Question

Consider para-azoxyanisole, which is a nematic liquid crystal in the temperature range of \(21{ }^{\circ} \mathrm{C}\) to \(47^{\circ} \mathrm{C}\) :

Short answer

Para-azoxyanisole is a nematic liquid crystal that exhibits unique physical and optical properties such as birefringence, fluidity, and anisotropic characteristics in the temperature range of \(21^{\circ} \mathrm{C}\) to \(47^{\circ} \mathrm{C}\). These properties make it suitable for various applications, mainly in liquid crystal displays (LCDs), thermometers, fiber-optic communication systems, and smart windows.

Step-by-step solution

Definition of Nematic Liquid Crystals

Nematic liquid crystals are a state of matter that occurs between the solid and liquid phases, in which the molecules are oriented in a parallel manner without forming a clearly defined arrangement. These materials exhibit unique physical and optical properties like viscosity, birefringence, and fluidity, which can be utilized in various applications such as liquid crystal displays (LCDs).

Temperature Range

The given temperature range of 21°C to 47°C tells us that para-azoxyanisole behaves as a nematic liquid crystal in this specific temperature interval. Below 21°C, it would be a solid, and above 47°C, it would become a conventional liquid with no orientation or special optical properties.

Physical Properties

In the nematic phase (between 21°C and 47°C), para-azoxyanisole demonstrates unique physical properties such as: 1. Birefringence: The ability to refract light differently depending on the polarization and direction of the incident light, resulting in different colors. 2. Fluidity: Despite having a parallel molecular orientation, nematic liquid crystals can flow like a liquid and orient themselves in response to external forces such as temperature, electric field, or mechanical stress. 3. Anisotropic properties: Nematic liquid crystals have varying properties depending on the direction being observed, such as electrical conductivity, optical refractive index, and thermal expansion.

Applications

Nematic liquid crystals, including para-azoxyanisole, find applications in various fields, mainly in liquid crystal displays (LCDs). They are used in watches, calculators, computer monitors, and televisions because of their ability to manipulate light and create images. They can also be employed in thermometers, fiber-optic communication systems, and smart windows to control light transmission.

Key concepts

Liquid Crystal Displays (LCDs)

Liquid crystal displays, commonly known as LCDs, are a prevalent type of display used in everything from calculators and watches to computer monitors and televisions. At their core, LCDs consist of a layer of liquid crystal substance sandwiched between transparent electrodes and polarizing filters.

The nematic liquid crystals in these displays, like para-azoxyanisole in the temperature range of 21°C to 47°C, reorient themselves when an electric field is applied. This reorientation affects the way light passes through the crystals and polarizing filters, ultimately controlling the display's transparency and color.

Since each pixel in an LCD can be individually controlled by its own electric field, this technology allows for high-resolution displays that consume less power than cathode ray tube (CRT) displays. The LCDs are also thin and lightweight, making them ideal for a wide range of portable electronic devices.

Temperature Range for Liquid Crystals

The behavior of liquid crystals can dramatically change depending on the temperature. Each liquid crystal material has a specific temperature range in which it forms its nematic phase, exemplified here by para-azoxyanisole, which displays nematic characteristics between 21°C to 47°C.

Below this temperature range, the material solidifies and loses its fluidity and optical characteristics which are crucial for applications like LCDs. If heated above 47°C, para-azoxyanisole would transform into a conventional liquid with no molecular order, hence, disallowing the controlled manipulation of light required for display technology.

The precise control of temperature is crucial in the manufacturing and operation of devices utilizing liquid crystals. Maintaining the ideal temperature range ensures the liquid crystals exhibit the desired anisotropic properties.

Physical Properties of Liquid Crystals

Liquid crystals, especially the nematic type used in devices like LCDs, have several distinct physical properties that allow them to function as unique display media. These properties include birefringence, which allows liquid crystals to split light into two distinct paths based on polarization, producing the vivid and variable images seen on screens.

Moreover, nematic liquid crystals are anisotropic, meaning their properties differ depending on the direction in which they’re measured. This anisotropy is pivotal for creating uniform images in LCDs as it affects how light propagates through each pixel.

Fluidity is another key aspect, as nematic liquid crystals can flow like a liquid, allowing for their alignment to be adjusted with electric fields, which is how pixels are controlled in LCDs. Collectively, these characteristics enable nematic liquid crystals to be widely employed in sophisticated technologies that rely heavily on precision and control of light transmission.