Electrokinetic and contact angle measurements of grafted carbon fibers

 The grafting method that has successfully been applied to methacrylic acid and liquid crystalline monomers was expanded to prepare amphoteric carbon fiber surfaces using 2-(N,N-dimethylamino)ethyl methacrylate as monomer. The obtained carbon fiber surfaces were characterized by contact angle and ζ-potential measurements. The expected basic behavior was not observed, instead an amphoteric character of the modified carbon fiber surface was found. The fiber surfaces display a basic character in the acidic pH-range, while they are acidic in the alkaline part of the pH-scale. An important influence is derived from the amount of initiator used to graft the monomers onto the fibers. The smaller the initiator concen-tration used during polymerization, the larger the amount of amino functionalities introduced to the carbon fiber surface. The wetting behavior versus water depends on the overall conformation of the immobilized polymer. During immersion into water the polymer acts hydrophobic, while during emersion, a hydrophilic character is observed, probably derived from conformational changes and swelling during the contact angle measure-ments in water. Received: 9 June 1998 Accepted: 13 August 1998