Bands during transient and steady shear

Porter have reported band formation during shear We have however 

More recently, the existence of transverse band structures during shear has been discounted. Ernst and Navard [56] used SALS of HPC -f water and found no patterns indicative of band structures, even at a shear rate when was negative. A confirming negative result was found by Picken ei al. [13], who used conoscopic SALS and found no evidence of meridional reflections during steady shear. 

The observation of bands during the start-up transient is probably a key observation in resolving the discrepancy between our report [18] that negative is correlated with the presence of transverse bands during shear and the observations of other authors. Although some authors have agreed that this was possible, the observation had never been duplicated. Nevertheless, as recently as 1994 Kim and Han [73] left the possibility open . .. at present there is no experimental evidence, which proves that the formation of banded structure and negative values of in TPLCs are necessarily related to each other.  

We feel now that the most likely explanation is that, due to lack of parallelism in the plates of our primitive shearing stage, we never achieved a true steady state, and that in fact the shear rate at the point of observation oscillated significantly. A certain pumping action could in fact be observed by eye, to the best of our recollection. It would be an interesting exercise to determine under what conditions of oscillating shear rate a quasi-steady state band structure could be formed. Either this will turn out to be relatively easy to do, or we were unbelievably lucky to observe it. Not so lucky, in fact, since it led to 

At relatively low shear rates the texture is controlled by the Ericksen number 

---