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van der Waals force

In molecular physics and chemistry, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond;[2] they are comparatively weak and therefore more susceptible to disturbance. The van der Waals force quickly vanishes at longer distances between interacting molecules.

Rainwater flux from a canopy. Among the forces that govern drop formation: Van der Waals force, surface tension, cohesion, Plateau–Rayleigh instability.
Microfiber cloth makes use of van der Waals force to remove dirt without scratches.[1]

Named after Dutch physicist Johannes Diderik van der Waals, the van der Waals force plays a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics. It also underlies many properties of organic compounds and molecular solids, including their solubility in polar and non-polar media.

If no other force is present, the distance between atoms at which the force becomes repulsive rather than attractive as the atoms approach one another is called the van der Waals contact distance; this phenomenon results from the mutual repulsion between the atoms' electron clouds.[3]

The van der Waals forces[4] are usually described as a combination of the London dispersion forces between "instantaneously induced dipoles",[5] Debye forces between permanent dipoles and induced dipoles, and the Keesom force between permanent molecular dipoles whose rotational orientations are dynamically averaged over time.

Definition Edit

Van der Waals forces include attraction and repulsions between atoms, molecules, as well as other intermolecular forces. They differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles (a consequence of quantum dynamics[6]).

The force results from a transient shift in electron density. Specifically, the electron density may temporarily shift more greatly to one side of the nucleus. This shift generates a transient charge which a nearby atom can be attracted to or repelled by. The force is repulsive at very short distances, reaches zero at an equilibrium distance characteristic for each atom, or molecule, and becomes attractive for distances larger than the equilibrium distance. For individual atoms, the equilibrium distance is between 0.3 nm and 0.5 nm, depending on the atomic-specific diameter.[7] When the interatomic distance is greater than 1.0 nm the force is not strong enough to be easily observed as it decreases as a function of distance r approximately with the 7th power (~r−7).[8]

Van der Waals forces are often among the weakest chemical forces. For example, the pairwise attractive van der Waals interaction energy between H (Hydrogen) atoms in different H2 molecules equals 0.06 kJ/mol (0.6 meV) and the pairwise attractive interaction energy between O (Oxygen) atoms in different O2 molecules equals 0.44 kJ/mol (4.6 meV).[9] The corresponding vaporization energies of H2 and O2 molecular liquids, which result as a sum of all van der Waals interactions per molecule in the molecular liquids, amount to 0.90 kJ/mol (9.3 meV) and 6.82 kJ/mol (70.7 meV), respectively, and thus approximately ~15 times the value of the individual pairwise interatomic interactions (excluding covalent bonds).

The strength of van-der-Waals bonds increases with higher polarizability of the participating atoms.[10] For example, the pairwise van der Waals interaction energy for more polarizable atoms such as S (Sulfur) atoms in H2S and sulfides exceeds 1 kJ/mol (10 meV), and the pairwise interaction energy between even larger, more polarizable Xe (Xenon) atoms is 2.35 kJ/mol (24.3 meV).[11] These van der Waals interactions are up to 40 times stronger than in H2, which has only one valence electron, and they are still not strong enough to achieve an aggregate state other than gas for Xe under standard conditions. The interactions between atoms in metals can also be effectively described as van-der-Waals interactions and account for the observed solid aggregate state with bonding strengths comparable to covalent and ionic interactions. The strength of pairwise van-der-Waals type interactions is on the order of 12 kJ/mol (120 meV) for low-melting Pb (Lead) and on the order of 32 kJ/mol (330 meV) for high-melting Pt (Platinum), which is about one order of magnitude stronger than in Xe due to the presence of a highly polarizable free electron gas.[12] Accordingly, van der Waals forces can range from weak to strong interactions, and support integral structural loads when multitudes of such interactions are present.

