Rate Of Particle Adsorption Research Articles

Properties and microstructure of pickering emulsion synergistically stabilized by silica particles and soy hull polysaccharides

A soy hull polysaccharide (SHP) and hydrophilic silica particle system has been proven to be effective emulsifiers for forming and stabilizing food emulsions. Adsorption of the SHP molecules onto the surface of the silica particles improved the particle wettability, resulting in greater interfacial stability at the oil-water interface, as shown by scanning electron microscopy, three-phase contact angle and interfacial intension analysis. The properties of the emulsion prepared with silica particles in the presence of SHP at different concentration were also investigated to explore the effect of polysaccharide–particle interactions on emulsion stabilization. As the SHP concentration increased, we observed a synergistic effect of reducing the interfacial tension (13 mN/m) and increasing the interface particle adsorption rate (66%) due to the complexation of SiO 2 -SHP by hydrogen bonding in the bulk and at the interface. Correspondingly, at high SHP concentrations (2%–4%), the formation of a colloidal gel in the continuous aqueous phase provided the emulsion with a yield stress, thereby giving it a gel-like and thus quiescent behavior under low-shear conditions. Moreover, quiescent emulsion gels were obtained with d 4,3 of about 12 μm, uniform appearance and microstructure, excellent storage stability (TSI<1.5, 30d), and good rheological properties including higher gel strength and viscosity. These results indicated a synergistic stabilization upon SHP addition and the formation of a hydrogel network in the continuous phase as well as around the droplet surfaces. • A combination of soy hull polysaccharide (SHP) and silica particles as emulsifier. • Silica particles wettability was increased by adsorption of the SHP molecules. • A synergistic effect of SiO 2 and SHP reduces the interfacial tension. • Quiescent emulsion gels were obtained by SiO 2 -SHP system containing 2%–4% SHP.

Atmospheric particle adsorption rates of plants in an industrial city of southwest Iran

• PM 2.5 accounts for 75–90% of the deposited particles on plants in Ahvaz, Iran. • Washingtonia filifera could retain the PM with the highest efficiencies. • Industrial land uses have contributed significantly to the distribution of PM. The present study is aimed at assessing the capability of plant species to adsorb particulate matter (PM) in an industrial city which hosts frequently occurring dust storms. To this end, samples were collected from different leaves (morphological properties) of different dominant species at 10 locations in Ahvaz, Iran which had different land uses (industrial, recreational, high-traffic and residential) in various time periods, including the first period (May 6-October 6), the second period (October 7-November 6), the third period (November 7-December 6), and the fourth period (December 7-March 6). Variations in mineral constituents of particulate matter and particle size distribution were analyzed using XRD and laser diffraction respectively. Results disclosed that the particle deposition of some plant species such as Phoenix dactylifera and Washingtonia filifera in various regions was significantly different from that of other species. The particles were generally composed of minerals such as calcite, silicate (quartz) and phyllosilicate which are derived from dust storms. Steel industries in Ahvaz are also one of the main sources of particles, but due to the fact that these particles are primarily made of iron, their adsorption is more likely to occur at distances close to this source. The findings of this study show that characteristics of different plant species have a significant effect on the adsorption of particles and the potential purification of urban air pollution. Therefore, the extension of green space using plant species with greater adsorption is recommended to pave the way for reducing urban air pollution.

Effect of sodium chloride on precipitation and adsorption behavior of polymer-surfactant complex particles in aqueous solution

