Custard/corn flour with water is not thixotropic

 We added water to a custard/corn flour mix. Above, it was flowing freely. Then we tried to stir it (below). It became solid and the stirrer wouldn't move.

I confidently told my class that the mixture is thixotropic. But apparently it isn't http://www.thenakedscientists.com/forum/index.php?topic=3697.5;wap2 It is similar but undergoes shear thickening instead. I'd never heard of this. Here's what I found https://en.wikipedia.org/wiki/Dilatant The custard mixture is essentially a suspension - ie tiny solid particles floating in water. Applying a shear stress (that's basically a tearing force) the particles get pushed close enough together that instead of electrostatic repulsion, they start to attract each other using forces called Hamaker forces. I've come across Van der Waals forces before where a negative charge on one particle repels electrons to the far side of the neighbouring particle, leaving the near side positive so that - hey presto! - they attract. Hamaker forces are this done with bigger particles. The particles in the suspension are pushed close enough together for this to happen and that grabs the particles into to order to be like a solid.