Emmanouil Chatzigiannakis

Last Name

Chatzigiannakis

First Name

Emmanouil

ORCID

0000-0001-6474-7662

Show all metadata

Search Results

Publications 1 - 9 of 9

Mimicking coalescence using a pressure-controlled dynamic thin film balance
Chatzigiannakis, Emmanouil; Veenstra, Peter; ten Bosch, Dick; et al. (2020)
Soft Matter
The dynamics of thin films containing polymer solutions are studied with a pressure-controlled thin film balance. The setup allows the control of both the magnitude and the sign as well as the duration of the pressure drop across the film. The process of coalescence can be thus studied by mimicking the evolution of pressure during the approach and separation of two bubbles. The drainage dynamics, shape evolution and stability of the films were found to depend non-trivially on the magnitude and the duration of the applied pressure. Film dynamics during the application of the negative pressure step are controlled by an interplay between capillarity and hydrodynamics. A negative hydrodynamic pressure gradient promoted the thickening of the film, while the time-dependent deformation of the Plateau border surrounding it caused its local thinning. Distinct regimes in film break-up were thus observed depending on which of these two effects prevailed. Our study provides new insight into the behaviour of films during bubble separation, allows the determination of the optimum conditions for the occurrence of coalescence, and facilitates the improvement of population balance models.
Thin Liquid Films: where Hydrodynamics, Capillarity, Surface Stresses, and Intermolecular Forces meet
Chatzigiannakis, Emmanouil; Jaensson, Nick; Vermant, Jan (2021)
Current Opinion in Colloid & Interface Science
Thin liquid films arise in many technological applications and biological phenomena. They also present a fascinating object of study, because of a rich interplay between capillarity, hydrodynamics, interfacial transport phenomena and interfacial rheology, as well as the effects of interaction forces when films thin down to molecular thicknesses. Recent advances in experimental techniques have given further insights in the variety of physical phenomena, which can occur. These techniques are briefly reviewed. How these techniques can be utilised is illustrated by recent studies addressing the effect of interfacial rheological stresses on drainage, the interplay between capillarity and hydrodynamics during film retraction, and the solutocapillary stabilisation of films. Finally, we briefly discuss the challenges of conducting drainage measurements at high and varied capillary numbers and how these could be overcome by the combined use of experiments and simulations.
Dynamic stabilisation during the drainage of thin film polymer solutions
Chatzigiannakis, Emmanouil; Vermant, Jan (2021)
Soft Matter
The drainage and rupture of polymer solutions was investigated using a dynamic thin film balance. The polymeric nature of the dissolved molecules leads to significant resistance to the deformation of the thin liquid films. The influence of concentration, molecular weight, and molecular weight distribution of the dissolved polymer on the lifetime of the films was systematically examined for varying hydrodynamic conditions. Depending on the value of the capillary number and the degree of confinement, different stabilisation mechanisms were observed. For low capillary numbers, the lifetime of the films was the highest for the highly concentrated, narrowly-distributed, low molecular weight polymers. In contrast, at high capillary numbers, the flow-induced concentration differences in the film resulted in lateral osmotic stresses, which caused a dynamic stabilisation of the films and the dependency on molecular weight distribution in particular becomes important. Phenomena such as cyclic dimple formation, vortices, and dimple recoil were observed, the occurrence of which depended on the relative magnitude of the lateral osmotic and the hydrodynamic stresses. The factors which lead to enhanced lifetime of the films as a consequence of these flow instabilities can be used to either stabilise foams or, conversely, prevent foam formation.
Studying coalescence at different lengthscales: from films to droplets
Chatzigiannakis, Emmanouil; Chen, Yun; Bachnak, Rana; et al. (2022)
Rheologica Acta
The hydrodynamics of thin films is an important factor when it comes to the stability and rheology of multiphasic materials, such as foams, emulsions, and polymer blends. However, there have so far been only limited experimental studies addressing the dynamics of individual free-standing thin films at conditions similar to those encountered on macroscopic scales. In this article, we study a well-characterized system of a water-in-oil emulsion stabilized by a non-ionic surfactant (SPAN80) close to its CMC. We employ a dynamic thin film balance, to study the dynamics of freestanding films under both constant and time-varied pressure drops. We compare with the recently published results of Narayan et al. (2020) on colliding droplets of the same system with a hydrodynamic microfluidic trap, and show for the first time that agreement between the two lengthscales is possible, which indicates that the coalescence is indeed dominated by the dynamics in the film. We then address the scatter in the coalescence times and show that it can be affected by extrinsic factors, as well as by variations in the collision angle. Finally, we discuss the difficulties of extracting insight on the coalescence mechanism from coalescence time distributions when different effects such as impurities, small pressure variations, collision angle variations, and possible Marangoni-related instabilities are at play.
From Individual Liquid Films to Macroscopic Foam Dynamics: A Comparison between Polymers and a Nonionic Surfactant
Mikhailovskaya, Alesya; Chatzigiannakis, Emmanouil; Renggli, Damian Simon; et al. (2022)
Langmuir
