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3D printing of hydrogels usually relies on a combination of fine-tuned material chemistry and polymer chain architecture to obtain an ink with adequate yield-stress flow, shear-thinning, and self-healing behavior. Recent approaches in hydrogel ink design include introduction of reversible covalent or supramolecular bonds or jamming of microparticles into a granular hydrogel. However, the dimensional stability of such systems is typically afforded by a post-printing covalent cross-linking step that impedes further on-demand degradation of the scaffolds. Here, a jammed micro-gels ink made of thermosensitive poly(N-isopropylacrylamide) micro-gels incorporating terpyridine ligand linkers are proposed as a 3D printable ink that is cured post-printing by iron (II) cations for long-term stabilization. The uncross-linked micro-gels ink exhibits the rheological characteristics of granular materials, meaning yield-stress, shear-thinning and fast recovery. Upon curing, iron (II)-bis-terpyridine coordination complexes between neighboring micro-gels are formed. The supramolecular bonds are sufficiently strong and long-lived to maintain scaffold integrity during manual handling or immersion in liquid medium for over two months. The thermosensitivity of the micro-gels endows the printed construct with reversible and cyclable temperature-induced resolution enhancement, while the supramolecular cross-linking provides an asset of disintegration on-demand. The proposed micro-gel scaffolds are biocompatible, revealing the potential for biomedical applications and 4D bioprinting.

International audience; The colloidal stability of non-motile algal cells in water drives their distribution in space. An accurate description of the interfacial properties of microalgae is therefore critical to understand how microalgae concentrations can change in their biotope or during harvesting processes. Here, we probe the surface charges of three unicellular algae─Chlorella vulgaris, Nannochloropsis oculata, and Tetraselmis suecica─through their electrophoretic mobility. Ohshima’s soft particle theory describes the electrokinetic properties of particles covered by a permeable polyelectrolyte layer, a usual case for biological particles. The results appear to fit the predictions of Ohshima’s theory, proving that all three microalgae behave electrokinetically as soft particles. This allowed us to estimate two characteristic parameters of the polyelectrolyte external layer of microalgae: the volume charge density and the hydrodynamic penetration length. Results were compared with transmission electron microscopy observations of the algal cells’ surfaces, and in particular of their extracellular polymeric layer, which was identified with the permeable shell evidenced by electrophoretic measurements. Noticeably, the algal surface potentials estimated from electrophoretic mobility using the soft particle theory are less negative than the apparent zeta potentials. This finding indicates that electrostatics are expected to play a minor role in phenomena of environmental and industrial importance, such as microalgae aggregation or adhesion.

The loss of dispersing ability by polycarboxylates ether superplasticizers in alkali-activated slag cements has been widely reported. However, no clear-cut explanation of this phenomenon can be found to date. Therefore, the behaviour of poly(methacrylate-g-poly(ethylene glycol)) superplasticizers in NaOH or Na2CO3 -activated slag pastes was investigated. The observed loss of efficiency of the polymer was not due to a specific property of the slag particles, nor to structural degradation of the polymer in the alkaline solutions. Actually, the ionic strength of the activating solution decreased the solvent quality and changed the polymer conformation, leading to a deterioration of the steric repulsion brought by the side-chains. Moreover, in the Na2CO3 -activated systems, the adsorption behaviour of the polymers was also significantly altered. Here, this was not caused by a low calcium concentration or by a preferential adsorption of the superplasticizer on calcite crystallites. The most plausible explanation was a competitive adsorption with CO32- ions.

An original route to develop an advanced class of microgel emulsifiers containing stimulable metallo-supramolecular instead of frozen covalent cross-links is reported. The poly(N-isopropylmethacryl...

The hardening of alkali-activated slags is a complicated process that leads to the formation of cementitious materials with a lower carbon footprint than ordinary Portland cement. These materials present varying rheological, mechanical and chemical properties, depending on the used activators and the preparation method. With a rapid stiffening often observed, the last major hindrance to their industrialisation at a large scale is the control of their workability. However, the use of traditional superplasticizers as polycarboxylates ethers has had only limited effects. To shed some light on the interactions between the three components, samples of slag activated with sodium hydroxide and admixed with polycarboxylate ethers are analysed by isothermal calorimetry, rheology, adsorption measurements, and pore solution chemical analysis. Depending on the polymer structure, we discuss a possible coupling between the adsorption and conformation of the polymer at the slag surface on the one hand, and solution chemistry on the other hand.

International audience; Biomimetic exploration of stimuli-responsive and crack-resistant hydrogels is of great academic and practical significance, although the rational design of tough hydrogels is limited by insufficient mechanism study due to the lack of imaging techniques to "see" hydrogels at mesoscale level. We designed a series of composite hydrogels with compartmentalized thermal response by incorporating aggregation-and polarity-sensitive fluorescent probes in a poly(N-isopropylacrylamide) (PNIPAM) network grafted with poly(N,N-dimethylacrylamide) side-chains. We explore the fluorescence technique as a powerful tool to directly visualize their hydrophilicity-hydrophobicity transformation and the composition-dependent microphase separation. Based on the morphological observation and mechanical measurements, the concept of morphomechanics with a comprehensive mechanism clarification is proposed. In this regard, the thermoresponsive toughening are attributed to the formation of multiple noncovalent interactions and the conformational changes of PNIPAM chains. The enhanced fracture energy by crack multifurcation is related to the tearing-like disruption of weak interfaces between the separated phases.

