Light-scattering Investigations Research Articles

Calorimetric and Light Scattering Investigations of the Transition from Spherical to Wormlike Micelles of C₁₄TAB Triggered by Salicylate.

Although wormlike micelles (WLM) were first described more than 30 years ago, many aspects of their formation process are still unclear. Herein, a systematic experimental investigation of the process for wormlike micelle (WLM) formation in mixtures of tetradecyltrimethylammonium bromide (C14TAB) and salicylate (2-hydroxybenzoate) was carried out. This system was used as a model to investigate the conditions for the formation of the giant aggregate. For comparison, the other two isomers of salicylate (3- and 4-hydroxybenzoate) were also investigated, once in these cases wormlike micelles are not formed. The studies were based on calorimetric titration, static light scattering, and rheological measurements. Enthalpy changes upon titration of C14TAB into 2-hydroxybenzoate solutions revealed a highly cooperative and exothermic process that was associated with micelle growth. The size of the aggregates, obtained by static light scattering measurements, confirms the shape transition. In addition, the correlation of these two sets of results with measurements of micelle charge surface indicates that this transition occurs around the point of charge neutralization.

Stimuli-Responsive PNIPAM Based Copolymers: Modeling and Light Scattering Investigations

Temperature dependent behavior of poly(N -isopropylacrylamide) (PNIPAM) copolymers was investigated in three bu er-stabilized environments. The tests were performed in thermostabilized goniometer by dynamic and static light scattering. From the dynamic light scattering hydrodynamic radius was obtained. Based on the static light scattering data, calculations of the particle radius from the form factor model were done. Depending of the kind of copolymer, the di erent material response to temperature was observed. Also the characterization of dry particles was done by scanning electron microscope. These scanning electron microscopy micrograms showed the possibility of particles to aggregation.

Stimuli-Responsive PNIPAM Based Copolymers: Modeling and Light Scattering Investigations

Stimuli-Responsive PNIPAM Based Copolymers: Modeling and Light Scattering Investigations

Effect of polymer on the elasticity of surfactant membranes: A light scattering study

We have performed a dynamic light-scattering (DLS) investigation of the effect of a water-soluble polymer, polyethylene glycol (PEG), on the bending elastic modulus κ of surfactant membranes. The polymer, in concentrations ranging from 0 to 8 g/L (0 to 0.4 mM), was incorporated into the solvent of sponge phases of the sodium dodecyl sulfate (SDS)-hexanol-brine system. PEG adsorbs into the SDS membranes. The correlation functions of the polymer-doped sponge phases displayed a stretched-exponential decay, appropriately described by the Zilman-Granek (Z-G) theory for fluctuating membranes. The dynamics of the surfactant bilayers was slowed down by the addition of the polymer: Increasing PEG concentrations increase the DLS relaxation times. From the Z-G model we extracted the membrane-bending elastic modulus, as a function of polymer concentration, C(PEG) = κ increases with C(PEG), a behavior opposite to that expected from available models for the interaction between fluid membranes and adsorbing polymers. Our results suggest that the polymer penetrates to some extent the surfactant bilayers.

Brillouin Light Scattering Investigations οf Magnetic and Elastic Properties in MBE Grown Trilayer Mo/Co/Au Systems

Brillouin Light Scattering Investigations οf Magnetic and Elastic Properties in MBE Grown Trilayer Mo/Co/Au Systems

Magnetic-field-induced optical anisotropy in ferrofluids: A time-dependent light-scattering investigation

We report an experimental investigation of time dependent anisotropic light scattering by an aqueous suspension of tetramethyl ammonium hydroxide coated Fe3O4 nanoparticles (approximately 6 nm) under the ON-OFF transient of an external dc magnetic field. The study employs the synchronized recording and measurement of the two magnetic-field-induced light-scattering patterns produced by two identical orthogonal He-Ne laser beams passing through the ferrofluid sample and propagating parallel and perpendicular to the applied field, respectively. From these patterns, we extract the time dependence of the induced optical anisotropy, which provides a measure of the characteristic time scale and kinematic response for field-induced structure formation in the sample. We propose that the time evolution of the scattering patterns, which is very fast at short times and significantly slower at long times, can be explained using a model based on a two-stage chain formation and coarsening processes.

