Interplay between Aggregation and Coalescence of Polymeric Particles: Experimental and Modeling Insights (original) (raw)
Related papers
1989
We report measurements on the aggregation processes in a colloidal solution of polystyrene particles performed by elastic (intensity) and quasielastic light scattering. In order to observe the different kinetics of aggregation of the system, reversible Aocculation, and the slow and the fast irreversible coagulation, the experiment was made varying the concentration of a simple electrolyte (NaC1) in the 0.01-3 mol/liter range. Intensity data give direct information that aggregated clusters are built with fractal structure and different kinetics; in the slow regime the aggregation process is reaction limited, whereas in the raft regime we have a diffusion-limited cluster-cluster aggregation. Dynamical data, showing well-defined scaling behavior in the measured mean linewidth, confirm such a picture and give a rough estimate of the cluster dimension. Experimental results are consistent with the Derjaguin-Landau-Verwey-Overbeek theory on colloidal stability [Derjaguin and Landau, Acta Phys. Chim. Debricina 14, 633 (1941); Verwey and Overbeek, Theory of the Sta bility ofLyophobic Colloids (Elsevier, Amsterdam, 1948)].
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
Monitoring coalescence behavior of soft colloidal particles in water by small-angle light scattering
Colloid and Polymer Science, 2012
The fractal dimension (D f) of the clusters formed during the aggregation of colloidal systems reflects correctly the coalescence extent among the particles (Gauer et al., Macromolecules 42:9103, 2009). In this work, we propose to use the fast small-angle light scattering (SALS) technique to determine the D f value during the aggregation. It is found that in the diffusion-limited aggregation regime, the D f value can be correctly determined from both the power law regime of the average structure factor of the clusters and the scaling of the zero angle intensity versus the average radius of gyration. The obtained D f value is equal to that estimated from the technique proposed in the above work, based on dynamic light scattering (DLS). In the reactionlimited aggregation (RLCA) regime, due to contamination of small clusters and primary particles, the power law regime of the average structure factor cannot be properly defined for the D f estimation. However, the scaling of the zero angle intensity versus the average radius of gyration is still well defined, thus allowing one to estimate the D f value, i.e., the coalescence extent. Therefore, when the DLS-based technique cannot be applied in the RLCA regime, one can apply the SALS technique to monitor the coalescence extent. Applicability and reliability of the technique have been assessed by applying it to an acrylate copolymer colloid.
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
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
Colloidal Dispersion Stability: Kinetic Modeling of Agglomeration and Aggregation
In this work we present a simple model for the kinetics of agglomeration and aggregation of colloidal particles. We consider that particles agglomerate rapidly and endothermically forming oligomers. These oligomers can, in turn, aggregate irreversibly, in a process that leads to the destabilization of the colloidal system. As these two processes have very different relative energy activations, they occur in different time-scales: the first step is faster and reaches a state of quasi-equilibrium. Because of this, the enthalpy change during the agglomeration can be experimentally determined through the variable temperature multiple light scattering (VTMLS) method. Interestingly, this value is related to the relative kinetic stability of the system and can be used to evaluate the stability of new colloidal compositions. Our results are in qualitative agreement with experimental data of low concentration colloidal dispersions consisted of polymer particles and/or surfactant-coated particles.
We employ a small scale Monte Carlo method plus microscopic liquid state integral equation theory to study two models (single and quenched disordered averaged) of fractal-like aggregates as a function of concentration dissolved in a polymer nanocomposite or suspension. When the primary particles interact as hard spheres the resulting center-of-mass level effective pair potential is of a distinctive soft repulsion form which is sensitive to whether geometric disorder at the single aggregate level is averaged over or not. The aggregate fluids show considerable amount of interpenetration and complex non-hard-sphere packing features in their pair correlation functions. The latter are also very different, both qualitatively and quantitatively, for the single versus average aggregate systems. Calculations of the collective static structure factor and compressibility or bulk modulus are in qualitative agreement with a recent scattering experiment on suspensions of fumed silica hard fractals. Use of the theoretical structural information in a microscopic dynamical theory of kinetic arrest suggests the presence of multiple length scales and disordered local packing in these aggregate fluids frustrates the formation of glasses even at ultra-high volume fractions.
Coalescence of polymer droplets: experiments on collision
Comptes Rendus de l'Académie des Sciences - Series IV - Physics, 2000
The coalescence of polymer droplets is a fundamental phenomenon which appears for example when mixing two polymers. When two polymeric droplets collide, a transient regime appears, which results from a competition between interfacial and viscoelastic effects : the spherical droplets deform to give birth to a new drop in a short time (t c) and the drop shape stabilizes after a long time. A novel method is proposed to study experimentally under a microscope the collision between two droplets of one polymer in another one, with different viscosity ratios. This allows to determine the characteristic time t c which defines this phenomenon. The experiments actually show that t c varies like the geometric mean of the viscosities of the two polymers, for the case of a polydimethylsiloxane/polyisobutylene system. Coalescence de gouttelettes de polymères : expériences de collision Résumé-La coalescence de gouttelettes de polymères est un phénomène fondamental qui intervient par exemple lorsque l'on mélange deux polymères. Lorsque deux gouttelettes de polymères rentrent en collision, un régime transitoire apparaît, qui est régi par la compétition entre les effets de surface et les effets viscoélastiques : les gouttelettes sphériques se déforment pour donner naissance à une nouvelle goutte dans un temps rapide (t c) et la forme de cette goutte se stabilise dans un temps long. Une nouvelle méthode est proposée pour étudier expérimentalement sous microscope la collision de deux gouttelettes d'un polymère dans un autre en faisant varier le rapport des viscosités. Ceci permet d'avoir accès au temps caractéristique t c qui définit le phénomène. Les expériences montrent que t c est en fait proportionnel à la moyenne géométrique des viscosités des deux polymères, dans le cas d'un système polydiméthylsiloxane/polyisobutylène.
Discrete Element Modeling (DEM) of Agglomeration of Polymer Particles
Procedia Engineering, 2012
The models of particle interaction in colloid systems present a valuable tool for the investigation of the stability of these systems. Our model is based on the Discrete Element Method (DEM) and describes each particle in the dispersion by its position, size, shape and velocity. Behavior of the system is described by various forces acting between the particles and/or between the surrounding fluid and the particle. We employ the DLVO theory, Brownian motion, Hooke's law and the viscous dissipation by Stokes law as the constitutive description of force interactions. The model is capable to simulate trajectories of hundreds of particles in two or three spatial dimensions as well as details of two-particle interactions. The model has been carefully validated to be in agreement with general thermodynamic theories. This means that our model realistically predicts not only mean velocity of colloid particles but also distribution of particle velocities and their mean square displacement consistent with Stokes-Einstein equation. Model results represent dynamics of aggregation of a colloidal system into gel-like network and dynamic evolution of meta-stable colloid dispersion. Thus we are also able to predict stability and dynamic evolution of the colloids with various thermodynamic parameters of the system, e.g., size of dispersed particles, concentration of ions in the surrounding electrolyte, etc. Modeling of particle agglomeration by DEM concept is helpful also in the characterization of morphologies of colloidal agglomerates.