The molecular structures of many common liquid crystals are long and rodlike. In addition, they contain polar groups. Explain how both characteristics of liquid crystals contribute to their anisotropic nature.

Liquid crystals display distinctive anisotropic properties, meaning their physical attributes such as optical, electrical, and thermal behaviors differ when measured along different directions. This directional dependency is central to their unique performance in applications such as LCD screens.

Anisotropy in these materials arises from the ordered arrangement of their molecules. Imagine it as the difference between a neatly stacked deck of cards and a random pile. In an isotropic liquid, like water, molecules tumble around with no preferential orientation, similar to the random pile. However, in liquid crystals, molecules tend to maintain a certain order, much like the stacked cards, but they still have the ability to flow.

This organized, yet fluid state endows liquid crystals with a blend of solid-like and liquid-like properties, allowing them to react predictably to external stimuli, such as electric fields or temperature changes. This reaction is often manipulated in electronic displays to control the light passage through the liquid crystal layer, resulting in the desired image on the screen.

The rodlike structure of liquid crystal molecules is a key contributor to their overall anisotropic nature. This elongated conformation promotes a uniform alignment within a certain direction, which is a principal behavior exhibited by liquid crystals.

Consider the molecules as tiny rods; when confined to a space, these rods naturally align parallel to one another due to their shape and the interactions between them. This phenomenon can be influenced by surface interactions in their container, electric or magnetic fields, and even the temperature of the surrounding environment.

The degree of alignment can greatly affect the liquid crystal's properties. For example, in displays, the precise control of molecular alignment adjusts the light modulating ability of the liquid crystal, which allows us to see images. In other contexts, changes in alignment can be harnessed for sensors or responsive materials, which respond to external stimuli by changing their molecular orientation and hence, their observable properties.

Dipole-dipole interactions are a type of force that occurs between molecules with permanent dipole moments; that is, molecules that have regions of positive and negative charge. These interactions play a pivotal role in the alignment of liquid crystal molecules which contributes to their anisotropic behavior.

Imagine each molecule as a tiny magnet with a north and south pole. When these 'magnets' are brought close together, they align themselves in a manner that reduces the overall energy of the system – positive to negative. In the case of liquid crystals, the polar groups within the molecules act as these 'magnets', orienting themselves in response to the presence of neighboring dipoles.

This interaction is crucial as it strengthens the overall molecular alignment, making it more robust to disturbances. It also is the reason why applying an electric field can effectively reorient liquid crystal molecules, as each dipole tries to align with the field, making it possible to manipulate the properties of liquid crystals in a controlled way for applications such as switchable windows and various types of sensors.