Light–scattering in turbid fluids: The single-scattering intensity

Conventionally, light-scattering investigations are restricted to rather transparent samples, because multiple-scattering contributions prevent straight forward evaluation, if the turbidity is high. Now, cross-correlation techniques enable to determine experimentally the intensity and the time correlation function of singly scattered light in the presence of multiple scattering. The analysis of the single-scattering properties is then carried out in the same way as for weakly scattering samples. However, the theoretical analysis indicates that this procedure may lead to erroneous interpretations. Simulations and analytical theory show that the distribution of the light paths in turbid samples is different from that in weakly scattering samples. Thus, with increasing turbidity the scattering center changes continuously from the low turbidity limit, which is conventionally assumed, to a location, where the laser impinges the sample. As demonstrated by analytical and numerical calculations as well as by cross-correlation experiments, this effect gives a contribution to the angular dependence of the single-scattering intensity in addition to that of the scattering cross-section of the scattering particles.

Calorimetric and Dynamic Light-Scattering Investigation of Cationic Surfactant−DNA Complexes

By means of combined calorimetric and dynamic light-scattering measurements, we have investigated the conformational behavior of DNA chains after thermal melting in the presence of a cationic surfactant at different concentrations, up to a surfactant-to-phosphate group molar ratio close to unity. Both the specific heat capacity, C(ex)(p) and the hydrodynamic radius R of the DNA chains provide support for the existence of two structural arrangements with different thermal stabilities, coexisting in the bulk solution. Although a component remains an elongated unfolded DNA chain originated in the thermal denaturation, the second component, consisting of DNA-surfactant complexes, assumes a compact structure with an average size of about 80 nm, whose thermal denaturation occurs at temperatures higher than 100 degrees C.

Light-Scattering Investigation on Microemulsion Formation in Mixtures of Diesel Oil (or Hydrocarbons) + Ethanol + Additives

Ethanol and diesel oil mixtures are potential candidates as fuels which display advantages such as a reduced emission of particulates and the use of a renewable fuel (ethanol). However, their use i...

Synthesis of colloidal aluminosilicate for light-scattering investigations

To develop a binary colloidal system with a slight index of refraction mismatch suitable for light scattering studies, pure silica particles synthesized by the method of Stöber were mixed with aluminosilicate colloids synthesized using a novel approach. With this, index-matching for one component allowed extraction of the spatial distribution of the other. In addition, it was observed that by varying the solvent, interactions between colloids could be tuned from purely repulsive to weakly attractive.

Colloid-borne americium migration in Gorleben groundwater: significance of iron secondary phase transformation.

The mobility of actinides in natural water may be enhanced by colloid-mediated transport. In this context the reversibility of actinide colloid interaction is a key factor. Iron is an element that can generate colloids under conditions found in natural waters. In this paper, the impact of hematite and the low-crystalline precursor 2-line ferrihydrite on colloid-mediated transport of americium(III) is investigated. Am(III)-containing iron colloids are generated from two different approaches, namely contact between the two in aqueous solution or coprecipitation of Am(III) during iron colloid generation. Dissolved organic carbon (DOC), especially humic substances, has a strong influence on the stability of inorganic colloids. In addition, humic substances interfere in the distribution and kinetics of exchange between groundwater and sediments. Four groundwaters from the Gorleben aquifer system are used with DOC concentrations varying between 0.9 and 81.6 mgC/L together with Pleistocene Aeolian quartz sand from this site. Batch and column experiments are conducted under near-natural conditions (Ar + 1% CO2). To study the influence of kinetics, contact times up to one month are studied. The dynamic light-scattering investigations show that the colloidal stability of the 2-line ferrihydrite increases with increasing DOC concentration. The low-crystalline iron colloids have a marginal influence on the Am(III) transport due to reversibility of americium sorption. Contrary to this, the crystalline hematite generated from coprecipitation of Am(III) leads to an increase of unretarded colloid-mediated Am(III) transport up to a factor of almost five. Chemical characterization of these hematite colloids shows that Am(III) is structurally entrapped in the hematite. The distribution of Am(III) and 2-line ferrihydrite between groundwater and sand sediment remained in disequilibrium even after one month. This shows that the kinetics of Am(III) distribution between the different phases (bulk solution/colloidal form/ sediment) is a key issue.

