  The shape of the building blocks plays a crucial role in directing
self-assembly towards desired architectures. Out of the many different shapes,
helix has a unique position. Helical structures are ubiquitous in nature and a
helical shape is exhibited by the most important biopolymers like
polynucleotides, polypeptides and polysaccharides as well as by cellular
organelles like flagella. Helical particles can self-assemble into chiral
superstructures, which may have a variety of applications, e.g. as photonic
(meta)materials. However,a clear and definite understanding of these structures
has not been entirely achieved yet. We have recently undertaken an extensive
investigation on the phase behaviour of hard helical particles, using numerical
simulations and classical density functional theory. Here we present a detailed
study of the phase diagram of hard helices as a function of their morphology.
This includes a variety of liquid-crystal phases, with different degrees of
orientational and positional ordering. We show how, by tuning the helix
parameters, it is possible to control the organization of the system. Starting
from slender helices, whose phase behaviour is similar to that of rodlike
particles, the increase in curliness leads to the onset of azimuthal
correlations between the particles and the formation of phases specific to
helices. These phases feature a new kind of screw order, of which there is
experimental evidence in colloidal suspensions of helical flagella.
