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1
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- Scattering of light in colloid
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2
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- Introduction
- Apparatus
- Calibration
- Sample Preparation
- Measurements and Data Analysis
- Results
- Conclusion
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3
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- 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
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4
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- 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
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5
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- 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
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6
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- Used single slit (D=10µm)
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7
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8
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- 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
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9
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10
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- Intensity vs. wave vector q
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11
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12
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13
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- 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.
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14
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- 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)
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15
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- Supervisor: Tahereh Mokhtari & Dr. Christopher Sorensen
- Thanks to
- Rajan Dhoubhadel
- & Hao Yan
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Notes