Fibrin is a key protein for various clinical applications such as tissue reconstruction. However, in contrast to type I collagen, fibrin shaping has so far faced major limitations related to the necessity to add thrombin enzyme to fibrinogen precursors to induce fibrin self-assembly. Here we report a thrombin-free gelation pathway of fibrinogen solutions by incubation at 37°C in mild acidic conditions. We unravel the biochemical mechanisms underlying the gelation process and draw comparison between fibrinogen and fibrin at both molecular and supramolecular levels in these conditions. The protocol enables to control the viscosity of fibrin(ogen) solutions, and to induce fibrin(ogen) gel formation by simple 37°C incubation, with a reinforcement effect at neutralization. It facilitates processing of fibrin(ogen) materials, for coating, molding and extrusion, and offers new possibilities such as 3D printing. This approach is further compatible with type I collagen processing and can provide advanced tissue engineering scaffolds with high bioactivity.

International audience; Understanding confined flows of complex fluids requires simultaneous access to the mechanical behaviour of the liquid and the boundary condition at the interfaces. Here, we use evanescent wave microscopy to investigate near-surface flows of semi-dilute, unentangled polyacrylamide solutions. By using both neutral and anionic polymers, we show that monomer charge plays a key role in confined polymer dynamics. For solutions in contact with glass, the neutral polymers display chain-sized adsorbed layers, while a shear-rate-dependent apparent slip length is observed for anionic polymer solutions. The slip lengths measured at all concentrations collapse onto a master curve when scaled using a simple two-layer depletion model with non-Newtonian viscosity. A transition from an apparent slip boundary condition to a chain-sized adsorption layer is moreover highlighted by screening the charge with additional salt in the anionic polymer solutions. We anticipate that our study will be a starting point for more complex studies relating the polymer dynamics at interfaces to their chemical and physical composition.

International audience; The objective of this work is to synthesize highly stable thermoresponsive microgels that could be used in diverse applications. To achieve this, N-isopropylacrylamide (NiPAM) based microgels were first synthesized by surfactant-free precipitation polymerization of NiPAM in the presence of poly(ethylene glycol)methacrylate (PEG) as a macro-comonomer and methylenebisacrylamide (MBA) as a chemical crosslinker. By combining a complete set of techniques such as dynamic light scattering (DLS), scanning electron microscopy (SEM), zetametry, 1H NMR and micro-differential scanning calorimetry (mDSC), we clearly demonstrate that (i) the incorporation of the PEG chains controls the size and the polydispersity of the NiPAM-based microgels, whereas the thermal behavior in solution (enthalpy, volume phase transition temperature (VPTT)) remains almost the same as for pure NiPAM microgels; (ii) the PEG chains are mainly located on the microgel periphery; and (iii) the presence of the PEG chains strongly increases the colloidal stability of microgels in electrolyte solutions at high temperatures.

International audience; The combination of supramolecular chemistry and soft colloids as microgels represents an ambitious way to develop multi‐versatile colloidal assemblies. Hereafter, terpyridine‐functionalized poly(N‐isopropylacrylamide) (PNiPAM) microgel building blocks are shown to undergo an assemble–freeze–disassemble process. The microgel assemblies, which are controlled by monitoring the attractive and repulsive potentials between the soft colloidal particles, are then frozen by forming inter‐particle metal–terpyridine bis‐complexes upon addition of the metallic cation (such as FeII, CoII). By oxidation of the metal–terpyridine bis‐complex links, the aggregates open up, which is due to the complex dissociation releasing the connected particles in the form of single microgels. We extended our work to the development of 1D filaments and 2D membranes materials made of soft particles connected via supramolecular chemistry.

Effective remote control of mechanical toughening can be achieved by using thermo-responsive grafts such as poly(N-isopropylacrylamide) (PNIPAm) in a hydrophilic covalently cross-linked polymer network. The weight ratio of PNIPAm grafts in the network may impart such a thermo-responsive mechanical reinforcement. Here, we show that the network topology – especially graft length – is likewise crucial. A series of covalently cross-linked poly(N,N-dimethylacrylamide) (PDMA) gels grafted with PNIPAm side-chains of different lengths were designed and studied on both sides of phase separation temperature Tc, at a fixed overall polymer concentration of 16.7 wt% and constant PDMA/PNIPAm weight ratio. Phase-separated PNIPAm organic micro-domains were expected to act as responsive fillers above Tc and to generate a purely organic nanocomposite (NC). In contrast to conventional NC gels where dissipative processes take place at the solid nanoparticle/matrix interface, here dissipation originates from the disruption of the filler itself by the unravelling of the PNIPAm grafts embedded in collapsed domains. Results show that PNIPAm graft length is a key parameter to enhance – reversibly and on-demand – the mechanical response. The longer the graft is, the more effective the mechanical toughening is. Interestingly, for long PNIPAm grafts, above Tc, the hydrogels combine perfect transparency together with both increased stiffness and fracture toughness (up to 150 J m−2) at constant macroscopic volume. As a proof of concept, stimuli-responsive adhesion and shape-memory properties were designed to probe the inter-chain bridging efficiency (in bulk or bridging the interface).

