Iridescent Chiral Nematic Mesoporous Organosilicas with Alkylene Spacers

Abstract

surfactants and inorganic precursors, it has been possible to create mesoporous materials with different symmetries and pore sizes, and diverse compositions. [5,8] For example, using chiral surfactants as a liquid crystal template has created chiral mesoporous materials with twisted helical structures. [13] In 1999, three research groups independently reported on the incorporation of organic groups into mesoporous silica by using (R′O) 3 SiRSi(OR′) 3 precursors in the place of Si(OR) 4 precursors for the sol-gel condensation. [7,9,14] It proved possible to construct periodic mesoporous silica with organic groups directly integrated into the walls of the mesoporous structure. [11,[15][16][17][18][19][20][21][22][23] Sol-gel processing of silicate materials is highly versatile-it can incorporate various types of precursors and can be carried out under a variety of reaction conditions (e.g., variable pH, temperature, concentration, and solvent mixtures). [24] Therefore, mesoporous organosilica materials have attracted increasing interest for applications including catalysis, [1,25] metal scavenging, [26] chromatography, [27] and biomedical applications. [2] Cellulose nanocrystals (CNCs) obtained from sulfuric-acidcatalyzed hydrolysis of biomass are remarkable materials. [28,29] In 1951, Rånby isolated the crystalline regions within plant cellulose microfibers to form colloidal CNCs with nanoscale dimensions. [28] CNCs have impressive mechanical properties that arise from their high crystallinity and large aspect ratios. [30] Remarkably, CNCs also form a chiral nematic liquid crystal in water. [31] This order can be retained upon drying the aqueous suspension to give a colored, iridescent film. [32] The CNCs arrange into a Bouligand structure, where the crystallites themselves are aligned in layers, but twist with a characteristic helical pitch, P. It is the repeating helicoidal structure that leads to diffraction of circularly polarized light from the CNC films. [33] Many researchers are making new materials that take advantage of the unique properties of CNCs. [30,[34][35][36][37][38][39][40][41][42][43][44][45][46][47] In 2010, we discovered that films of mesoporous silica with chiral nematic structure could be prepared using CNCs as a template. [20] When Si(OR) 4 is condensed with CNCs in water, the resulting composite film contains silica and a chiral nematic assembly of CNCs. CNCs can be removed from the composite materials using pyrolysis, leaving behind thin films of iridescent mesoporous silica with a chiral nematic arrangement of pores inside the glass. These materials are of interest Mesoporous organosilica films with chiral nematic structures are prepared with a bridging urea group and with alkylene bridges, where the length of the alkylene bridge varies from C 1 -C 6 . To synthesize these materials, cellulose nanocrystals (CNCs) are used as liquid crystal templates, which coassemble with the organosilica precursor to give composite materials with a chiral nematic structure of CNCs embedded within. Remova...

From Equilibrium Liquid Crystal Formation and Kinetic Arrest to Photonic Bandgap Films Using Suspensions of Cellulose Nanocrystals

“…Concerning the colloidal stability of the, usually highly charged, CNCs in non-aqueous solvents, a variety of different approaches can be found in the literature. The most straightforward way is to choose other polar solvents such as the conventional organic solvents dimethyl sulfoxide (DMSO), N, N-dimethyl formamide (DMF) or tetrahydrofuran (THF) [142][143][144][145][146][147] or mixtures with ionic liquids [148][149][150]. Okura et al [151] investigated the dispersibility and shear-induced birefringence of CNCs that had been produced by HCl hydrolysis in 21 different solvents.…”

Iridescent Cellulose Nanocrystal Films Modified with Hydroxypropyl Cellulose

“…10,13 The resultant thin film has a left-handed chiral nematic structure, resulting in brilliant iridescence. These properties have been exploited in a number of ways to make new classes of optical materials including, hydrogels, 14 organosilicas, 15 and thin films, 16,17 to name a few. Another important feature of CNCs is that they have very high intrinsic strength and stiffness, which makes them attractive for the development of new ultrastrong materials.…”

“…These charged groups allow the CNCs to be dispersed in water and provide colloidal stability because of charge repulsion. ,− Interestingly, at appropriate concentrations, CNCs organize into a chiral nematic lyotropic liquid crystalline phase that can be captured in a solid film when the dispersing medium is slowly evaporated. , The resultant thin film has a left-handed chiral nematic structure, resulting in brilliant iridescence. These properties have been exploited in a number of ways to make new classes of optical materials including, hydrogels, organosilicas, and thin films, , to name a few. Another important feature of CNCs is that they have very high intrinsic strength and stiffness, which makes them attractive for the development of new ultrastrong materials …”

Porous organic–inorganic hybrid materials for catalysis, energy and environmental applications

“…MacLachlan et al extended this investigation by incorporating a bridging urea group and long alkylene spacers varying from C 1 -C 6 with the aim to modify the properties of (CNMOs). 64 The issue of phase separation between the aqueous CNC suspension and organosilica precursors was resolved by either mixing long alkylene-bridged precursors with shorter ones or by using a binary solvent system (water and DMF) during self-assembly. Recently, a chiral bis-organosilane precursor 1,1 0 -((1R,2R)-1,2-diphenylethane-1,2-diyl)bis(3-(3-(triethoxysilyl)propyl)urea) was condensed in an EtOH/water mixture in the presence of CTAB as an SDA to produce chiral PMO nanoparticles by Reziq and Omar in 2020.…”