Deposition Of Latex Particles Research Articles

Cellulose Nanocrystals Mimicking Micron-Sized Fibers to Assess the Deposition of Latex Particles on Cotton

We report the interactions of cationic latex particles synthesized by RAFT/MADIX-mediated emulsion polymerization with anionic cellulose nanocrystals (CNCs) and cotton fabrics. Latexes in the size range 200-300 nm with poly(butyl acrylate) or poly(2-ethylhexyl acrylate) hydropho-bic cores and hydrophilic shell are synthesized. We show that the latex/CNC interaction is me-diated by electrostatics, the interaction being the strongest with the most charged particles. The adsorption process is efficient and does not require any functionalization step for either cellulose or latex. A major result is the observation by cryogenic transmission electron micros-copy of latexes coated with entangled arrays of CNCs, and for the softer particles a notable deformation of their structure into faceted polyhedra. By labeling the latexes with hydrophobic carbocyanine dyes, their deposition on woven cotton fabrics is studied in situ and quantified by fluorescence microscopy. As with the CNCs, the highest deposition on cotton in the wet and dried states is achieved with the most charged latexes. This demonstrates that CNCs can serve as models to adjust the interactions of latex particles with cotton, and thus optimize manufac-turing processes for the development of advanced textiles.

Tunable Plasmonic Silver Nanodomes for Surface-Enhanced Raman Scattering

Surface-enhanced Raman scattering (SERS) is an emerging analytical method used in biological and non-biological structure characterization. Since the nanostructure plasmonic properties is a significant factor for SERS performance, nanostructure fabrication with tunable plasmonic properties are crucial in SERS studies. In this study, a novel method for fabrication of tunable plasmonic silver nanodomes (AgNDs) is presented. The convective-assembly method is preferred for the deposition of latex particles uniformly on a regular glass slide and used as a template for polydimethylsiloxane (PDMS) to prepare nanovoids on a PDMS surface. The obtained nanovoids on the PDMS are used as a mold for AgNDs fabrication. The nanovoids are filled with Ag deposition by the electrochemical method to obtain metallic AgNDs. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) are used for characterization of the structural properties of all fabricated AgNDs. The optical properties of AgNDs are characterized with the evaluation of SERS activity of 4-aminothiphonel and rhodamine 6G. In addition to experimental characterizations, the finite difference time domain (FDTD) method is used for the theoretical plasmonic properties calculation of the AgNDs. The experimental and theoretical results show that the SERS performance of AgNDs is strongly dependent on the heights and diameters of the AgNDs.

A microfluidic system for studying particle deposition during ultrafiltration

A significant limitation in the application of membrane filtration is fouling caused by particle deposition. To better understand the key mechanisms of particle deposition, a microfluidic filtration system was developed that combined confocal scanning laser microscopy (CSLM) and a dual syringe pump flow control setup. It has been used successfully to visualize in real-time and quantify the deposition of latex particles (0.4µm) onto membranes during cross-flow ultrafiltration at two different KCl concentrations (0.01M and 1M). Particle deposition was initially present on the membrane as individual particles, which when deposited, acted as seeds for further particle deposition for both KCl concentrations. Aggregates were only observed after individual particles had already been deposited. After 45min filtration, only monolayer coverage was observed, despite the formation and deposition of aggregates on the membrane. The main deposition on membranes was mostly of individual particles at 0.01M KCl, and of large aggregates at 1M KCl. This difference in particle deposition behaviour can be attributed to the electrostatic changes in the particle-particle and particle-membrane interactions. These findings have important implications for fouling in real systems, where the control of electrostatic interactions may be used to optimize filtration processes.

Kinetics of fluorescent latex particle deposition at polyelectrolyte monolayers determined by in situ measurements

A new flow cell was constructed for studying in situ kinetics of particle and macromolecule adsorption using fluorescence microscopy. Using the cell, calibration experiments were performed for fluorescent latex particles on mica coated by cationic polyelectrolytes: polyallylamine hydrochloride (PAH) and poly(diallyldimethylammonium chloride) (PDADMAC). Formation of polyelectrolyte monolayers was controlled via streaming potential measurements in the flow cell. The bulk latex properties were determined by dynamic light scattering (DLS) and microelectrophoresis. The hydrodynamic diameter of particles varied in the range 528–574nm, depending on ionic strength. The electrophoretic mobility measurements revealed that the zeta potential of particles was negative varying between −56mV for I=10−4M, and −42mV for I=0.15M. The kinetics of latex particle deposition at mica coated by saturated polyelectrolyte layers was studied in situ as a function of ionic strength under diffusion-controlled conditions. The coverage was determined by direct enumeration of particles using the fluorescent microscopy and AFM. The experimental results were adequately interpreted in terms of numerical solutions of the mass transport equation with the blocking function derived from the random sequential adsorption (RSA) approach. Additionally, the dependence of integrated fluorescence intensity on particle coverage was determined, which enables a quasi-continuous measurements of particle deposition kinetics. It was concluded that the cell is versatile tool for determining mechanism of particle deposition at interfaces.

