ABSTRACT
The investigation of molecular movements is of utmost importance
for the characterization of liquid-crystalline (LC) dendrimers both
in their fundamental and technological oriented aspects. In this
chapter we will discuss the application of experimental techniques
presented in Chapter 7 to the study of molecular dynamics in the
mesophases of various LC dendrimers among those introduced in
Chapter 3. As pointed out before, different types of molecular move-
ments exhibited by liquid crystals (namely rotations/reorientations,
self-diffusion, and collective modes) can be detected by proton
nuclear magnetic resonance (NMR) relaxometry. The characteristic
timescales of specific molecular motions vary over several orders of
magnitude and can be probed by using values of NMR static field,
corresponding to Larmor frequencies of the order of the inverse
of those timescales. Therefore, having access to a wide range of
NMR frequencies is ideal for molecular dynamics investigations.
This is achieved through the combination of standard and fast-
field-cycling (FFC) NMR techniques. Typically, in low-molecular-
weight liquid crystals, the molecular dynamics timescales vary from
picoseconds to nanoseconds formolecular rotations/reorientations,
from nanoseconds to microseconds for molecular self-diffusion and
frommicroseconds tomilliseconds or slower in the case of collective
motions.
