Elaboration of Cellulose Nanocrystal/Ge-Imogolite Nanotube Multilayered Thin Films

Hydrophobic, Sustainable, High-Barrier Regenerated Cellulose Film via a Simple One-Step Silylation Reaction

With the increasing importance of environmental protection, high-performance biopolymer films have received considerable attention as effective alternatives to petroleum-based polymer films. In this study, we developed hydrophobic regenerated cellulose (RC) films with good barrier properties through a simple gas-solid reaction via the chemical vapor deposition of alkyltrichlorosilane. RC films were employed to construct a biodegradable, free-standing substrate matrix, and methyltrichlorosilane (MTS) was used as a hydrophobic coating material to control the wettability and improve the barrier properties of the final films. MTS readily coupled with hydroxyl groups on the RC surface through a condensation reaction. We demonstrated that the MTS-modified RC (MTS/RC) films were optically transparent, mechanically strong, and hydrophobic. In particular, the obtained MTS/RC films exhibited a low oxygen transmission rate of 3 cm³/m² per day and a low water vapor transmission rate of 41 g/m² per day, which are superior to those of other hydrophobic biopolymer films.

Accelerating the electrical response of solvent-dispersed imogolite nanotubes through structural organisation

Structural organisation of solvent-dispersed imogolite nanotubes accelerated their electrical response, resulting in birefringence variations analogous to a liquid crystal system. Crosslinking, confinement, and helical structuring of the imogolite nanotubes in the solvent led to the cooperative aggregation and dissociation of the dispersed nanotubes, which induced rapid changes in their birefringence.

Structure and Properties of Hybrid Film Fabricated by Spin-Assisted Layer-by-Layer Assembly of Sacran and Imogolite Nanotubes

A free-standing (biomacomolecule/synthetic inorganic nanotubes) hybrid film was fabricated through an alternative layer-by-layer (LBL) assembly of sacran and imogolite nanotubes. Sacran is a natural polysaccharide extracted from the cyanobacterium Aphanothece sacrum, while imogolite is a natural tubular aluminosilicate clay found in volcano ash. The hybrid film thickness increased linearly with the number of the bilayers, because of the interaction between the negatively charged surface of sacran and the positively charged surface of imogolite. UV-vis spectroscopy indicated that the LBL film exhibited good transparency. The surface morphology of the LBL film was smooth in the micrometer scale; many imogolite nanotubes were adsorbed onto the sacran layer, while no imogolite clusters were observed. Furthermore, the structure, stability, gas permeability, and mechanical properties of the LBL films were investigated.

Colloidal Stability of Imogolite Nanotube Dispersions: A Phase Diagram Study

In this article, we revisit the colloidal stability of clay imogolite nanotubes by studying the effect of electrostatic interactions on geo-inspired synthetic nanotubes in aqueous dispersions. The nanotubes in question are double-walled aluminogermanate imogolite nanotubes (Ge-DWINTs) with a well-defined diameter (4.3 nm) and with an aspect ratio around 4. Surface charge properties are assessed by electrophoretic measurements, revealing that the outer surfaces of Ge-DWINT are positively charged up to high pH values. A series of Ge-DWINT dispersions have been prepared by osmotic stress to control both the ionic strength of the dispersion and the volume fraction in nanotubes. Optical observations coupled to small and wide-angle X-ray scattering (SAXS/WAXS) experiments allow us to unravel different nanotube organizations. At low ionic strength (IS < 10^-2 mol L^-1), Ge-DWINTs are fully dispersed in water while they form an arrested gel phase above a given concentration threshold, which shifts toward higher volume fraction with increasing ionic strength. The swelling law, derived from the evolution of the mean intertube distance as a function of the nanotube concentration, evidences a transition from isotropic swelling at low volume fractions to one-dimensional swelling at higher volume fractions. These results show that the colloidal stability of Ge-DWINT is driven by repulsive interactions for ionic strengths lower than 10^-2 mol L^-1. By contrast, higher salt concentrations lead to attractive interactions that destabilize the colloid suspension, inducing nanotube coagulation into larger structures that settle over time or form opaque gels. Detailed simulations of the WAXS diagram reveal that aggregates are mainly formed by an isotropic distribution of small bundles (less than four nanotubes) in which the nanotubes organized themselves in parallel orientation. Altogether, these measurements allow us to give the first overview of the phase diagram of colloidal dispersions based on geo-inspired imogolite-like nanotubes.

Ultrathin Films of Cellulose: A Materials Perspective

A literature review on ultrathin films of cellulose is presented. The review focuses on different deposition methods of the films-all the way from simple monocomponent films to more elaborate multicomponent structures-and the use of the film structures in the vast realm of materials science. The common approach of utilizing cellulose thin films as experimental models is therefore omitted. The reader will find that modern usage of cellulose thin films constitutes an exciting emerging area within materials science and it goes far beyond the traditional usage of the films as model systems.

Organic-Inorganic Hybrid Thin Films Fabricated by Layer-by-Layer Assembly of the Phosphorylated Cellulose Nanocrystal and Imogolite Nanotubes

Phosphorylated cellulose nanocrystal (P-CNC)/imogolite nanotube (natural aluminosilicate nanotube) hybrid thin films were fabricated by spin-assisted layer-by-layer assembly. Phosphorylation of CNC with diammonium hydrogen phosphate ((NH₄)₂HPO₄) was carried out to introduce phosphate groups on the CNC surface for enhanced interaction with imogolite. Structure of the P-CNC/imogolite thin film was characterized by atomic force microscopy, scanning electron microscopy, X-ray diffraction (XRD), and grazing incidence wide-angle XRD. The film thickness increased linearly with the increment of the P-CNC/imogolite bilayer. Benefitting from the strong affinity between the phosphate group of the P-CNC and the Al-OH group of imogolite, the P-CNC/imogolite thin films were quite stable in water within a wide range of pH values, compared with the deterioration of the CNC/imogolite film under same soaking conditions.

Imogolite Nanotubes: A Flexible Nanoplatform with Multipurpose Applications

Among a wide variety of inorganic nanotubes, imogolite nanotubes (INTs) represent a model of nanoplatforms with an untapped potential for advanced technological applications. Easily synthesized by sol-gel methods, these nanotubes are directly obtained with a monodisperse pore size. Coupled with the possibility to adjust their surface properties by using straightforward functionalization processes, INTs form a unique class of diameter-controlled nanotubes with functional interfaces. The purpose of this review is to provide the reader with an overview of the synthesis and functionalization of INTs. The properties of INTs will be stated afterwards into perspective with the recent development on their applications, in particular for polymer/INTs nanocomposites, molecular confinement or catalysis.