Anisotropy vs Isotropy
The words isotropy and anisotropy are used in various fields. According to where it is used, the meaning may be slightly different. However, the fundamental concept behind these two words is similar and independent from where they are used. Isotropy and anisotropy are often used to describe properties of macroscopic bodies. They depend on the scale of the macroscopic body. For instance, one crystal can be anisotropic, and when many crystals are together, they can be isotropic.
What is Isotropy?
The word “isotropy” is related with uniformity. The meaning of the word itself is “uniformity in all directions.” As stated in the introduction, the meaning may slightly differ according to the subject area. For example, when talking about the isotropy of a material or mineral, it means having the same properties in all directions. In industrial processes isotropy means having the same rate in all the steps regardless of the direction. Molecules having kinetic energy are said to be moving randomly to any direction. Therefore, in a given time, there will be many molecules moving in a similar direction, hence show isotropy. Isotropy can be a property of some materials. Those materials will have the same properties in all the directions (ex: Amorphous solids). For example, if a solid expands in a similar manner in all directions, when heat is applied, is said to be isotropic.
What is Anisotropy?
Anisotropy, on the other hand, is dependent on the direction. It is the opposite of isotropy. The measured properties of a material differ in various directions in anisotropy. These properties can be physical or mechanical properties like conductivity, tensile strength or absorbance. Like the word isotropy, anisotropy also has slightly different meanings in different subjects where it is used. Normally, liquids have no order in molecules. Anisotropic liquids are liquid with a structural order in contrast to other common liquids. The sedimentary materials can have electrical anisotropy, where the electrical conductivity differs from one direction to another direction. The rock forming minerals are anisotropic in relative to their optical properties. The orientation of nuclei of a molecule differs with the strength of the applied magnetic field in NMR spectroscopy. In this case, anisotropic systems are referred to the molecules with high electron density. Because of the anisotropic effect (in molecules with high electron density), the applied magnetic field is felt differently to the molecule (most often less than the real value); therefore, the chemical shift varies. In fluorescence spectroscopy also anisotropic measurement of the fluorescence polarization is used, to determine the molecular structures. Further, anisotropy is a common concept in medicine when talking about the ultrasound imaging.
What is the difference between Anisotropy and Isotropy?
• Isotropy is directionally dependent, and anisotropy is directionally independent.
• Isotropic means having the same property in all directions. If the properties of a material are different in different directions, it is said to be anisotropic.