Aggregation in Pickering emulsions

Individual Coating of Entomopathogenic Nematodes with Titania (TiO2) Nanoparticles Based on Oil-in-Water Pickering Emulsion: A New Formulation for Biopesticides

This study presents a new eco-friendly formulation of entomopathogenic nematodes (EPNs) based on individual coating of EPNs with titanium dioxide (TiO₂) nanoparticles (NPs) and mineral oil via oil-in-water Pickering emulsions. Mineral oil-in-water emulsions stabilized by amine-functionalized titanium dioxide (TiO₂-NH₂) particles were prepared. 40:60 and 50:50 oil-water volume ratios using 2 wt % TiO₂-NH₂ particles were found to be the most stable emulsions with a droplet size suitable for the formulation and were further studied for their toxicity against the incorporated EPNs. Carboxyfluorescein was covalently bonded to TiO₂-NH₂ NPs, and the resulting composite was observed via fluorescence confocal microscopy. The dry coating was evaluated using SEM and confocal microscopy, which showed significant nematode coverage by the particles and oil. The final formulation was biocompatible with the studied EPNs, where the viability of the EPNs in the formulation was equivalent to control aqueous suspension after 120 days. Finally, yields of nematodes from infected Galleria mellonella cadavers collected for 150 days showed no significant differences (P > 0.05) using the tested emulsions compared to the control containing nematodes in water.

Therapeutic Effect of Calcipotriol Pickering Nanoemulsions Prepared by Exopolysaccharides Produced by Bacillus halotolerans FYS Strain on Psoriasis

Purpose

Many exopolysaccharides (EPS) have significant emulsifying activity. Some EPS produced by the marine bacterial strain FYS have stronger emulsifying activity in the form of nanoparticles, suggesting that they could potentially form Pickering emulsions. We prepared novel EPS/CT Pickering nanoemulsions (ECPN) with EPS as emulsifiers and assessed their ability to ameliorate the poor permeability of calcipotriol (CT) in skin affected by psoriasis vulgaris.

Methods

A strain of marine bacterium FYS was identified. Molecular weight, monosaccharide composition and microstructure of EPS were determined by gel permeation chromatography, high-performance liquid chromatography and scanning electron microscopy. EPS nanoparticles were prepared by adjusting the pH, and the emulsifying activity was studied at different pH. ECPN were prepared by ultrasound and optimized by the response surface method. The size distribution, microstructure, stability and in vitro drug release of ECPN were studied. The therapeutic effect of ECPN on psoriasis vulgaris was explored by animal experiments and characterizing histomorphology in vivo.

Results

A phylogenetic tree revealed that FYS was a Bacillus halodurans strain. EPS produced by the strain were heteropolysaccharides with a three-dimensional network composed of glucose, galactose, glucuronic acid, rhamnose, galacturonic acid and mannose (32.0:34.3:9.7:7.4:10.3:6.3). The EPS can form nanoparticles at pH = 4–6 with enhanced emulsifying ability. Transmission electron microscopy revealed that EPS nanoparticles adhered to the surface of oil droplets to stabilize the emulsions via a Pickering emulsification mechanism. The prepared ECPN have high stability with a sustained-release effect. Finally, animal experiments showed that ECPN effectively shortened the treatment course of psoriasis vulgaris.

Conclusion

EPS is highly possible to have the potential Pickering emulsification mechanism. The stability of the nanoemulsion was high. ECPN also showed potential for use in the treatment of psoriasis vulgaris. This study provides new insight into the medical applications of EPS and the treatment of psoriasis.

