Small angle neutron scattering studies on the interaction of cationic surfactants with bovine serum albumin

The structure of the protein-surfactant complex of bovine serum albumin (BSA) and cationic surfactants has been studied by small angle neutron scattering. At low concentrations, the CTAB monomers are observed to bind to the protein leading to an increase in its size. On the other hand at high concentrations, surfactant molecules aggregate along the unfolded polypeptide chain of the protein resulting in the formation of a fractal structure representing a necklace model of micelle-like clusters randomly distributed along the polypeptide chain. The fractal dimension as well as the size and number of micelles attached to the complex have been determined.      

Small angle neutron scattering study of temperature-independent formulation of mixed micellar structures

SANS measurements have been performed on mixed systems of ionic surfactant sodium dodecyl sulphate (SDS) and nonionic surfactant polyoxyethylene 10 lauryl ether (C12E10). The total concentration of the mixed system was kept fixed (10 wt%) and the ionic to nonionic surfactant ratio varied in the range 0 to 1. The temperature effect on the structures of mixed micelles has been studied for temperatures between 30 and 75°C. Micelles of pure ionic and nonionic surfactants show opposite trends when the temperature is increased. Sizes of pure ionic micelles decrease and those of nonionic micelles increase with increase in temperature. We show a formulation balancing these two effects which is temperature-independent and consists of about 25% of ionic surfactants in the mixed system. Contrast variation SANS measurements by contrast matching one of the surfactant components to the solvent suggest homogeneous single mixed micelles of the two components in the mixed systems.      

Small angle neutron scattering from micellar solutions

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.     

Small angle neutron scattering study of mixed micelles of oppositely charged surfactants

Structures of mixed micelles of oppositely charged surfactants dodecyltrimethylammonium bromide (DTAB) and sodium dodecyl sulphate (SDS) have been studied using small angle neutron scattering. The concentration of one of the components was kept fixed (0.3 M) and that of another varied in the range 0 to 0.1 M. The aggregation number and micellar size increase and fractional charge decreases dramatically with the addition of small amount of oppositely charged surfactant. The effect of addition of SDS on DTAB is significantly different from that of the addition of DTAB on SDS. The contrast variation SANS experiments using deuterated surfactant suggests the homogeneous mixing of two components in mixed micellar system.      

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 pointT _cp ～ 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 approachesT _cp, 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)/k _B 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 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 study on the aggregation behaviour of PEO-PPO-PEO copolymers in the presence of a hydrophobic diol

Small angle neutron scattering (SANS) measurements on aqueous solutions of four polyethylene oxide-polypropylene oxide-polyethylene oxide block copolymers (commercially known as Pluronic®)F88, P85, F127 and P123 in the presence of hydrophobic C14Diol (also known as Surfynol® 104) reveal information on micellization, micellar size and micellar transitions. While most hydrophilic F88 (with least PPO/PEO ratio) remained unimers in water at 30°C, other copolymers formed micellar solutions. Surfynol® 104 is sparingly soluble in water to only about ～0.1 wt%, but on addition to pluronic solution, it gets incorporated in the micellar region of block copolymer which leads to increase in aggregation number and transformation of spherical to ellipsoidal micelles. The added diol-induced micellization in F88, though hydrophilic copolymers F88 and F127 did not show any appreciable micellar growth or shape changes as observed for P85 and P123 (which are comparatively more hydrophobic). The SANS results on copolymer pairs with same molecular weight PPO but different % PEO (viz. F88 and P85, F127 and P123) and with same molecular weight PEO but different PPO (F88 and F127) reveal that the copolymer with large PPO/PEO ratio facilitate micellar transition in the presence of diol. An increase in temperature and presence of added electrolyte (sodium chloride) in the solution further enhances these effects. The micellar parameters for these systems were found out using available software and are reported.     

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.     

Probing polymer nanocomposite morphology by small angle neutron scattering

Polyamide nanocomposite films were prepared from nanometer-sized silica particles having particle radius of gyration (R _g) of about 66 Å and trimesoyl chloride-m-phenylene diamine-based polyamides having macromolecular units of about 100–140 Å. The nanoscale morphology of the samples was characterized using small angle neutron scattering (SANS). SANS reveals that silica nanoparticles interact well with the polyamide units only at limited silica loading.     

