Large Polystyrene Particles Research Articles

Particle Adsorption Using a Quartz Crystal Microbalance with Dissipation by Applying a Kelvin-Voigt-Based Viscoelastic Model and the Gauss-Newton Method.

The use of a quartz crystal microbalance with dissipation (QCM-D) to study the adsorption of particles larger than 100 nm, such as liposomes, viruses, and nano/micro-plastics, remains challenging owing to the lack of appropriate models for data evaluation. This study presents a method for quantifying the adsorption of negatively charged polystyrene latex (100 nm-1 μm) at the solid-liquid interface. The validity of a viscoelastic model based on Kelvin-Voigt theory was assessed, and the model was used to evaluate particle adsorption data obtained from QCM-D measurements. The Gauss-Newton method was used to fit the data; the values obtained were larger than results from atomic force microscopy, indicating that the viscoelastic model combined with the Gauss-Newton method can quantify the adsorption of large polystyrene particles and the surrounding water around them. We suggested that QCM-D, in combination with an appropriate viscoelastic model, is applicable to estimate adsorption at the solid-liquid interface even for soft particles larger than 1 μm, which are out of the range of applications to the hydrodynamics model. Furthermore, we successfully showed that the recorded dissipation reflects the viscoelastic properties of the layer. The viscoelastic model allowed quantification of the rheological properties of the layer. The ratio of the viscous and elastic contributions was characterized by using loss tangent (tan δ) values that were extracted from the experimental data by applying the viscoelastic model. These values were lower for the adsorption of the negatively charged polystyrene particles on a positive surface than on a negative surface. This suggests that tan δ reflects the strength of the contact between the particle and substrate.

Bridging and depletion mechanisms in colloid-colloid effective interactions: A reentrant phase diagram.

A general class of nonadditive sticky-hard-sphere binary mixtures, where small and large spheres represent the solvent and the solute, respectively, is introduced. The solute-solute and solvent-solvent interactions are of hard-sphere type, while the solute-solvent interactions are of sticky-hard-sphere type with tunable degrees of size nonadditivity and stickiness. Two particular and complementary limits are studied using analytical and semi-analytical tools. The first case is characterized by zero nonadditivity, lending itself to a Percus-Yevick approximate solution from which the impact of stickiness on the spinodal curves and on the effective solute-solute potential is analyzed. In the opposite nonadditive case, the solvent-solvent diameter is zero and the model can then be reckoned as an extension of the well-known Asakura-Oosawa model with additional sticky solute-solvent interaction. This latter model has the property that its exact effective one-component problem involves only solute-solute pair potentials for size ratios such that a solvent particle fits inside the interstitial region of three touching solutes. In particular, we explicitly identify the three competing physical mechanisms (depletion, pulling, and bridging) giving rise to the effective interaction. Some remarks on the phase diagram of these two complementary models are also addressed through the use of the Noro-Frenkel criterion and a first-order perturbation analysis. Our findings suggest reentrance of the fluid-fluid instability as solvent density (in the first model) or adhesion (in the second model) is varied. Some perspectives in terms of the interpretation of recent experimental studies of microgels adsorbed onto large polystyrene particles are discussed.

Preparation of Raspberry-like Polymer Particles by a Heterocoagulation Technique Utilizing Hydrogen Bonding Interactions between Steric Stabilizers

Large polystyrene particles stabilized by poly(acrylic acid) (PAA) (L-PS(PAA)) (as the core) and small polystyrene particles stabilized by poly(vinyl pyrrolidone) (PVP) (S-PS(PVP)) (as the corona) were successfully used to prepare raspberry-like particles by a heterocoagulation technique utilizing the hydrogen bonding interaction between PAA and PVP. The coverage of L-PS(PAA) by S-PS(PVP) could be controlled by adding PVP homopolymer to the L-PS(PAA) dispersion and by changing the molecular weight of the stabilizers. Moreover, the heterocoagulation of large poly(methyl methacrylate) particles stabilized by PAA (L-PMMA(PAA)) and S-PS(PVP) particles was also accomplished, resulting in the formation of L-PMMA(PAA)-core/S-PS(PVP)-corona raspberry-like composite particles. These results suggested that the raspberry-like particles composed of various polymer particles could be formed by the heterocoagulation technique utilizing the hydrogen bonding interaction.

Effect of some solid properties on gas–liquid mass transfer in a bubble column

Abstract The knowledge about the effects of solids on gas–liquid systems and the respective physical mechanisms are not yet totally clarified. In this work, the effect of the solids on the mass transfer characteristics in a bubble column was studied experimentally for the systems air/water/expandable polystyrene (EPS) beads and air/water/glass beads. Volumetric liquid side mass transfer coefficient, k L a, was determined under different solid concentrations (up to 30 vol.%), superficial gas velocities (up to 2.7 mm/s) and mean diameters (1100, 770 and 591 μm for EPS and 9.6 μm for glass beads). The presence of EPS solids affects negatively k L a being this effect more pronounced for the smaller particles. Also, a decrease in k L a occurs when the solid loading increases. Experiments done with large polystyrene particles ( d p ≥ 591 μm) contaminated with very fine EPS particles ( d p ≅ 0.1 μm) indicate that very fine particles play an important role on gas–liquid mass transfer. Mass transfer experiments in a hollow glass spheres three-phase slurry showed a dual effect of solids loading on k L a, contrarily to what happens with the previous particles. These results can be associated with the different surface properties of the particles studied. An empirical correlation for k L a on the experimental variables was developed.