Fabrication and Characterization of Novel Water-Insoluble Protein Porous Materials Derived from Pickering High Internal-Phase Emulsions Stabilized by Gliadin-Chitosan-Complex Particles

Pickering high internal-phase emulsions (HIPEs) and porous materials derived from the Pickering HIPEs have received increased attention in various research fields. Nevertheless, nondegradable inorganic and synthetic stabilizers present toxicity risks, thus greatly limiting their wider applications. In this work, we successfully developed nontoxic porous materials through the Pickering HIPE-templating process without chemical reactions. The obtained porous materials exhibited appreciable absorption capacity to corn oil and reached the state of saturated absorption within 3 min. The Pickering HIPE templates were stabilized by gliadin-chitosan complex particles (GCCPs), in which the volume fraction of the dispersed phase (90%) was the highest of all reported food-grade-particle-stabilized Pickering HIPEs so far, further contributing to the interconnected pore structure and high porosity (>90%) of porous materials. The interfacial particle barrier (Pickering mechanism) and three-dimensional network formed by the GCCPs in the continuous phase play crucial roles in stabilization of HIPEs with viscoelastic and self-supporting attributes and also facilitate the development of porous materials with designed pore structure. These materials, with favorable biocompatibility and biodegradability, possess excellent application prospects in foods, pharmaceuticals, materials, environmental applications, and so on.

Pickering nano-emulsion as a nanocarrier for pH-triggered drug release

This study investigates the formulation of surfactant-free Pickering nano-emulsions able to release a drug at specific pH, in order to enhance its oral bioavailability. The stabilizing nanoparticles composed of magnesium hydroxide, were obtained by nano-precipitation method. The oil-in-water Pickering nano-emulsions stabilized with Mg(OH)₂ nanoparticles, and encapsulating a model of hydrophobic drug (ibuprofen) were formulated following a high-energy process, using a sonication probe. The experimental approach explored the impact of all formulation parameters, composition and size of Mg(OH)₂ nanoparticles, on the physico-chemical properties of the Pickering nano-emulsions. The system was characterized by DLS and transmission electron microscopy. In addition, Mg(OH)₂ has the advantage of being solubilized in an acid medium leading to the destabilization of the nano-emulsion and the release of the active ingredient orally. The acid release study (pH = 1.2) showed cumulative release as a function of initial nanodroplet loading and saturation concentration. In basic media (pH = 6.8), we found a significant release of ibuprofen from the nano-emulsions that already had saturation in an acid medium. These nano-emulsions can not only protect patients from the side effects of acid medicines through the basic properties of hydroxides but also can contribute to the increase of the bioavailability of these drugs. In addition, once in the stomach pH is increased by hydroxides and promotes the release of active ingredients such as ibuprofen whose solubility is strongly influenced by pH.

Microstructure and Elastic Properties of Colloidal Gel Foams

Colloidal gel foams are composed of a continuous, attractive particle network that surrounds and interconnects dispersed bubbles. Here, we investigate their stability, morphology, and elasticity as a function of foaming intensity, surfactant concentration and hydrophobicity, pH, and colloid volume fraction. Upon optimizing these parameters, highly stable colloidal gel foams are created. Within this stability region, the specific interfacial area between the continuous (colloidal gel) and dispersed (bubble) phase can be varied over 2 orders of magnitude leading to a concomitant increase in storage modulus, which scales nearly linearly with specific interfacial area. Our observations provide design guidelines for attractive-particle stabilized foams that enable the programmable assembly of architected porous materials.

Preparation and characterization of core-shell oil absorption materials stabilized by modified fumed silica

The core-shell oil absorption material (OAM) with fumed silica shell was achieved from Pickering polymerization. The modified fumed silica wall could well stabilize both Pickering emulsion and Pickering polymerization. The particle size of encapsulated OAMs decreased with the increasing concentration of fumed silica and remained unchanged when the concentration was more than 1 wt.%. This fumed silica shell had little effect on the oil absorption rate of OAM. The importance was that the shell reversed the surface property and improved the alkali resistance of OAM. We believe that our core-shell OAMs could reach the self-healing ability of the oil well cement.

