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Chapter 11: Problem 72

The smectic liquid crystalline phase can be said to be more highly ordered than the nematic phase. In what sense is this true?

Short Answer

Expert verified
The smectic liquid crystalline phase is more highly ordered than the nematic phase because it exhibits both positional and orientational order among its molecules. In the smectic phase, molecules are arranged in well-defined layers with similar orientation, while in the nematic phase, molecules only have long-range orientational order but lack positional order. This results in a more structured and orderly molecular arrangement in the smectic phase compared to the fluid and disordered nematic phase.

Step by step solution

01

Understand the nematic and smectic phases

Nematic and smectic phases are two types of liquid crystal phases that exhibit distinct structural and orientational orders. In the nematic phase, molecules have no positional order but exhibit long-range orientational order, meaning they roughly point in the same direction. The smectic phase, on the other hand, exhibits both positional and orientational order. The molecules are arranged in layers, and within these layers, they have a similar orientation as those in the nematic phase.
02

Compare the structural organization of nematic and smectic phases

In the nematic phase, molecules have long-range orientational order, but they lack a regular arrangement or positional order. This means that the molecules in the nematic phase can be considered more fluid and disordered compared to those in the smectic phase. In the smectic phase, molecules are arranged in defined layers, meaning they have positional order in addition to the orientational order. Each layer has a well-defined structure and thickness, leading to a regular, more ordered arrangement of molecules in the smectic phase.
03

Analyze the molecular arrangement and interactions in nematic and smectic phases

In the nematic phase, molecules interact with their neighbors via weak, non-specific forces, such as van der Waals forces or dipole-dipole interactions. These relatively weak interactions contribute to the fluidity and lack of positional order found within the nematic phase. In contrast, intermolecular interactions in the smectic phase are more specific and directional, facilitating the formation of well-organized layers. These interactions result in a higher degree of positional order and a more rigid structure when compared to the nematic phase.
04

Conclusion

The smectic liquid crystalline phase can be said to be more highly ordered than the nematic phase in the sense that it exhibits both positional and orientational order among its molecules, whereas the nematic phase only has orientational order. This difference in organization and arrangement leads to a more structured and orderly molecular arrangement in the smectic phase compared to the more fluid and disordered nematic phase.

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Most popular questions from this chapter

(a) What is the significance of the critical point in a phase diagram? (b) Why does the line that separates the gas and liquid phases end at the critical point?

It often happens that a substance possessing a smectic liquid crystalline phase just above the melting point passes into a nematic liquid crystalline phase at a higher temperature. Account for this type of behavior.

(a) When you exercise vigorously, you sweat. How does this help your body cool? (b) A flask of water is connected to a vacuum pump. A few moments after the pump is turned on, the water begins to boil. After a few minutes, the water begins to freeze. Explain why these processes occur.

The fluorocarbon compound \(\mathrm{C}_{2} \mathrm{Cl}_{3} \mathrm{~F}_{3}\) has a normal boiling point of \(47.6^{\circ} \mathrm{C}\). The specific heats of \(\mathrm{C}_{2} \mathrm{Cl}_{3} \mathrm{~F}_{3}(l)\) and \(\mathrm{C}_{2} \mathrm{Cl}_{3} \mathrm{~F}_{3}(g)\) are \(0.91\) and \(0.67 \mathrm{~J} / \mathrm{g}-\mathrm{K}\), respectively. The heat of vaporization for the compound is \(27.49 \mathrm{~kJ} / \mathrm{mol}\). Calculate the heat required to convert \(35.0 \mathrm{~g}\) of \(\mathrm{C}_{2} \mathrm{Cl}_{3} \mathrm{~F}_{3}\) from a liquid at \(10.00{ }^{\circ} \mathrm{C}\) to a gas at \(105.00{ }^{\circ} \mathrm{C}\).

Which of the following affects the vapor pressure of a liquid? (a) Volume of the liquid, (b) surface area, (c) intermolecular attractive forces, (d) temperature, (e) density of the liquid.
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