Mechanical Interlocking to Unlock the Reinforcing Potential of Carbon Nanotubes.

Single-walled carbon nanotubes (SWNTs) present extraordinary mechanical properties, with Youngs' modulus>1 TPa and tensile strength>50 GPa; this makes them ideal candidates as fillers for the reinforcement of polymers. However, the performance of SWNTs in this field has fallen behind expectations. This is due to a combination of imperfect individualization of the SWNTs and poor load transfer from the polymer to the SWNTs. Here, we study the reinforcement of polymers of different chemical nature using mechanically interlocked derivatives of single-walled carbon nanotubes (MINTs). We compare the mechanical properties of fibers made of poly (methyl methacrylate) (PMMA) and polysulfone (PSU) and their composites made with pristine SWNTs, MINTs, and the corresponding supramolecular models. With very low loading of MINTs (0.01 % w/w), improvements of more than 100 % on Youngs Modulus and the tensile strength are observed for both the nonpolar aliphatic PMMA and the very polar aromatic PSU polymers, while pristine carbon nanotubes and the supramolecular nanofillers showed smaller reinforcement. These data, together with our previous report on the reinforcement of polystyrene (nonpolar and aromatic), indicate that derivatization of SWNTs as MINTs is a valid general strategy to optimize the interaction between SWNT fillers and the polymer matrix.

Mechanically interlocked materials. Rotaxanes and catenanes beyond the small molecule.

A mechanical bond presents a combination of the best features of covalent and supramolecular chemistries (stability and structural integrity), plus a unique dynamic nature, that makes it a very interesting tool for materials chemistry. Here, we overview the chemistry of the mechanical bond applied to polymers, metal-organic frameworks (MOFs) and carbon nanotubes. We first describe synthetic strategies towards polycatenanes and polyrotaxanes, and highlight their potential impact in polymer chemistry, exemplified by their use to make stimuli-responsive gels and as binders in battery electrodes. We continue by showing how to include mechanically interlocked components in MOFs, and analyse the distinctive dynamic properties of the final constructs. Finally, we describe the strategies towards mechanically interlocked derivatives of single-walled carbon nanotubes (SWNTs), and discuss the potential of the mechanical bond to tackle some of the classic problems of SWNT chemistry.

Chemical sensing of water contaminants by a colloid of a fluorescent imine-linked covalent organic framework.

A two-dimensional imine-linked covalent organic framework bearing pyrene has been prepared and exfoliated in water as nanosheets to produce a stable water colloid. As a proof-of-concept, this COF colloid has been used to detect the presence of several organic dyes and polynitro-aromatic derivatives. These results show the high potential of these nanomaterials for applications in chemical sensing of pollutants directly in water.

Phospholipid-polymer amphiphile hybrid assemblies and their interaction with macrophages.

Recently, the combination of lipids and block copolymers has become an alternative to liposomes and polymersomes as nano-sized drug carriers. We synthesize novel block copolymers consisting of poly(cholesteryl acrylate) as the hydrophobic core and poly(N-isopropylacrylamide) (PNIPAAm) as the hydrophilic extensions. Their successful phospholipid-assisted assembly into vesicles is demonstrated using the evaporation-hydration method. The preserved thermo-responsive property of the lipid-polymer hybrids is shown by a temperature dependent adsorption behaviour of the vesicles to poly(l lysine) coated surfaces. As expected, the vesicle adsorption is found to be higher at elevated temperatures. The cellular uptake efficiency of hybrids is assessed using macrophages with applied shear stress. The amount of adhering macrophages is affected by the time and level of applied shear stress. Further, it is found that shorter PNIPAAm extensions lead to higher uptake of the assemblies by the macrophages with applied shear stress. No inherent cytotoxicity is observed at the tested conditions. Taken together, this first example of responsive lipid-polymer hybrids, and their positive biological evaluation makes them promising nano-sized drug carrier candidates.