Molecules Aggregating on a Surface that includes a Scratch

In summary, the conversation discussed the phenomenon of molecules preferentially aggregating on burned fused silica rather than unburned fused silica. The expert suggested that this could be due to the surface morphology of the silica chip, where the burned region had a higher surface energy compared to the unburned region. This could be caused by the presence of non-volatile substances in the air that lower the surface energy of the silica. The expert also mentioned that the geometry of the burned region, whether it is a bump or a groove, would not affect this phenomenon as long as it is not nanostructured. They also suggested looking into the "lotus effect" and the role of surface roughness in changing wetting properties.
  • #1
Sciencestd
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fused silica.jpg

View from above of fused silica chip.

In the image is fused silica and the black line is burned fused silica caused by laser, when I cast droplet that contains molecules, never mind which kind of aggregation I tried different kinds of molecules, the aggregation is more preferably on the burned fused silica rather than unburned fused silica, the burning it seems that it caused to a groove in the sample.. so I have two questions:
1- Why the molecules prefer to aggregate more on the burned region, what is the physics behind that??
2- Could the result be changed if the burned region is like a bump and not a groove?

Thank you,
 
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  • #2
Surface morphology can change wetting properties, especially if there is a regular structure at the nanoscale (google "lotus effect" for example). But if your laser was powerful enough to melt silica (mp 1710 C) and you're seeing the irradiated areas gather liquid, I imagine what happened was that you started with a silica chip that's had no special precautions taken to protect it from ambient, so that it's got a nice thick layer of low-surface-energy crud on it that's come from the air. This happens: bare clean silica has a very high surface energy, and if there's non-volatile schmutz floating around in the air (aerosolized pump oil, dust and dirt from HVAC units, or whatever), it will land on the surface, stick permanently, and lower the surface energy. Irradiating with a laser in air will burn that crud off, leaving behind an area of clean silica, which has a much higher surface energy. When a liquid meets a surface, it will preferentially cover the areas with the highest surface energy. That's my guess as to what's happening here.
 
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  • #3
Thank you so much for your answer! :) It gives me the way to think about it, really thank you!
I just have couple of questions more, do you think if the groove was like a bump so it will be different? and how the roughness of the surface can change the wetting?
 
  • #4
Sciencestd said:
do you think if the groove was like a bump so it will be different?
The mechanism I hypothesized would be the same regardless of the geometry, as long as that geometry wasn’t nanostructured.
Sciencestd said:
how the roughness of the surface can change the wetting?
Please google “lotus effect.”

Edit: also, the Wiki page on ultrahydrophobicity has some enlightening pictures.
 
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1. What causes molecules to aggregate on a surface that includes a scratch?

Molecules aggregate on a surface that includes a scratch due to the presence of surface defects or irregularities. These defects act as nucleation sites, where molecules can easily attach and form aggregates.

2. Is the aggregation of molecules on a scratched surface a natural process?

Yes, the aggregation of molecules on a scratched surface is a natural process that occurs due to the inherent properties of molecules and surfaces. It is a result of the minimization of surface energy and the tendency of molecules to form stable structures.

3. Can the size of the scratch affect the aggregation of molecules?

Yes, the size of the scratch can significantly affect the aggregation of molecules. A larger scratch provides more surface area for molecules to aggregate, leading to larger and more stable aggregates. On the other hand, a smaller scratch may result in smaller and less stable aggregates.

4. How does the type of molecules involved affect the aggregation on a scratched surface?

The type of molecules involved can greatly influence the aggregation on a scratched surface. Some molecules may have a higher affinity for the surface defects, leading to more significant aggregation. Additionally, the shape and size of the molecules can also impact the formation and stability of aggregates.

5. Can the environmental conditions affect the aggregation of molecules on a scratched surface?

Yes, environmental conditions such as temperature, humidity, and pH can affect the aggregation of molecules on a scratched surface. These factors can alter the surface properties, which can impact the nucleation and growth of aggregates. Additionally, the presence of other substances or impurities on the surface can also influence the aggregation process.

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