The present work aims at studying the outcome and kinetics of competitive adsorption between low and high molar mass chains of neutral polyacrylamide (PAM) or partially hydrolyzed polyacrylamide (HPAM) in aqueous solution at the surface of siliceous material. Monodisperse neutral and charged polymers, PAM and HPAM, were synthesized by RAFT/MADIX polymerization and their adsorption, alone or in competitive process, was studied. The analysis of adsorption measurements were carried out quantitatively by size exclusion chromatography which allows for distinguishing the relative adsorption of the chains depending on their molar masses. The effect of the average molar mass, dispersity as well as the kinetics of the displacement of pre-adsorbed polymer chains onto the surface by longer chains was investigated. We evidenced that both PAM and HPAM exhibit the same trend. Close to surface saturation, the high molar mass chains desorb polymer chains of lower molar mass. Moreover, by mixing different monodisperse polymers we were able to model the behavior of the polydisperse systems usually encountered in practical applications. By following adsorption over time, our results show that while low molar mass polymers diffuse rapidly and adsorb first, they are displaced by high molar mass ones once they reach the surface. This result remains unchanged even if the low molar mass chains are added several hours before the higher ones, showing that there is no kinetic limitation to the displacement of low molar mass PAM and HPAM by higher molar mass ones. The understanding and prediction of this complex competitive adsorption behavior over time is of utter importance for the control of the mechanism of action of these polymers notably in industrial processes.

International audience; Hypothesis: Adsorption of high molecular mass polymers impacts flow in porous media. In the industrially crucial case of acrylamide-based polymers in porous silicates, the very occurrence of adsorption is still debated. Thus, the present work aimed at establishing a clear correlation between adsorption of acrylamide-based polymers and injectivity loss in porous silica. Experiments: A review of the literature revealed apparent discrepancies regarding the affinity of acrylamide-based polymers for siliceous materials having ostensibly the same chemical composition. Through a deeper analysis of the reported literature and new experimental measurements on well-defined polymers and surfaces, we investigated the relation between the silica surface properties and the acrylamide-based polymer adsorption. Our observations were confronted with water injection experiments in porous media of different surface compositions previously put in contact with polymers. Findings: The polymer affinity towards the silica surface depended on the density of hydroxyl groups at the surface of the oxide, its thermal treatment, storage condition and purity. This demonstrated that the impact of adsorption on acrylamide-based polymer flow within porous silicates heavily depends on the silicate surface composition and must be carefully evaluated. In view of the continually expanding use of acrylamide-based polymers, notably in enhanced oil recovery, such considerations provide interesting insights into the effect of adsorption on their flow into porous materials.

International audience; A new electrochemical label has been developed, which is made up of silver nanoparticles (AgNPs) coated with a mixture of zwitterionic and biotinylated zwitterionic polymers. These polymers improve colloidal stability in physiological medium and ensure biorecognition while direct electrochemical oxidation of silver nanoparticles strongly enhances the detection signal. The resulting hybrid nanomaterials are used as labels in the electrochemical sensing of avidin using sandwich assays elaborated using the biotin-avidin biorecognition system.

International audience; Dual thermo-responsive chemical hydrogels, combining poly(N-isopropylacrylamide) (PNIPAm) side-chains within a poly(N-acryloylglycinamide) (PNAGA) network, were designed following a simple and versatile procedure. These hydrogels exhibit two phase transitions both at low (upper critical solution temperature, UCST) and high (lower critical solution temperature, LCST) temperatures thereby modifying their swelling, rheological and mechanical properties. These novel thermo-schizophrenic hydrogels pave the way for the development of thermo-toughening wet materials in a broad range of temperatures.-2

International audience; We investigate the colloidal stability of gold nanoparticles (AuNPs) coated with zwitterionic sulfobetaine polymers in aqueous solution. Zwitterionic polymers with different molar masses, synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization of N,N'-dimethyl(methacrylamido propyl)ammonium propanesulfonate (SPP) exhibit a well known Upper Critical Solution Temperature (UCST) in water, i.e., phase separate at low temperature. The colloidal stability of gold nanoparticles grafted with PSPP was studied as a function of the temperature. The effects of the molar mass of the grafted polymers, the salt concentration, and the presence of free polymer chains in solution were investigated. UV-vis spectroscopy and dynamic light scattering measurements show that whatever the molar mass of the grafted polymer, the nanoparticles never aggregate at low temperature in pure water. However, a reversible thermal-driven aggregation process of the gold nanoparticles is observed in presence of free polymer chains in solution and explained by a depletion process. (C) 2014 Elsevier Inc. All rights reserved.

PolyCarboxylate ether-based superplasticizers (PCEs) are a type of comb-shaped copolymers used as polymeric dispersants in cementitious materials. PCEs have a high degree of dispersity, which limits the suitability of conventional characterization techniques, such as Size Exclusion Chromatography (SEC). Properties of PCEs strongly depend on their molecular structure and a comprehensive characterization is needed to fully understand the structure–property relationships. PCEs with well-defined molecular structures were synthesized to study their solution conformation by SEC and scattering techniques. The combined use of SEC, dynamic light scattering and small-angle neutron scattering allowed us to demonstrate the validity of a scaling law describing the radius of gyration of comb-shaped copolymers as a function of their molecular structure. Moreover, we show that the use of SEC with standard calibration, although widely spread, is not adequate for PCEs.

