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 well as for a broad range of applications, in particular in the field of biological applications. Recent tremendous developments in their synthesis open access to systems with complex architectures and compositions allowing for tailoring microgels with specific properties. At the same time state-of-the-art theoretical and simulation approaches offer deeper understanding of the behavior and structure of nano- and microgels under external influences and confinement at interfaces or at high volume fractions. Developments in the experimental analysis of nano- and microgels have become particularly important for structural investigations covering a broad range of length scales relevant to the internal structure, the overall size and shape, and interparticle interactions in concentrated samples. Here we provide an overview of the state-of-the-art, recent developments as well as emerging trends in the field of nano- and microgels. The following aspects build the focus of our discussion: tailoring (multi)functionality through synthesis; the role in biological and biomedical applications; the structure and properties as a model system, e.g., for densely packed arrangements in bulk and at interfaces; as well as the theory and computer simulation.
In this research, we studied, in detail, the behavior of common PNIPAM microgels, obtained through surfactant-free precipitation polymerization, in a number of organic solvents. We showed that many ...of the selected solvents serve as good solvents for the PNIPAM microgels and that the size and architecture of the microgels depend on the solvent chosen. Expanding the range of solvents used for PNIPAM microgel incubation greatly enhances the possible routes for microparticle functionalization and modification, as well as the encapsulation of water-insoluble species. In this demonstration, we successfully encapsulated water-insoluble Sudan III dye in PNIPAM microgels and prepared the aqueous dispersions of such composite-colored microparticles.
Abstract
The development of biomedical glues is an important, yet challenging task as seemingly mutually exclusive properties need to be combined in one material, i.e. strong adhesion and adaption to ...remodeling processes in healing tissue. Here, we report a biocompatible and biodegradable protein-based adhesive with high adhesion strengths. The maximum strength reaches 16.5 ± 2.2 MPa on hard substrates, which is comparable to that of commercial cyanoacrylate superglue and higher than other protein-based adhesives by at least one order of magnitude. Moreover, the strong adhesion on soft tissues qualifies the adhesive as biomedical glue outperforming some commercial products. Robust mechanical properties are realized without covalent bond formation during the adhesion process. A complex consisting of cationic supercharged polypeptides and anionic aromatic surfactants with lysine to surfactant molar ratio of 1:0.9 is driven by multiple supramolecular interactions enabling such strong adhesion. We demonstrate the glue’s robust performance in vitro and in vivo for cosmetic and hemostasis applications and accelerated wound healing by comparison to surgical wound closures.
We investigate the influence of a solid core and of the cross-link density on the compression of microgel particles at oil–water interfaces by means of compression isotherms and computer simulations. ...We investigate particles with different morphology, namely core–shell particles containing a solid silica core surrounded by a cross-linked polymer shell of poly(N-isopropylacrylamide), and the corresponding hollow microgels where the core was dissolved. The polymer shell contains different amounts of cross-linker. The compression isotherms show that the removal of the core leads to an increase of the surface pressure at low compression, and the same effect can be observed when the polymer cross-link density is decreased. Low cross-link density and a missing core thus facilitate spreading of the polymer chains at the interface and, at high compression, hinder the transition to close hexagonal packing. Furthermore, the compression modulus only depends on the cross-link density at low compression, and no difference can be observed between the core–shell particles and the corresponding hollow microgels. It is especially remarkable that a low cross-link density leads to a high compression modulus at low compression, while this behavior is reversed at high compression. Thus, the core does not influence the particle behavior until the polymer shell is highly compressed and the core is directly exposed to the pressure. This is related to an enhanced spreading of polymer chains at the interface and thus high adsorption energy. These conclusions are fully supported by computer simulations which show that the cross-link density of the polymer shell defines the degree of deformation at the interface. Additionally, the core restricts the spreading of polymer chains at the interface. These results illustrate the special behavior of soft microgels at liquid interfaces.
Microgels are solvent-swollen nano- and microparticles that show prevalent colloidal-like behavior despite their polymeric nature. Here we study ultra-low crosslinked poly(N-isopropylacrylamide) ...microgels (ULC), which can behave like colloids or flexible polymers depending on dimensionality, compression or other external stimuli. Small-angle neutron scattering shows that the structure of the ULC microgels in bulk aqueous solution is characterized by a density profile that decays smoothly from the center to a fuzzy surface. Their phase behavior and rheological properties are those of soft colloids. However, when these microgels are confined at an oil-water interface, their behavior resembles that of flexible macromolecules. Once monolayers of ultra-low crosslinked microgels are compressed, deposited on solid substrate and studied with atomic-force microscopy, a concentration-dependent topography is observed. Depending on the compression, these microgels can behave as flexible polymers, covering the substrate with a uniform film, or as colloidal microgels leading to a monolayer of particles.
