Jérôme J. Crassous

RWTH Aachen University · Institute of Physical Chemistry

Cellular engulfment and uptake of macromolecular assemblies or nanoparticles via endocytosis can be associated to both healthy and disease-related biological processes as well as delivery of drug nanoparticles and potential nanotoxicity of pollutants. Depending on the physical and chemical properties of the system, the adsorbed particles may remain...

Hollow microgels are fascinating model systems at the crossover between polymer vesicles, emulsions, and colloids as they deform, interpenetrate, and eventually shrink at higher volume fraction or when subjected to an external stress. Here, we introduce a system consisting of microgels with a micrometer-sized cavity enabling a straightforward chara...

Complex‐shaped microgels are promising building blocks for soft metamaterials. Their active and remote orientational control provides significant potential in architecting them in time and space. This work describes the use of magnetically actuable microgels of complex shape for spatio‐temporal flow control and showcases the concept for microfluidi...

The rapid development in micro‐machinery enabled the investigation of smart materials that can embody fast response, programmable actuation, and flexibility to perform mechanical work. Soft magnetic actuators represent an interesting platform toward combining those properties. This study focuses on the synthesis of micro‐actuators that respond to t...

Micron‐scale anisometric microgels have received increasing attention to replace macromolecule solutions to create injectable 3D regenerative hydrogels. Interlinking these rod‐shaped microgels results in microporous constructs, while incorporating magnetic nanoparticles inside the microgels enables their alignment to introduce directionality. This...

The interactions between oppositely charged multi-indented lock- and spherical key-particles are investigated by means of Monte Carlo simulations at low volume fractions. The specificity of the interactions is initially investigated in an excess of either lock- or key-particles, and we find ordered clusters with highly directional bonds. This sugge...

Softness plays a key role in determining the macroscopic properties of colloidal systems, from synthetic nanogels to biological macromolecules, from viruses to star polymers. However, we are missing a way to quantify what the term "softness" means in nanoscience. Having quantitative parameters is fundamental to compare different systems and underst...

Microgels, cross-linked polymers with submicrometer size, are ideal soft model systems. While spherical microgels have been studied extensively, anisotropic microgels have been hardly investigated. In this study, we compare the interfacial deformation and assembly of anisotropic core-shell and hollow microgels. The core-shell microgel consists of a...

Significance Microgel aqueous dispersions are shown to display drying behavior in between that of a colloidal dispersion and a polymer solution. Like a colloidal dispersion, drying proceeds through the propagation of a drying front separating a dense film from the dispersion’s bulk. However, microgels are able to deform, interpenetrate, and deswell...

Anisotropic, submicrometer sized particles are versatile systems providing interesting features in creating ordering in 2-dimensional systems. Combining hard ellipsoids with a soft shell further enhances the opportunities to trigger and control order and alignment. In this work, we report a rich 2D phase behavior and show how softness affects the o...

Nature suggests that complex materials result from a hierarchical organization of matter at different length scales. At the nano- and micrometer scale, macromolecules and supra- molecular aggregates spontaneously assemble into supracolloidal structures whose complexity is given by the coexistence of various colloidal entities and the specific inter...

Hybrid anisotropic microgels were synthesised using mesoporous silica as core particles. By finely controlling the synthesis conditions, the latter can be obtained with different shapes such as platelets, primary particles or rods. Using the core particles as seeds for precipitation polymerisation, a crosslinked poly(N-isopropylacrylamide) (PNIPAM)...

The unique pH and temperature responsiveness of PNIPAM-based microgels make them a promising target for novel biomedical applications such as cellular drug delivery systems. However, we lack a comprehensive understanding of how the physico-chemical properties of microgels relate to their interaction with cells. Here, we show that HEK293T cells take...

A simple Pickering emulsion route has been developed for the assembly of temperature-responsive poly(N-isopropylacrylamide) (PNIPAM) microgel particles into colloidal molecules comprising a small number of discrete microgel interaction sites on a central oil emulsion droplet. Here, the surface activity of the microgels serves to drive their assembl...

Anisotropic dynamics on the colloidal length scale is ubiquitous in nature. Of particular interest is the dynamics of systems approaching a kinetically arrested state. The failure of classical techniques for investigating the dynamics of highly turbid suspensions has contributed toward the limited experimental information available up until now. Ex...

Exploiting soft, adaptive microgels as building blocks for soft materials with controlled and predictable viscoelastic properties is of great interest for both industry and fundamental research. Here the flow properties of different poly(N-isopropylacrylamide) (pNIPAM) microgels are compared: regularly crosslinked versus ultra-low crosslinked (ULC)...

The development of soft anisotropic building blocks is of great interest for various applications in soft matter. Furthermore, such systems would be important model systems for ordering phenomena in fundamental soft matter science. In this work, we address the challenge of creating hollow and anisotropically-shaped thermoresponsive microgels, polym...

