Static Light-scattering Techniques Research Articles

Elongated Rodlike Particle Formation of Methyl Cellulose in Aqueous Solution.

The conformation and structure of methyl cellulose (MC) ether samples dissolved in pure water under dilute conditions were carefully reconsidered based on the results obtained using small-to-wide-angle neutron scattering (S-WANS), static light scattering (SLS), dynamic light scattering (DLS), and viscometric techniques. The examined MC samples possessed an average degree of substitution by methyl groups per glucose unit of ca 1.8 and weight average molar masses (Mw), ranging from 23 to 790 kg mol–1. S-WANS experiments clearly demonstrated that the samples possess highly elongated rigid rodlike local structures in deuterium oxide solutions with weak periodicities of ca 0.4 and 1.0 nm on a length scale, which correspond to the average intermolecular distance between molecular chain portions facing each other in the formed rodlike structure and the repeating length of the monomeric cellobiose unit of molecular chains, respectively. Ratios of the particle length (L) to the radius of gyration (Rg) determined by SLS techniques approximately showed the relationship LRg–1 = holding in rigid rods over the entire Mw range examined in this study. However, the folding number, defined as the ratio of the average molecular contour length (l) to L, remained at the value of lL–1 ∼ 2, representing an elongated one-folded hairpin structure, until Mw ∼ 300 kg mol–1 and increased substantially up to ca 4.9 at the highest Mw of 790 kg mol–1. The observed increase in the lL–1 value corresponded well with an increase in the diameter of the formed rod with increasing Mw observed in the S-WANS data. The Mw dependencies of the translational diffusion coefficient determined via DLS measurements and that of the intrinsic viscosity detected via viscometric techniques also distinctly demonstrated that particles formed by the MC samples dissolved in aqueous solution behave as elongated rigid rods irrespective of Mw.

Evidence of Long Two-Dimensional Folding Chain Structure Formation of Poly(vinylidene fluoride) in N-Methylpyrrolidone Solution: Total Form Factor Determination by Combining Multiscattering Data.

Very recently, we proposed that poly(vinylidene fluoride) (PVDF) dissolves in a long rectangular column conformation induced by the formation of a two-dimensional folding chain structure in an N-methylpyrrolidone (NMP) solution based on the results obtained from static light scattering (SLS), small- to wide-angle X-ray scattering (S-WAXS), and viscometric experiments. Small- to wide-angle neutron scattering (S-WANS) experiments were able to provide clear decisive evidence for the presence of such a two-dimensional folding chain structure in a deuterated (d)NMP solution of PVDF samples with two different weight average molar masses (Mw) of 100 and 1200 kg mol–1, even under dilute conditions at concentrations less than the overlapping concentrations due to the quite high neutron scattering contrast obtained by using (d)NMP as a solvent. An increase in Mw from 100 to 1200 kg mol–1 substantially increases the particle length and width from L = 80 to 350 nm and w2 = 5.0 to 15 nm, respectively, while the thickness, w1, is maintained at 0.3 nm. Since L is much longer than w2 irrespective of Mw, the particles formed by PVDF molecules in NMP simply behave as long rigid rods in a scattering vector (q) range covered by SLS measurements. A combination study of S-WANS and S-WAXS experiments covering a higher q range with the SLS techniques could clearly reveal increases in both the L and w2 values with increasing Mw.

Synthesis and characterization of novel 99mTc-DGC nano-complexes for improvement of heart diagnostic.

In this research, early diagnosis of cardiovascular diseases can reduce their mortality and burden. In our study, we developed a new nano-agent, 99mTc-Dendrimer Glyco Conjugate (99mTc-DGC), and assessed its safety and capability for myocardial viability scan. To develop 99mTc-DGC, we first synthesized the dendrimer and then, glucose has been conjugated. Afterwards, we measured toxicity of the product on normal cells by XTT and apoptosis/necrosis methods. We compared the myocardial viability scan (measured by SPECT and dynamic planar imaging) in two rabbit models, with and without infarction. We also assessed the biodistribution of 99mTc-DGC in rats with no infarction. DGC synthesis was confirmed by Fourier transform infrared (FT-IR), proton nuclear magnetic resonance (1H NMR), liquid chromatography-mass spectrometry (LC-MS), dynamic light scattering (DLS) and static light scattering techniques (SLS). Then radiochemical purity (RCP) was done to present the stability and potential of DGC to complex formation with 99mTc. In vitro cytotoxicity showed nontoxic concentration up to 8mg/mL. Single Photon Emission Computed Tomography (SPECT) and dynamic planar imaging clearly showed the accumulation of 99mTc-DGC in myocardial. Biodistribution result showed the 2.60% accumulation of 99mTc-DGC in myocardial after 2h. Our findings indicated 99mTc-DGC to be safe and can accurately diagnose myocardial infarctions at early stages. Human studies to further assess such effects are critical.

