Mono domain nematic elastomers change shape by as much as 400% on being heated from the nematic to isotropic state. The reason is that nematic order, Q, elongates the distribution of chains and thus the network that they form. Experimental evidence for this, and simple theory is presented. A novel method to change Q, and hence obtain an analogous elastic strain, is to bend the nematic's rods by photoisomerization. On absorbing a photon, photochromes such as azo rods leave the (straight) trans state and adopt the cis (bent) form. We show data and give simple theory to explain this remarkable, reversible elastic phenomenon. 相似文献
Nanoscale fibers with embedded, aligned, and percolated non‐functionalized multiwalled carbon nanotubes (MWCNTs) were fabricated through electrospinning dispersions based on melt‐compounded thermoplastic polyurethane/MWCNT nanocomposite, with up to 10 wt.‐% MWCNTs. Transmission electron microscopy indicated that the nanotubes were highly oriented and percolated throughout the fibers, even at high MWCNT concentrations. The coupling of efficient melt compounding with electrospinning eliminated the need for intensive surface functionalization or sonication of the MWCNTs, and the high aspect ratio as well as the electrical and mechanical properties of the nanotubes were retained. This method provides a more efficient technique to generate one‐dimensional nanofibers with aligned MWCNTs.
The synthesis of an oriented liquid‐crystalline photoresponsive polymer, prepared by polymerization of mono‐ and di‐acrylates, both of which contain azobenzene chromophores, is reported. The prepared free‐standing polymer film shows strong reversible photoinduced deformation upon exposure to unpolarized UV light at 366 nm, as a result of an optically induced isomeric change of the azobenzene moieties in the polymer network. The synthesis process is relatively simple and more efficient compared to conventional ones, and can be used to synthesize other liquid‐crystalline photoresponsive polymers. The use of this photoresponsive polymer film as an optical high‐pass/low‐pass switch under UV or natural light irradiation for a laser beam is demonstrated. This photoresponsive polymer may have applications in robotic systems, artificial muscles, and actuators in microelectromechanical systems (MEMS) and labs on chips.
In this work we present the synthesis of a biodegradable, elastomeric material with a wide range of mechanical properties. The synthesis of the material was done by condensation polymerization of malic acid and 1,12–dodecandiol. The synthesized materials have low Young’s modulus ranging from about 1 to 4 MPa and a high elongation at break of 25–737% depending on the crosslinking density of the system. The cell growth observed under microscope showed good proliferation at 3 days of culture indicating good biocompatibility and support of L929 cells growth. The fabrication of 3D scaffold from these materials using the super critical CO2 foaming method was also attempted. This method of scaffold fabrication is appropriate for materials that are easily hydrolysable and it also has the advantage of being a solvent free process. These materials are generally soft, biocompatible and biodegradable making them suitable for tissue engineering of soft tissues that are elastic in nature like muscles and blood vessels. 相似文献
The helical mechanoclinic deformation of a main‐chain chiral smectic elastomer, which is prepared by a crosslinking reaction under twist deformation, is investigated. The twist deformation induces a layer tilt angle that depends on the handedness of twist. The layer tilt angle in the right‐handedly twisted elastomer, of which the handedness is consistent with that of the helix in the SmC* phase of the non‐crosslinked backbone polymer, is estimated to be up to 16° at room temperature, although that in the left‐handedly twisted elastomer is less than several degrees. The experiments provide evidence of chiral coupling between tilt and twist for helical mechanoclinic deformation in the chiral smectic system.
Poly(trimethylene terephthalate)(PTT)/thermoplastic polyester elastomer (TPEE) blends were prepared and their miscibility, crystallization and melting behaviors, phase morphology, dynamic mechanical behavior, rheology behavior, spherulites morphology, and mechanical properties were investigated by differential scanning calorimetry (DSC), scanning electron microscopy (SEM), dynamic mechanical analysis (DMA), parallel-plate rotational rheometry, polarized optical microscopy (POM), wide angle X-ray diffraction (WAXD), universal tensile tester and impact tester, respectively. The results suggested that PTT and TPEE were partially miscible in the amorphous state, the TPEE rich phase was dispersed uniformly in the solid matrix with a size smaller than 2 μm, and the glass transition temperatures of the blends decreased with increasing TPEE content. The TPEE component had a good effect on toughening the PTT without depressing the tensile strength. The blends had improved melt viscosities for processing. When the blends crystallized from the melt state, the onset crystallization temperature decreased, but they had a faster crystallization rate at low temperatures. All the blends’ melts exhibited a predominantly viscous behavior rather than an elastic behavior, but the melt elasticity increased with increasing TPEE content. When the blends crystallized from the melt, the PTT component could form spherulites but their morphology was imperfect with a small size. The blends had larger storage moduli at low temperatures than that of pure PTT. 相似文献
Functional in-chain silyl-hydride(Si-H) SBR copolymers of 4-vinyiphenyldimethylsilanol(VPDMS) and butadiene were synthesized by living anionic polymerization,in which active group Si-H was not lost and its content was controllable. Corresponding self-crosslinking elastomers were obtained by hydrosilation of Si-H group with vinyl bonds in chain.The copolymers and elastomers were characterized by ~1H NMR,size exclusion chromatography(SEC),Fourier transform infrared (FTIR) spectroscopy,differential scanning calorimetry(DSC),and thermogravimetry analysis(TGA) techniques. 相似文献