Diffúzió- és konvekció-szabályozott mintázatképződés = Diffusion- and convention-induced spatiotemporal pattern formation

Bemutattuk, hogy izoterm autokatalitikus reakció három térbeli dimenzióra való kiterjesztése időben állandó szimmetrikus gömbalakzat létrejöttét eredményezi, mely a diffúziókülönbségek révén, anguláris perturbáció hatására elveszítheti stabilitását. A megfelelően kialakított elektromos erőtérben lejátszódó autokatalitikus ionreakciók esetén megfogalmaztuk a migrációvezérelt laterális instabilitás létrejöttének feltételeit és hajtóerejét. Továbbá bemutattuk, hogy ionreakciókban felépülő helyi elektromos erőtér is megváltoztathatja a diffúzióvezérelt instabilitás mértékét. A mintázatképződés mennyiségi leírásához szükséges a diffúzióállandók ismerete, ezért ezek in situ méréseit 1H- és 13C- PFGSE-NMR módszerrel megkezdtük. A konvekció mintázatképző szerepét különböző geometriájú edényekben kezdeti síkfrontból kialakuló cellás szerkezet vizsgálatával szemléltettük. A mintázatképződés hosszútávú alakulása egyrészt állandó sebességgel és alakkal jellemezhető, egymásba áttranszformálható egycellás szerkezetet, másrészt folytonos változással bíró mintázatot eredményez. A hőmérséklet-változás sűrűségváltozásra gyakorolt hatásának megszüntetésével kimutattuk a hőmérséklet stabilizáló hatását. Az oldat viszkozitásának növelése a közegmozgás lelassulását és az instabilitás csökkenését eredményezi. Pórusos rendszerek egyszerű analógjainak tekinthető periodikus heterogenitást tartalmazó edényekben lejátszatott frontoknál rezonanciaerősítést mutattunk ki. | Three-dimensional stability of stationary reaction balls is investigated in a simple autocatalytic reaction followed by a slow decay of the autocatalyst. Stationary spherical structures lose stability to angular perturbations because of diffusional differences. We have determined the conditions and the driving force of migration-driven instabilities in simple autocatalytic reactions carried out in an appropriately oriented external electric field. Furthermore, we have showed that the local electric field built up in ionic systems may significantly alter the stability of reaction fronts. The knowledge of diffusion coefficients is important for the quantitative characterization of the spatiotemporal pattern formation, therefore we have started their in situ measurement by 1H- and 13C-PFGSE-NMR. We have shown that convection can be a major driving force for spatiotemporal pattern formation by altering the inital planar front to cellular structure. The longtime behavior can be described by either a stable single cell or by continuous tip splitting depending on the experimental conditions. By eliminating thermal effects, we have shown their stabilizing contribution on the pattern formation. The increase of solution viscosity results in slower convection and hence lower instability. Resonance amplification is exhibited in fronts traveling in reaction vessels with periodic heterogeneity

Sol-gel transition programmed self-propulsion of chitosan hydrogel

Active soft materials exhibit various dynamics ranging from boat pulsation to thin membrane deformation. In the present work, in situ prepared ethanol-containing chitosan gels propel in continuous and intermittent motion. The active life of the organic material loaded to the constant fuel level follows a linear scaling, and its maximal velocity and projection area decrease steeply with chitosan concentration. A thin propelling platelet forms at low polymer content, leading to the suppression of intermittent motion. Moreover, the fast accelerating thin gels can split into a crescent and circular-like shape or fission into multiple asymmetric fragments. Published under an exclusive license by AIP Publishing

Self-assembly to synchrony of active gels

Self-assembly functionalizes active constituents to perform rhythmic activities. Here, our results show that the capillary-Marangoni interaction of irregularly moving gel beads develops complex patterns at the air-liquid interface. The collective behavior of the self-assembled structures exhibits breathing dynamics, polygonal oscillating rings, and cluster synchrony of chains. Interestingly, the trapping of soft particles generates relay synchronization of a rotor. Swarming of clusters is found to form rhythmic shrinking and expanding multiple-ring patterns. The development of self-organized spatiotemporal patterns of our active gel system provides a new way of creating collective oscillations

Spatial precipitate separation enhanced by complex formation

The separation of inorganic precipitates with similar solubility products is a challenging task in chemical engineering. We present a computational fluid dynamics study of a precipitation reaction in a flow-driven reactor. For a reference study, the cobalt(II)-copper(II)-oxalate system is selected, where precipitation occurs simultaneously and the difference in solubility is within an order of magnitude as shown experimentally. For general description of two metal ions competing for one common anion, several parameters have been varied to identify the factors responsible for spatial separation. Two new quantities, the mean position of sedimented particles and the precipitation excess, are introduced to characterize the extent of separation. The calculations have shown that complex formation prior to nucleation makes the separation feasible for a wide range of thermodynamic or kinetic parameters. The injection rate can be used for fine tuning both the amounts of precipitate and their spatial separation when complexes are present. (C) 2022 The Author(s). Published by Elsevier Ltd

From Balloon to Crystalline Structure in the Calcium Phosphate Flow-Driven Chemical Garden

We have studied the calcium phosphate precipitation reaction by producing chemical gardens in a controlled manner using a three-dimensional flow-driven technique. The injection of the phosphate containing solution into the calcium ion reservoir has resulted in structures varying from membranes to crystals. Dynamical phase diagrams are constructed by varying chemical composition and flow rates from which three different growth mechanisms have been revealed. The microstructural analysis by scanning electron microscopy and powder X-ray diffraction confirmed the morpho-logical transition from membrane tubes to crystalline branches upon decreasing pH

Growth and Photosynthetic Response of Capsicum Annuum L. in Biochar Amended Soil

The present study investigated the growth of Capsicum annuum L. (pepper) in an outdoor pot experiment. Changes in the plants’ aboveground and root biomass, leaf area, plant height, stem thickness, and yield, as a response to different doses of biochar amendments were observed. During the 12.5-week-long study, four treatments with biochar amounts of 0, 0.5%, 2.5%, and 5.0% (by weight) were added to silt loam soil. Photochemical responses of plants, the plants photochemical reflectance index (PRI) modified by the different doses of biochar were continuously monitored. Plant height and fruit yield were initially the highest for BC5.0; however, by the end of the experiment, both parameters showed higher values for BC2.5, e.g., 15.9 and 9.1% higher plant height and 32.5 and 22.6% higher fruit yield for BC2.5 and BC5.0 compared to control, respectively. By the end of the experiment the BC2.5 treatments had significantly higher stem thickness (p < 0.001) compared to all other amendments. Root dry matter in biochar treatments increased relative to controls with the highest values (54.9% increase) observed in the BC2.5 treatment. Biochar treatment increased leaf area index (LAI) values for the higher doses (1.58, 1.59, 2.03, and 1.89 for C, BC0.5, BC2.5, and BC5.0, respectively). Significant differences between control and biochar amended soils’ PRI measurements were observed (p < 0.001), showing less plant sensitivity to environmental changes when biochar was applied to the soil. While biochar amendment could greatly enhance plant growth and development, there is an optimal amount of biochar after which additional amount might not result in substantial differences, or even can result in lower fruit yield as found in the present study