Study of the α-Conformation of the Conjugated Polymer Poly(9,9-dioctylfluorene) in Dilute Solution

In this work, the alpha-conformation (individual locally separated chain) of the conjugated polymer poly(9,9-dioctylfluorene) (PFO) in dilute solution is studied by the following three points: the Mark-Houwink exponent a, the fractal dimension D, and the form factor R-g/R-h. From the result of a, the alpha-conformation of PFO is considered to have a semirigid chain conformation in dilute solution. We establish the mathematical relationship between the Mark-Houwink exponent a and the fractal dimension D in dilute solution. To prove the rationality of this mathematical relationship, the classic polymer polystyrene (PS) is used for comparison. According to the result of D, it can be known that the alpha-conformation of PFO has a relatively loose and extended chain conformation. Moreover, we use light scattering to get the form factor R-g/R-h of the PFO solution in which the alpha-conformation and beta-conformation coexist. It is found that R-g/R-h increases with the proportion of alpha-conformation, which indicates that the alpha-conformation of PFO has a loose and extended chain conformation, and this result agrees well with the conclusions drawn from a and D. On the basis of the fact that the beta-conformation (ordered conformation) and alpha-conformation of PFO can transform into each other in solution, this work is significant for the control of the beta-conformation and will have a potential meaning to increase the charge carrier mobility and efficiency from the PFO solution to films.