Coherent stacking of carbon nanotubes and polymer lamellar crystals: Toward oriented hybrid arrays within network valley domains. (28th March 2018) - Huang, Sin-Ru
Abstract: As a result of horizontal phase distribution during solvent evaporation, island-like insulating domains of poly(methyl methacrylate) and network valleys of semiconductive poly(9, 9′-dioctylfluorene) (PFO) spread through prepared films, which is accompanied with self-assembly of individual PFO-wrapped multi-walled carbon nanotubes selectively into PFO valleys. Considering the wrapping of molecular chains on nanotubes as a mixing status prevailingly preserved within valley domains, the detachment of molecular coils is viewed as a result of phase separation, which is only favorable above a critical temperature level. As the detachment of molecular coils from nanotubes is the prerequisite, the occurrence of nucleation of PFO lamellar crystals via annealing is observed to occur only within a narrow temperature range below the melting temperature. During the growth of lamellar crystals, the oriented hybrid stacking arrays with the intercalation of individual carbon nanotubes is able to evolve upon the mutual impingement between dispersed nanotubes and lamellar crystals. Nevertheless, depending on the number density of crystalline lamellae, this mutual impingement is also able to arrest the aligning process and randomize the hybrid dispersion. Based on the exploration of several influential factors, including the nanotube diameter and crystallization temperature, the interplay between nanotube dispersion and crystal growth has been elucidated as the governing mechanism for this mutual impingement within valley domains, and thus various patterns of hybrid dispersion. Graphical abstract: The mutual influences between the nanotube dispersion and crystal growth have been envisaged as the comprehensive guidance for the alignment of hybrid dispersion. Upon adequately adjusted nanotube density and crystallization rate, oriented arrays of dense hybrid stacking with few layers of lamellar crystals between two neighboring nanotubes are able to evolve upon encountered steric impingement. Highlights: The oriented hybrid stacking of carbon nanotubes and lamellar crystals within the continuous network valleys of phase domains has been accomplished. Upon the dispersion of carbon nanotubes, the detachment of molecular chains from nanotubes is identified as a prerequisite for the nucleation. The nanotube diameter is illustrated as an influential factor for the unveiled detachment-controlled nucleation. The dispersion of carbon nanotubes is realized helpful for the regular stacking of lamellar crystals of polymer via the mutual impingement. The influence of mutual impingement on hybrid stacking is clarified to mainly depend on the density of carbon nanotubes and the growth rate of lamellar crystals.