More broadly, intermolecular forces have several possible contributions:

  1. A repulsive component resulting from the Pauli exclusion principle that prevents close contact of atoms, or the collapse of molecules.
  2. Attractive or repulsive electrostatic interactions between permanent charges (in the case of molecular ions), dipoles (in the case of molecules without inversion centre), quadrupoles (all molecules with symmetry lower than cubic), and in general between permanent multipoles. These interactions also include hydrogen bonds, cation-pi, and pi-stacking interactions. Orientation-averaged contributions from electrostatic interactions are sometimes called the Keesom interaction or Keesom force after Willem Hendrik Keesom.
  3. Induction (also known as polarization), which is the attractive interaction between a permanent multipole on one molecule with an induced multipole on another. This interaction is sometimes called Debye force after Peter J.W. Debye.
  4. Dispersion (usually named London dispersion interactions after Fritz London), which is the attractive interaction between any pair of molecules, including non-polar atoms, arising from the interactions of instantaneous multipoles.

Hereby, different texts may refer to a different spectrum of interactions using the term "van der Waals force". Typically, contributions (1) and (4) are considered as van-der-Waals forces, excluding effects from permanent multipoles as described in (2) and from permanent polarization in (3). However, some texts describe the van der Waals force as the totality of forces, including repulsion; others mean all the attractive forces (and then sometimes distinguish van der Waals–Keesom, van der Waals–Debye, and van der Waals–London).

All intermolecular/van der Waals forces are anisotropic (except those between two noble gas atoms), which means that they depend on the relative orientation of the molecules. The induction and dispersion interactions are always attractive, irrespective of orientation, but the electrostatic interaction changes sign upon rotation of the molecules. That is, the electrostatic force can be attractive or repulsive, depending on the mutual orientation of the molecules. When molecules are in thermal motion, as they are in the gas and liquid phase, the electrostatic force is averaged out to a large extent because the molecules thermally rotate and thus probe both repulsive and attractive parts of the electrostatic force. Random thermal motion can disrupt or overcome the electrostatic component of the van der Waals force but the averaging effect is much less pronounced for the attractive induction and dispersion forces.

The Lennard-Jones potential is often used as an approximate model for the isotropic part of a total (repulsion plus attraction) van der Waals force as a function of distance.

Van der Waals forces are responsible for certain cases of pressure broadening (van der Waals broadening) of spectral lines and the formation of van der Waals molecules. The London–van der Waals forces are related to the Casimir effect for dielectric media, the former being the microscopic description of the latter bulk property. The first detailed calculations of this were done in 1955 by E. M. Lifshitz.[13] A more general theory of van der Waals forces has also been developed.[14][15]

The main characteristics of van der Waals forces are:[16]

  • They are weaker than normal covalent and ionic bonds.
  • The Van der Waals forces are additive in nature, consisting of several individual interactions, and cannot be saturated.
  • They have no directional characteristic.
  • They are all short-range forces and hence only interactions between the nearest particles need to be considered (instead of all the particles). Van der Waals attraction is greater if the molecules are closer.
  • Van der Waals forces are independent of temperature except for dipole-dipole interactions.

In low molecular weight alcohols, the hydrogen-bonding properties of their polar hydroxyl group dominate other weaker van der Waals interactions. In higher molecular weight alcohols, the properties of the nonpolar hydrocarbon chain(s) dominate and determine their solubility.

Van der Waals forces are also responsible for the weak hydrogen bond interactions between unpolarized dipoles particularly in acid-base aqueous solution and between biological molecules.

London dispersion force Edit

London dispersion forces, named after the German-American physicist Fritz London, are weak intermolecular forces that arise from the interactive forces between instantaneous multipoles in molecules without permanent multipole moments. In and between organic molecules the multitude of contacts can lead to larger contribution of dispersive attraction, particularly in the presence of heteroatoms. London dispersion forces are also known as 'dispersion forces', 'London forces', or 'instantaneous dipole–induced dipole forces'. The strength of London dispersion forces is proportional to the polarizability of the molecule, which in turn depends on the total number of electrons and the area over which they are spread. Hydrocarbons display small dispersive contributions, the presence of heteroatoms lead to increased LD forces as function of their polarizability, e.g. in the sequence RI>RBr>RCl>RF.[17] In absence of solvents weakly polarizable hydrocarbons form crystals due to dispersive forces; their sublimation heat is a measure of the dispersive interaction.

