Nematic Dispersions of Nanoporous Silica Hollow Spheres with Potential for Smart Window Applications

Nanoporous silica hollow spheres (NPSHSs) with a microscale diameter and high roughness of outer and inner surfaces can be well suspended in a nematic liquid crystal (NLC). Nanopores allow nematics to fill the NPSHS and form inner nematic droplets with an order due to the randomness of pores uncorrelated with outer nematic ordering. Due to the nanoconfinement effect and the strong local anchoring of rough nanostructure on the NPSHS surface, the binary mixture of nematic molecules and NPSHSs demonstrates the effectiveness of nanomorphology on aggregation suppression. The calorimetry showed a decrease in nematic transition enthalpy; optical microscopy indicated decoupled nematic ordering inside and outside NPSHSs, characterized by bubbles, and laser tweezers helped to identify a reduction of the minimum intershell distance for notable attractive interactions. In line with the observations, simulations prove the existence of disordered NLC layers on the NPSHS surfaces characterized by weak effective planar degenerate nematic anchoring. The resulting aggregation suppression, negligible gravitational sedimentation due to nanoshell lightness, and decoupling of inner and outer nematics to offer their separate manipulation are promising for optoelectronic applications of NLC dispersions of NPSHSs. We illustrate that together with their high chemical stability, these dispersions open possibilities for applications in smart windows based on LC-controlled transparency, where more scattering domains can enhance tunability and contrast.