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Andrij Pich - One of the best experts on this subject based on the ideXlab platform.
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Electroactive and degradable supramolecular Microgels.
Soft matter, 2019Co-Authors: Olga Mergel, Puja Jain, Huan Peng, Khosrow Rahimi, Smriti Singh, Felix A. Plamper, Andrij PichAbstract:In this work, we synthesized electroactive and degradable Microgels based on biomacromolecular building blocks, which enable the controlled release of therapeutic drugs. Functional chitosan–poly(hydroquinone) (Ch:PHQ) Microgels exhibiting redox-active and pH-sensitive properties were synthesized by an oxidative polymerization in an inverse miniemulsion system. Physically crosslinked Microgels were formed by polymerization of hydroquinone in the presence of chitosan through the formation of hydrogen bonds between PHQ and Ch. A series of microgel samples with variable Ch : PHQ ratios were synthesized. These obtained Microgels exhibit pH-responsive properties due to the protonation/deprotonation of amino-groups of chitosan in the microgel system. Poly(hydroquinone) is a redox-active polymer exhibiting a two-electron/proton-transfer behavior and conveys this property to the Microgels as confirmed by cyclic voltammetry. In addition, the Microgels can be switched by electrochemical means: they swell in the oxidized state or shrink in the reduced state. In the presence of urea or lysozyme, the Microgels undergo a fast degradation due to the disruption of hydrogen bonds acting as physical crosslinks in the microgel networks or due to the cleavage of glucosidic linkages of the incorporated chitosan scaffold, respectively. Doxorubicin (DOX), an anticancer drug, could be effectively encapsulated into the Microgels and released in the presence of an enzyme, indicating that these biodegradable Microgels could be used as drug delivery vehicles for tumor cells.
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Tunable clustering of magnetic nanoparticles in Microgels: enhanced magnetic relaxivity by modulation of network architecture
Nanoscale, 2018Co-Authors: K. Herman, M. E. Lang, Andrij PichAbstract:In the present work we used Microgels as colloidal containers for the loading of hydrophobic magnetic nanoparticles using the solvent exchange method. We varied systematically two parameters: (i) the crosslinking degree of Microgels (1–4.5 mol% crosslinker) and (ii) loading of hydrophobic magnetite nanoparticles (d = 7 nm) in Microgels (2–10 wt%). The experimental data show that the interplay between these two parameters provides efficient control over the clustering of magnetic nanoparticles in the microgel structure. Transverse magnetization relaxation measurements indicate that the formation of nanoparticle clusters in Microgels induces non-linear enhancement of the relaxivity with the increase of nanoparticle loading in Microgels. The results suggest that the modulation of the microgel network architecture can be efficiently applied to trigger self-assembly processes inside Microgels and design hybrid colloids with unusual morphologies and properties.
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Polyampholyte Microgels with Anionic Core and Cationic Shell
Macromolecules, 2010Co-Authors: Susann Schachschal, Walter Richtering, Andreea Balaceanu, Claudiu Melian, Dan E. Demco, Thomas Eckert, Andrij PichAbstract:We report synthesis of amphoteric Microgels by copolymerization of N-vinylcaprolactam (VCL), itaconic acid dimethyl ester (IADME), and vinylimidazole (VIm) in the precipitation−polymerization process. After hydrolysis of ester groups of IADME, component Microgels contain acidic and basic groups in their structure. Proton high-resolution transverse magnetization relaxation under magic angle sample spinning (MAS) was used to measure the dynamic heterogeneity corroborated with the chemical structure of a multicomponent amphoteric microgel. NMR results indicate that itaconic acid groups (originated from hydrolyzed IADME component) are localized mostly in the microgel core. The core−shell morphology of poly(N-vinylcaprolactam)-based Microgels was suggested with carboxylic acid groups in the core and imidazole groups in the shell. The variation of the IADME and VIm content in microgel structure allows varying microgel charge and swelling degree in basic and acidic pH, respectively. Obtained amphoteric Microgels...
