Effect of interface modifiers on the cure, mechanical and viscoelastic properties of hierarchical carbon nanotube composites.

Addition of carbon nanotubes (CNTs) to traditional fiber-reinforced polymer composites (FRPs) has led to significant improvements in multifunctional capabilities of these materials. However, achieving these superior properties require incorporating relatively large CNT mass fractions (greater than 1%) where methods of dispersing CNTs in polymer matrix fail. Directly grafting CNTs onto fiber surfaces prior to resin infusion is a viable alternative and here this is achieved by using an electrophoretic deposition (EPD) process. To deposit the CNTs on fiber surfaces, they are first oxidized and mixed with a polyelectrolyte (such as polyethyleneimine (PEI)) which upon protonation is used to drive the CNTs onto fiber surfaces. In our previous study, we observed that the presence of small percentages of PEI affects the viscoelastic properties and the hydrogen dynamics of the composite. Here we aim to isolate the effect of PEI in the absence of CNTs and glass fibers and study its effect on the cure kinetics, mechanical properties and viscoelastic characteristics of the resin system. The cure process is understood using differential scanning calorimetry, the viscoelastic characteristics using dynamic mechanical thermal analysis and the mechanical properties using tensile testing.