Formation and Phase Transformations of Helical Structures of Colloidal Spheres

We experimentally explore the ordering of thermal quasi-one dimensional helical structures of monodisperse spheres.~ Helical packings of thermoresponsive colloid particles are formed in glass microcapillaries and display evidence of long-range orientational order at high volume fractions.~ As volume fraction is decreased, these ordered packings transition to structurally disordered states.~ Orientational order parameters and susceptibilities demonstrate the abrupt nature of this crossover.~ Coexistence of ordered and disordered states is also exhibited at lower volume fractions, as well as coexistence of ordered domains with different pitch and chirality.~ Such coexistence lends credence to the notion of discontinuous transitions in these structures.~ We also present preliminary experimental work on producing and controlling the formation of ordered helical structures of unconfined colloids by tuning both short-range attractive and dipolar interactions between particles.