Hydrophilic Silica Particles Research Articles

Influence of particle parameters on deposition onto healthy and damaged human hair.

This research investigates how particle parameters, such as zeta potential, size, functional group, material composition, and hydrophobicity affect their affinity and deposition of particles onto hair. Streaming potential was used as the technique for analysis. The streaming potential data obtained was then converted to surface coverage data. Scanning electron microscopy (SEM) was also done to visualize particle localization on the hair surface. This study found stronger particle affinity on healthy than on damaged (oxidatively bleached) hair, due to diminished interaction sites from the removal of the hair shaft's external lipid layer. SEM imaging supported these findings and offered insights into particle localization. Hydrophilic silica particles accumulated along the exposed hydrophilic cuticle edges of healthy hair, due to hydrogen bonding with the exposed endocuticle. This localization is hypothesized to be due to the limited hydrophilic binding sites on the hydrophobic healthy hair cuticle surface. In damaged hair, an abundance of hydrophilic sites across the cuticle surface results in more dispersed binding. Hydrogen bonding and electrostatic attraction were shown to be the predominant forces influencing deposition, with hydrophobic interactions playing a less influential role. The affinity studies also proved that electrostatic attractions work over a longer range and are more effective at lower particle conditions compared with hydrogen bonding which only start to play a bigger role at higher particle concentrations. Steric hindrance of bulky side groups acted as a significant repulsive force. Results also revealed that larger particles deposit poorly on both healthy and damaged hair compared with smaller ones. Compared with neutrally charged silica nanoparticles (SN-2), positively charged PMMA particles (PN+16) have a stronger affinity to healthy hair, with highly charged particles (PN+49) depositing most rapidly. This study provides a fundamental understanding of how particle-surface parameters influence their affinity to hair and how damaging hair affects deposition.

Study on the hydrate growth characteristics and rheology of silica-containing sand water-in-oil emulsion system

Understanding the transportability of silica-sand-containing hydrate slurries is crucial for production safety of non-consolidated natural gas hydrate reservoirs, especially when solid-state fluidization technology is utilized. Despite some research on silica sand and marine sediments’ influence on hydrate formation kinetics, rheological studies are scarce for systems with silica sands. The formation process of cyclopentane hydrates under the coexistence of hydrophilic silica particles and surfactants were observed. The effects of the concentration and particle size of silica sands as well as the water cut and surfactant concentration of emulsion on the rheological properties of hydrate slurries were investigated using a rheometer. The results indicated: (1) Hydrophilic sand aggregates were entrapped in water droplets, indirectly affecting the oil–water contact area due to the increase in water droplet volume, which was conducive to the combination of alkanes and water molecules to form a hydrate shell; silica particles provided nucleation sites at the oil–water interface to promote the adsorption and aggregation of cyclopentane molecules. (2) The synergistic effect of silica sand and surfactants significantly shortened the induction time of hydrates and increased the viscosity of the slurry. As the concentration of silica sand (1 wt%, 5 wt%, 10 wt%) increased, the induction time of hydrate formation decreased by 44.8 min. Within the concentration range below 5 wt%, the viscosity of the slurry increased as the concentration increased, with an amplitude of 13830.7 mPa·s. The induction time of hydrate formation decreased with increasing silica sand particle size (2 μm, 6.5 μm, 12 μm), but the size of silica sand particles had no significant effect on the viscosity of the slurry. (3) Hydrate slurries in all systems exhibited shear-thinning behavior. There was no obvious relationship between the yield stress of slurry under different silica sand concentrations. However, the yield stress of the slurry was inversely proportional to the size of silica sand particles. The yield stress decreased by 141.13 Pa when the size of silica sand particles increased from 2 μm to 12 μm. Overall, this study highlighted the influence of silica sand presence on flow safety assurance in solid-state fluidization technology.

