Andreas Walther

Social Self-Sorting of Colloidal Families in Co-Assembling Microgel Systems

Colloids are valuable model systems to understand the structure and dynamics of matter, explore new self-assembly concepts, and realize advanced materials. Herein, we demonstrate social self-sorting of co-assembled families of colloids by orthogonal host/guest recognition using cyclodextrins. We show that mixtures of four partners self-sort into their respective families without mutual interference. Additionally, the self-assemblies and their interactions are switchable using orthogonal triggers. This study goes beyond previous features of molecular self-sorting, and opens the design space for future self-sorting colloidal systems via rationally designed molecular recognition.

Dynamic covalent single chain nanoparticles based on hetero Diels–Alder chemistry

We introduce the fully reversible folding of single chain nanoparticles (SCNPs) based on covalent hetero Diels-Alder (HDA) chemistry. A cyclopentadiene (Cp)-protected cyanodithioester (CDTE) monomer is designed and copolymerized with methyl methacrylate (MMA) via RAFT polymerization. The polymer chains are folded and subsequently unfolded by exploiting the reversible nature of the HDA reaction.

Photonic Devices Out of Equilibrium: Transient Memory, Signal Propagation, and Sensing

Soft photonic materials are important for sensors, displays, or energy management and have become switchable under static equilibrium conditions by integration of responsive polymer features. The next step is to equip such materials with the ability for autonomously dynamic and self-regulating behavior, which would advance their functionality and application possibilities to new levels. Here, this study shows the system integration of a nonlinear, biocatalytic pH-feedback system with a pH-responsive block copolymer photonic gel, and demonstrates autonomous transient memories, remotely controlled signal propagation, and sensing. This study utilizes an enzymatic switch to program the lifetime of the reflective state of a photonic gel, and induces propagation of pH-waves extinguishable by illumination with UV-light. The described combination of nonlinear chemistry and responsive photonic gels opens pathways toward out-of-equilibrium photonic devices with active and autonomous behavior useful for sensing, computation, and communication.

Counterion Size and Nature Control Structural and Mechanical Response in Cellulose Nanofibril Nanopapers

Nanopapers formed from aqueous dispersions of cellulose nanofibrils (CNFs) combine stiffness, strength, and toughness. Yet, delicate interactions operate between the CNFs during nanopaper formation and mechanical deformation. We unravel in detail how counterions, being either of the organic alkyl ammonium kind (NR4+) or of the earth metal series (Li+, Na+, Cs+), need to be chosen to achieve outstanding combinations of stiffness, strength, and toughness, extending to previously unreached territories. We relate structure formation processes in terms of colloidal stabilization to nanostructural details such as porosity and ability for swelling, as well as to interfibrillar interactions in bulk and macroscale mechanical properties. We demonstrate that our understanding also leads to new levels of ductility in bioinspired CNF/polymer nanocomposites at high levels of reinforcements. These results contribute to future rational design of CNF-based high-performance materials.

Block Copolymer Micelles with Inverted Morphologies

Beyond the crew cut: Highly asymmetric block copolymers self-assemble into microparticles with inverse morphologies far beyond the crew-cut regime. These particles enclose highly ordered channel systems with simple cubic, double diamond, and hexagonally packed hollow-hoop symmetry. The extensive interface and confinement of these particles could enable applications in the storage of cargo, templating, and chemical reactions.

Pathway-controlled formation of mesostructured all-DNA colloids and superstructures

DNA has traditionally been used for the programmable design of nanostructures by exploiting its sequence-defined supramolecular recognition. However, control on larger length scales or even hierarchical materials that translate to the macroscale remain difficult to construct. Here, we show that the polymer character of single-stranded DNA (ssDNA) can be activated via a nucleobase-specific lower critical solution temperature, which provides a unique access to mesoscale structuring mechanisms on larger length scales. We integrate both effects into ssDNA multiblock copolymers that code sequences for phase separation, hybridization and functionalization. Kinetic pathway guidance using temperature ramps balances the counteracting mesoscale phase separation during heating with nanoscale duplex recognition during cooling to yield a diversity of complex all-DNA colloids with control over the internal dynamics and of their superstructures. Our approach provides a facile and versatile platform to add mesostructural layers into hierarchical all-DNA materials. The high density of addressable ssDNA blocks opens routes for applications such as gene delivery, artificial evolution or spatially encoded (bio)materials.Single-stranded DNA with purine-rich poly-A and poly-G sequences can undergo a defined lower critical solution temperature-type phase transition at elevated temperature like other polymers, which can be exploited to realize defined kinetic microparticle assemblies.

Facile and On-Demand Cross-Linking of Nacre-Mimetic Nanocomposites Using Tailor-Made Polymers with Latent Reactivity

The development of on-demand cross-linking strategies is a key aspect in promoting mechanical properties of high-performance bioinspired nanocomposites. Here, we embed styrene sulfonyl azide groups with latent chemical reactivity into water-soluble copolymers and assemble those with high-aspect-ratio synthetic nanoclays to generate well-defined layered polymer/nanoclay nacre-mimetics. A considerable stiffening and strengthening occurs upon activation of the covalent cross-linking using simple heating. Varying the amount of cross-linkable units allows molecular control of mechanical properties from ductile to stiff and strong. Moreover, the covalent cross-linking enhances the moisture stability of water-borne nacre-mimetics. The strategy is facile and versatile allowing for a transfer into applications.