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Microgel/clay nanohybrids as responsive scavenger systems
Polymer, 2010Co-Authors: Sebastian Berger, Rekha Singh, J. D. Sudha, Hans-juergen P. Adler, Andrij PichAbstract:Abstract Microgel–clay composite particles were prepared by one-step surfactant–free precipitation polymerization. Laponite nanoparticles present in the reaction mixture become encapsulated during the microgel formation process. Microgel–clay composites based on poly( N -vinylcaprolactam- co -acetoacetoxyethyl methacrylate) containing different amount of incorporated clay nanoparticles were synthesized. The clay content was varied from 2 wt% to 18 wt%. The extremely high incorporation efficiency of the clay nanoparticles into Microgels was detected. The size of the hybrid Microgels was decreased from 700 nm to 100 nm by increase of the clay concentration in the reaction mixture. Obtained hybrid Microgels exhibit negative surface charge and excellent colloidal stability. Microgel–clay composite particles display temperature-sensitive behaviour in water. The swelling degree of the hybrid Microgels decreases with increase of the clay loading. Microgel–clay composite particles exhibit temperature-controlled uptake of the cationic dye, Methylene blue, and can be used as scavenger systems in aqueous media.
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Microgels by precipitation polymerization synthesis characterization and functionalization
Advances in Polymer Science, 2010Co-Authors: Andrij Pich, Walter RichteringAbstract:This chapter reviews recent work on the synthesis of aqueous microgel particles by precipitation polymerization. Precipitation polymerization allows flexible control over important physicochemical properties of aqueous Microgels, such as size distribution, surface charge, chemical composition, and microstructure. The microgel systems discussed in this review are mainly based on poly(N-isopropyl acrylamide) and poly(N-vinylcaprolactam) due to their ability to react to external stimuli such as the pH or temperature of the surrounding medium. We discuss synthetic routes to obtain Microgels based on homo- or copolymers as well as colloids with complex core-shell morphology. The functionalization of Microgels is of crucial importance from the application point of view. Different routes for incorporation of functional groups, synthetic polymers, proteins, or nanoparticles in microgel structures are discussed.
Valérie Ravaine - One of the best experts on this subject based on the ideXlab platform.
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Pickering emulsions stabilized by thermoresponsive oligo(ethylene glycol)-based Microgels: effect of temperature-sensitivity on emulsion stability
Journal of Colloid and Interface Science, 2021Co-Authors: Marie Charlotte Tatry, Véronique Schmitt, Patrick Garrigue, Veronique Lapeyre, Paul Galanopoulo, Léa Waldmann, Valérie RavaineAbstract:Hypothesis: The stability of emulsions stabilized by soft and responsive Microgels and their macroscopic properties are governed by the microstructure of Microgels, in particular their deformability. However, little is known about the role of the microgel chemistry, though it is expected that polymeric backbone with an amphiphilic structure is a requirement for their adsorption at the oil-water interface. Experiments: A series of biocompatible, thermoresponsive and amphiphilic poly(oligoethylene glycol)methacrylate (pOEMA) Microgels is synthesized, with varying hydrophobic-hydrophilic balance, or equivalent varying volume phase transition temperature (VPTT). Their behavior in the bulk phase and at solid interfaces is compared to their behavior at liquid interfaces, studied on flat and model interfaces by the pendant drop method, and on drops, in microgel-stabilized emulsions. Findings: Controlling the composition of Microgels by simply changing the number of ethylene oxide in the hydrophilic side chain allows a precise tuning of their VPTT in the range of 20 to 60°C. Simultaneously, the swelling ratio and the deformability of the Microgels increase by increasing the hydrophilicity, as a result of the polymerization process. Regardless of their hydrophilicity, all the swollen pOEMA Microgels adsorb at the liquid interface and stabilize emulsions, whose flocculation state and mechanical stability depends on the microgel deformability. Unexpectedly, most emulsions remain stable upon heating above the VPTT of the Microgels. Such feature highlights their extreme robustness, whose origin is discussed. This study opens new opportunities for the use of biocompatible Pickering emulsifiers.
