Self‐oscillating pH‐responsive cryogels as possible candidates of soft materials for generating mechanical energy

Abstract

This research highlights the use of poly(acrylic acid) (PAAc) cryogels as a pH oscillator in oscillatory bromate-sulfite-ferrocyanide reactions. The cryogels were prepared from frozen aqueous solutions of acrylic acid monomer and N,N 0 -methylenebis(acrylamide) crosslinker at À18C. Fast responsive macroporous PAAc cryogels were obtained at or below 4 w/v % initial monomer concentration. SEM images of PAAc cryogel networks exhibited a heterogeneous morphology consisting of pores of sizes 10 1 lm, typical for macroporous networks formed by the cryogelation technique. PAAc cryogels coupled with the bromate oscillator oscillate between swollen and collapsed states, during which a cyclic three-fold change in the gel volume was observed. The results show that, due to the fast response rate of cryogels, macroscopic gel samples can be used as a pH oscillator which would provide generation of significant amount of mechanical energy.

pH-oscillations in the bromate–sulfite reaction in semibatch and in gel-fed batch reactors

“…The -Fe(CN) 6 4and BrO 3 --SO 3 2--Mn(II) CSTR pH-oscillators were applied to generate periodic pulses in the concentration of some nonredox ions (Ca 2þ , Al 3þ , F -,…), 11 to see oscillatory distribution of species in the Ni 2þ -histidine complex formation reaction 12 and in changes in the volume of hydrogels. 13 These experiments could probably be carried out and the same information would be gained if semibatch or closed arrangements were used. When the CSTR BrO 3 --SO 3…”

Porous Materials for Hydrolytic Dehydrogenation of Ammonia Borane

“…Upon the polymerization of the nonfrozen phase, 3-D gel formation occurs around the growing ice crystals which act as a template for the formation of the pores. Due to the crosslinking of polymer–polymer chains, a stable structure with macroporous gel network is revealed upon melting of the ice crystals at room temperature [ 79 , 80 ].…”

Experimental Evidence of Large Amplitude pH Mediated Autonomous Chemomechanical Oscillation

“…In the first type, the mechanical oscillations of the gel are merely slaved to the chemical oscillation kinetics. The gel is immersed in oscillatory reaction components [ 2 , 8 , 9 , 10 , 11 ] or the oscillations can take place inside the gel when introducing appropriate reactants into the polymer network [ 5 , 6 , 12 , 13 , 14 ] or when the reactant species act as an active cross-linker of the gel [ 15 ]. In the second type, instabilities are generated by the interactions between the gel and non-oscillatory reaction, which can be further classified into two scenarios: “long-range activation” and “synergetic chemomechanical oscillation”.…”