How the Type of Cosurfactant Impacts Strongly on the Size and Interfacial Composition in Gemini 12-2-12 RMs Explored by DLS, SLS, and FTIR Techniques.

The limited amount of information about reverse micelles (RMs) made with gemini surfactants, the effect of the n-alcohols in their interface, and the water-entrapped structure in the polar core motivated us to perform this work. Thus, in the present contribution, we use dynamic light scattering (DLS), static light scattering (SLS), and FT-IR techniques to obtain information on RMs structure created, with the gemini dimethylene-1,2-bis(dodecyldimethylammonium) bromide (G12-2-12) surfactant and compare the results with its monomer: dodecyltrimethylammonium bromide (DTAB). In this way, the size of the aggregates formed in different nonpolar organic solvents, the effect of the chain length of n-alcohols used as cosurfactants, and the water-entrapped structure were explored. The data show that the structure of the cosurfactant needed to stabilize the RMs plays a fundamental role, affecting the size and behavior of the aggregates. In contrast to what happens with the RMs formed with the monomer DTAB, water entrapped inside G12-2-12 RMs displays different interaction with the interface depending on the hydrocarbon chain length of the n-alcohol used as cosurfactant. Thus, n-pentanol and n-octanol molecules are located in different regions in the RMs interfaces formed with the gemini surfactant. n-Octanol locates at the RMs interface among the surfactant hydrocarbon tails increasing the water-surfactant polar headgroup interaction. On the other hand, n-pentanol locates at the RMs interface near the polar core, limiting the interaction of water with the micellar inner interface and favoring the water-water interaction in the polar core.

Micellization behavior of model asymmetric miktoarm star copolymers of the AA′B type, where A is polyisoprene and B is polystyrene

Model asymmetric miktoarm star copolymers of the type AA′B, where A and A′ are polyisoprenes (PIs) and B is deuterated polystyrene (PS), were synthesized by anionic polymerization high-vacuum techniques. Their micellization behavior was studied in n-decane, a selective solvent for the PI blocks, and N,N-dimethylacetamide (DMA), selective for the PS blocks. Utilizing static and dynamic light-scattering techniques along with dilute solution viscometry, parameters such as the aggregation number, Nw, the hydrodynamic and viscometric radii were determined. Based on these results, structural parameters of the micelles, that is, core and corona radii, as well as core-corona interfacial area, were calculated. The thermal stability of the micelles was also examined in both selective solvents. The macromolecular architecture was found to have a considerable effect on the micellization behavior of the block copolymers. Static light-scattering techniques were utilized to study the micellization behavior of model asymmetric miktoarm star copolymers of the type AA′B, where A and A′ are polyisoprenes (PIs) and B is deuterated polystyrene (PS). In n-decane, a selective solvent for the PI blocks the comparison between linear PS–PI diblocks, symmetric PS(PI)2 and asymmetric PS(PI)(PI′) miktoarm stars, and confirms that the aggregation numbers (Nw) and, in general, the micellar properties can be manipulated at will, and that tailor-made micelles can be constructed changing the macromolecular architecture.

Modulated 3D cross-correlation light scattering: Improving turbid sample characterization

Accurate characterization using static light scattering (SLS) and dynamic light scattering (DLS) methods mandates the measurement and analysis of singly scattered light. In turbid samples, the suppression of multiple scattering is therefore required to obtain meaningful results. One powerful technique for achieving this, known as 3D cross-correlation, uses two simultaneous light scattering experiments performed at the same scattering vector on the same sample volume in order to extract only the single scattering information common to both. Here we present a significant improvement to this method in which the two scattering experiments are temporally separated by modulating the incident laser beams and gating the detector outputs at frequencies exceeding the timescale of the system dynamics. This robust modulation scheme eliminates cross-talk between the two beam-detector pairs and leads to a fourfold improvement in the cross-correlation intercept. We measure the dynamic and angular-dependent scattering intensity of turbid colloidal suspensions and exploit the improved signal quality of the modulated 3D cross-correlation DLS and SLS techniques.

