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Is there a way to maximize van der Waals forces between two materials, by electrifying one material, thus creating dipoles/instantaneous dipoles and thus creating stronger van der Waals forces? has this been documented?

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  • $\begingroup$ In dielectric media you could do the reverse of "index matching" to maximise the hamacker constant, i.e. choose materials that have highly different refractive indices. Of course electrostatic interaction would work even better, but then its no longer van-der-Waals interaction $\endgroup$ – Bort Jul 28 '15 at 15:26
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There are three main types of van der Waals forces:

Keesom forces: Dipole to dipole attraction between oppositely charged ends of permanent dipole molecules. Hydrogen bonding is an especially strong form of Keesom force. It's responsible for water condensing into liquid and solid form at temperatures prevailing on our planet, and for loosely maintaining the characteristic shapes of proteins and DNA. Without this form of van der Waals bonding, life as we know it would not be possible.

London dispersion forces: If the electron clouds of electrically neutral atoms in a molecule temporarily fluctuate to one side, they may induce electrons in a neighboring molecule to fly to the opposite side, which creates a ripple effect among nearby molecules. Temporarily positive and negative poles of adjoining molecules may begin to oscillate in unison, which creates a temporary bond among them. London dispersion forces make by far the largest contribution to van der Waals bonding in most cases with the exception of water .

Debye forces: A permanent dipole molecule may induce a temporary dipole in an adjacent molecule.

These are all very weak interactions, as the table of dipole moments in this link shows: http://www.chemguide.co.uk/atoms/bonding/vdwstrengths.html (scroll down to table 10.2 - the dipole moment is a vector that measures the degree of polarity).

You could induce a magnetic field in a paramagnetic or ferromagnetic material by bringing it into close proximity to a permanent magnet, causing the molecules to align, but the resulting attraction to other materials would not be a van der Waals force.

Likewise, if you run electric current through a material, you can induce a magnetic field, but that would not be a van der Waals force. As Bort noted in his comment, inducing electrostatic interaction also would not be a van der Waals force.

Judicious choice of materials, reduction of the space separating the materials, and increasing the amount of surface area in contact are the methods generally used to augment the effect of van der Waals forces. Researchers have turned to geckos (http://news.sciencemag.org/2002/08/how-geckos-stick-der-waals) for clues to increasing the strength. Here is an account of how this research is being used to design climbing pads: http://physicsbuzz.physicscentral.com/2014/11/gecko-style-climbing-becomes-reality.html.

Here is an account of the van der Waals technology used by geckos, which has been used to develop synthetic releasable tape and other adhesives. You may click on the menu at the upper left side of the link for more information about adhesives that have been developed, a bibliography, and even a DIY video: http://robotics.eecs.berkeley.edu/~ronf/Gecko/gecko-facts.html. And here is a more technical article on one group's development of gecko-like climbing technology scaled for human use: http://rsif.royalsocietypublishing.org/content/12/102/20140675#ref-14

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  • $\begingroup$ so there is no way to intensify van der Waals forces? mainly London dispersion forces? what other intermolecular forces could make two non magnetic surfaces attach? $\endgroup$ – sloupioc Jul 28 '15 at 16:52
  • $\begingroup$ I want to electrify a material and increase the adhension, I don't want to do that by increasing surface area, because it will be permanent: I want to switch it on and off $\endgroup$ – sloupioc Jul 28 '15 at 17:28
  • $\begingroup$ @sloupioc: I see what you are trying to do, now. Take a look at the climbing paddles described in the last link I provided in my answer. Geckos are able to turn the effect of the van der Waals force on and off by shifting the orientation of the surfaces. $\endgroup$ – Ernie Jul 28 '15 at 17:43
  • $\begingroup$ Ernie, how many square meters is the surface of the gecko hand? $\endgroup$ – sloupioc Jul 29 '15 at 10:05
  • $\begingroup$ @sloupioc: There are 5 footpads per gecko foot with surface of 400 square millimeters for the entire foot. Each footpad contains 500,000 setae ("hairs"). Each setae contains hundreds of spatulas. Each spatula is about 0.2 micrometers long x .1 wide. I added an additional reference to the answer, about synthetic gecko adhesives that are releasable. $\endgroup$ – Ernie Jul 29 '15 at 15:28

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