Hairy Particles Research Articles

Synthesis of hairy acrylic core-shell particles as toughening agents for epoxy networks

Hairy poly(butyl acrylate) (PBuA) core-shell particles with a crosslinked shell were prepared by soap-free emulsion polymerization. The incorporation of the hairy structure was obtained either by surface polymerization of a methacrylate (MMA) terminated poly(ethylene oxide) (PEO), or by physical adsorption of poly(ethylene oxide)-poly(propylene oxide) (PPO)-poly(ethylene oxide) triblock copolymers. The particle shell was crosslinked during the synthesis so as to keep the integrity and morphology of the particle upon curing the epoxy network. Particle sizes and size distributions were determined both by quasi-elastic light scattering and transmission electron microscopy. Particle morphology was investigated by electron and atomic force microscopies. The presence of the poly(ethylene oxide) layer was evidenced by direct analysis of the latexes by means of 1H NMR spectroscopy. Mixing of the core shell rubber particles with the reactive epoxy and processing of the toughened-epoxy networks are described. The influence of the hairy layer (with regards to density and PEO chain length) on particle dispersion within the epoxy network, the resulting rheological behaviour of the core-shell (CS)/prepolymer epoxy blends, and mechanical properties of the modified epoxy were examined and discussed.

Synthesis and characterization of chitosan-modified polymethyl methacrylate latex particles

Stable chitosan-modified polymethyl methacrylate (PMMA) latex particles were prepared by using 2,2′-azobis(2-amidinopropane) dihydrochloride (V-50) as the cationic initiator. The polymerization rate (Rp) is controlled by the V-50 concentration ([V-50]) and Rp is less sensitive to the chitosan concentration ([C]) used in the synthesis work. The reaction system follows Smith–Ewart Case III kinetics due to the relatively large particles produced. The zeta potential data show that the isoelectric point (pI) of the latex particles is 10.7. The amounts of V-50 (CV-50) and chitosan (Cc) ultimately incorporated into the particles correlate reasonably well with [V-50] and [C], respectively. At pH 7, the quantity of the negatively charged bovine serum albumin (BSA, pI = 4.8) adsorbed on the positively charged chitosan-free particles (Q) via the electrostatic interaction increases with increasing CV-50. However, Q is relatively insensitive to changes in Cc. This result implies that only the outermost region of the hairy chitosan-modified particles is available for adsorption of the relatively large protein species. Colloidal stability shows a significant influence on the BSA adsorption process. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1489–1499, 1999

Effect of dextran on the deposition of latex on a glass surface

Adsorption of dextran on hairy latex particles affects the electrophoretic mobility differently, depending on the salt concentration. At a low salt concentration, dextran adsorbs between the hairs, and the expected decrease of mobility with dextran concentration is observed. When the thickness of the dextran layer is greater than the length of the hairs, the anomalous deposition of latex on glass, thought to be caused by the hairs, is eliminated.

Deposition of hairy latex particles onto a glass surface

Hairy latex particles are observed to deposit on a glass surface under conditions for which the DLVO theory predicts no deposition. From electrophoretic mobility and dynamic light scattering experiments it can be concluded that the surfactant-free polystyrene latex particles used in this study are “hairy”, with the length of the hairs being more than 5nm. It is speculated that the hairs can tunnel through the energy barrier and make contact with the glass since deposition occurs when the length of the hairs is comparable to the minimum distance of approach calculated from DLVO theory. Consistent with this model, it is found that the deposition rates increase with salt concentration, while the detachment rates decrease with salt concentration.

Nonlinear Hairy Layer Theory of Electrophoretic Fingerprinting Applied to Consecutive Layer by Layer Polyelectrolyte Adsorption onto Charged Polystyrene Latex Particles

The consecutive layer-by-layer adsorption of poly(allylamine hydrochloride) (PAH) and poly(styrenesulfonate) (PSS) on colloidal charged latex particles is investigated by measuring the electrophoretic mobility as a function of pH and ionic strength over a broad range (electrophoretic fingerprinting). Meaningful interpretation of the data required the development of a nonlinear approach to hairy particle electrophoresis including dissociation, adsorption, and association. Steric and electrostatic exclusion of mobile ions from the hairy layer has been considered. Also, the surface conductivity correction is extended to the case of charged hairy layer particles. We deposited up to three polyelectrolyte layers. The following were found: (i) Each layer deposition is accompanied by charge overcompensation and (ii) Not only the top layer but also the underneath layers and the naked latex particle surface contribute to the particle mobility. This can be interpreted as an incomplete coverage or a polyelectrolyte ...

