2007-11-27 - JMFrost - Jenny Nelson Journal Club - PFO

The earliest talk from my PhD I've managed to find so far; a journal club presentation.

Transcript

1. Bottle Brushes and Hairy Helical Worms: The Strange Case of Crystalline PF 2,6 Jarvist Frost – Jenny Nelson Journal Club - 28th November 2007
2. PolyFluorene is Stiff: So how does it coil? Flat Monomer... (1998 Acta Cryst. Leclerc) But a non coaxial polymer: a 'dihedral' of ~19° (Grell Acta Polymerica 1998)
3. 1D of Freedom (succesive Twist of the monomers) Lots of Shapes
4. “Exceedingly Well Aligned Samples” PF2/6 “PF2/6 was sheared in the melt state on a smooth surface and allowed to cool slowly to room temperature.” Zone Casting? “...reflections tend to fan out due to axial spread of the polymers and paracrystalline nature of hexagonal packing.” “...experimental evidence of 5-fold periodicity is based on just two meridional layer lines in the X-Ray diffraction ... paterns of orientated fibres and thin films.”
5. Lots of Data! Dashes are proposed 21-fold helix lines These Data are superior to the 2000 Lieser data :– More Reflections have lead to a greater refinement of the structure
6. Two Possibilities – 21/4 and 21/8 21/4 with Tau~=65° Nb: Picture is of PF di-octyl, but with Tau set to match 21-helix from paper. 21 monomers present A Hairy Worm
7. 21/8 with Tau~=136° A Bottle Brush
8. 21/4 21/8
9. 21/4 vs. 21/8 has large implications for the charge transfer - 21/8 (Bottlebrush) has a long persistence length backbone (therefore greater conjugation & intra chain transport?) Backbone in centre of Helix (therefore inter chain distances greater?) - 21/4 has the backbone spiralling around the core (therefore lower conjugation & reduced intra transport?) But maybe the inter chain distances are less?
10. Some Expt. Support for 21/4 1) Monomer repeat less than for non-branched PF (therefore, shortened coil preferred) 2) Intensities on hk0 plane agree with lateral dimensions of 21/4 3) Strong intensities on l=4 and l=25 may be actual pitch But: This 21/4 Motif is not necessarily that of the backbone (Instead a staggered 21/8 set of helices could produce it)
12. Triple Helix 21-Helix has a 3 fold screw axis
13. Conclusions Strong support for Helical Nature 21/4 & 21/8 is approx. equiv to 5/1 & 5/2 Side chains disordered Some 21/4 motif visible Possibility of even more complex helices
14. Conjecture When we consider PF stiff, its actually that PF readily forms (helcial?) rods, even though the polymer chain itself is flexible. Side chains substitution in PFs will have a large effect on the transport properties by directly influencing the structure of the backbone