The formation of self-organized structures in poly(9,9-di-$n$-alkylfluorene)s ∼1 vol % methylcyclohexane (MCH) and deuterated MCH (MCH-$d_{14}$) solutions was studied at room temperature using neutron and x-ray scattering (with the overall $q$ range of 0.000 58–4.29 Å${}^{-1}$) and optical spectroscopy. The number of side chain carbons $(N)$ ranged from 6 to 10. The phase behavior was rationalized in terms of polymer overlap, cross-link density, and blending rules. For $N=6-9$, the system contains isotropic areas and lyotropic areas where sheetlike assemblies (lateral size of >400 Å) and free polymer chains form ribbonlike agglomerates (characteristic dimension of >1500 Å) leading to a gel-like appearance of the solutions. The ribbons are largely packed together with surface fractal characteristics for $N=6-7$ but become open networklike structures with mass fractal characteristics for $N=8-9$, until the system goes through a transition to an isotropic phase of overlapping rodlike polymers for $N=10$. The polymer order within sheets varies allowing classification for loose membranes and ordered sheets, including the so-called β phase. The polymers within the ordered sheets have restricted motion for $N=6-7$ but more freedom to vibrate for $N=8-9$. The nodes in the ribbon network are suggested to contain ordered sheets cross-linking the ribbons together, while the nodes in the isotropic phase appear as weak density fluctuations cross-linking individual chains together. The tendencies for macrophase separation and the formation of non beta sheets decrease while the proportion of free chains increases with increasing $N$. The fraction of β phase varies nonlinearly, reaching its maximum at $N$ $=$ 8.

• Received 2 February 2011

DOI:https://doi.org/10.1103/PhysRevE.83.051803