Polymer-surfactant complex particles formed by dilution of shampoo play an important role in the sensory properties of shampoo, but their microscopic mechanism has not been clarified yet. This study clarifies the change mechanism influencing hair surface smoothness induced by this complex. The degrees of precipitation and adsorption of the polymer-surfactant complex particles are varied by changing the sodium chloride (NaCl) concentration in the shampoo formulation; hence, the relationships between the frictional and sensory properties during rinsing, the particle formation numbers in water, and the particle adsorption rate on the hair surface are investigated. The frictional property measurement and microscopic observation of human hair treated with the various shampoo solutions confirm that two different particle types, floating and adsorptive, are formed in water during the shampoo dilution process, both of which contribute to improving the hair smoothness. Then, NaCl is added to the basic shampoo composition to control the formation of these two particle types. The particle size distribution and chemical identification show formation of submicron-sized particles mainly consisting of cationized polymer in water with less than 0.20-wt % NaCl, which do not adsorb on the hair surface. For 0.75–3.00-wt.% NaCl, polymer-surfactant complex particles are formed, which easily adsorb on hair. Finally, we propose an optimal NaCl concentration of 0.75 wt.% to obtain excellent frictional properties. The result will contribute to the formulation of cosmetic products based on microscopic mechanism.

Coalescence stability of Pickering emulsions produced with lipid particles: A microfluidic study

In the quest to find approaches to prepare food grade Pickering emulsions, we studied the formation and stability to coalescence of colloidal lipid particle (CLP)-stabilized emulsions within a cross-flow microfluidic device. We show that the particles can either stabilize or destabilize the emulsions depending on the particle adsorption rate versus droplet formation rate, and on the resulting surface coverage when the droplet is formed. At low surface coverage, when droplet formation is significantly faster than adsorption, CLPs have a destabilizing effect as incomplete surface coverage leads to droplet-droplet bridging. At high surface coverage, the dense particle layer results in an effective barrier against droplet coalescence, resulting in physically stable emulsions. The observed non-monotonic dependency of emulsion droplet stability on surface coverage of CLP-stabilized emulsions is in stark contrast to what is observed for conventional surfactant-stabilized emulsions, and thus should be taken into account for the rational design of Pickering emulsions.

A new perspective of particle adsorption: Dispersed oil and granular materials interactions in simulated coastal environment

This study, adsorption behaviors of dispersed oil in seawaters by granular materials were explored in simulation environment. We quantitatively demonstrated the dispersed oil adsorbed by granular materials were both dissolved petroleum hydrocarbons (DPHs) and oil droplets. Furthermore, DPHs were accounted for 42.5%, 63.4%, and 85.2% (35.5% was emulsion adsorption) in the adsorption of dispersed oil by coastal rocks, sediments, and bacterial strain particles respectively. Effects of controlling parameters, such as temperature, particle size and concentration on adsorption of petroleum hydrocarbons were described in detail. Most strikingly, adsorption concentration was followed a decreasing order of bacterial strain (0.5–2μm)>sediments (0.005–0.625mm)>coastal rocks (0.2–1cm). With particle concentration or temperature increased, adsorption concentration increased for coastal rocks particle but decreased for sediments particle. Besides, particle adsorption rate of petroleum hydrocarbons (n-alkanes and PAHs) was different among granular materials during 60 days.

Using a Molecular Stopwatch to Study Particle Uptake in Pickering Emulsions.

Colloidal PMMA particles and an interfacially assembled, pH-switchable lipid film (tetradecylammonium hydrogen phosphate, TAHP) were combined to form emulsion droplets with composite interfaces. Two time scales govern the interfacial structure and droplet size of the system: the rate of particle adsorption and the rate of film assembly. We tune these two time scales by varying the particle size (in the case of the particles) and aqueous pH (in the case of the lipid film). Three rates of film assembly are studied: rapid (pH 5), slow (pH 7), and inactive (pH 9). At pH 5, small droplets coated with a mixed interfacial structure are formed, and increasing particle volume fraction does not change the droplet size. At pH 7, the slowed kinetics of TAHP film assembly results in the particle size having a systematic effect upon droplet size: the smaller the particles, the smaller the droplets. At pH 9, TAHP plays no role in the system, and more familiar Pickering emulsions are observed. Finally, we show that at pH 5 both the interfacial particle density and droplet size can be readily tuned in our system. This suggests potential applications in the rational design of capsules and emulsion droplets with tunable interfacial structure.

