Cher Ling Toh

A biomimetic approach to enhancing interfacial interactions: polydopamine-coated clay as reinforcement for epoxy resin.

A facile biomimetic method was developed to enhance the interfacial interaction in polymer-layered silicate nanocomposites. By mimicking mussel adhesive proteins, a monolayer of polydopamine was constructed on clay surface by a controllable coating method. The modified clay (D-clay) was incorporated into an epoxy resin, it is found that the strong interfacial interactions brought by the polydopamine benefits not only the dispersion of the D-clay in the epoxy but also the effective interfacial stress transfer, leading to greatly improved thermomechanical properties at very low inorganic loadings. Rheological and infrared spectroscopic studies show that the interfacial interactions between the D-clay and epoxy are dominated by the hydrogen bonds between the catechol-enriched polydopamine and the epoxy.

Polyhedral oligomeric silsesquioxanes tethered with perfluoroalkylthioether corner groups: Facile synthesis and enhancement of hydrophobicity of their polymer blends

Octa(vinyl)-POSS or octa(vinyldimethylsilyloxy)-POSS reacts with perfluoroalkyl thiol in the presence of 2,2′-azobisisobutyronitrile to afford perfluoroalkylthioether substituted POSS compounds in high yields. 29Si NMR and MALDI-TOF mass spectroscopic analyses indicate that the eight perfluoroalkylthioether chains are attached to the POSS core structure. Studies on poly(methyl methacrylate) (PMMA) blends with 5 wt% fluorinated POSS (fluoroPOSS) reveal that the POSS molecules considerably enhance the hydrophobicity of polymer blend surfaces as evidenced by significant increases in water contact angles from 71° for pure PMMA to 114–124° for fluoroPOSS-blends, making this type of fluoroPOSS a promising new class of highly hydrophobic hybrid materials.

Highly conductive graphene by low-temperature thermal reduction and in situ preparation of conductive polymer nanocomposites

Polydopamine-coated graphene oxide (DGO) films exhibit electrical conductivities of 11,000 S m(-1) and 30,000 S m(-1) upon vacuum annealing at 130 °C and 180 °C, respectively. Conductive poly(vinyl alcohol)/graphene and epoxy/graphene nanocomposites show low percolation thresholds due to the excellent dispersibility of the DGO sheets and their effective in situ reduction.

Synthesis and characterisation of main‐chain hydrogen‐bonded supramolecular liquid crystalline complexes formed by azo‐containing compounds

A series of azopyridine‐containing hydrogen bonding acceptors (4a–c) with flexible spacers of oligo(methylene) were synthesised. Hydrogen‐bonded polymeric complexes 4/5 and trimeric complexes 4/62 , where 5 and 6 are aromatic dicarboxylic acids and monocarboxylic acids, respectively, were prepared and their liquid crystallinity was examined using differential scanning calorimetry and polarising optical microscopy. The study showed that most of the complexes displayed reversible thermotropic nematic phase. The isotropic to nematic phase transition temperatures of polymeric complexes 4/5 and trimeric complexes 4/62 in general decreased with the increase in length of spacers and terminal groups in the corresponding proton acceptors 4 and the proton donors 5 and 6, respectively. Hydrogen bonding interactions in complexes 4/5 and 4/62 were studied by X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy.

Packing Behaviors of Structurally Different Polyhedral Oligomeric Silsesquioxane-Imidazolium Surfactants in Clay

This paper reports the packing structures of two types of polyhedral oligomeric silsesquioxane (POSS)-imidazolium surfactants with different molecular rigidity in the intergalleries of montmorillonite clay. Wide-angle X-ray scattering (WAXS) and molecular modeling studies suggest that the POSS-imidazolium cations have a bilayer packing structure in clay with the long axes of the molecules largely tilted with respect to the basal plane. Direct evidence for the bilayer structure is provided by transmission electron microscopy (TEM). WAXS and differential scanning calorimetry (DSC) results indicate that the relatively flexible POSS-imidazolium cation is able to form a two-dimensionally ordered structure in the clay intergalleries, while the relatively rigid one exhibits a disordered structure in clay. Furthermore, with reducing surfactant loading, the clay modified with the rigid surfactant exhibits increased interlayer d-spacings probably because the surfactant is able to take more extended conformation at lower loadings. With its low organic content and disordered surfactant packing structure, the clay modified with the rigid surfactant also exhibits excellent thermal and thermo-oxidative stabilities.