Surface modification of unsized PAN- based carbon fiber by using high frequency single and dual RF discharge system

Erözbek Güngör, Ümmügül
The aim of this thesis is to examine the effects of HF-RF nitrogen plasma treatment on unsized PAN-based carbon fiber surfaces. The fibers were treated under different plasma processing conditions; exposure times, RF powers and gas pressures in a homemade RF-PECVD reactor having two modes; single “40.68 MHz” and dual “40.68 /2.1 MHz”. Then, Raman and FT-IR spectroscopies were used to analyze the structure and functional groups of the fibers, respectively. Also, tensile strain of the samples was tested with micromechanical analyzer. In addition, the plasma parameters were diagnosed by using single and double Langmuir probes. In this thesis, the first-order Raman-band peaks “D and G” of the fibers were investigated to be aware of changes in order/disorder structure, crystallinity and strain. In single RF mode, at low pressures, the degree of disordered structure increases with HF-RF power and process time. However, at high pressures, 84.51 % - very high order structure “crystallinity” is observed. In dual RF mode, structural ordering effects are explicitly observed at all pressures, powers and treatment times. Moreover, plasma diagnostic results revealed that single RF mode has two transition points. The first transition “-” was seen at 0.3 Torr whereas the other one “-” was observed at 0.3 Torr-150 Watt. And, according to strain analysis, the fibers were generally more strengthened after -mode plasma treatments while they were more weakened with -mode plasma treatments. Lastly, FT-IR spectroscopy results showed that the chemical structure of the treated carbon fibers was changed due to plasma treatment conditions.