Stabilization of Oil-in-Water Emulsions with Noninterfacially Adsorbed Particles

Classical (surfactant stabilized) and Pickering (particle stabilized) type emulsions have been widely studied to elucidate the mechanisms by which emulsion stabilization is achieved. In Pickering emulsions, a key defining factor is that the stabilizing particles reside at the liquid-liquid interface providing a mechanical barrier to droplet coalescence. This interfacial adsorption is achieved through the use of nanoparticles that are partially wet by both liquid phases, often through covalent surface modification of or surfactant adsorption to the nanoparticle surfaces. Herein, we demonstrate particle-induced stabilization of an oil-in-water emulsion with fully water wet nanoparticles (no interfacial adsorption) via synergistic interaction with low concentrations of surfactants. Laser scanning confocal microscopy analysis allows for unique and vital insights into the properties of these emulsions via both three-dimensional imaging and real-time monitoring of particle dynamics at the oil-water interface. Investigation of these "non-Pickering" particle stabilized emulsions suggests that the nonadsorbed particles impart stability to the emulsion primarily via entropic forces imparted by the accumulation of silica nanoparticles in the coherent phase between dispersed oil droplets.

Supramolecular colloidosomes based on tri(dodecyltrimethylammonium) phosphotungstate: a bottom-up approach

Hybrid tri(dodecyldimethylammonium) phosphotungstate ([C12]3[PW12O40]) amphiphilic nanoparticles self-assemble in situ at the water/toluene interface to form stable water-in-oil (W/O) Pickering emulsions (droplet size ≈ 20 μm). These emulsions are used as a template for the preparation of colloidosomes (ϕ ≈ 5 μm), which are produced solely through the self-assembly properties of the [C12]3[PW12O40] nanoparticles into a "fused" phase on the water-drop surface in contact with toluene. The structure of the emulsions has been determined using optical and cross-polarized light microscopy, while the colloidosomes have been characterized by scanning electron microscopy (SEM). The structure as well as the aggregation behavior of these nanoparticles has been investigated. Small- and wide-angle X-ray scattering (SWAXS) and transmission electron microscopy (TEM) experiments have revealed a lamellar organization of the inorganic polyoxometalate anions because of the van der Waals interactions between the alkyl chains of the organic cations. According to the solvent, the internal molecular arrangement inside the nanoparticles can be modified: in water, the nanoparticles tend to aggregate in a lamellar structure, whereas in toluene, the nanoparticles are "fused" or coagulated.

Pickering emulsions prepared by layered niobate K₄Nb₆O₁₇ intercalated with organic cations and photocatalytic dye decomposition in the emulsions

We investigated emulsions stabilized with particles of layered hexaniobate, known as a semiconductor photocatalyst, and photocatalytic degradation of dyes in the emulsions. Hydrophobicity of the niobate particles was adjusted with the intercalation of alkylammonium ions into the interlayer spaces to enable emulsification in a toluene-water system. After the modification of interlayer space with hexylammonium ions, the niobate stabilized water-in-oil (w/o) emulsions in a broad composition range. Optical microscopy showed that the niobate particles covered the surfaces of emulsion droplets and played a role of emulsifying agents. The niobate particles also enabled the generation of oil-in-water (o/w) emulsions in a limited composition range. Modification with dodecylammonium ions, which turned the niobate particles more hydrophobic, only gave w/o emulsions, and the particles were located not only at the toluene-water interface but also inside the toluene continuous phase. On the other hand, interlayer modification with butylammonium ions led to the formation of o/w emulsions. When porphyrin dyes were added to the system, the cationic dye was adsorbed on niobate particles at the emulsion droplets whereas the lipophilic dye was dissolved in toluene. Upon UV irradiation, both of the dyes were degraded photocatalytically. When the cationic and lipophilic porphyrin molecules were simultaneously added to the emulsions, both of the dyes were photodecomposed nonselectively.

Stabilization of miniemulsion droplets by cerium oxide nanoparticles: a step toward the elaboration of armored composite latexes

