After a short review on the physics of pulled threads and their mechanical
properties, the paper reports and discusses on the strand elongation of
disordered columnar phases, hexagonal or lamello-columnar, of small molecules
or polymers. The mechanical properties appear to be relevant to the length of
the columns of molecules compared to the thread length, instead of the usual
correlation length. When short, the column entanglement being taken into
account, the strand exhibits rather fluid properties that may even look like
nematic at a macroscopic scale. Then, the Plateau-Rayleigh instability soon
breaks the thread. However, the hydrodynamic objects being the columns instead
of the molecules, the viscosity is anomalously large. The observations show
that the strands of columnar phases are made of filaments, or fibrils, that
indeed are bundles of columns of molecules. They both explain the grooves and
rings observed on the antenna or bamboo-like strand profiles. On pulling a
strand, the elongation stress eventually exceeds the plasticity threshold, thus
breaking columns and filaments. Cracks, more exactly, giant dislocations are
thus formed. They change the strand thickness by steps of different
birefringence colours. Interestingly, adding a solute may drastically change
the effective viscosity of the columnar phase and its mechanical properties.
Some solutes as alcanes, exhibit lubricant and detangling properties, while
others as triphenylene, are quite anti-lubricant