Deformation of the water/oil interface during the adsorption of sterically stabilized particles.

The adsorption of sterically stabilized colloids at water/oil (w/o) interfaces is studied experimentally by the formation of Pickering emulsions. Specifically, the effect of the steric stabilizer with respect to the rate of particle adsorption is investigated. Uniform, micrometer-sized poly(methyl methacrylate) (pMMA) particles, which are sterically stabilized with poly(isobutylene) (pIB), are used. The pIB concentration on the particle surface (ΓPIB) is controlled during the synthesis by adjusting the pIB/monomer ratio. Pickering emulsions are formed directly by the addition of water to the nonaqueous pMMA dispersions and subsequent emulsification. A strong dependence of the rate of particle adsorption on ΓPIB is found. The rate constant k for particle adsorption decays exponentially with ΓPIB, which suggest the use of a Boltzmann factor to model the experimentally found rate constants. The experimental results can be explained when the activation barrier for particle adsorption EA is of the same order as the average kinetic energy EK of a particle colliding with an emulsion droplet, which is equivalent to 10(5) kBT. Interestingly, this makes EA several orders of magnitude greater than the steric interaction with another particle. A possible mechanism that can lead to such a significant repulsive force is the inhibited drainage of solvent between the particle and o/w interface. Deformation of the o/w interface then occurs, when the solvent does not have time to drain, which results in a dramatic increase in the interfacial energy. This study identified the relevance of drainage in the formation of Pickering emulsions.

Effect of particle adsorption rates on the disproportionation process in pickering stabilised bubbles

The degree of shrinkage of particle stabilised bubbles of various sizes, in a polydisperse bubble dispersion, has been investigated in the light of the finite adsorption times for the particles and the disproportionation kinetics of the bubbles. For the case where the system contains an abundance of particles we find a threshold radius, above which bubbles are stabilised without any significant reduction in their size. Bubbles with an initial radius below this threshold on the other hand undergo a large degree of shrinkage prior to stabilisation. As the ratio of the available particles to the bubbles is reduced, it is shown that the final bubble size, for the larger bubbles in the distribution, becomes increasingly governed by the number of particles, rather than their adsorption time per se. For systems with "adsorption controlled" shrinkage ratio, the final bubble distribution is found to be wider than the initial one, while for a "particle number controlled" case it is actually narrower. Starting from a unimodal bubble size distribution, we predict that at intermediate times, prior to the full stabilisation of all bubbles, the distribution breaks up into a bimodal one. However, the effect is transient and a unimodal final bubble size distribution is recovered, when all the bubbles are stabilised by the particles.

Irreversible adsorption of gold nanospheres on fiber optical tapers and microspheres

We study the adsorption of gold nanospheres onto cylindrical and spherical glass surfaces from quiescent particle suspensions. The surfaces consist of tapers and microspheres fabricated from optical fibers and were coated with a polycation, enabling irreversible nanosphere adsorption. Our results fit well with theory, which predicts that particle adsorption rates depend strongly on surface geometry and can exceed the planar surface deposition rate by over two orders of magnitude when particle diffusion length is large compared to surface curvature. This is particularly important for plasmonic sensors and other devices fabricated by depositing nanoparticles from suspensions onto surfaces with non-trivial geometries.

Probing timescales for colloidal particle adsorption using slug bubbles in rectangular microchannels

The adsorption of particles to fluid–fluid interfaces is a key step in the generation of colloidosomes and particle-stabilized emulsions. Microfluidic channels are a promising tool for generating particle-stabilized drops and bubbles with independent control over the bubble size and the concentration of particles adsorbed at the fluid interface. In this paper, we present experimental observations of the adsorption of a nanoparticle-surfactant suspension to confined bubbles translating along a microchannel. Long bubbles exhibit a unique two-lobed shape that is linked to the adsorption of surface-active particles to the interface at a timescale comparable to the residence time in the channel. An accompanying decrease in the bubble velocity results from the added viscous drag at the bubble interface. We develop a transport model to describe the rate of particle adsorption to the interface and find good agreement between the model estimates of bubble shape changes and experimental observation. The formation of the two-lobed shape is due to a difference in the velocity of the front and rear of the bubble, which can promote bubble break-up.

