Organic one-dimensional ordered nanostructures are known to possess unique mechanical, electronic, and optical properties, such as, for example, enhanced conductivity, polarized photoluminescence, polarization dependent propagation of optical waves, and others. These properties are generally expressed in terms of the macroscopic properties of the nanostructure/host system.
In this vein, a method for controlling the orientation of 1D nanofibers, grown in a mixture of solvents is demonstrated by a collaboration of Swedish and US research teams. The nanofibers are fabricated from poly-3-hexylthiophene (P3HT) and are dynamically oriented using an alternating poling electric field, employing the ability of P3HT nanofibers to align along the electric field lines. Switching of the nanofibers’ orientation is granted by using a suitable set of poling electrodes. The collectively oriented P3HT nanofibers possess a strong birefringence in the spectral range 600 – 1500 nm, i.e. different refractive indices for perpendicular electric field components of propagating light, similar to the calcite crystal. This birefringence of the nanofibers is imparted on the macroscopic properties of the solution in which the nanofibers are dispersed.
Thus, by controlling the orientation of the nanofibers, the refractive index of the entire solution can be modulated. This, in turn, can be utilized for designing optical modulators, switches, polarization controllers of a new type. Such dynamically controllable and versatile materials enable using 1D nanostructures for applications where traditional techniques, e.g. liquid crystals, cannot be used due to limitations of inherent properties and technological difficulties.
