Cellulose liquid crystal templated TiO2 chiral nematic foams

Aerogels with chiral nematic structure are promising candidates for structural coatings and optical devices. Cellulose nanocrystals (CNCs) are excellent photonic building blocks for the fabrication of chiral nematic aerogels. Conventional bottom-up fabrication process usually is complicated, energy and time consumption. Herein, a simple method for fabricating CNCs and polyethylene glycol (PEG) based foams with chiral nematic structure was proposed. After CNCs-PEG based solid films were swollen with N-methylmorpholine N-oxide (NMMO) aqueous solutions, the obtained hydrogels were freeze-dried, resulting in chiral nematic foams. During the process, both macropores and mesopores were created with chiral nematic phase retained inside foam walls. Owning numerous macropores and chiral nematic walls of varying axial directions, the chiral nematic foams exhibited a broad-band reflection phenomenon. Moreover, the representative Titanium diisopropoxide(bis-2,4-pentanedionate) was permeated into foam walls, and transformed into chiral nematic TiO2 foams after annealing. We envisage that the chiral nematic foams may have a promising application in the fields of chiral separation or chiral catalysis.