Detachment of Rough Colloids from Liquid-Liquid Interfaces.

Particle surface roughness and chemistry play a pivotal role in the design of new particle-based materials. Although the adsorption of rough particles has been studied in the literature, desorption of such particles remains poorly understood. In this work, we specifically focus on the detachment of rough and chemically modified raspberry-like microparticles from water/oil interfaces using colloidal-probe atomic force microscopy.

Role of Pickering stabilization and bulk gelation for the preparation and properties of solid silica foams.

Foaming of particulate suspensions, followed by foam drying, is developed as an efficient method for production of highly porous materials with various applications. A key factor for success is the appropriate choice of surfactants which both modify the particle surface and stabilize the foam. Here we compare the efficiency of this method for silica suspensions containing two surfactants which lead to very different types of foam stabilization.

Efficient self-emulsification via cooling-heating cycles.

In self-emulsification higher-energy micrometre and sub-micrometre oil droplets are spontaneously produced from larger ones and only a few such methods are known. They usually involve a one-time reduction in oil solubility in the continuous medium via changing temperature or solvents or a phase inversion in which the preferred curvature of the interfacial surfactant layer changes its sign. Here we harness narrow-range temperature cycling to cause repeated breakup of droplets to higher-energy states.

Particle detachment from fluid interfaces: theory vs. experiments.

Microparticle adsorption and self-assembly at fluid interfaces are strongly affected by the particle three-phase contact angle θ. On the single-particle level, θ can be determined by several techniques, including colloidal-probe AFM, the gel-trapping technique (GTT) and the freeze-fracture shadow-casting (FreSCa) method. While GTT and FreSCa provide contact angle distributions measured over many particles, colloidal-probe AFM measures the wettability of an individual (specified) particle attached onto an AFM cantilever.

Control of drop shape transformations in cooled emulsions.

The general mechanisms of structure and form generation are the keys to understanding the fundamental processes of morphogenesis in living and non-living systems. In our recent study (Denkov et al., Nature 528 (2015) 392) we showed that micrometer sized n-alkane drops, dispersed in aqueous surfactant solutions, can break symmetry upon cooling and "self-shape" into a series of geometric shapes with complex internal structure.

Self-shaping of oil droplets via the formation of intermediate rotator phases upon cooling.

Revealing the chemical and physical mechanisms underlying symmetry breaking and shape transformations is key to understanding morphogenesis. If we are to synthesize artificial structures with similar control and complexity to biological systems, we need energy- and material-efficient bottom-up processes to create building blocks of various shapes that can further assemble into hierarchical structures. Lithographic top-down processing allows a high level of structural control in microparticle production but at the expense of limited productivity.

Factors controlling the formation and stability of foams used as precursors of porous materials.

The remarkable stability of particle-stabilized foams and the opportunity to use them for production of novel porous materials have been attracting the researchers' attention in the recent years. The major aim of the current study is to clarify the factors, controlling the foamability and stability of foams, formed from concentrated silica suspensions in the presence of the amphoteric surfactant CAPB. The experiments showed that: (1) two regions can be defined with respect to suspension foaminess: Region 1 - good foaming and Region 2 - strongly suppressed foaming.

Efficient emulsification of viscous oils at high drop volume fraction.

It is shown experimentally in this study that the increase of drop volume fraction can be used as an efficient tool for emulsification of viscous oils in turbulent flow. In a systematic series of experiments, the effects of drop volume fraction and viscosity of the dispersed phase on the mean, d(32), and maximum, d(V95), diameters of the drops, formed during emulsification, are quantified. The volume fraction, Φ, of the dispersed oily phase is varied between 1% and 90%, and oils with viscosity varying between 3 and 10,000 mPa.