Van der Waals forces between macroscopic objects Edit

For macroscopic bodies with known volumes and numbers of atoms or molecules per unit volume, the total van der Waals force is often computed based on the "microscopic theory" as the sum over all interacting pairs. It is necessary to integrate over the total volume of the object, which makes the calculation dependent on the objects' shapes. For example, the van der Waals interaction energy between spherical bodies of radii R1 and R2 and with smooth surfaces was approximated in 1937 by Hamaker[18] (using London's famous 1937 equation for the dispersion interaction energy between atoms/molecules[19] as the starting point) by:

 

 

 

 

 

(1)

where A is the Hamaker coefficient, which is a constant (~10−19 − 10−20 J) that depends on the material properties (it can be positive or negative in sign depending on the intervening medium), and z is the center-to-center distance; i.e., the sum of R1, R2, and r (the distance between the surfaces):  .

The van der Waals force between two spheres of constant radii (R1 and R2 are treated as parameters) is then a function of separation since the force on an object is the negative of the derivative of the potential energy function, . This yields:

 

 

 

 

 

(2)

In the limit of close-approach, the spheres are sufficiently large compared to the distance between them; i.e.,   or  , so that equation (1) for the potential energy function simplifies to:

 

 

 

 

 

(3)

with the force:

 

 

 

 

 

(4)

The van der Waals forces between objects with other geometries using the Hamaker model have been published in the literature.[20][21][22]

From the expression above, it is seen that the van der Waals force decreases with decreasing size of bodies (R). Nevertheless, the strength of inertial forces, such as gravity and drag/lift, decrease to a greater extent. Consequently, the van der Waals forces become dominant for collections of very small particles such as very fine-grained dry powders (where there are no capillary forces present) even though the force of attraction is smaller in magnitude than it is for larger particles of the same substance. Such powders are said to be cohesive, meaning they are not as easily fluidized or pneumatically conveyed as their more coarse-grained counterparts. Generally, free-flow occurs with particles greater than about 250 μm.

The van der Waals force of adhesion is also dependent on the surface topography. If there are surface asperities, or protuberances, that result in a greater total area of contact between two particles or between a particle and a wall, this increases the van der Waals force of attraction as well as the tendency for mechanical interlocking.

The microscopic theory assumes pairwise additivity. It neglects many-body interactions and retardation. A more rigorous approach accounting for these effects, called the "macroscopic theory" was developed by Lifshitz in 1956.[23] Langbein derived a much more cumbersome "exact" expression in 1970 for spherical bodies within the framework of the Lifshitz theory[24] while a simpler macroscopic model approximation had been made by Derjaguin as early as 1934.[25] Expressions for the van der Waals forces for many different geometries using the Lifshitz theory have likewise been published.

Use by geckos and arthropods Edit

 
Gecko climbing a glass surface

The ability of geckos – which can hang on a glass surface using only one toe – to climb on sheer surfaces has been for many years mainly attributed to the van der Waals forces between these surfaces and the spatulae, or microscopic projections, which cover the hair-like setae found on their footpads.[26][27]

There were efforts in 2008 to create a dry glue that exploits the effect,[28] and success was achieved in 2011 to create an adhesive tape on similar grounds[29] (i.e. based on van der Waals forces). In 2011, a paper was published relating the effect to both velcro-like hairs and the presence of lipids in gecko footprints.[30]

A later study suggested that capillary adhesion might play a role,[31] but that hypothesis has been rejected by more recent studies.[32][33][34]

A 2014 study has shown that gecko adhesion to smooth Teflon and polydimethylsiloxane surfaces is mainly determined by electrostatic interaction (caused by contact electrification), not van der Waals or capillary forces.[35]

Among the arthropods, some spiders have similar setae on their scopulae or scopula pads, enabling them to climb or hang upside-down from extremely smooth surfaces such as glass or porcelain.[36][37]

