Difference between revisions of "Van der Waals force"
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=== Bond trustworthiness, bond area and temperature === | === Bond trustworthiness, bond area and temperature === | ||
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| + | The question: VdW forces are "weak", so are they sufficient to hold stuff trustworthily together? | ||
At room temperature a C-C bond practically does not break due to thermal motions. | At room temperature a C-C bond practically does not break due to thermal motions. | ||
Revision as of 18:30, 20 August 2018
This page is not going to discuss the origin and nature of the VdW force but is focusing on practical applications and an intuitive understanding.
Contents
Practical usage
Bond trustworthiness, bond area and temperature
The question: VdW forces are "weak", so are they sufficient to hold stuff trustworthily together?
At room temperature a C-C bond practically does not break due to thermal motions. So a VdW bond with an area big enough to provide the same bonding energy will too practically not break at room temperature. This area is not all that big (relative of the area of a single C-C bond), so one might rely on VdW forces for reliably holding things together quite early on in the size scales of crystolecules.
So to prevent thermal motion from knocking VdW bonds open it might not be necessary to do some clever form closure designs (that are then strongly locked at a bigger size scale) except maybe for very small parts at very high temperatures.
(wiki-TODO: Make a table comparing energy, force and stiffness of a single covalent C-C bond to a surface to surface contact VdW bond by showing the areas that are necessary such that the VdW bond can provide the equivalent values than the single C-C bond. Note that these are three different areas.)
Comparison
Two coplanar atomically flat surfaces attract each other quite a lot.
- ~1nN per square nm this equates to around ~10,000 bar.
Original Source: (Nanosystems 9.7.1.)
indirect source: [1] (beware: the noted binding energy is mistakenly taken from a covalent interface - Nanosystems 9.7.3.)
double indirect source: [2] - ~2.7nN per square Nm 1/20 the tensile strength of diamond
Source: (Nanosystems 3.5.1.b) (more than titanium and low grade steel)
Especially if there is superlubrication) they can still slide effortlessly along each other (that is part motion may even be triggered by thermal motion) so depending on the use case male protrusions penetrating female indents may be needed to prevent that.
(related: intuitive feel)
(wiki-TODO: find the missing value)
Theory
Please use external sources - there are plenty out there.
Wikipedia: [3]