Small-angle neutron scattering study of aggregate structures of multi-headed pyridinium surfactants in aqueous solution

The aggregate structures of a set of novel single-chain surfactants bearing one, two and three pyridinium headgroups have been studied using small-angle neutron scattering (SANS). It is found that the nature of aggregate structures of these cationic surfactants depend on the number of headgroups present in the surfactants. The single-headed pyridinium surfactant forms the lamellar structure, whereas surfactants with double and triple headgroups form micelles in water. The aggregates shrink in size with increase in the number of headgroups in the surfactants. The aggregation number (N) continually decreases and the fractional charge (α) increases with more number of headgroups on the surfactants. The semimajor axis (a) and semiminor axis (b = c) of the micelle also decrease with the increase in the number of headgroups in the surfactants. This indicates that hydrocarbon chains in such micelles prepared from multiheaded surfactants adopt bent conformation and no longer stay in extended conformation.     

Small angle neutron scattering studies on protein denaturation induced by different methods

Small angle neutron scattering (SANS) has been used to study conformational changes in protein bovine serum albumin (BSA) as induced by varying temperature and in the presence of protein denaturating agents urea and surfactant. BSA has prolate ellipsoidal shape and is found to be stable up to 60°C above which it denaturates and subsequently leads to aggregation. The protein solution exhibits a fractal structure at temperatures above 64°C, with fractal dimension increasing with temperature. BSA protein is found to unfold in the presence of urea at concentrations greater than 4 M and acquires a random coil Gaussian chain conformation. The conformation of the unfolded protein in the presence of surfactant has been determined directly using contrast variation SANS measurements by contrast matching surfactant molecules. The protein acquires a random coil Gaussian conformation on unfolding with its radius of gyration increasing with increase in surfactant concentration      

Small angle neutron scattering study of pore microstructure in ceria compacts

Ceria powders were prepared by gel combustion process using cerium nitrate and hitherto unexplored amino acids such as aspartic acid, arginine and valine as fuels. The powders have been characterized by X-ray and laser diffraction. Cold pressed compacts of these powders have been sintered at 1250°C for 2 h. Internal pore microstructure of the sintered compacts has been investigated by small angle neutron scattering (SANS) over a scattering wave vector q range of 0.003–0.17 nm⁻¹. The SANS profiles indicate surface fractal morphology of the pore space with fractal dimensionality lying between 2.70 and 2.76.      

Small angle neutron scattering study of doxorubicin-surfactant complexes encapsulated in block copolymer micelles

Self-assembling behaviour of block copolymers and their ability to evade the immune system through polyethylene oxide stealth makes it an attractive candidate for drug encapsulation. Micelles formed by polyethylene oxide-polypropylene oxide- polyethylene oxide triblock copolymers (PEO-PPO-PEO), pluronic P123, have been employed for encapsulating the anti-cancer drug doxorubicin hydrochloride. The binding affinity of doxorubicin within the micelle carrier is enhanced through complex formation of drug and anionic surfactant, aerosol OT (AOT). Electrostatic binding of doxorubicin with negatively charged surfactants leads to the formation of hydrophobic drug-surfactant complexes. Surfactant-induced partitioning of the anti-cancer drug into nonpolar solvents such as chloroform is investigated. SANS measurements were performed on pluronic P123 micelles in the presence of drug-surfactant complex. No significant changes in the structure of the micelles are observed upon drug encapsulation. This demonstrates that surfactant- drug complexes can be encapsulated in block copolymer micelles without disrupting the structure of aggregates.      

Small-angle neutron scattering study of the structure of mixed micellar solutions based on nonionic and two cationic surfactants

The aggregation in mixed water systems based on nonionic surfactant, i.e., heptaethylene glycol monotetradecyl ether (C14E7), and cationic surfactants, i.e., cetyltrimethylammonium bromide (CTAB) and cetyltrimethylammonium chloride (CTAC), has been investigated using the small-angle neutron scattering method. The preliminary results of the study of the behavior of C14E7 aqueous solutions (for a concentration of 0.17%) when adding various small amounts of classical cationic surfactants (CTAB and CTAC) have been presented.     