Hydrophilic and LCST polymer chains, poly(N,N-dimethylacrylamide) (PDMA) and poly(Nisopropylacrylamide)(PNIPA), were combined in semi-interpenetrated architectures toinvestigate their responsive properties in swollen isochoric conditions comparatively tografted network structures. Using equal weight fractions of PDMA and PNIPA, semi-IPNdesigned with opposite topologies have demonstrated a thermoresponsive behavior with verydifferent structure/properties relationships as investigated by calorimetry, swellingexperiments, tensile tests and 2D neutron scattering at rest and under deformation. In the caseof the PDMA network interpenetrated by linear PNIPA chains, the phase transition of PNIPAgives rise to the formation of large microdomains, loosely percolating the PDMA network.Above the transition, the enhancement of the mechanical properties remains low in terms ofelastic modulus and fracture energy. Conversely, the opposite topology, with PDMA chainsinterpenetrating the crosslinked PNIPA network, brings a large improvement of themechanical properties at high temperature with a 10-fold increase of the modulus and veryhigh fracture energy. By comparison with grafted hydrogels of similar composition anddifferent topologies, the impact of the primary structure over the phase-separated morphologyand the resulting mechanical properties was clearly highlighted., Macromolecules, American Chemical Society, 2016

International audience; A novel mode of gel toughening displaying crack bifurcation is highlighted in phase-separated hydrogels. By exploring original covalent network topologies, phase-separated gels under isochoric conditions demonstrate advanced thermoresponsive mechanical properties: excellent fatigue resistance, self-healing, and remarkable fracture energies. Beyond the phase-transition temperature, the fracture proceeds by a systematic crack-bifurcation process, unreported so far in gels.

International audience; The challenge of this work was to investigate the role of topology in LCST hydrogels that strongly and reversibly thermo-reinforce their mechanical strength under isochoric conditions. To achieve this, two different hydrogels with opposite topologies were designed on the basis of grafted architectures using equal amounts of water-soluble chains (poly(N,N-dimethylacrylamide) = PDMA) and LCST polymer chains (poly(N-isopropylacrylamide) = PNIPA). By working under isochoric conditions, with almost 85 wt % of water in the whole temperature range (20–60 °C), we were able to clearly highlight the impact of the phase transition of PNIPA on the mechanical reinforcement of the gel without any interference of the volume transition. These graft hydrogels, designed with PNIPA in the backbone (GPN-D) or as pendant chains (GPD-N), have been studied more specifically by tensile tests and 2D neutron scattering at rest and under deformation. From these complementary techniques, we show that PNIPA side-chains in GPD-N self-assemble above their transition temperature into a micellar network greatly interfering with the covalent PDMA frame. While the elastic modulus increases reversibly more than ten times throughout the phase transition, other properties like elongation at break and fracture resistance are greatly enhanced with temperature. At high temperature and under extension, SANS data highlight the affine deformation of PNIPA domains. By comparison, the opposite topology with PNIPA forming the cross-linked backbone undergoes a similar phase separation with temperature and gives rise to a bicontinuous structure that aligns under loading. The collapsed phase being topologically defined as the load bearing phase, GPN-D displays remarkable fracture toughening with crack bifurcation at high temperature whereas GPD-N gels fracture in a more conventional way.

Highly monodisperse poly(N-isopropylacrylamide), PNiPAM, microgels were prepared by the conventional radical polymerization of NiPAM in the presence of dimethylamino ethyl methacrylate (DMAEMA) monomers at various concentrations. The effect of DMAEMA on the polymerization of PNiPAM microgels was examined at constant initiator (V50) and cross-linker (MBA) concentrations. The presence of DMAEMA in the synthesis batch allows for the preparation of PNiPAM microgels with controlled size and a narrow size distribution. The oil(dodecane)/water interfacial properties of the model PNiPAM microgels were then investigated. The pendant drop technique was used to measure the interfacial tensions as a function of temperature. Over the whole range of temperature (20-45 degrees C), the interfacial tension remains low (on the order of 17 mN/m) and goes through a minimum (12 mN/m) at a temperature of about 34 degrees C, which well matches the volume phase transition temperature (VPTT) of PNiPAM microgels. Below the VPTT, the decrease in the interfacial tension with temperature is likely to be due to the adsorption of dense layers because of the decrease of the excluded volume interactions. Above the VPTT, we suggest that the increase in the interfacial tension with temperature comes from the adsorption of loosely packed PNiPAM microgels. We also studied the effect of temperature on the stability of emulsions. Dodecane in water emulsions, which form at ambient temperature, are destabilized as the temperature exceeds the VPTT. In light of the interfacial tension results, we suggest that emulsion destabilization arises from the adsorption of aggregates above the VPTT and not from an important desorption of microgels. Aggregate adsorption would bring a sufficiently high number of dodecane molecules into contact with water to induce coalescence without changing the interfacial tension very much.

Two amino-terminated amphiphilic copolymers, M600 and M1000, with different ethylene oxide to propylene oxide EO/PO ratios, 1/9 and 19/3, respectively, were coupled by thioctic acid, which allows an excellent affinity with gold surface. Then, amphiphilic thermally responsive gold nanoparticles (AuNPs) were prepared either by ligands exchange on precursor gold nanoparticles or by direct reduction of gold source in presence of stabilizing copolymers. The as-obtained AuNPs are monodisperse with a size varying from 2 to 17 nm depending on the synthesis used. The main parameters controlling the AuNPs assemblies were identified: the ethylene oxide to propylene oxide ratio in the polymer corona, the ionic strength of the solution, and the curvature of AuNPs. An interesting result is the possibility to tune the aggregation temperature from 8 to 15 degrees C of AuNPs coated by the same polymer only by changing the curvature of the AuNPs from 17 to 2 nm. This temperature change versus the curvature of the nanoparticle is ascribed to the decrease in hydration volume per hydrophilic group in the corona due to the change of the polymer chain conformation with changing the particle size. Moreover, one unique aggregation temperature between 12 and 60 degrees C can be also obtained by mixing copolymers with different EO/PO ratios. Then, the corona, constituted by a mixture of polymers, behaves as a corona composed by an average statistic copolymer with the intermediate composition.

