Colloidal Latex Research Articles

Effects of Environmental and Clinical Interferents on the Host Capture Efficiency of Immobilized Bacteriophages

Bacteriophage-functionalized surfaces are a new class of advanced functional material and have been demonstrated to be applicable for use as antimicrobial surfaces in medical applications (e.g., indwelling medical devices or wound dressings) or as biosensors for bacterial capture and detection. However, the complex composition of many real life samples (e.g., blood, natural waters, etc.) can potentially interfere with the interaction of phage and its bacterial host, leading to a decline in the efficiency of the phage-functionalized surface. In this study, the bacterial capture efficiency of two model phage-functionalized surfaces was assessed in the presence of potential environmental and biomedical interferents. The two phage-bacteria systems used in this study are PRD1 with Salmonella Typhimurium and T4 with Escherichia coli. The potential interferents tested included humic and fulvic acids, natural groundwater, colloidal latex microspheres, host extracellular polymeric substances (EPS), albumin, fibrinogen, and human serum. EPS and human serum decreased the host capture efficiency for immobilized PRD1 and T4, and also impaired the infectivity of the nonimmobilized (planktonic) phage. Interestingly, humic and fulvic acids reduced the capture efficiency of T4-functionalized surfaces, even though they did not lead to inactivation of the suspended virions. Neither humic nor fulvic acids affected the capture efficiency of PRD1. These findings demonstrate the inadequacy of traditional phage selection methods (i.e., infectivity of suspended phage toward its host in clean buffer) for designing advanced functional materials and further highlight the importance of taking into account the environmental conditions in which the immobilized phage is expected to function.

Predicting Aggregation Rates of Colloidal Particles from Direct Force Measurements

Direct force measurements between negatively charged colloidal latex particles of a diameter of 1 μm were carried out in aqueous solutions of various inorganic monovalent and multivalent cations with the multiparticle colloidal probe technique based on the atomic force microscope (AFM). The observed force profiles were rationalized within the theory of Derjaguin, Landau, Verwey, and Overbeek (DLVO). In the presence of monovalent and divalent cations, this theory was capable to describe the force profiles correctly down to distances of a few nm. At shorter distances, however, a strong non-DLVO attraction was identified. For more highly charged cations, an additional and more long-ranged non-DLVO attractive force is observed, and it was interpreted by surface charge heterogeneities. On the basis of these force profiles, the aggregation rates, which were independently measured by light scattering, can be predicted relatively well. The main conclusion of this study is that, in the present system, direct force measurements do capture the principal interactions driving aggregation in colloidal suspensions.

Bacterial anti-adhesive properties of polysulfone membranes modified with polyelectrolyte multilayers

The bacterial anti-adhesive properties of polysulfone (PSU) microfiltration membranes modified with poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) polyelectrolyte multilayers (PEMs) were investigated in this study. Using a direct microscopic observation membrane filtration system, the deposition kinetics of Escherichia coli cells on the membrane surfaces, as well as the reversibility of bacterial deposition, were examined in the absence and presence of calcium. The PEM-modified membranes exhibited significantly improved bacterial anti-adhesive properties compared to the PSU base membranes in both the tested solution chemistries. Specifically, the bacterial deposition kinetics on the modified membranes were slower than the deposition kinetics on the base membranes. Furthermore, the bacterial removal efficiency was significantly enhanced from <10% to as high as 99% after PEM modification. Interaction force measurements conducted through atomic force microscopy revealed strong, long-ranged repulsive interactions between a carboxylate modified latex colloid probe and PEM-modified membranes, while attractive interactions were detected between the colloid probe and PSU base membranes. The bacterial anti-adhesive properties exhibited by the PEM-modified membranes were attributed to the highly swollen and hydrated PEMs that inhibit the direct contact or close approach of bacteria to the underlying PSU membranes.

