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

In this work, the α-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 Rg/Rh. From the result of a, the α-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 α-conformation of PFO has a relatively loose and extended chain conformation. Moreover, we use light scattering to get the form factor Rg/Rh of the PFO solution in which the α-conformation and β-conformation coexist. It is found that Rg/Rh increases with the proportion of α-conformation, which indicates that the α-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 β-conformation (ordered conformation) and α-conformation of PFO can transform into each other in solution, this work is significant for the control of the β-conformation and will have a potential meaning to increase the charge carrier mobility and efficiency from the PFO solution to films.