Antonio Stocco

University of Strasbourg | UNISTRA · Institut Charles Sadron

Dynamics of microparticles close to interfaces is a relevant topic in Soft Matter. Translational and rotational dynamics of particles possessing different shapes govern a broad range of interfacial phenomena from...

Gemini surfactants are ideal systems to study a wide range of rheological behaviours in soft matter, showing fascinating analogies with living polymers and polyelectrolytes. By only changing the concentration, the...

Our ability to design artificial micro/nanomachines able to perform sophisticated tasks crucially depends on our understanding of their interaction with biosystems and their compatibility with the biological environment. Here, we...

Entry of micro- or nanosized objects into cells or vesicles made of lipid membranes occurs in many processes such as entry of viruses into host cells, microplastics pollution, drug delivery, or biomedical imaging. Here we investigate the microparticle crossing of lipid membranes in giant unilamellar vesicles in the absence of strong binding interac...

In this article, we present the mobilities of prolate ellipsoidal micrometric particles close to an air-water interface measured by dual wave reflection interference microscopy. Particle's position and orientation with respect to the interface are simultaneously measured as a function of time. From the measured mean square displacement, five partic...

Entry of micro- or nano-sized objects into cells or vesicles made of lipid membranes occur in many processes such as entry of viruses in host cells, microplastics pollution, drug delivery or biomedical imaging. Here, we investigated the microparticle crossing of lipid membranes in giant unilamellar vesicles in the absence of strong binding interact...

Hypothesis Although the dynamics of colloids in the vicinity of a solid interface has been widely characterized in the past, experimental studies of Brownian diffusion close to an air-water interface are rare and limited to particle-interface gap distances larger than the particle size. At the still unexplored lower distances, the dynamics is expec...

Although the dynamics of colloids in the vicinity of a solid interface has been widely characterized in the past, experimental studies of Brownian diffusion close to an air-water interface are rare and limited to particle-interface gap distances larger than the particle size. Using a specially designed dual wave interferometric setup, the 3D dynami...

Food transition requires the replacement in human diet of animal-based proteins by alternative sources of proteins including plant-based proteins. This calls for a detailed knowledge of the functional properties of plant-based proteins, including their surface activity. In this framework, we provide here a comparative study of the interfacial prope...

The interaction between Janus colloids and giant lipid vesicles was experimentally investigated to elucidate the dynamics and mechanisms related to microparticle engulfment by lipid vesicles. Janus (Pt–SiO2 and Pt–MF, where MF is melamine formaldehyde) colloids do not spontaneously adhere to POPC or DOPC bilayers, but by applying external forces vi...

Living or artificial self-propelled colloidal particles show original dynamics when they interact with other objects like passive particles, interfaces or membranes. These active colloids can transport small cargos or can be guided by passive objects, performing simple tasks that could be implemented in more complex systems. Here, we present an exp...

The adsorption of a sunflower protein extract at two air-water and oil-water interfaces is investigated using tensiometry, dilational viscoelasticity, and ellipsometry. For both interfaces, a three step mechanism was evidenced thanks to master curve representations of the data taken at different aging times and protein concentrations. At short time...

In this article, we review both theoretical models and experimental results on the motion of micro- and nano- particles that are close to a fluid interface or move in between two fluids. Viscous drags together with dissipations due to fluctuations of the fluid interface and its physicochemical properties affect strongly the translational and rotati...

We report the measurement of the interaction energy between a charged Brownian polystyrene particle and an air-water interface. The interaction potential is obtained from Boltzmann equation by tracking particle interface distance with a specifically designed Dual-Wave Reflection Interference Microscopy (DW-RIM) setup. The particle has two equilibri...

We have investigated the wetting and surface diffusion of mesoporous colloidal silica particles at the water surface; and the adsorption of cationic cetyltrimethylammonium (CTA+) surfactant on these particles. Porous silica colloids diffuse at the surface of water and in the volume, interacting with cationic surfactants that can adsorb inside the p...

Separation efficiency is ideally controlled by molecular diffusion in capillary electrophoresis (CE). However, other adverse phenomena, such as solute adsorption on capillary surface, tend to increase the peak dispersion. An interesting alternative to limit the solute adsorption is to avoid as much as possible the contact of the solute with the cap...

