Polymers Rayleigh velocity

In materials of lower velocity the situation becomes simpler. If the shear critical angle is outside the lens angle, then there will be no Rayleigh phenomena. Such materials would include many polymers and composites. There may still be longitudinal head waves, and these can reveal some of the features associated with Rayleigh wave imaging, such as surface cracks. But two further factors enhance subsurface imaging. First, because the velocity is lower, the... 

What about ascending fronts If a front were to propagate upward, then the hot polymer-monomer solution in the reaction zone could rise because of buoyancy, removing enough heat at the polymer-monomer interface to quench the front. With a front that produces a solid product, the onset of convection is more complicated than the cases that we considered in Chapter 9, because the critical Rayleigh number is a function of the velocity (Volpert et al., 1996). Bowden et al. (1997) studied ascending fronts of acrylamide polymerization in dimethyl sulfoxide. As in the iodate-arsenous acid fronts, the first unstable mode is an antisymmetric one followed by an axisymmetric one. Unlike that system, in the polymerization front the stability of the front depends on both the solution viscosity and the front velocity. The faster the front, the lower the viscosity necessary to sustain a stable front. 

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