic ations. It has been found that the technique of Small Angle Neutron Scattering (SANS) is ideally suited for the above studies. This paper gives an introdu ction to the technique of SANS and discusses the results of typical SANS studies dealing with the mice llar Structure and the inter-Micellar interactions.
P Thiyagarajan - One of the best experts on this subject based on the ideXlab platform.
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small angle neutron scattering and viscosity studies of ctab nasal viscoelastic Micellar solutions
Journal of Physical Chemistry B, 1998Co-Authors: V Aswal K And, P. S. Goyal, P ThiyagarajanAbstract:Micellar solutions of cationic surfactant cetyltrimethylammonium bromide (CTAB) in the presence of sodium salicylate (NaSal) show a viscoelastic behavior. Small-angle neutron-scattering (SANS) and viscosity studies from CTAB/NaSal Micellar solutions are reported. Zero-shear viscosity of these solutions as a function of NaSal concentration (Cs), at all the four measured surfactant concentrations (Cd) of 12.5. 25, 50 and 100 mM, show a double-peak behavior. The effect of Cs/Cd on two viscosity maxima and a minimum has been examined, and the scaling relations are obtained. SANS experiments have been carried out at different NaSal concentrations, beyond the first viscosity maximum for two surfactant concentrations of 25 and 100 mM. It is found that micelles are rigid rods and their exponential length distribution shows that they behave as living polymers beyond the first viscosity maximum. The Micellar Structure does not change in the living polymer regime, whereas viscosity varies with increase in NaSal conc...
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small angle neutron scattering study of Micellar Structure and interparticle interactions in triton x 100 solutions
Physical Review E, 1995Co-Authors: P. S. Goyal, S V G Menon, B A Dasannacharya, P ThiyagarajanAbstract:Extensive measurements of small-angle nuetron-scattering cross sections from the nonionic Micellar solutions of Triton X-100 in D[sub 2]O are reported. An analysis of data at ambient temperature shows that the micelles are oblate ellipsoids of revolution with an axial ratio around two even at a concentration as low as 1% Triton X-100, and that there are about 20 molecules of D[sub 2]O per surfactant molecule in the hydrophilic region. This Micellar model---without invoking any further growth---is shown to explain the data for a wide range of concentrations at ambient temperature. Information about interMicellar interactions is obtained by analyzing the data using Baxter's sticky hard-sphere model, which assumes a square-well attractive potential between the micelles. This model is found to provide a qualitative interpretation of the temperature dependence of the data. However, important differences are noted for low momentum transfers. Some drawbacks of the model for characterizing the entire set of scattering data are brought out and discussed.
Gregory G Warr - One of the best experts on this subject based on the ideXlab platform.
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Micellar Structure in gemini nonionic surfactants from small angle neutron scattering
Langmuir, 2005Co-Authors: Paul A Fitzgerald, Tim W Davey, Gregory G WarrAbstract:The size and shape of micelles formed by dimeric polyoxyethylene (nonionic gemini) surfactants having the Structure (Cn-2H2n-3CHCH2(OCH2CH2)mOH)2(CH2)6 with alkyl and ethoxy chain lengths ranging from n = 12-20 and m = 5-30 have been determined using small angle neutron scattering (SANS). The surfactants are polydisperse in the hydrophilic groups but otherwise analogous to the widely studied monomeric poly(oxyethylene) alkanols. We find that longer ethoxylated chains are needed to confer solubility on the gemini surfactants and that these chains in the hydrophilic corona around the alkyl core of the micelles are reasonably well described as a homogeneous random coil in a good solvent. Spherical micelles are formed by the surfactants with the longest ethoxylated chains. Shorter chains lead first to rods and ultimately a vesicle dispersion. These solutions exhibit conventional cloud point behavior, and on warming, a sphere to rod transition can be observed. For the n = 20 and m = 15 surfactant, this shape transition is accompanied by a striking increase in viscosity at low concentration and gelation at higher concentrations.
Toshiyuki Shikata - One of the best experts on this subject based on the ideXlab platform.
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rheo sans studies on shear thickening thinning in aqueous rodlike Micellar solutions
Langmuir, 2011Co-Authors: Makiko Takeda, Takumi Kusano, Takuro Matsunaga, Hitoshi Endo, Mitsuhiro Shibayama, Toshiyuki ShikataAbstract:Shear-induced thickening/thinning phenomena of aqueous rodlike Micellar solutions of cetyltrimethylammonium bromide (CTAB) and sodium p-toluene sulfonate (NapTS) were investigated by means of simultaneous measurements of rheology and small-angle neutron scattering (SANS), the so-called Rheo-SANS. The aqueous CTAB/NapTS solutions were classified into five different categories dependent on their flow behavior and Micellar Structure. By increasing salt concentration and/or shear rates, the micelles underwent morphological transition from (i) spherical or short rodlike micelles to (ii) long rodlike micelles without entanglements, followed by (iii) those with entanglements. These transitions were recognized as changes in flow behavior from Newtonian to shear-thickening and shear-thinning flow, respectively. In the latter two cases, anisotropic SANS patterns appeared around these critical shear rates. The physical meaning of the anisotropic SANS patterns accompanied by shear-thickening flow behavior is discussed in conjunction with other shear-thickening systems.