Size distribution of colloidal silica in sodium silicate solutions investigated by dynamic light scattering and viscosity measurements

Three types of aqueous sodium silicate solutions characterized by molar SiO(2):Na(2)O ratios of 2.2, 3.3, and 3.9 were investigated by dynamic light scattering and viscosity measurements. The solutions were prepared by diluting concentrated commercial products to SiO(2) content between 0.5 and 15 wt%. Dynamic light scattering (DLS) was used for the investigation of size distributions of colloids immediately after dilution. At least three size classes of colloidal particles were detected, which exist in parallel in the solutions. The respective radii are 0.4 to 0.6 nm, 2.5 to 13 nm, and 75 to 85 nm. The larger colloids dominate the mass distribution, whereas the smaller colloids control the surface area of the colloidal fraction. Material properties such as pH, viscosity, refractive index, and density were measured as a function of dilution. The evaluation of the viscosity data indicated that the colloids have a lower density than dense amorphous silica. Aging effects could be suppressed by measuring within 1 h after dilution.     

Comparison of nanoparticle size and electrophoretic mobility measurements using a carbon-nanotube-based coulter counter, dynamic light scattering, transmission electron microscopy, and phase analysis light scattering

The precision and accuracy of measurements of the diameter and electrophoretic mobility (mu) of polymeric nanoparticles is compared using four different analytical approaches: carbon-nanotube-based Coulter counting, dynamic light scattering (DLS), transmission electron microscopy (TEM), and phase analysis light scattering (PALS). Carbon-nanotube-based Coulter counters (CNCCs) use a 132 nm diameter channel to simultaneously determine the diameter (28-90 nm) and mu value for individual nanoparticles. These measurements are made without calibration of the CNCC and without labeling the sample. Moreover, because CNCCs measure the properties of individual particles, they provide true averages and polydispersities that are not convoluted into the intrinsic instrumental response function of the CNCC. CNCCs can be used to measure the size of individual nanoparticles dispersed in aqueous solutions, which contrasts with the TEM-measured size of individual dehydrated particles and the ensemble size averages of dispersed particles provided by DLS. CNCCs provide more precise values of mu than PALS.     

Voltammetric,dynamic light scattering (DLS) and electrophoretic mobility characterization of FeS nanoparticles (NPs) in different electrolyte solutions

Voltammetric response of FeS nanoparticles (NPs) dispersion based on the oxidation exchange voltammetric peak between Hg electrode and FeS NPs at around ?0.45 V was studied in different electrolytes (chloride, acetate, perchlorate). Several experiments were designed to monitor in parallel to voltammetric measurements, physicochemical and surface characteristics of the formed FeS NPs (ζ-potential and size) under same experimental conditions. It was shown that recorded voltammetric peak produced by FeS NPs from bulk solution is changing with electrolyte concentration and composition, as well as observed size and ζ-potential of the studied FeS NPs. Our measurements indicate relationship between measured ζ-potential of FeS NPs dispersions and recorded voltametric peak charge and potential, pointing to a promising potential of voltammetry in characterization of physicochemical and surface chemistry features of metal sulphide NPs in water environment. The best voltammetric response is obtained in presence of small NPs, <100 nm.     

Characterization of riboflavin-photosensitized changes in aqueous solutions of alginate by dynamic light scattering

The effect of irradiation, in the wavelength range of 310-800 nm, on aqueous solutions (pH = 7.4) of alginate in the presence of the photosensitizer riboflavin (RF) has been investigated with the aid of dynamic light scattering (DLS). Under aerobic conditions light irradiation of RF causes scission of the polymer chains which affects the polymer dynamics. The time correlation data obtained from DLS experiments showed at all conditions the existence of two relaxation modes: one single exponential at short times, followed by a stretched exponential at longer times. The slow relaxation time revealed, over the whole considered concentration range, lower values for the alginate/RF system, whereas no effect of photochemical degradation was observed for the fast relaxation time in the semidilute regime. The results suggest that the photochemically induced fragmentation of alginate affects the slow relaxation mode, associated with disengagement relaxation of individual chains or cluster relaxation, in a similar way as the zero-shear viscosity. These findings provide detailed insight into the dynamics of the polymer matrix, and this knowledge can be useful in the context of controlled-release delivery of drugs. The chemical units of alginate (M = mannuronic acid and G = guluronic acid).     

