Three-dimensional spiral waves in the Belousov-Zhabotinsky reaction are pinned to unexcitable heterogeneities. This pinning can prevent the collapse of scroll rings even if the heterogeneity does not extend along the entire wave filament. In the latter case, frequency differences create stationary gradients in the rotation phase. These twist patterns and their frequencies agree with algebraic solutions of the forced Burgers equation revealing insights into the phase coupling of scroll waves.

For the first time, we studied frontal polymerization with ionic liquid monomers. We synthesized a series of compounds from the neutralization reaction between trialkylamines (tributylamine, trihexylamine, trioctylamine, and (2-dimethylamino)ethyl methacrylate) and acrylic or methacrylic acid. For the ionic liquids prepared from the unreactive amines, frontal polymerization could not be achieved without the addition of a diacrylate. With the addition of a diacrylate, the front velocities were slower than for dodecyl acrylate (with the diacrylate), a compound of comparable molecular weight. Monomers prepared from the (2-dimethylamino)ethyl methacrylate could support frontal polymerization alone but the front velocities were lower than dodecyl (meth)acrylate. These results are contrasted with recent results of Jiménez et al. for room temperature kinetics. Finally, the polymers prepared were comparable to those prepared by batch curing at 75 8C except for the monomethacrylate ionic liquid, which lost some tertiary amine by dissociation and evaporation.

Scroll rings are three-dimensional excitation waves rotating around one-dimensional filament loops. In experiments with the Belousov-Zhabotinsky reaction we show that the collapse of these loops can be stopped by local pinning to only two unexcitable heterogeneities. The resulting vortices rotate around stationary but curved filaments. The absence of filament motion can be explained by repulsive interaction that counteracts the expected curvature-induced motion. The shape and key dependencies of the stationary filaments are well described by a curvature-flow model with additive interaction velocities that rapidly decrease with filament distance.

Scroll waves are three-dimensional excitation vortices rotating around one-dimensional phase singularities called filaments. In experiments with a chemical reaction-diffusion system and in numerical simulations, we study the pinning of closed filament loops to inert cylindrical heterogeneities. We show that the filament wraps itself around the heterogeneity and thus avoids contraction and annihilation. This entwining steadily increases the total length of the pinned filament and reshapes the entire rotation backbone of the vortex. Self-pinning is fastest for thin cylinders with radii not much larger than the core of the unpinned rotor. The process ends when the filament is attached to the entire length of the cylinder. The possible importance of self-pinning in cardiac systems is discussed.

We report a zwitterionic block copolymer composed of N-isopropylacrylamide and N,N-dimethyl-N-(3-(methacrylamido)propyl)ammoniopropanesulfonate monomers which self-assembles into different structures depending on the solution temperature. As the temperature is increased from 20 to 70°C, the solubility of the polymer switches direction from insoluble to soluble to insoluble to soluble. During this process, the polymer self-assembly changes from polymersomes to micelles. These extraordinary transitions are possible because of the hydrophilic−hydrophobic ratio of the polymer blocks and the presence of a carboxyl end group attached to the end of the poly(N-isopropylacrylamide) chain. Additionally, one of these transitions can be controlled by the pH of the solution thanks to the protonation−deprotonation of the carbonyl and the charge neutralization of the ammonium moieties. The present work opens the possibility of designing polymers with temperature driven self-assembly properties that could be used for biomedical applications. ■ INTRODUCTIONWater-soluble polymers that switch hydrophilicity upon temperature variations are a type of thermoresponsive polymer. When the polymer becomes soluble or insoluble by increasing temperature, it is said to show an upper critical solution temperature 1 (UCST) or lower critical solution temperature (LCST), respectively. 2 This responsivity can be exploited in tissue engineering, 3 chromatography for the separation of biomolecules, 4 patterned-switchable surfaces, 5 preparations for cancer therapy, 6−8 optical devices for sensing and biosensing, 9 DNA transfection, 10 and functional hydrogels, 11 among others. Some zwitterionic polymers like poly(sulfobetaines) show UCST behavior in water. These betaines are ionic polymers derived of dimethylaminoalkyl acrylate or acrylamide monomers containing ammonium and sulfonic ions. Their solubility in water is poor, but an increase in temperature and/or the addition of low-molecular-weight salts solubilize the polymer thanks to the disruption of the ionic network. 12 Additional to the thermoresponsivity, poly(sulfobetaines) have the chemical characteristics necessary to prepare nonfouling materials 13 which make them attractive for the preparation of biomaterials. On the other hand, polymers with LCST transitions like poly(N-isopropylacrylamide) or poly(NIPAAm) become more hydrophobic at higher temperatures and therefore insoluble in water. In a dilute aqueous solution, poly(NIPAAm) is in the extended coil state which collapses into a compact globule state and aggregates above 32°C (LCST). 14 This transition temperature can be shifted to human body temperature by copolymerization with hydrophilic monomers, making it suitable for biomedical applications. 15 Copolymers exhibiting both UCST and LCST transition temperatures can be prepared by synthesis of block copolymers, where each block is responsible for one of the transitions. 16−25 This type of polymer offers a hydrophobic and a hydrophilic block which make them susceptible to self-organiz...