ULC microgels Urheberrecht: A. Scotti

Exploring the colloid-to-polymer transition for ultra-low crosslinked microgels from three to two dimensions

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.

A. Scotti, S. Bochenek, M. Brugnoni, M. A. Fernandez-Rodriguez, M. F. Schulte, J. E. Houston, A. P. H. Gelissen, I. I. Potemkin, L. Isa, and W. Richtering

Nature Communications 10, 1418 (2019).




  Biosoft-Poster Hollow Microgels Urheberrecht: Monia Brugnoni



Hollow microgels squeezed in overcrowded environments

microgel blue Urheberrecht: Walter Richtering

A. Scotti, M. Brugnoni, A. A. Rudov, J. E. Houston, I. I. Potemkin, and W. Richtering

The Journal of Chemical Physics 148, 174903 (2018)

We study how a cavity changes the response of hollow microgels with respect to regular ones in
overcrowded environments. The structural changes of hollowpoly(N-isopropylacrylamide) microgels
embedded within a matrix of regular ones are probed by small-angle neutron scattering with contrast
variation. The form factors of the microgels at increasing compressions are directly measured. The
decrease of the cavity size with increasing concentration shows that the hollow microgels have an
alternative way with respect to regular cross-linked ones to respond to the squeezing due to their
neighbors. The structural changes under compression are supported by the radial density profiles
obtained with computer simulations. The presence of the cavity offers to the polymer network the
possibility to expand toward the center of the microgels in response to the overcrowded environment.
Furthermore, upon increasing compression, a two step transition occurs: First the microgels are
compressed but the internal structure is unchanged; then, further compression causes the fuzzy shell
to collapse completely and reduce the size of the cavity. Computer simulations also allow studying
higher compression degrees than in the experiments leading to the microgel’s faceting.



Anionic shell shields a cationic core allowing for uptake and release of polyelectrolytes within core-shell responsive microgels

pic showing polyelectrolyte Urheberrecht: A. Gelissen

Arjan P. H. Gelissen, Andrea Scotti, Sarah K. Turnhoff, Corinna Janssen, Aurel Radulescu, Andrij Pich, Andrey A. Rudov, Igor I. Potemkin and Walter Richtering , Soft Matter , 2018, Advance Article,

DOI: 10.1039/C8SM00397A

To realize carriers for drug delivery, cationic containers are required for anionic guests. Nevertheless, the toxicity of cationic carriers limits their practical use. In this study, we investigate a model system of polyampholyte N-isopropylacrylamide (NIPAM)-based microgels with a cationic core and an anionic shell to study whether the presence of a negative shell allows shielding the cationic core while still enabling the uptake and release of the anionic guest polyelectrolytes. These microgels are loaded with polystyrene sulfonate of different molecular weights. By means of small-angle neutron scattering, we evaluate the spatial distribution of polystyrene sulfonate within the microgels. The guest molecules are located in different parts of the core-shell microgels depending on their size. By combining these scattering results with UV-Vis and electrophoretic mobility we gain complementary results to investigate the uptake and release process of polyelectrolytes in polyampholyte core-shell microgels. Moreover, Brownian molecular dynamic simulations are performed to compare experimental and theoretical results of this model. Our findings demonstrate that the presence of a shell still enables efficient uptake into the cationic core of guest molecules. These anionic guest molecules can be released through an anionic shell. Furthermore, the presence of a shell enhances the stability of the microgel-polyelectrolyte complexes with respect to the cationic precursor microgel alone.



Probing the Internal Heterogeneity of Responsive Microgels Adsorbed to an Interface by a Sharp SFM Tip: Comparing Core-Shell and Hollow Microgels

pic showing microgel Urheberrecht: M. F. Schulte

M. F. Schulte, A. Scotti, A. P. H. Gelissen, W. Richtering, A. Mourran, Langmuir 2018 (accepted).

DOI: 10.1021/acs.langmuir.7b03811

Silica core – PNIPAM shell and corresponding hollow microgels were studied by scanning force microscopy (SFM). We show that swollen microgels are penetrated strongly by a sharp SFM tip. The force profile during insertion of the tip into the polymer network enables to determine a depth-dependent contact resistance which closely correlates with the density profiles determined in solution by small-angle neutron scattering (SANS). Remarkably, while currently used techniques only generate an average of the z-profile, SFM provides spatially resolved internal structure information of individual microgels. We found that the cavity of the swollen hollow microgels is still present when adsorbed to the solid substrate.



