K. Marinova, Slavka Tcholakova, Nikolai D. Denkov, Stoian Roussev, Martial Deruelle,
... Mixed Oil−Silica AntifoamsKrastanka G. Marinova, Slavka Tcholakova, Nikolai D. Denkov, Stoian Roussev, and Martial DeruelleView Author Information Laboratory ...
Tópico(s): Force Microscopy Techniques and Applications
2003 - American Chemical Society | Langmuir
Orlin D. Velev, Nikolai D. Denkov, Vesselin N. Paunov, Peter A. Kralchevsky, Kuniaki Nagayama,
... ISSUEPREVArticleNEXTDirect measurement of lateral capillary forcesOrlin D. Velev, Nikolai D. Denkov, Vesselin N. Paunov, Peter A. Kralchevsky, and Kuniaki ...
Tópico(s): Magnetic and Electromagnetic Effects
1993 - American Chemical Society | Langmuir
Diana Cholakova, Zahari Vinarov, Slavka Tcholakova, Nikolai D. Denkov,
Tópico(s): Microencapsulation and Drying Processes
2022 - Elsevier BV | Current Opinion in Colloid & Interface Science
Z. Mitrinova, Hristo Alexandrov, Nikolai D. Denkov, Slavka Tcholakova,
The effects of the charge, size and concentration of counter-ions (Na+, NH4+, K+, Mg2+, Ca2+ and Al3+) on the rheological properties of 300 mM SLES+CAPB surfactant solutions are studied and compared with results available in the literature for the effects of Na+ and K+ on SLES solution. The results show that all counter-ions studied are able to induce formation of wormlike micelles in a certain concentration range – as a consequence, the solution viscosity passes through a high maximum as a function ...
Tópico(s): Spectroscopy and Quantum Chemical Studies
2022 - Elsevier BV | Colloids and Surfaces A Physicochemical and Engineering Aspects
Shirin Alexander, Andrew R. Barron, Nikolai D. Denkov, Paul Grassia, Sajad Kiani, Masanobu Sagisaka, Mohammad Javad Shojaei, Nima Shokri,
Understanding how the surfactant molecular structure affects foam stability is important in various applications, such as soil remediation, the food industry, enhanced oil recovery, and hydraulic fracturing. In this study, we conduct a systematic series of experiments in a Hele–Shaw cell to assess and explain the effect of surfactants on foamability and foam stability in the absence and presence of oil and asphaltene aggregates. Four surfactants with different molecular weights were studied, including ...
Tópico(s): Surfactants and Colloidal Systems
2021 - American Chemical Society | Industrial & Engineering Chemistry Research
Diana Cholakova, Desislava Glushkova, Zhulieta Valkova, Sonya Tsibranska, Krastina Tsvetkova, Slavka Tcholakova, Nikolai D. Denkov,
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 that thin layers of plastic rotator phase form at the drop surface around the freezing temperature of the oil. This mechanism has been supported by several ...
Tópico(s): Surfactants and Colloidal Systems
2021 - Elsevier BV | Journal of Colloid and Interface Science
B. Petkova, Slavka Tcholakova, Nikolai D. Denkov,
The foamability of surfactant solutions depends strongly on the adsorption properties of the surfactants, their concentrations, and the foaming test used for foam generation. The aim of the current study is to analyse the subtle interplay between the hydrodynamic conditions and the surfactant adsorption layers formed during foaming. We compare the results from three foam tests, characterized with very different hydrodynamic conditions. The Bartsch test (fast-foaming method) is characterized by a ...
Tópico(s): Minerals Flotation and Separation Techniques
2021 - Elsevier BV | Colloids and Surfaces A Physicochemical and Engineering Aspects
Diana Cholakova, Krastina Tsvetkova, Slavka Tcholakova, Nikolai D. Denkov,
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 cosmetic products, for the flow of various phase-change materials used in energy storage and transport, and for several processes in living nature, such as the ...
