Thermodynamics of Rigid Rod Polyelectrolytes with Focus on CNT-Superacid Solutions and Second Virial Theory of Finite Rods
Pinnick, Robert Andrew
Master of Science
This thesis investigates the thermodynamics of rigid rod polyelectrolytes for carbon nanotube (CNT) - superacid solutions by classical acid-base chemistry and for finite rods by second virial theory. For CNT-superacids, the fractional charge on different batches of CNTs in mixtures of superacids is measured. The equilibrium protonation of CNTs in superacids follows a dissociative Langmuir isotherm. The free energy of protonation is determined to be positive and to depend on the batch of CNTs. The magnitude of this free energy change decreases with increasing CNT diameter. For rigid rod polyelectrolytes, the entropic interactions due to excluded volume act to align the rods as parallel while the enthalpic interactions due to electrostatics act to orient the rods to be perpendicular. When the potential energy for electrostatic interactions is derived from infinite rods, only a nematic liquid crystalline phase is predicted according to literature. However, when the potential energy for electrostatic interactions is derived for finite rods, a new phase is predicted when the rod length is one order of magnitude larger than the Debye length at high effective concentrations. The new phase is characterized by an order parameter based on the 14th Legendre polynomial instead of the nematic order parameter based on the 2nd Legendre polynomial. As a side project, the impact of chirality on the tensile strength of CNT fibers is also investigated in this thesis.