See also Edit

References Edit

  1. ^ Woodford, Chris (2 July 2008). "How do microfiber cloths work? | The science of cleaning". Explain that Stuff. Retrieved 11 February 2022.
  2. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "van der Waals forces". doi:10.1351/goldbook.V06597
  3. ^ Garrett, Reginald H.; Grisham, Charles M. (2016). Biochemistry (6th ed.). University of Virginia. pp. 12–13.
  4. ^ Tschumper, Gregory S. (20 October 2008). "Reliable Electronic Structure Computations for Weak Noncovalent Interactions in Clusters". In Lipkowitz, Kenny B.; Cundari, Thomas R. (eds.). Reviews in Computational Chemistry. Vol. 26. John Wiley & Sons. pp. 39–90. doi:10.1002/9780470399545.ch2. ISBN 9780470399545.
  5. ^ Mahan, Gerald D. (2009). Quantum mechanics in a nutshell. Princeton: Princeton University Press. ISBN 978-0-691-13713-1. OCLC 226037727.
  6. ^ A.A. Abrikosov; L.P. Gorkov; I.E. Dzyaloshinsky (1963–1975). Methods of Quantum Field Theory in Statistical Physics. Dover Publications. ISBN 978-0-486-63228-5. Chapter 6 Electromagnetic Radiation in an Absorbing Medium
  7. ^ Batsanov, S. S. (2001). "Van der Waals Radii of Elements". Inorganic Materials. 37 (9): 871–885. doi:10.1023/A:1011625728803. S2CID 52088903.
  8. ^ Hirschfelder, Joseph O. (1954). Molecular theory of gases and liquids. Charles F. Curtiss, R. Byron Bird, University of Wisconsin. Naval Research Laboratory. New York: Wiley. ISBN 0-471-40065-3. OCLC 534717.
  9. ^ Wang, Shiyi; Hou, Kaiyi; Heinz, Hendrik (10 August 2021). "Accurate and Compatible Force Fields for Molecular Oxygen, Nitrogen, and Hydrogen to Simulate Gases, Electrolytes, and Heterogeneous Interfaces". Journal of Chemical Theory and Computation. 17 (8): 5198–5213. doi:10.1021/acs.jctc.0c01132. ISSN 1549-9618. PMID 34255965. S2CID 235823673.
  10. ^ Heinz, Hendrik; Lin, Tzu-Jen; Kishore Mishra, Ratan; Emami, Fateme S. (12 February 2013). "Thermodynamically Consistent Force Fields for the Assembly of Inorganic, Organic, and Biological Nanostructures: The INTERFACE Force Field". Langmuir. 29 (6): 1754–1765. doi:10.1021/la3038846. ISSN 0743-7463. PMID 23276161.
  11. ^ Halgren, Thomas A. (September 1992). "The representation of van der Waals (vdW) interactions in molecular mechanics force fields: potential form, combination rules, and vdW parameters". Journal of the American Chemical Society. 114 (20): 7827–7843. doi:10.1021/ja00046a032. ISSN 0002-7863.
  12. ^ Heinz, Hendrik; Vaia, R. A.; Farmer, B. L.; Naik, R. R. (6 November 2008). "Accurate Simulation of Surfaces and Interfaces of Face-Centered Cubic Metals Using 12−6 and 9−6 Lennard-Jones Potentials". The Journal of Physical Chemistry C. 112 (44): 17281–17290. doi:10.1021/jp801931d. ISSN 1932-7447.
