Presence Of Latex Particles Research Articles

Charging and Aggregation of Positively Charged Colloidal Latex Particles in Presence of Multivalent Polycarboxylate Anions

Abstract Colloidal stability and charging behavior of amidine latex particles in the presence of multivalent oligomers of acrylic acid was investigated by electrophoresis and light scattering. The data were interpreted quantitatively with the theory of Derjaguin, Landau, Verwey and Overbeek (DLVO) whereby the surface potentials were estimated from electrophoresis. Monomer leads to slow aggregation at low concentrations and to rapid aggregation at high concentrations, as characteristic for simple salts. The oligomers induce a charge reversal of the particles. Close to the isoelectric point (IEP) aggregation is rapid while the suspension becomes stable away from this point. At high oligomer concentrations, the aggregation becomes rapid again. The agreement between DLVO theory and experiment is good close to the IEP. At higher oligomer concentrations, the theory predicts larger stabilities than observed experimentally. While inter-particle forces seem to be well described by DLVO theory near the IEP, additional attractive non-DLVO forces are becoming relevant at higher concentrations.

Dynamics at the air-water interface revealed by evanescent wave light scattering

A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle illumination. Peak width and height are affected by the interfacial profile and the focusing of the beam. In addition, the propagation of capillary waves was studied at the surface of pure water and in the presence of latex particles and amphiphilic diblock copolymers. The range of the scattering vectors where propagating surface waves were detected is by far wider than standard surface quasi-elastic light scattering (SQELS) and comparable with those of X-ray photon correlation spectroscopy (XPCS).

Morphologies and droplet sizes of alkyd–acrylic hybrids with high solids content

Alkyd–acrylic hybrids having final solids content of 75–80% were prepared by dropping alkyd resin into an acrylic dispersion. The resulting suspo emulsion structures and the alkyd droplet sizes in the hybrids were dependent on the preparation procedure as well as the interfacial tension between the two liquid phases, σ12, the shear rate, γ˙, the latex/alkyd ratio and the viscosity ratio, p, between the viscosity of the dispersed phase, ηd, and the viscosity of the matrix, ηm. σ12 was varied by changing the surfactant concentration and pH of the hybrids, ηd was varied by changing the viscosity of the alkyd phase but was also affected by variations in the pH, and finally the shear stress was varied by varying the solids content and the amount of latex in the hybrid systems. Parameters that effected the ratio, p, were also studied separately and in combination, and by varying parameters such as the presence of latex particles, alkyd viscosity and solids content, the effect of p on the alkyd droplet size was determined.Different liquid structures were obtained depending on how the surfactant was added to the system. When surfactant was added to the latex prior to the addition of the alkyd, an O/W emulsion was formed. However, if the surfactant was added to the alkyd prior to the addition of the alkyd to the latex, a multi-emulsion (W/O/W) of alkyd was formed, which was also observed when the hybrids were prepared at a high pH. The structures obtained were stable over time and remained unchanged even after ageing for 1 year at room temperature.

Neutron scattering of hydrophobically modified poly(ethylene oxide) in aqueous solutions in the presence of latex particles

The structure of aqueous solutions of hydrophobically end-capped poly(ethylene oxide), PEOM, in the presence of solid particles (latex) was investigated by small angle neutron scattering. Mono- and di-functionalised PEOMs with the same ratio of hydrophilic to aliphatic (C 16H 33) hydrophobic groups of molecular weights 16 000 and 32 000 g mol −1, respectively, were compared. We used solvent conditions in which either PEOM or latex were matched by varying the ratio of water to heavy water. Initially, a decrease in the scattering intensity at small angles was observed when PEOM was added to a suspension of latex at constant concentration. A peak was observed in the structure factor which indicated repulsion between particles. The position of the peak lied at a lower q value for mono-functionalised PEO than for di-functionalised PEO. This observation may be explained by the formation of bridges between aggregates by the di-functionalised PEOM. On varying the solvent, the characteristic peak of PEOM alone disappears at low polymer concentrations due to PEOM adsorption onto the latex particles but reappears at higher polymer concentrations.

Conformations of tethered polymer chains: a fluorescence energy transfer study

Investigations have been carried out to probe the conformations of tethered poly(ethyleneglycol) (PEG) chains anchored on polystyrene (PS) latex particles in presence of an anionic surfactant, sodium dodecyl sulfate (SDS) and two inorganic salts, sodium and potassium chloride. For this purpose, PS latex particles were labeled with pyrene and mononaphthayl PEG ester. Distance dependent nonradiative energy transfer from naphthalene moieties to pyrene moieties was used as a ruler in this study. Results showed that the separation distance between the acceptor and the donor changes with external stimuli. Analysis of the results suggested that there is considerable contraction of the polymer chain upon interaction with salts and surfactant below its critical micelle concentration. The study also reveals that SDS interacts with PEG chains bellow its critical micellar concentration, probably due to binding of SDS counterions to PEG chains.

