Ch.12 - Solids and Modern Materials

Brown - Chemistry: The Central Science 14th Edition

Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo

Brown 14th Edition

Ch.12 - Solids and Modern Materials

Problema 72

Capitolo 12, Problema 72

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

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1. The smectic and nematic phases are two different types of liquid crystal phases. Liquid crystals are a state of matter that has properties between those of conventional liquids and those of solid crystals.

2. In the nematic phase, the molecules are aligned along a common direction, known as the director. However, there is no positional order, meaning the molecules can move freely and are not arranged in a specific pattern.

3. In contrast, the smectic phase has both orientational and positional order. The molecules are not only aligned along a common direction, but they also form layers. Within each layer, the molecules may either have a specific arrangement (smectic A phase) or be randomly positioned (smectic C phase).

4. Therefore, the smectic phase is considered to be more highly ordered than the nematic phase because it has an additional level of organization - the formation of layers.

5. This increased order in the smectic phase is often associated with a lower temperature than the nematic phase, as more energy is required to disrupt the additional layering structure.

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Liquid Crystals

Liquid crystals are materials that exhibit properties between those of conventional liquids and solid crystals. They can flow like a liquid but have some degree of molecular order, which allows them to respond to electric and magnetic fields. Understanding the different phases of liquid crystals, such as nematic and smectic, is crucial for applications in displays and other technologies.

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The crystal field splitting pattern for octahedral complexes has the d orbitals on or along the axes as having the higher energy.

Nematic Phase

The nematic phase is a type of liquid crystal phase where the molecules are oriented in the same direction but do not have positional order. This means that while the long axes of the molecules are aligned, they can move freely, leading to fluid-like behavior. The lack of positional order distinguishes it from more ordered phases, such as smectic.

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Phase Changes in Diagrams

Smectic Phase

The smectic phase is characterized by a higher degree of order compared to the nematic phase. In this phase, molecules are not only aligned in the same direction but also organized into layers, with positional order within each layer. This layered structure contributes to unique physical properties, such as increased viscosity and different optical characteristics, making it more ordered than the nematic phase.

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Phase Changes in Diagrams

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