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Sugar-responsive Pickering emulsions mediated by switching hydrophobicity in Microgels
Journal of Colloid and Interface Science, 2020Co-Authors: Marie Charlotte Tatry, Véronique Schmitt, Patrick Garrigue, Veronique Lapeyre, Yating Qiu, Valérie RavaineAbstract:Hypothesis: Pickering emulsions stabilized by soft and responsive Microgels can demulsify on demand upon microgel collapse. The concept has been explored with simple model Microgels such as poly(Nisopropylacrylamide) (pNIPAM) and their derivatives, but the role of functionalization is largely unexplored. Experiments: Saccharide-responsive phenylboronic-modified Microgels are used as Pickering emulsion stabilizers. Emulsion stability and microgel organization at drop surface are studied as a function of saccharide concentration. Better insight into their behavior at interfaces is gained through adsorption kinetics and Langmuir film studies at air-water interface. Findings: The functionalization of water-swollen Microgels by phenylboronic functions imparts some hydrophobicity to the structure, at the origin of additional internal cross-links analogous which rigidify the structure compared to non-functionalized Microgels, as proved by their slow adsorption kinetics and poor interfacial compressibility. Upon boronate ester formation with diol groups of the saccharide, the hydrophobic character of the phenylboronic acid decreases, increasing the adsorption kinetics and their interfacial compressibility. Emulsions are stable in the presence of saccharide, given the high deformability of the yet-hydrophilic Microgels, and mechanically unstable with less deformable particles in low
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Kinetics of spontaneous Microgels adsorption and stabilization of emulsions produced using microfluidics
Journal of Colloid and Interface Science, 2019Co-Authors: Marie Charlotte Tatry, Eric Laurichesse, Adeline Perro, Valérie Ravaine, Véronique SchmittAbstract:The aim of the paper is to examine the adsorption kinetics of soft Microgels and to understand the role of fundamental parameters such as electrostatics and deformability on the process. This knowledge is further exploited to produce microgel-stabilized emulsions using a co-flow microfluidic device. Uncharged Microgels made of poly(N isopropylacrylamide) are synthesized with variable cross-linker contents, and charged ones are produced by introducing pH sensitive co-monomers during the synthesis. The study is carried out by measuring the Microgels adsorption kinetics by means of the pendant drop method. The surface pressure is derived from the previous results as a function of time and is measured as a function of the area compression using a Langmuir trough. Emulsions are produced using a microfluidic device varying the Microgels concentration and their stability is visually assessed. The Microgels deformability as well as higher particle concentrations favour their adsorption. The adsorption is not governed by diffusion, it is cooperative and irreversible. Conversely, the kinetics is slowed down for increasing cross-linking density. The presence of charges slows down the kinetics of adsorption. In the presence of electrolyte, the kinetics accelerates and becomes similar to the one of neutral Microgels. The original features of microgel adsorption is highlighted and the differences with adsorption of polymers, star polymers, proteins, and polyelectrolytes are emphasized. Taking benefit from the adsorption kinetics, the required formulation conditions for producing microgel-stabilized emulsions using a co-flow microfluidic device are derived. There exists a critical concentration above which Microgels spontaneously adsorb in a sufficient way to decrease the interfacial tension. This critical microgel concentration increases with the cross-linking density and is higher for charged Microgels. Whatever the kinetics, the same surface pressure is finally reached. This peculiar behaviour is likely a consequence of the presence of dangling chains in the as-prepared Microgels. Consequently, a microgel excess is required to produce emulsions using microfluidics where adsorption has to be spontaneous.
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Impact of Electrostatics on the Adsorption of Microgels at the Interface of Pickering Emulsions
Langmuir, 2014Co-Authors: Pascal Massé, Véronique Schmitt, Elisabeth Sellier, Valérie RavaineAbstract:The importance of electrostatics on microgel adsorption at a liquid interface is studied, as well as its consequence on emulsion stabilization. In this work, poly(Nisopropylacrylamide) (pNIPAM) Microgels bearing different numbers of charges and various distribution profiles are studied, both in solution and at the oil−water interface of emulsion drops. Charged Microgels are compared to neutral ones, and electrostatic interactions are screened by adding salt to the aqueous solution. In solution, electrostatics has a significant impact on microgel swelling, as induced by the osmotic pressure exerted by mobile counterions in the gel network. At the interface of drops, Microgels pack in a hexagonal array, whose lattice parameter is independent of the number of charges and range of electrostatic interactions. Microgel morphology and packing are ruled only by the adsorption of the pNIPAM chain at the interface. Conversely, decreasing the charge density of Microgels by the protonation of the carboxylic groups leads to unstable emulsions, possibly as a result of the impact of hydrogen bonding on microgel deformability.