We report the synthesis of zwitterionic poly(N,N-dimethyl-N-(3-methacrylamidopropyl)-N-(3-sulfopropyl) ammonium betaine-isopropylacrylamide) (poly(NIPAm-SPP)) microgels prepared by free-radical precipitation polymerization. We investigated the influence of the amount of SPP and the effect of the variations in temperature, pH, and electrolyte concentration on the microgel dimensions. In the range of the concentrations of SPP studied in the present work, no expected antipolyelectrolyte behavior of the microgels was observed and the particles showed polyelectrolyte properties. The zwitterionic properties of the microgels were used for in situ template-based synthesis of gold, silver, and bimetallic gold−silver nanoparticles.

International audience; This work, based on structure/properties relationships of associating polymers, aims to investigate the role of topology in the self-assembling behavior of responsive graft copolymers. For that purpose, two graft copolymers with inverse topologies were prepared with similar amounts of water-soluble chains (poly(N,N-dimethylacrylamide) = PDMA) and LCST polymer chains (poly(N-isopropylacrylamide) = PNIPA). In pure water, and above 3 wt%, PNIPA-g-PDMA and PDMA-g-PNIPA exhibit very similar macroscopic properties with a sol/gel transition above 35 °C related to the microphase separation of PNIPA sequences. From complementary experiments, performed by DSC, 1H NMR and small angle neutron scattering, we show that the phase transition of PNIPA is more abrupt when NIPA units are located within the backbone, compared to side-chains. Nevertheless, well above their transition temperature, the two copolymers display very similar bicontinuous structures where PNIPA sequences self aggregate into concentrated percolating domains (about 70 wt% at 60 °C) characterized by a frozen dynamics. On the other hand, when salt or surfactant molecules are added into unentangled semi-dilute aqueous solution, the PNIPA-g-PDMA sample does not percolate anymore above the transition temperature while PDMA-g-PNIPA still demonstrate thermothickening properties that are correlated to the ability of water-soluble PDMA chains to bridge PNIPA aggregates.

Photothermally driven volume transitions in polymer microgels have promising applications for site-specific drug delivery and photodynamic therapy. We studied the temperature-induced volume phase transitions for a series of thermoresponsive microgels of various compositions to find a system with a sharp transition in the physiologically relevant range spanning 38-41 degrees C in 0.01 M phosphate-buffered saline solution (pH = 7.4). We found that the poly(N-isopropylacrylamide-maleic acid) microgels showed an 8-fold decrease in size under the aforementioned conditions. These microgels were loaded with gold nanorods designed to absorb in the near-IR spectral range. Following irradiation at lambda = 809 nm, the microgels underwent a large, reversible, photothermally triggered change in volume. We believe that this microgel system is a promising candidate for photothermally controlled drug release.

A family of nanocomposites formed by intercalation of negatively charged Ni-based nanoparticles in Mg/Al layered double hydroxide (LDH) has been prepared by following the anion exchange route. The composites differ by the amount of loaded Ni entities. Suspensions of Ni nanoparticles have been priorily prepared by controlled hydroxylation of Ni2+ cations in the presence of citrate complexing ions. Intercalated Ni complex colloids exhibit the same behavior in the different composites upon reduction. The nanocomposite route leads after reduction at 1023 K to controlled amounts of metal Ni nanoparticles presenting a similar mean size of 5 nm and a high degree of dispersion on a magnesium/aluminum oxide matrix.

We recently reported on the controlled formation of highly stable metal hydroxide nanoparticles. Growth control and stabilization of particles were achieved by performing hydrolysis and polycondensation reactions of polymer-complexed metal cations, the polymers being double hydrophilic block copolymers (DHBCs). The present paper focuses on the characterization of the intermediate species in the formation process, namely the mixture of multivalent metal cations plus the oppositely charged polyelectrolyte–neutral block copolymers. Complexation of metal cations by the anionic block of the DHBCs leads to the spontaneous formation of colloidal objects. Small angle neutron scattering experiments show that the aggregates exhibit a well defined core–corona architecture: the core is compact and homogeneous while the diffuse corona is constituted of polymer segments in a good solvent. The core formation is due to the water insoluble metal cation–polyacrylate complex while the corona is constituted of the water soluble neutral polymer blocks. Cryo-TEM images allowed the revelation of well-dispersed inorganic-rich domains. The presence of the longer neutral blocks prevents macroscopic phase separation of the complex and leads to the formation of hybrid micellar aggregates.