  13. ^ For further investigation, one may consult the University of St. Andrews' levitation work in a popular article: Science Journal: New way to levitate objects discovered, and in a more scholarly version: Leonhardt, Ulf; Philbin, Thomas G. (2007). "Quantum levitation by left-handed metamaterials". New Journal of Physics. 9 (8): 254. arXiv:quant-ph/0608115. Bibcode:2007NJPh....9..254L. doi:10.1088/1367-2630/9/8/254. S2CID 463815., which relate the Casimir effect to the gecko and how the reversal of the Casimir effect can result in physical levitation of tiny objects.
  14. ^ Dzyaloshinskii, I E; Lifshitz, E M; Pitaevskii, Lev P (1961). "General theory of van der waals' forces". Soviet Physics Uspekhi. 4 (2): 153. Bibcode:1961SvPhU...4..153D. doi:10.1070/PU1961v004n02ABEH003330.
  15. ^ Zheng, Y.; Narayanaswamy, A. (2011). "Lifshitz Theory of van der Waals Pressure in Dissipative Media". Phys. Rev. A. 83 (4): 042504. arXiv:1011.5433. Bibcode:2011PhRvA..83d2504Z. doi:10.1103/PhysRevA.83.042504. S2CID 64619547.
  16. ^ Sethi, M. S.; Satake, M. (1992). Chemical bonding. New Delhi: Discovery Publishing House. ISBN 978-81-7141-163-4. OCLC 912437861.
  17. ^ Schneider, Hans-Jörg (2015). "Dispersive Interactions in Solution Complexes". Accounts of Chemical Research. 48 (7): 1815–1822. doi:10.1021/acs.accounts.5b00111. PMID 26083908.
  18. ^ H. C. Hamaker, Physica, 4(10), 1058–1072 (1937)
  19. ^ F. London, Transactions of the Faraday Society, 33, 8–26 (1937)
  20. ^ R. Tadmor (March 2001). "The London–Van der Waals interaction energy between objects of various geometries". Journal of Physics: Condensed Matter. 13 (9): L195–L202. Bibcode:2001JPCM...13L.195T. doi:10.1088/0953-8984/13/9/101. S2CID 250790137.
  21. ^ Israelachvili J. (1985–2004). Intermolecular and Surface Forces. Academic Press. ISBN 978-0-12-375181-2.
  22. ^ V. A. Parsegian (2006). Van der Waals Forces: A Handbook for Biologists, Chemists, Engineers, and Physicists. Cambridge University Press. ISBN 978-0-521-83906-8.
  23. ^ E. M. Lifshitz, Soviet Phys. JETP, 2, 73 (1956)
  24. ^ D. Langbein, Phys. Rev. B, 2, 3371 (1970)
  25. ^ B. V. Derjaguin, Kolloid-Z., 69, 155–64 (1934)
  26. ^ Russell, Anthony P.; Higham, Timothy. E. (2009). "A new angle on clinging in geckos: incline, not substrate, triggers the deployment of the adhesive system". Proceedings of the Royal Society B: Biological Sciences. 276 (1673): 3705–3709. doi:10.1098/rspb.2009.0946. ISSN 0962-8452. PMC 2817305. PMID 19656797.
  27. ^ Autumn, Kellar; Sitti, Metin; Liang, Yiching A.; Peattie, Anne M.; Hansen, Wendy R.; Sponberg, Simon; Kenny, Thomas W.; Fearing, Ronald; Israelachvili, Jacob N.; Full, Robert J. (2002). "Evidence for van der Waals adhesion in gecko setae". Proceedings of the National Academy of Sciences. 99 (19): 12252–6. Bibcode:2002PNAS...9912252A. doi:10.1073/pnas.192252799. PMC 129431. PMID 12198184.
  28. ^ Steenhuysen, Julie (8 October 2008). "Gecko-like glue is said to be stickiest yet". Reuters. Retrieved 5 October 2016.