Synergy between hydrophilic silica nanoparticles and poly(vinylpyrrolidone) for long-term foam stabilization with little energy input

The role of solid particles to act as foam and emulsion stabilizers is well known, providing long-term stability to the two-phase system. However, the ability for particles to generate large volumes of foam with little energy input (low agitation speeds and short agitation times) is difficult to achieve. Poor foamability is due to the slow particle adsorption dynamics and the high adsorption barrier at the air–water interface. In contrast, common surfactants and some surface active polymers which adsorb more readily at the air–water interface exhibit good foamability but often poor foam stability due to the mutual action of multiple destabilization mechanisms. In the current study, we reported a simple bi-component system of hydrophilic silica nanoparticles and poly(vinylpyrrolidone) (PVP) polymer to produce foams with both high foamability and foam stability via simply hand shaking for 1 min. Foams are stabilized by PVP coated silica composite nanoparticles (CPs) with a well-defined core–shell structure. The strong adsorption of PVP onto silica was demonstrated using Quartz Crystal Microbalance with Dissipation monitoring (QCM-D), confirming the formation of an irreversibly and robust adsorbed polymer layer. To better understand the mechanisms for enhanced foamability and foam stability, the interfacial dynamics and the 2-dimensional mechanical properties of the particle-polymer network partitioned at the air–water interface were assessed. The presence of the PVP polymer corona substantially enhanced the adsorption and retention of hydrophilic silica particles at the air/water interface, while the rigid interfacial network formed by the silica nanoparticles guaranteed long-term foam stability (excess of one week), with coarsening fund to be the dominating destabilization mechanism for foam. The enhanced performance is in stark contrast to the individual components, which could only provide good foamability other than foam stability.

Effects of particle concentration and dispersion rheology on the breakup of nanoparticle clusters through ultrasonication

A key step in the manufacture of numerous high-performance products with nanoparticles in their formulation requires process intensification to achieve the deagglomeration of particle clusters and generate a fine dispersion. Concentrated dispersions as master batches offer several advantages and at the same time challenges due to the resulting complex rheology. This study, performed using an ultrasonicator as the energy intensive device, aimed at addressing the challenges relating to dispersion rheology resulting from increased powder concentration and continuous phase viscosity with the objective of obtaining process relevant recommendations based on the kinetics and mechanisms of deagglomeration. Findings obtained with representative test systems, dispersions of hydrophilic silica particles in water and aqueous solutions, allowed recommendations to be obtained beyond the specifics of the study. Mechanism of break up was consistent with that observed using other process devices and hence can be used as guidance for equipment selection at large scale. The complex, non-Newtonian rheology of the pre-dispersions with increases in concentration and continuous phase viscosity slowed down deagglomeration kinetics, evolved during the course of deagglomeration and pointed out the need for careful design to achieve homogeneity within the dispersion in order to achieve the desired outcome from an energy intensive process.

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.

Comparative Studies of the Dielectric Properties of Polyester Imide Composite Membranes Containing Hydrophilic and Hydrophobic Mesoporous Silica Particles.

In this paper, comparative studies of hydrophilic and hydrophobic mesoporous silica particles (MSPs) on the dielectric properties of their derivative polyester imide (PEI) composite membranes were investigated. A series of hydrophilic and hydrophobic MSPs were synthesized with the base-catalyzed sol-gel process of TEOS, MTMS, and APTES at a distinctive feeding ratio with a non-surfactant template of D-(-)-Fructose as the pore-forming agent. Subsequently, the MSPs were blended with the diamine of APAB, followed by introducing the dianhydride of TAHQ with mechanical stirring for 24 h. The obtained viscous solution was subsequently coated onto a copper foil, 36 μm in thickness, followed by performing thermal imidization at specifically programmed heating. The dielectric constant of the prepared membranes was found to show an obvious trend: PEI containing hydrophilic MSPs > PEI > PEI containing hydrophobic MSPs. Moreover, the higher the loading of hydrophilic MSPs, the higher the value of the dielectric constant and loss tangent. On the contrary, the higher the loading of hydrophobic MSPs, the lower the value of the dielectric constant with an almost unchanged loss tangent.

Foam stability of temperature-resistant hydrophobic silica particles in porous media.

