The structural adaption of microgels to the environment involves a unique transition from a flexible, swollen finite-size macromolecular network, characterized by a fuzzy surface, to a colloidal particle with homogeneous density and a sharp surface. In this contribution, we determine, for the first time, the structural evolution during the microgel-to-particle transition. Time-resolved small-angle x-ray scattering experiments and computer simulations unambiguously reveal a two-stage process: In a first, very fast process, collapsed clusters form at the periphery, leading to an intermediate, hollowish core-shell structure that slowly transforms to a globule. This structural evolution is independent of the type of stimulus and thus applies to instantaneous transitions as in a temperature jump or to slower stimuli that rely on the uptake of active molecules from and/or exchange with the environment. The fast transitions of size and shape provide unique opportunities for various applications as, for example, in uptake and release, catalysis, or sensing.
The full paper is available open-access via the DOI
Prof. Walter Richerting also gave an
interview (in German) in "Welt der Physik".
In this work we study ultra-low crosslinked poly(N-isopropylacrylamide) microgels (ULC), which can behave like colloids or flexible polymers depending on their environment, e.g. 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 colloids interacting with a soft potential. 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.
This article is also featured on Nature Communications Editors’ Highlights webpage of recent research on Organic Chemistry and Chemical Biology.
Amphiphilic arborescent block copolymers generate different structures in selective solvents as revealed in computer simulations. The macromolecules do not aggregate in the solution and form monomolecular micelles. Both single- and multicore micelles can be stable. Adsorption of such macromolecules on liquid (oil−water) interface leads to their flattening and segregation of the blocks: hydrophilic and hydrophobic blocks are exposed toward water and oil, respectively. Even in a dense monolayer, the macromolecules do not interpenetrate, resembling leaves of water lilies. Pretty fast adsorption kinetics of the macromolecules makes them efficient stabilizers of emulsions.
A new publication by Felix A. Plamper and Prof. Walter Richtering was just made publicly available. Check out their review of "Functional Microgels and Microgel Systems" in the latest special issue of Accounts in Chemical Research "Stimuli-Responsive Hydrogels":
Compression and deposition of microgel monolayers from fluid interfaces: particle size effects on interface microstructure and nanolithography
Antonio Sechi and co-workers describe the fabrication of highly functional and stimuli-responsive nanogel arrays grafted onto glass surfaces by a printing process using wrinkled PDMS templates in article 1600455. These nanogels influence size and dynamics of focal adhesions as well as cell motility forcing cells to move along highly directional trajectories. The modulation of nanogel topographical and mechanical properties by temperature or spacing serves as an effective tool for the regulation of cell motility.
We compare the behavior of hollow microgels and microgels with a rigid silica core at water–oil interfaces. Compression isotherms and computer simulations demonstrate an enhanced deformation for the hollow microgels at the interface. Interestingly, a lower cross-link density leads to a higher compression modulus at low compression, whereas this behavior is reversed at high compression. This is related to an enhanced spreading of network strands at the interface. 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.
For more information, see "Hollow and Core–Shell Microgels at Oil–Water Interfaces: Spreading of Soft Particles Reduces the Compressibility of the Monolayer" by Karen Geisel, Andrey A. Rudov, Igor I. Potemkin and Walter Richtering
Am 13. Mai 2015 wurde die Gründung der neuen Sektion JARA-SOFT (Soft Matter Science) mit einem Festakt gefeiert. JARA-SOFT widmet sich der multidisziplinaren Erforschung der Weichen Materie. Weiche Materie umfasst sowohl synthetische und biologische Makromoleküle als auch kolloidale und amphiphile Systeme. Ihre Einsatzmöglichkeiten reichen vom Medikamententransport im Körper bis zur verbesserten Straßenhaftung von Autoreifen. Die im Soft Matter Bereich vorhandenen Expertisen am Forschungszentrum Jülich, dem Leibniz-Institut DWI sowie der RWTH Aachen University ergänzen sich hervorragend und liefern das Fundament für die erfolgreiche Forschung in JARA-SOFT.