  29. ^ Quick, Darren (6 November 2011). "Biologically inspired adhesive tape can be reused thousands of times". New Atlas. Retrieved 5 October 2016.
  30. ^ Hsu, Ping Yuan; Ge, Liehui; Li, Xiaopeng; Stark, Alyssa Y.; Wesdemiotis, Chrys; Niewiarowski, Peter H.; Dhinojwala, Ali (24 August 2011). "Direct evidence of phospholipids in gecko footprints and spatula-substrate contact interface detected using surface-sensitive spectroscopy". Journal of the Royal Society Interface. 9 (69): 657–664. doi:10.1098/rsif.2011.0370. ISSN 1742-5689. PMC 3284128. PMID 21865250.
  31. ^ Huber, Gerrit; Mantz, Hubert; Spolenak, Ralph; Mecke, Klaus; Jacobs, Karin; Gorb, Stanislav N.; Arzt, Eduard (2005). "Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements". Proceedings of the National Academy of Sciences. 102 (45): 16293–6. Bibcode:2005PNAS..10216293H. doi:10.1073/pnas.0506328102. PMC 1283435. PMID 16260737.
  32. ^ Chen, Bin; Gao, Huajian (2010). "An alternative explanation of the effect of humidity in gecko adhesion: stiffness reduction enhances adhesion on a rough surface". Int J Appl Mech. 2: 1–9. Bibcode:2010IJAM...02....1C. doi:10.1142/s1758825110000433.
  33. ^ Puthoff, Jonathan B.; Prowse, Michael S.; Wilkinson, Matt; Autumn, Kellar (2010). "Changes in materials properties explain the effects of humidity on gecko adhesion". J Exp Biol. 213 (21): 3699–3704. doi:10.1242/jeb.047654. PMID 20952618.
  34. ^ Prowse, Michael S.; Wilkinson, Matt; Puthoff, Michael; Mayer, George; Autumn, Kellar (February 2011). "Effects of humidity on the mechanical properties of gecko setae". Acta Biomaterialia. 7 (2): 733–738. doi:10.1016/j.actbio.2010.09.036. PMID 20920615.
  35. ^ Izadi, H.; Stewart, K. M. E.; Penlidis, A. (9 July 2014). "Role of contact electrification and electrostatic interactions in gecko adhesion". Journal of the Royal Society Interface. 11 (98): 20140371. doi:10.1098/rsif.2014.0371. PMC 4233685. PMID 25008078. We have demonstrated that it is the CE-driven electrostatic interactions which dictate the strength of gecko adhesion, and not the van der Waals or capillary forces which are conventionally considered as the main source of gecko adhesion.
  36. ^ Kesel, Antonia B.; Martin, Andrew; Seidl, Tobias (19 April 2004). "Getting a grip on spider attachment: an AFM approach to microstructure adhesion in arthropods". Smart Materials and Structures. 13 (3): 512–518. Bibcode:2004SMaS...13..512K. doi:10.1088/0964-1726/13/3/009. ISSN 0964-1726. S2CID 250841250.
  37. ^ Wolff, Jonas O.; Gorb, Stanislav N. (7 January 2012). "The influence of humidity on the attachment ability of the spider Philodromus dispar (Araneae, Philodromidae)". Proceedings of the Royal Society B. 279 (1726): 139–143. doi:10.1098/rspb.2011.0505. PMC 3223641. PMID 21593034.

