It is highly desirable to improve attractive interactions between carbon fibers and unreactive thermoplastic matrices to the possible maximum. This could be achieved by a simple grafting process to create a covalently bonded interface or interlayer, which should result in cohesive interactions between the polymer-grafted fibers and the same matrix material, leading to a better adhesion strength in the obtained composite material. Here, we are describing the grafting of styrene onto unmodified and unsized carbon fibers via free-radical bulk polymerization in the presence of fibers. After grafting, the surface properties of the carbon fiber *Author to whom correspondence should be addressed. E-mail: a.bismarck@imperial.ac.uk approach those of pure polystyrene which was proven by contact angle and zeta (-) potential measurements. As indicated by the water contact angle, the carbon fiber surface becomes more hydrophobic. Scanning electron microscopy (SEM) provides evidence of grafted polymer. This simple procedure results in a continuous polystyrene coating. The fiber diameter increases significantly after polymer grafting. The adhesion and fracture behavior between the original and polystyrene-grafted carbon fibers to a polystyrene (VESTYRON Õ ) matrix was characterized using the single-fiber pull-out test. There is a considerable increase in the measurable adhesion, i.e., the interfacial shear strength IFSS , by almost 300% between the grafted fibers and polystyrene as compared to untreated original fibers. Two planes of interfacial failure could be distinguished; first in the fiber coating interface leading to lower interfacial shear strength and second in the PS-matrix-PS-coating interphase resulting in a higher interfacial shear strength. In addition to the improved adhesion, there are also clear differences in the pull-out behavior between the nongrafted and grafted fibers. After the initial debonding process corresponding to the maximal pull-out force is completed, the pull-out force is increasing again.

A one-step copolymerization of ferroelectric methacrylate monomers leading to networks is presented. Oriented networks are obtained and electro-optical investigations are described. Smectic C* and another smectic phase are found in slightly crosslinked networks. For higher crosslinking densities, only the high temperature smectic C* phase was found. Electro-optical measurements were performed on the networks, and significant changes in the ferroelectrical properties were found. For crosslinking densities higher than 0.5 mol-%, switching times increased dramatically and the spontaneous polarization decreased. Networks with crosslinking densities of 2 mol-% did not exhibit ferroelectric properties.

A simple, reproducible method for grafting different carbon fibers (modified and unmodified, high-modulus, and high-tensile) with methacrylic acid is presented. The grafted carbon fibers were characterized by wetting measurements and electrokinetic studies. Scanning electron microscopy micrographs showed grafted polymer chains on all carbon fiber surfaces. The success of the grafting procedure depends on a suitable modification of the fiber surface. The amount and size of the grafted polymer chains on modified carbon fibers depend on the amount of initiator used. Contact angle measurements indicate an increase of the contact angle versus water and a decrease versus diiodomethane. The surface polarity calculated from the surface tensions obtained from contact angle values decreases for all systems under investigation. Zeta () potential measurements confirmed these results.

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ABSTRACT:Results of grafting reactions of a liquid crystalline (lc) monomer onto carbon fiber surfaces are presented and compared with results of noncovalently bonded lc polymer, which is proved reproducible by scanning electron microscopy. Electrooptical investigations under a polarizing microscope hints of the possibility of changing lc polymer and lc low molecular mass matrix molecules properties by applying a certain voltage to the carbon fibers. Wetting and electrokinetic measurements were performed and correlated with grafting reaction parameters. Those investigations revealed a nearly complete coverage of the carbon fiber surfaces by lc polymers. These measurements are suitable to characterize carbon fibers modified by grafted or coated polymers.