Tópico(s): Polymer crystallization and properties
2021 - Elsevier BV | Colloids and Surfaces A Physicochemical and Engineering Aspects
Nikolai D. Denkov, Slavka Tcholakova, Nadya Politova-Brinkova,
This article summarizes our recent understanding on how various essential foam properties could be controlled (viz. modified in a desired way) using appropriate surfactants, polymers, particles and their mixtures as foaming agents. In particular, we consider the effects of these agents on the foaminess of solutions and suspensions (foam volume and bubble size after foaming); foam stability to liquid drainage, bubble coalescence and bubble Ostwald ripening; foam rheological properties and bubble size ...
Tópico(s): Surfactants and Colloidal Systems
2020 - Elsevier BV | Current Opinion in Colloid & Interface Science
Diana Cholakova, Desislava Glushkova, Slavka Tcholakova, Nikolai D. Denkov,
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. These nanopores are spontaneously impregnated (flooded) by water when appropriate surfactants are present, thus fracturing the lipid structure at a nanoscale. ...
Tópico(s): Phase Equilibria and Thermodynamics
2020 - American Chemical Society | ACS Nano
Pierre A. Haas, Diana Cholakova, Nikolai D. Denkov, Raymond E. Goldstein, Stoyan K. Smoukov,
Oil droplets in aqueous surfactant solutions flatten into a host of polyhedral and polygonal shapes on slow cooling. These intriguing transformations promise novel synthesis methods for small polymeric particles. This paper reveals an intermediate octahedral stage that explain how icosahedral droplets flatten into polygonal platelets.
Tópico(s): Micro and Nano Robotics
2019 - American Physical Society | Physical Review Research
Dilek Gazolu-Rusanova, Fatmegul Mustan, Zahari Vinarov, Slavka Tcholakova, Nikolai D. Denkov, Simeon D. Stoyanov, Julius W. J. de Folter,
This study aims to clarify and explain the similarities and differences in the behavior of adsorption layers of native egg yolk (EY) and enzymatically modified egg yolk (MEY) at a soybean oil-water interface. For this purpose, the interfacial tension and the surface dilatational modulus of EY and MEY solutions are measured and compared. The interactions between two adsorption layers, formed from these solutions on an oil-water or air-water interface, are also studied by optical observations of thin ...
Tópico(s): Surfactants and Colloidal Systems
2019 - Elsevier BV | Food Hydrocolloids
Diana Cholakova, Nikolai D. Denkov,
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 long-range positional order while preserving certain mobility to rotate, which results in complex visco-plastic rheological behaviour. The current article presents ...
Tópico(s): Material Dynamics and Properties
2019 - Elsevier BV | Advances in Colloid and Interface Science
Nikolai D. Denkov, Slavka Tcholakova, Diana Cholakova,
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 brief outlook of the emerging opportunities in this area. Three topics are emphasized: (1) the use of surfactant mixtures for inducing phase transitions ...
Tópico(s): Surfactants and Colloidal Systems
2019 - Elsevier BV | Current Opinion in Colloid & Interface Science
Dilek Gazolu-Rusanova, Ivan Lesov, Slavka Tcholakova, Nikolai D. Denkov, Badreddine Ahtchi,
High-pressure homogenizers, typically used for producing nanoemulsions at the industrial scale, are energy and maintenance intensive, and limited to produce only dilute, low viscosity nanoemulsions. We propose an alternative approach to produce dilute to concentrated food-grade nanoemulsions with droplet size ranging between 100 and 500 nm using rotor-stator homogenization. Gum Arabic (GA) or modified starch (MS) was used as both viscosity modifier and emulsion stabilizer. GA and MS have relatively ...
Tópico(s): Polysaccharides Composition and Applications
2019 - Elsevier BV | Food Hydrocolloids
B. Petkova, Slavka Tcholakova, M. Chenkova, Konstantin Golemanov, Nikolai D. Denkov, D. Thorley, Simeon D. Stoyanov,
In this paper we study the main surface characteristics which control the foamability of solutions of various surfactants. Systematic series of experiments with anionic, cationic and nonionic surfactants with different head groups and chain lengths are performed in a wide concentration range, from 0.001 mM to 100 mM. The electrolyte (NaCl) concentration is also varied from 0 up to 100 mM. For all surfactants studied, three regions in the dependence of the foamability, VA, on the logarithm of surfactant ...
