Gold nanoparticles as additives for liquid crystals
Dr Torsten Hegmann, Kent State University, USA
Gold nanoparticles (Au NPs) have emerged as a promising class of materials with an enormous potential for modulating and improving the characteristics of liquid crystals (LCs) used in device applications. Recent, global research activities including research performed in our lab show that Au NPs induce distinct effects in LCs that may point to new directions for the use of these LC colloids in optical and sensing applications.[1,2] This talk will summarize recent fundamental research performed in my lab on nematic liquid crystals doped with functionalized Au NPs and position these results within the field. We have demonstrated the use of chiral dopant, (S)-naproxen, decorated Au NPs that effectively induce chiral nematic LC phases not only with a stronger CD response (tighter helical pitch) but also with the opposite helical sense in comparison to pure (S)- naproxen doped into the same nematic host. We have established that parameters such as the nature of the interface as well as the concentration and surface modification of the NPs doped into a nematic host can be tuned to either result in the formation of unique defect patterns (i.e. the formation of birefringent stripes surrounded by larger domains with homeotropic alignment) or produce a temperature-dependent alignment change from planar to vertical that could be exploited for sensor applications. We also showed an unprecedented dual alignment/switching mode with drastically reduced values of the threshold voltage (Vth) by doping LCs with gold NPs, and the formation of convection rolls (Williams Kapustin domains). This research is currently expanded to Au nanorods, gold nanostars, and magic-sized quantum dots.
 (a) O Stamatoiu, M Mirzaei, X Feng, T Hegmann, Top Curr Chem 2012, in press (b) U Shivakumar, J Mirzaei, X Feng, A Sharma, P Moreira, T Hegmann, Liq Cryst 2011, 38, 1495-1514.
 (a) H Qi, T Hegmann, J Mater Chem 2008, 18, 3288-3294; (b) T Hegmann, H Qi, V M Marx, J Inorg Organomet Polym Mater 2007, 17, 483-508.
 (a) H Qi, J O’Neil, T Hegmann, J Mater Chem 2008, 18, 374-380; (b) H Qi, T Hegmann, JACS 2008, 130, 14201-14206.
 (a) H Qi, T Hegmann, J Mater Chem 2006, 16, 4197-4205; (b) M Urbanski, B Kinkead, H Qi, T Hegmann, H -S Kitzerow, Nanoscale 2010, 2, 1118-1121; (c) B Kinkead, M Urbanski, H Qi, H -S Kitzerow, T Hegmann, Proc SPIE 2010, 7775, 777511
 H Qi, T Hegmann, ACS Appl Mater Interfaces 2009, 1, 1731-1738.
 H Qi, B Kinkead, T Hegmann, Adv Funct Mater 2008, 18, 212-221.
 M Urbanski, B Kinkead, T Hegmann, H -S Kitzerow, Liq Cryst 2010, 37, 1151-1156.
 S Umadevi, X Feng, T Hegmann, Ferroelectrics 2012, in press
 M Mirzaei, M Urbanski, K Yu, H -S Kitzerow, T Hegmann, J Mater Chem 2011, 21, 12710-12716.
Strong coupling between ferromagnetic particles and rod-like particles in aqueous suspensions
Professor Yuriy Reznikov, Institute of Physics of National Academy of Sciences of Ukraine, Ukraine
Yuriy Reznikov, PhD, Professor in Physics, head of the Department of Crystals at the Institute of Physics (Kyiv, Ukraine). His primary interests are photo-induced and surface phenomena in liquid crystals as well as novel LCD technologies and nanophysics of liquid crystals. Yuriy Reznikov is a co-inventor of effect of photoalignment of liquid crystals. He has been focusing on the study and application of liquid crystal nano-colloids, electro-optics, photorefraction and photonics effects in liquid crystals. Yuriy Reznikov is a co-author of 19 USA patents including basic patents on photoalignment technology, more than 170 papers.
A two-component dispersion of hard rods, one of which is magnetically sensitive, is studied theoretically and experimentally. It is shown that control of the ordering of the magneto-sensitive component by H-field provides effective way to order the non-magnetic component. We found that magnetically-induced ordering of low concentrated ferromagnetic nanoparticles in isotropic phase of the suspension of V2O5 rods in water results in a strong birefringence of the suspension despite V2O5 rods themselves not being sensitive to magnetic field. Furthermore, ferromagnetic nanoparticles also cause extremely high sensitivity of the suspension in the nematic phase; if the native suspension requires magnetic field, H> 7kGs to be reoriented, the doped suspension effectively responds to the magnetic field, H< 30Gs.