Basics of Infrared Spectroscopy in Textile

Basics of Infrared Spectroscopy in Textile
Jaiparkash Kaushik
Department of Textile Technology
The Technological Institute of Textile and Sciences,
Bhiwani, India
Email: jaiparkashkaushik@gmail.com



Introduction
Infrared Spectroscopy or IR Spectroscopy is used used to investigate vibrational structure of molecules or bonds in textile material. They are also used to investigate the type of bonding between the applied chemical and the textile substrate. Hence, a basic knowledge of IR Spectroscopy is important.

Spectroscopy is the study of the interaction of matter with the electromagnetic spectrum:
 
1. Electromagnetic radiation displays the properties of both particles and waves,
 
2. The particle component is called a photon,
 
3. The energy (E) component of a photon is proportional to the frequency . Where h is Planck’s constant and n is the frequency in Hertz (cycles per second),
 
E = hn 
 
4. The term “photon” is implied to mean a small, massless particle that contains a small wave-packet of EM radiation/light – we will use this terminology in the course,
 
5. Because the speed of light, c, is constant, the frequency, n, (number of cycles of the wave per second) can complete in the same time, must be inversely proportional to how long the oscillation is, or wavelength.
 
6. Amplitude, A, describes the wave height, or strength of the oscillation,
 
7. Because the atomic particles in matter also exhibit wave and particle properties (though opposite in how much) EM radiation can interact with matter in two ways:
  • Collision – particle-to-particle – energy is lost as heat and movement
  • Coupling – the wave property of the radiation matches the wave property of the particle and “couple” to the next higher quantum mechanical energy level
8. The entire electromagnetic spectrum is used by chemists.
 
The IR Spectroscopic Process
1. The quantum mechanical energy levels observed in IR spectroscopy are those of molecular vibration,
 
2. We perceive this vibration as heat,
 
3. When we say a covalent bond between two atoms is of a certain length, we are citing an average because the bond behaves as if it were a vibrating spring connecting the two atoms,
 
4. For a simple diatomic molecule, this model is easy to visualize,
 
5. There are two types of bond vibration:
  • Stretch – Vibration or oscillation along the line of the bond 
Stretch
  • Bend – Vibration or oscillation not along the line of the bond
Bend
6. As a covalent bond oscillates – due to the oscillation of the dipole of the molecule – a varying electromagnetic field is produced,
 
7. The greater the dipole moment change through the vibration, the more intense the EM field that is generated,
 
8. When a wave of infrared light encounters this oscillating EM field generated by the oscillating dipole of the same frequency, the two waves couple, and IR light is absorbed,
 
9. The coupled wave now vibrates with twice the amplitude.

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