Tópico(s): Enhanced Oil Recovery Techniques
2019 - Elsevier BV | Advances in Colloid and Interface Science
Sonya Tsibranska, Anela Ivanova, Slavka Tcholakova, Nikolai D. Denkov,
Saponins are natural surfactants with high surface activity and unique surface properties. Escin is a triterpenoid saponin which has unusually high surface viscoelasticity [Golemanov et al. Soft Matter 2013, 9, 5738] and low permittivity to molecular gas diffusion of its adsorption layers. In our previous study [Tsibranska et al. Langmuir 2017, 33, 8330], we investigated the molecular origin of this unconventional behavior and found that escin molecules rapidly assemble in a compact and stable surface ...
Tópico(s): Spectroscopy and Quantum Chemical Studies
2019 - American Chemical Society | Langmuir
Diana Cholakova, Nikolai D. Denkov, Slavka Tcholakova, Zhulieta Valkova, Stoyan K. Smoukov,
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, N., Nature 2015, 528, 392; Cholakova, D., Adv. Colloid Interface Sci. 2016, 235, 90). These drop-shape transformations were explained by assuming that intermediate plastic rotator phase, composed ...
Tópico(s): Proteins in Food Systems
2019 - American Chemical Society | Langmuir
Sonya Tsibranska, Slavka Tcholakova, Konstantin Golemanov, Nikolai D. Denkov, Eddie G. Pelan, Simeon D. Stoyanov,
Saponins are natural surfactants which can provide highly viscoelastic interfaces. This property can be used to quantify precisely the effect of interfacial dilatational elasticity on the various rheological properties of bulk emulsions. We measured the interfacial dilatational elasticity of adsorption layers from four saponins (Quillaja, Escin, Berry, Tea) adsorbed on hexadecane-water and sunflower oil-water interfaces. In parallel, the rheological properties under steady and oscillatory shear deformations ...
Tópico(s): Polysaccharides Composition and Applications
2019 - Elsevier BV | Journal of Colloid and Interface Science
Zahari Vinarov, Vladimir Katev, Nikola Burdzhiev, Slavka Tcholakova, Nikolai D. Denkov,
Biorelevant dissolution media (BDM) methods are commonly employed to investigate the oral absorption of poorly water-soluble drugs. Despite the significant progress in this area, the effect of commonly employed pharmaceutical excipients, such as surfactants, on the solubility of drugs in BDM has not been characterized in detail. The aim of this study is to clarify the impact of surfactant–bile interactions on drug solubility by using a set of 12 surfactants, 3 model hydrophobic drugs (fenofibrate, ...
Tópico(s): Analytical Chemistry and Chromatography
2018 - American Chemical Society | Molecular Pharmaceutics
Ivan Lesov, Zhulieta Valkova, Elena Vassileva, George Georgiev, Konstans Ruseva, Marin Simeonov, Slavka Tcholakova, Nikolai D. Denkov, Stoyan K. Smoukov,
Shape-anisotropic polymeric micro- and nanoparticles are of significant interest for the development of novel composite materials, lock-and-key assemblies, and drug carriers. Currently, syntheses require external confinement in microfluidic devices or lithographic techniques associated with significant infrastructure and low productivity, so new methods are necessary to scale-up such production efficiently. Here we report bottom-up polymerization of regular shape-anisotropic particles (polygonal ...
Tópico(s): Advanced Sensor and Energy Harvesting Materials
2018 - American Chemical Society | Macromolecules
Zahari Vinarov, Denitsa Radeva, Vladimir Katev, Slavka Tcholakova, Nikolai D. Denkov,
Poor aqueous solubility limits the bioavailability of hydrophobic drugs. Thus, there is an increasing interest in new micelle-forming, drug-solubilizing molecules that can offer improved effectiveness and safety. The effect of 13 saponin extracts on the solubility of fenofibrate and danazol was studied and the relationship between saponin molecular structure and drug solubilisation capacity was assessed. Drug solubility was measured by high-performance liquid chromatography and saponin solubilisation ...
