Huanjun Li

A water contact angle exceeding 170° is exhibited by the surface of aligned polyacrylonitrile (PAN) nanofibers without any surface treatment (the picture shows a cross-sectional view of the as-synthesized nanofibers). The nanofibers were obtained by simply extruding a PAN solution through an anodic alumina template into a solidifying solution. The factors that govern the hydrophobicity of aligned nanostructures are discussed.

The process of forming the unique organic/inorganic network structure of nanocomposite hydrogels (NC gels) was studied through changes in viscosity, optical transparency, X-ray diffraction, and mechanical properties. It was concluded that, during the preparation of the initial reaction solutions, a specific solution structure was formed from monomer (NIPA) and clay, where NIPA prevents gel formation of clay itself, and initiator (KPS) is located near the clay surface through ionic interactions. In subsequent in-situ free-radical polymerization, it was observed that the viscosity increased markedly during NC gel syntheses and in a manner similar to that in OR gel syntheses. Also, NC gels with different polymer contents exhibit characteristic two-step changes in the stress−strain curves, which correspond to the primary network formation and subsequent increase of cross-link density. These are because the polymerization proceeds on the clay particles which are relatively immobile, and clay platelets act as effective multifunctional cross-linking agents (plane cross-link). Then, it was proposed that clay−brush particles, consisting of exfoliated clay platelets with numbers of polymer chains grafted to their surfaces, were formed in the very early stage of polymerization, at around 7% of monomer conversion. Novel decreases in transparency were observed corresponding to the formation of clay−brush particles, but transparency recovered on further polymerization. Clay−brush particle formation was confirmed by XRD measurements on dried NC gels prepared using small amounts of monomer. Thus, a mechanism for forming the unique organic/inorganic network structure, including the formation of clay−brush particles in the synthetic pathway, is proposed. Furthermore, it was found that NC gels with excellent mechanical properties and structural homogeneity could not be prepared using other methods such as mixing clay and polymer solutions or by in-situ polymerization in the presence of the other inorganic nanoparticles instead of clay. These results indicate that the formation of organic/inorganic network structures in NC gels is highly specific and only realized by in-situ free-radical polymerization in the presence of clay.

Fluoroalkylsilane treatment of super-hydrophobic, aligned carbon nanotube films (see electron micrograph) prepared by pyrolysis of metal phthalocyanines results in the films having both super-hydrophobic and super-lipophobic properties, namely they are super-“amphiphobic” surfaces. Supporting information for this article is available on the WWW under http://www.wiley-vch.de/contents/jc_2002/2001/z15871_s.pdf or from the author. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

The mechanical properties and structures of nanocomposite gels (NC gels), consisting of poly(N-isopropylacrylamide) (PNIPA) and inorganic clay (hectorite), prepared using a wide range of clay concentration (∼25 mol % against water) were investigated. All NC gels were uniform and transparent, almost independent of the clay content, Cclay. The tensile modulus (E) and the strength (σ) were controlled without sacrificing extensibility by changing Cclay. The E, σ, and fracture energy observed for as-prepared NC gels attained 1.1 MPa, 453 kPa, and 3300 times that of a conventional chemically cross-linked gel, respectively, and σ increased to 3.0 MPa for a once-elongated NC25 gel. From the tensile and compression properties, in addition to optical transparency, it was concluded that a unique organic/inorganic network structure was retained regardless of Cclay. The effects of Cclay on the tensile mechanical properties on the first and second cycles, the time-dependent recovery from the first large elongation and the optical anisotropy of NC gels, and also the disappearance of the glass transition and the formation of clay−polymer intercalation in the dried NC gel were revealed. Thus, it became clear that the properties and the structure changed dramatically for an NC gel with a critical clay content ( ≈ NC10) or above. The structural models for NC gels with low and high Cclay, exhibiting different clay orientation and residual strain, were depicted.

Honeycomb-like aligned carbon nanotube films were grown by pyrolysis of iron phthalocyanine. The patterned structure was characterized by a scanning electron micrograph (SEM) and an atomic force micrograph (AFM). Wettability studies revealed the film surface showed a super-hydrophobic property with much higher contact angle (163.4 ± 1.4°) and lower sliding angle (less than 5°)a water droplet moved easily on the surface. In contrast to a densely packed aligned carbon nanotube, the sliding feature was strongly affected by microstructure of surface.