  Dual mechanical braiding experiments provide a useful tool with which
investigate the nature of interactions between rod-like molecules, for instance
actin and DNA. In conditions close to molecular condensation, one would expect
an appearance of a local minimum in the interaction potential between the two
molecules. We investigate this situation, introducing an attractive component
into the interaction potential, using a model developed for describing such
experiments. We consider attraction that does not depend on molecular
structure, as well that which depends on a DNA-like helix structure. In
braiding experiments, an attractive term may lead to certain effects. A local
minimum may cause molecules to collapse from a loosely braided configuration
into a tight one, occurring at a critical value of the moment applied about the
axis of the braid. For a fixed number of braid pitches, this may lead to
coexistence between the two braiding states, tight and loose. Coexistence
implies certain proportions of the braid are in each state, their relative size
depending on the number of braid pitches. This manifests itself as linear
dependence in numerically calculated quantities as functions of the number of
braid pitches. Also, in the collapsed state, the braid radius stays roughly
constant. Furthermore, if the attractive interaction is helix dependent, the
left-right handed braid symmetry is broken. For a DNA like charge distribution,
using the Kornyshev-Leikin interaction model, our results suggest that
significant braid collapse and coexistence only occurs for left handed braids.
Regardless of the interaction model, the study highlights the possible
qualitative physics of braid collapse and coexistence; and the role helix
specific forces might play, if important. The model could be used to connect
other microscopic theories of interaction with braiding experiments.
