Question

In terms of the arrangement and freedom of motion of the molecules, how are the nematic liquid crystalline phase and an ordinary liquid phase similar? How are they different?

Short answer

Both nematic liquid crystals and ordinary liquids have fluid-like properties and lack long-range order found in solids. However, nematic liquid crystals exhibit a directional order where molecules align parallel to each other, while ordinary liquids have randomly oriented and arranged molecules. Nematic liquid crystals have less freedom of motion compared to ordinary liquids and are more responsive to external stimuli due to their molecular alignment.

Step-by-step solution

Introduction to Liquid Crystals

Liquid crystals are a unique state of matter that exists between the solid and liquid phases. They exhibit properties of both solid and liquid phases making them partially ordered. There are different types of liquid crystals, with nematic liquid crystals being the most common.

Introduction to Nematic Liquid Crystals

A nematic liquid crystal is characterized by its long, rod-shaped molecules. These molecules tend to align parallel to one another giving the nematic phase a directional order, unlike an ordinary liquid. The nematic phase occurs at a temperature range between the melting point of a solid crystal and the isotropic phase (normal liquid state).

Introduction to Ordinary Liquids

An ordinary liquid is an isotropic phase where molecules show random orientation and arrangement. In this phase, molecules can freely move and slide past one another. This leads to a more disordered system compared to nematic liquid crystals.

Similarities in Molecular Arrangement and Freedom of Motion

Both nematic liquid crystals and ordinary liquids share the following similarities: 1. In both phases, molecules have the freedom to move and flow, although to different extents. This property makes nematic liquid crystals and ordinary liquids more fluid-like. 2. Both phases lack the long-range order found in solid crystals. In other words, the positions of molecules are not fixed in a repeating pattern, which causes a level of disorder in both phases.

Differences in Molecular Arrangement and Freedom of Motion

Nematic liquid crystals and ordinary liquids have the following differences: 1. Molecular arrangement: Nematic liquid crystals have a directional order where molecules align parallel to each other. Ordinary liquids, on the other hand, have randomly oriented and arranged molecules. 2. Degree of freedom of motion: Nematic liquid crystals exhibit a higher degree of order compared to ordinary liquids; hence, the molecules in nematic phase don't move as freely as those in the isotropic phase. 3. Response to external stimuli: Due to their partial order, nematic liquid crystals are more responsive to external stimuli like electric and magnetic fields compared to isotropic liquids. This property largely stems from their molecular alignment and interaction. In conclusion, nematic liquid crystals and ordinary liquid phases exhibit both similarities and differences in their molecular arrangement and freedom of motion. While both phases have fluid-like properties and lack the long-range order found in solids, nematic liquid crystals have a higher degree of order and molecular alignment, making them more responsive to external stimuli. On the other hand, ordinary liquids display random molecular arrangement and greater freedom of motion for the molecules.