Photorefractivity of Carbon Nanotube Doped Nematic Liquid Crystals

Dean Kissinger

Mentor: Dr. I.C. Khoo

 

            At the presence of incident light, the photorefractive effect is caused by the formation of a local variation in electrical field.  This electric field modulates the index of refraction of the material.  The photorefractivity of materials may prove to be very practical in applications such as holography and real time information processing.

            Nematic liquid crystals (NLC) have a very large birefringency (Dn ~ 0.3).  They also possess orientational nonlinearity.  Using carbon nanotubes as a dopant in liquid crystals has been shown to be an effective way to get a higher efficiency of photorefractivity in dye-doped NLC. 

Previous experiments in the laboratory using carbon nanotube doped NLC have yielded very good results.  However, the results have not been consistent from sample to sample.  We are postulating that the increased photorefractive efficiency comes from the modification of the elastic constant by the carbon nanotubes; however, the inconsistency may be caused by impurities in carbon nanotube bundles or from inconsistency in sample preparation.  Recently, Dr. Peter Eklund’s research group has developed a method to isolate single carbon nanotubes from bundles.  Dissolving the unbundled carbon nanotubes into a NLC solution will eliminate errors in purity and sample preparation. 

We will compare the photorefractive efficiency of carbon nanotube doped NLC solution to undoped NLC and unbundled carbon nanotube doped NLC.  If possible, we would like to investigate the orientation of the liquid crystal cells both before and after they are exposed to laser radiation.  We will attempt to explain the role of the carbon nanotubes in the increased efficiency of photorefractivity in dye-doped NLC.  Specifically, we will investigate the possibility that the elasticity or space charge field of the liquid crystal sample is changed by the introduction of carbon nanotubes.