Photon Correlation Spectroscopy
- 2. Contents : • PRINCIPLE • INSTRUMENTATION DESIGN • STABILITY OF SAMPLE • ADVANTAGES • DISADVANTAGES
- 3. PRINCIPLE: Other names for PCS –DLS,IFS,QES. Principle : particle size – measuring the changes –intensity of scattered light from a suspension or solution due to Brownian motion. Illuminates the Sample 173 90
- 4. LIGHT SCATTERING FLUCTUATIONS DUE TO BROWNIAN MOTION VS. TIME AUTOCORRELATION FUNCTION FROM PCS For a sample where all of the particles are the same size. The optical signal shows random changes due to the randomly changing relative position of the particles The signal can be interpreted using an autocorrelation function. Incoming data is processed in real time with a digital signal processing device known as a correlator and the autocorrelation function
- 5. Where: Dh = the hydrodynamic diameter Dt = the translational diffusion coefficient kB = Boltzmann’s constant T = temperature η = dynamic viscosity
- 6. INSTRUMENTATION DESIGN: Light source : sufficiently intense light source –narrow band ,polarized , monochromatic.
- 7. • Optical system : lens is enclosed in a temperature controlled scattering cell surrounded by refractive index matching liquid. Typically all experiments -10-160 degrees angular range. • Detectors: PMT,APD & SPCM.
- 8. Digital correlator: ACF –formed by recording number of photons arriving in each sample time & bits registered are used to maintain the records of photon counts.
- 9. Stability of sample: • An unstable sample –inappropriate sample preparation. • Hydrophilic sample surfaces-treat with stabilizing surfactant. • Hydrophobic samples surfaces-treat with methyl alcohol. • Use appropriate surfactants-to remove dust, use of deionised and filtered water is utmost important in any serious size measurements.
- 11. ADVANTAGES: • Mini. Information –sample. • Mixtures of samples – viscosity of medium must be known accurately. • Mini. amount of sample. • Fast , simple & no destructive –sample recover is possible.
- 12. DISADVANTAGES: • Extremely low resolution : particle size must differ by 50% or more to reliably detect two peaks. • A small quantity of small size particles can easily be ‘hidden’ in a much larger quantity of larger size particles.