Thermal aggregation of methylcellulose with different molecular weights

Thermal aggregation of methylcellulose with different molecular weights was investigated in an aqueous system by static light-scattering technique to trace the transition of its molecular size and shape upon heating. Temperature-dependence of some rheological parameters was also examined to make a bridge between the macroscopic changes of methylcellulose and its molecular transition during thermal gelation. At 15 °C, the lowest temperature assessed, weight-average molecular weight M w of methylcellulose used ranged from 43.6×10 3 to 37.7×10 4 g/mol, and z-average root-mean-square radius of gyration R g ranged between 24.2 and 85.6 nm. M w and R g were almost temperature-independent within the range 15–60 °C for each methylcellulose (0.03 w/v%) but increased markedly at over 60 °C when the initial M w was larger than approx. 30.0×10 4 g/mol. The Flory exponent for these methylcelluloses decreased markedly at over 60 °C to values corresponding to the behavior of a sphere configuration. Dynamic storage modulus G′ for methylcellulose (0.5 and 1 w/v%) increased with temperature in two separate stages. These transitions were almost independent of the initial M w, and the second transition at a higher temperature coincided with the increase in M w and R g as well as in turbidity for methylcellulose with the initial M w>approx. 30.0×10 4 g/mol. These results suggest that the gelation behavior of methylcellulose depends on its M w; methylcellulose with relatively large M w (e.g.,>approx. 30.0×10 4 g/mol) aggregates at higher temperatures (e.g.,>60 °C) to form compact or tightly packed configuration. The results also suggest that thermal aggregation of methylcellulose contributes to the formation of network structure between the molecules, consequently leading to the increase in modulus.

Food hydrocolloids control the gelatinization and retrogradation behavior of starch. 2a. Functions of guar gums with different molecular weights on the gelatinization behavior of corn starch

Gelatinization behavior of starch in an aqueous system was studied in the presence or absence of various guar gum samples with different molecular weights in order to clarify the difference in functions of each guar to starch. Some native corn starches with different amylose/amylopectin ratios were used to clarify which fraction of starch the gums act on. Weight-average molecular weight M w of the guar samples ranged from 4.7×10 5 to 34.6×10 5 g/mol, whereas z-average root-mean-square radius of gyration R g ranged between 82 and 233 nm from static light-scattering technique. Relationship between M w and R g was expressed by the Flory exponent of 0.503. Also, intrinsic viscosity [ η] of the guar samples in aqueous solution was in good agreement with M w determined, and relationship between M w and [ η] was expressed by the Mark–Houwink–Sakurada exponent of 0.517. Gelatinization behavior of starch/guar system was investigated from its viscosity profiles. Guars with M w values higher than 12.2×10 5 g/mol shifted the onset of viscosity increase for the system to lower temperatures and increased its peak viscosity upon heating at a relatively low starch concentration (e.g. 5 w/v%). The earlier onset of viscosity increase was independent of M w of guar, while the increase in peak viscosity was dependent on its M w. These guars shifted the onset of viscosity increase for the system upward, on the contrary, at a relatively high starch concentration (e.g. 15%). Interaction between guar and starch components, amylose and amylopectin, was hypothesized as one of the factors to govern the gelatinization behavior of starch.

Aggregation Kinetics and Fractal Structure of γ-Alumina Assemblages

Suspensions of a variety of different aluminum oxides have previously been shown to require very high concentrations of chloride and nitrate anions (>0.5 M) to induce rapid aggregation. This high stability has been accredited to the presence of surface forces considered to be due to the formation of highly charged Al13 polymeric species at slightly acidic pH's and aluminum oxyhydroxide gel formation under alkaline conditions. The effect of this stability on the structure of the resulting aggregates is investigated here using well-established static light-scattering techniques. Power law behavior of scattered light intensity as a function of scattering wave vector is observed in all cases and is suggestive of fractal structure. The fractal dimensions obtained fall within the expected range of 1.8 to 2.3 observed for colloidal aggregates but do not appear to follow the typical observations for colloids destabilized by indifferent electrolytes where lower fractal dimensions are associated with rapid (diffusion-limited) aggregation and higher fractal dimensions with slower (reaction-limited) aggregation. Indeed, relatively constant fractal dimensions (2.10 to 2.25) are observed over the range of salt concentrations at which the slow to rapid aggregation rate transformation occurs with, if anything, a slightly higher fractal dimension observed for higher aggregation rates. The presence of specifically binding sulfate anions appears to negate the strong near-distance repulsive forces leading to rapid aggregation at low (1 to 2 mM) sulfate concentrations. Significantly lower fractal dimensions (1.85 to 1.91) are observed for aggregates formed by destabilization using sulfate ions than obtained when chloride or nitrate are used with, again, an apparent slight increase in fractal dimension upon increasing aggregation rate.

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.