Continuous separation of colloidal particles using dielectrophoresis

Dielectrophoresis is the movement of particles in nonuniform electric fields and has been of interest for application to manipulation and separation at and below the microscale. This technique has the advantages of being noninvasive, nondestructive, and noncontact, with the movement of particle achieved by means of electric fields generated by miniaturized electrodes and microfluidic systems. Although the majority of applications have been above the microscale, there is increasing interest in application to colloidal particles around a micron and smaller. This paper begins with a review of colloidal and nanoscale dielectrophoresis with specific attention paid to separation applications. An innovative design of integrated microelectrode array and its application to flow-through, continuous separation of colloidal particles is then presented. The details of the angled chevron microelectrode array and the test microfluidic system are then discussed. The variation in device operation with applied signal voltage is presented and discussed in terms of separation efficiency, demonstrating 99.9% separation of a mixture of colloidal latex spheres.

Analysis of latex, gold and smectite colloid transport and retention in artificial fractures in crystalline rock

The transport behavior of artificial (gold and latex) and natural (smectite) colloids within artificial fractures in natural crystalline rock was analyzed. The selected colloids presented different size, shape, density and surface charge: the effects of these parameters on their transport and retention in the fractures were evaluated in conjunction with the effects of the hydrodynamic characteristics of the system (water velocity/residence time in the fracture and fracture width). Resultshowed that, in crystalline rock fractures, all the analyzed colloids travel as fast as or faster than water (retardation factors, Rf≤1). Different parameters were identified to simultaneously control the velocity of colloids in the fracture, and an efficient analysis of Rf values could be performed relating them to the Taylor dispersion. This parameter accounts for the Brownian diffusion (colloid size), the mean water velocity and the fracture width.All the experiments were carried out under unfavorable electrostatic conditions (rock and colloids both negatively charged) and, in spite of clear exclusion effects observed, colloids were retained on the fracture surface. Under similar water velocities, the recovery of smectite colloids was always higher than that of latex and gold colloids, most probably due to the different morphology of the particles.Colloid retention was observed mainly in zone of the rock with defects, micro-fractures and grain boundaries and increased significantly as the water flow rate decreased. The retention behavior observed could not be totally explained considering only sedimentation and Brownian motion effects.

Charging and aggregation of negatively charged colloidal latex particles in the presence of multivalent oligoamine cations

Charging and aggregation of negatively charged carboxyl latex particles in the presence of positively charged linear oligoamines containing 1–6 amine groups were investigated by electrophoretic mobility and dynamic light scattering. The oligoamines of low valence resemble simple inert salts and destabilize the suspensions by screening their charge. The oligoamines of higher valence induce overcharging at low concentrations, whereby destabilization is triggered by charge neutralization. At higher concentrations, destabilization is also induced by screening. The onset of first fast aggregation regime scales with the inverse six power of the valence in agreement with the Schulze–Hardy rule. The aggregation rates can be relatively well described by the DLVO theory which indicates that the interactions are governed by van der Waals and electrostatic double layer forces.

AFM force spectroscopy study of carboxylated latex colloids interacting with mineral surfaces

Interaction of carboxylated latex colloids with several mineral surfaces (quartz, muscovite, biotite, K-feldspar, apatite and titanite) is studied with the AFM colloid probe technique. Aqueous sample solutions are varied in pH from 2 to 10 at constant ionic strength and additionally, experiments with groundwater from the Grimsel site are carried out. Strong attractive forces are measured at pH values close to or below the expected point of zero charge (pHpzc) of the mineral surfaces. In addition, the influence of Eu(III) and Ca(II) on the colloid–mineral surface interaction is investigated. Depending on pH and mineral surface, an increase of attractive forces is observed in presence of Eu(III) and Ca(II). Furthermore, AFM results are compared with theoretical DLVO calculations. These calculations show that experimental results can be well predicted by theory. However, the actual calculations do not consider hydration forces, which may prevent colloid adsorption. The present study reveals that colloid–mineral surface interaction is determined by electrostatic surfaces forces. Therefore, colloid adsorption in the alkaline regime can only be observed on apatite in sample solutions containing, e.g., Ca(II) or Grimsel groundwater.

