Investigation On Interfacial Self Assembly Of CF/Epoxy And CF/PI Composites

In this dissertation, a new method based on molecular self-assembly on carbon fiber surface was proposed for obtaining the controlled interphase between carbon fiber and epoxy matrix in a composite system. The interfacial interactions between reinforcement and matrix were discussed at the molecular level. This research plays an important theoretical role and has great significance for developing the surface modification methods of carbon fiber and clarifying the mechanisms of interfacial interaction.For epoxy resin matrix, composite interphase was modified by thiols/Ag self-assembly systems. First, the carbon fiber surfaces were metallized by the electroless Ag plating. The plating time of 0.5min and coating thickness of 80nm were determined by atomic force microscopy (AFM) in the noncontact mode or in force modulation mode. The crystallization parameters and tightness of Ag plating layers to carbon fiber were investigated by X-ray diffraction (XRD) technique and cold-heat circulation method. The results showed that plating layers with uniformity, denseness and strong tightness were appropriate for the following molecular self-assembly.The molecular self-assembly was proceeded on Ag-plated carbon fiber surfaces. Three types of thiols compounds were chosen: hydroxyl-substituted alkanethiols, substituted aromatic thiols and heterocyclic thiols. The self assembly films were characterized by surface-enhanced Raman spectroscopy (SERS) and X-ray photoelectron spectroscopy (XPS). SERS analysis showed that self-assembly films chemisorbed onto the Ag-plated carbon fiber by the formation of Ag-S or Ag-N bonds. Accoring to SERS selection rules, alkanethiols were oriented on carbon fiber surface in the form of stand-up phase, while aromatic thiols and heterocyclic thiols were oriented on the carbon fiber surface in the form of lying-down or slight tiltation. XPS further demonstrated this chemisorption of self-assembly films on the carbon fiber surfaces.The effect of self-assembly films on the interfacial properties of epoxy composites was discussed. The interfacial shear strength (IFSS) test showed that modified CF improved the interfacial bonding strength of its composites.