Browsing by Author "Khan, Muhammad Turab Ali"

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Open Access
Chemical tracking of temperature by concurrent periodic precipitation pattern formation in polyacrylamide gels
(American Chemical Society, 2022-01-20) Khan, Muhammad Turab Ali; Kwiczak-Yiğitbaşı, Joanna; Tootoonchian, Pedram; Morsali, Mohammad; Lagzi, Istvan; Baytekin, Bilge
In nature, nonequilibrium systems reflect environmental changes, and these changes are often “recorded” in their solid body as they develop. Periodic precipitation patterns, aka Liesegang patterns (LPs), are visual sums of complex events in nonequilibrium reaction–diffusion processes. Here we aim to achieve an artificial system that “records” the temperature changes in the environment with the concurrent LP formation. We first illustrate the differences in 1-D LPs developing at different temperatures in terms of band spacings, which can demonstrate the time, ramp steepness, and extent of a temperature change. These results are discussed and augmented by a mathematical model. Using scanning electron microscopy, we show that the average size of the CuCrO4 precipitate also reflects the temperature changes. Finally, we show that these changes can also be “recorded” in the 2-D and 3-D LPs, which can have applications in long-term temperature tracking and complex soft material design.
Open Access
The effect of temperature on the formation of liesegang patterns of copper(II) chromate in polyacrylamide gels
(2020-09) Khan, Muhammad Turab Ali
Liesegang patterns (LPs) are a subclass of periodic precipitation patterns that result in a reaction-diffusion (RD) without convection. Since their discovery, LPs have been studied to understand the effect of different parameters such as electric field, magnetic field, or concentration of ions/ gels and to elucidate the mechanism of pattern formation. LPs are visual "complex sums" of the chemical reactions forming the patterns, the diffusion of the chemicals, and the physical changes in the reaction environment. Different physical environments produce different patterns and therefore the patterns formed can be used to „sense‟ the physical environment, in which the patterns are formed – if the changing physical parameter of the environment is previously linked to the various patterns forming under these conditions. In this study, we aim to achieve an LP system (CuCl2(outer electrolyte)/K2CrO4(inner electrolyte) in polyacrylamide gel) that senses temperature by monitoring concurrent pattern formation. First, we illustrate the visual differences in LPs occurring at different temperatures. We unveil the changes in the diffusion of ions, the reaction rate, and the precipitation threshold inside the gel media for LP forming at different temperatures. LP's behaviors under different temperature ramp conditions leading to a difference in pattern evolution in terms of spacing, width, and time laws are shown. Finally, we show that temperature provides a degree of freedom towards material design through RD.
Open Access
Mechanical control of periodic precipitation in stretchable gels to retrieve information on slastic deformation and for the complex patterning of matter
(Wiley-VCH Verlag, 2020-03) Morsali, Mohammad; Khan, Muhammad Turab Ali; Ashirov, Rahym; Holló, G.; Baytekin, H. Tarık; Lagzi, I.; Baytekin, Bilge
Material design using nonequilibrium systems provides straightforward access to complexity levels that are possible through dynamic processes. Pattern formation through nonequilibrium processes and reaction–diffusion can be used to achieve this goal. Liesegang patterns (LPs) are a kind of periodic precipitation patterns formed through reaction–diffusion. So far, it has been shown that the periodic band structure of LPs and the geometry of the pattern can be controlled by experimental conditions and external fields (e.g., electrical or magnetic). However, there are no examples of these systems being used to retrieve information about the changes in the environment as they form, and there are no studies making use of these patterns for complex material preparation. This work shows the formation of LPs by a diffusion–precipitation reaction in a stretchable hydrogel and the control of the obtained patterns by the unprecedented and uncommon method of mechanical input. Additionally, how to use this protocol and how deviations from “LP behavior” of the patterns can be used to “write and store” information about the time, duration, extent, and direction of gel deformation are presented. Finally, an example of using complex patterning to deposit polypyrrole by using precipitation patterns is shown as a template.
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Turgut Özal’s political and economic reforms in Turkish history
(Bilkent University, 2016) Wahab, Abdul; Pitafi, Faria; Çelik, Harun; Rabbani, Maria; Khan, Muhammad Turab Ali