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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
In conclusion, the smectic liquid crystalline phase is more highly ordered than the nematic phase due to the presence of both long-range orientational order and positional order within distinct layers. In contrast, the nematic phase only exhibits long-range orientational order and lacks the organized layer structure found in the smectic phase. The restriction of molecular movement within the layers in the smectic phase further contributes to its higher degree of order.

Step by step solution

01

Understand the Nematic Phase

In the nematic phase, the liquid crystal molecules have relatively long pitches which lead to molecular ordering along a single axis known as the director. The molecules are free to move in all directions, and their positions are not governed by any regular lattice. They mainly depict long-range orientational order but no positional order.
02

Understand the Smectic Phase

In the smectic phase, molecules are organized in distinct layers, leading to a higher degree of ordering. They exhibit both long-range orientational order and positional order within the layers. In this phase, the molecules can slide past each other, but the movement is restricted to the plane of their respective layers. Based on the relative orientation of the molecules within the layers, smectic phase can be further classified into different types such as SmA, SmB, and SmC.
03

Compare the different orders of Nematic and Smectic Phases

Now that we understand the characteristics of both nematic and smectic phases, we can compare the ordering of molecules in both these phases. In the nematic phase, there is only orientational order, while in the smectic phase, there is both positional and orientational order. The additional positional order in the smectic phase is characterized by the formation of layers, which restricts molecular movement within their respective planes. This organized layer structure is absent in the nematic phase.
04

Conclusion

In conclusion, the smectic liquid crystalline phase is more highly ordered than the nematic phase, as it possesses both long-range orientational order and positional order within the layers, while nematic phases only have the long-range orientational order. The presence of distinct layers in the smectic phase and the restriction of molecular movement within these layers contributes to its higher degree of order.

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Most popular questions from this chapter

Appendix \(\mathrm{B}\) lists the vapor pressure of water at various external pressures. (a) Plot the data in Appendix B,vapor pressure versus temperature $\left({ }^{\circ} \mathrm{C}\right) .$ From your plot, estimate the vapor pressure of water at body temperature, \(37^{\circ} \mathrm{C}\). (b) Explain the significance of the data point at $101.3 \mathrm{kPa}, 100^{\circ} \mathrm{C} .(\mathbf{c}) \mathrm{A}\( city at an altitude of \)1525 \mathrm{~m}$ above sea level has a barometric pressure of \(84.3 \mathrm{kPa}\). To what temperature would you have to heat water to boil it in this city? (d) A city at an altitude of \(150 \mathrm{~m}\) below sea level would have a barometric pressure of \(103.14 \mathrm{kPa}\). To what temperature would you have to heat water to boil it in this city?

(a) Which is generally stronger, intermolecular interactions or intramolecular interactions? (b) Which of these kinds of interactions are broken when a liquid is converted to a gas?

Ethyl chloride \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}\right)\) boils at \(12^{\circ} \mathrm{C}\). When liquid $\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}$ under pressure is sprayed on a room-temperature $\left(25^{\circ} \mathrm{C}\right)$ surface in air, the surface is cooled considerably. (a) What does this observation tell us about the specific heat of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(g)\) as compared with that of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Cl}(l) ?(\mathbf{b})\) Assume that the heat lost by the surface is gained by ethyl chloride. What enthalpies must you consider if you were to calculate the final temperature of the surface?

Look up and compare the normal boiling points and normal melting points of \(\mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{H}_{2} \mathrm{~S}\). Based on these physical properties, which substance has stronger intermolecular forces? What kinds of intermolecular forces exist for each molecule?

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.
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