No abstract

We report a simple way to obtain polymercoated multiwalled boron nitride nanotubes (BNNTs) conducted under mild conditions compatible with fragile biopolymers. The approach converts aggregated pristine BNNTs into colloidally stable dispersions in water without requiring treatment at high temperature or in strongly oxidative conditions. The method relies on our experimental observation that glycine (NH 2 −CH 2 −COOH, Gly) interacts with BNNTs, in accordance with theoretical calculations. The role of glycine in this process is 2-fold: the Gly amine group binds to the B-sites of BNNTs, while the Gly carboxylic acid function provides ionic anchoring sites for interactions with polyelectrolytes. The formation of Gly-BNNTs proved to be essential, since they readily disperse in water as disentangled objects and spontaneously adsorb polycations, such as chitosan (CH), polyanions, such as hyaluronan (HA), and polyzwitterionic polymers, such as chitosan-phosphorylcholine (CH-PC). Treatment of aqueous dispersions of coarsely coated BNNTs with an immiscible solvent (hexane) resulted in the complete coverage of the BNNT surfaces via oil/water interfacial assembly. This work provides a rapid, mild, and scalable route to waterdispersible biofunctional BNNTs that may serve as drug delivery vehicles or scaffolds in tissue engineering.

In this article, we addressed the applicability of time-of-flight secondary ion mass spectrometry (TOF-SIMS) to examine the effects of molecular weight and of flexible-segment length on the polymer chain arrangement at the folding surfaces of the lamellae. Poly(bisphenol A-etheralkane) (Cn) contains both rigid aromatic and flexible aliphatic CH(2) segments. The number of CH(2) units per flexible segment, n, varies from 8 to 12. Principal component analysis (PCA) of TOF-SIMS data revealed the chemical and structural variations of the folding surfaces of these polymers and identified the ion peaks contributing to these variations. We highlighted the discriminating power of PCA to distinguish the structural conformations of the amorphous and flat-on lamellar surfaces of these polymers. PCA loadings analyses showed that relatively more flexible structures were deposited on the folding surfaces when the flexible-segment length increased from 8 to 10 CH(2) units. The concentration of short loops at folding surfaces and the disorder of folding surfaces increased when the molecular weight increased. All these results led us to conclude that TOF-SIMS has great potential for probing the chemical composition of the folding surfaces of polymers.

This report provides detailed experimental results of thermal and surface characterization on untreated and surface-treated halloysite nanotubes (HNTs) obtained from two geographic areas. Surface characterization techniques, including XPS and time-of-flight secondary ion mass spectrometry (ToF-SIMS) were used. ToF-SIMS surface analysis experiments were performed with both atomic and cluster ion beams. Higher ion yields and more high-mass ions were obtained with the cluster ion beams. Static ToF-SIMS spectra were analyzed with principal component analysis (PCA). Morphological diversities were observed in the samples although they mainly contained tubular structures. Thermogravimetric data indicated that aqueous hydrogen peroxide solution could remove inorganic salt impurities, such as alkali metal salts. The amount of grafting of benzalkonium chloride of HNT surface was determined by thermogravimetic analysis. PCA of ToF-SIMS spectra could distinguish the samples mined from different geographical locations as well as among surface-treated and untreated samples.