Dust deposition: iron source or sink? A case study

Abstract. A significant decrease of dissolved iron (DFe) concentration has been observed after dust addition into mesocosms during the DUst experiment in a low Nutrient low chlorophyll Ecosystem (DUNE), carried out in the summer of 2008. Due to low biological productivity at the experiment site, biological consumption of iron can not explain the magnitude of DFe decrease. To understand processes regulating the observed DFe variation, we simulated the experiment using a one-dimensional model of the Fe biogeochemical cycle, coupled with a simple ecosystem model. Different size classes of particles and particle aggregation are taken into account to describe the particle dynamics. DFe concentration is regulated in the model by dissolution from dust particles and adsorption onto particle surfaces, biological uptake, and photochemical mobilisation of particulate iron. The model reproduces the observed DFe decrease after dust addition well. This is essentially explained by particle adsorption and particle aggregation that produces a high export within the first 24 h. The estimated particle adsorption rates range between the measured adsorption rates of soluble iron and those of colloidal iron, indicating both processes controlling the DFe removal during the experiment. A dissolution timescale of 3 days is used in the model, instead of an instantaneous dissolution, underlining the importance of dissolution kinetics on the short-term impact of dust deposition on seawater DFe. Sensitivity studies reveal that initial DFe concentration before dust addition was crucial for the net impact of dust addition on DFe during the DUNE experiment. Based on the balance between abiotic sinks and sources of DFe, a critical DFe concentration has been defined, above which dust deposition acts as a net sink of DFe, rather than a source. Taking into account the role of excess iron binding ligands and biotic processes, the critical DFe concentration might be applied to explain the short-term variability of DFe after natural dust deposition in various different ocean regions.

Synoptic evaluation of regional PM2.5 concentrations

By comparing short-term fluctuations in PM2.5 species concentrations among nearby air quality monitors and among species, it becomes possible to understand the regional and local events leading to higher concentrations. This approach was applied at thirteen sites in the Maryland area for the 2001–2006 timeframe in order to identify and explain the behavior of eighteen different analytes as well as the daily Air Quality Index. Findings included identification of local upwind events such as fireworks displays, construction and demolition, the spatial extent of sulfate, nitrate, and ammonium correlations between ground-level monitors, correlations between some crustal species to indicate similar emissions sources in urban areas, and indicators of particle adsorption as a rate-limiting step for certain species. For example, the bromine behavior suggests that bromine concentrations on particulate matter may be limited by the particle adsorption rate and thus show a dependence on the Air Quality Index measurements.

Reduction of nonspecific surface-particle interactions in optoelectronic tweezers

We demonstrate three-dimensional optoelectronic tweezers (3D OET) for the adsorption-free manipulation of microparticles. In typical OET, nonspecific interactions between the manipulated particles and the device surfaces, such as hydrophobic, Van der Waals, and electrostatic interactions, interfere with the effective microparticle manipulation. Here, by using the 3D OET device, which is composed of two photoconductive layers, we succeeded in three-dimensional focusing and manipulating polystyrene microbeads in a channel-less microenvironment without the particle adsorption. The 3D OET with the light-induced negative dielectrophoresis also shows a higher particle trapping efficiency and less particle adsorption rate than typical OET.

A Study of Silica Nanoparticle Adsorption Using Optical Reflectometry and Streaming Potential Techniques

The kinetics of adsorption of monodisperse nanosized silica particles (32−190 nm diameter) on silicon wafers modified with an aminopropylsilane have been studied by optical reflectometry under stagnant-flow conditions. The adsorption of negatively charged particles on a positively charged wafer surface is driven by electrical double layer attraction and was not found to be measurably reversible. The initial rate of particle adsorption decreases with increasing particle size while the equilibrium amount adsorbed increases with electrolyte concentration. The effect of particle adsorption on the ζ potential of similarly modified glass slides was measured using streaming potential apparatus. The coverage of particles was varied using electrolyte as indicated by the reflectometry measurements. The results suggest that displacement of the plane of shear is not localized to particle covered areas.

