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Food Analysis Lecture 17 (3/29/2005)

Food Analysis Lecture 17 (3/29/2005). Particle Size Analyzer. Qingrong Huang Department of Food Science. Brownian Motion-Diffusion Molecules in Solutions. Dynamic Light scattering. Originating from concentration fluctuation. Scattered Light from Molecules in Solution.

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Food Analysis Lecture 17 (3/29/2005)

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  1. Food Analysis Lecture 17 (3/29/2005) Particle Size Analyzer Qingrong Huang Department of Food Science

  2. Brownian Motion-Diffusion Molecules in Solutions

  3. Dynamic Light scattering • Originating from concentration fluctuation

  4. Scattered Light from Molecules in Solution

  5. Autocorrelation Function The property A(t) fluctuates in time as the molecules move around in the fluid. The time axis is divided into Discrete intervals, t. Theorem: Ensemble average is equivalent to time average.

  6. Instrumentation

  7. DLS Applications • Determination of critical micelle concentration (CMC); • Vesicle size distribution determination; • Insulin structure as a function of pH; • Thermal dissociation and denaturation of proteins; • Characterization of low molecular weight peptides; • Sizes of polysaccharide fractionations; • Stability of colloids for medical imaging; • BSA monomer and dimer; • Gold colloids, etc….

  8. Summary of Operation

  9. Data Analysis • From correlator, intensity-intensity autocorrelation function, G(q,t), • was obtained; • The normalized autocorrelation function, g(q,t), was calculated using • Sigert relation: • g(q,t)=[G(q,t)-1]1/2 • William-Watts (WW)-stretched exponential function is used to fit • the experimental data; • g(q,t)=exp[-(t/)] • Here  is the distribution parameter. For diffusing particles of equal • size a simple relaxation process with =1 is expected. For all the • solutions we study in the paper,  is within the range of 0.9 ~ 1. • The mean relaxation times are calculated by using

  10. Data Analysis (continue) • The diffusion coefficient D were calculated according to D=<>-1q -2, • where q is the amplitude of scattering vector defined as • q=(4n/)sin(/2), n is the solution refractive index, • the laser wavelength and  the scattering angle. • The diffusion coefficient D can be converted into hydrodynamics • radius Rh using the Stokes-Einstein equation: • Rh=kT/(6D)

  11. Data Analysis (Example) Fitting function: G(q,t)=a+b*(exp(-(t/c)d)2 Where c (also ) is the average relaxation time q2= (4nsin(/2)/)2=(4*3.142*1.401*sin(110/2)/(6.9*10-5))2=4.37*1010 cm-2 D=-1 q-2 =(0.00003*4.37*1010)-1 =7.63*10-7 cm2/s=7.63*10-11 m2/s Rh=KT/(6D)=1.38*10-23*298/(6*3.142*0.000456*7.63*10-11)=6.3*10-9 m=6.3 nm

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