Critical behavior of 2,6-dimethylpyridine-water: measurements of specific heat, dynamic light scattering, and shear viscosity

The specific heat C(p) at constant pressure, the shear viscosity eta(s), and the mutual diffusion coefficient D of the 2,6-dimethylpyridine-water mixture of critical composition have been measured in the homogeneous phase at various temperatures near the lower critical demixing temperature T(c). The amplitude of the fluctuation correlation length xi(0)=(0.198+/-0.004) nm has been derived from a combined evaluation of the eta(s) and D data. This value is in reasonable agreement with the one obtained from the amplitude A(+)=(0.26+/-0.01) J(g K) of the critical term in the specific heat, using the two-scale-factor universality relation. Within the limits of error the relaxation rate Gamma of order parameter fluctuations follows power law with the theoretical universal exponent and with the amplitude Gamma=(25+/-1)x10(9) s(-1). No indications of interferences of the critical fluctuations with other elementary chemical reactions have been found. A noteworthy result is the agreement of the background viscosity eta(b), resulting from the treatment of eta(s) and D data, with the viscosity eta(s)(nu=0) extrapolated from high-frequency viscosity data. The latter have been measured in the frequency range of 5-130 MHz using a novel shear impedance spectrometer.     

Investigation of the solution structure of hyaluronic acid by light scattering,SAXS, and viscosity measurements

Summary Hyaluronic acid in water exhibits a non-monotonous scattering function, which is explained in terms of multimerization leading to gel-like supermolecular particles. This tendency is highest in water, lower in buffer, and lowest in isotonic NaCl-solution + NaN₃. Viscosity measurements show that with increasing concentration a network solution is formed. SAXS-measurements show that nonaggregated Hyaluronic acid is present either in form of double strands, or as supercoils with helical portions.

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Zusammenfassung Hyaluronsäure zeigt in Wasser eine nicht-monotone Streufunktion, die als Ausdruck einer Multimerisation gedeutet wird, welche zu gelartigen übermolekularen Teilchen führt. Diese Tendenz ist in Wasser am stärksten, schwächer in Puffern, und am schwächsten in isotoner NaCl-Lösung + NaN₃. Viskositätsmessungen zeigen, daß bei höheren Konzentrationen eine Netzwerk-Lösung gebildet wird. Röntgenkleinwinkel-Messungen ergeben, daß die nicht aggregierte Hyaluronsäure entweder in Form von Doppelsträngen oder als Superknäuel mit helikalen Anteilen vorliegt.

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With 14 figures and 4 tables     

Stabilizer-induced viscosity alteration biases nanoparticle sizing via dynamic light scattering

The size dependent features of colloids at the nanometer scale have been issues of increasingly intensive research. In order to be able to correctly relate characteristics to certain size-populations, accurate and reliable particle sizing by dynamic light scattering (DLS) is a main prerequisite. So far, the complexity of the systems due to the presence of surfactants, proteins, and so forth in the nanoparticle suspensions has not been accounted for. In this work, practically relevant quantities of the frequently used PEO-PPO triblock copolymer surfactant Pluronic F-68 were studied for their effect on the size determination of nanoparticles by DLS. Induced changes in the tenside-content of the nanosphere suspension were monitored using a photometric assay and were correlated to the respective variances in mean particle size. These measurements showed that alterations in the range from 0.005 to 2% of Pluronic content are associated with shifts in diameter of 200 nm-particles by as much as 65 nm. The considerable changes that were found have been attributed to the surfactant-concentration-dependent fluctuations in the viscosity of the nanoparticle suspension, which affect the dimensions of colloids calculated according to the Stokes-Einstein relation.     