Hematite nanoparticle monolayers on mica: Characterization by colloid deposition

Colloid particle deposition (also referred to as colloid enhancement, CE) was applied to characterize hematite nanoparticle monolayers on mica. The average size of hematite particles (determined by AFM and dynamic light scattering) was 22nm. The monolayers were produced under diffusion-controlled transport from suspensions of various bulk concentration at pH 3.5, I=10−2M, where the particles exhibited a positive zeta potential of 39mV. The monolayer coverage, quantitatively determined by AFM and SEM, was regulated within broad limits by adjusting the deposition time. The electrokinetic properties of hematite monolayers produced in this way were studied using the streaming potential method. The dependencies of the monolayer zeta potential on the coverage, pH and ionic strength were determined. Hematite monolayers were used as heterogeneous substrates for colloid particle deposition studies involving negatively charged polystyrene latex particles (800nm in diameter). An anomalous deposition of latex particles on substrates exhibiting a mean negative zeta potential was observed for higher ionic strength. These deviations from the classical DLVO theory were quantitatively interpreted in terms of the heterogeneous nanoparticle coverage distribution governed by fluctuation theory. However, for low ionic strength of 10−4M latex particle deposition proceeded in accordance with the DLVO theory. These data obtained for hematite can be used as useful reference states for analyzing particle or bacteria adhesion to heterogeneous surfaces covered by macromolecules and proteins.

Deposition of latex particles encapsulated in polyelectrolyte shells at heterogeneous metal surfaces modified by multilayer films

We used an oblique impinging jet (OIJ) cell to determine the initial deposition rate for the microcapsules deposited on the heterogeneous metal surfaces bare or modified by polyelectrolyte (PE) films. The dependence of reduced particle flux on the Reynolds number of the flow in the OIJ cell was determined by direct counting of particles deposited on the studied surfaces. We used fluorescently labelled latex particles and microcapsules built on these fluorescent cores and the use of fluorescent microscope allowed us to observe “in situ” the deposition processes of particles on rough, highly reflective surfaces. We demonstrated that modification of metallic surfaces of various materials and heterogeneity by the multilayer PE films result in the formation of uniformly charged film of nanometers thickness. The formation of such a film leads to the increase of deposition efficiency and its initial rate is governed by the charge of the film covered surface and the outermost layer of the capsule shell being in agreement with the prediction of the convective-diffusion theory.

Characterization of poly(ethylene imine) layers on mica by the streaming potential and particle deposition methods

Deposition kinetics of polystyrene latex (averaged particle size of 0.66 μm) on mica covered by poly(ethylene imine) (PEI), a cationic polyelectrolyte having an average molecular mass of 75,000 g mol −1, was studied using the impinging-jet method. The hydrodynamic radius of PEI, determined by PCS measurements, was 5.3 nm. The electrophoretic mobility of PEI was measured as a function of pH for ionic strengths of 10 −3 and 10 −2 M, which made it possible one to determine the amount of electrokinetic charge of the molecule and its zeta potential. Formation of the polyelectrolyte layer on mica was followed by measuring the streaming potential in the parallel-plate channel. From these measurements, the dependence of the apparent zeta potential of mica on the surface coverage of PEI was determined. The amount of adsorbed PEI on mica was calculated from the convective diffusion theory. These results were quantitatively interpreted in terms of the theoretical model postulating a particle-like adsorption mechanism for PEI with not too significant shape deformation upon adsorption. On the other hand, the Gouy–Chapman model postulating the adsorption in the form of flat disks was proved inappropriate. After the surface was fully characterized, particle deposition experiments were carried out with the aim of finding the correlation between the polymer coverage and the initial rate of latex particle deposition. In the range of small polyelectrolyte coverage, a monotonic relation between the polymer coverage and the initial deposition rate of particles, as well as the jamming coverage, was found. For Θ PEI > 0.25 , the initial particle deposition rate attained the value predicted from the convective diffusion theory for homogeneous surfaces. These results were interpreted theoretically by postulating that an effective immobilization of colloid particles occurred on local polyelectrolyte assemblages containing between two and three PEI molecules.

