P. S. Goyal

Shapes and sizes of micelles in CTAB solutions

SANS from micellar solutions of pure cetyltrimethyl ammonium bromide (CTAB) with and without addition of NaSal has been studied. It is found that micelles are ellipsoidal (C=A≠B) and the BA ratio depends on concentrations of CTAB and NaSal and on the temperature of the solution. The BA values over a range of concentration and temperature are obtained.

SANS from micellar solutions of CTAB and sodium salicylate

SANS from 0.1M solution of CTAB without and with addition of varying concentrations of NaSal has been studied. The measured spectra show that on addition of NaSal two or more of CTAB micelles join together to form a bigger micelle. These micelles disintegrate to smaller ones on heating.

Small angle neutron scattering from micellar solutions of triton X-100

Micellar solutions of non-ionic surfactant triton X-100 (8% by weight) show phase separation at cloud pointTcp ∼ 335 K. This paper reports results of small angle neutron scattering (SANS) experiments from this solution as a function of temperature between 298 and 332 K. The range of wave-vector transferQ, covered in these experiments is from 0.02 to 0.15 Å−1. It is seen that as one approachesTcp, the neutron scattering cross section diverges in the region of lowQ (<0.06 Å−1) while it is independent of temperature in region of largeQ(>0.06 Å−1). We believe that the divergence of scattering at lowQ with an increase in temperature is because of changes in the structure factorS(Q) of the solution. The measured distributions have been analyzed using four different models for inter-micellar potential. The models used to calculate the structure factorS(Q) are (1) mean spherical approximation (MSA) with Yukawa tail for attractive potential, (2) MSA with an attractive square well potential, (3) random phase approximation (RPA) with an attractive square-well potential and (4) Sticky hard sphere model (attractive square-well potential with Percus-Yevick approximation). The strengths of the attractive potential required to fit the SANS data are (−6.6 to − 14.4)/kt for model (1), (− 6.6 to − 15.0)/kt for model (2), (− 3.8 to − 7.3)/kB T for model (3) and (−2 to −2.7)/kt for model (4). On the basis of reasonableness of the derived strength of the potential near the phase separation temperature and its relative temperature dependence, it is concluded that present data favour the Sticky hard sphere model.

Small-angle neutron scattering studies of sodium butyl benzene sulfonate aggregates in aqueous solution

The aggregation behaviour of a hydrotrope, sodiumn-butyl benzene sulfonate (Na-NBBS), in aqueous solutions is investigated by small-angle neutron scattering (SANS). Nearly ellipsoidal aggregates of Na-NBBS at concentrations well above its minimum hydrotrope concentration were detected by SANS. The hydrotrope seems to form self-assemblies with aggregation number of 36–40 with a substantial charge on the aggregate. This aggregation number is weakly affected by the hydrotrope concentration.

Small angle neutron scattering from micellar solutions

Abstract Small angle neutron scattering (SANS) is an ideal tool for studying structures of macromolecules and colloidal solutions. A number of micellar solutions have been studied in our laboratory using a home built SANS spectrometer. This paper gives an introduction to the technique of SANS and gives a brief survey of the results obtained at Trombay.

Counterion condensation in ionic micelles as studied by a combined use of SANS and SAXS

We report a combined use of small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS) to the study of counterion condensation in ionic micelles. Small-angle neutron and X-ray scattering measurements have been carried out on two surfactants cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium chloride (CTACl), which are similar but having different counterions. SANS measurements show that CTABr surfactant forms much larger micelles than CTACl. This is explained in terms of higher condensation of Br− counterions than Cl− counterions. SAXS data on these systems suggest that the Br− counterions are condensed around the micelles over smaller thickness than those of Cl− counterions.

Small-angle neutron scattering studies of nonionic surfactant: Effect of sugars

Micellar solution of nonionic surfactantn-dodecyloligo ethyleneoxide surfactant, decaoxyethylene monododecyl ether [CH3(CH2)11(OCH2CH2)10OH], C12E10 in D2O solution have been analysed by small-angle neutron scattering (SANS) at different temperatures (30, 45 and 60° C) both in the presence and absence of sugars. The structural parameters like micelle shape and size, aggregation number and micellar density have been determined. It is found that the micellar structure significantly depends on the temperature and concentration of sugars. The micelles are found to be prolate ellipsoids at 30° C and the axial ratio of the micelle increases with the increase in temperature. The presence of lower concentration of sugar reduces the size of micelles and it grows at higher concentration of sugar. The structure of micelles is almost independent of the different types of sugars used.

Small-angle neutron scattering from micellar solutions

Micellar solutions are the suspension of the colloidal aggregates of the sur-factant molecules in aqueous solutions. The structure (shape and size) and the interaction of these aggregates, referred to as micelles, depend on the molecular architecture of the surfactant molecule, presence of additives and the solution conditions such as temperature, concentration etc. This paper gives the usefulness of small-angle neutron scattering to the study of micellar solutions with some of our recent results.

Neutron scattering from glycine and deuterated glycine

Abstract Dynamics of α-glycine from normal, C-deuterated and N-deuterated samples at 20 K has been investigated through high-resolution neutron-scattering experiments in the energy-transfer range 5–250 meV. Torsional peak of NH + 3 is found to be split, an observation made for the first time using neutrons. The torsional potential is seen to be anharmonic. Coupling of other modes to the motion of hydrogen atoms of NH + 3 and CH 2 is discussed.

Small-angle neutron and dynamic light scattering study of gelatin coacervates

The state of intermolecular aggregates and that of folded gelatin molecules could be characterized by dynamic laser light and small-angle neutron scattering experiments, which implied spontaneous segregation of particle sizes preceding coacervation, which is a liquid-liquid phase transition phenomenon. Dynamic light scattering (DLS) data analysis revealed two particle sizes until precipitation was reached. The smaller particles having a diameter of ∼50 nm (stable nanoparticles prepared by coacervation method) were detected in the supernatant, whereas the inter-molecular aggregates having a diameter of ∼400 nm gave rise to coacervation. Small-angle neutron scattering (SANS) experiments revealed that typical mesh size of the networks exist in polymer dense phase (coacervates) [1]. Analysis of the SANS structure factor showed the presence of two length scales associated with this system that were identified as the correlation length or mesh size, ξ = 10.6 Å of the network and the other is the size of inhomogeneities = 21.4 Å. Observations were discussed based on the results obtained from SANS experiments performed in 5% (w/v) gelatin solution at 60°C (ξ = 50 Å, ζ = 113 Å) and 5% (w/v) gel at 28°C (ξ = 47 Å, ζ = 115 Å) in aqueous phase [2] indicating smaller length scales in coacervate as compared to sol and gel.