Habilitation Dissertation

Hypothesis Rotational Brownian diffusions of colloidal particles at a fluid interface play important roles in particle self-assembly and in surface microrheology. Recent experiments on translational Brownian motion of spherical particles at the air-water interface show a significant slowing down of the translational diffusion with respect to the hy...

Pattern formation and periodical regimes are generally observed for reactive nonlinear chemical systems. They are here obtained for a non-reactive system constituted by an oil (dichloromethane) drop deposited on a surfactant (cetyltrimethylammonium bromide) aqueous solution. The interplay between physicochemical processes (evaporation, solubilizati...

The possibility to impart surface properties to any polymeric substrate using a fast, reproducible, and industrially friendly procedure, without the need for surface pretreatment, is highly sought after. This is in particular true in the frame of antibacterial surfaces to hinder the threat of biofilm formation. In this study, the potential of aryl‐...

Surface‐inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil‐in‐water emulsions. This is a result of attractive van der Waals forces between particles and oil droplets in water, which are sufficient to trap the particles in close proximity to oil‐water interfaces when the repulsive forces between particles...

Surface‐inactive, highly hydrophilic particles are utilized to effectively and reversibly stabilize oil‐in‐water emulsions. This is a result of attractive van der Waals forces between particles and oil droplets in water, which are sufficient to trap the particles in close proximity to oil‐water interfaces when the repulsive forces between particles...

The characterization of nanoparticles in dispersions, in particular measuring their size and size distribution, is a prerequisite before they can be used in toxicological testing. Such characterization requires reliable methods with good reproducibility. The aim of this study was to evaluate the reproducibility, and thus the potential of Dynamic Li...

Gliadins are edible wheat storage proteins well known for their surface active properties. In this paper, we present experimental results on the interfacial properties of acidic solutions of gliadin studied over 5 decades of concentrations, from 0.001 to 110 g/L. Dynamic pendant drop tensiometry reveals that the surface pressure Π of gliadin soluti...

Aqueous interfaces are ubiquitous in Nature and play a fundamental role in environmental, biological processes, or modern nanotechnologies. These interfaces are negatively charged and despite several decades of research, the rationale behind this phenomenon is still under debate. Two main controversial schools of thought argue on this issue; the fi...

Biological or artificial microswimmers move performing trajectories of different kinds such as rectilinear, circular or spiral ones. Here, we report on circular trajectories observed for active Janus colloids trapped at the air-water interface. Circular motion is due to asymmetric and non-uniform surface properties of the particles caused by fabric...

Controlling the interface between TiO2 nanocrystals and ionic liquids is of high fundamental and applied interest for energy storage and conversion devices. Phase transfer of nanoparticles from a synthesis medium to a processing or an application medium plays a significant role in nanotechnology. Here we demonstrate that surface modification with p...

Lignin is one of the most abundant bio-polymers present in nature and its valorization still represents a challenge to an economically feasible biorefinery concept. Lignin's heterogeneity and scarce reactivity represent significant hurdles to the development of new valorization processes. We propose an in-situ extraction electrochemical depolymeriz...

In a recent article Toro-Mendoza et al. (DOI: 10.1039/C6CP07442A), considered an elastic response of the interface in order to explain the enhanced lateral drag of solid particles straddling fluid interfaces we recently measured. In this comment, we would like to point out a number of critical aspects beyond such an approach.

In this critical review we compare two geometries in partial wetting: a liquid drop on a planar substrate and a spherical particle at a planar liquid interface. We show that this comparison is far from being trivial even if the same physical interactions are at play in both geometries. Similarities and differences in terms of free energies and fric...

The interface between two fluids is never flat at the nanoscale, and this is important for transport across interfaces. In absence of any external field, the surface roughness is due to thermally excited capillary waves possessing subnanometric amplitudes in the case of simple liquids. Here, we investigate the effect of ultrasound on the surface ro...

We study the dynamics of individual polystyrene ellipsoids of different aspect ratios trapped at the air-water interface. Using particle tracking and in situ vertical scanning interferometry techniques we are able to measure translational drags and the protrusion in air of the ellipsoids. We report that translational drags on the ellipsoid are unex...

A mild and simple way to prepare stable aqueous colloidal suspensions of composite particles made of a cellulosic material (Sigmacell cellulose) and multiwalled carbon nanotubes (MWCNTs) is reported. These suspensions can be dried and redispersed in water at pH 10.5. Starting with rather crude initial materials, commercial Sigmacell cellulose and M...