Swelling of a Responsive Network within Different Constraints in Multi-Thermosensitive Microgels

pic showing microgel Urheberrecht: M. Brugnoni

M. Brugnoni, A. Scotti, A. A. Rudov, A. P. H. Gelissen, T. Caumanns, A. Radulescu, T. Eckert, A. Pich, I. I. Potemkin, W. Richtering, 2018, Macromolecules, DOI: 10.1021/acs.macromol.7b02722.

Silica-core double-shell and hollow double-shell microgels made of an inner poly(N-isopropylmethacrylamide) and an outer poly(N-isopropylacrylamide) shell are studied by exploiting the distinct temperature sensitivities of the polymers. The swelling states of the two shells can be tuned by temperature changes enabling three different swelling states: above, below, and between the distinct volume phase transition temperatures of the two polymers. This enables to investigate the effect of different constraints on the swelling of the inner network. Small-angle neutron scattering with contrast variation discloses how the expansion of the inner shell strongly depends on the material and swelling state of its constraints. In the presence of the stiff core, the microgels show a considerable interpenetration of the polymeric shells: the inner network expands into the outer deswollen shell. This interpenetration vanishes when the outer network is swollen. Furthermore, as predicted by our computer simulations, an appropriate choice of cross-linking density enables the generation of hollow double-shell nanocapsules. Finally, the inner shell undergoes a push−pull effect. At high temperature, the collapsed outer shell pushes the swollen inner network into the cavity. At lower temperature, the swelling of the outer network contrary pulls the inner shell back toward the external periphery.



How do microgels collapse?

microgel collapsing Urheberrecht: Walter Richtering

Time-resolved structural evolution during the collapse of responsive hydrogels: The microgel-to-particle transition

R. Keidel , A. Ghavami, D.M. Lugo, G. Lotze, O. Virtanen, P. Beumers, J.S. Pedersen, A. Bardow, R.G. Winkler and W. Richtering

Science Advances 06 Apr 2018:
Vol. 4, no. 4, eaao7086
DOI: 10.1126/sciadv.aao7086

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.

Interview & Video


  Titelseite des Journals PCCP 19 2017 Urheberrecht: Lucio Isa

Compression and deposition of microgel monolayers from fluid interfaces: particle size effects on interface microstructure and nanolithography

L. Scheidegger, M.A. Fernandez-Rodriguez, K. Geisel, M. Zanini, R. Elnathan, W. Richtering and L. Isa
Physical Chemistry Chemical Physics, 2017, 19(13), 8671-8680.

Controlling the microstructure of monolayers of microgels confined at a water/oil interface is the key to their successful application as nanolithography masks after deposition on a solid substrate. Previous work demonstrated that compression of the monolayer can be used to tune the microgel arrangement and to explore the full two-dimensional area–pressure phase diagram of the particles trapped at the interface. Here, we explore a new size range, using microgels with 210 nm and 1.45 μm bulk diameters, respectively.



  Titelseite des Journals ACS Special Issue 2017

Plamper, F. A.; Richtering, W. Functional Microgels and Microgel Systems. Accounts of Chemical Research 2017, 50, 131–140


  Microgels enable capacious uptake Urheberrecht: Walter Richtering

Microgels enable capacious uptake and controlled release of architecturally complex macromolecular species

Stefan Walta, Dmitry V. Pergushov, Alex Oppermann, Alexander A. Steinschulte, Karen Geisel, Larisa V. Sigolaeva, Felix A. Plamper, Dominik Wöll, Walter Richtering, Polymer 119 (2017) 50-58, DOI: 10.1016/j.polymer.2017.05.008

Abstract:This study highlights the use of microgels as containers of high capacity for uptake and triggered release of multi-functional guests. As a model guest, heteroarm star-shaped copolymers (miktoarm stars) are chosen, as their certain arms could carry different active moieties, while other arms could act as “stickers” to the microgel host. The miktoarm stars are able to penetrate into the microgels to compensate their negatively charged groups.. Furthermore, a jump-wise increase of ionic strength in solutions of the complexes triggers the complete release of the miktoarm stars from the microgel, and the system stays always colloidally stable. Thus, microgel-based polylectrolyte complexes provide opportunities for many important applications, especially in targeted/controlled delivery.


  Funktionelle Mikrogele und Mikrogelsysteme Urheberrecht: AK Richtering

Functional Microgels and Microgel Systems

F. A. Plamper und W. Richtering
Acc. Chem. Res., 2017, 50(2), 131-140.

Mikrogele vereinen die Eigenschaften sehr verschiedener Materialklassen. Sie ermöglichen in einzigartiger Weise die Kombination von Merkmalen der chemischen Funktionalität, strukturellen Integrität, makromolekularen Architektur, Anpassbarkeit, Permeabilität und Verformbarkeit um so das Beste aus den Welten der Kolloide, Polymere und Tenside zu vereinen. Dies wird die Tür für viele neuartige Anwendungen in sehr unterschiedlichen Bereichen wie etwa der Sensorik, der Katalyse und der Trenntechnik öffnen.