International audience; We report the behavior of thermosensitive soft microgel particles adsorbed at the air-water interface. We study the effect of temperature on the adsorption, interfacial diffusion, and surface rheology of pure N-isopropylacrylamide (NiPAM) microgel particles at the air-water interface. We find that the surface tensions of the solutions are the same as those of polyNiPAM solution; hence, their adsorption properties are dominated by the surface activity of the NiPAM repeat units of the particles. Particle-tracking experiments show that the particles adsorb irreversibly at the interface and form stable clusters at very low concentrations, e.g., 5.10(-3) wt%. We suggest that attractions between dangling arms or capillary interaction may be responsible for the formation of these clusters. For concentrations above 10(-2) wt%, the interface is filled with particles, and their Brownian diffusivity is arrested. The compression elastic moduli-measured using the pendant drop method-are one or two orders of magnitude below those obtained for hard particles and NiPAM chains, and their value is probably dominated by the intrinsic compressibility of the particles. The thin liquid films made from microgels exhibit a symmetric drainage, consistent with a high surface viscosity, but their lifetime is surprisingly short, illustrating the fragility of the films. We observed the formation of a monolayer of microgels bridging the two interfaces of the film outside the dimple. This zone grows and thins over time to a point where the microgels are highly compressed and stretched, resulting in the rupture of the film

International audience; A new cold nanowelding technique for cetyltrimethylammonium bromide (CTAB)-stabilized colloidal nanorods in water is reported. This technique leads to the formation of micrometric nanowires by end-to-end self-organization and welding of nanorods. This cold welding strategy could be generally applicable to colloidal nanoparticles and opens new outlooks for the bottom-up fabrication of nanodevices using colloidal building blocks.

International audience; Hybrid polyion complex (HPIC) micelles are nanoaggregates obtained by complexation of multivalent metal ions by double hydrophilic block copolymers (DHBC). Solutions of DHBC such as the poly(acrylic acid)-block-poly(acrylamide) (PAA-b-PAM) or poly(acrylic acid)-block-poly(2-hydroxyethylacrylate) (PAA-b-PHEA), constituted of an ionizable complexing block and a neutral stabilizing block, were mixed with solutions of metal ions, which are either monoatomic ions or metal polycations, such as Al3+, La3+, or Al-13(7+). The physicochemical properties of the HPIC micelles were investigated by small angle neutron scattering (SANS) and dynamic light scattering (DLS) as a function of the polymer block lengths and the nature of the cation. Mixtures of metal cations and asymmetric block copolymers with a complexing block smaller than the stabilizing block lead to the formation of stable colloidal HPIC micelles. The hydrodynamic radius of the HPIC micelles varies with the polymer molecular weight as M-0.6. In addition, the variation of R-h of the HPIC micelle is stronger when the complexing block length is increased than when the neutral block length is increased. R-h is highly sensitive to the polymer asymmetry degree (block weight ratio), and this is even more true when the polymer asymmetry degree goes down to values close to 3. SANS experiments reveal that HPIC micelles exhibit a well-defined core-corona nanostructure; the core is formed by the insoluble dense poly(acrylate)/metal cation complex, and the diffuse corona is constituted of swollen neutral polymer chains. The scattering curves were modeled by an analytical function of the form factor; the fitting parameters of the Pedersen's model provide information on the core size, the corona thickness, and the aggregation number of the micelles. For a given metal ion, the micelle core radius increases as the PAA block length. The radius of gyration of the micelle is very close to the value of the core radius, while it varies very weakly with the neutral block length. Nevertheless, the radius of gyration of the micelle is highly dependent on the asymmetry degree of the polymer: if the neutral block length increases in a large extent, the micelle radius of gyration decreases due to a decrease of the micelle aggregation number. The variation of the R-g/R-h ratio as a function of the polymer block lengths confirms the nanostructure associating a dense spherical core and a diffuse corona. Finally, the high stability of HPIC micelles with increasing concentration is the result of the nature of the coordination complex bonds in the micelle core.

Aggregation of thermosensitive polymer-coated gold nanoparticles was performed in aqueous solution in the presence of a triblock copolymer poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic P123, PEO(20)-PPO(68)-PEO(20)). The gold nanoparticles, AuNPs, which are covered by thermosensitive statistical copolymers poly(EO(x)-st-PO(y)), aggregate when the temperature is higher than the phase transition temperature of the polymer, leading to a macroscopic precipitation. The presence of Pluronic chains in solution prevents the uncontrolled aggregation of the AuNPs at higher temperature than both the aggregation temperature of the AuNPs (T(agg)) and the critical micellization temperature (cmt) of the Pluronic. The size, the colloidal stability, and the optical properties of the AuNPs aggregates are modulated as a function of the P123-to-AuNP ratio, which constitutes the critical parameter of the system. Moreover, the AuNP aggregation is totally reversible upon decreasing the temperature below T(agg). Our approach constitutes an easy way to the formation of well-controlled nanoparticle aggregates with well-defined sizes. The resulting aggregates have been characterized by UV-vis spectroscopy, dynamic light scattering, and electron microscopy.

International audience; The formation of thermoresponsive poly(N,N-diethylacrylamide) (PDEAAm) nanogels via an aqueous dispersion polymerization process in the presence of poly(ethylene oxide)-b-poly(N,Ndimethylacrylamide) macromolecular reversible addition-fragmentation chain transfer agents (macroRAFT agents) was studied. The latter exhibit a hydrophobic trithiocarbonate reactive group with a dodecyl substituent, and had previously proved to act simultaneously as control agents and stabilizers in such a synthesis process (Rieger et al., J. Polym. Sci. Part A: Polym. Chem., 2009, 47, 2373). The nanogel size and stability were found to depend strongly on the chain length of the macroRAFT agents, but also on the crosslinker (N,N 0-methylene bisacrylamide) and monomer concentrations. The aim of the present work was to better understand the mechanisms that govern the nanogel formation in such heterogeneous polymerization conditions performed under RAFT control, with special emphasis on the role of the macroRAFT agents. In the first part, the aqueous solution properties of the macroRAFT agents in the conditions of the dispersion polymerizations were studied by light scattering and fluorescence spectroscopy and it was found that they self-assemble to form star micelles. In the second part, the nanogel formation at different DEAAm and crosslinker concentrations was monitored by dynamic and static light scattering, and by size exclusion chromatography. It appeared that at low monomer conversion the calculated number of chains per nanogel particle was close to the aggregation number, N agg , of the macroRAFT agent micelles. With increasing conversions, however, the number of chains clearly increased and exceeded the initial N agg. Higher monomer concentrations hardly influenced the formation process and thus the gel particle size, whereas enhanced crosslinker concentration had a strong impact on the latter. These results strongly suggest that precursor particles are formed very rapidly at the polymerization onset and then aggregate with each other to form complex inter-crosslinked particles.