Electrosynthesis of structured derivated polythiophenes: Application to electrodeposition of latex particles on these substrates

Synthesis of super-structured polymers is a great challenge because these entities could present a large choice of applications. Synthesis and electropolymerisation of thiophene derivatives are reported. Star-shaped 3D molecules are chosen because these structures ensure a high electronic conductivity. Three-dimensional structures could also assist the conductivity. 1,3,5-tris[5-(2,2′-dithienyl)]benzene 1, tris(2,2′-dithienyl)methylcarbinol 2, tris(5(2,2′:5′2″-terthienyl)methylcarbinol 3 are synthetised by different ways. UV and IR analysis are reported along with an AFM examination of the film. The first attempt of latex particle deposition on the film is also reported showing promising results in view of surface functionalisation.

Deposition of latex particles at heterogeneous surfaces

Irreversible adsorption (deposition) of colloid particles at heterogeneous surfaces was studied experimentally. The substrate surfaces of desired heterogeneity were produced by covering mica surfaces by positively charged polystyrene latex particles. Then, deposition kinetics of negatively charged latex was studied under diffusion-controlled transport conditions. Particle distributions over surfaces and coverage were quantitatively evaluated using the direct microscope observation technique. Using this method, jamming coverage of colloid particles as a function of the heterogeneity degree (smaller particle coverage) was determined. These experimental data confirmed, in accordance with numerical simulations that the adsorption site multiplicity exerted a pronounced effect on the structure of adsorbed layers and the jamming coverage.

Development of W/WO3Sensors for the Measurement of pH in An Emulsion Polymerization System

This paper describes the development of a rugged pH sensor that can be used to monitor hydrogen ion activity in an emulsion polymerization system under demanding reaction conditions. To inhibit deposition of the latex onto the sensor surface, a sensor was chosen to have the same surface charge as that on the latex particles at the pH of the emulsion system. An analysis of pzc (pH of zero charge) of the emulsion latex, as inferred from the zeta potential, the expected pH of the latex, and the known pzc values for various metal oxides, indicated that the W/WO3 electrode should be a viable pH sensor for the particular latex system of interest. It was concluded that the pzc values for both the latex and the pH sensor would lie below the expected pH of the latex, rendering the surfaces of both systems negatively charged. Coulombic repulsion should therefore inhibit the deposition of latex particles onto the pH sensor surface, thereby avoiding possible interference with the pH-determining reactions. Measurement of the W/WO3 sensor potential against a Ag/AgCl, KCl (sat.) reference electrode has shown that the sensor potential varies linearly with pH over a wide pH range, as established by various borate buffers, at temperatures of 25 °C, 70 °C and 130 °C. The slope of the potential versus pH correlation at each temperature is slightly less than the theoretical value indicated by the Nernst equation for a system at electrochemical equilibrium. This deviation, which has been noted in previous work on the W/WO3 sensor in homogeneous aqueous systems, is attributed to the fact that the sensor is not strictly at equilibrium, but instead displays a mixed potential. The W/WO3 sensor can be accurately calibrated over the conditions that exist in the latex system explored in this work and, while no independently measured pH data are available for the latex at elevated temperatures, the value determined by the W/WO3 sensor is consistent with expectations. To our knowledge, this work represents the first measurement of proton activity in a latex system under polymerization reaction conditions.

In situ studies of particle deposition on non-transparent substrates

An oblique impinging-jet (OBIJ) cell was developed, suitable for colloid deposition studies at various interfaces including the practically significant case of non-transparent substrates. Particle transport conditions in the cell were quantitatively evaluated by studying kinetics of polystyrene latex particle deposition on mica. The dependence of the reduced particle flux (mass transfer coefficient) on the flow Reynolds number (Re) was determined by in situ microscope enumeration of adsorbed particles. It was demonstrated, in accordance with previous results for the orthogonal impinging-jet cell, that the flux increased significantly with the Re number. This was interpreted in terms of the convective diffusion theory incorporating the hydrodynamic and specific interactions. The governing transport equation originating from this theory was solved numerically, for the region near the stagnation point, by using the finite-difference method. These numerical solutions were used for nonlinear fitting of the flow intensity parameter α dependence on the Re number. In this way, the transport conditions in the vicinity of the stagnation point were fully characterized. The method was applied for studying kinetics of latex adsorption on non-transparent, plasma treated polymeric substrates. It was demonstrated that a prolonged treatment (ca. 20min) enhanced considerably particle deposition rate that attained values pertinent to the model mica substrate.