Further reading Edit

  • Brevik, Iver; Marachevsky, V. N.; Milton, Kimball A. (1999). "Identity of the van der Waals Force and the Casimir Effect and the Irrelevance of These Phenomena to Sonoluminescence". Physical Review Letters. 82 (20): 3948–3951. arXiv:hep-th/9810062. Bibcode:1999PhRvL..82.3948B. doi:10.1103/PhysRevLett.82.3948. S2CID 14762105.
  • Dzyaloshinskii, I. D.; Lifshitz, E. M.; Pitaevskii, Lev P. (1961). "Общая теория ван-дер-ваальсовых сил" [General theory of van der Waals forces] (PDF). Uspekhi Fizicheskikh Nauk (in Russian). 73 (381).
    • English translation: Dzyaloshinskii, I. D.; Lifshitz, E. M.; Pitaevskii, L. P. (1961). "General theory of van der Waals' forces". Soviet Physics Uspekhi. 4 (2): 153. Bibcode:1961SvPhU...4..153D. doi:10.1070/PU1961v004n02ABEH003330.
  • Landau, L. D.; Lifshitz, E. M. (1960). Electrodynamics of Continuous Media. Oxford: Pergamon. pp. 368–376.
  • Langbein, Dieter (1974). Theory of Van der Waals Attraction. Springer Tracts in Modern Physics. Vol. 72. New York, Heidelberg: Springer-Verlag.
  • Lefers, Mark. . Life Science Glossary. Holmgren Lab. Archived from the original on 24 July 2019. Retrieved 2 October 2017.
  • Lifshitz, E. M. (1955). "Russian title is missing" [The Theory of Molecular Attractive Forces between Solids]. Zhurnal Éksperimental'noĭ i Teoreticheskoĭ Fiziki (in Russian). 29 (1): 94.
    • English translation: Lifshitz, E. M. (January 1956). (PDF). Soviet Physics. 2 (1): 73. Archived from the original (PDF) on 13 July 2019. Retrieved 8 August 2020.
  • "London force animation". Intermolecular Forces. Western Oregon University.
  • Lyklema, J. Fundamentals of Interface and Colloid Science. p. 4.43.
  • Israelachvili, Jacob N. (1992). Intermolecular and Surface Forces. Academic Press. ISBN 9780123751812.

External links Edit

  • Senese, Fred (1999). "What are van der Waals forces?". Frostburg State University. Retrieved 1 March 2010. An introductory description of the van der Waals force (as a sum of attractive components only)
  • "Robert Full: Learning from the gecko's tail". TED. 1 February 2009. Retrieved 5 October 2016. TED Talk on biomimicry, including applications of van der Waals force.
  • Wolff, J. O.; Gorb, S. N. (18 May 2011). "The influence of humidity on the attachment ability of the spider Philodromus dispar (Araneae, Philodromidae)". Proceedings of the Royal Society B: Biological Sciences. 279 (1726): 139–143. doi:10.1098/rspb.2011.0505. PMC 3223641. PMID 21593034.