Stable methyl methacrylate (MMA) miniemulsions were successfully prepared using for the first time cerium oxide (CeO(2)) nanoparticles as solid stabilizers in the absence of any molecular surfactant. The interaction between MMA droplets and CeO(2) nanoparticles was induced by the use of methacrylic acid (MAA) as a comonomer. Both MAA and CeO(2) contents played a key role on the diameter and the stability of the droplets formed during the emulsification step. Cryo-transmission electron microscopy (TEM) images of the suspensions formed with 35 wt % of CeO(2) showed the presence of polydisperse 50-150 nm spherical droplets. More surprisingly, some nonspherical (likely discoidal) objects that could be the result of the sonication step were also observed. The subsequent polymerization of these Pickering miniemulsion droplets led to the formation of composite PMMA latex particles armored with CeO(2). In all cases, the conversion was limited to ca. 85%, concomitant with a loss of stability of the latex for CeO(2) contents lower than 35 wt %. This stability issues were likely related to the screening of the cationic charges present on CeO(2) nanoparticles upon polymerization. TEM images showed mostly spherical particles with a diameter ranging from 100 to 400 nm and homogeneously covered with CeO(2). Besides, for particles typically larger than 200 nm, a buckled morphology was observed supporting the presence of residual monomer at the end of the polymerization and consistent with the limited conversion. The versatility of these systems was further demonstrated using 35 wt % of CeO(2) and replacing MMA by n-butyl acrylate (BA) either alone or in combination with MMA. Stable monomer emulsions were always obtained, with the droplet size increasing with the hydrophobicity of the oil phase, pointing out the key influence of the wettability of the solid stabilizer. The polymerization of Pickering miniemulsion stabilized by CeO(2) nanoparticles proved to be an efficient strategy to form armored composite latex particles which may find applications in coating technology.

Characteristics of pickering emulsion gels formed by droplet bridging

We experimentally characterize the microstructure and rheology of a carefully designed mixture of immiscible fluids and near-neutral-wetting colloidal particles. Particle bridging across two fluid interfaces provides a route to highly stable gel-like emulsions at volume fractions of the dispersed phase well below the random close-packing limit for spheres. We investigate the microstructural origins of this behavior by confocal microscopy and reveal a percolating network of colloidal particles that serves as a cohesive scaffold, bridging together droplets of the dispersed phase. Remarkably, the mixture's salient rheological characteristics are governed predominantly by the solids loading and can be tailored irrespective of the droplet volume fraction. The identification of this rheological hallmark could provide a means toward the improved design of modern products that utilize solid-stabilized interfaces.

Nanoparticle coated submicron emulsions: sustained in-vitro release and improved dermal delivery of all-trans-retinol

PURPOSE

The aim of this research is to investigate the dermal delivery of all-trans-retinol from nanoparticle-coated submicron oil-in-water emulsions as a function of the initial emulsifier type, the loading phase of nanoparticles, and the interfacial structure of nanoparticle layers.

METHODS

The interfacial structure of emulsions was characterized using freeze-fracture-SEM. In-vitro release and skin penetration of all-trans-retinol were studied using Franz diffusion cells with cellulose acetate membrane, and excised porcine skin. The distribution profile was obtained by horizontal sectioning of the skin using microtome-cryostat and HPLC assay.

RESULTS

The steady-state flux of all-trans-retinol from silica-coated lecithin emulsions was decreased (up to 90%) and was highly dependent on the initial loading phase of nanoparticles; incorporation from the aqueous phase provided more pronounced sustained release. For oleylamine emulsions, sustained release effect was not affected by initial location of nanoparticles. The skin retention significantly (p < or = 0.05) increased and was higher for positive oleylamine-stabilised droplets. All-trans-retinol was mainly localized in the epidermis with deeper distribution to viable skin layers in the presence of nanoparticles, yet negligible permeation (approximately 1% of topically applied dose) through full-thickness skin.

CONCLUSIONS

Sustained release and targeted dermal delivery of all-trans-retinol from oil-in-water emulsions by inclusion of silica nanoparticles is demonstrated.

Evaporation of an emulsion trapped in a yield stress fluid

The present work deals with emulsions of volatile alkanes in an aqueous clay suspension, Laponite, which forms a yield stress fluid. For a large enough yield stress (i.e. Laponite concentration), the oil droplets are prevented from creaming and the emulsions are thus mechanically stabilized. We have studied the evaporation kinetics of the oil phase of those emulsions in contact with the atmosphere. We show that the evaporation process is characterized by the formation of a sharp front separating the emulsion from a droplet-free Laponite phase, and that the displacement of the front vs. time follows a diffusion law. Experimental data are confronted to a diffusion-controlled model, in the case where the limiting step is the diffusion of the dissolved oil through the aqueous phase. The nature of the alkane, as well as its volume fraction in the emulsion, has been varied. Quantitative agreement with the model is achieved without any adjustable parameter and we describe the mechanism leading to the formation of a front.