Kinetics of particle deposition in the oblique impinging jet cell

A new oblique impinging-jet (OBIJ) cell was developed, suitable for colloid deposition studies at various interfaces. In contrast to previously used orthogonal cells, the OBIJ construction makes possible direct microscope observations of particle deposition on nontransparent substrates. The cell performance was tested by studying kinetics of polystyrene latex particle deposition on mica. Two limiting cell configuration were used in the experiments: (i) the lower position (inverted microscope observation of substrate surface through air) and (ii) the upper position (observation of the substrate surface with adsorbed particles through the suspension layer). The dependence of local mass transfer rate (particle flux) on the position over the substrate surface was studied for various flow Reynolds numbers. It was demonstrated that deposition rate attained maximum at the flow stagnation point whose position was dependent on Re number. Moreover, it was shown that the local flux decreased at much slower rate when moving in the downstream direction, than for previously used impinging-jet cells. Consequently, the area of uniform transport conditions was larger, enabling more precise determination of the limiting particle flux at the stagnation-point. The dependence of the flux on Re number was systematically studied for various ionic strength of the suspension. It was demonstrated, in accordance with previous results for the ordinary impinging-jet, that the flux increased significantly for low ionic strength and high Re number. This phenomenon, referred to as the inverse salt effect, was interpreted in terms of the convective diffusion theory. The governing transport equation originating from this theory was solved numerically, for the region near the stagnation point, using the finite-difference method. These numerical solutions were used for nonlinear fitting of the flow intensity parameter dependence on the Re number. In this way the flow field in the vicinity of the stagnation point was fully characterized. It was concluded that the new cell can be exploited as an effective experimental tool for colloid deposition studies on various substrates.

Latex deposition on glass—monolayer, multilayer and the effect of “free charge”

Deposition of latex particles on oppositely charged glass substrate is driven by electrostatic attraction and a monolayer of latex particles covering the surface is achieved. A multilayer is formed by alternating the charge of latex. However, the presence of any free charged components such as emulsifiers and by-products of polymerization, which are not an integral part of latex particles, affects the course of deposition and may prevent deposition altogether.

Relationship between Cake Structure and Membrane Pore Size in Crossflow Filtration of Microbial Cell Suspension Containing Fine Particles.

The structural change of a filter cake and its effect on permeation flux in crossflow filtration of a suspension containing particles different in size were studied. A suspension containing yeast cells (5 μm in average diameter) and polystyrene latex particles (0.5 μm) with different compositions was used as a model. The change in the structure of the filter cake formed on the membrane surface was observed by using a scanning electron microscope. When the pore size was smaller than the latex particle size, a yeast cell layer containing latex particles was formed on the membrane at the initial stage of filtration. Then, the yeast cell layer was replaced by the latex particle layer. The increase of the circulation flow rate decreased the amount of the filter cake to increase the permeation flux in this case. On the other hand, when the membrane pore size was larger than the latex particle size, a yeast cell layer was first formed on the membrane surface followed by deposition of latex particles on it. The permeation flux was relatively higher than the former case. However, the permeation flux slightly increased with the increase of the circulation flow rate although the weight of the filter cake decreased in the latter case. Thus, a small amount of the latex particles in the cell suspension considerably decreased the permeation flux in crossflow filtration of the suspension. In addition the dependence of the permeation flux on the circulation flow rate was proved to be different whether the small particles were smaller than the membrane pores. These findings including the structure of the filter cakes will be helpful to understand the permeation behaviors in the crossflow filtration of microbial broths which usually contain small particles.