Site-Specific Retention of Colloids at Rough Rock Surfaces

The spatial deposition of polystyrene latex colloids (d = 1 μm) at rough mineral and rock surfaces was investigated quantitatively as a function of Eu(III) concentration. Granodiorite samples from Grimsel test site (GTS), Switzerland, were used as collector surfaces for sorption experiments. At a scan area of 300 × 300 μm(2), the surface roughness (rms roughness, Rq) range was 100-2000 nm, including roughness contribution from asperities of several tens of nanometers in height to the sample topography. Although, an increase in both roughness and [Eu(III)] resulted in enhanced colloid deposition on granodiorite surfaces, surface roughness governs colloid deposition mainly at low Eu(III) concentrations (≤5 × 10(-7) M). Highest deposition efficiency on granodiorite has been found at walls of intergranular pores at surface sections with roughness Rq = 500-2000 nm. An about 2 orders of magnitude lower colloid deposition has been observed at granodiorite sections with low surface roughness (Rq < 500 nm), such as large and smooth feldspar or quartz crystal surface sections as well as intragranular pores. The site-specific deposition of colloids at intergranular pores is induced by small scale protrusions (mean height = 0.5 ± 0.3 μm). These protrusions diminish locally the overall DLVO interaction energy at the interface. The protrusions prevent further rolling over the surface by increasing the hydrodynamic drag required for detachment. Moreover, colloid sorption is favored at surface sections with high density of small protrusions (density (D) = 2.6 ± 0.55 μm(-1), asperity diameter (φ) = 0.6 ± 0.2 μm, height (h) = 0.4 ± 0.1 μm) in contrast to surface sections with larger asperities and lower asperity density (D = 1.2 ± 0.6 μm(-1), φ = 1.4 ± 0.4 μm, h = 0.6 ± 0.2 μm). The study elucidates the importance to include surface roughness parameters into predictive colloid-borne contaminant migration calculations.

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.

Deposition of Latex Colloids at Rough Mineral Surfaces: An Analogue Study Using Nanopatterned Surfaces

Deposition of latex colloids on a structured silicon surface was investigated. The surface with well-defined roughness and topography pattern served as an analogue for rough mineral surfaces with half-pores in the submicrometer size. The silicon topography consists of a regular pit pattern (pit diameter = 400 nm, pit spacing = 400 nm, pit depth = 100 nm). Effects of hydrodynamics and colloidal interactions in transport and deposition dynamics of a colloidal suspension were investigated in a parallel plate flow chamber. The experiments were conducted at pH ∼ 5.5 under both favorable and unfavorable adsorption conditions using carboxylate functionalized colloids to study the impact of surface topography on particle retention. Vertical scanning interferometry (VSI) was applied for both surface topography characterization and the quantification of colloidal retention over large fields of view. The influence of particle diameter variation (d = 0.3-2 μm) on retention of monodisperse as well as polydisperse suspensions was studied as a function of flow velocity. Despite electrostatically unfavorable conditions, at all flow velocities, an increased retention of colloids was observed at the rough surface compared to a smooth surface without surface pattern. The impact of surface roughness on retention was found to be more significant for smaller colloids (d = 0.3, 0.43 vs. 1, 2 μm). From smooth to rough surfaces, the deposition rate of 0.3 and 0.43 μm colloids increased by a factor of ∼2.7 compared to a factor of 1.2 or 1.8 for 1 and 2 μm colloids, respectively. For a substrate herein, with constant surface topography, the ratio between substrate roughness and radius of colloid, Rq/rc, determined the deposition efficiency. As Rq/rc increased, particle-substrate overall DLVO interaction energy decreased. Larger colloids (1 and 2 μm) beyond a critical velocity (7 × 10(-5) and 3 × 10(-6) m/s) (when drag force exceeds adhesion force) tend to detach from the surface irrespective of the impact of roughness. For polydisperse solutions, an increase in the polydispersity and flow velocity resulted in a reduction of colloid deposition efficiency due to the resulting enhanced double-layer repulsion. Quantification of surface topography variations of two endmembers of natural grain surfaces showed that half-pore depths and roughness of sedimentary quartz grains are mainly in the micrometer range. Grains with diagenetically formed quartz overgrowths, however, show surface roughness mainly in the submicrometer range. Thus, surface topography features applied in the here presented analogue study and resulting variation in particle retention can serve as quantitative analogue for particle reactions in diagenetically altered quartz sands and sandstones. The reported impact of particle polydispersity can have an important application for quantitative prediction of retention of varying types of minerals, such as different clay minerals in the environment under prevailing unfavorable conditions.

