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Isotropic and Anisotropic are terms used to explain the properties of the material in basic crystallography. Isotropic refers to materials that are direction-independent, while Anisotropic are direction-dependent material. The two terms are used to refer to the properties of materials in crystallography. These differences between Isotropic and Anisotropic occur due to differences in atom orientation in crystals. Cubic symmetry crystals, glass, etc are some examples of isotropic materials while some examples of anisotropic materials are composite materials, wood, etc.
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Key Terms: Isotropic Material, Anisotropic Material, Crystallography, Crystals, Cubic Symmetry, Metals, Homogenous Materials, Strength, Refraction, Refractive Index
What are Isotropic Materials?
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The term Isotropic derives from the Greek words “isos” meaning equal and “tropos” which means way. Isotropic materials refer to those materials which often show similar characteristics such as strength. This type of behaviour exhibited in materials is called isotropic behaviour. Some examples of isotropic materials include cubic symmetry, glass, crystal, glass, metals etc. Sometimes isotropic materials may be confused with homogenous materials, however, homogenous materials have uniformity in structure, while isotropic materials have uniformity in their physical properties from all directions.
Isotropic Uniform Structure
Read More: Solute- Definition, Characteristics, Types, Examples
What are Anisotropic Materials?
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Anisotropic derives from the Greek term “an” meaning without, “isos” means equal and “tropos” means way. Hence, anisotropic means when materials have different physical properties in different directions. And so, the physical properties of these materials are heavily dependent on their directions. Therefore, isotropic and anisotropic are opposite terms. The materials that show such properties are noted to have anisotropic behaviour. Some examples of anisotropic materials are Wood, a good majority of biological tissues are also considered anisotropic.
Anisotropic Layered Structure
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Difference Between Isotropic And Anisotropic Materials
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The key differences between isotropic and anisotropic materials are as follows:
| Isotropic Materials | Anisotropic Materials |
|---|---|
| Isotropic materials are independent of direction. | Anisotropic materials are dependent on direction. |
| Isotropic materials have only one refractive index. | Anisotropic materials have more than one refractive index. |
| No light can pass through isotropic materials. | Light can pass through anisotropic materials. |
| Isotropic materials have the same velocity of light from all directions. | Anisotropic materials have different velocities of light from all different directions. |
| Isotropic materials are often used in lenses. | Anisotropic materials are often used in Polarizers. |
| Isotropic materials have a darker appearance. | Anisotropic materials usually have a lighter appearance. |
| Double refractions are not possible in isotropic materials. | Double refractions are possible in anisotropic materials. |
| Isotropic materials have consistent chemical bonding. | Anisotropic materials have uncertain chemical bonding. |
Read More: Physical Properties of Metals and Non-Metals
Things to Remember
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- Isotropic and Anisotropic materials are terms used to refer to the different properties of materials in crystallography.
- Isotropic materials are direction-independent while anisotropic materials are direction-dependent.
- Isotropic materials exhibit isotropic behaviour while Anisotropic materials have anisotropic behaviour.
- Isotropic materials may be confused with homogenous materials, however, homogenous materials have uniformity in structure, while isotropic materials have uniformity in their physical properties from all directions.
- Isotropic materials have a consistent chemical bonding, while anisotropic materials have inconsistent or uncertain chemical bonding.
Sample Questions
Ques. Mention whether the mentioned terms are Isotropic: (3 Marks)
(a)Crystal
(b)Wood
(c)Glass
(d)Metals
(e)Cubic symmetry glass
(f)Plastics
(b) Wood = Not isotropic, it is anisotropic
(c) Glass = Isotropic
(d) Metals = Isotropic
(e) Cubic symmetry glass = Isotropic
(f) Plastics = Isotropic
Ques. Mention whether the mentioned terms are Anisotropic: (3 Marks)
(a)Ice crystals
(b)Biological tissues
(c)Glass
(d)Rubber
(e)Aluminium
(f)Diamond
Ans. (a) Ice Crystals = Anisotropic
(b) Biological tissues = Anisotropic
(c) Glass = Not Anisotropic, it is isotropic
(d) Rubber = Not Anisotropic, it is isotropic
(e) Aluminium = Not Anisotropic, it is isotropic
(f) Diamond = Not Anisotropic, it is isotropic
Ques. Why amorphous solids are isotropic? (3 Marks)
Ans. While crystalline solids are anisotropic, amorphous solids are isotropic. The reason for amorphous solids having an isotropic nature is because there is no long-range order present. Due to this, they do not have irregular directions. This is one of the key characteristics/ features of isotropic materials is that they are direction-independent. Meaning they do not have a uniform direction. Hence, amorphous solids are isotropic substances.
