We are also interested in the self-assembly of liquid crystalline materials in confined spaces of mesoporous silica films. Therefore, our modular approach was adapted for the investigation of inorganic/organic hybrid materials. An interesting feature of the mesoporous silica films is that they are obtained by soft-templating with cellulose nanocrystals, which yield mesoporous materials with the chiral-nematic structure of the template imprinted in the nanostructure of the films. The nanostructure of the films represents a one-dimensional photonic crystal (for comparison see photonic sensing) and selectively reflects light of a specific wavelength and handedness. The color of this reflection depends on the periodicity (helical pitch) of the chiral-nematic structure, which cannot be changed due to the limited flexibility of silica. However, a second handle to manipulate the photonic properties of the mesoporous materials is given by the refractive index contrast between the host material (silica) and the guest (air) in the pores. Therefore, the infiltration of the pores with a guest which shows temperature-depending changes in the refractive index, such as liquid crystals, allows for the control of the photonic reflection by temperature. Our studies on the mesoporous silica films infiltrated by hydrogen-bonded liquid crystals show that the pores size controls the liquid crystalline behavior of the mesogens and that the mesogenic guests enable to change the photonic response of the nanostructured silica by temperature and UV-light (due to a photo-initiated phase transition, see Figure 1).

​
​Figure 1: Schematic representation of the synthesis of the thermochromic hybrid materials (A) as well as their UV-Vis spectra of the hybrid material upon heating and cooling.

Recent Publication

“Hydrogen‐Bonded Liquid Crystals in Confined Spaces—Toward Photonic Hybrid Materials” – M. Spengler, R.Y. Dong, C.A. Michal, W.Y. Hamad, M. J. MacLachlan,* M. Giese,* Adv. Funct. Mater. 2018, 28, 1800207-1800207.

“Tuning the photonic properties of chiral nematic mesoporous organosilica with hydrogen-bonded liquid-crystalline assemblies” – M. Giese,* T. Krappitz, R.Y. Dong, C.A. Michal, W.Y. Hamad, B.O. Patrick, M. J. MacLachlan,* J. Mater. Chem. C 2015, 3, 1537-1545. (Hot Article)