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Gel time of different volume fractions of polystyrene particles

Gel time of different volume fractions of polystyrene particles. Scattering of light in colloid. Rakshya Khatiwada. 08/03/06. Outline. Introduction Apparatus Calibration Sample Preparation Measurements and Data Analysis Results Conclusion. Introduction.

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Gel time of different volume fractions of polystyrene particles

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  1. Gel time of different volume fractions of polystyrene particles Scattering of light in colloid Rakshya Khatiwada 08/03/06

  2. Outline • Introduction • Apparatus • Calibration • Sample Preparation • Measurements and Data Analysis • Results • Conclusion

  3. Introduction • 3D solid objects don’t coalesce like liquids • They form fractals with some different dimension • In dilute systems, including aerosols and colloids the dimension is 1.8

  4. What is gelation of colloids? • Network of smaller particles/monomers • The particles exhibiting Brownian motion stop/slow down • How do we know when the gel point is reached? The intensity of light doesn’t change much because the network stops growing

  5. What is polystyrene? • Micro spheres of 24nm diameter • About same charge • MgCl2 forms ions which screen the coulomb charge repulsion allowing them to stick together with van der Waal’s force

  6. Sample CCD camera Filter Small mirror CalibrationApparatus • Used single slit (D=10µm) 488nm laser beam

  7. Single slit diffraction: Scattering wave vector Unit: 1/m gives the size of the aggregate

  8. Sample preparation • Different volume fractions of polystyrene: • 9.14E-4 • 7.03E-4 • 5.41E-4 • 4.16E-4 • 3.20E-4 • 2.46E-4 • 35mM of MgCl2

  9. 50μl of Polystyrene+50μl of MgCl2 MgCl2 Polystyrene Sample Holder

  10. Intensity vs. wave vector q Measurements and Data Analysis

  11. Gel time vs. volume fraction Theoretical gel time:

  12. ResultsGel time vs. volume fraction

  13. Conclusion • Reproducible data • Lower volume fractions, longer gel time • Experimental gel times longer than theoretical • Literature values compared to our theory are consistent with our conclusions here.

  14. Possibilities • Maybe theory has simplified so many details (example: same cluster size) • Maybe stoppage of system to evolve is not good indication of gel time. • Need a better way of finding gel point • Like Dynamic light scattering (can see particles moving)

  15. Acknowledgement Supervisor: Tahereh Mokhtari & Dr. Christopher Sorensen Thanks to Rajan Dhoubhadel & Hao Yan

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