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Gel time of different volume fractions of polystyrene particlesPowerPoint Presentation

Gel time of different volume fractions of polystyrene particles

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Gel time of different volume fractions of polystyrene particles

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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

- Introduction
- Apparatus
- Calibration
- Sample Preparation
- Measurements and Data Analysis
- Results
- Conclusion

- 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

- 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

- 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

Sample

CCD camera

Filter

Small mirror

- Used single slit (D=10µm)

488nm laser beam

Scattering wave vector

Unit: 1/m gives the size of the aggregate

- 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

MgCl2

Polystyrene

Sample Holder

Intensity vs. wave vector q

Theoretical gel time:

- 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.

- 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)

Supervisor: Tahereh Mokhtari & Dr. Christopher Sorensen

Thanks to

Rajan Dhoubhadel

& Hao Yan