Colloidal molecules
are ideal model systems for mimicking real
molecules and can serve as versatile building blocks for the bottom-up
self-assembly of flexible and smart materials. While most colloidal
molecules are rigid objects, the development of colloidal joints has
made it possible to endow them with conformational flexibility. However,
their unrestricted range of motion does not capture the limited movement
and
bond directionality that is instead typical of real molecules. In
this work, we create flexible colloidal molecules with anin situcontrollable motion range and bond directionality
by assembling spherical particles onto cubes functionalized with complementary
surface-mobile DNA. By varying the sphere-to-cube size ratio, we obtain
colloidal molecules with different coordination numbers and find that
they feature a constrained range of motion above a critical size ratio.
Using theory and simulations, we show that the particle shape together
with the multivalent bonds creates an effective free-energy landscape
for the motion of the sphere on the surface of the cube. We quantify
the confinement of the spheres on the surface of the cube and the
probability to change facet. We find that temperature can be used
as an extra control parameter to switchin situbetween
full and constrained flexibility. These flexible colloidal molecules
with a temperature switching motion range can be used to investigate
the effect of directional yet flexible bonds in determining their
self-assembly and phase behavior, and may be employed as constructional
units in microrobotics and smart materials.