A mild and simple way to prepare stable aqueous colloidal suspensions of composite particles made of a cellulosic material (Sigmacell cellulose) and multiwalled carbon nanotubes (MWCNTs) is reported. These suspensions can be dried and redispersed in water at pH 10.5. Starting with rather crude initial materials, commercial Sigmacell cellulose and M...

Janus colloidal particles show remarkable properties in terms of surface activity, self-assembly and wetting. Moreover they can perform autonomous motion if they can chemically react with the liquid in which they are immersed. In order to understand the self-propelled motion of catalytic Janus colloids at the air-water interface, wetting and the o...

Commercial carboxymethylcellulose was used to prepare dispersible multi-walled carbon nanotubes-based composites. These composites were employed to prepare Pickering oil-in-water emulsions. Emulsion-templated macroporous materials were then prepared by embedding the oil droplets into a polymer resin arising from the polycondensation of furfural and...

For a droplet or a bubble of dimensions below 100 nm long-range surface forces such as long range van der Waals forces can compete with capillarity, which leads to a size dependence of the contact angle. This is discussed in this work, where we also show that the effect cannot simply be described by a normalized line tension. We calculate interfaci...

The dynamics of colloidal particles at the interface between two fluids plays a central role in biofilms formation [1], water remediation [2] or interface driven assembly of materials [3]. Common intuition corroborated by hydrodynamic theories [4] suggests that such a dynamics is governed by a viscous force lower than the one observed in the more v...

Active colloids are an emerging and promising class of colloidal particles, which are designed to perform autonomous motion by transforming chemical or other form of energies into work and propulsion. Here, we have investigated the active motion of self-propelled colloids confined at the air-water interface. The two dimensional motion of micron-siz...

The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than t...

The dynamics of colloidal particles at interfaces between two fluids plays a central role in microrheology, encapsulation, emulsification, biofilm formation, water remediation and the interface-driven assembly of materials. Common intuition corroborated by hydrodynamic theories suggests that such dynamics is governed by a viscous force lower than t...

One among other remarkable methods to produce multifunctional assemblies with different spatial organizations is the use of liquid-liquid (L-L) interfaces. Herein a droplet microfluidic-based method is reported as a strategy for the assembly of asymmetrical inorganic nanohybrid structures. As a proof of concept and motivated by their wide applicati...

Solid micron- and nano- particles have been extensively used to stabilize dispersions such Pickering emulsions and particle-stabilized foams. In many cases, particle's adsorption onto the fluid interfaces represents a limiting step for the stability of the dispersion since adsorption can be very slow or even hindered by interfacial potential barrie...

Dynamics of partially wetted colloids at the interface between two fluids is a crucial and timeliness topic: for instance, it governs the behavior of kinetically arrested colloidal gels, the formation of bacteria based biofilm and the cellular signaling via membrane proteins. Moreover, this subject is also challenging from a theoretical point of vi...

Here multiple angle of incidence ellipsometry was successfully applied to in situ assess the contact angle and surface coverage of gold nanoparticles as small as 18 nm, coated with stimuli-responsive polymers, at water-oil and water-air interfaces in the presence of NaCl and NaOH, respectively. The interfacial adsorption of the nanoparticles was fo...

The dynamics of colloids at the interface between two fluids is a crucial and timeliness research topic as it governs the behavior of kinetically arrested colloidal gels in interfacial microrheology, the formation of bacteria based biofilm and the cellular signaling via membrane proteins. Moreover, this subject is also challenging from a theoretica...

In industrial and biological applications, we often handle colloids at a fluid-fluid interface. Some examples are removal of contaminants from wastewater, the study of cellular signaling or the stabilization of Pickering emulsion. For a more fundamental point of view, because of their range in size, shapes and material, colloids are also suitable p...

Proteins in Solution and at Interfaces is divided into two parts: •Part One introduces concepts as well as theoretical and experimental techniques that are used to study protein systems, including X-ray crystallography, nuclear magnetic resonance, small angle scattering, and spectroscopic methods •Part Two examines current and emerging application...

This chapter describes the equilibrium state of mixed protein/surfactant adsorption layers and the mechanisms of their formation by thermodynamic and kinetics theories. Measurements of the equilibrium adsorption state are surface or interfacial tension isotherms. While tensiometry allows following the formation of adsorption layers over a certain t...