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Adsorption of Microgels at an oil–water interface: correlation between packing and 2D elasticity
Soft Matter, 2014Co-Authors: Florent Pinaud, Walter Richtering, Valérie Ravaine, Pascal Massé, Karen Geisel, Bogdan Catargi, Lucio Isa, Véronique SchmittAbstract:The aim of this paper is to determine how Microgels adsorb at a model oil–water interface and how they adapt their conformation to compression, which gives rise to surface elasticity depending on the microgel packing. The structure of the film is determined by the Langmuir films approach (forced compression) and compared to spontaneous adsorption using the pendant drop method. The behaviour of Microgels differs significantly from that of non-deformable particles but resembles that of linear polymers or proteins. We also correlate the properties of Microgels spontaneously adsorbed at model interfaces to their forced adsorption during emulsification. Finally we propose a route to easily control a posteriori the microgel packing at the surface of droplets and the flow properties of emulsions stabilised by the Microgels.
Walter Richtering - One of the best experts on this subject based on the ideXlab platform.
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Surface Functionalization by Stimuli-Sensitive Microgels for Effective Enzyme Uptake and Rational Design of Biosensor Setups
MDPI AG, 2018Co-Authors: Larisa V. Sigolaeva, Felix A. Plamper, Dmitry V. Pergushov, Marina Oelmann, Simona Schwarz, Monia Brugnoni, Ilya N. Kurochkin, Andreas Fery, Walter RichteringAbstract:We highlight microgel/enzyme thin films that were deposited onto solid interfaces via two sequential steps, the adsorption of temperature- and pH-sensitive Microgels, followed by their complexation with the enzyme choline oxidase, ChO. Two kinds of functional (ionic) Microgels were compared in this work in regard to their adsorptive behavior and interaction with ChO, that is, poly(N-isopropylacrylamide-co-N-(3-aminopropyl)methacrylamide), P(NIPAM-co-APMA), bearing primary amino groups, and poly(N-isopropylacrylamide-co-N-[3-(dimethylamino) propyl]methacrylamide), P(NIPAM-co-DMAPMA), bearing tertiary amino groups. The stimuli-sensitive properties of the Microgels in the solution were characterized by potentiometric titration, dynamic light scattering (DLS), and laser microelectrophoresis. The peculiarities of the adsorptive behavior of both the Microgels and the specific character of their interaction with ChO were revealed by a combination of surface characterization techniques. The surface charge was characterized by electrokinetic analysis (EKA) for the initial graphite surface and the same one after the subsequent deposition of the Microgels and the enzyme under different adsorption regimes. The masses of wet microgel and microgel/enzyme films were determined by quartz crystal microbalance with dissipation monitoring (QCM-D) upon the subsequent deposition of the components under the same adsorption conditions, on a surface of gold-coated quartz crystals. Finally, the enzymatic responses of the microgel/enzyme films deposited on graphite electrodes to choline were tested amperometrically. The presence of functional primary amino groups in the P(NIPAM-co-APMA) microgel enables a covalent enzyme-to-microgel coupling via glutar aldehyde cross-linking, thereby resulting in a considerable improvement of the biosensor operational stability
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Microgel stabilized emulsions: Breaking on demand
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2016Co-Authors: Susanne Wiese, Yoanna Tsvetkova, Nadine J.e. Daleiden, Antje Spieß, Walter RichteringAbstract:Abstract Here, we report on how to stabilize and break emulsions that are compatible with enzymatic reaction conditions. Many substrates of enzymatic reactions are soluble in unpolar organic solvents whereas the enzymes themselves often need an aqueous environment. We use a buffer solution (triethanolamine hydrochloride) as aqueous and MtBE (tert-butyl methyl ether) as organic phase which provide good enzyme compatibility. We are able to break emulsions in a desired temperature range by using NiPAM–NiPMAM Microgels with different monomer compositions and architecture, respectively. Our Microgels need to deswell to about 55% of its swollen size at room temperature to let the emulsion break. Emulsions can be broken such that the Microgels are either colloidally stable in the aqueous phase or flocculated. The temperature interval in which the Microgels stay colloidally stable while the emulsion is broken is broader for the core–shell microgel than for the copolymer microgel. The behavior of the Microgels in aqueous solution allows predicting: (i) the temperature at which the emulsion breaks and (ii) whether Microgels flocculate or not during breaking the emulsion. However, the partial miscibility of the organic phase with the aqueous phase has to be taken into account. Thus, we are able to stabilize and break emulsions by employing Microgels as responsive emulsifiers and to adapt the Microgels to the requirements of biocatalytic processes.