•Low-temperature steam conversion of flare gases into methane-rich mixtures.•Conversion of C2+-hydrocarbons to CH4, CO2 and H2.•Lowering net calorific value, Wobbe index and dew point temperature of ...the gas.•Partial conversion of C2H6 and C3H8 to reach desired gas properties.•Kinetic simulation and prediction of optimal reaction conditions.
The present work aims at studying low-temperature steam conversion of model flare gas mixtures containing C2H6-C5H12 in methane excess over industrial Ni-based catalyst. It is shown that at 250–350 °C and H2O/CC2+ molar ratio of 0.7–1.0, steam conversion can be applied to convert C2+-hydrocarbons into CH4, CO2 and H2, which results in the lowering net calorific value, the Wobbe index and dew point temperature of the gas obtained. However, complete conversion is not necessary for certain applications. In these cases, kinetically controlled partial conversion of ethane and propane enables one to obtain methane-rich mixtures with desired calorific properties for various applications. This idea has been experimentally verified. Kinetic study of C2H6-C5H12 low-temperature steam conversion has been performed. A simple macrokinetic model, which included irreversible first-order kinetics for C2H6-C5H12 steam conversion and quasi-equilibrium mode for CO2 methanation, has been suggested. The model adequately describes the experimental data on the conversion of model flare gas mixtures at various temperatures and flow rates and has been applied to predict the reaction conditions which would allow one to obtain methane-rich mixtures with the desired properties for various applications.
Dissipative particle dynamics was applied to simulate solvent vapor annealing in films of cylinder-forming diblock copolymers. Our simulations reveal a wide range of conditions, under which the ...vertical domain orientation is promoted by the fast solvent evaporation. First, the order-to-disorder transition must be induced upon swelling of the film. This condition ensures the independence of the structure formation during drying on the history, i.e., the preparation conditions. Second, the weak segregation regime has to be achievable during the evaporation process. This condition provides more “pathways” for structural transformations which are not accompanied by a strong penalty in the interfacial energy. The third condition for vertical orientation of the cylindrical nanodomains is a weak selectivity of the solvent. In the swollen state, a stronger swelling of the majority domains results in the formation of spherical micelles (rather than cylindrical). Upon drying of the film, these spherical micelles join to form cylinders, which align in parallel to the (vertical) solvent flow. Possible mechanisms of the alignment are discussed. In addition, the effects of varying film thickness, the degree of swelling, segregation regime, and the selectivity of the free surface of the film are studied. Computer simulations of the solvent vapor annealing and thermal annealing of equivalent dry films reveal considerable differences in the final film structures.
Efficient capture and recycling of CO2 enable not only prevention of global warming but also the supply of useful low-carbon fuels. The catalytic conversion of CO2 into an organic compound is a ...promising recycling approach which opens new concepts and opportunities for catalytic and industrial development. Here we report about template-assisted wet-combustion synthesis of a one-dimensional nickel-based catalyst for carbon dioxide methanation and methane steam reforming. Because of a high temperature achieved in a short time during reaction and a large amount of evolved gases, the wet-combustion synthesis yields homogeneously precipitated nanoparticles of NiO with average particle size of 4 nm on alumina nanofibers covered with a NiAl2O4 nanolayer. The as-synthesized core–shell structured fibers exhibit outstanding activity in steam reforming of methane and sufficient activity in carbon dioxide methanation with 100% selectivity toward methane formation. The as-synthesized catalyst shows stable operation under the reaction conditions for at least 50 h.
Microgels are nanometer-to-micrometer-sized cross-linked polymer networks that swell when dispersed in a good solvent. These soft colloids have emerged as versatile building blocks of smart ...materials, which are distinguished by their unique ability to adapt their behavior to changes in external stimuli. Using X-ray and neutron scattering and molecular simulation methods, we systematically measured and modeled the response to crowding of compressible, deformable microgels with varying cross-link densities and internal architectures. Our experiments and simulations demonstrate that incorporating a solvent-filled cavity during chemical synthesis provides an independent means of controlling microgel swelling that complements the influence of changing cross-link density. In other words, knowledge of the content of cross-links alone cannot be used to define microgel softness, but microgel architecture is another key property that affects softness. These results are potentially important for biomedical applications, such as drug delivery and biosensing.
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