Liquid crystals are unique materials that exhibit properties between those of conventional liquids and solid crystals. They are widely used in various applications, such as displays, sensors, and optical devices. The properties of liquid crystals are highly sensitive to temperature and external electric fields, which can significantly affect their behavior and performance.1. Temperature: The phase transitions and properties of liquid crystals are strongly influenced by temperature. As the temperature changes, liquid crystals can undergo phase transitions between different mesophases e.g., nematic, smectic, and cholesteric phases or between a mesophase and an isotropic liquid or solid phase. These phase transitions are accompanied by changes in the molecular order, optical properties, and viscosity of the material.- Molecular order: As the temperature increases, the molecular order of liquid crystals generally decreases, leading to a transition from a more ordered phase e.g., smectic to a less ordered phase e.g., nematic or an isotropic liquid. Conversely, cooling the material can increase the molecular order and promote the formation of more ordered phases.- Optical properties: The optical properties of liquid crystals, such as birefringence and optical rotation, are strongly dependent on the molecular order and arrangement of the material. As the temperature changes and the molecular order is altered, the optical properties can also change significantly.- Viscosity: The viscosity of liquid crystals typically decreases with increasing temperature, which can affect the response time and flow behavior of the material.2. External electric fields: The application of an external electric field can also have a significant impact on the properties of liquid crystals, particularly for those materials with a strong dielectric anisotropy i.e., a difference in the dielectric constant along different molecular axes .- Alignment and reorientation: In the presence of an electric field, the liquid crystal molecules tend to align themselves with the field direction, leading to a change in the molecular arrangement and orientation. This reorientation can affect the optical properties of the material, such as birefringence and optical rotation, and is the basis for the operation of liquid crystal displays LCDs .- Phase transitions: External electric fields can also induce phase transitions in liquid crystals, either by stabilizing a particular phase or by promoting the formation of a new phase with a different molecular arrangement. This can lead to changes in the material's properties, such as its optical behavior and viscosity.- Electro-optic effects: The interaction between liquid crystals and electric fields can give rise to various electro-optic effects, such as the Kerr effect and the Pockels effect, which can be exploited for optical modulation and switching applications.In summary, the properties of liquid crystals are strongly influenced by temperature and external electric fields, which can affect their molecular order, optical properties, and viscosity. These effects can be harnessed for various applications, such as displays, sensors, and optical devices, by carefully controlling the temperature and electric field conditions.