Internally structured pickering emulsions stabilized by clay mineral particles

The present study aims to describe emulsion particles containing a dispersed phase composed of nanostructured lipid mesophases and stabilized by montmorillonite and/or Laponite clay platelets. The size distributions of these emulsion particles were found independent of the clay mineral content and of the initial internal composition that determines the internal structure. The stabilization of the droplets by a shell of smectite layers was found possible even by montmorillonite which has a length of the same order or more than the droplets to stabilize. The clay platelets give a local flatness to the droplets that may influence the internal structure. In this paper, we describe the conditions to obtain such soft particles of about 220 nm, and we show by direct visualization the internal mesophase complexity and the shape of the particles. In particular, TEM analysis showed elongated particles with bent-back channels at their center but a different morphology at the periphery due to flat border conditions imposed by the presence of the clay minerals.

Colloidosomes from the controlled interaction of submicrometer triglyceride droplets and hydrophilic silica nanoparticles

The self-assembly of hydrophilic silica nanoparticles at the surface of charged submicrometer triglyceride droplets has been investigated with the aim to optimize the preparation of stable colloidosomes. The droplet charge, oil phase volume fraction, droplet/nanoparticle ratio, and salt concentration play important roles in controlling nanoparticle interactions and are reflected in the colloidosome zeta potential, size, stability, and interfacial structure (visualized by freeze-fracture SEM). Silica nanoparticle interactions with negatively charged droplets are weak, and partially covered droplets are identified. Positively charged droplets are strongly coated by silica nanoparticles and undergo charge reversal at specific droplet to nanoparticle ratios and electrolyte concentrations. Droplets at volume fractions (varphi) <10 (-4) undergo time-dependent limited coalescence until nanoparticle coverage is complete. For varphi in the range 10 (-4) to 2.5 x 10 (-4) and at certain critical droplet to nanoparticle ratios, droplets undergo neutralization or charge reversal coupled with aggregation and precipitation; this occurs in a time-independent manner. Specific conditions have been identified where stable 1-3 mum colloidosomes can be phase separated from heterocoagulates of droplets and nanoparticles.

Thermosensitive pickering emulsion stabilized by poly(N-isopropylacrylamide)-carrying particles

Poly(N-isopropylacrylamide) (PNIPAM)-carrying particles were characterized as thermosensitive Pickering emulsifiers. Emulsions were prepared from various oils, such as heptane, hexadecane, trichloroethylene, and toluene, with PNIPAM-carrying particles. PNIPAM-carrying particles preferentially formed oil-in-water (O/W)-type emulsions with a variety of oils. All the emulsions stabilized by PNIPAM-carrying particles were stable for more than 3 months as long as they were stored at room temperature. However, when the emulsions were heated from room temperature to 40 degrees C, at which point the PNIPAM layer caused a coil-to-globule transition, phase separation occurred. Thus, by using thermosensitive PNIPAM-carrying particles as emulsifiers, the stability of the Pickering emulsions could be controlled by a slight change in temperature.

