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Hard spheres confined to narrow quasi-one-dimensional cylindrical channelsform perfect helical structures at close packing. Here, we use moleculardynamics simulation to show that the thermodynamics, structure and dynamics ofthe fluid below close packing are dominated by the presence of topologicaldefects that reverse the local twist direction of the helix. When compressedfrom a random, low density state, or decompressed from high density orderedstates with zero excess helical twist, the system equilibrates to an achiralfluid that exhibits two heat capacity maxima along the equation of state. Thelow density heat capacity maximum corresponds to the onset of helix formationand the high density maximum occurs when the system rapidly loses defects in aSchottky-like anomaly. The local twist auto-correlation function in the achiralfluid exhibits a stretched exponential decay and the structural relaxationtimes undergo a fragile-to-strong crossover located at the high density heatcapacity maximum. We also study the effect of excess helical twist by usinginitial starting configurations consisting of two helical domains with oppositetwist directions of different lengths. This leads to the formation oftopologically protected states that are characterized by the presence ofloosely bound defect pairs which become more tightly bound with increasingexcess helical twist. The local twist auto-correlation function in the chiralfluid decays as a power law at long times. The possible kinetic orthermodynamic origin of this topological protection is discussed.

Thermodynamics, structure and dynamics of cylindrically confined hard spheres: The role of excess helical twist