  We find that introducing segmented isotopic disorder patterns may
considerably reduce the thermal conductivity of pristine carbon nanotubes below
the uncorrelated disorder value. This is a result of the interplay between
different length scales in the phonon scattering process. We use ab-initio
atomistic Green's function calculations to quantify the effect of various types
of segmentation similar to that experimentally produced by coalescence of
isotope-engineered fullerenes.
