Hydrogels and organogels made from polymer networks are widely used in biomedical applications and soft, active devices for which the ability to sustain large deformations is required. The strain at ...which polymer networks fracture is typically improved through the addition of elements that dissipate energy, but these materials require extra work to achieve a given, desired level of deformation. Here, the addition of mechanically “invisible” supramolecular crosslinks causes substantial increases in the ultimate gel properties without incurring the added energetic costs of dissipation.
Preparation, substrate scope, and activity of a previously reported mechanically activated metathesis catalyst were investigated. Scission of the catalyst under ultrasound irradiation was followed by ...GPC, which showed a first-order scission rate constant of 0.011 min–1. The resulting active species was shown to have catalytic reactivity in ring closing metathesis (RCM) of various (un)hindered substrates. Further investigations of the active species showed that it was not influenced by radicals formed during ultrasound and that the most effective method to increase its lifetime was an increase in the substrate concentration. In ring-opening metathesis polymerization (ROMP), the lifetime of the active species was shown to be several hours, in contrast to the short lifetimes found in RCM. ROMP experiments also showed that all of the latent precatalyst broken leads to active catalyst species.
The cytoskeleton is a highly adaptive network of filamentous proteins capable of stiffening under stress even as it dynamically assembles and disassembles with time constants of minutes. Synthetic ...materials that combine reversibility and strain-stiffening properties remain elusive. Here, strain-stiffening hydrogels that have dynamic fibrous polymers as their main structural components are reported. The fibers form via self-assembly of bolaamphiphiles (BA) in water and have a well-defined cross-section of 9 to 10 molecules. Fiber length recovery after sonication, H/D exchange experiments, and rheology confirm the dynamic nature of the fibers. Cross-linking of the fibers yields strain-stiffening, self-healing hydrogels that closely mimic the mechanics of biological networks, with mechanical properties that can be modulated by chemical modification of the components. Comparison of the supramolecular networks with covalently fixated networks shows that the noncovalent nature of the fibers limits the maximum stress that fibers can bear and, hence, limits the range of stiffening.
Supramolecular Polymerization De Greef, Tom F. A; Smulders, Maarten M. J; Wolffs, Martin ...
Chemical reviews,
11/2009, Letnik:
109, Številka:
11
Journal Article
Recenzirano
The supramolecular polymerization of ditopic monomers is explored. Although kinetic and thermodynamic models are readily available in the literature, more research is needed, in order for such ...synthetic materials to approach the level of natural ones.
The Preisach model has been a cornerstone in the fields of ferromagnetism and ferroelectricity since its inception. It describes a real, non-ideal, ferroic material as the sum of a distribution of ...ideal 'hysterons'. However, the physical reality of the model in ferroelectrics has been hard to establish. Here, we experimentally determine the Preisach (hysteron) distribution for two ferroelectric systems and show how its broadening directly relates to the materials' morphology. We connect the Preisach distribution to measured microscopic switching kinetics that underlay the macroscopic dispersive switching kinetics as commonly observed for practical ferroelectrics. The presented results reveal that the in principle mathematical construct of the Preisach model has a strong physical basis and is a powerful tool to explain polarization switching at all time scales in different types of ferroelectrics. These insights lead to guidelines for further advancement of the ferroelectric materials both for conventional and multi-bit data storage applications.
The development of a nanoporous material from a columnar liquid crystalline complex between a polymerizable benzoic acid derivative and a 1,3,5‐tris(1H‐benzodimidazol‐2‐yl)benzene template molecule ...is described. The morphology of the liquid crystalline complex is retained upon polymerization and quantitative removal of the template molecule affords a nanoporous material with the same lattice parameters. The nanoporous material selectively binds cations from aqueous solution, with selectivity for sodium and potassium ions over lithium and barium ions, as shown with FT‐IR. Binding is also quantified gravimetrically with a quartz crystal microbalance with dissipation monitoring, a technique that is used for this purpose for the first time here.
A nanoporous material was developed by the self‐assembly and cross‐linking of a hydrogen‐bonded columnar liquid crystalline complex. Subsequent quantitative removal of the template affords the nanoporous material that size‐selectively binds sodium and potassium ions over other ions. This is analyzed for the first time by utilizing the quartz crystal microbalance.
The formation of isocyanurates via cyclotrimerization of aromatic isocyanates is widely used to enhance the physical properties of a variety of polyurethanes. The most commonly used catalysts in ...industries are carboxylates for which the exact catalytically active species have remained controversial. We investigated how acetate and other carboxylates react with aromatic isocyanates in a stepwise manner and identified that the carboxylates are only precatalysts in the reaction. The reaction of carboxylates with an excess of aromatic isocyanates leads to irreversible formation of corresponding deprotonated amide species that are strongly nucleophilic and basic. As a result, they are active catalysts during the nucleophilic anionic trimerization, but can also deprotonate urethane and urea species present, which in turn catalyze the isocyanurate formation. The current study also shows how quantum chemical calculations can be used to direct spectroscopic identification of reactive intermediates formed during the active catalytic cycle with predictive accuracy.
We have demonstrated the formation of segregated enantiomeric dynamic rods in water, from the self-sorting of chiral trans-1,2-bisureido cyclohexane-based bolaamphiphiles. Fluorescence probes have ...been used to investigate the self-sorting through forming exciplex and FRET.
PDF
