gel time of different volume fractions of polystyrene particles
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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

Gel time of different volume fractions of polystyrene particles

Scattering of light in colloid

Rakshya Khatiwada

08/03/06

outline
Outline
  • Introduction
  • Apparatus
  • Calibration
  • Sample Preparation
  • Measurements and Data Analysis
  • Results
  • Conclusion
introduction
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
slide4
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

what is polystyrene
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
calibration apparatus
Sample

CCD camera

Filter

Small mirror

CalibrationApparatus
  • Used single slit (D=10µm)

488nm laser beam

single slit diffraction
Single slit diffraction:

Scattering wave vector

Unit: 1/m gives the size of the aggregate

sample preparation
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
50 l of polystyrene 50 l of mgcl 2
50μl of Polystyrene+50μl of MgCl2

MgCl2

Polystyrene

Sample Holder

gel time vs volume fraction
Gel time vs. volume fraction

Theoretical gel time:

conclusion
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.
possibilities
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)
acknowledgement
Acknowledgement

Supervisor: Tahereh Mokhtari & Dr. Christopher Sorensen

Thanks to

Rajan Dhoubhadel

& Hao Yan

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