6/30/2023 0 Comments Define precipitate chemistry terms![]() ![]() In addition, reaction-diffusion–type equations have been used to model neural signals ( 8), cardiac arrhythmias ( 9, 10), uterine contractions ( 11), and a broad range of other dynamical processes ( 12). Specifically, Turing formulated the possible chemical basis for stationary spatial patterns that are now being discussed as the source patterns on mollusk shells ( 4), zebra stripes and leopard spots ( 5), and even cortical folding ( 6, 7). Alan Turing, a pioneer of biological pattern formation, recognized that a “system of chemical substances…reacting together and diffusing through a tissue is adequate to account for the main phenomena of morphogenesis” ( 3). Thus it is not surprising that reaction-transport phenomena are ubiquitous in nature and represent the de facto mode of operation in living systems. They allow the relay of information over macroscopic length scales and, hence, potentially bridge the gap between the molecular world and the realm of microstructures and devices. The coupling of nonlinear reactions and transport processes is ideally suited to create and maintain steep concentration gradients that can serve as positional and directional guides for the synthesis and/or assembly of materials. Because of the complexity of the involved processes and the wide range of relevant length scales, these models also present unique computational challenges that need to be met to arrive at a paradigm shift from current synthetic approaches to controlled, “lifelike” nonequilibrium methods. ![]() The most important initial challenge for the production of similar, nonbiological materials is the selection of suitable model systems that can serve as stepping stones toward technologically relevant applications however, even for simple systems, progress can be expected to be slow, unless theoretical research develops mechanistic models. Instead of bulk crystals or individual nanoparticles with tailored but limited properties, these natural materials typically consist of thousands of nanosized building blocks that assemble into functionality-enhancing hierarchies of structures. For instance, biominerals, such as bones and tooth enamel, are strikingly different from-and in many ways, superior to-the crystal structures formed near the thermodynamic equilibrium by direct mixing of the reactants ( 2). A plethora of examples, providing inspiration and proof of concept, is found among biological systems that use nonconventional bottom-up strategies to produce remarkable materials. Progress toward this goal requires an understanding of how materials synthesis is affected by transport processes, steep concentration gradients, and other factors that arise from reaction conditions far from the equilibrium. The rational design of systems that create complex materials and functional devices by externally controlled self-organization holds great promise for modern materials science ( 1). ![]() We discuss how mesoscopic aspects of the product structures can be modeled by reaction-transport equations and suggest important targets for future studies that should also include materials features at the nanoscale. In this research field, progress requires mechanistic insights that cannot be derived from experiments alone. ![]() We summarize recent experimental progress that often involves growth under tightly regulated conditions by means of wet stamping, holographic heating, and controlled electric, magnetic, or pH perturbations. In many cases, these systems show intricate structural hierarchies that span from the nanometer scale into the macroscopic world. These classes are hollow micro- and macrotubes in chemical gardens, polycrystalline silica carbonate aggregates (biomorphs), Liesegang bands, and propagating precipitation-dissolution fronts. We review four distinct classes of precipitation reactions, describe similarities and differences, and discuss related challenges for theoretical studies. Unlike the dissipative patterns in other self-organizing reactions, these features can be permanent, suggesting potential applications in materials science and engineering. Far from the thermodynamic equilibrium, many precipitation reactions create complex product structures with fascinating features caused by their unusual origins. ![]()
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