Low-Temperature Alignment of Conjugated Polymers by Plasticizer-Aided Physical Rubbing

Abstract

Rubbing-induced alignment of conjugated polymers is systematically investigated in terms of intra- and inter-molecular interaction. Various polymer films with a broad range of polymer chain rigidity are rubbed, and the degree of polymer chain alignment is quantitatively characterized. The rubbing technique effectively aligns crystalline domains in conjugated polymer films when the temperature approaches the critical rubbing temperature ( $T_r^c$ ), at which the rearrangement and the slip of polymer chains are possible. A polymer with significant intra-/inter-molecular interactions exhibits higher $T_r^c$ , though quantitative analysis reveals an intermediately aligned state at temperature T_r ' lower than $T_r^c$ . This state originates from polymer chain aggregation in an amorphous domain. The intermediately aligned state can be controlled by plasticizer, which enables low-temperature alignment of high-mobility polymer film by reducing T_r ' to near 100 °C, increases the crystallinity, and improves the alignment effect at this state comparable to that of the completely aligned state obtained at extremely high temperatures.

Keywords: alignment; crystallinity; organic semiconductors; plasticizer; rubbings.