Tópico(s): Natural product bioactivities and synthesis
2018 - Medknow | Indian Journal of Pharmaceutical Sciences
J. Penfold, Robert K. Thomas, I. Tucker, Jordan T. Petkov, Simeon D. Stoyanov, Nikolai D. Denkov, Konstantin Golemanov, Slavka Tcholakova, John R. P. Webster,
Saponins are a large group of glycosides present in many plant species. They exhibit high surface activity, which arises from a hydrophobic scaffold of triterpenoid or steroid groups and attached hydrophilic saccharide chains. The diversity of molecular structures, present in various plants, gives rise to a rich variety of physicochemical properties and biological activity and results in a wide range of applications in foods, cosmetics, medicine, and several other industrial sectors. Saponin surface ...
Tópico(s): Proteins in Food Systems
2018 - American Chemical Society | Langmuir
Zahari Vinarov, Vladimir Katev, Denitsa Radeva, Slavka Tcholakova, Nikolai D. Denkov,
This study aims to clarify the role of surfactant and drug molecular structures on drug solubility in micellar surfactant solutions.(1) Rationale for surfactant selection is provided; (2) the large data set can be used for validation of the drug solubility parameters used in oral absorption models.Equilibrium solubility of two hydrophobic drugs and one model hydrophobic steroid in micellar solutions of 19 surfactants was measured by HPLC. The drug solubilization locus in the micelles was assessed ...
Tópico(s): Drug Solubulity and Delivery Systems
2017 - Taylor & Francis | Drug Development and Industrial Pharmacy
Diana Cholakova, Zhulieta Valkova, Slavka Tcholakova, Nikolai D. Denkov, Stoyan K. Smoukov,
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 Nature 2015, 528, 392−395]. This process involves the formation of a plastic rotator phase of self-assembled oil molecules beneath the drop surface. The plastic phase spontaneously forms a frame of plastic rods at the oil drop perimeter which supports the polygonal shapes. However, most of the common ...
Tópico(s): Electrohydrodynamics and Fluid Dynamics
2017 - American Chemical Society | Langmuir
Ivan Lesov, Slavka Tcholakova, M. Kovadjieva, Tamar Saison, M. Lamblet, Nikolai D. Denkov,
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. Cationic TTAB leads to particle-stabilized foams (Pickering ...
Tópico(s): Mesoporous Materials and Catalysis
2017 - Elsevier BV | Journal of Colloid and Interface Science
Sonya Tsibranska, Anela Ivanova, Slavka Tcholakova, Nikolai D. Denkov,
Escin belongs to a large class of natural biosurfactants, called saponins, that are present in more than 500 plant species. Saponins are applied in the pharmaceutical, cosmetics, and food and beverage industries due to their variously expressed bioactivity and surface activity. In particular, escin adsorption layers at the air-water interface exhibit an unusually high surface elastic modulus (>1100 mN/m) and a high surface viscosity (ca. 130 N·s/m). The molecular origin of these unusual surface rheological ...
Tópico(s): Polysaccharides and Plant Cell Walls
2017 - American Chemical Society | Langmuir
Pierre A. Haas, Raymond E. Goldstein, Stoyan K. Smoukov, Diana Cholakova, Nikolai D. Denkov,
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 recover the observed sequence of shapes and their statistics in qualitative agreement with experiments. Extending the model to capture some of the three- ...
Tópico(s): Surfactants and Colloidal Systems
2017 - American Physical Society | Physical Review Letters
Zhulieta Valkova, Diana Cholakova, Slavka Tcholakova, Nikolai D. Denkov, Stoyan K. Smoukov,
Emulsification requires drop breakage and creation of a large interfacial area between immiscible liquid phases. Usually, high-shear or high-pressure emulsification devices that generate heat and increase the emulsion temperature are used to obtain emulsions with micrometer and submicrometer droplets. Recently, we reported a new, efficient procedure of self-emulsification (Tcholakova et al. Nat. Commun. 2017, 8, 15012), which consists of one to several cycles of freezing and melting of predispersed ...
Tópico(s): Pickering emulsions and particle stabilization
2017 - American Chemical Society | Langmuir
Slavka Tcholakova, Zhulieta Valkova, Diana Cholakova, Zahari Vinarov, Ivan Lesov, Nikolai D. Denkov, Stoyan K. Smoukov,
Abstract 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 ...
Tópico(s): Electrohydrodynamics and Fluid Dynamics
2017 - Nature Portfolio | Nature Communications