Ques. Differentiate between an isotropic and an anisotropic medium? (5 Marks)
Ans. The differences between isotropic mediums and anisotropic mediums are as follows:
- Isotropic Medium
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- In Isotropic mediums the properties of substances are uniform.
- It is direction-independent.
- They have consistent chemical bonding.
- It has a uniform velocity of light in all directions.
- Examples of Isotropic mediums include optics, optical eye drops.
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- Anisotropic Medium
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- In anisotropic mediums the properties of the substances are not uniform, they are different in different directions.
- It is direction-dependent.
- The chemical bonding in the anisotropic medium is inconsistent.
- It does not have a uniform velocity of light, it is dependent on the direction.
- Examples of anisotropic medium include wood, composite materials.
Ques. What is anisotropic stress? (3 Marks)
Ans. Anisotropic stresses refer to the stresses that are formed due to the formations not being isotropic. The direction and magnitude of the stresses often depend on factors such as tectonic related conditions. Due to being anisotropic, which are non-uniform, inconsistent, and direction-dependent, the stresses are often non-homogenous. Along with that anisotropic stresses are also compressive. In rock formation, the anisotropic and also the non-homogenous nature of these formations leads to the formation of the actual state of stress in the rock formation which is very complex.
Ques. Why do crystalline solids are anisotropic and amorphous solids are isotropic? (3 Marks)
Ans. A key difference between anisotropic and isotropic materials is the difference that isotropic materials have or exhibit the same properties regardless of their directions. Anisotropic materials exhibit different properties dependent on their direction. Hence, they are often labelled as direction-dependent, while isotropic materials are noted as direction-independent.
Following this differentiation, crystalline solids and amorphous solids are differentiated. Crystalline solids are anisotropic because they exhibit different geometric formations in different directions. Amorphous solids are isotropic because when only viewed from different angles they exhibit irregular arrangement, however, they have the same properties across all directions.
Ques. Define the following: (3 Marks)
(a)Dichroism
(b)Optically Active Crystals
(c)Dispersion
Ans. (a) Dichroism: Some crystals rotate when polarized light is passed through them. The ability of a crystal to absorb electromagnetic waves along two different vibrational axes is called Dichroism.
(b) Optically Active Crystals: Some crystals rotate when polarized light is passed through them. They are called optically active crystals.
(c) Dispersion: When an optically active crystal has differential refraction of a different wavelength of light, it is noted as Dispersion.
Ques. Which crystal system is isotropic and why? (3 Marks)
Ans. An example of a crystal system that is isotropic is diamond. Diamond is isotropic because it has the same properties all across different directions, that is, crystallographic directions. Crystal systems have an isometric or cubic system. With three axes all of which intersect at 90 degrees to each other. This equality of the axis makes it isotropic.
Ques. What are some of the unique properties of anisotropic materials? (3 Marks)
Ans. Some unique properties of anisotropic materials include:
- Anisotropic materials are more common in nature than isotropic materials, this is because of the variation in the atomic orientations.
- Anisotropic materials also have more than one refractive index due to this, anisotropic crystals are affected by things such as optical activity, birefringence, dichroism.
- Cytoplasm (inner part of plant cells) are labelled as anisotropic because of the presence of intracellular organisms.
Ques. Differentiate between homogeneous and isotropic materials. (5 Marks)
Ans. The difference between homogeneous and isotropic materials are as follows:
- Homogeneous Material
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- Homogeneous materials have uniformity in their matter structure.
- The properties of homogeneous structures are not a function of position.
- Homogeneous materials are not always isotropic.
- Homogeneous materials have uniformity throughout.
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- Isotropic Material
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- Isotropic materials have uniformity in their physical properties from all directions.
- While isotropic materials don’t change their physical properties in different directions.
- Isotropic materials are always homogeneous.
- Isotropic materials have uniformity from certain directions.
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