Question $4$

$($i$)$ Why does a liquid crystalline fluid appear cloudy, but when heated sufficiently

appears transparent?

$20\%$

$($ii$)$ When a supersaturated solution of aluminium and copper is aged, metastable pre$-$

cipitates such as ${}^{\text{'}}$ or ${}^{\text{'}\text{'}}$ form first, rather than the equilibrium $A{l}_{2}Cu.$ Explain

why this happens. Why is the solubility of copper in aluminium larger when in

equilibrium with a metastable precipitate?

$40\%$

$($iii$)$ Derive an equation that relates solidification velocity $v$ to the activation barrier $Q$

for the transfer of atoms from liquid to solid and the magnitude of the driving force

for solidification, $|G|.$