Diana Cholakova

Sofia University "St. Kliment Ohridski" · Department of Chemical and Pharmaceutical Engineering

Rotator phases are rotationally disordered plastic crystals, some of which can form upon freezing of alkane at alkane-water interfaces. Existing X-ray diffraction studies show only partial unit cell information for rotator phases of some alkanes. This includes the rotator phase of n-hexadecane, which is a transient metastable phase in pure alkane s...

Triacylglycerols (TAGs) are among the most important ingredients in food, cosmetic and pharmaceutical products. Many physical properties of such products, incl. morphology, texture and rheology, are determined by the phase behaviour of the included TAGs. Triglycerides are also of special interest for the production of solid lipid nanoparticles, app...

Emulsion droplets, composed of long linear molecules (e.g. n-alkanes) and stabilized by long chain surfactants, can spontaneously change their shape upon cooling and morph from spheres into regular polyhedra, polygonal platelets, rods and thin fibers. Until now, these dynamic shape changes have been studied upon continuous temperature decrease. The...

Lipid nanoemulsions and nanosuspensions are used as flavor carriers and bubble stabilizers in soft drinks and foods, as well as delivery vehicles for lipophilic drugs in pharmaceutics. Common techniques for their formation are the high-pressure and ultrasonic homogenizers. These techniques dissipate most of the input energy, which results in excess...

Lipid nanoemulsions and nanosuspensions are used as flavor carriers and bubble stabilizers in soft drinks and foods, as well as delivery vehicles for lipophilic drugs in pharmaceutics. Common techniques for their formation are the high-pressure and ultrasonic homogenizers. These techniques dissipate most of the input energy, which results in excess...

The interest in the low energy self-emulsification techniques has exploded in the recent years, driven by three main trends: by the transition to "greener" technologies in both its aspects - less energy consumption and replacement of the petrochemicals by natural ingredients; by the costly and maintenance demanding equipment for nanoemulsification;...

The interest in the low energy self-emulsification techniques has exploded in the recent years, driven by three main trends: by the transition to “greener” technologies in both its aspects – less energy consumption and replacement of the petrochemicals by natural ingredients; by the costly and maintenance demanding equipment for nanoemulsification;...

Linear long-chain organic molecules are known to form lamellar intermediate phases (called also rotator phases) between their fully ordered crystalline phases and their isotropic liquid phases. The properties of intermediate rotator phases are crucially important for various industrial and living nature processes, but the data for their rheological...

Linear long-chain organic molecules are known to form lamellar intermediate phases (called also rotator phases) between their fully ordered crystalline phases and their isotropic liquid phases. The temperature range of occurrence and the properties of these intermediate rotator phases are crucially important for the texture of many food and cosmeti...

The design of artificial microswimmers is often inspired by the strategies of natural microorganisms. Many of these creatures exploit the fact that elasticity breaks the time-reversal symmetry of motion at low Reynolds numbers, but this principle has been notably absent from model systems of active, self-propelled microswimmers. Here we introduce a...

Correction for ‘Spontaneous particle desorption and “Gorgon” drop formation from particle-armored oil drops upon cooling’ by Diana Cholakova et al. , Soft Matter , 2020, 16 , 2480–2496, DOI: 10.1039/C9SM02354B.

The design of artificial microswimmers is often inspired by the strategies of natural microorganisms. Many of these creatures exploit the fact that elasticity breaks the time-reversal symmetry of motion at low Reynolds numbers, but this principle has been notably absent from model systems of active, self-propelled microswimmers. Here we introduce a...

Micrometer sized alkane-in-water emulsion drops, stabilized by appropriate long-chain surfactants, spontaneously break symmetry upon cooling and transform consecutively into series of regular shapes (Denkov et al., Nature 2015, 528, 392). Two mechanisms were proposed to explain this phenomenon of drop "self-shaping". One of these mechanisms assumes...

Hypothesis Micrometer sized alkane-in-water emulsion drops, stabilized by appropriate long-chain surfactants, spontaneously break symmetry upon cooling and transform consecutively into series of regular shapes (Denkov et al., Nature 2015, 528, 392). Two mechanisms were proposed to explain this phenomenon of drop “self-shaping”. One of these mechani...

DOI:https://doi.org/10.1103/PhysRevLett.126.259801

The preparation of nanoemulsions of triglyceride oils in water usually requires high mechanical energy and sophisticated equipment. Recently, we showed that α-to-β (viz., gel-to-crystal) phase transition, observed with most lipid substances (triglycerides, diglycerides, phospholipids, alkanes, etc.), may cause spontaneous disintegration of micropar...

Garc\'ia-Aguilar et al. [Phys. Rev. Lett 126, 038001 (2021)] have shown that the deformations of "shape-shifting droplets" are consistent with an elastic model, that, unlike previous models, includes the intrinsic curvature of the frozen surfactant layer. In this Comment, we show that the interplay between surface tension and intrinsic curvature in...

Preparation of nanoemulsions of triglyceride oils in water usually requires high mechanical energy and sophisticated equipment. Recently, we showed that alpha-to-beta (viz. gel-to-crystal) phase transition, observed with most lipid substances (triglycerides, diglycerides, phospholipids, alkanes, etc.), may cause spontaneous disintegration of micro-...

We describe several unexpected phenomena, caused by a solid-solid phase transition (gel-to-crystal) typical for all main classes of lipid substances: phospholipids, triglycerides, diglycerides, alkanes, etc. We discovered that this transition leads to spontaneous formation of a network of nanopores, spreading across the entire lipid structure. Thes...

