Charged Polystyrene Particles Research Articles

Structure factors of charged bidispersed colloidal suspensions

In the present study, the effects of charge bidispersity on static structure factors of dilute charged aqueous colloidal suspensions, for compositions covering the full molar fraction range, are investigated using static light-scattering experiments and integral equation theory. The suspensions under study are made from different charged polystyrene particles with an average diameter of 100 nm. The experimentally-observed static structure factors are then compared with theoretical results obtained from the hypernetted chain approximation. The values of both charges are determined by fitting the scattering data of the two pure components and are kept constant for the mixtures. In order to fully describe the experimental data, the effects of the intrinsic polydispersity have to be taken into account. It is found that the height of the main peak of the measured static structure factor, SM(q), changes monotonically as a function of the composition.

Static structure factors of binary suspensions of charged polystyrene spheres: experiment against theory and computer simulation

The microscopic static structure of dilute binary colloidal suspensions, for compositions covering the full molar fraction range, are investigated using static light scattering experiments. The mixtures of liquid-like ordered suspensions are made from charged polystyrene particles having averaged radii of 42 nm and 65 nm. The data are compared with the results of integral equation theories using the extended re-scaled mean spherical approximation and the hypernetted chain approximation and Rogers-Young closure schemes, and to Monte Carlo computer simulations. The values of charges needed in the Yukawa-type pair potentials are determined from fits to the scattering data of the pure components, and they are kept constant for the mixtures. Of the various theoretical schemes used, the Rogers-Young method is found to be the most satisfactory. In order to fully describe the experimental data, it is necessary to take the intrinsic polydispersity of the two pure components into account.

Adsorption of anionic surfactants on positively charged polystyrene particles II

In the case of cationic polystyrene latex, the adsorption of anionic surfactants involves a strong electrostatic interaction between both the particle and the surfactant, which may affect the conformation of the surfactant molecules adsorbed onto the latex-particle surface. The adsorption isotherms showed that adsorption takes place according to two different mechanisms. First, the initial adsorption of the anionic surfactant molecules on cationic polystyrene surface would be due to the attractive electrostatic interaction between both ionic groups, laying the alkyl-chains of surfactant molecules flat on the surface as a consequence of the hydrophobic interaction between these chains and the polystyrene particle surface, which is predominantly hydrophobic. Second, at higher surface coverage the adsorbed surfactant molecules may move into a partly vertical orientation with some head groups facing the solution. According to this second mechanism the hydrophobic interactions of hydrocarbon chains play an important role in the adsorption of surfactant molecules at high surface coverage. This would account for the very high negative mobilities obtained at surfactant concentration higher than 5×10−7 M. Under high surface-coverage conditions, some electrophoretic mobility measurements were performed at different ionic strength. The appearance of a maximum in the mobility-ionic strength curves seems to depend upon alkyl-chain length. Also the effects of temperature and pH on mobilities of anionic surfactant-cationic latex particles have been studied. The mobility of the particles covered by alkyl-sulphonate surfactants varied with the pH in a similar manner as it does with negatively charged sulphated latex particles, which indicates that the surfactant now controls the surface charge and the hydrophobic-hydrophilic character of the surface.

Scattering studies on polymer colloids under shear

Neutron beams are easily transmitted through optically opaque samples and therefore provide an excellent means of examining concentrated colloidal dispersions. Small-angle neutron scattering studies can, moreover, provide a means of determining the structure of such systems both in an equilibrium mode and under dynamic conditions. The present investigation is concerned with the latter and describes the examination of two types of colloidal dispersion in a quartz Couette viscometer at shear rates up to 10,000 s −1. In the case of an aqueous dispersion of monodisperse charged polystyrene particles the system under static conditions was quasi-crystalline but “melted” under the influence of the shear field. With sterically stabilized dispersions of poly(methyl methacrylate) particles in dodecane it was found that under shear different structural arrangements of the particles occurred in directions perpendicular and parallel to the direction of flow.

