Trigger wave

Jorne (1980) confirmed the findings of earlier researchers that the trigger wave propagation in the ferroin catalyzed B-Z reaction is caused by the coupling between autocatalytic mechanism and diffusion. 

IIIC) Jorne, J. Role of Diffusion in Trigger Wave Propagation in the Belousov-Zhabotinskii... 

Figure L Control of the spiral shape in the oscillatory Belousov-Zhabotinsky reaction. Ru(bpy)3 was used as catalyst. Ar laser beam was irradiated (illustrated by white arrow) at the core of the rotating spiral to increase the size of the core region. The morphology of spiral changed reversibly from Archimedean to logarithmic, and the wave profile from trigger-wave to phase-wave. Controlling global structure by local control of singular region is characteristic in dissipative structures.

Figure 3. Turbid trigger wave in a pH responsive gel cylinder. The photographs are tilted by 9(P. Snapshots from top to bottom at 0, 110, 220 minutes. Experimental conditions d=lmm, [OH ]o=5.3xlO M. White scale bar=3mm.

Note that, in the present case, trigger waves and oscillations exist only in a narrow range of parameter. The reason for this, is that the polymer network bears acidic functions in order to make it pH-responsive. Introducing immobile proton binding sites into the gel slows down the effective diffusion of protons and, as a consequence, reduces the range of parameter over which the excitability and oscillations are observed (Szalai, I. Private communication). 

Figure 6, Non equilibrium phase diagram of the pH responsive gels coupled to the CT reaction, o swollen state x trigger waves A volume oscillations collapsed state A transition of the CSTR into the T state. The parameter d is the inner diameter of the mold.

On the other hand, trigger waves (first reported by Zaikin and Zhabotinsky, 1970) may appear in quiescent as well as oscillatory reagent and are dependent on diffusion. They are waves of excitation conducted through the medium in a manner analogous to the spread of a grass fire. 

Simultaneously and independently Theones (1973) published the same explanation of frequency gradient waves. Unfortunately, he erred in claiming to explain trigger waves (target patterns and spirals) in terms of frequency gradients without diffusive coupling between spatially neighboring points. 

Scroll waves and target patterns (as well as solitary trigger waves) share the common property of dependence on the interaction of reaction and diffusion, as witnessed by the fact that they are all blocked by impermeable barriers. 

Ce ] return to the vicinity of the steady state. This refractionness explains the mutual annihilation of trigger waves upon collision. 

Field and Noyes (1974b) have suggested a simple model for the propagation of trigger waves based on the FKN mechanism (Chapter II). 

Travelling waves These may be classified as (i) phase or kinematic waves, (ii) trigger waves and (iii) self-accelerating meta-waves, a general account of which is given below. 

Experimental results on velocity of trigger waves in acidic bromate oxidation of ferroin have been reported by Field and Noyes [18] and Showalter [24]. A semi-quantitative comparison with experimental results shows that the observed velocity is proportional to square root of the product of [H+] and [BrOj ] as theoretically predicted. However, deviations have been observed depending on experimental conditions. Thus, in the case of malonic acid -I- bromate -t- manganous sulphate -1- ferroin in H2SO4 medium, the wave velocity is found [25] to be proportional to [Br03 ]y [H+]. Similar results are obtained for citric acid -I- BrOj -I- Mn - - H2SO4 system [26]. 

Showalter, K., Noyes, R. M. Turner, H. Detailed studies of trigger wave initiation and detection. J. Am. Chem. Soc., 101, 7463-9. 

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