Question

What properties of the typical nematic liquid crystalline molecule are likely to cause it to reorient when it is placed in an electrical field that is perpendicular to the direction of orientation of the molecules?

Short answer

The major property of a typical nematic liquid crystalline molecule that is likely to cause it to reorient when placed in an electric field perpendicular to the orientation of the molecules is its molecular polarizability. This property allows the molecule's electron cloud to be easily distorted, creating an induced dipole moment in the direction of the electric field. The interaction between the induced dipole and electric field leads to a torque that rotates the molecules to align with the electric field, resulting in the reorientation of the molecules.

Step-by-step solution

Understanding Nematic Liquid Crystals

Nematic liquid crystals are a phase of matter that exhibit properties between those of conventional liquids and those of solid crystals. In this phase, liquid crystal molecules have no positional order but possess orientational order, meaning that the molecules tend to align in a preferred direction. This preferred direction is known as the director.\newline

Identifying Molecular Property to Consider

In order to understand what properties cause nematic liquid crystal molecules to reorient when placed in an electric field, we need to focus on the molecular property that interacts with electric fields. The polarization of the molecules, more specifically, the polarizability, should be considered as the main factor.\newline

Understanding Molecular Polarizability

Molecular polarizability is a measure of how easily a molecule's electron cloud can be distorted by an electric field. When a molecule is placed in an electric field, it acquires an induced dipole moment proportional to the strength of the electric field. The proportionality constant is the polarizability of the molecule.\newline

Effect of Polarizability on Reorientation

When an electric field is applied perpendicular to the director of the nematic liquid crystal, molecules with high polarizability will have their electron clouds easily distorted. This causes an induced dipole moment in the direction of the electric field. The interaction between the induced dipole and electric field leads to a torque that tends to rotate the molecules to align with the electric field. This is the reorientation of the molecules.\newline

Summary of the Main Property:

The major property of a typical nematic liquid crystalline molecule that is likely to cause it to reorient when placed in an electric field perpendicular to the orientation of the molecules is its molecular polarizability. This property results in induced dipoles and an interaction with the electric field, ultimately leading to the reorientation of the molecules.