We have developed a novel surface coating for semiconductor quantum dots (QDs) based on a heterobifunctional ligand that overcomes most of the previous limits of these fluorescent probes in bioimaging applications. Here we show that QDs capped with bidentate zwitterionic dihydrolipoic acid-sulfobetaine (DHLA-SB) ligands are a favorable alternative to polyethylene glycol-coated nanoparticles since they combine small sizes, low nonspecific adsorption, preserved optical properties, and excellent stability over time and a wide range of pH and salinity. Additionally, these QDs can easily be functionalized with biomolecules such as streptavidin (SA) and biotin. We applied streptavidin-functionalized DHLA-SB QDs to track the intracellular recycling of cannabinoid receptor 1 (CB1R) in live cells. These QDs selectively recognized the pool of receptors at the cell surface via SA-biotin interactions with negligible nonspecific adsorption. The QDs retained their optical properties, allowing the internalization of CB1R into endosomes to be followed. Moreover, the cellular activity was apparently unaffected by the probe.

Stable hairy lanthanum hydroxide nanoparticles were synthesized in water by performing hydrolysis and condensation reactions of lanthanum cations in the presence of double hydrophilic polyacrylic acid-b-polyacrylamide block copolymers (PAA-b-PAM). In the first step, the addition of asymmetric PAA-b-PAM copolymers (M-w,M-PAA < M-w,M-PAM) to lanthanum salt solutions, both at pH = 5.5, induces the formation of monodispersed micellar aggregates, which are predominantly isotropic. The core of the hybrid aggregates is constituted of a lanthanum polyacrylate complex whose formation is due to bidentate coordination bonding between La3+ and acrylate groups, as shown by ATR-FTIR experiments and pH measurements. The size of the micellar aggregates depends on the molecular weight of the copolymer but is independent of the copolymer to metal ratio in solution. In the second step, the hydrolysis of lanthanum ions is induced by addition of a strong base such as sodium hydroxide. Either. occulated suspensions or stable anisotropic or spherical nanoparticles of lanthanum hydrolysis products were obtained depending on the metal complexation ratio [ acrylate]/[La]. The variation of that parameter also enables the control of the size of the core-corona nanoparticles obtained by lanthanum hydroxylation. The asymmetry degree of the copolymer was shown to influence both the size and the shape of the particles. Elongated particles with a high aspect ratio, up to 10, were obtained with very asymmetric copolymers (M-w,M-PAM/ M-w,M-PAA >= 10) while shorter rice grain- like particles were obtained with a less asymmetric copolymer. The asymmetry degree also influences the value of the critical metal complexation degree required to obtain stable colloidal suspensions of polymer-stabilized lanthanum hydroxide.

The present paper describes a simple route to prepare organic-inorganic colloids with a core-corona structure. Colloids are obtained by complexation of multivalent metal cations by anionic-neutral double hydrophilic block copolymers leading to hybrid polyion complex micelles. The hybrid colloids can then be mineralized in suspension by performing hydrolysis of metal cations within the micelles. The present study focuses on the structural characterization of the colloidal complexes and of the mineralized nanoparticles using a combination of transmission electron microscopy (TEM ) techniques including conventional bright-field imaging (with and without negative staining) and cryo-TEM observations. It is shown that the different types of TEM observations are complementary and necessary to get a complete picture of the core-corona colloids.

Ni nanoparticle/layered double hydroxides (LDH) composites were prepared with the aim to obtain precursors of supported Ni catalysts exhibiting well dispersed metal particles of controlled size. Three different preparation methods relying on host-guest interaction between colloidal suspensions of Ni nanoparticles and Mg/Al LDH or oxide were investigated. Ni based colloids were prepared by controlled hydroxylation of metal cations in the presence of various amounts of citrate complexing agents. A careful control of the charge and size of the Ni-based colloids allowed to tailor the Ni nanoparticle sizes in the final reduced samples only when the Ni/LDH composites were prepared by the anionic exchange preparation route.

This review compares conventional and controlled radical polymerization techniques and processes in preparing nano-/microgels. Special focus is made on the synthetic parameters that allow controlling their size, morphology, composition, and structural homogeneity.