We describe several unexpected phenomena, caused by a solid-solid phase transition (gel-to-crystal) typical for all main classes of lipid substances - phospholipids, triglycerides, diglycerides, alkanes, etc. We discovered that this transition leads to spontaneous formation of a network of nanopores, spreading across the entire lipid structure. The...

We study how the phenomenon of drop “self-shaping” (Denkov et al., Nature, 528, 2015, 392), in which oily emulsion drops undergo a spontaneous series of shape transformations upon emulsion cooling, is affected by the presence of adsorbed solid particles, like those used in Pickering emulsion stabilization. Experiments with several types of latex pa...

Surface phase transitions in surfactant adsorption layers are known to affect the dynamic properties of foams and to induce surface nucleation in freezing emulsion drops. Recently, these transitions were found to play a role in several other phenomena, opening new opportunities for controlling foam and emulsion properties. This review presents a br...

Surface phase transitions in surfactant adsorption layers are known to affect the dynamic properties of foams and to induce surface nucleation in freezing emulsion drops. Recently, these transitions were found to play a role in several other phenomena, opening new opportunities for controlling foam and emulsion properties. This review presents a br...

Cooled oil emulsion droplets in aqueous surfactant solution have been observed to flatten into a remarkable host of polygonal shapes with straight edges and sharp corners, but different driving mechanisms—(i) a partial phase transition of the liquid bulk oil into a plastic rotator phase near the droplet interface and (ii) buckling of the interfacia...

Medium- and long-chain alkanes and their mixtures possess a remarkable physical property – they form intermediate structured phases between their isotropic liquid phase and their fully ordered crystal phase. These intermediate phases are called “rotator phases” or “plastic phases” (soft solids) because the incorporated alkane molecules possess a lo...

In several recent studies we showed that micrometer sized oil-in-water emulsion droplets from alkanes, alkenes, alcohols, triglycerides or mixtures of these components can spontaneously “self-shape” upon cooling into various regular shapes, such as regular polyhedrons, platelets, rods and fibers (Denkov et al., Nature 2015, 528, 392; Cholakova et a...

Cooled oil emulsion droplets in aqueous surfactant solution have been observed to flatten into a remarkable host of polygonal shapes with straight edges and sharp corners, but different driving mechanisms - (i) a partial phase transition of the liquid bulk oil into a plastic rotator phase near the droplet interface and (ii) buckling of the interfac...

Emulsification requires drop breakage and creation of large interfacial area between immiscible liquid phases. Usually, high shear or high pressure emulsification devices which generate heat and increase emulsion temperature are used to obtain emulsions with micrometer and sub-micrometer droplets. Recently we reported a new efficient procedure of s...

A method for preparation of liquid, semi-liquid or solid particles through formation of an initial emulsion and consecutive deformation and/or breakage of the particles by means of temperature change. The formed particles may further be polymerized, physically or chemically modified and/or functionalized. The shape and size of the particles depend...

In our recent study we showed that single-component emulsion drops, stabilized by proper surfactants, can spontaneously break symmetry and transform into various polygonal shapes during cooling (Denkov et al., Nature 2015, 528, 392-395). This process involves the formation of a plastic rotator phase of self-assembled oil molecules beneath the drop...

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 inte...

Supplementary Figures, Supplementary Methods and Supplementary Reference

Melting of a frozen hexagonal platelet. The system is a pentadecane drop (C15) in 1.5 wt. % of C16SorbEO20 surfactant solution. Upon melting, hundreds of droplets are spontaneously formed, due to the process of crystal-melt fragmentation. Scale bar, 20 μm.

Melting of frozen hexagonal platelets of hexadecane (C16) in 1.5 wt. % of C18SorbEO20 surfactant solution. Upon melting, each hexagonal platelet melts back into one to several liquid drops, viz. no intensive crystal-melt fragmentation is observed (compare with Supplementary Movie 3). Scale bar, 20 μm.

Separation of natural fats into unsaturated (liquid) and saturated (solid) components. The surfactant mixture contains 0.05 wt. % (in total) of 7:3 by weight LAS:EO7 surfactants. The fat globules are composed of a 7:3 soybean oil:tristearin mixture. Scale bar, 20 μm.

Drop shape evolution of hexadecane-in-water drops, stabilized by the nonionic surfactant C18EO20, at a cooling rate of 1.44 K min-1 and initial drop size dini ≈ 33 μm. One sees consecutive cycles of drop self-shaping and breakage events. The final observed shapes are platelets and ellipsoidal droplets, extruding thin fibers with diameter < 1 μm. Sc...

Melting of a frozen trigonal platelet with long coiled protrusions. The system is a hexadecane drop (C16) in 0.38 wt. % C18H37SO4Na surfactant solution. Upon fibre melting, thousands of small droplets with diameter ≈ 1 μm are formed, due to a Rayleigh-Plateau instability, whereas the central triangular region melts into several big droplets. Scale...

Recent studies of cooled oil emulsion droplets uncovered transformations into a host of flattened shapes with straight edges and sharp corners, driven by a partial phase transition of the bulk liquid phase. Here, we explore theoretically the simplest geometric competition between this phase transition and surface tension in planar polygons and reco...

Recent studies of cooled oil emulsion droplets uncovered transformations into a host of flattened shapes with straight edges and sharp corners, driven by a partial phase transition of the bulk liquid phase. Here, we explore theoretically the simplest geometric competition between this phase transition and surface tension in planar polygons, and rec...

Two recent studies (Denkov et al., Nature 528 (2015) 392 and Guttman et al. PNAS 113 (2016) 493) demonstrated that micrometer sized n-alkane drops, dispersed in aqueous surfactant solutions, can break their spherical symmetry upon cooling and "self-shape" into a variety of regular shapes, such as fluid polyhedra, platelet-shaped hexagons, triangles...

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 t...