Effect of Different Layer Thicknesses and Boundary Conditions of Confined Liquid Crystal on Dynamics of Director Relaxation: Dynamic Light Scattering Investigations

ABSTRACTDynamic light scattering (DLS) has been used to study the influence of boundary conditions (planar-axial and homeotropic-radial) and layer thickness of liquid crystal (8CB) confined to cylindrical pores on phase transitions and relaxation of director orientational fluctuations. For confined 8CB in the nematic phase two well-defined relaxation processes were observed for both axial and radial orientations of the liquid crystal. The first relaxation is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation (with relaxation time slower than the first one) is most likely due to the fluctuations in the layers nearest the wall surface. In samples with radial boundary conditions, we observed the onset of smectic-A phase order formation on the pore wall even though the rest of the liquid crystal could be in the nematic phase. The influence of pore wall-liquid crystal interactions on the properties of the confined 8CB was stronger for radial boundary conditions of confined liquid crystal, than in the case of axial orientation‥ The separation between the first and the second (slow) process was clearer for thinner layers and the amplitude of the slow process was greater for thinner layers. This suggests that the slow process was related to surface relaxation of director fluctuations.

Time-resolved studies of the interactions between pulsed lasers and aerosols.

Studies of the interaction between a pulsed CO2 laser and micrometer-sized aqueous and organic particles by use of light-scattering methods and step-scan Fourier-transform infrared (FTIR) spectroscopy are reported. Visible two-color extinction experiments indicate primary particle shattering, accompanied by a high fraction of vaporization, followed by secondary particle evaporation. The extent of the latter depends on the pulse intensity and particle composition. Angle-resolved light-scattering investigations provide insight into the aerosol size distribution and temperature following the pulsed heating event. The time dependence of the vapor plume, monitored with step-scan FTIR spectroscopy, confirms that a large fraction of the initial particle is quickly evaporated during the shattering event, followed by secondary fragment evaporation and thermal expansion.

Light scattering investigations on dilute nonionic oil-in-water microemulsions.

Dilute 3-component nonionic oil-in-water microemulsions formulated with either a polyoxyethylene surfactant (C18:1E10 or C12E10) or the alkylamine-N-oxide surfactant, DDAO (C12AO), and containing either a triglyceride or an ethyl ester oil have been examined using dynamic and static light-scattering techniques. Analysis of the results showed distinct differences in the tested oil's mode of incorporation into the microemulsion droplets, with both the molecular volume of the oil and the hydrophobic chain length of the surfactant being important. For example, microemulsions formulated by C18:1E10 and containing one of the larger molecular volume oils (that is, either a triglyceride, Miglyol 812, or soybean oil) or the ethyl ester of fatty acid oil, ethyl oleate, exhibited first a decrease and then an increase in hydrodynamic size and surfactant aggregation number, suggesting that the asymmetric C18:1E10 micelles became spherical upon the addition of a small amount of oil and grew thereafter because of further oil being incorporated into the core of the spherical microemulsion droplet. A similar conclusion of sphericity could not be drawn for microemulsions stabilized by C18:1E10 and containing one of the oils smaller in molecular volume (namely tributyrin, ethyl butyrate, or ethyl caprylate) where neither the aggregation number nor the hydrodynamic radius changed much upon the addition of oil. This result suggested that these oils were preferentially located in the interfacial surfactant monolayer, behaving in much the same way as a cosurfactant. A different trend of results, however, was seen for microemulsions prepared using C12E10 and C12AO, most likely because these surfactants produced approximately spherical micelles. In this case, the microemulsions containing the oils larger in molecular volume tended to exhibit an increase in surfactant aggregation number and hydrodynamic size, suggesting the growth of spherical micelles, while the smaller oils (in particular ethyl butyrate) caused a significant decrease in surfactant aggregation number incompatible with their being incorporated into the centre of the droplet, suggesting that the oils were being located in the interfacial surfactant monolayer. These results suggest that the various oils are incorporated into the microemulsions in very different ways.

