The encapsulation process of a filament-forming bicopper complex within the fibrils of an isotactic polystyrene (iPS) thermoreversible gel has been studied as a function of the solvent isomer. Differential scanning calorimetry (DSC) and small-angle neutron scattering (SANS) have been used. It is observed through the evolution of the gelation threshold and the alteration of the molecular structure of both the gel fibrils and the bicopper complex threads that the latter act as a nucleating agent for the fibrils growth in gels from iPS/trans-decalin but not in gels from iPS/cis-decalin. Molecular encapsulation of the bicopper complex filaments by a polymer sheath is therefore achieved in trans-decalin, whereas in cis-decalin, the 1-D filaments are not stable and eventually the bicopper complex crystallizes under the form of 3-D crystals. The possible origin of these differing types of behavior is briefly discussed.