Demonstration of cell-ricin interaction by electrophoretic light scattering

Electrophoretic light scattering has been used to investigate the interaction of ricin, a vegetal toxin, with cells. This technique allowed measurements in the presence of free ligand and proved particularly useful for the study of a system with low affinity. The electrophoretic mobility of erythrocytes and oligodendrocytes was found equal to 2.08 x 10(-8) and 2.35 x 10(-8)m2s-1V-1, respectively. Upon ricin binding, these values decreased significantly. This change was related to the saturation of the binding sites. The specificity of the interaction was demonstrated by conducting the experiments in the presence of lactose. This specific inhibitor fully prevented the ricin-cell interaction.     

The characterization of silica microparticles by electrophoretic mobility measurements

Summary Electrophoretic mobility measurements in the pH 2‐10 range are described for several commercial HPLC silica microparticles and a laboratory-produced product. The content of metal impurities for the silicas was also determined by AAS. An acidic/hydrothermal treatment was used to generate a more homogenous surface for some of the silicas. The zero points of charge (zpc) for both a native and a treated silica plus several commercial HPLC silicas were compared. The electrophoretic mobility method may be useful in predicting the utility of certain types of silica supports for chromatographic separations.     

Study of aqueous solutions of fullerenol-d by the dynamic light scattering method

Dynamic light scattering method was used to determine the average size of fullerenol-d associates and the dependence of the electrokinetic ζ-potential on the concentration of aqueous solutions of fullerenol-d.     

Polarized and depolarized dynamic light scattering of concentrated polystyrene solutions

Polarized and depolarized dynamic light scattering have been used to examine the dynamics of concentrated polystyrene solutions in dioctyl phthalate and toluene. Time-temperature superposition of the depolarized intensity correlation functions gave master curves covering more than 10 decades on the time scale. Polarized correlation functions are resolved into relaxational and diffusive components having different temperature dependences. When the relaxation rate of the concentration fluctuations approaches the reorientational relaxation rate, the concentration fluctuations become q-independent i.e. the diffusional relaxation is rate-determined by the backbone mobility. With a small molecule solvent as toluene, however, a part of the concentration fluctuations relaxes faster than the orientational relaxation, i.e., the diffusion occurs in the free volume within the “frozen” network.     

Interpretation of quasi-elastic light scattering measurements from moderately concentrated solutions

The autocorrelation functions of elastic and quasi-elastic light scattering measurements of polystyrene ($\text{M}{}_{\mathrm{<mtext>w</mtext>}}\text{= 670,000}$) in toluene at 20° and cyclohexane at 35° at concentrations up to 0·07 g cm^?3 are examined employing a scattering law that includes both the self and distinct part of the time-dependent pair correlation function. By taking the convolution approximation of Vineyard, it is shown that within experimental accuracy both terms are governed by the translational diffusion coefficient.     

Interplay between electrophoretic mobility and intrinsic viscosity of polypeptide chains

The present work is motivated specifically by the need to find a simple interplay between experimental values of electrophoretic mobility and intrinsic viscosity (IV) of polypeptides. The connection between these two properties, as they are evaluated experimentally in a formulated dilute solution, may provide relevant information concerning the physicochemical characterization and separation of electrically charged chains such as polypeptides. Based on this aspect, a study on the relation between the effective electrophoretic mobility and the IV of the following globular proteins is carried out: bovine carbonic anhydrase, staphylococcal nuclease, human carbonic anhydrase, lysozyme, human serum albumin. The basic interpretation of the IV through polypeptide chain conformations involves two unknowns: one is the Flory characteristic ratio involving short-range intramolecular interactions and the other is the Mark-Houwink exponent associated with large-range intramolecular interactions. Here, it will be shown via basic and well-established electrokinetic theories and scaling concepts that the IV and global chain flexibility of polypeptides in dilute solutions may be estimated from capillary zone electrophoresis, in addition to classical transport properties. The polypeptide local chain flexibility may change due to electrostatic interactions among closer chain ionizing groups and the hindrance effect of their associated structural water.     

