Small angle light scattering studies concerning aggregation processes (original) (raw)
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Two limiting regimes for colloidal particle aggregation are well described in the literature: diffusion-limited cluster aggregation and reaction-limited cluster aggregation. Between these two limiting regimes, a vast transition region is expected. In this paper, the transition region is studied by means of static and dynamic light scattering. Therefore, a system of latex particles is aggregated at different electrolyte concentrations. The time dependence of the average diffusion coefficient is fitted considering the Brownian kernel and the kernel proposed by Schmitt et al. [Phys. Rev. E 62, 8335 (2000)]. The first fits the experimental data only at high electrolyte concentrations while the latter, which considers multiple cluster–cluster contacts, is found to fit the complete set of experimental data. C 2001 Academic Press
A Study of Colloidal Particle Brownian Aggregation by Light Scattering Techniques
Journal of Colloid and Interface Science, 1997
volved, such as particle size, shape, polydispersity, physico-Aggregation kinetics and aggregate structure are studied for chemical interactions, aggregate hydrodynamic behavior, monodisperse polystyrene latex particles of diameter 60 and 140 and restructuring, the picture of aggregation kinetics and nm. The experimental part consists of measurements over a rather structure formation is far from unified and complete. broad range of electrolyte concentrations (0.1 to 0.8 M NaCl) and
Cluster-size distribution in colloidal aggregation monitored by single-cluster light scattering
Physica A-statistical Mechanics and Its Applications, 1996
The aggregation of polymer colloids is studied in processes induced at high ionic concentration. Cluster-size distributions are measured with a single-cluster light scattering instrument constructed by our team. A brief description of the instrument is given and its proper performance is checked. The results are interpreted with the framework of Smoluchowski's equation. The rate constant for dimer formation is measured
Binary diffusion-limited cluster-cluster aggregation processes are studied as a function of the relative concentration of the two species. Both, short and long time behaviors are investigated by means of three-dimensional off-lattice Brownian Dynamics simulations. At short aggregation times, the validity of the Hogg-Healy-Fuerstenau approximation is shown. At long times, a single large cluster containing all initial particles is found to be formed when the relative concentration of the minority particles lies above a critical value. Below that value, stable aggregates remain in the system. These stable aggregates are composed by a few minority particles that are highly covered by majority ones. Our off-lattice simulations reveal a value of approximately 0.15 for the critical relative concentration. A qualitative explanation scheme for the formation and growth of the stable aggregates is developed. The simulations also explain the phenomenon of monomer discrimination that was observed recently in single cluster light scattering experiments.
Nucleation and clustering: a microscopic study of the aggregation behaviour in metastable solutions
Journal of Non-crystalline Solids, 1995
The aggregation state of metastable solutions has been studied by small angle neutron scattering. The variation of the scattering curves was monitored during continuous cooling for aqueous solutions of ND4C1. The analysis of the data indicates the existence of finite-sized domains responsible for the variation of the scattering density on undercooling. The data have been analyzed using a Percus-Yevick hard-sphere model which gives cluster sizes between 10 and 30 nm with an average interparticle distance of 100-200 nm.
Concentration Dependence of Structural and Dynamical Quantities in Colloidal Aggregation
We have performed extensive numerical simulations of diffusion-limited ͑DLCA͒ and reaction-limited ͑RLCA͒ colloid aggregation to obtain the dependence on concentration of several structural and dynamical quantities, among them the fractal dimension of the clusters before gelation, the average cluster sizes, and the scaling of the cluster size distribution function. A range in volume fraction spanning two and a half decades was used for this study. For DLCA, a square root type of increase of the fractal dimension with concentration from its zero-concentration value was found:
Structure and kinetics of reaction-limited aggregation
1988
Several different models are used to investigate reaction-limited cluster-cluster aggregation and the crossover from diffusion-limited to reaction-limited aggregation. The results obtained from these models are consistent with each other, if finite-size and finite-concentration effects are taken into account. For reaction-limited aggregation in three dimensions we find, in the case where the probability that two clusters will combine depends only on the time that they spend in contact with each other, that the mean cluster size S(t) increases exponentially with time t and that the clustersize distribution N, (t) (of clusters of size s at time t) decays as N, (t)-s with~having a value larger than 1.5. For the case where the probability that two clusters will combine depends only on the number of times they collide with each other, we find a power-law growth in the mean cluster size, S(t)-t with z-2.0-2. 5, and a cluster-size-distribution exponent~close to 1.0. Our results indicate that the approach to asymptotic behavior may be quite slow and that the effective fractal dimensionality of the clusters depends both on the aggregation kinetics and on the extent of aggregation. We find that if the rate of bonding between two clusters depends on their collision frequency, then the exponent v has a value close to 1 for the aggregation of small rigid clusters and close to 2 for the aggregation of large floppy clusters.
Langmuir, 2014
Brownian aggregation in concentrated hard-sphere dispersions is studied using models and Brownian dynamics (BD) simulations. Two new theoretical models are presented and compared to several existing approaches and BD simulation results, which serve as benchmarks. The first new model is an improvement over an existing local density approximation (LDA)-based model. The other is based on the more rigorous Fundamental measure theory (FMT) applied to the "liquid-state" dynamic density-functional theory (DDFT). Both models provide significant improvements over the classical Smoluchowski model. The predictions of the new FM-DDFT-based model for aggregation kinetics are in excellent agreement with BD simulation results for dispersions with initial particle volume fractions, ϕ, up to 0.35 (close to the hard-sphere freezing transition at ϕ = 0.494). In contrast to previous approaches, the nonideal particle diffusion effects and the initial and time-dependent short-range ordering in concentrated dispersions due to entropic packing effects are explicitly considered here, in addition to the unsteady-state effects. The greater accuracy of the FM-DDFT-based model compared to that of the LDA-based models indicates that nonlocal contributions to particle diffusion (only accounted for in the former) play important roles in aggregation. At high concentrations, the FM-DDFT-based model predicts aggregation halftimes and gelation times that are up to 2 orders of magnitude shorter than those of the Smoluchowski model. Moreover, the FM-DDFT-based model predicts asymmetric cluster-cluster aggregation rate constants, at least for short times. Overall, a rigorous mechanistic understanding of the enhancement of aggregation kinetics in concentrated dispersions is provided.
Sol-gel process simulation by cluster-cluster aggregation
Journal of Non-Crystalline Solids, 1995
The pair-correlation function g(r, t) and its Fourier transform, the structure factor S(q, t), are computed during the gelation process of identical spherical particles using the diffusion-limited cluster-cluster aggregation model in a
Dispersed Molecular Aggregates
Journal of Colloid and Interface Science, 2001
Colloidal dispersions of tungstic acid (H 2 WO 4 ) have been prepared in water/(TX-100 + alkanol)/n-heptane water-in-oil microemulsion media by reacting Na 2 WO 4 with HCl. The effects of alkanol chain length, TX-100/alkanol mass ratio, temperature, and dilution at different [water]/[TX-100] mole ratios (ω) have been studied by the dynamic light scattering technique. The formation of H 2 WO 4 in the microwater pool has been established by FT-IR measurements. The particle sizes and shapes in microemulsion media and in isolated states have been measured by TEM and SEM techniques. The enthalpy of formation of H 2 WO 4 in the water pool of the microemulsions has also been determined microcalorimetrically. C 2001 Academic Press