Jerzy Maselko

From Chemical Gardens to Chemobrionics

Chemical gardens in laboratory chemistries ranging from silicates to polyoxometalates, in applications ranging from corrosion products to the hydration of Portland cement, and in natural settings ranging from hydrothermal vents in the ocean depths to brinicles beneath sea ice. In many chemical-garden experiments, the structure forms as a solid seed of a soluble ionic compound dissolves in a solution containing another reactive ion. In general any alkali silicate solution can be used due to their high solubility at high pH. The cation should not precipitate with the counterion of the metal salt used as seed. A main property of seed chemical-garden experiments is that initially, when the fluid is not moving under buoyancy or osmosis, the delivery of the inner reactant is diffusion controlled. Another experimental technique that isolates one aspect of chemical-garden formation is to produce precipitation membranes between different aqueous solutions by introducing the two solutions on either side of an inert carrier matrix. Chemical gardens may be grown upon injection of solutions into a so-called Hele-Shaw cell, a quasi-two-dimensional reactor consisting in two parallel plates separated by a small gap.

Chemical waves in inhomogeneous excitable media

Abstract Propagating chemical waves are typically studied in homogeneous, excitable reaction mixtures. Chemical waves in an inhomogeneous excitable medium are examined in this paper. Cation exchange beads, loaded with ferroin, are bathed in Belousov-Zhabotinsky reaction mixtures containing no catalyst. Spiral waves are spontaneously initiated above a critical bromate concentration, which is dependent on the size of the ferroin-loaded beads. At high bromate concentrations, irregular patterns are formed due to an overcrowding of spirals. An upper limit in the number of individual waves is exhibited, which is independent on the bead size. Regular and irregular patterns are analyzed by calculating spatial correlation functions from digital images.

Precipitation Pattern Formation in the Copper(II) Oxalate System with Gravity Flow and Axial Symmetry

Chemical systems that are far from thermodynamic equilibrium may form complex temporal and spatiotemporal structures. In our paper, we present unusual precipitation patterns that have been observed in the system of Cu(II)-oxalate. Starting with a pellet of copper sulfate immersed in or by pumping copper sulfate solution into a horizontal layer of sodium oxalate solution, we have observed the formation of a precipitate ring and an array of radially oriented thin fingers. The development of these patterns is related to the internal structure of the different crystals, the gravity flow, and the circular symmetry of the experimental arrangement.

Self-construction of complex forms in a simple chemical system

Abstract We observed spontaneous formation of very complex structures, measurable on the centimeter and millimeter scales, in a simple dual-component inorganic chemical system. The diffusion, convection, and chemical reactions self-organize in space and time and produce domes, multi-arms, or more complex structures with different spatial organization depending on the concentration of reagents in the aqueous environment into which the ‘seed’ is immersed.

Self-organization as a new method for synthesizing smart and structured materials

Abstract Self-organization in chemical systems may be a basis for entirely new 21st-century technologies. During self-organization, concentrations of chemical species spontaneously organize in space and time, forming a variety of complex structures. Examples of these structures are Turing patterns which result from interaction between chemical kinetics and diffusion. In this paper we report numerical studies of Turing structures that develop spontaneously from single perturbations. Many of these structures are built from layers of different chemical concentrations. Others form skeletal type patterns, or respond to environment. These structures may find applications in formation of highly structured or smart materials.

Transverse coupling of chemical waves

The transverse coupling of chemical waves is investigated using a model scheme for excitable media. Chemical waves supported on the surfaces of a semipermeable membrane couple via diffusion through the membrane, resulting in new types of spatiotemporal behavior. The model studies show that spontaneous wave sources may develop from interacting planar waves, giving rise to a complex sequence of patterns accessible only by perturbation. Coupled circular waves result in the spontaneous formation of spiral waves, which subsequently develop patterns in distinct domains with characteristic features. The long time entrainment behavior of coupled spiral waves reveals regions of 1:2 phase locking.