Aryl Amidine and Tertiary Amine Switchable Surfactants and Their Application in the Emulsion Polymerization of Methyl Methacrylate

The switchability and bicarbonate formation of CO2 triggered aryl amidine and tertiary amine switchable surfactants have been investigated. Despite the lower basicity of these compounds compared to alkylacetamidine switchable surfactants, it was found that amidinium and ammonium bicarbonates could be formed in sufficiently high enough concentrations to perform emulsion polymerization of methyl methacrylate and stabilize the resulting colloidal latexes. Particle sizes ranging from 80 to 470 nm were obtained, and the effects of surfactant concentration, surfactant basicity, initiator type, initiator concentration, and CO2 pressure on particle size and ζ-potential have been examined. Destabilization of latexes is traditionally achieved by addition of salts, strong acids for anionically stabilized latexes, or alkalis for cationically stabilized latexes. However, with CO2-triggered switchable surfactants, only air and heat are required to destabilize the latex by removing CO2 from the system and switching the ...

Simple fabrication of snowman-like colloids

Anisotropic colloidal particles consisting of different compositions and geometry are useful for various applications. These include optical biosensing, antireflective coatings and electronic displays. In this work we demonstrate a simple and cost-effective method for fabricating anisotropic colloidal particles bearing a snowman-like shape. This is achieved by first settling the positively-charged polystyrene latex (PSL) colloids and negatively-charged silica colloids in deionized water onto a glass substrate, forming heterodoublets. The temperature is then raised above the glass transition temperature of the polymer. As a result, the silica particle spontaneously rises to the top of the PSL particle forming a snowman like structure. We have extended this method to different sizes and shown that the structure of the hybrid particles can be tuned by adjusting the size ratio between the silica and the PSL colloids. The surface coverage of the PSL, and hence of the snowman particles, on the glass substrate can also be varied by changing the ionic strength of the solution during the adhesion of PSL to the glass.

Giant thermophoresis of poly(N-isopropylacrylamide) microgel particles

Thermophoresis is the rectification of Brownian motion induced by the presence of a thermal gradient ∇T, yielding a net drift of colloidal particles along or against the direction of ∇T. The effect is known to depend on the specific interactions between solute and solvent, and quantitative theoretical models are lacking except in a few simple experimental cases. Both the order of magnitude and the temperature dependence of the thermophoretic mobility DT are known to be very similar for a wide class of aqueous colloidal systems, ranging from latex colloids to polymers, surfactant micelles, proteins, and DNA. Here we show that thermoresponsive microgel particles made of poly(N-isopropylacrylamide) (PNIPAM) do not share, in the temperature range around the ϑ-point, these common features. Instead, DT displays an unusually strong temperature dependence, maintaining a linear growth across the collapse transition. This behaviour is not shared by linear PNIPAM chains, for which existing data show DT falling at the transition, with similar values between the expanded coil and collapsed globule states away from the transition point. A possible connection of the observed giant temperature dependence of DT to microgel hydration is suggested.

