The key difference between thermotropic and lyotropic liquid crystals is that thermotropic liquid crystals only have mesophase, whereas lyotropic liquid crystals can have a variety of phases.
Liquid crystals can be described as the fourth state of matter that occurs between the solid and liquid phases of matter. This state of matter represents an intermediate phase between crystalline solids and isotropic liquids. Furthermore, there are two major forms of liquid crystals; they are thermotropic and lyotropic liquid crystals.
CONTENTS
1. Overview and Key Difference
2. What are Thermotropic Liquid Crystals
3. What are Lyotropic Liquid Crystals
4. Thermotropic vs Lyotropic Liquid Crystals in Tabular Form
5. Summary – Thermotropic vs Lyotropic Liquid Crystals
What are Thermotropic Liquid Crystals?
Thermotropic liquid crystals are crystals having a mesophase within a certain temperature range. When these crystals are placed under a spectrometer magnet, molecules of the crystals tend to orient to a common direction. The direction is either along the external magnetic field or in a perpendicular direction to the field.
These liquid crystals consist of small molecules that have many applications as display materials, information storing materials, optical couplers, and optical waveguides. These materials usually have nematic, smectic and cholesteric states.
What are Lyotropic Liquid Crystals?
Lyotropic liquid crystals are crystals forms that form from the dissolution of an amphiphilic mesogen in a suitable solvent. A mesogen is a substance that can display liquid crystal properties, and we can describe them as disordered solids or ordered liquid forms. In order to form a lyotropic liquid crystal, it requires proper conditions of concentration, temperature, and pressure. An everyday example of lyotropic liquid crystals is a mixture of soap in water.
However, this term was used earlier to describe the common behavior of materials consisting of amphiphilic molecules when we add a solvent to that material. These materials contain a water-loving hydrophilic head group that is bound to a water-resisting hydrophobic group.
When considering the formation of a lyotropic liquid crystal, it occurs with the microphase segregation of two incompatible components (on a nanometer scale), which enables the formation of solvent-induced extended anisotropic arrangement. This formation depends on the volume balances between the hydrophobic and hydrophilic parts of the molecule. This combination can result in the formation of long-range order of the phases having solvent molecules that fill inside the spaces around the compounds in order to provide fluidity to this network system.
What is the Difference Between Thermotropic and Lyotropic Liquid Crystals?
Thermotropic and lyotropic are two types of liquid crystals. Thermotropic liquid crystals are crystals having a mesophase within a certain temperature range, while lyotropic liquid crystals are crystals forms that form from the dissolution of an amphiphilic mesogen in a suitable solvent. The key difference between thermotropic and lyotropic liquid crystals is that thermotropic liquid crystals only have mesophase, whereas lyotropic liquid crystals can have a variety of phases. This is because the concentration of lyotropic liquid crystals enables them to induce a variety of different phases. Moreover, another difference between thermotropic and lyotropic liquid crystals is that the thermotropic liquid crystals exhibit a phase transition upon temperature change while lyotropic liquid crystals do not exhibit a phase transition upon temperature change.
The following infographic summarizes the difference between thermotropic and lyotropic liquid crystals in tabular form.
Summary – Thermotropic vs Lyotropic Liquid Crystals
Liquid crystals can be described as the fourth state of matter that occurs between solid and liquid phases of matter. There are two major forms: thermotropic and lyotropic liquid crystals. The key difference between thermotropic and lyotropic liquid crystals is that thermotropic liquid crystals only have mesophase whereas lyotropic liquid crystals can have a variety of phases.
Reference:
1. “Lyotropic Liquid Crystal.” Wikipedia, Wikimedia Foundation, 11 Dec. 2020.
2. “Thermotropic Liquid Crystal.” An Overview | ScienceDirect Topics.
Image Courtesy:
1. “Lyotropic1” (CC BY-SA 3.0) via Commons Wikimedia
2. “Nematische Phase Schlierentextur” By Minutemen – Own work (CC BY-SA 3.0) via Commons Wikimedia