Structural Transitions in a Bicationic Amphiphile System Studied by Light-Scattering, Conductivity, and Surface Tension Measurements

Vesicles were found to form easily in diluted aqueous mixtures of two cationic amphiphiles, the double-tailed, bilayer-forming didodecyldimethylammonium bromide (DDAB) and the single-tailed, micelle-forming dodecyltrimethylammonium chloride (DTAC), and therefore are believed to be spontaneous. A combination of equilibrium tensiometry, conductivity, and static light-scattering techniques enabled the determination of critical aggregation concentrations corresponding to the structural transitions monomers ↔ vesicles (CVC) and vesicles ↔ micelles (CMC), at several DDAB/DTAC molar ratios, thus delimiting the composition range of the vesicle stability, at 25 °C. It was found that the monomers ↔ vesicles transition, at lower total surfactant concentrations, is driven by the double-chained DDAB, while the vesicles ↔ micelles transition, at higher total surfactant concentrations, is mainly determined by the single-chained DTAC. A region of coexistence of vesicles and micelles was found, whose limiting lower and up...

Relation between the solubility and the effective solute—solute interaction for C 60 solutions and lysozyme solutions: a comparison using the sticky hard-sphere potential

We present a study of the solute-solute interaction and solubility for C 60 in CS 2 solution. We have evidenced and characterised, by a second virial coefficient A 2, an attractive C 60-C 60 interaction in CS 2 by small-angle neutron scattering. We present results about the temperature dependence of the C 60 solubility in CS 2 obtained with a static light-scattering technique. We have compared the dependence of the solubility versus solute-solute interaction for C 60 in CS 2 to that of lysozyme in aqueous solutions, using the effective hard-sphere adhesive potential for the solute-solute interactions in both systems. This comparison between C 60, a simple model particle for short-range interactions, and other much more complex molecules like proteins shows the analogies between the two systems.

Viscometric and Light Scattering Studies on Microgel Formation by γ-Ray Irradiation to Aqueous Oxygen-free Solutions of Poly(vinyl alcohol)

The gelation process of aqueous oxygen-free solutions containing poly(vinyl alcohol) (PVA) by γ-ray irradiation was studied as a function of polymer concentration. Dynamic and static light-scattering techniques as well as the usual viscometric method were employed. PVA solutions turned into a bulk gel upon irradiation at high concentrations around 20 g/L, which corresponds to about 10 times that termed the critical concentration. Increases in the intrinsic viscosity ([n]) and hydrodynamic radius (R h ) were observed before the gelation. The bulk gel did not form from diluted PVA solutions (1.6-2.0 g/L) but the solution became turbid due to the formation of microgel particles. In this process, both [n] and R h rapidly increased when increasing the irradiation dose up to a certain level (ca. 0.3 Mrad) at which solution turbidity appeared. When the irradiation was continued over this dose, [n] decreased and R h leveled off. We thus examined the changes in the molecular weight (M w ) and radius of gyration (Rg) and found that R g decreased while M w increased almost linearly. Thus, a decrease in R g /R h from 1.5 to 0.98 was observed in doses > 0.3 Mrad. On the basis of the results obtained, we discussed in detail the mechanism ofmicrogel formation from PVA in its diluted solution by γ-ray irradiation.

Aggregation of colloidal nickel hydroxycarbonate studied by light scattering

The aggregation kinetics of nickel hydroxycarbonate particles in aqueous solution have been studied using dynamic and static light-scattering techniques. Different aggregation kinetics were observed, which depended on the concentration of electrolyte dissolved in the dispersion. At low concentration, slow reaction-limited aggregation and an exponential increase of aggregate size over time was found. The aggregates are characterized by a fractal dimension D = 2.0–2.1. At high electrolyte concentration fast diffusion-limited aggregation behavior was observed as was an increase in aggregate size over time described by a power law. The aggregates are characterized by a fractal dimension D = 1.7–1.8. Crossover from reaction-limited to diffusion-limited aggregation behavior was observed for large clusters. Under shear flow a drastic change of fractal dimension was noted. It was most pronounced for aggregates grown at low electrolyte concentration, where D increased from 2.0 at zero shear to D = 2.7 at a shear rate of 200 s −1. This is more drastic than computer simulations predict. At high electrolyte concentration, D increases from 1.7 at zero shear to D = 2.2 at a shear rate of 200 s −1, which is in line with results of computer simulation.

A two-step silica sol-gel process investigated with static and dynamic light-scattering measurements

The hydrolysis-condensation reactions in mixtures of tetraethoxysilane, ethanol and water were followed in the basic step of a two-step silica sol-gel process with dynamic and static light-scattering techniques. The radii of the particles formed were found to be about 1.5 nm and in agreement with the results found with specific surface area measurements on the corresponding dried silica gels. The relatively high scattering found for mixtures having incomplete hydrolysis in the acid step was ascribed to the formation of large particles caused by prolonged hydrolysis-condensation in the basic step. The decreased light transmission as a function of the decreasing density of dried silica gels was assigned to Rayleigh scattering by pores.