Small clusters of spherical colloids that mimic real molecules, so-called colloidal molecules, hold great promise as building blocks in bottom-up routes to new materials. However, their typical hard sphere nature has hampered their assembly into ordered structures, largely due to a lack of control of the inter-particle interactions. In the present...

Thermoresponsive microgels are soft colloids that find widespread use as model systems for soft matter physics. Their complex internal architecture, made of a disordered and heterogeneous polymer network, has been so far a major challenge for computer simulations. In this work, we put forward a coarse-grained model of microgels whose structural pro...

The interaction of oppositely charged lock- and key-colloids is investigated using computer simulations. We show that indented spheres, i.e., lock-particles, can be specifically assembled with spherical key- particles using solely electrostatic interactions in addition to a hard overlap potential. An analytic description of the entropic and energet...

We develop a new strategy that involves formation of microgels (MG) decorated liquid crystal (LC) droplets, which show a remarkable stability. This system facilitates analysis of the LC droplets that...

Nanogels and microgels are soft, deformable and penetrable objects with an internal gel-like structure that is swollen by the dispersing solvent. Their softness and the potential to respond to external stimuli like temperature, pressure, pH, ionic strength and different analytes make them interesting as soft model systems in fundamental research as...

Significance Soft microgel-based colloids consisting of a responsive polymer network offer an ideal platform for exploring the interactions between nanomaterials and artificial model membranes. Here, we report a modality to pattern and assemble responsive colloids as microgels or lipogels—i.e., microgels associated with small lipid vesicles—to desi...

The lamellar-to-sponge phase transition of fluorescently labelled large unilamellar vesicles (LUVs) of the non-ionic surfactant triethylene glycol mono n-decyl ether (C10E3) was investigated in situ by confocal laser scanning microscopy (CLSM). Stable dispersions of micrometer-sized C10E3 LUVs were prepared at 20 °C and quickly heated at different...

We investigate the collective behavior of suspended thermoresponsive microgels, that expel solvent and subsequently decrease in size upon heating. Using a binary mixture of differently thermoresponsive microgels, we demonstrate how distinctly different gel structures form, depending on the heating profile used. Confocal laser scanning microscopy (C...

Thermoresponsive microgels are soft colloids that find widespread use as model systems for soft matter physics. Their complex internal architecture, made of a disordered and heterogenous polymer network, has been so far a major challenge for computer simulations. In this work we introduce an advanced coarse-grained model of microgels whose structur...

While colloids have been widely employed as models for atoms and molecules, the current study proposes to extend their use as building blocks for supracolloidal frameworks. Hereby, the self‐assembly between highly anisotropic supramolecular microtubules and soft spherical fluorescent microgels is explored using confocal laser scanning microscopy. T...

Soft particles such as polymeric microgels can form ultra-dense phases, where the average center-to-center distance a s can be smaller than the initial unperturbed particle diameter σ 0, due to their ability to interpenetrate and compress. However, despite of the effort devoted to microgels at ultrahigh densities, we know surprisingly little about...

The interplay between shape anisotropy and directed long-range interactions enables the self-assembly of complex colloidal structures. As a recent highlight, ellipsoidal particles polarized in an external electric field were observed to associate into well-defined tubular structures. In this study, we investigate systematically such directed self-a...

We describe the synthesis of hybrid magnetic ellipsoidal nanoparticles that consist of a mixture of two different iron oxide phases, hematite (α-Fe2O3) and maghemite (γ-Fe2O3), and characterize their magnetic field-driven self-assembly. We demonstrate that the relative amount of the two phases can be adjusted in a continuous way by varying the reac...

We have seen a considerable effort in colloid sciences to copy Nature’s successful strategies to fabricate complex functional structures through self-assembly. This includes attempts to design colloidal building blocks and their intermolecular interactions, such as creating the colloidal analogs of directional molecular interactions, molecular reco...

For decades, scientists and engineers have strived to design means of assembling colloids into ordered structures. By now, the literature is quite peppered with reports of colloidal assemblies. However, the available methods can assemble only a narrow range of structures or are applicable to specific types of colloids. There are still only few gene...

We characterize the structural properties of magnetic ellipsoidal hematite colloids with an aspect ratio ρ ≈ 2.3 using a combination of small-angle X-ray scattering and computer simulations. The evolution of the phase diagram with packing fraction ϕ and the strength of an applied magnetic field B is described, and the coupling between orientational...

This study explored the application of localized electric fields for reversible directed self-assembly of colloidal particles in 3 dimensions. Electric field microgradients, arising from the use of micro-patterned electrodes, were utilized to direct the localization and self-assembly of polarizable (charged) particles resulting from a combination o...

Highly monodisperse polystyrene/poly(N-isopropylmethacrylamide) (PS-PNIPMAM) core-shell composite microgels were synthesized and further nanoengineered in either ellipsoidal, faceted or bowl-shaped particles. Beside their anisotropy in shape, the microgel design enables an exquisite control of the particle conformation, size and interactions from s...