Suppression of scattering resonances in inhomogeneous microdroplets

Resonance structure in elastic scattering was measured for evaporating micrometer-sized glycerol droplets suspended in an electrodynamic trap. Seeding the droplets with polystyrene latex particles having a diameter of 30 nm ≤ d ≤ 105 nm broadens and attenuates the highest Q (with bare Q ≈ 103−105) resonances, where Q is defined as the ratio of the energy stored to the energy lost from a cavity per cycle. Regardless of whether resonance conditions are satisfied, the presence of latex particles causes fluctuations in the scattering with an amplitude of up to ≈30% of the total signal. Model calculations suggest that the fluctuations may be due at least partially to agglomerated latex particles passing through hot-spot regions within the droplet.

Ultrastructural changes produced in Ehrlich ascites carcinoma cells by ultraviolet-visible radiation in the presence of melanins.

Irradiation of Ehrlich ascites carcinoma (EAC) cells in the presence of pheomelanin, i.e., red hair melanin (RHM), has been reported to produce extensive cell lysis. Irradiation in the presence of eumelanin, i.e., black hair melanin (BHM), or irradiation in the absence of either type of melanin did not produce this effect. We observed that RHM particles penetrated the cell membrane without apparent structural damage to the cell or the cell membrane. Irradiation of the cells in the absence of melanin did not produce any changes in the ultrastructure of the cells. Incubation of the cells in the dark in the presence of RHM produced only minor structural, mainly cytoplasmic changes. Irradiation of the cells in the presence of RHM produced extensive ultrastructural changes prior to complete cell lysis; these changes were more severe than the effects of incubation of the cells in the dark in the presence of RHM. When the cells incubated in the dark or irradiated in the presence of latex particles or either one of the eumelanins particles, viz. BHM or synthetic dopa melanin, these particles did not penetrate into the cells or produce any ultrastructural changes. These particles were in fact not even ingested by the cells.

Effect of deuterium oxide on neutrophil oxidative metabolism, phagocytosis, and lysosomal enzyme release.

We have previously shown that deuterium oxide (D2O) enhances the oxidation of methionine, a myeloperoxidase (MPO) -mediated reaction, by human neutrophils during phagocytosis. However, D2O has no effect on the oxidation of methionine by the purified MPO-H2O2-Cl- system. To explain this observation, we studied the effect of D2O on the oxidative metabolism, phagocytosis, and lysosomal enzyme release by human neutrophils. D2O stimulated the hexose monophosphate shunt (HMS) activity of resting neutrophils in a dose-response fashion. In the presence of latex particles or phorbol myristate acetate (PMA), D2O brought about an exaggerated stimulation of the HMS activity. This enhancement of the HMS activity by D2O was markedly reduced when neutrophils form two patients with X-linked chronic granulomatous disease (CGD) were used, either in the presence or absence of latex particles or PMA. Superoxide and H2O2 production by neutrophils in the presence of latex particles or PMA were also stimulated by D2O. In contrast, D2O inhibited the ingestion of latex particles. D2O enhanced the extracellular release of MPO, but not lactate dehydrogenase, by neutrophils only in the simultaneous presence of cytochalasin B and latex particles. The enhancement of HMS activity and MPO release by D2O was partially inhibited by colchicine. Our results suggest that enhancement of neutrophil oxidative metabolism by D2O may in part explain the stimulation of methionine oxidation by phagocytosing neutrophils.

Biological defense mechanisms. The production by leukocytes of superoxide, a potential bactericidal agent.

As a highly reactive substance produced in biological systems by the one-electron reduction of oxygen, superoxide (O(2) (-)) seemed a likely candidate as a bactericidal agent in leukocytes. The reduction of cytochrome c, a process in which O(2) (-) may serve as an electron donor, was found to occur when the cytochrome was incubated with leukocytes. O(2) (-) was identified as the agent responsible for the leukocyte-mediated reduction of cytochrome c by the demonstration that the reaction was abolished by superoxide dismutase, an enzyme that destroys O(2) (-), but not by boiled dismutase, albumin, or catalase. Leukocyte O(2) (-) production doubled in the presence of latex particles. The average rate of formation of O(2) (-) in the presence of these particles was 1.03 nmol/10(7) cells per 15 min. This rate, however, is only a lower limit of the true rate of O(2) (-) production, since any O(2) (-) which reacted with constituents other than cytochrome c would have gone undetected. Thus. O(2) (-) is made by leukocytes under circumstances which suggest that it may be involved in bacterial killing.