Liquid Crystalline Phase Behavior and Sol–Gel Transition in Aqueous Halloysite Nanotube Dispersions

Abstract

The liquid crystalline phase behavior and sol-gel transition in halloysite nanotubes (HNTs) aqueous dispersions have been investigated by applying polarized optical microscopy (POM), macroscopic observation, rheometer, small-angle X-ray scattering, scanning electron microscopy, and transmission electron microscopy. The liquid crystalline phase starts to form at the HNT concentration of 1 wt %, and a full liquid crystalline phase forms at the HNT concentration of 25 wt % as observed by POM and macroscopic observation. Rheological measurements indicate a typical shear flow behavior for the HNT aqueous dispersions with concentrations above 20 wt % and further confirm that the sol-gel transition occurs at the HNT concentration of 37 wt %. Furthermore, the HNT aqueous dispersions exhibit pH-induced gelation with more intense birefringence when hydrochloric acid (HCl) is added. The above findings shed light on the phase behaviors of diversely topological HNTs and lay the foundation for fabrication of the long-range ordered nano-objects.

Isotropic–nematic phase transition in aqueous sepiolite suspensions

“…A liquid crystalline phase in aqueous suspensions of imogolite was reported by Kajiwara et al [9] and reproduced by others on natural [10] and synthetic imogolite [11]. There have also been claims of a liquid crystalline phase in suspensions of halloysite, although no clear separation between isotropic (disordered) and nematic (liquid crystalline) phase was visible [12]. A characteristic common to both these rod-like clay minerals (imogolite and halloysite) are that they have a cylindrical particle symmetry.…”

Stability of Halloysite, Imogolite, and Boron Nitride Nanotubes in Solvent Media

“…HNTs' aqueous dispersions can form liquid crystalline phases when high concentrations are approached [53]. Moreover, the transition can be controlled by pH, providing an interesting system for obtaining birifrangent materials under controlled chemical stimuli [53].…”

“…HNTs' aqueous dispersions can form liquid crystalline phases when high concentrations are approached [53]. Moreover, the transition can be controlled by pH, providing an interesting system for obtaining birifrangent materials under controlled chemical stimuli [53]. In light of that, different strategies for the manipulation of chemico-physical properties into aqueous media are pursued by the most appropriate functionalization of halloysite internal or external surfaces by electrostatic interactions with differently charged surfactants or polyelectrolytes.…”

Halloysite nanotubes loaded with peppermint essential oil as filler for functional biopolymer film

“…10-30 nm and 40-70 nm, respectively . Halloysite possesses a positive alumina inner lumen and a negative silica outer surface allowing its selective functionalization (Arcudi et al, 2014;Cavallaro, Lazzara, & Milioto, 2012), the formation of a liquid crystalline phase (Luo et al, 2013) and the encapsulation of chemically and biologically active compounds Lvov, Shchukin, Möhwald, & Price, 2008;Lvov, Wang, Zhang, & Fakhrullin, 2016;Lvov, DeVilliers, & Fakhrullin, 2016;Shutava, Fakhrullin, & Lvov, 2014;), such as drugs (Aguzzi, Cerezo, Viseras, & Caramella, 2007;Lun, Ouyang, & Yang, 2014), natural molecules (Massaro, Piana et al, 2015), marine biocides (Wei et al, 2014), cosmetics (Suh et al, 2011), and other functional agents (Abdullayev, Price, Shchukin, & Lvov, 2009). HNT are suitable as catalytic supports (Machado, de Freitas Castro, Wypych, & Nakagaki, 2008;Massaro et al, 2014;, adsorbent nanomaterials for wastewater decontamination (Szczepanik & Słomkiewicz, 2016;Zhang et al, 2016), and nanofiller for sustainable packaging (Liu, Wu, Jiao, Xiong, & Zhou, 2013;Tescione, Buonocore, Stanzione, Oliviero, & Lavorgna, 2014).…”