Latex-particle-stabilized emulsions of anti-Bancroft type

Here, we investigate water-in-oil (W/O) emulsions that are stabilized by polystyrene latex particles with sulfate surface groups. The particles, which play the role of emulsifier, are initially contained in the disperse (water) phase. The existence of such emulsions formally contradicts the empirical Bancroft rule. Theoretical considerations predict that the drop diameter has to be inversely proportional to the particle concentration, but should be independent of the volume fraction of water. In addition, there should be a second emulsification regime, in which the drop diameter is determined by the input mechanical energy during the homogenization. The existence of these two regimes has been experimentally confirmed, and the obtained data agree well with the theoretical model. Stable W/O emulsions have been produced with hexadecane and tetradecane, while, in the case of more viscous and polar oils (soybean and silicone oil), the particles enter into the oily phase, and Pickering emulsions cannot be obtained. The formation of stable emulsions demands the presence of a relatively high concentration of electrolyte that lowers the electrostatic barrier to particle adsorption at the oil-water interface. Because the attachment of particles at the drop surfaces represents a kind of coagulation, it turns out that the Schulze-Hardy rule for the critical concentration of coagulation is applicable also to emulsification, which has been confirmed with suspensions containing Na(+), Mg(2+), and Al(3+) counterions. The increase of the particle and electrolyte concentrations and the decrease of the volume fraction of water are other factors that facilitate emulsification in the investigated system. To quantify the combined action of these factors, an experimental stability-instability diagram has been obtained.

Effect of high salt concentrations on the stabilization of bubbles by silica particles

The stabilization of air bubbles by hydrophobically modified silica particles has been investigated in detail. The silica particles used had a nominal primary particle size of 20 nm and were made hydrophobic by treatment with dichlorodimethylsilane to yield particles with varying percent grafting of alkyl chains ("% SiOR"). Contact-angle (theta) measurements of pure water droplets on flats made from compressed samples of the particles showed a steep increase in theta above ca. 20% SiOR. Other measurements also showed a significant increase in theta when the salt concentration was raised to 1-3 mol dm(-3). Bubbles were formed in a sonicated dispersion of particles by suddenly lowering the pressure. Maximum stability was obtained with 33% SiOR particles and 2-3 mol dm(-3) NaCl. Under these conditions, theta was around 40 degrees. Above a threshold size of around 70 microm, bubbles were extremely stable to disproportionation and coalescence and bubble stability increased significantly with an increase in the NaCl concentration from 0.5 to 3 mol dm(-3). Furthermore, rheological measurements showed that at NaCl concentrations in this range weak particle gels were formed with a finite yield stress. The strength of these gels increased with an increasing NaCl concentration between 0.5 and 3 mol dm(-3) and with an increasing time of aging the dispersions, implicating this as part of the mechanism leading to an increased bubble stability in these systems. Dispersions in the absence of NaCl showed little or no foamability at all. Use of CaCl2 and Al(NO)3 at similar ionic strengths showed that equivalent stability could not be obtained with these salts. Atomic force microscopy (AFM) measurements of the adhesion between a pure (0% SiOR) silica sphere and flat showed a significant increase in the adhesion between 0.5 and 3 mol dm(-3) NaCl, even though in this concentration range no significant change in the electrostatic repulsion might be expected. It is concluded that the increased particle-particle adhesion, effective hydrophobicity, and bubble-stabilization properties of the particles at high NaCl concentrations are probably due to the collapse of protruding polysilicic acid chains on the surface of the silica.

Particle-interface interaction across a nonpolar medium in relation to the production of particle-stabilized emulsions

Quantitative theory of the particle-interface interaction across a nonpolar medium is developed. We consider a spherical dielectric particle (phase 1), which is immersed in a nonpolar medium (phase 2), near its boundary with a third dielectric medium (phase 3). The interaction originates from electric charges at the particle surface (e.g., the surface of a silica particle immersed in oil). The theoretical problem is solved exactly, in terms of Legendre polynomials, for arbitrary values of the dielectric constants of the three phases. As a result, expressions for calculating the interaction force and energy are derived. These expressions generalize the known theory of the electrostatic image force (acing on point charges) to the case of particles that have finite size and uniform surface charge density. For typical parameter values (silica or glass particles immersed in tetradecane), the image-force interaction becomes significant for particles of radius R > 30 nm. At fixed relative particle-to-interface distance, the force increases with the cube of the particle radius. In general, this is a strong and long-range interaction. For micrometer-sized particles, the interaction energy could be on the order of 10(5) k(B)T at close contact, and, in addition, the interaction range could be about 10(5) particle radii. The sign of the interaction depends on the difference between the dielectric constants of phases 2 and 3. When phase 3 has a smaller dielectric constant (e.g., air), the interface repels the particle. In contrast, when phase 3 has a greater dielectric constant (e.g., water), the interaction is attractive. Especially, water drops attract charged hydrophobic particles dispersed in the oily phase, and thus favor the formation of reverse particle-stabilized (Pickering) emulsions. The particle-interface interaction across the oily phase is insensitive to the concentration of electrolyte in the third, aqueous phase.