The world is rich in heavy oil resources, however, the recovery difficulty and cost are both higher than that of conventional crude oil. To date, the most common method of recovering heavy oil is steam flooding. However, once the steam breaks through the geological formation, gas channeling readily occurs, which leads to a rapid decrease of the steam drive efficiency. To improve the swept volume of steam in the geological formation, a series of hydrophobic silica particles for stabilizing foam was synthesized. This kind of particles used hydrophilic nano silica particles as reactant. Hydrophobic groups with cationic long carbon chains were grafted onto the surface of hydrophilic silica particles by synthetic silane quaternary ammonium salt. When the quantity of silane quaternary ammonium salt used in the modification reaction is different, the product had various degrees of wettability. The hydrophobic particles with the contact angle closest to 90° had the best foam stabilization effect on the betaine zwitterionic surfactant LAB. For LAB solution with mass fraction of 0.3%, the half-life of foam was extended into 160% when the mass fraction of particles was 0.5%. The higher the gas-liquid ratio, the better the plugging effect of foam agent with hydrophobic particles presented in porous media. The adsorption test of hydrophobic particles indicated that hydrophobic particles improved the stability of foam liquid membrane by improving the adsorption capacity of surfactant molecules. The thermal stability of hydrophobic silica particles exceeded 200°C, and the good foam stability made it a potential additive for foam oil displacement in high-temperature geological formation.

Linking intermolecular interactions and rheological behaviour in capillary suspensions

HypothesisCapillary suspensions feature networks of particles connected by liquid bridges, which are obtained by adding a small amount of a second immiscible liquid to a suspension. It is possible to link the network formation as well as the rheological behaviour of capillary suspensions to the intermolecular interactions of their constituents. Experiments and simulationsThrough a combination of experimental and numerical methods, we present a novel approach, based on Hansen solubility parameters computed from Molecular Dynamics (MD) simulations, to rationalize and predict the rheological behaviour of capillary suspensions. We investigated the formation of capillary suspensions for various combinations of bulk and secondary liquids mixed with hydrophilic silica particles. The predictions were confirmed experimentally by rheological analysis, interfacial tension measurements and microscopy (CLSM) imaging. FindingsNumerical and experimental results show that the Hansen solubility parameters theory allows to predict the formation of capillary suspensions, whose strength exponentially decays with decreasing intermolecular interactions between the secondary liquids and the dispersed particles. High immiscibility between the bulk and secondary liquid strengthens the gel up to a critical immiscibility point, above which the strength of the gel remains mostly affected by the affinity between the secondary liquids and the dispersed particles. Furthermore, we find that hydrogen-bonding and polar interactions control the formation of capillary suspensions. This simple approach can guide the selection of adequate solvents and immiscible secondary liquids, allowing an easy formulation of new particulate-based gels.

Rheology and structure of Pickering emulsions undergoing transitional phase inversion using a mixture of hydrophilic and hydrophobic silica particles

We investigate the stability and the structure of Polydimethylsiloxane (PDMS)/water emulsions stabilized by a mixture of partially hydrophobic (Aerosil® R816) and hydrophilic silica particles (LUDOX TM 50). Transitional phase inversion from oil-in-water (O/W) to water-in-oil (W/O) is observed by changing the hydrophobic/hydrophilic particles ratio as well as the viscosity of the oil phase. A higher concentration of hydrophilic particles is needed to promote phase inversion for the less viscous oil. Adding gradually hydrophilic silica particles in the water phase leads to the decrease of the fraction of effective emulsified phase i.e. the dispersed phase and the increase of the droplet size which promotes the phase inversion. In addition, all these changes are accompanied by the decrease of the elastic moduli of the emulsions which may be correlated to their complex structure and the interactions of the two types of particles at the interface of the droplets.

Evaluation of Hydrophilic and Hydrophobic Silica Particles on the Release Kinetics of Essential Oil Pickering Emulsions.

Colloidal particle-stabilized emulsions have recently gained increasing interest as delivery systems for essential oils. Despite the use of silica particles in food and pharmaceutical applications, the formation and release of hydrophilic and hydrophobic silica particle-stabilized emulsions are still not well studied. Thus, in this study, the structures of hydrophilic (A200, A380, 244FP, and 3150) and hydrophobic (R202 and R106) silica were deeply characterized using the solid state, contact angle, and other properties that could affect the formation of emulsions. Following that, Mosla chinensis essential oil emulsions were stabilized with different types of silica, and their characteristics, particularly their release behavior, were studied. Fick’s second law was used to investigate the mechanism of release. Additionally, six mathematical models were employed to assess the experimental data of release: zero-order, first-order, Higuchi, Hixson–Crowell, Peppas, and Page models. The release mechanism of essential oils demonstrated that diffusion was the dominant mechanism, and the fitting results for the release kinetics confirmed that the release profiles were governed by the Higuchi model. The contact angle and specific surface area were the key properties that affect the release of essential oils from emulsions. Hydrophilic A200 was found to be capable of delivering essential oils more efficiently, and silica particles could be extended to achieve the controlled release of bioactives. This study showed that understanding the impact of silica particles on the release behavior provided the basis for modulating and mapping material properties to optimize the performance of emulsion products.