Influence of associations on self-diffusion of styrene-methylmethacrylate random copolymers in semidilute acetone solution

The self-diffusion of four styrene–methylmethacrylate random copolymers dissolved in acetone, a thermodynamically bad solvent for the styrene sequences in the copolymer, were investigated by pulsed-field gradient NMR. The echo attenuations Sinc(q,t) are dominated by diffusion of clusters. At higher concentrations, physical gelation sets in (formation of a transient network), which is manifested in an anomalous, restricted diffusion at short observation times. The measured fluctuations of the positions of the chain segments in the transient network have an amplitude of about 100 nm. The free long-range diffusion attained at long observation times shows a much stronger concentration dependence than in the nonassociating solvent benzene. The results are in accord with light-scattering investigations. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2931–2939, 1998

Extended Light Scattering Investigations on Dihydroxy Bile Salt Micelles in Low-Salt Aqueous Solutions

Extended static and dynamic light scattering results on micellar solutions of the dihydroxy bile salt NaGDC (sodium glycodeoxycholate) are presented. From the measurements the apparent molar mass and the mean aggregation number, the apparent diffusion coefficient and the mean hydrodynamic radius for the micelles as a function of NaGDC concentration (8.5−28.0 g/L), ionic strength of the solution (0.03−0.2 M NaCl added), and temperature (20−35 °C) are deduced. The apparent micellar size versus surfactant concentration is discussed only in the context of intermicellar interactions. Growth processes are not taken into account. A self-consistent calculation of the concentration dependence of the diffusion coefficient very similar to that of Dorshow et al.1,2 is applied in order to determine the potential of the micelles using the DLVO theory. The fractional ionization of the micelle surface is estimated. Moreover, the expansion of the analysis from Dorshow et al. shows that Hamaker's constant is proportional t...

A Brillouin light-scattering investigation of the glass-transition in low molecular weight network glass-formers

The temperature dependence of the phase velocity and attenuation of hypersonic longitudinal waves across the glass transition is monitored in two samples of monohydric alcohols by means of Brillouin (inelastic) light scattering. The behaviour with temperature of parameters characterizing the elastic and relaxational responses of the samples is discussed in some detail.

A Brillouin light-scattering investigation of the glass-transition in low molecular weight network glass-formers

The temperature dependence of the phase velocity and attenuation of hypersonic longitudinal waves across the glass transition is monitored in two samples of monohydric alcohols by means of Brillouin (inelastic) light scattering. The behaviour with temperature of parameters characterizing the elastic and relaxational responses of the samples is discussed in some detail.

Sizing of colloidal particles with light scattering: corrections for beginning multiple scattering

Static light scattering is widely used for sizing of particles with radii in the range of 50 nm up to several micrometers. These experiments usually require very low particle concentrations (<10(-4)) for prevention of multiple scattering. As a consequence, nonabsorbing samples that are suited for light-scattering investigations must be transparent so that the transmittance of the incident light is typically above 95%. Investigations of less translucent samples require corrective terms for the beginning of multiple scattering to retrieve the particle-size distribution successfully. We applied a computationally convenient first-order approximation for the multiple-scattering problem that has Hartel's approach in its first steps. When incorporated into our inversion technique, this approximation functions well for samples with transmittances above 30%. We present examples of applications to experimental data.

Electric and Magnetic Field Studies on Rodlike fd-Virus Suspensions

The electrical and optical properties of rodlike fd-virus particles (L=880 nm, D=9 nm) are investigated by magnetic and electric birefringence experiments and supplemented by electric field light-scattering measurements. In aqueous suspension the fd-virus particles are negatively charged and surrounded by diffuse counterion clouds. The examinations are performed at very low ionic strength (10 -6 M). Under these conditions a liquid crystalline phase already occurs at fd-particle concentrations above 0.6 mg/mL. In magnetic fields the rodlike fd-virus is aligned parallel to the magnetic field due to its diamagnetic anisotropy. Almost complete particle alignment in magnetic fields is obtained for liquid crystalline samples, and the saturation value of the birefringence is determined. The application of electric fields results in a polarization of the counterion clouds and a statistical orientation of the dispersed particles. In low electric fields Kerr behavior is found, providing the electric anisotropy Δα el of a single rod. At higher electric fields the diffuse Debye cloud is partly stripped away and a complete particle orientation is hindered. Electric field light-scattering investigations yield quantitatively the decrease of the electric anisotropy Δα el in high electric fields