Double hydrophilic block copolymers were used to control the growth of inorganic particles and directly prepare hybrid colloidal suspensions. Colloids of metal hydrous oxides were obtained by forced hydrolysis of metal ions in presence of the copolymers. The block copolymers contain a metal-complexing polyelectrolyte block and a stabilizing neutral block. The role of the first block is to ensure a controlled growth of the inorganic phase, while simultaneously, the second block ensures the colloidal stabilization. Phase diagrams presenting the conditions under which precipitation is inhibited are established. The nanoparticles are then characterized in terms of sizes, morphologies and surface charges. The main parameters controlling the size were identified: the copolymer-to-metal ratio and the metal prehydrolysis ratio. The synthesis steps were characterized. First, a key step of induced micellization of the hydrophilic copolymers leads to hybrid core-shell assemblies. The second step consists in mineralization of the micellar core. The suspension polycondensation leads to hairy particles whose morphologies depend on the nature of the metal and on synthesis parameters.

We report on the synthesis of stimulable microgels that are used as building-block for colloidal assemblies in dispersions or at interfaces. To achieve this goal, we synthesized thermosensitive poly(N-isopropylacrylamide), PNiPAM, microgels copolymerized with poly(ethyleneglycol) grafts bearing either a hydroxyl (PEGMAOH) or a terpyridine (PEGMATpy) terminated function. The incorporation and localization of the PEGylated grafts within the microgels network enables a control on both the size and colloidal stability of the microgels without changing their thermosensitivity. The functionalized microgels were then used as building-blocks to build assemblies in dispersions by means of metallo-supramolecular interactions. These interactions are induced by the formation of coordination complexes, [MIITpy2]2+, between the terpyridine functions of the microgels and metallic cations (FeII, CoII, …). We studied the effects of physico-chemical parameters such as salinity, temperature, pH, addition of a depletant polymer on the formation of inter-microgels assemblies. The stimulability via an oxidative medium of the supramolecular interactions allows to dissociating the assemblies into individualized microgels in solution. The formation of [MIITpy2]2+ complexes also allows the synthesis of supramolecular microgels, supra-MG, which internal structure is maintained by supramolecular crosslinks. These microgels, which network structure can be cleaved, are used as emulsifiers of Pickering-Ramsden emulsions. The liquid-liquid dispersions can be destabilized on demand by electrochemical stimulation., Nous avons élaboré des microgels stimulables pouvant servir de briques élémentaires pour des assemblages colloïdaux en dispersion ou aux interfaces. Pour cela, des microgels thermosensibles de poly(N-isopropylacrylamide), PNiPAM, co-polymérisés avec des greffons poly(éthylèneglycol) terminés par une fonction soit hydroxyle (PEGMAOH) soit terpyridine (PEGMATpy) sont synthétisés. L’incorporation et la localisation des greffons PEGylés dans le réseau des microgels permet de contrôler la taille et la stabilité colloïdale des microgels sans affecter leurs propriétés thermosensibles. Les microgels fonctionnalisés sont utilisés comme briques élémentaires pour former des assemblages en dispersion via des interactions métallo-supramoléculaires. Ces interactions sont induites par la formation de complexes de coordination, [MIITpy2]2+, entre les fonctions terpyridine portées par les microgels et des cations métalliques (FeII, CoII, …). L’effet de paramètres physico-chimiques tels que la salinité, la température, le pH, l’ajout d’un polymère déplétant sur la formation d’assemblages entre microgels est étudié. La stimulabilité des interactions supramoléculaires en milieu oxydant permet de dissocier les assemblages formés en microgels individualisés en solution. La formation des complexes [MIITpy2]2+ permet également la synthèse de microgels supramoléculaires, supra-MG, dont la structure interne est contrainte par des points de réticulation supramoléculaires. Ces microgels dont la structure interne est clivable sont utilisés comme émulsifiants d’émulsions de type Pickering-Ramsden pouvant être déstabilisées par stimulation électrochimique.

Thermo-responsive linear graft copolymers and hydrogels with different topologies have been designed and their nanostructure, their rheological properties as well as their tunable mechanical properties have been investigated. In the case of hydrogels, the self-assembly of the thermo-responsive sequences, which serve as secondary interactions, induces in isochoric conditions a strong enhancement of both stiffness and elongation at break, including also remarkable fatigue properties. Specifically, this reinforcement is totally reversible by switching on/off the associations. It is clearly shown that the topology of the network displays a crucial influence on the mechanical performance of hydrogels, especially the resistance to fracture. After a careful investigation of the structure by 2-D neutron scattering and tensile experiments, different nanostructures are proposed according to the topology. Finally, this concept of thermo-toughening of hydrogels through a controlled microphase separation has been extended to other polymeric networks combining LCST and UCST type polymers., Différentes architectures macromoléculaires sensibles à la température, des copolymères linéaires greffés et des hydrogels, ont été développées et leur structure, leurs propriétés rhéologiques ainsi que leurs propriétés mécaniques ont été étudiées. Dans le cas des hydrogels, le phénomène de séparation de phase des segments thermosensibles conduit, en conditions isochores, à une augmentation de la rigidité et de l'élongation à la rupture ainsi qu'à de remarquables propriétés de fatigue. Ce renforcement est de plus totalement réversible en pilotant le processus d'association/dissociation des interactions avec la température. Nous montrons que la topologie des réseaux joue un rôle important sur les performances mécaniques des hydrogels et plus spécialement sur le mode de propagation de fissure au sein de la structure. A partir d'études structurales par diffusion de neutrons complétées par des expériences sous traction, différentes nanostructures sont proposées en fonction de la topologie. Enfin, ce concept de renforcement stimulable des propriétés mécaniques des hydrogels, induit par un mécanisme de micro-séparation de phase, a été élargi à d'autres réseaux polymères combinant des propriétés thermodynamiques de LCST et UCST.