Kinetics of localized adsorption of colloid particles

Methods of analyzing localized adsorption of colloid particles at solid/liquid interfaces were extensively reviewed. First, the initial adsorption fluxes calculated using the Levich-Smoluchowski approximation were discussed. The uniformly, and nonuniformly accessible interfaces were distinguished and the superiority of the former in experimental studies was pointed out. A criterion was introduced for estimating the relative significance of the bulk transfer and surface adsorption steps. It was shown that for the majority of experimental and practical situations the surface mass balance equation can be decoupled from the bulk continuity equation. Thus, in due course attention was focused on theoretical and experimental methods of determining the surface blocking parameter B. It was shown that for low and moderate surface concentration range the statistical mechanic approach can be effectively used for predicting B. By introducing the equivalent hard sphere radius r ∗ it became possible to analyze quantitatively blocking effects of interacting as well as nonspherical particles. The analytical solutions were compared with numerical simulation methods valid for the entire range of surface concentrations. The Monte-Carlo algorithm based on the random sequential adsorption (RSA) concept was compared with the sequential Brownian-Dynamics (SBD) method. Theoretical results obtained using these approaches were extensively discussed especially the role of repulsive electrostatic interaction among adsorbing particles. It was shown that these interactions diminish profoundly both the particle adsorption rate and the maximum surface concentration of particles forming “random” monolayers. When the electrostatic forces were operating (lower ionic strength) two distinctive adsorption regimes were predicted (i) fast Langmuir-type adsorption for short times and then (ii) very slow RSA-type approach to the maximum surface concentrations. As discussed such long lasting transient adsorption states could erroneously be interpreted as equilibrium adsorption isotherms. Then, the indirect and direct experimental methods aimed at a quantitative determination of particle adsorption kinetics were described. Illustrative experimental results performed for model latex suspensions were evoked. A satisfactory agreement with theoretical predictions was found for a variety of important physicochemical parameters studied. The RSA approach was found useful for describing particle adsorption kinetics for low and moderate surface concentrations in the case when the flow induced effects could be neglected. On the other hand, the SBD method was found of general validity especially in describing the hydrodynamic scattering effect observed experimentally for higher shear rates. Finally, the theoretical and experimental results concerning structure formation in adsorption processes were presented. The experimentally measured two-dimensional (2D) pair correlation function g12 of adsorbed particles suggested a liquid-like short range ordering occurring for larger surface concentrations. The extent of the 2D ordering was influenced by the adsorption mechanisms of particles, especially the presence of external field of forces.

Monte Carlo simulation of particle adsorption rates at high cell concentration

A practical method of simulating Brownian diffusion of small particles and their adsorption by randomly placed cells is used to estimate the adsorption process rate constant. The ratio of the rate constant to its classical value, 4 pi RD for dilute perfectly adsorbing spheres, is found to be determined by cellular excluded volume. This ratio varies from 1 for dilute solutions of spheres to approximately 40 for spheres in the maximum possible concentration. A function that usefully estimates the rate constant for all possible values of cell concentration, cell radius, and particle diffusion constant is given for random fields of identical spherical cells. The method is also applied to primitive cubic, body centered, and face centered lattices of spheres. At any given excluded volume and concentration the face and body centered lattices have about the same adsorption rate constant whereas the primitive cubic lattices has a smaller one which is, in turn, greater than that for randomly placed spheres. The results will be useful in determining diffusion limited reaction rates under high excluded volume conditions. These include adsorption by red blood cells at normal concentration, the adsorption of molecules by beads in a column, and adsorption of bacteriophage at very high bacterial concentrations.