Chemical precipitation structures formed by drops impacting on a deep pool

The experiments described here are at the intersection of two dynamical systems with long pedigrees for forming interesting patterns: liquid droplet impacts and precipitation membranes. Drops of calcium chloride solution have been allowed to impact on a deep pool of sodium silicate solution. The precipitation structures produced by this method, and how these structures subsequently evolve, have been observed. Many interesting patterns can be formed from this process. It is observed that the precipitation patterns produced are sensitive to the shape of the drop when it impacts the pools surface. Also, at large drop heights, we determine two critical Weber numbers: one for forming a skirt around the structures and the other for breakup of the structures. On longer time scales, open tubes grow from the closed precipitation shell produced at lower drop heights. These tubes can appear in large numbers with nearly identical sizes and diameters as small as 50 μm.

Metabolic photofragmentation kinetics for a minimal protocell: Rate-limiting factors, efficiency, and implications for evolution

A key requirement of an autonomous self-replicating molecular machine, a protocell, is the ability to digest resources and turn them into building blocks. Thus a protocell needs a set of metabolic processes fueled by external free energy in the form of available chemical redox potential or light. We introduce and investigate a minimal photodriven metabolic system, which is based on photofragmentation of resource molecules catalyzed by genetic molecules. We represent and analyze the full metabolic set of reaction-kinetic equations and, through a set of approximations, simplify the reaction kinetics so that analytical expressions can be obtained for the building block production. The analytical approximations are compared with the full equation set and with corresponding experimental results to the extent they are available. It should be noted, however, that the proposed metabolic system has not been experimentally implemented, so this investigation is conducted to obtain a deeper understanding of its dynamics and perhaps to anticipate its limitations. We demonstrate that this type of minimal photodriven metabolic scheme is typically rate-limited by the front-end photoexcitation process, while its yield is determined by the genetic catalysis. We further predict that gene-catalyzed metabolic reactions can undergo evolutionary selection only for certain combinations of the involved reaction rates due to their intricate interactions. We finally discuss how the expected range of metabolic rates likely affects other key protocellular processes such as container growth and division as well as gene replication.

Growing a Chemical Garden at the Air-Fluid Interface.

Here we grow chemical gardens using a novel, quasi two-dimensional, experimental configuration. Buoyant calcium chloride solution is pumped onto the surface of sodium silicate solution. The solutions react to form a precipitation structure on the surface. Initially, an open channel forms that grows in a spiral. This transitions to radially spreading and branching fingers, which typically oscillate in transparency as they grow. The depth of the radial spreading, and the fractal dimension of the finger growth, are surprisingly robust, being insensitive to the pumping rate. The curvature of the channel membrane and the depth of the radially spreading solution can be explained in terms of the solution densities and the interfacial tension across the semipermeable membrane. These unusually beautiful structures provide new insights into the dynamics of precipitation structures and may lead to new technologies where structures are grown instead of assembled.

Temporal and spatial organization of chemical and hydrodynamic processes. the system Pb2+-Chlorite-Thiourea

Precise spatio-temporal organization of chemical, hydrodynamic, and mechanical processes is typical for biological systems where particular chemical reactions have to accrue in precisely assignment place and time. It is rarely studied and observed in chemical systems. We report unusual precipitation pattern formation of PbSO(4) in chemical media (Pb(2+)-Chlorite-Thiourea System). We have found that there is a region in a plane of initial concentrations of chlorite ions and thiourea where precipitation of lead sulfate appears in a form of ring if a pellet of lead nitrate is placed into the system. The whole process may be divided into three stages: movement of first circular front of lead containing solution, formation of a ringlike pattern of lead sulfate, and finally, propagation of this pattern resulting in a formation of ring with final inside diameter. Our experiments indicate that the following values are reproducible and quantify the PbSO(4) ring evolution: induction time, radius of the ring birth, speed of ring propagation toward the center, and final inside radius of the ring. Numerical solution of kinetic equations allowed us to give a qualitative explanation for the phenomenon observed. Formation and evolution of the PbSO(4) rings are caused by interplay of concentration gradients in the system and chemical reactions that occur in excitable chlorite-thiourea system. Chemical reactions and hydrodynamic processes form a complex causal network that made morphogenesis of this unusual pattern possible.