Temperature dependent intercalation of molten 1-hexadecanol into Brodie graphite oxide

Intercalation of very long molecules into the structure of multi-layered graphene oxide was studied using example of 1-hexadecanol (C16), an alcohol molecule with 16 carbon atoms and length of about 22Å. Brodie graphite oxide (BGO) immersed in excess of liquid 1-hexadecanol just above the melting point shows expansion of c-unit cell parameter from ~6Å to ~48.76 Å forming a structure with two densely packed layers of C16 molecules in a vertical “stand up” orientation relative to graphene oxide planes (α-phase). Heating of the BGO-C16 α-phase in excess of C16 melt results in reversible phase transition into β-phase at 336-342K. The β-phase shows much smaller c-unit cell of 29.83 Å (363K). Analysis of data obtained using vacuum-driven evaporation of C16 from the β-phase and set of experiments with samples pre-mixed with different BGO:C16 proportions provides evidence for structure of β-phase consisting of five layers of C16 molecules in parallel to GO plane orientation. Therefore, the transition from α- to β- phase corresponds to change in orientation C16 molecules from vertical to parallel to GO planes and significant decrease in amount of intercalated solvent. Cooling of β-phase in absence of C16 melt is found to result in the formation of γ-phase with interlayer distance of ~26.5Å. This distance corresponds to one layer of C16 molecules intercalated in vertical relative to GO planes orientation. Finally, structures with one and two layers of C16 molecules parallel to GO planes were identified in samples with rather small initial loading of C16. Surprisingly rich variety of structures revealed in BGO-C16 system provides opportunities to create materials with precisely controlled GO inter-layer distance.