Sustained Large-Amplitude Chemomechanical Oscillations Induced by the Landolt Clock Reaction

Abstract

Synergetic chemomechanical oscillators represent a fundamentally new class of oscillators, where a clock reaction, owning no oscillatory chemical kinetics, generates shrinking-swelling cycles in a chemoresponsive gel under appropriate fixed nonequilibrium boundary conditions. Sufficiently large size-changes are a condition for continually switching between a reacted and an unreacted chemical state in the gel through sufficiently large differences in the diffusion time between the environment and the core of the gel. Two former experimental demonstrations with acid autocatalytic reactions were frustrated either by complex behaviors (chlorite-tetrathionate system) or by side reactions with the gel matrix (bromate-sulfite system). With the Landolt (iodate-sulfite) reaction, regular large-amplitude chemomechanical oscillations can be sustained for more than a week. This enabled a fine study of the temperature and stoichiometry range of operation. I have identified several key steps that are experimentally essential to the systematic design of further synergetic oscillators. The robust realization of this type of self-organization in artificial systems is currently unique.

Chemically coded time-programmed self-assembly

“…Each of these clock variants behaved somewhat individually against buffering from the point of view of, e.g., the upper limit concentration of the H +binding units that would cause the complete damping of the pH. [20][21][22] So a new reaction has to be experimentally tested with a buffer having a pK a value similar to the functions of the driven components.…”

“…For details of the synthesis refer to our previous works. [20][21][22] For the dependence of the swelling-shrinking rate and the sharpness of the pH-response on the synthesis parameters (solvent composition, initiator), see the ESI. † The obtained polyNIPA-based gel filaments exhibited the sharpest swollen to shrunken transition at 26°C, from pH 8.00 to pH 9.25.…”

“…[14][15][16][17] At the material level, diverse modes of periodic actuation with no external stimuli have been elaborated via coupling nonlinear (oscillatory or even simple clock-type) chemical reactions with physicochemical processes in elastic materials. 2,[18][19][20][21][22][23][24] Autonomous periodic viscosity changes have been brought about through subsequently building and breaking chemical or physical links between the building blocks. [25][26][27] In the past few years periodic interconversion of building blocks with time has been successfully realized by using pH oscillators in a continuously stirred-tank reactor.…”

Light-Triggered Soft Artificial Muscles: Molecular-Level Amplification of Actuation Control Signals

“…In this work, the iodate concentration (19 mM) and sulphite concentration (60 mM) are kept constant and at a ratio of 3.16, close to the stoichiometric composition of Reaction 2 and 3 where the greatest pH drop can occur 28 (Supplementary Fig. 4 ).…”

“… 26 . Although most subsequent research in this area has employed the Belousov−Zhabotinsky (BZ) reaction 27 , there has been use of other systems including work by Horváth with the Landolt system 28 . Here we harness excitability 29 , 30 , another property of such autocatalytic reactions but one which has not been applied to the actuation of hydrogels.…”