Foams can resist destabilizaton in ways that appear similar on a macroscopic scale, but the microscopic origins of the stability and the loss thereof can be quite diverse. Here, we compare both the macroscopic drainage and ultimate collapse of aqueous foams stabilized by either a partially hydrolyzed poly(vinyl alcohol) (PVA) or a nonionic low-molecular-weight surfactant (BrijO10) with the dynamics of individual thin films at the microscale. From this comparison, we gain significant insight regarding the effect of both surface stresses and intermolecular forces on macroscopic foam stability. Distinct regimes in the lifetime of the foams were observed. Drainage at early stages is controlled by the different stress-boundary conditions at the surfaces of the bubbles between the polymer and the surfactant. The stress-carrying capacity of PVA-stabilized interfaces is a result of the mutual contribution of Marangoni stresses and surface shear viscosity. In contrast, surface shear inviscidity and much weaker Marangoni stresses were observed for the nonionic surfactant surfaces, resulting in faster drainage times, both at the level of the single film and the macroscopic foam. At longer times, the PVA foams present a regime of homogeneous coalescence where isolated coalescence events are observed. This regime, which is observed only for PVA foams, occurs when the capillary pressure reaches the maximum disjoining pressure. A final regime is then observed for both systems where a fast coalescence front propagates from the top to the bottom of the foams. The critical liquid fractions and capillary pressures at which this regime is obtained are similar for both PVA and BrijO10 foams, which most likely indicates that collapse is related to a universal mechanism that seems unrelated to the stabilizer interfacial dynamics.
PERSPECTIVE: Interfacial stresses in thin film drainage: Subtle yet significant
Chatzigiannakis, Emmanouil; Vermant, Jan (2024)
Journal of Rheology
Film drainage, essential in droplet and bubble coalescence and surface wetting, is influenced strongly by the stress boundary condition, in particular, when interfacial stresses are present. These stresses, caused by ubiquitous surface-active components, significantly impact the dynamics of liquid films. Through dynamic thin film balance experiments, we compare the effects of Marangoni stresses, interfacial viscosity, and interfacial viscoelasticity on the drainage of free-standing thin liquid films. These data serve to demonstrate that film deformation intricately depends on the interplay between these stresses and capillarity, resulting in widely varied drainage times. Seemingly subtle changes, especially in the local stress-carrying capacity of the interface, can lead to significant differences in film dynamics. This makes it a promising area for research into interfacial-rheologically active materials for stabilizing potentially more sustainable multiphase materials. (c) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY)license (https://creativecommons.org/licenses/by/4.0/).
The Influence of the Surface Chemistry of Cellulose Nanocrystals on Ethyl Lauroyl Arginate Foam Stability
Czakaj, Agnieszka; Chatzigiannakis, Emmanouil; Vermant, Jan; et al. (2022)
Polymers
Guanidine-based surfactant ethyl lauroyl arginate (LAE) and cellulose nanocrystals (CNCs) form complexes of enhanced surface activity when compared to pure surfactants. The LAE-CNC mixtures show enhanced foaming properties. The dynamic thin-film balance technique (DTFB) was used to study the morphology, drainage and rupture of LAE-CNC thin liquid films under constant driving pressure. A total of three concentrations of surfactant and the corresponding mixtures of LAE with sulfated (sCNC) and carboxylated (cCNC) cellulose nanocrystals were studied. The sCNC and cCNC suspension with LAE formed thin films, with stability increasing with surfactant concentration and with complex rheological properties. In the presence of LAE, the aggregation of CNC was observed. While the sCNC aggregates were preferentially present in the film volume with a small fraction at the surface, the cCNC aggregates, due to their higher hydrophobicity, were preferentially located at film interfaces, forming compact layers. The presence of both types of aggregates decreased the stability of the thin liquid film compared to the one for the LAE solution with the same concentration. The addition of CNC to LAE was critical for foam formation, and foam stability was in qualitative agreement with the thin films’ lifetimes. The foam volume increased with the LAE concentration. However, there was an optimum surfactant concentration to achieve stable foam. In particular, the very resistant foam was obtained with cCNC suspensions that formed the interfaces with a complex structure and rheology. On the other hand, at high LAE concentrations, the aggregates of CNC may exhibit antifoaming properties.
Thin liquid films: where hydrodynamics, capillarity, interfacial stresses, and intermolecular forces meet
Chatzigiannakis, Emmanouil (2021)
The hidden subtlety of beer foam stability: A blueprint for advanced foam formulations
Chatzigiannakis, Emmanouil; Alicke, Alexandra; Le Bars, Léa; et al. (2025)
Physics of Fluids
It is believed that the structure and properties of protein-rich layers influence beer foam stability through their impact on both surface tension and surface viscosity. However, our experiments employing surface rheometry, tensiometry, and dynamic thin-film balance reveal that the governing mechanism is actually more subtle, and depends on the beer type. While film stability in lager beers does hinge on surface viscosity, as previously reported, Belgian ales (such as Trappist beers) display minimal surface viscosities and instead rely on viscoelastic stresses or Marangoni stresses for stabilization. Especially robust, recirculating Marangoni flows significantly extend film and foam longevity. Moreover, proteomic analyses confirmed that the abundance and specific modifications of lipid transfer protein 1 play a pivotal role in foam stabilization, especially in blond Belgian ales. The strength of Marangoni stresses—and thus foam stability—also depends on the number of fermentations, with triple-fermented Belgian ales outperforming single-fermented ones. Together, these findings offer direct experimental insight into the dynamics of beer foam, facilitating a deeper understanding of foam physics not only in beer but also in other complex surface-active mixtures.

Publications 1 - 9 of 9

Emmanouil Chatzigiannakis

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results