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new insight into microgel stabilized emulsions using transmission x ray microscopy nonuniform deformation and arrangement of Microgels at liquid interfaces
Langmuir, 2015Co-Authors: Karen Geisel, Katja Henzler, Peter Guttmann, Walter RichteringAbstract:Microgel-covered interfaces, e.g., in emulsions, have attracted much interest lately. Different imaging techniques have been used to image these interfaces, either flat or curved, to investigate their properties and appearance. Techniques such as cryogenic scanning electron microscopy (cryo-SEM) and confocal microscopy have provided valuable insight into microgel-covered systems but still have some disadvantages such as part of the Microgels being trapped in vitrified liquid or the need for fluorescent markers. Some of these disadvantages can be overcome by using transmission X-ray microscopy (TXM), which has the advantage of allowing the investigation of adsorbed and free Microgels simultaneously. We used TXM to acquire tomographic image series of microgel-covered droplets and calculated 3D reconstructions from these image stacks. As a result, we could show that Microgels deform anisotropically and penetrate the oil droplets in the hydrated state. Additionally, 3D reconstruction gives an idea of the arra...
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Adsorption of Microgels at an oil–water interface: correlation between packing and 2D elasticity
Soft Matter, 2014Co-Authors: Florent Pinaud, Walter Richtering, Valérie Ravaine, Pascal Massé, Karen Geisel, Bogdan Catargi, Lucio Isa, Véronique SchmittAbstract:The aim of this paper is to determine how Microgels adsorb at a model oil–water interface and how they adapt their conformation to compression, which gives rise to surface elasticity depending on the microgel packing. The structure of the film is determined by the Langmuir films approach (forced compression) and compared to spontaneous adsorption using the pendant drop method. The behaviour of Microgels differs significantly from that of non-deformable particles but resembles that of linear polymers or proteins. We also correlate the properties of Microgels spontaneously adsorbed at model interfaces to their forced adsorption during emulsification. Finally we propose a route to easily control a posteriori the microgel packing at the surface of droplets and the flow properties of emulsions stabilised by the Microgels.
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responsive emulsions stabilized by stimuli sensitive Microgels emulsions with special non pickering properties
Langmuir, 2012Co-Authors: Walter RichteringAbstract:Recent studies revealing the unique properties of microgel-stabilized responsive emulsions are discussed, and Microgels are compared to classical rigid-particle Pickering stabilizers. Microgels are strongly swollen, lyophilic particles that become deformed at the oil-water interface and protrude only a little into the oil phase. Temperature- and pH-sensitive Microgels allow us to prepare temperature- and pH-sensitive emulsions and thus enable us to prepare and break emulsions on demand. Although such emulsions are sensitive to pH, the stabilization of droplets is not due to electrostatic repulsion, instead the viscoelastic properties of the interface seem to dominate droplet stability. Being soft and porous, Microgels behave distinctly differently from rigid particles at the interface: they are deformed and strongly flattened especially in the case of oil-in-water emulsions. The Microgels are located mainly on the water side of the interface for both oil-in-water and water-in-oil emulsions. In contrast to rigid, solid particles, the behavior of Microgels at oil-water interfaces does not depend only on the interfacial tension but also on the balance among the interfacial tension, swelling, elasticity, and deformability of the microgel, which needs to be considered. It is obvious that Microgels as soft, porous particles are significantly different from classical rigid colloidal stabilizers in Pickering emulsions and we suggest avoiding the term Pickering emulsion when swollen Microgels are employed. Microgel-stabilized emulsions require the development of new theoretical models to understand their properties. They open the door to new sophisticated applications.
Véronique Schmitt - One of the best experts on this subject based on the ideXlab platform.
