surface science: physical chemistry of surfaces massimiliano bestetti lesson n° 3 - 13 october 2011
TRANSCRIPT
Surface science: physical chemistry of surfaces
Massimiliano Bestetti
Lesson N° 3 - 13 October 2011
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2
Surface topography
1. Parameters
2. Measurements
3. Surface topography modification: examples
4. Standards
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3Terminology and parameters
http://www.imagemet.com/WebHelp/spip.htm#roughness_parameters.htm
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4Terminology and parameters
Surface roughness parameters associated with irregularity properties in the profile length direction
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5Terminology and parameters
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6Terminology and parameters
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7Terminology and parameters
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8Terminology and parameters
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9Terminology and parameters
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10Terminology and parameters
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11Terminology and parameters
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12Terminology and parameters
Surface roughness parameters associated with profile irregularity form
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13Terminology and parameters
Surface roughness parameters associated with profile irregularity form
Kurtosis
n
ii
q
ynR
Ku1
44
11
http://downloads.mts.hindawi.com/MTS-Files/MS/papers/regular/305312.v1.pdf?AWSAccessKeyId=0CX53QQSTHRYZZQRKA02&Expires=1318514056&Signature=R9%2BnfYFwXo%2FUPzZ0ojTw4tc3tF8%3D
… For dental implants the primary rationale of surface roughness is to get an increased retention
strength. Implant surface roughness is normally characterized by a number of surface parameters.
There is no consensu as to which combination of roughness paramaters that best characterize the
important topopgraphycal featurs of implant surface roughness ...
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14Terminology and parameters
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15Terminology and parameters
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16Terminology and parameters
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17Terminology and parameters
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18Terminology and parameters
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19Terminology and parameters
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20Terminology and parameters
Numerical examples
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21Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
Pressure-sensitive-adhesives (PSA) → adhesive joint after a short
contact time under a light pressure (vdW forces).
Mechanical contact between. If the surface of the adhesive or that of
the substrate are rough, this contact can be incomplete and evolve with
contact time (→ role of this incomplete contact on the subsequent
debonding process).
Air bubbles could be trapped at the interface between the adhesive and
the surface and they could act as nucleating sites for cavities in the
early stages of the failure process.
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22Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
Pressure-sensitive-adhesives (PSA) → ability to form bridging fibrils
across the two surfaces, during the debonding stage.
The fibrils are initiated by the formation of cavities at the interface
between the adhesive and the hard surface or in the bulk of the
adhesive.
The role of the surface topography in the cavity nucleation process
(changing the shape or length scale of the surface roughness) has
been investigated in a systematic manner.
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23Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
PSA poly (2-ethylhexyl acrylate)
t ~ 100 µm
Glass
Stainless steel ( 5 mm)
Ra 11 - 148 nm (5 levels)
Temperature 23°C
Nominal contact pressure 1 MPa
Contact time 1 s
Debonding rate 30 µm/s
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24Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
Schematic of a nominal stress versus strain curve during the debonding stage. Wadh is taken as the integral under the curve and represents the external work done for debonding.
By measuring the contact area at the beginning of the pulloff stage (with the video camera) and the thickness of the adhesive layer, we can plot a nominal stress versus strain curve.
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25Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
Steel ball surface roughness (WYKO optical profilometer used in vertical scanning interferometry mode (VSI) to map out the surface)
Ra, λ →
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26Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
Ra, λ →
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27Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
A (Ra 11 nm) E (Ra 148 nm)
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28Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
A (Ra 11 nm) E (Ra 148 nm)
Wadh decreases with increasing roughness, from about 25 J/m2 for A to 15 J/m2 for E.
Ra (nm)
11
23
46
114
148
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29Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
A (Ra 11 nm) E (Ra 148 nm)
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30Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
A (Ra 11 nm) E (Ra 148 nm)
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31Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
A (Ra 11 nm) E (Ra 148 nm)
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32Example VI. The role of surface roughness in controlling the adhesion of a soft adhesive on a hard surface
Dependence of σmax on the characteristic amplitude of the grooves made by the polishing wheels on the steel surfaces. Since the maximum in stress is due to the nucleation of cavities, the grooves undoubtedly play an essential role in the level of stress at which a cavity can nucleate in the adhesive layer.
The role of surface roughness is to create weak spots under residual tension
which will therefore allow cavity growth at a lower level of nominal stress.
The presence of deeper grooves can:
– increase the size of air pockets trapped during the contact stage;
– alter the stress distribution near the surface in such a way that more spots are under residual tension stresses.
The second effect of the presence of topographical asperities is the slowing down of the propagation of these cavities along the surface (the propagation of the crack front may be more dissipative).