Self-organization of agitated microspheres on various substrates.

The vibration dynamics of relatively large granular grains is extensively treated in the literature, but comparable studies on the self-assembly of smaller agitated beads are lacking. In this work, we investigate how the particle properties and the properties of the underlying substrate surface affect the dynamics and self-organization of horizontally agitated monodisperse microspheres with diameters between 3 and 10 μm. Upon agitation, the agglomerated hydrophilic silica particles locally leave traces of particle monolayers as they move across the flat uncoated and fluorocarbon-coated silicon substrates. However, on the micromachined silicon tray with relatively large surface roughness, the agitated silica agglomerates form segregated bands reminiscent of earlier studies on granular suspensions or Faraday heaps. On the other hand, the less agglomerated hydrophobic polystyrene particles form densely occupied monolayer arrangements regardless of the underlying substrate. We explain the observations by considering the relevant adhesion and friction forces between particles and underlying substrates as well as those among the particles themselves. Interestingly, for both types of microspheres, large areas of the fluorocarbon-coated substrates are covered with densely occupied particle monolayers. By qualitatively examining the morphology of the self-organized particle monolayers using the Voronoi approach, it is understood that these monolayers are highly disordered, i.e., multiple symmetries coexist in the self-organized monolayers. However, more structured symmetries are identified in the monolayers of the agitated polystyrene microspheres on all the substrates, albeit not all precisely positioned on a hexagonal lattice. On the other hand, both the silica and polystyrene monolayers on the bare silicon substrates transition into less disordered structures as time progresses. Using Kelvin probe force microscopy measurements, we show that due to the tribocharging phenomenon, the formation of particle monolayers is promoted on the fluorocarbon surface, i.e., a local electrostatic attraction exists between the particle and the substrate.

Durable Underwater Superoleophobic Coatings via Dispersed Micro Particle-Induced Hierarchical Structures Inspired by Pomfret Skin.

Underwater superoleophobic materials due to its excellent antioil and self-cleaning performance have attracted tremendous attention. Current underwater superoleophobic surfaces usually use complex methods to construct the surface structure limiting the yield and not suitable for large-scale production. Here, inspired by the superoleophobicity of pomfret skin, we developed a strategy to fabricate superoleophobic coatings with hierarchical micro/nano structures by doping hydrophilic micro silica particle in calcium alginate hydrogel. The introduction of micro particles significantly reduces the adhesion of oil and improves the mechanical properties of the coatings. The prepared coatings also survived in high temperature and high salinity environment and the dried for free-standing films. The free-standing dry coating films can be used like wallpaper to decorate the targeted surface and endow them with underwater superoleophobicity. We expect that this work will provide a new method for designing underwater superoleophobic coatings and the wallpaper-like coating films allow large-scale production and will also promote the commercialization of oil-repellent materials.

Pickering high internal phase emulsion costabilized by a low amount of bio-based rigid surfactant with microsilica via depletion interaction and synergistic effect

A series of green bio-based polyether surfactant were synthesized based on dehydroabietic acid and used to construct Pickering high internal phase emulsions (HIPEs) with microsilica particles which the dispersed phase fraction could up to 90%. Such surfactants have a high surface activity so that the Pickering HIPEs could be stabilized stably at low concentrations with micron-size silica. The microstructure, droplet size and rheology property of Pickering HIPEs could be regulated by varying the microsilica content or dispersed phase fraction. The QCM-D measurements revealed that the nonionic surfactant could adsorb on surface of silica particles, giving rise to the change of wettability of the hydrophilic particles and rendering the particles surface-active. The coated particles were more likely to adsorb at the oil-water interface of droplets. The synergistic effects of hydrophilic silica particles and this nonionic surfactant promoted the formation of stable Pickering HIPEs. Moreover, the depletion interaction between droplets and hydrophilic particles was also the vital factor in the stability of the Pickering HIPEs. Once particles were adsorbed, particles at the interface were inhibited desorption by depletion attraction. This work suggests another possible mechanism for better stability of Pickering HIPEs in nonionic surfactant/particles system, and our strategy to preparing Pickering HIPEs is environmentally friendly by using a bio-based surfactant, which has wide potential application in cosmetics, pharmaceuticals, food, environmental protection, materials, and so on.