Effects of sodium oleate and calcium chloride on the deposition of latex particles on an air/water interface

Sodium oleate and calcium chloride are used as de-inking chemicals in the flotation of ink particles in a slurry of recycled papers. Together they form calcium oleate particles which increase the efficiency of ink removal. To simulate this process we studied how latex particles, with carboxylated charge groups on their surface to model ink surfaces, deposit on an air/water interface in the presence of calcium oleate. The deposition was observed with the impinging jet technique. At the same time, homo- and heteroflocculation studies of latex and calcium oleate were performed. It was found that deposition occurs when latex particles are heteroflocculated with calcium oleate particles, which occurs near the critical coagulation concentration for homocoagulation of calcium oleate. Direct observations of the deposition process indicate that calcium oleate particles act as a bridge between latex particles and the air/water interface. When calcium chloride is added to a latex-dispersion containing oleate, the formation of calcium oleate particles results in a reduction of oleate adsorbed on the latex particles, thus reducing their surface charge.

Determination of the Isoelectric Point of Planar Oxide Surfaces by a Particle Adhesion Method

Abstract A particle adhesion method for the determination of the isoelectric point (iep) of planar oxide surfaces in aqueous media is described. The experiment consists in measuring the rate of deposition of latex particles as a function of pH. We have measured the iep of fused silica, soda-lime silicate glass and thin films of different metal oxides: tin, aluminum, iridium and tungsten. We find our results in good agreement with data from the literature obtained with other experimental techniques.

Electrokinetic Characteristics of Nitride Wafers in Aqueous Solutions and Their Impact on Particulate Deposition

The electrokinetic characteristics of low pressure and plasma‐enhanced chemical vapor deposited silicon nitride wafers subjected to different cleaning procedures were measured using a streaming potential technique. A streaming potential cell for handling 5 in. wafers was designed and fabricated to make these measurements. The isoelectric point (IEP) of silicon nitride was dependent on the cleaning method as well as the deposition technique. X‐ray photoelectron spectroscopic measurement of Si/O and Si/N ratio of films was made to explain the difference in the measured IEP values. Polystyrene latex particle deposition from aqueous solutions onto silicon nitride wafers was investigated and correlated with the electrokinetic potential data.

Colloid Deposition Kinetics with Surface-Active Agents: Evidence for Discrete Surface Charge Effects

Interest in the subject of colloid-mediated contaminant transport in porous media has stimulated numerous investigators to define the conditions under which particle movement may be environmentally relevant. Latex particle deposition kinetics in granular quartz beds were compared with and without surface-active agents to evaluate the effects of surface heterogeneities. Hydrophobic regions or metal oxide impurities were masked with sodium dodecyl sulfate (SDS) or phosphate, respectively. Deposition rates exhibited a remarkable ionic strength sensitivity in the presence of 10[sup [minus]3] M SDS that was similar to unfavorable filtration predictions using DLVO theory. The strong influence of SDS on particle deposition rates indirectly suggests that particle attachment is enhanced by uncharged, hydrophobic regions of the latex or quartz. Phosphate had little effect on either electrophoretic mobilities or particle deposition rates.

Co-deposition of fine particles on glass surfaces

The deposition of latex particles on glass surfaces in the presence of a CaF 2 precipitant has been studied in the impinging jet cell. The initial flux of latex particles in 5 × 10 −4 M CaCl 2 solution was increased by a factor of thirty when the glass collector surface was modified by contact with CaF 2 precipitant. However, after a period of time necessary to dissolve the positively charged CaF 2, the flux had declined and eventually the previously deposited particles were washed out. Small amounts of the CaF 2 precipitant added to the latex solution also promoted deposition, although in this case the flux increase was not as large as it was previously. Significant influence of the CaF 2 precipitant on the latex particles flux to the glass collector was noted even for quantities of CaF 2 which should have dissolved after being added to the latex suspension. For very small amounts of CaF 2 precipitant, the initially constant flux declined sharply after some period of time. However, one could not see the escape of the deposited particles. The experimental data presented herein indicate a great number of possible interactions during the deposition process from binary mixtures of chemically dissimilar colloid particles. This paper also briefly presents a theory of the phenomenon.

The influence of polymer adsorption on deposition kinetics of colloid particles II. Experimental studies

The influence of polymer adsorption on deposition rate of submicron particles has been studied experimentally by direct observation. The deposition of latex particles was determined in the vicinity of the stagnation point at the collector surface (mica sheets) exposed to an impinging jet of suspension. The initial particle flux decreases with addition of polymer [poly (ethylene oxide) and poly (vinyl alcohol) ] to an extent depending on type, molecular weight and concentration of polymer and ionic strength of the suspension. The results obtained were interpreted in terms of an increased hydrodynamic resistance and the specific interaction energy change caused by polymer adsorption according to the theory developed in Part 1.