Physical and Rheological Properties of Maleic Anhydride-Incorporated PVDF: Does MAH Act as a Physical Crosslinking Point for PVDF Molecular Chains?

The miscibility and physical and rheological properties of binary poly(vinylidene fluoride)/maleic anhydride (PVDF/MAH) blends have been systematically investigated. MAH was found to be miscible with PVDF by scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Fourier transform infrared (FTIR) investigations provided positive evidence for the specific interaction between the carbonyl groups of MAH and the methylene groups of PVDF. Rheological measurements showed that both the storage modulus and the melt viscosity of PVDF increase with the addition of MAH, followed by a decrease with excess MAH. In addition, the elongation of the PVDF/MAH blend with 10 wt % MAH is 589.7%, which is almost 5 times that of neat PVDF. It is concluded that MAH small molecules act as physical "crosslinking" points for the neighboring PVDF molecule chains due to this specific interaction between PVDF and MAH. Such a physical crosslinking function enhances the storage modulus, viscosity, and mechanical properties of PVDF.

Fabrication of Superhydrophobic Surfaces with Controllable Electrical Conductivity and Water Adhesion.

A facile and versatile strategy for fabricating superhydrophobic surfaces with controllable electrical conductivity and water adhesion is reported. "Vine-on-fence"-structured and cerebral cortex-like superhydrophobic surfaces are constructed by filtering a suspension of multiwalled carbon nanotubes (MWCNTs), using polyoxymethylene nonwovens as the filter paper. The nonwovens with micro- and nanoporous two-tier structures act as the skeleton, introducing a microscale structure. The MWCNTs act as nanoscale structures, creating hierarchical surface roughness. The surface topography and the electrical conductivity of the superhydrophobic surfaces are controlled by varying the MWCNT loading. The vine-on-fence-structured surfaces exhibit "sticky" superhydrophobicity with high water adhesion. The cerebral cortex-like surfaces exhibit self-cleaning properties with low water adhesion. The as-prepared superhydrophobic surfaces are chemically resistant to acidic and alkaline environments of pH 2-12. They therefore have potential in applications such as droplet-based microreactors and thin-film microextraction. These findings aid our understanding of the role that surface topography plays in the design and fabrication of superhydrophobic surfaces with different water-adhesion properties.

Crystallization-modulated nanoporous polymeric materials with hierarchical patterned surfaces and 3D interpenetrated internal channels.

Poly(oxymethylene)/poly(L-lactic acid) (POM/PLLA) blends are typical melt-miscible binary systems. During isothermal crystallization at various temperatures, in the presence of amorphous PLLA chains, POM crystallizes into banded spherulites with different band spaces, which forms a continuous crystalline phase and serves as a sturdy frame in the final porous materials. On the other hand, the amorphous PLLA chains are simultaneously expelled out from POM crystal lamellae to generate the other continuous phase during the crystallization of POM. Consequently, the interpenetration of the POM lamellae and the amorphous PLLA phase construct a cocontinuous phase structure. All the PLLA constituents are fully included in the interlamellar or interfibrillar of POM crystals. Thus, nanoporous POM materials with hierarchical patterned surface and 3D interpenetrated internal channels have been successfully obtained by extracting the amorphous PLLA phase. It is further found that the POM crystal morphologies in the blends are much dependent on the crystallization conditions. Therefore, the hierarchical patterned structure and the size of internal channels (pore size) can be modulated by adjusting the crystallization conditions.