Pickering Emulsions of Hydrophilic Silica Particles and Symmetrical Organic Electrolytes.

At high pH, bare silica particles are not an effective Pickering emulsion stabilizer of nonpolar oils with water due to their high surface charge. One way to promote particle adsorption to the oil-water interface is to add salt to the aqueous phase, although particle flocculation normally ensues. In most cases, inorganic salts are added, while little attention has been paid to the use of organic salts. Here, we describe the effects of adding tetraalkylammonium salts (R4NX, X is an anion) to aqueous dispersions of silica nanoparticles at high pH and investigating the possibility of subsequently stabilizing octane-in-water (o/w) emulsions. The chain length of the R group is systematically increased from 1 (methyl) to 4 (butyl). Unlike inorganic electrolytes, the addition of these salts does not lead to particle flocculation in water, although the particle charge is reduced. No stable emulsion forms for the methyl analogue, but very stable o/w emulsions can be prepared with the other three members, with the minimum concentration of salt being required decreasing with R chain length to as low as 5 × 10-5 M. The three-phase oil-water-solid contact angle increases with salt concentration and R chain length, confirming the increase in particle hydrophobicity on addition of salt. We show that the butyl analogue behaves similarly to that of cetyltrimethylammonium bromide surfactant with respect to promoting silica particles to emulsion drop interfaces. Finally, we compare the arrangement of micrometer-sized silica particles at both curved droplet interfaces and at a planar oil-water interface at different concentrations of the most hydrophobic salt.

Study of submicrocapsules structure stabilized by modified silica dioxide nanoparticles

In this research the structures of Miglyol 812 submicrocapsules, stabilized by silica dioxide nanoparticles, modified by oleic acid, were studied. It was found that the size distribution of silica particles modified with oleic acid depends on the amount of oleic acid. There is a limit to the ratio of oleic acid to silica at modification of silica particles with oleic acid. Experimental results have shown that the optimal ratio of oleic acid to silica is in the range from 110−2 to 5 10−1. The use of silica particles modified with oleic acid allows to obtain an emulsion with a 30 % of oil phase, with an average size from 80-300 nm. Thus, modification of hydrophilic silica particles with surfactants such as oleic acid in order to make them more hydrophilic and able to be adsorbed at the oil / water interface can be used to prepare a stable Pickering emulsion. As a result the stable Pickering emulsions which can be used for encapsulation of various substances were obtained, and the use of microcapsules allows one to decrease their impact on environment and increase efficiency of usage.

Selective aggregation by ultrasonic standing waves through gas nuclei on the particle surface.

Gas nuclei in water are usually too small to be directly observed. They will grow into bubbles under the negative pressure, which is called cavitation (heterogeneous cavitation). In this study, the gas nuclei in the hydrophilic and hydrophobic silica particle suspension were investigated using the transient cavitation threshold measured by a high-intensity focused ultrasound (HIFU). The transient cavitation bubbles were also observed by a high-speed camera. The results showed that the nuclei only exist on the surface of hydrophobic particles. Furthermore, the aggregation experiments revealed that the aggregates were only formed in the hydrophobic silica suspension by ultrasonic standing waves (USW) at 200kHz. This distinct difference was mainly due to the formation of gas nuclei on hydrophobic silica particles, which grew and coalesced into stable bubbles under the 200kHz USW. The aggregation process in suspension was observed by a CCD camera. Moreover, the cavitation thresholds and acoustic radiation forces were analyzed to explain the mechanism of the acoustic aggregation. This study showed a very promising acoustic method for the selective aggregation of hydrophobic particles, which might be efficiently used in the mineral separation industry.