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Pickering emulsions stabilized by thermoresponsive oligo(ethylene glycol)-based Microgels: effect of temperature-sensitivity on emulsion stability
Journal of Colloid and Interface Science, 2021Co-Authors: Marie Charlotte Tatry, Véronique Schmitt, Patrick Garrigue, Veronique Lapeyre, Paul Galanopoulo, Léa Waldmann, Valérie RavaineAbstract:Hypothesis: The stability of emulsions stabilized by soft and responsive Microgels and their macroscopic properties are governed by the microstructure of Microgels, in particular their deformability. However, little is known about the role of the microgel chemistry, though it is expected that polymeric backbone with an amphiphilic structure is a requirement for their adsorption at the oil-water interface. Experiments: A series of biocompatible, thermoresponsive and amphiphilic poly(oligoethylene glycol)methacrylate (pOEMA) Microgels is synthesized, with varying hydrophobic-hydrophilic balance, or equivalent varying volume phase transition temperature (VPTT). Their behavior in the bulk phase and at solid interfaces is compared to their behavior at liquid interfaces, studied on flat and model interfaces by the pendant drop method, and on drops, in microgel-stabilized emulsions. Findings: Controlling the composition of Microgels by simply changing the number of ethylene oxide in the hydrophilic side chain allows a precise tuning of their VPTT in the range of 20 to 60°C. Simultaneously, the swelling ratio and the deformability of the Microgels increase by increasing the hydrophilicity, as a result of the polymerization process. Regardless of their hydrophilicity, all the swollen pOEMA Microgels adsorb at the liquid interface and stabilize emulsions, whose flocculation state and mechanical stability depends on the microgel deformability. Unexpectedly, most emulsions remain stable upon heating above the VPTT of the Microgels. Such feature highlights their extreme robustness, whose origin is discussed. This study opens new opportunities for the use of biocompatible Pickering emulsifiers.
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Sugar-responsive Pickering emulsions mediated by switching hydrophobicity in Microgels
Journal of Colloid and Interface Science, 2020Co-Authors: Marie Charlotte Tatry, Véronique Schmitt, Patrick Garrigue, Veronique Lapeyre, Yating Qiu, Valérie RavaineAbstract:Hypothesis: Pickering emulsions stabilized by soft and responsive Microgels can demulsify on demand upon microgel collapse. The concept has been explored with simple model Microgels such as poly(Nisopropylacrylamide) (pNIPAM) and their derivatives, but the role of functionalization is largely unexplored. Experiments: Saccharide-responsive phenylboronic-modified Microgels are used as Pickering emulsion stabilizers. Emulsion stability and microgel organization at drop surface are studied as a function of saccharide concentration. Better insight into their behavior at interfaces is gained through adsorption kinetics and Langmuir film studies at air-water interface. Findings: The functionalization of water-swollen Microgels by phenylboronic functions imparts some hydrophobicity to the structure, at the origin of additional internal cross-links analogous which rigidify the structure compared to non-functionalized Microgels, as proved by their slow adsorption kinetics and poor interfacial compressibility. Upon boronate ester formation with diol groups of the saccharide, the hydrophobic character of the phenylboronic acid decreases, increasing the adsorption kinetics and their interfacial compressibility. Emulsions are stable in the presence of saccharide, given the high deformability of the yet-hydrophilic Microgels, and mechanically unstable with less deformable particles in low
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Kinetics of spontaneous Microgels adsorption and stabilization of emulsions produced using microfluidics
Journal of Colloid and Interface Science, 2019Co-Authors: Marie Charlotte Tatry, Eric Laurichesse, Adeline Perro, Valérie Ravaine, Véronique SchmittAbstract:The aim of the paper is to examine the adsorption kinetics of soft Microgels and to understand the role of fundamental parameters such as electrostatics and deformability on the process. This knowledge is further exploited to produce microgel-stabilized emulsions using a co-flow microfluidic device. Uncharged Microgels made of poly(N isopropylacrylamide) are synthesized with variable cross-linker contents, and charged ones are produced by introducing pH sensitive co-monomers during the synthesis. The study is carried out by measuring the Microgels adsorption kinetics by means of the pendant drop method. The surface pressure is derived from the previous results as a function of time and is measured as a function of the area compression using a Langmuir trough. Emulsions are produced using a microfluidic device varying the Microgels concentration and their stability is visually assessed. The Microgels deformability as well as higher particle concentrations favour their adsorption. The adsorption is not governed by diffusion, it is cooperative and irreversible. Conversely, the kinetics is slowed down for increasing cross-linking density. The presence of charges slows down the kinetics of adsorption. In the presence of electrolyte, the kinetics accelerates and becomes similar to the one of neutral Microgels. The original features of microgel adsorption is highlighted and the differences with adsorption of polymers, star polymers, proteins, and polyelectrolytes are emphasized. Taking benefit from the adsorption kinetics, the required formulation conditions for producing microgel-stabilized emulsions using a co-flow microfluidic device are derived. There exists a critical concentration above which Microgels spontaneously adsorb in a sufficient way to decrease the interfacial tension. This critical microgel concentration increases with the cross-linking density and is higher for charged Microgels. Whatever the kinetics, the same surface pressure is finally reached. This peculiar behaviour is likely a consequence of the presence of dangling chains in the as-prepared Microgels. Consequently, a microgel excess is required to produce emulsions using microfluidics where adsorption has to be spontaneous.