In situ measurements of nanotube dimensions in suspensions by depolarized dynamic light scattering

We show that the dimensions of carbon nanotubes (CNTs) in suspension can be characterized by depolarized dynamic light scattering. Taking advantages of this in situ technique, we investigate in detail the influence of sonication procedures on the length and diameter of CNTs in surfactant solutions. Sonication power is shown to be particularly efficient at unbundling nanotubes, whereas a long sonication time at low power can be sufficient to cut the bundles with limited unbundling. We finally demonstrate the influence of CNT dimensions on the electrical properties of CNT fibers. Slightly varying the sonication conditions, and thereby the suspended nanotube dimensions, can affect the fibers conductivity by almost 2 orders of magnitude.     

Simultaneous measurements of the electrophoretic mobility,diffusion coefficient and orientation of dsDNA during electrophoresis in polymer solutions

We determined simultaneously the electrophoretic mobility, diffusion coefficient D and molecular orientation during electrophoresis of dsDNAs in polymer solutions ranging from the dilute to the semidilute regime. We established, for the first time, master scaling laws for the diffusion coefficient showing a universal behavior. A model found in the literature designed for the dilute regime allows, surprisingly, to describe the mobility data over the whole range of concentrations studied and at the same time the biased reptation with fluctuations (BRF) failed for the semidilute regime, even when constraint release of the network was taken into account. These quantitative determinations of D are of practical interest to evaluate band broadening during capillary electrophoresis and provide data for stimulating investigation of the physics of DNA electrophoretic motion.     

Dynamic and electrophoretic light scattering of poly(dimethyldiallylammonium chloride) in salt-free solutions

Dynamic and electrophoretic light scattering were used to study the diffusion and electrophoretic mobility of poly(dimethyldiallylammonium chloride) as a function of polymer molecular weight in salt-free solutions. Two relaxation modes characterized as fast diffusion (D_f) and slow diffusion (D_s) were obtained from dynamic light scattering. Although the slow diffusion coefficient D_s strongly depends on molecular weight (M_w), the fast diffusion coefficient D_f was found to be independent of M_w over the range in the study. The fast diffusion was considered as the diffusion of a part of the polymer chain; the slow diffusion was interpreted by multichain diffusion. Electrophoretic light scattering results in the salt-free solution show that the electrophoretic mobility of the polymer is independent of M_w. © 1996 John Wiley & Sons, Inc.     

Inelastic light scattering measurements from linear polyelectrolyte aqueous salt solutions

Inelastic light scattering experiments demonstrate the existence of a conformational change upon ionization of a weak acid polyelectrolyte in aqueous salt solutions. The swelling of the polymeric coil occurs at a neutralization degree increasing with molecular weight.     

Viscosity of aqueous DNA solutions determined using dynamic light scattering

Viscosity is a key parameter for characterising the behaviour of liquids and their flow. It is, however, difficult to measure precisely, reproducibly and accurately for aqueous solutions on a micro-litre volume scale, which is what is usually needed for biological samples. We report the development of a new method for measuring dynamic viscosity by measuring dynamic light scattering (DLS) data for a range of particles of well-defined size. Most applications of DLS involve determining particle size for samples of known viscosity. We inverted the usual protocol and endeavoured to determine viscosity for samples of known particle size. Viscosity measurements for water and aqueous solutions of calf thymus DNA made using DLS were compared with those from a U-tube viscometer. The styrene particles, frequently used as particle size standards, gave unsatisfactory results for our DNA samples as did C-6 derivatized silica and positively charged amino polystyrene microspheres. However, negatively charged carboxylate polystyrene microspheres particles readily gave accurate viscosity measurements over a range of temperatures (0-100 °C). The sample volume required depends on the cuvette used to measure DLS, but can be performed with samples sizes ranging from 40 to 3000 μL. The sample can then be recovered for subsequent experiments. The DLS method is simple to perform at different temperatures and provides data of accuracy significantly above that of a U-tube viscometer. Our results also indicate a way forward to account accurately for solution viscosity in the normal applications of DLS to particle size determination by including the appropriate non-interacting particles as an internal standard.