The Influence of the Molecular Weight on the Thermotropic Alignment and Self-Organized Structure Formation of Branched Side Chain Hairy-Rod Polyfluorene in Thin Films
Citations Over TimeTop 10% of 2005 papers
Abstract
We report on the influence of the molecular weight (Mn) on the alignment and structure of poly(9,9-bis(ethylhexyl)fluorene-2,7-diyl) (PF2/6) in thin films on rubbed polyimide in the equilibrium. The degree of alignment has been studied using optical spectroscopy and compared to theoretical arguments. The structure of PF2/6 has been studied using grazing-incidence X-ray diffraction. PF2/6 realizes a threshold molecular weight Mn* = 104 g/mol separating a low Mn(LMW, Mn Mn*) region. LMW materials show only the nematic (Nem) phase while HMW compounds show hexagonal (Hex) and Nem phases at low and high temperatures, respectively. LMW samples align equally well at any temperature above the glass transition, and the dichroic ratio, R, increases with Mn. HMW material aligns well in the Nem regime, and R drops exponentially with Mn, which is in agreement with the theory. The orientational order is maximized near Mn*, and the orientational order parameter is >0.9. HMW samples, whether aligned or not, reveal two kinds of coexistent Hex crystallites distributed in the sample plane having one crystal axis a perpendicular or parallel to the surface. Local order within the triaxially aligned Hex phase surpasses that of the in-plane aligned Hex phase.
Related Papers
- → Polyfluorenes without Monoalkylfluorene Defects(2007)147 cited
- → Evidence for 21-Helicity of Poly[9,9-bis(2-ethylhexyl)fluorene-2,7-diyl](2007)31 cited
- → Light emitting polyfluorene derivatives with three different structural configurations(2004)13 cited
- → Incorporation of Thermotropic Liquid Crystals in Phospholipid Monolayers: Necessary Condition or Homeotropic Anchoring(1997)12 cited
- Synthesis of poly(fluorene) containing end-group of hydroxy(2006)