Surface Roughness vs. Contact Angle
Posted by Frank Hild on Wed, Feb 25, 2009 @ 11:14 AM
In surface science, the use of a goniometer (contact angle meter) is common to determine the wettability of a surface. What is clear is that every material has a specific surface energy. But, may not be clear is that the surface topography of that material also effects the contact angle.
Surface roughness can change the contact angle without plasma or other surface treatment. When a device is molded or machined, the surface finish of the device can have a functional as well as a aesthetic purpose. The functional purpose can be microscopic capillary channel as in microfluidic devices. The aesthetic purpose can be feel or finish of the part as in grips or sunglasses. The data below shows the effects of surface roughness in RMS versus natural, plasma treated hydrophilic, and plasma treated hydrophobic.
| RMS | Type
| Untreated
| Philic
| Phobic
|
16
| Grind
| 80.0
| 24.5
| 108.0
|
32
| Grind | 85.0
| 31.0
| 113.5
|
63
| Grind
| 92.0
| 30.0
| 112.0
|
125
| Grind
| 99.0
| 29.0
| 115.0
|
Notice the general trends in contact angle relative to surface roughness.
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