Light scattering from colloids

This paper presents a review of light scattering results on static and dynamic properties of ordered colloidal suspensions of charged polystyrene particles and fractal colloidal aggregates. Our studies on static structure factor,S(Q), of ordered monodisperse colloidal suspensions and binary mixtures of particles with different particle diameters, measured by angle-resolved Rayleigh scattering will be discussed. This will include determination of bulk modulus using gravitational compression and observation of colloidal glass (inferred from splitting of the second peak inS(Q)). Dynamic light scattering, with real time analysis of scattered intensity fluctuations, is used to get information about Brownian dynamics of the particles. Recent advances in the field of light scattering from colloidal aggregates which show fractal geometry will also be discussed.

The effect of adsorbed charged polypeptides on the electrophoretic mobility of positively and negatively charged polystyrene latices

Electrophoretic mobilities of negatively charged polystyrene particles that are covered with variable amounts of positively charged poly- l -lysine (of different molecular weights) and of positively charged polystyrene latices that have analogously been modified with negatively charged poly- l -glutamic acid are reported. Particles that are fully covered with oppositely charged polyelectrolyte exhibit a maximum in the electrophoretic mobility as a function of the ionic strength. This is an indication that the maxima in the zeta potential of untreated polystyrene latices as a function of electrolyte concentration can possibly be ascribed to the presence of polyelectrolytes on these “bare” particles as well.

Kossel Line Analysis on Colloidal Crystals in Semidilute Aqueous Solutions

An analysis of Kossel lines is reported for colloidal crystals of highly charged polystyrene particles in semidilute aqueous solutions. The phase transformation between fcc and bcc structures and their coexistence is observed. Lattice constants are found to be systematically smaller than those calculated from the uniform particle distribution throughout solution. This observation shows that a long-range weak attraction also exists between colloidal particles. The fine structure of the Kossel line is explained by use of dynamical theory.

Characterization of aerosol mobility distributions by integral mobility analysis—the method of mobility moments

A procedure was developed for generating moments of aerosol mobility distributions using the charged particle precipitation properties of the low pass (integral) mobility analyzer. Application of the moment technique was demonstrated through two types of experiments using nearly monodisperse polystyrene particles. In one set of experiments a measurement of the first and second moments of the mobility distribution for singly charged polystyrene particles was used to infer the mean particle size and size standard deviation for two different Dow polystyrene latex batches. The size measurements were found to be in agreement with several other independent sizing studies. In a separate experiment the first two mobility moments were used to characterize the distribution of electric charge on an aerosol of polystyrene particles exposed to unipolar air ions. Mean aerosol charge and charge standard deviations were determined by the moment method and by a simpler, but less rigorous technique in which analyzer mobility resolution was assumed to be ideal. The mean charge and charge standard deviation measured by the two methods were found to be in good agreement, even though analyzer mobility resolution was only 10 per cent

Quasielastic light scattering study of charged polystrene particles in water

We have measured intensity correlation functions for a water suspension of charged polystyrene particles in the ranges: 0.84×107–3.13×107 m−1 for the scattering vector q, 1 μs–3 ms for the delay time, and 0.15–2.1 mg/cm3 for the concentration. At low ionic strength the functions show an initial decay as well as a long time decay, characterized by the effective diffusion coeficients Deff and DL, respectively. Both Deff and DL have a minimum at the same q value and Deff scales with the inverse static structure factor. The data are analyzed using a model in which a particle is diffusing within a diffusing cage yielding values for their diffusion coefficients and for the ’’free’’ transit time of the particle in the cage. Attempts are made to correct the data for the effect of multiple scattering.

The adsorption of human plasma albumin and bovine pancreas ribonuclease at negatively charged polystyrene surfaces: II. Hydrogen ion titrations

As a sequel to a previous study of the adsorption of human plasma albumin (HPA) and bovine pancreas ribonuclease (RNase) on negatively charged polystyrene particles, potentiometric proton titration curves of the proteins in the adsorbed and the dissolved state have been determined. The titration behavior of adsorbed RNase and adsorbed HPA supports the conclusion made previously, i.e., RNase adsorbs without conspicuous structural changes, whereas HPA molecules undergo substantial structural alterations, the more so the more the pH of adsorption differs from the isoelectric point of the protein in solution. In the adsorbed state, a fraction of the positively charged groups of the protein is prevented from deprotonation, probably on account of ion-pair formation with negatively charged sulfate groups at the latex surface. It was also found that, contrary to expectation, the carboxyl groups of the adsorbed protein tend to accumulate close to the negatively charged polystyrene surface.