On the thermodynamics of particle-stabilized emulsions: curvature effects and catastrophic phase inversion

The flexural properties of a particle adsorption monolayer are investigated theoretically. If the particles are not densely packed, the interfacial bending moment and the spontaneous curvature (due to the particles) are equal to zero. The situation changes if the particles are closely packed. Then the particle adsorption monolayer possesses a significant bending moment, and the interfacial energies of bending and dilatation become comparable. In this case, the bending energy can either stabilize or destabilize the Pickering emulsion, depending on whether the particle contact angle is smaller or greater than 90 degrees . Theoretical expressions are derived for the bending moment, for the curvature elastic modulus, and for the work of interfacial deformation and emulsification. The latter is dominated by the work for creation of a new oil-water interface and by the work for particle adsorption. The curvature effects give a contribution of second order, which is significant only for emulsification at 50:50 water/oil volume fractions. A thermodynamic criterion for the type of the formed emulsion is proposed. It predicts the existence of a catastrophic phase inversion in particle-stabilized emulsions, in agreement with the experimental observations. The derived theoretical expressions could find application for interpretation of experimental data on production and stability of Pickering emulsions.

Preparation of nanostructured materials by heterocoagulation-interaction of montmorillonite with synthetic hematite particles

A nanostructured, porous material was prepared by heterocoagulation of negatively charged montmorillonite with positively charged synthetic spherical hematite particles. The process of heterocoagulation of such particles was monitored by turbidimetric titrations over the pH range 2.5-7.5. On the basis of the results of turbidimetric measurements, a series of solid materials were prepared for further characterization using ESEM, BET, XRD, and FTIR techniques. Environmental scanning electron microscopy detected isolated hematite particles or small hematite aggregates on montmorillonite surfaces (mass ratios 8:1 and 4:1). At a mass ratio of 1:1, exfoliated montmorillonite layers, covering the hematite particles as semi-transparent blankets were seen. A low mass ratio led to compact hematite particle aggregates covering the montmorillonite surfaces. Nitrogen-gas-adsorption isotherms revealed the sorption properties to be gradually dependent upon mass ratios. Pore volume distributions showed that mesopores with diameter of about 10-20 nm were produced in the heterocoagulates with mass ratios of 4:1, 1:1, and 1:8. The sample prepared with a 4:1 mass ratio showed the greatest BET surface area, which decreased slightly upon sample calcination at 500 degrees C. X-ray diffraction measurements were used to investigate layer stacking, by comparing the integral intensities of d(001) reflection. For this purpose, samples with 4:1 mass ratios, prepared both by heterocoagulation and mechanical grinding, were used. It was found that heterocoagulation effectively diminished the stacking of the layers to about 85%; hence, a significant amount of fundamental, 1 nm thick montmorillonite layers was achieved in this sample.

Biocide squirting from an elastomeric tri-layer film

Protective layers typically act in a passive way by simply separating two sides. Protection is only efficient as long as the layers are intact. If a high level of protection has to be achieved by thin layers, complementary measures need to be in place to ensure safety, even after breakage of the layer-an important issue in medical applications. Here, we present a novel approach for integrating a biocide liquid into a protective film (about 300-500 microm thick), which guarantees that a sufficient amount of biocide is rapidly released when the film is punctured. The film is composed of a middle layer, containing the liquid in droplet-like compartments, sandwiched between two elastomeric boundary layers. When the film is punctured, the liquid squirts out of the middle layer. A theoretical model was used to determine the size and density of droplets that are necessary to ensure a sufficient quantity of biocide is expelled from an adequately elastic matrix to provide protection at the site of damage. We demonstrate the utility of this approach for the fabrication of surgical gloves.