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Impact of Electrostatics on the Adsorption of Microgels at the Interface of Pickering Emulsions
Langmuir, 2014Co-Authors: Pascal Massé, Véronique Schmitt, Elisabeth Sellier, Valérie RavaineAbstract:The importance of electrostatics on microgel adsorption at a liquid interface is studied, as well as its consequence on emulsion stabilization. In this work, poly(Nisopropylacrylamide) (pNIPAM) Microgels bearing different numbers of charges and various distribution profiles are studied, both in solution and at the oil−water interface of emulsion drops. Charged Microgels are compared to neutral ones, and electrostatic interactions are screened by adding salt to the aqueous solution. In solution, electrostatics has a significant impact on microgel swelling, as induced by the osmotic pressure exerted by mobile counterions in the gel network. At the interface of drops, Microgels pack in a hexagonal array, whose lattice parameter is independent of the number of charges and range of electrostatic interactions. Microgel morphology and packing are ruled only by the adsorption of the pNIPAM chain at the interface. Conversely, decreasing the charge density of Microgels by the protonation of the carboxylic groups leads to unstable emulsions, possibly as a result of the impact of hydrogen bonding on microgel deformability.
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Adsorption of Microgels at an oil–water interface: correlation between packing and 2D elasticity
Soft Matter, 2014Co-Authors: Florent Pinaud, Walter Richtering, Valérie Ravaine, Pascal Massé, Karen Geisel, Bogdan Catargi, Lucio Isa, Véronique SchmittAbstract:The aim of this paper is to determine how Microgels adsorb at a model oil–water interface and how they adapt their conformation to compression, which gives rise to surface elasticity depending on the microgel packing. The structure of the film is determined by the Langmuir films approach (forced compression) and compared to spontaneous adsorption using the pendant drop method. The behaviour of Microgels differs significantly from that of non-deformable particles but resembles that of linear polymers or proteins. We also correlate the properties of Microgels spontaneously adsorbed at model interfaces to their forced adsorption during emulsification. Finally we propose a route to easily control a posteriori the microgel packing at the surface of droplets and the flow properties of emulsions stabilised by the Microgels.
Andrij Pich - One of the best experts on this subject based on the ideXlab platform.
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Aqueous Microgels modified with photosensitive wedge-shaped amphiphilic molecules: synthesis, structure and photochemical behaviour
Photochemical & Photobiological Sciences, 2019Co-Authors: Andrey Dolgopolov, Kseniia Grafskaia, Polina Bovsunovskaya, Elina Melnikova, Dimitri Ivanov, Andrij Pich, Xiaomin Zhu, Martin MöllerAbstract:Aqueous Microgels based on poly(N-vinylcaprolactam) with reversible temperature-induced volume transition are promising “smart” materials for various applications. In this work, the Microgels are modified via acid–base interaction by wedge-shaped amphiphilic sulfonic acid molecules with alkyl chains of different lengths and an azobenzene group. In contrast to the pristine microgel the modified Microgels retain colloidal stability in water and show different responses to the change of temperature and pH. The azobenzene group in the ligand molecules acts as a spectroscopic and kinetic probe sensing the microenvironment inside the microgel particles. Thus, the observed hyperchromicity upon heating suggests the enhancement of hydrophobicity with the increase of temperature. The hydrophobicity of the microgel interior increases with the increase of the modification degree as indicated by the increase of activation energy of the thermal Z/E isomerization of the azobenzene group.