Enhanced Transport of Colloidal Oil Droplets in Saturated and Unsaturated Sand Columns

Colloidal-sized triacylglycerol droplets demonstrated enhanced transport compared to ideal latex colloid spheres in both saturated and unsaturated quartz sand columns. Oil droplets (mean diameter 0.74 ± 0.03 μm, density 0.92 g cm(-3), ζ-potential -34 ± 1 mV) were injected simultaneously with latex microsphere colloids (FluoSpheres; density 1.055 g cm(-3), diameters 0.02, 0.2, and 1.0 μm, ζ-potentials -16 ± 1, -30 ± 2, and -49 ± 1, respectively) and bromide into natural quartz sand (ζ-potential -63 ± 2 mV) via short-pulse column breakthrough experiments. Tests were conducted under both saturated and unsaturated conditions. Breakthrough of oil droplets preceded bromide and FluoSpheres. Recovery of oil droplets was 20% greater than similarly sized FluoSpheres in the saturated column, and 16% greater in the 0.18 ± 0.01 volumetric water content (VWC) unsaturated column. Higher variability was observed in the 0.14 ± 0.01 VWC column experiments with oil droplet recovery only slightly greater than similarly sized FluoSpheres. The research presents for the first time the direct comparison of colloidal oil droplet transport in porous media with that of other colloids, and demonstrates transport under unsaturated conditions. Based on experimental results and theoretical analyses, we discuss possible mechanisms that lead to the observed enhanced mobility of oil droplets compared to FluoSpheres with similar size and electrostatic properties.

Removal of colloidal particles in ceramic depth filters based on diatomaceous earth

Safe drinking water is still not accessible to more than 15% of the world’s population. Decentralised water treatment with ceramic filter candles at the point-of-use (POU) level provides a low-cost and single-stage filtration process with which pathogenic microorganisms can be removed. However, the retention performance of such depth filters scatters for microbiological contaminants in literature. The purpose of this study was to gain a better understanding on the removal mechanisms in ceramic depth filters based on the natural material diatomaceous earth (DE). Therefore, we manufactured so-called ceramic filter candles by ram-extrusion process and subjected these filters to a detailed physical characterisation regarding porosity, pore size distribution, specific surface area, flowrate, surface charge and microstructure. Next, we investigated experimentally the removal of colloidal latex (polystyrene) particles having diameters from 100 to 500 nm under various ionic strengths. Such particles were found to be removed due to adsorption of the colloids. Extended DLVO-theory was used to investigate the forces that account for the adsorption suggesting that hydrophobic interactions drag latex particles onto specific adsorption sites of the filter. It is hypothesised that these specific adsorption sites originate from the unique nanostructured surface of the diatomaceous earth. Furthermore, we believe that such latex particles may be suitable to model the removal of microorganisms if the surrogate and the target pathogen have similar characteristics.

Colloid particle and protein deposition — Electrokinetic studies

Recent developments in the electrokinetic determination of particle, polyelectrolyte and protein deposition at solid/electrolyte interfaces, are reviewed. In the first section basic theoretical results are discussed enabling a quantitative interpretation of the streaming current/potential and microelectrophoretic measurements. Experimental results are presented, pertinent to electrokinetic characteristics of simple (homogeneous) surfaces such as mica, silica and various polymeric surfaces used in protein studies. The influence of the ionic strength, background electrolyte composition and pH is discussed, and the effective (electrokientic) charge of these interfaces is evaluated. In the next section, experimental data obtained by streaming potential measurements for colloid particle mono- and bilayers are presented and interpreted successfully in terms of available theoretical approaches. These results, obtained for model systems of monodisperse colloid particles are used as reference data for discussion of more complicated experiments performed for polyelectrolyte and protein covered surfaces. Results are discussed, obtained for cationic polyelectrolytes (PEI, PAH) and fibrinogen adsorbing on mica, interpreted quantitatively in terms of the theoretical approach postulating a heterogeneous 3D charge distribution. The Gouy–Chapman model, based on the continuous charge distribution proved inadequate. Interesting experimental data are also discussed, obtained by electrophoretic methods in the case of protein adsorption on colloid latex particles. In the last section, supplementary results on particle deposition on heterogeneous surfaces produced by controlled protein adsorption are discussed. Quantitative relationships between the amount of adsorbed protein, zeta potential of the interface and the particle coverage are specified. Possibility of evaluating the heterogeneity of protein charge distribution is pointed out. The anomalous deposition of colloid particles on protein molecules bearing the same sign of zeta potential, which contradicts classical DLVO theory, is interpreted in terms of the fluctuation theory. It is concluded that theoretical and experimental results obtained for model colloid systems and flat interfaces can be effectively used for interpretation of protein adsorption phenomena, studied by electrophoresis. In this way the universality of electrokinetic phenomena is underlined.