Colloidal stability of silica and graphite in aqueous suspensions

In order to investigate the effect of surface wettability on colloidal stability, aggregation/dispersion behaviors of fine silica and graphite in aqueous suspensions have been investigated. It was found that hydrophobic graphite particles showed a high aggregation degree in low pH suspensions, while it showed very low aggregation degree in high pH suspensions due to the strong electrostatic repulsions between graphite particles. On the other hand, silica particles showed stable dispersion behaviors even under strong Van der Waals attraction in low pH suspensions, which could not be explained by DLVO theory. Solvation factor on hydrophilic silica particles was applied to prove the strong hydration of silica, and it is the hydration repulsion forces among silica particles that determined the stable dispersion of silica particles in a wide pH range. Therefore, it was concluded that hydration layers formed on hydrophilic mineral surfaces played an important role in colloidal stability.

Influence of alternating current (AC) corona discharge on the superhydrophobicity of SiO2/fluorosilicon resin nano-composite coating

Superhydrophobic surface is ideal for outdoor insulation due to its low surface energy and excellent self-cleaning ability. However, superhydrophobicity would become weak or lost under corona discharge, which is inevitable in high voltage transmission lines. Composite superhydrophobic surface was fabricated with fluorosilicone resin and silica nanoparticles. It was transformed to superhydrophilicity under corona discharge, but it could recover superhydrophobicity under low intensity corona discharge. Electrostatic charges were proposed to result in temporary superhydrophilicity. When corona discharge intensity was high, hydrophilic silica particles covered with fluorosilicone resin were exposed to air. Adsorbed water film was formed on the surface and prevented the recovery of superhydrophobicity.

Encapsulation of oils and fragrances by core-in-shell structures from silica particles, polymers and surfactants: The brick-and-mortar concept

Colloidosomes provide a possibility to encapsulate oily substances in water in the form of core-in-shell structures. In this study, we produced microcapsules with shell from colloidal particles, where the interparticle openings are blocked by mixed layers from polymer and surfactant that prevent the leakage of cargo molecules. In other words, the particles and polymer play the role of bricks and mortar. For this goal, we used hydrophilic silica particles, which were partially hydrophobized by the adsorption of potassium oleate to enable them to stabilize Pickering emulsions. Various polymers were tested to select the most appropriate one. The procedure of encapsulation is simple and includes single homogenization by ultrasound. The produced capsules are pH responsive. They are stable in aqueous phase of pH in the range 3–6, but at pH > 6 they are destabilized and their cargo is released. With the optimized formulation of silica particles, polymer, oleate and NaCl, we were able to encapsulate various oils and fragrances, such as tetradecane, limonene, benzyl salicylate and citronellol. All of them have a limited and not too high solubility in water. In contrast, no stable microcapsules were obtained with oils that either have zero water solubility (mineral and silicone oil) or higher water solubility (phenoxyethanol and benzyl alcohol). By analysis of results from additional interfacial-tension and thin-film experiments, we concluded that a key factor for obtaining stable capsules is the irreversible adsorption of the polymer at the oil/water interface. The hydrophobization of the particles by surfactant adsorption (instead of silanization) plays an important role for the pH responsiveness of the produced capsules. The obtained information about the role of various factors for the stabilization of microcapsules, which are based on the brick-and-mortar concept, can be further used to achieve better stability; selection of polymers that are appropriate for different classes of oils, as well as for the production of smaller capsules stabilized by nanoparticles.

CH4 Nanobubbles on the Hydrophobic Solid-Water Interface Serving as the Nucleation Sites of Methane Hydrate.

The surface hydrophobicity of solid particles plays a critical role in the nucleation of gas hydrate formation, and it was found that the hydrophobic surface will promote this nucleation process, but the underlying mechanism is still unveiled. Herein, we proposed for the first time our new theory that the formation of methane nanoscale gas bubbles on the hydrophobic surface provides the nuclei sites for further formation of methane hydrate. First, we studied the effect of hydrophobicity of particles on the nucleation of hydrate. It was found that the hydrophobic graphite and silica particles would promote the nucleation of hydrate, but the hydrophilic silica particles did not promote the methane hydrate nucleation. Then, we designed the atomic force microscopy experiment to explain this mechanism from a nanometer scale. The results showed that the methane nanobubbles were formed on the hydrophobic highly ordered pyrolytic graphite surface, but they were hard to form on the hydrophilic mica surface. These results indicated that the methane nanobubbles on the hydrophobic surface could provide the gas hydrate nucleation sites and may induce a rapid nucleation of methane hydrate.