Swap transactions: Bidirectional spontaneous transfer of gold nanoparticles coated with stimuli-responsive polymer brushes across oil-water interfaces has been implemented. The water-to-oil transfer of the gold nanoparticles is dictated by the ionic strength in water, while the nanoparticle oil-to-water transfer occurs only when the environmental t...

The conformation and the dilatational properties of three non-ionic triblock PEO-PPO-PEO (where PEO is polyethyleneoxide and PPO is polypropyleneoxide) copolymers of different hydrophobicity and molecular weight were investigated at the water-hexane interface. The interfacial behavior of the copolymers was studied by combining dilatational rheology...

In this paper the mechanism behind the stabilization of Pickering emulsions by stacked catanionic micro-crystals is described. A temperature-quench of mixtures of oppositely charged surfactants (catanionics) and tetradecane from above the chain melting temperature to room temperature produces stable oil-in-water (o/w) Pickering emulsions in the abs...

The present work is devoted to the study of interactions between a cationic polyelectrolyte and an anionic surfactant in the solution bulk and at the water/air and water/oil interfaces. For this purpose surface and interfacial tensions, zeta potential, ellipsometry and dynamic light scattering (DLS) were used to describe the formation of complexes...

Two polyisoprene-polyethyleneoxide diblock copolymers with different block length ratios adsorbed to the water surface were investigated by multiple angle of incidence ellipsometry, evanescent wave light scattering, and surface tension experiments. In a semidilute interfacial regime, the transition from a two-dimensional to a "mushroom" regime, in...

Foams are dispersions of bubbles in liquids, often water. They are frequently stabilized by surfactant or polymer, but like Pickering emulsions, they can be also stabilized solely by particles. If the particles have a moderate hydrophobicity, the foams can be extremely stable (lifetimes of the order of years). Due to technical preparation difficult...

The stabilization of aqueous foams solely by solid particles is an active field of research. Thanks to controlled particle chemistry and production devices, we are able to generate large volumes of such foams. We previously investigated some of their unique properties, especially the strongly reduced coarsening. Here we report another type of study...

A light-scattering goniometer for evanescent-wave dynamic light scattering (EWDLS) measurements at a liquid-fluid interface is introduced, and used for measurements on two charge-stabilized polystyrene colloid systems adsorbed to alkane-water interfaces. The goniometer allows an independent variation of the penetration depth and the scattering vect...

We show that aqueous foams stabilised by nanoparticles can be easily imaged using an X-ray laboratory source. We have used hydrophobically modified silica nanoparticles that confer to the foam a remarkable stability. The X-ray tomography observations were compared with the information obtained using a multiple light scattering technique. Both techn...

In this paper the mechanism behind the stabilization of Pickering emulsions by stacked catanionic micro-crystals is described. A temperature-quench of mixtures of oppositely charged surfactants (catanionics) and tetradecane from above the chain melting temperature to room temperature produces stable oil-in-water (o/w) Pickering emulsions in the abs...

We show that aqueous foams stabilised by nanoparticles can be easily imaged using an X-ray laboratory source. We have used hydrophobically modified silica nanoparticles that confer to the foam a remarkable stability. The X-ray tomography observations were compared with the information obtained using a multiple light scattering technique. Both techn...

We report a dramatic increase in foam stability for catanionic mixtures (myristic acid and cetyl trimethylammonium bromide, CTABr) with respect to that of CTABr solutions. This increase was related to the low surface tension, high surface concentration, and high viscoelastic compression moduli, as measured with rising bubble experiments and ellipso...

In this article, highly accurate experimental results reveal the interfacial profile between different macroscopic fluid phases. The deviation from a step profile, quantified by the ellipsometric quantity J1, shows a strong correlation with the cohesive energy quantified by the Gordon parameter G . Surprisingly, at high values of G , J 1( < 0) devi...

We have studied silica nanoparticle layers spread at the air/water interface. The surface pressure of the layers has been determined in a Langmuir trough via two orthogonal Wilhelmy plates. We observed significant differences in surface pressure according to the preparation protocol: layers spread then compressed or layers obtained after successive...

A new tool to study surface phenomena by evanescent wave light scattering is employed for an investigation of an aqueous surface through the water phase. When the angle of incidence passes the critical angle of total internal reflection, a high and narrow scattering peak is observed. It is discussed as an enhancement of scattering at critical angle...