Hexadecapolar nematic colloids and new material designs

Outermost occupied electron shells of chemical elements resemble monopoles, dipoles, quadrupoles, and octupoles corresponding to filled s-, p-, d-, and f-atomic orbitals. Theoretically, elements with hexadecapolar outer shells could also exist, but none of the known stable elements have filled g-orbitals. On the other hand, the research paradigm of “colloidal atoms” displays complexity of physical behavior of colloidal particles exceeding that of their atomic counterparts, allowing for switching between colloidal elastic dipole and quadrupole configurations using weak external stimuli. This lecture will describe colloidal elastic hexadecapoles formed by polymer microspheres dispersed in a liquid crystal, a nematic fluid of orientationally ordered molecular rods. The solid microspheres locally perturb the uniform molecular alignment of the nematic host, inducing hexadecapolar and other elastic multipoles that drive highly anisotropic colloidal interactions. We uncover physical underpinnings behind the spontaneous formation of colloidal elastic hexadecapoles and describe the ensuing particle bonding inaccessible to colloids studied previously. The lecture will conclude with discussion of practical applications that can be enabled by combining unique properties of metal and semiconductor nanoparticles with facile switching of self-assembled ordered superstructures that they exhibit in nematic hosts.