Electrochemical behavior of hairy carbons

Hairy carbons were prepared by catalytic growth of carbon hairs (diameter 0.05–0.2 μm, at least partly crystalline) on carbon black, graphite particle and carbon fiber substrates. Of the substrates used, the most abundant hair growth was achieved using carbon black, due to the confinement of the catalyst size by the pores in the carbon black. The cyclic voltammetric response of all hairy carbons was superior to that of the corresponding substrate materials. In the case of hairy carbon black, reversibility was achieved and capacitance, electrochemical area and specific surface area were greatly decreased. In the case of hairy graphite particles and hairy carbon fibers, the electron transfer rate k s (as studied via the Fe 2+ Fe 3+ redox couple) was increased, but, in contrast to the hairy carbon black, capacitance and electrochemical area were increased. Hair growth, followed by an oxidation heat-treatment, resulted in oxidized hairy carbon black which exhibited higher k s and better electrochemical reversibility than as-received carbon black, oxidized carbon black, hairy (but not oxidized) carbon black, carbon filaments (i.e. hair by itself) and hairy carbon fibers. This is partly due to the enhancement of the packing density by both hair growth and oxidation. The oxidized hairy carbon black exhibited much lower capacitance and much lower electrochemical area compared to as-received carbon black. The combination of high k s and low capacitance makes oxidized hairy carbon black technologically attractive for battery and analytical electrodes. The particulate nature of oxidized hairy carbon black is in contrast to the fibrous nature of carbon fibers or carbon filaments, which require secondary operations for dispersion. Additionally, hairy carbon black allows good compaction and electrochemical reversibility without the need for a binder.

Characterization of Hairy Latex Particles with Colloidal Particle Scattering

Many experiments in the literature suggest that the surfaces of colloidal latex particles suspended in water are not smooth. The surface roughness is often referred to as being “hairy”. We determined the thickness of the hairy layer on two 5 μm latex particles by colloidal particle scattering, a new method recently developed by us to measure surface forces. The results are consistent with electrophoretic mobility measurements. The thickness can be determined with an error of 1 nm. Besides the layer thickness, qualitative information about the evenness of the hairy layer can also be obtained. According to our calculations, the stabilizing mechanism under our experimental conditions is related to the hairy layer but cannot be ascribed to steric repulsion. Instead, a layer of immobilized water in the hairy layer effectively lowers the van der Waals interactions, thus increasing the relative importance of electrostatic repulsion. Hamaker constant measurements on the same latex samples indicate that there is n...

Electrophoresis of Hairy Particles

Electrophoresis of Hairy Particles

The electrokinetic response of surface-modified polymer latexes: Effects of grafted water-soluble polymer and heat treatment

Low-frequency dielectric spectroscopy and electrophoretic light scattering were used to test the applicability of classical electrokinetic theory to latex particles with and without surface grafted water-soluble polymer. Dielectric measurements on the “hairy” latex reveal large discrepancies between theory and experiment. At the same time, the “bare” latex exhibits qualitatively similar, but smaller, discrepancies. High temperature treatment of the latexes alters the particles and the discrepancies are reduced. The heat-treated bare latex behaves according to the classical theory; the heat-treated hairy latex exhibits greatly reduced deviations from theory. Electrophoretic mobility measurements spanning 2 decades in ionic strength show that the mobilities of the bare and hairy particles converge following heat treatment, suggesting that the surface contrast between the two particles is diminished. A mechanism involving transport processes within a hairy layer is proposed to explain the inadequacy of classical electrokinetic theory with latex particles.

Polystyrene latex particle surface characteristics

Various monodisperse polystyrene latices of identical particle size, but of widely different particle surface charge density of sulphate (<0.2–1.8 μeq m −2), were prepared. The surface polarity of the polystyrene latex particle, determined from contact angle measurements of an octane drop at the latex sphere “film”/water interface, was found to increase with increasing sulphate charge density. The critical flocculation concentration of the latices increased with increasing density. The zeta potential was highly dependent on the sulphate group charge density as was the variation of the zeta potential with ionic strength. These results are indicative of a hairy particle surface layer. In addition, the plateau level adsorptions of sodium dodecyl sulphate and nonylphenol, substituted with 10 ethylene oxide units, on polystyrene latices of different charge density were determined. The adsorption data were in agreement with Vijayendran's model for the relationship between surfactant adsorption and polymer polarity (in Polymer Colloids II, R.M. Fitch (Ed.), Plenum Press, New York, 1978). Experimental evidence was obtained for the hypothesis that in the adsorption of sodium dodecyl sulphate on the various polystyrene latices not only differences in surface polarity but also electrostatic repulsions were reflected, which is contrary to the adsorption of a nonionic surfactant reflecting polarity effects only.