DOI: 10.1021/acs.accounts.6b00544


  Illustration zum Paper Urheberrecht: Dominik Wöll

3D Structures of Responsive Nanocompartmentalized Microgels

A. P. H. Gelissen, A. Oppermann, T. Caumanns, P. Hebbeker, S. K. Turnhoff, R. Tiwari, S. Eisold, U. Simon, Y. Lu, J. Mayer, W. Richtering, A. Walther, D. Wöll
Nano Letters, 2016.

A combination of in situ electron microscopy and superresolved fluorescence localization microscopy allows for a determination of 3D compartmentalization of core-shell microgel structures. A software package to evaluate 2D microscopy images to obtain 3D structures is provided.

DOI: 10.1021/acs.nanolett.6b03940



The Next Step in Precipitation Polymerization of N-Isopropylacrylamide: Particle Number Density Control by Monochain Globule Surface Charge Modulation.

O. L. J. Virtanen, M. Brugnoni, M. Kather, A. Pich, W. Richtering
Polymer Chemistry, 2016, 7, 5123-5131.

DOI: 10.1039/C6PY01195K


  Multi-Shell Hollow Nanogels with Responsive Shell Permeability Urheberrecht: AK Richtering

Multi-Shell Hollow Nanogels with Responsive Shell Permeability

A. J. Schmid, J. Dubbert, A. A. Rudov, J. S. Pedersen, P. Lindner, M. Karg, I. I. Potemkin and W. Richtering
Scientific Reports, 2016, 6, Article number: 22736.

DOI: 10.1038/srep22736



Persulfate Initiated Ultra-Low Cross-Linked Poly(N-Isopropylacrylamide) Microgels Possess an Unusual Inverted Cross-Linking Structure

O. L. J. Virtanen, A. Mourran, P. T. Pinard, W. Richtering
Soft Matter 2016, 12, 3919–3928.
DOI: 10.1039/C6SM00140H

  Hollow and Core–Shell Microgels at Oil–Water Interfaces

Hollow and Core–Shell Microgels at Oil–Water Interfaces: Spreading of Soft Particles Reduces the Compressibility of the Monolayer

K. Geisel, A. A. Rudov, I. I. Potemkin and W. Richtering
Langmuir, 2015, 31 (48),13145–13154.
DOI: 10.1021/acs.langmuir.5b03530


JARA-SOFT: Soft Matter Science made in Aachen und Jülich

Sechste JARA-Sektion startet mit großartigem Auftakt

  Core–Shell–Shell and Hollow Double-Shell Microgels

Core–Shell–Shell and Hollow Double-Shell Microgels with Advanced Temperature Responsiveness

Janine Dubbert, Katja Nothdurft, Matthias Karg and Walter Richtering
Macromol. Rapid Commun., 2015, 36(2), 159-164.
DOI: 10.1002/marc.201400495

  Methanol-induced change

Methanol-induced change of the mechanism of the temperature- and pressure-induced collapse of N-Substituted acrylamide copolymers

Christian H. Hofmann, Sebastian Grobelny, Paweł T. Panek, Laura K. M. Heinen, Ann-Kristin Wiegand, Felix A. Plamper, Christoph R. Jacob, Roland Winter and Walter Richtering
Journal of Polymer Science Part B: Polymer Physics, 53(7), 532-544, 2015.
DOI: 10.1002/polb.23676

  Effect of the Molecular Architecture

Effect of the Molecular Architecture on the Internal Complexation Behavior of Linear Copolymers and Miktoarm Star Polymers

Pascal Hebbeker, Felix A. Plamper and Stefanie Schneider
Macromolecular Theory and Simulations, 2015.
DOI: 10.1002/mats.201400077

  How Hollow Are Thermoresponsive Hollow Nanogels?

How Hollow Are Thermoresponsive Hollow Nanogels?

Janine Dubbert et al.
Macromolecules, 47 (24), 8700–8708, 2014.

DOI: 10.1021/ma502056y

  Highly ordered 2D microgel arrays

Highly ordered 2D microgel arrays: compression versus self-assembly

Karen Geisel, Walter Richtering and Lucio Isa
Soft Matter, 10, 7968-7976, 2014. DOI: 10.1039/C4SM01166J
2014 Soft Matter Hot Papers