Properties of Single-Walled Aluminosilicate Nanotube/Poly(vinyl alcohol) Aqueous Dispersions

Effect of Polymer Length on the Adsorption onto Aluminogermanate Imogolite Nanotubes

This study evidences the adsorption of model nonionic polymers onto aluminogermanate imogolite nanotubes, attractive porous nanofillers with potential molecular loading and release applications. We resolve the underlying mechanisms between nanotubes and polyethylene glycols with different molecular weights by means of nanoisothermal titration calorimetry. The analysis of the results provides a direct thermodynamic characterization, allowing us to propose a detailed description of the energetics involved in the formation of polymer/imogolite complexes. The affinity toward the nanotube surface is enthalpy-driven and strongly depends on the polymer chain length, which significantly affects the polymer configuration and the flow properties of the resulting complexes, probed by small-angle neutron scattering and rheology, respectively. These findings open new avenues for the rational design of these hybrid mixtures for advanced applications.

Rheological and rheo-birefringence features of semidilute ethyl cellulose dispersions under steady shear flow

We have conducted comprehensive rheological and rheo-birefringence characterizations of a series of semidilute ethyl cellulose (EC)/α-terpineol dispersions under steady shear flow. The EC dispersions investigated have commonly been utilized as a binder agent in fabricating metal/metal-oxide pastes for a number of industrial applications, and were recently demonstrated to foster nearly monodisperse spherical aggregates under dilute conditions. Herein, semidilute EC dispersions are shown to exhibit rheological features practically no different from those known for standard entangled polymer solutions. The corresponding rheo-birefringence responses, however, reveal microstructural features that are reminiscent of general colloidal systems. The steady-state feature reveals a universal stress-birefringence relationship at various EC concentrations, along with a common critical stress (∼200 Pa) at which the EC network breaks into smaller clusters. The transient feature displays prominent and long-persisting periodic oscillations that have previously been observed only for nearly monodisperse rod-like colloids or liquid crystals. The overall findings shed new light on the role of EC serving as a commonplace polymer binder in industry and, from a scientific perspective, raise interesting questions related to the characteristic rheological and microstructural features of general polymer dispersions in overlapped regimes.

Inorganic Nanotube Mesophases Enable Strong Self-Healing Fibers

The assembly of one-dimensional nanomaterials into macroscopic fibers can improve mechanical as well as multifunctional performance. Double-walled aluminogermanate imogolite nanotubes are geo-inspired analogues of carbon nanotubes, synthesized at low temperature, with complementary properties. Here, continuous imogolite-based fibers are wet-spun within a poly(vinyl alcohol) matrix. The lyotropic liquid crystallinity of the system produces highly aligned fibers with tensile stiffness and strength up to 24.1 GPa (14.1 N tex^-1) and 0.8 GPa (0.46 N tex^-1), respectively. Significant enhancements over the pure polymer control are quantitatively attributed to both matrix refinement and direct nanoscale reinforcement, by fitting an analytical model. Most intriguingly, imogolite-based fibers show a high degree of healability via evaporation-induced self-assembly, recovering up to 44% and 19% of the original fiber tensile stiffness and strength, respectively. This recovery at high absolute strength highlights a general strategy for the development of high-performance healable fibers relevant to composite structures and other applications.

Percolation behaviors of model carbon black pastes

The percolation behaviors of a series of high-structured carbon black (CB) pastes (CB weight fractions 10-25 wt%, ethyl cellulose as the binder, α-terpineol as the solvent) were systematically investigated using analyses of rheology and impedance spectra together with characterization via small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM). When the CB concentration was near the static percolation threshold (∼20 wt%), the permittivity, ac conductance, and elastic modulus of the paste displayed notable increases, whereas the SAXS profile revealed the prevalence of isolated CB aggregates (mean radius of gyration ∼40 nm). Upon further aging at 25 and 40 °C (up to 6 h), two CB pastes near the static percolation threshold (i.e., 20 and 25 wt%) exhibited prominent temporally evolving responses, including more than tenfold increases in their ac conductance and elastic modulus, as well as a pronounced upturn in the low-q SAXS profile (q < 0.03 nm-1) and the formation of a (partially) interconnected cluster network in SEM observations of the morphologies of screen-printed films. In this case, we provide the first evidence of "(aging) Time-(relaxation) Time-Temperature-Concentration Superposition (TTTCS)" for the dynamic modulus data over a frequency range of seven orders of magnitude. This suggests that prolonged aging time imparted to CB aggregate interaction and restructuring (or gelation) may work in tandem with the known effects of the system temperature and concentration to further extend the accessible range of dynamic modulus data, in a similar way to recent reports on the effect of the curing (crosslinking) time on a carbon nanotube suspension and caramel. In combination with existing (three) master curves for two different colloidal materials, we show that there is a reasonable superposition of all the dynamic modulus data over a frequency range of 12 orders of magnitude.

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.