Problem 65 - Chemistry The Central Science

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?

Step-by-Step Solution

Answer

In both the nematic liquid crystal phase and ordinary liquid phase, molecules have freedom of movement and there is no long-range positional order. However, they differ in molecular arrangement and orientation. In a nematic liquid crystal phase, molecules are parallel to each other with some degree of orientational order, while in an ordinary liquid phase, the arrangement appears random and disordered. Additionally, the movement in nematic liquid crystal phase is more constrained due to the orientational order, leading to preferential movement along the direction of alignment, as opposed to isotropic movement in all directions in ordinary liquid phase.

Step 1: Understanding Nematic Liquid Crystal Phase

A nematic liquid crystal phase is an intermediate phase between a solid and a liquid. In this state, the molecules have some degree of positional order, but they still have freedom to move. Specifically, molecules in the nematic phase are oriented in such a way that they are parallel to one another, but there is no long-range positional order like in a solid.

Step 2: Understanding Ordinary Liquid Phase

In the ordinary liquid phase, molecules are close together and continuously moving but they lack any particular arrangement or orientation. Molecules in a liquid state have more freedom to move in comparison to those in solid, and there is no long-range positional or orientational order.

Step 3: Similarities between Nematic Liquid Crystal Phase and Ordinary Liquid Phase

Both the nematic liquid crystal phase and ordinary liquid phase exhibit some degree of freedom for the movement of their molecules. In both phases, molecules can flow and change their positions. There is no long-range positional order present in both nematic and ordinary liquid phases.

Step 4: Differences between Nematic Liquid Crystal Phase and Ordinary Liquid Phase

The main difference lies in the arrangement and orientation of their molecules. In a nematic liquid crystal phase, molecules exhibit a certain degree of orientational order as they align parallel to each other. In contrast, in an ordinary liquid phase, molecules lack any specific orientation and their arrangement appears random and disordered. In terms of molecular motion, the movement in nematic liquid crystal phase is more constrained compared to ordinary liquid phase due to the orientational order. The orientational order of nematic liquid crystal phase causes the molecules to preferentially move along the direction of alignment, while ordinary liquids allow isotropic movement in all directions.