Inter and Intramolecular Contributions to the Proton Dipolar and Rotating Frame Spin-Lattice Relaxation Times in the Nematic Phase of the Liquid Crystal 5CB-d 11

An isotopic dilution study of the proton dipolar and rotating frame spin-lattice relaxation times (T ₁ D and T ₁ p) in the nematic liquid crystal 4-cyano-4′-n-pentyl-d ₁₁-biphenyl (5CB-d ₁₁) at 13.8 MHz over the nematic phase temperature range was used to separate the intermolecular and intramolecular contributions to the ring proton relaxation rates. This is the first such study to be reported. Combined with our earlier proton study of inter/intra Zeeman spin-lattice relaxation (T ₁) in 5CB-d ₁₁, these data permit a critical study of the soft-mode dynamics in the system. A qualitative explanation of the T ₁ D> results is presented, but a complete explanation of the T ₁ p results is not possible with existing theory.