We describe a route towards self-assembled colloidal molecules, where thermoresponsive microgels serve as discrete, externally tunable interaction sites. The ability of poly(N-isopropylacrylamide) (PNIPAM) and poly(N-isopropylmethacrylamide) (PNIPMAM) microgels to adsorb to the oil/water (O/W) interface and create Pickering-stabilized mini-emulsion...

Current theoretical attempts to understand the reversible formation of stable microtubules and virus shells are generally based on shape-specific building blocks or monomers, where the local curvature of the resulting structure is explicitly built-in via the monomer geometry. Here we demonstrate that even simple ellipsoidal colloids can reversibly...

We extend the commonly used synthesis strategies for responsive microgels to the design of novel multiresponsive and multifunctional nanoparticles that combine inorganic magnetic, metallic/catalytic and thermoresponsive organic moieties. Magnetic responsiveness is implemented through the integration of silica-coated maghemite nanoparticles into flu...

We describe a combined experimental, theoretical, and simulation study of the structural correlations between cross-linked highly monodisperse and swollen Poly(N-isopropylacrylamide) microgel dispersions in the fluid phase in order to obtain the effective pair-interaction potential between the microgels. The density-dependent experimental pair dist...

A simple procedure is developed to probe in situ the association between lipid bilayers and colloidal particles. Here, a one-step method is applied to generate giant unilamellar 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) vesicles (GUVs) by application of an alternating electric field directly in the presence of thermoresponsive poly(Nisopropyl...

The interfacial structure of natural rubber (NR) colloids is investigated by means of cryogenic transmission electron microscopy (cryo-TEM) and electrokinetics over a broad range of KNOB3B electrolyte concentrations (4 to 300 mM) and pH values (1 to 8). The asymptotic plateau value reached by NR electrophoretic mobility (m) in the thin double layer...

We report on the use of binary mixtures of oppositely charged gold nanoparticles (AuNPs) and spherical polyelectrolyte brushes (SPBs), consisting of a polystyrene core onto which long polystyrene sulfonate chains are grafted, as a simple model system to investigate the influence of directional interactions on self-assembly. We demonstrate that the...

We use a a combination of different scattering techniques and rheology to highlight the link between structure and dynamics of dense aqueous suspensions of soft repulsive colloids in the vicinity of a glass transition. Three different latex formulations with an increasing amount of the hydrophilic component resulting in either purely electrostatica...

An innovative associative strategy, crystallization-driven self-assembly, is discussed for hybrid inorganic-organic materials. We report the use of a semicrystalline poly(butadiene)-b-poly(ethylene oxide)(PB-b-PEO) diblock copolymer (BCP) that self-assembles with silica nanoparticles (NPs) in a selective solvent. In ethanol, at 60 °C, that is above...

We present an approximation scheme to the master kinetic equations for aggregation and gelation with thermal breakup in colloidal systems with variable attraction energy. With the cluster fractal dimension df as the only phenomenological parameter, rich physical behavior is predicted. The viscosity, the gelation time, and the cluster size are predi...

We use monodisperse poly(N-isopropylacrylamide) (PNIPAM) microgels as a model system for soft repulsive colloids and study their density dependent structural ordering and phase behaviour using confocal laser scanning microscopy (CLSM). The experiments are carried out at low temperatures, where the particles are in the swollen state and interact via...

We report the synthesis of thermosensitive raspberry-like hybrid microgels. They consist of a poly(N-isopropylacrylamide) core deco-rated with in situ formed silica particles. A linking silane agent was copolymerized to help the anchoring of silica particles formed by a controlled silica precursor addition onto the outer shell. The ther-mosensitive...

Prolate model colloids with defined properties can be obtained by the stretching of spherical polymeric particles, which is well-known for polystyrene and poly(methyl methacrylate) latices. The present study aims to extend this approach to functional core–shell particles in order to achieve a new class of anisotropic colloidal materials where both...

We present the morphological phase map of semicrystalline poly(butadiene)-b-poly(ethylene oxide) (PB-b-PEO) diblock copolymers (BCP) in dilute n-heptane solutions. The solutions of the diblock copolymer have been quenched from 70 °C, that is above the melting temperature Tm of the PEO block, following two thermal pathways: (A) by direct immersion i...

The electrostatically driven self-assembly of oppositely charged gold nanoparticles (Au NPs) and polystyrene/poly(N-isopropylacrylamide) (PS/PNIPAm) core-shell microgels (CSMs) has been investigated. The co-assembly was accomplished by addition of smaller Au NPs to CSMs in dilute conditions up to a number ratio of about 1:1, when the suspension is...

We present a novel method which allows one to quantify the binding energy between complex hydrophobic nanoparticles in bulk aqueous solutions by means of light scattering. We tested the method on the case of thermosensitive nanoparticles made of a solid polymeric core onto which a thermosensitive p-NIPAM microgel shell is grafted. The microgel shri...

We present the morphological phase map of semicry