Emulsion Polymerization of Styrene and Methyl Methacrylate Using Cationic Switchable Surfactants

Colloidal latexes of polystyrene and poly(methyl methacrylate) have been prepared by emulsion polymerization using cationic amidine-based switchable surfactants. Particles with sizes ranging from 50 to 350 nm were obtained and the effect of factors such as initiator type, initiator amount, surfactant amount, and solid content on the particle size and ζ-potential of the resulting latexes have been examined. Destabilization of the latexes, which is commonly achieved by addition of salts or either strong acids for anionically stabilized latexes or alkalis for cationically stabilized latexes, requires only air and heat, which destabilize the latex by removing CO2 from the system and switching the active amidinium bicarbonate surfactant to a surface inactive amidine compound. The resulting micrometer-sized particles can be easily filtered to yield a dry polymer powder and a clear aqueous phase.

Fabrication and characterization of colloidal crystal thin films

We present a laboratory experiment that allows undergraduate or graduate students to get introduced to colloidal crystal research concepts in an interesting way. Moreover, such experiments and studies can also be useful in the field of crystallography or solid-state physics. The work concerns the growth of colloidal crystal thin films obtained from the crystallization of a latex colloidal solution in a wedge cell. Depending on the thickness of the sample, microcrystals with different structures and orientation are obtained. Colloidal arrangements are studied by scanning electronic microscopy images of the top and edge views of several areas of the crystals.

Maskless Fabrication of Nanowells Using Chemically Reactive Colloids

This letter describes the maskless fabrication of nanowells on a silicon substrate using chemically reactive nanoparticles. The amidine-functionalized polystyrene latex (APSL) colloids are adhered onto a silicon wafer, and hydrolysis of the particles' amidine groups generates the ammonium hydroxide etchant locally. The localized release of reactive species and its fast diffusion into the bulk liquid ensure that the silicon etching takes place only under the APSL colloids. Thus, the basal length of the nanowells is precisely controlled by the diameter of the APSL particles. The shape of the nanowells depends on the structure of the substrate: inverted pyramids on silicon (100) and hexagonal pits on silicon (111). The method described here provides an easy, inexpensive, safe, and high-throughput approach for generating nanowells on silicon surfaces. This maskless and simple nanofabrication method will open doors for new applications with locally generated or locally delivered chemistry from nanoparticles.

The Migration of Styrene Butadiene Latex during the Drying of Coating Suspensions: When and How Does Migration of Colloidal Particles Occur?

Surface elemental compositions of model latex clay coatings on an impervious substrate consolidated under various conditions were measured using the XPS technique, in order to clarify when and how colloidal latex particles migrate to the surface during drying. Under similar drying conditions, surface carbon content decreased with the addition of a water-soluble polymer to the coating colors, while remaining virtually unchanged for coatings of different coat weights made with a given color, indicating that surface carbon content variation is mainly caused by migration of latex rather than of water-soluble polymer. The results also showed that for coatings made with a given suspension, surface carbon content decreased with increasing delay time between coating and heating. For coatings frozen during consolidation and dried by sublimation, surface carbon content increased with increasing drying time before freezing. These results suggest that for the model coatings studied, latex migration mainly occurs after coating application before capillary formation during the initial drying stage when coatings are in the liquid phase, contradicting both the conventional capillary transport and boundary wall migration mechanisms. An alternative mechanism which attributes latex migration to surface trapping effect and to higher Brownian mobility of the smaller latex particles compared with pigment appears to provide a systematically consistent explanation to those phenomena. The new particle migration mechanism implies that segregation of colloidal particles is a ubiquitous phenomenon that would occur not only during the drying of paper coatings but also during consolidation of colloidal films containing particles of different sizes. This is of great importance in the control of surface compositions of nanocomposite coatings.