Chemical Tracking of Temperature by Concurrent Periodic Precipitation Pattern Formation in Polyacrylamide Gels

Abstract

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 CuCrO 4 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.

Effect of the Polarity of Solvents on Periodic Precipitation: Formation of Hierarchical Revert Liesegang Patterns

“…According to this behavior, LP could be employed for practical purposes to track the polarity changes in unknown solvents, similar to the use of LPs for tracking environmental changes. 15 , 16 , 30 Moreover, tuning the solvent polarity can be a promising strategy to control, tailor, and design both regular LPs and new hierarchical structures. In addition, hierarchical layered structures are of great importance for the design of self-organized functional materials from nano- to macroscale.…”

“…Based on this result, we constructed one possible model, and simulation using this model showed good qualitative agreement with experimental observations. According to this behavior, LP could be employed for practical purposes to track the polarity changes in unknown solvents, similar to the use of LPs for tracking environmental changes. ,, Moreover, tuning the solvent polarity can be a promising strategy to control, tailor, and design both regular LPs and new hierarchical structures. In addition, hierarchical layered structures are of great importance for the design of self-organized functional materials from nano- to macroscale. − Some recent studies showed that LPs can be formed using some functional materials (e.g., metal nanoparticles and metal–organic frameworks), and another study indicated how to form microscale periodicity. ,,, By combining this knowledge with our strategy of polarity-based LP control, LP could be a potential candidate for the generation of self-organized hierarchical layered structures with various functions and structures.…”

“… 24 − 27 Also, some LPs sometimes showed the formation of hierarchical layered structures with the coexistence of two patterns with different frequencies of periodicity. 21 , 28 , 29 Furthermore, recent studies on LPs have focused on investigating, in both simulations and experiments, how the periodicity of LPs is controlled and designed in response to physical and chemical conditions of the environment (such as the temperature, 30 gel concentration, 15 direct and alternating electric field, 31 , 32 and mechanical deformation of the gel 16 ). These factors can affect the precipitation by influencing the diffusion of M + , the chemical reaction between M + and X – , and the nucleation and aggregation of the precipitate.…”

“…Generally, Δ x n increases with increasing n , and this type of pattern is called regular LP. , The regular-type LP generation can be observed in the CuCrO 4 system and many other precipitation systems. ,− However, when Pb 2+ is used instead of Cu 2+ as an outer electrolyte, exceptional LP can be formed, in which Δ x n decreases in contrast to the regular-type pattern, which is the so-called revert (invert) LP. − This difference was discussed from the perspective of the property of colloidal stability. − Also, some LPs sometimes showed the formation of hierarchical layered structures with the coexistence of two patterns with different frequencies of periodicity. ,, Furthermore, recent studies on LPs have focused on investigating, in both simulations and experiments, how the periodicity of LPs is controlled and designed in response to physical and chemical conditions of the environment (such as the temperature, gel concentration, direct and alternating electric field, , and mechanical deformation of the gel). These factors can affect the precipitation by influencing the diffusion of M + , the chemical reaction between M + and X – , and the nucleation and aggregation of the precipitate.…”

Tunability of Self-Organized Structures Based on Thermodynamic Flux

“…The formation of the periodic zone was apparent at [KI] above 0.1 M on the line profile. A further increase in [KI] moved the position of the periodic band farther away from the interface, which is a general feature of Liesegang pattern formation. − Two empirical rules, namely, a spacing law and the Matalon–Packter law, can be used to confirm that the observed periodic band may be classified as a Liesegang band. The spacing law implies that the distance, x n , from the interface to the n th band obeys the following relationship (eq ): where n and p are the band number and spacing coefficient, respectively.…”