Undulating Cylinder-in-Lamellae Morphologies Formed in Giant Bolaform Lipids

Unconventional phases are often assembled from molecules with unique chemical structures. Herein, we report the facile synthesis and phase behavior of a series of giant bolaform lipids featuring an oligosiloxane-functionalized polyhedral oligomeric silsesquioxane (Si _x POSS) tethered at the middle of a polystyrene (PS) chain and two perfluoroalkyl-functionalized POSS (FPOSS) moieties attached, one at each terminus. By tuning the volume fraction of the Si _x POSS, various phases have been identified utilizing small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM), including lamellae (LAM), three-phase-four-layer lamellae (LAM₃), and a unique column in undulating lamellae phase with c2mm symmetry (Col _c2-in-LAM_u). Temperature-dependent experiments and a semiquantitative calculation of the structural parameters were carried out to analyze the structural feature and formation mechanism of this unconventional phase. Notably, the thin film morphologies of these giant bolaform lipids exhibit similar features with the lamellar layers oriented parallel to the silicon wafer surface. This study provides valuable insights into fine-tuning macromolecular assembly and understanding the rationale of unconventional phase formation via molecular topology engineering.