CHEMISTRY DEPARTMENT SEMINAR: “Self-organization in precipitation reactions: Liesegang phenomenon”
Dr. István Lagzi
Budapest University of Technology and Economics
Precipitation reactions coupled to mass transport of chemicals in hydrogels can result in impressive micro- and macrostructured patterns known as periodic precipitation (or Liesegang phenomenon). Liesegang patterns consist of parallel precipitation bands/zones or rings depending on the geometry of the experimental setup. In my talk, I will present recent advances in this field, namely understanding helical pattern formation in precipitation reactions, formation of precipitation waves and using Liesegang pattern formation for synthesis of micro- and nanoparticles. In some chemical systems, helical and helicoidal precipitation patterns emerge in the wake of reaction-diffusion fronts. In our experiments, these chiral structures arise with well-defined probabilities controlled by experimental conditions such as the initial concentration of the reagents. We developed a model which describes the observed experimental trends. The results suggest that the probability of emergence of helicoidal pattern is determined by a delicate interplay among the time and length scales related to the front and to the unstable precipitation modes. Additionally, the random noise also plays a quantifiable role.
Formation of chemical waves in excitable media have attracted considerable scientific interest in the context of nonlinear chemical kinetics because of a new approach to micro and nanofabrication, in addition to some biological aspects. All precipitation patterns share common morphological characteristics, namely the formed patterns are stationary and no dynamical patterns can be observed in these chemical systems. We showed that in several circumstances dynamic patterns (precipitation waves) can exist in purely inorganic precipitation systems similar to the well-known and studied waves in Belousov–Zhabotinsky reaction. In the talk, I will present how the pattern characteristics can be controlled (such as the wavelength and the pattern morphology).
The synthesis of different sizes of nanoparticles and microparticles is important in designing nanostructured materials with various properties. Wet synthesis methods lack the flexibility to create various sizes of particles (particle libraries) using fixed conditions without the repetition of the steps in the method with a new set of parameters. I will present a synthesis method based on nucleation and particle growth in the wake of a moving chemical front in a gel matrix. The process yields well-separated regions (bands) filled with nearly monodisperse nanoparticles and microparticles, with the size of the particles varying from band to band in a predictable way. The origin of the effect is due to an interplay of a precipitation reaction of the reagents and their diffusion that is controlled in space and time by the moving chemical front. The method represents a new approach and a promising tool for the fast and competitive method for the synthesis of various sizes of colloidal particles. Finally, I will present that similar precipitation patterns can emerge in the interaction of oppositely charged nanoparticles showing the universal behavior of this phenomenon.
H Nakanishi, A Deák, G Hólló, I Lagzi, Existence of a precipitation threshold in the electrostatic precipitation of oppositely charged nanoparticles, Angewandte Chemie International Edition, 2018, 57 (49), 16062-16066
R Tóth, RM Walliser, I Lagzi, F Boudoire, M Düggelin, A Braun, C E Housecroft, E C Constable, Probing the mystery of Liesegang band formation: revealing the origin of self-organized dual-frequency micro and nanoparticle arrays, Soft Matter, 2016, 12 (40), 8367-8374
R M Walliser, F Boudoire, E Orosz, R Tóth, A Braun, E C Constable, Z Rácz, I. Lagzi, Growth of nanoparticles and microparticles by controlled reaction-diffusion processes, Langmuir, 2015, 31 (5), 1828-1834
M M Ayass, M Al-Ghoul, I Lagzi, Chemical waves in heterogeneous media, Journal of Physical Chemistry A, 2014, 118 (50), 11678-11682
S Thomas, I Lagzi, F Molnár Jr, Z Rácz, Probability of the emergence of helical precipitation patterns in the wake of reaction-diffusion fronts, Physical Review Letters, 2013, 110 (7), 078303
Date: July 29, 2019 (Monday)
Place: UNAM Conference Hall #SU-01
All interested are cordially invited.