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Aqueous Microgels modified by wedge-shaped amphiphilic molecules: hydrophilic microcontainers with hydrophobic nanodomains.
Langmuir, 2010Co-Authors: Cheng Cheng, Andrij Pich, Xiaomin Zhu, Martin MöllerAbstract:A simple route for the design of hydrophilic Microgels comprising inner hydrophobic nanodomains has been developed based on postmodification of Microgels by complexation of wedge-shaped amphiphilic molecules with complementary functional groups. Aqueous Microgels functionalized with imidazole groups were transferred into an organic medium, where imidazole groups were neutralized by water-insoluble wedge-shaped molecules bearing a sulfonic acid group at the tip of the wedge and a large hydrocarbon body. After redispersion of the modified microgel particles into the aqueous phase, wedge-shaped amphiphiles ionically attached to the polymer chains self-assembled into discrete nanodomains in the interior of the polymer colloids due to the hydrophobic attraction force. The loading of the wedge-shaped molecules into Microgels can be controlled by variation of the amount of imidazole groups integrated into the microgel network as well as the neutralization degree. The experimental results suggested that incorporation of hydrophobic domains into hydrophilic colloids induced dramatic changes of their properties such as swelling degree, surface charge, and responsiveness toward temperature and pH. Finally, we demonstrated that internally hydrophobized microgel particles are very effective in uptake of hydrophobic molecules in aqueous media.
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Hybrid Microgels with antibacterial properties.
Macromolecular bioscience, 2009Co-Authors: Nadine Häntzschel, Marc Schrinner, Rolf-dieter Hund, Heike Hund, Christian Lück, Andrij PichAbstract:In the present work, we have used aqueous Microgels as containers for the deposition of silver nanoparticles (AgNPs). It has been shown that AgNPs can be effectively incorporated in the microgel interior during the in situ reduction of silver ions. Obtained hybrid Microgels with variable AgNPs loading (from 1 to 12 wt.-%) have been used as antibacterial agents for two bacteria types. The experimental results indicate that porous microgel structure allows the release of the silver ions from the AgNPs surface into an aqueous phase. This ensures effective reduction in the number of bacterial colonies in test plates and complete bacteria killing. The antibacterial efficiency of the microgel particles increases with AgNPs loading.
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The influence of PEG macromonomers on the size and properties of thermosensitive aqueous Microgels
Colloid and Polymer Science, 2009Co-Authors: Andrij Pich, Sebastian Berger, Olga Ornatsky, Vladimir Baranov, Mitchell A. WinnikAbstract:We describe the preparation and thermal response of aqueous Microgels based on poly( N -vinyl caprolactam) containing grafted poly(ethylene glycol) (PEG) chains. These Microgels were synthesized by free radical copolymerization of vinyl caprolactam and acetoacetoxyethyl methacrylate in the presence of methoxy-capped poly(ethylene glycol)methacrylate macromonomers. We show that variation of the amount of PEG macromonomer or the length of the PEG chain provides effective control of the microgel diameter in the range 60–220 nm. The presence of the grafted PEG chains improves the colloidal stability of the Microgels. The incorporation of the PEG macromonomers into microgel structure decreases the swelling degree and induces a shift of the volume phase transition to higher temperatures.
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Design of Multicomponent Microgels by Selective Deposition of Nanomaterials
Small (Weinheim an der Bergstrasse Germany), 2008Co-Authors: Jessica Hain, Marc Schrinner, Andrij PichAbstract:In the present paper a method for the targeted deposition of different nanomaterials on aqueous Microgels is described. In the first stage poly(3,4-ethylenedioxythiophene) (PEDOT) nanorods are introduced into the microgel structure by in situ oxidative polymerization. In the second stage hydrogen tetrachloroaurate is used to transform PEDOT chains to an oxidized state in the microgel structure, leading to the fixation of chloroaurate anions on the surface of the PEDOT nanorods. The reduction of chloroaurate ions induces the formation of gold nanoparticles (AuNPs) predominantly located on the PEDOT surface. Obtained microgel/PEDOT/AuNP hybrid particles with different nanoparticle loadings exhibit superior colloidal stability and temperature sensitivity. The microgel/PEDOT/AuNP hybrid Microgels exhibit extraordinary catalytic activity in aqueous media.