Small angle neutron scattering and small angle X-ray scattering studies of platinum-loaded carbon foams

The morphology of carbon nanofoam samples comprising platinum nanoparticles dispersed in the matrix was characterized by small angle neutron scattering (SANS) and small angle X-ray scattering (SAXS) techniques. Results show that the structure of pores of carbon matrix exhibits a mass (pore) fractal nature and the average radius of the platinum particles is about 2.5 nm. The fractal dimension as well as the size distribution parameters of platinum particles varies markedly with the platinum content and annealing temperature. Transmission electron micrographs of the samples corroborate the SANS and SAXS results.      

A small angle neutron scattering (SANS) experiment using very cold neutrons (VCN)

This paper describes the results of SANS measurements of small samples using the very cold neutron (VCN) beam of the PF2 instrument at the Institut Laue Langevin (ILL), France. In addition to a classical SANS pinhole collimation, the experiment used a polarizing supermirror as a monochromator and a magnetic sextupole lens to focus the neutron beam in order to gain intensity and avoid any material in the neutron beam besides the sample.     

Morphology of carbon nanotubes prepared via chemical vapour deposition technique using acetylene: A small angle neutron scattering investigation

Small angle neutron scattering (SANS) has been utilized to study the morphology of the multi-walled carbon nanotubes prepared by chemical vapour deposition of acetylene. The effects of various synthesis parameters like temperature, catalyst concentration and catalyst support on the size distribution of the nanotubes are investigated. Distribution of nanotube radii in two length scales has been observed. The number density of the smaller diameter tubes was found more in number compared to the bigger one for all the cases studied. No prominent scaling of the structure factor was observed for the different synthesis conditions.      

A small angle neutron scattering study on the mixtures of pluronic L121 and anionic surfactant AOT

Small angle neutron scattering (SANS) experiments have been carried out on the micellar solutions containing mixtures of a hydrophobic triblock copolymer (L121, EO₅PO₆₈EO₅) and a hydrophobic anionic surfactant (AOT, sodium bis(2-ethylhexyl)sulphosuccinate) in water with varying ratio (R) of AOT to L121 for R = 0.15, 0.2, 0.3, 0.5 and 0.6. It is known that either L121 or AOT alone forms vesicles in water, but in the mixture with appropriate ratio of the two components a thermodynamically stable, isotropic solution of apparently small micelle-like aggregates is formed. We find that these micelles are prolate ellipsoidal.      

Investigation on pore structure and small-scale agglomeration behaviour in liquid phase sintered SiC using small angle neutron scattering

Mesoscopic density fluctuations in liquid phase sintered silicon carbide have been investigated using small angle neutron scattering (SANS). The increase in the additives results in the modification in the pore size distribution and to some extent the total porosity. SANS revealed a mass fractal nature of the agglomerated matrix microstructure. The fractal dimension of the matrix does not change appreciably with the additives although the upper cut-off value of the fractal decreases significantly with the increase in the additives. The liquid phase sintering due to the presence of additives helps to achieve higher level of densification. However, the agglomeration hinders achievement of the fully dense pellets.      

Computation of small angle neutron scattering functions for molecules of arbitrary shapes

A computer program has been developed to analyze small angle neutron scattering (SANS) data by using the Debye method of spherical modification proposed by Glatter. In the calculational procedure the model shape is emulated with a large number of overlapping small spheres which fill the volume of the model shape. A technique is described for fitting experimental data to a resolution-broadened model scattering function. At each stage of the iterative procedure the radius of gyration is computed. The program is able to calculate the scattering function of the mixture of two different molecules. This facility even allows one to calculate the scattering function of the mixture of monomer and dimer of a particular molecule in aqueous solution. In case a portion of the molecule has a different weight from the rest, the program has a variation to calculate the scattering function of that model as well.