Cytotoxicity of nanoparticles independent from oxidative stress

The use of nano-sized materials offers exciting new options in technical and medical applications. On the other hand, adverse effects on cells have been reported and may limit their use. In addition to physico-chemical parameters such as contamination with toxic elements, fibrous structure and high surface charge, the generation of radical species was identified as key mechanism for cytotoxic action of nanoparticles. The cytotoxic potential of nanoparticles in the absence of radical generation is less well investigated. This study aims to investigate the size-dependent effect of carboxyl polystyrene particles on cells to identify potential adverse effects of these particles. Particles were characterized in different solutions to assess the influence of the medium on size and surface charge. Viability, membrane integrity, apoptosis, proliferation and generation of oxidative stress were investigated. In addition the intracellular localization of the particles was recorded. 20 nm polystyrene particles induced cellular damage by induction of apoptosis and necrosis. These particles generated radicals to the same degree as larger polystyrene particles. Particles were taken up into endosomes and lysosomes in a size-dependent manner. Protein containing solutions led to increases in particle size, decreased cytotoxicity and reduced cellular uptake. It can be concluded that even in the absence of high surface reactivity and not linked to the generation of radicals nano-sized particles may cause cell damage. The mechanism of this damage includes apoptosis, necrosis and inhibition of proliferation.

Modelling secondary particle formation in emulsion polymerisation: application to making core–shell morphologies

A simple model for particle formation in surfactant-free emulsion polymerisation [Macromol. Symp. 92 (1995) 13; Emulsion polymerization: a mechanistic approach, 1995], with extension to allow for induced decomposition of initiator, is explored. The object is to find conditions for secondary particle formation, especially to find conditions under which it would be possible to grow core–shell particles of vinyl acetate in styrene, and vice versa; core–shell particle formation requires that secondary particle formation be avoided. The system is described by homogeneous nucleation: a radical generated in the aqueous phase will either enter a latex particle, undergo termination, or grow in the aqueous phase until it becomes the nucleus of a new particle. The simplified kinetic description contains only easily specified parameter values and requires minimal computational resources. The model implies that secondary particle formation is suppressed by decreasing seed radius, by increasing solids content, and by starved-feed conditions; seed radius is by far the most influential, while monomer-catalysed initiator decomposition has negligible effect. The model predicts that new particle formation will be rampant when vinyl acetate is polymerised in the presence of large polystyrene particles (implying that large core–shell polystyrene/poly(vinyl acetate) (PS/PVAc) particles cannot be obtained in this way), but that there should be relatively little secondary particle formation when styrene is polymerised in the presence of large PVAc particles (implying that large core–shell PS/PVAc particles can be created by inverse core–shell polymerisation). The model was also used to estimate the particle numbers expected in ab initio, surfactant-free styrene and vinyl acetate systems. The model explains why such styrene systems give large, monodisperse particles, whereas such vinyl acetate systems give much smaller particles. Comparison of predictions of the model with those of more sophisticated treatments suggests that model contains the kinetic events which are most essential in determining the rate of particle formation, and thus is sufficient for stating whether or not massive secondary nucleation will occur.

Particle-turbulence interaction in a boundary layer

Particle-turbulence interaction in wall turbulent flows has been studied. A series of experiments varying particle size, particle density, particle loading and flow Re has been conducted. The results show that the larger polystyrene particles (1100 μm) cause an increase in the number of wall ejections, giving rise to an increase in the measured values of the turbulence intensities and Reynolds stresses. On the other hand, the smaller polystyrene particles (120 μm) bring about a decrease in the number of wall ejections, causing a decrease in the measured intensities and Reynolds stresses. These effects are enhanced as the particle loading is increased. It was also found that the heavier glass particles (88 μm) do not bring about any significant modulation of turbulence. In addition, measurements of the burst frequency and the mean streak-spacing show no significant change with increase in particle loading. Based on these observations, a mechanism of particle transport in wall turbulent flows has been proposed, in which the particles are transported (depending on their size, density and flow Re) by the bursting events of the wall regions.

The effect of deposits of small particles on the resistance of leaves and petals to water loss

Small particles of quartz and a naturally occurring clay significantly increased water loss when deposited onto the cuticles of a range of flowers, petals and young leaves taken from plants grown under glass or in the field. Deposits from aqueous suspensions of titanium dioxide, glass spheres and silica gel significantly increased water loss from leaves and petals; deposits of silicon carbide and the larger polystyrene particles did not; results for the smaller polystyrene spheres were inconclusive.

Thin Colloidal Crystals

Colloidal crystals, made of large polystyrene particles (1.1 \ensuremath{\mu}m in diameter), are confined into a thin layer between two glass boundaries. When the thickness $h$ of the layer is increased progressively from zero, a sequence of structures $S(h)$ is detected from direct observations in an optical microscope. These structures are stacks of $n$ square (\ensuremath{\square})---or triangular $(\ensuremath{\Delta})$---ordered layers. For $nl~7$, the sequence $S(h)$ is $\dots{}n\ensuremath{\Delta}\ensuremath{\rightarrow}(n+1)\ensuremath{\square}\ensuremath{\rightarrow}(n+1)\ensuremath{\Delta}\ensuremath{\rightarrow}\dots{}$.

Blood clearance and organ deposition of intravenously administered colloidal particles. The effects of particle size, nature and shape

The blood clearance and organ deposition of polystyrene and cellulose (DEAE) particles have been studied in the rabbit using labelled material and the technique of gamma scintigraphy in order to investigate the importance of particle size, shape and nature. Small (1.27 μm diameter) polystyrene microspheres were taken up by the reticuloendothelial system of the liver, while large polystyrene particles (15.8 μm diameter) were mechanically filtered by capillary beds of the lungs. Cellulose microspheres and fibres were also taken up into lung tissue. Large cellulose fibres, 30 μm diameter, proved to be toxic whereas large cellulose microspheres were well tolerated. The implications for drug targeting are discussed.