waals, force, molecular, physics, chemistry, distance, dependent, interaction, between, atoms, molecules, unlike, ionic, covalent, bonds, these, attractions, result, from, chemical, electronic, bond, they, comparatively, weak, therefore, more, susceptible, dis. In molecular physics and chemistry the van der Waals force is a distance dependent interaction between atoms or molecules Unlike ionic or covalent bonds these attractions do not result from a chemical electronic bond 2 they are comparatively weak and therefore more susceptible to disturbance The van der Waals force quickly vanishes at longer distances between interacting molecules Rainwater flux from a canopy Among the forces that govern drop formation Van der Waals force surface tension cohesion Plateau Rayleigh instability Microfiber cloth makes use of van der Waals force to remove dirt without scratches 1 Named after Dutch physicist Johannes Diderik van der Waals the van der Waals force plays a fundamental role in fields as diverse as supramolecular chemistry structural biology polymer science nanotechnology surface science and condensed matter physics It also underlies many properties of organic compounds and molecular solids including their solubility in polar and non polar media If no other force is present the distance between atoms at which the force becomes repulsive rather than attractive as the atoms approach one another is called the van der Waals contact distance this phenomenon results from the mutual repulsion between the atoms electron clouds 3 The van der Waals forces 4 are usually described as a combination of the London dispersion forces between instantaneously induced dipoles 5 Debye forces between permanent dipoles and induced dipoles and the Keesom force between permanent molecular dipoles whose rotational orientations are dynamically averaged over time Contents 1 Definition 2 London dispersion force 3 Van der Waals forces between macroscopic objects 4 Use by geckos and arthropods 5 See also 6 References 7 Further reading 8 External linksDefinition EditVan der Waals forces include attraction and repulsions between atoms molecules as well as other intermolecular forces They differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles a consequence of quantum dynamics 6 The force results from a transient shift in electron density Specifically the electron density may temporarily shift more greatly to one side of the nucleus This shift generates a transient charge which a nearby atom can be attracted to or repelled by The force is repulsive at very short distances reaches zero at an equilibrium distance characteristic for each atom or molecule and becomes attractive for distances larger than the equilibrium distance For individual atoms the equilibrium distance is between 0 3 nm and 0 5 nm depending on the atomic specific diameter 7 When the interatomic distance is greater than 1 0 nm the force is not strong enough to be easily observed as it decreases as a function of distance r approximately with the 7th power r 7 8 Van der Waals forces are often among the weakest chemical forces For example the pairwise attractive van der Waals interaction energy between H Hydrogen atoms in different H2 molecules equals 0 06 kJ mol 0 6 meV and the pairwise attractive interaction energy between O Oxygen atoms in different O2 molecules equals 0 44 kJ mol 4 6 meV 9 The corresponding vaporization energies of H2 and O2 molecular liquids which result as a sum of all van der Waals interactions per molecule in the molecular liquids amount to 0 90 kJ mol 9 3 meV and 6 82 kJ mol 70 7 meV respectively and thus approximately 15 times the value of the individual pairwise interatomic interactions excluding covalent bonds The strength of van der Waals bonds increases with higher polarizability of the participating atoms 10 For example the pairwise van der Waals interaction energy for more polarizable atoms such as S Sulfur atoms in H2S and sulfides exceeds 1 kJ mol 10 meV and the pairwise interaction energy between even larger more polarizable Xe Xenon atoms is 2 35 kJ mol 24 3 meV 11 These van der Waals interactions are up to 40 times stronger than in H2 which has only one valence electron and they are still not strong enough to achieve an aggregate state other than gas for Xe under standard conditions The interactions between atoms in metals can also be effectively described as van der Waals interactions and account for the observed solid aggregate state with bonding strengths comparable to covalent and ionic interactions The strength of pairwise van der Waals type interactions is on the order of 12 kJ mol 120 meV for low melting Pb Lead and on the order of 32 kJ mol 330 meV for high melting Pt Platinum which is about one order of magnitude stronger than in Xe due to the presence of a highly polarizable free electron gas 12 Accordingly van der Waals forces can range from weak to strong interactions and support integral structural loads when multitudes of such interactions are present More broadly intermolecular forces have several possible contributions A repulsive component resulting from the Pauli exclusion principle that prevents close contact of atoms or the collapse of molecules Attractive or repulsive electrostatic interactions between permanent charges in the case of molecular ions dipoles in the case of molecules without inversion centre quadrupoles all molecules with symmetry lower than cubic and in general between permanent multipoles These interactions also include hydrogen bonds cation pi and pi stacking interactions Orientation averaged contributions from electrostatic interactions are sometimes called the Keesom interaction or Keesom force after Willem Hendrik Keesom Induction also known as polarization which is the attractive interaction between a permanent multipole on one molecule with an induced multipole on another This interaction is sometimes called Debye force after Peter J W Debye Dispersion usually named London dispersion interactions after Fritz London which is the attractive interaction between any pair of molecules including non polar atoms arising from the interactions of instantaneous multipoles Hereby different texts may refer to a different spectrum of interactions using the term van der Waals force Typically contributions 1 and 4 are considered as van der Waals forces excluding effects from permanent multipoles as described in 2 and from permanent polarization in 3 However some texts describe the van der Waals force as the totality of forces including repulsion others mean all the attractive forces and then sometimes distinguish van der Waals Keesom van der Waals Debye and van der Waals London All intermolecular van der Waals forces are anisotropic except those between two noble gas atoms which means that they depend on the relative orientation of the molecules The induction and dispersion interactions are always attractive irrespective of orientation but the electrostatic interaction changes sign upon rotation of the molecules That is the electrostatic force can be attractive or repulsive depending on the mutual orientation of the molecules When molecules are in thermal motion as they are in the gas and liquid phase the electrostatic force is averaged out to a large extent because the molecules thermally rotate and thus probe both repulsive and attractive parts of the electrostatic force Random thermal motion can disrupt or overcome the electrostatic component of the van der Waals force but the averaging effect is much less pronounced for the attractive induction and dispersion forces The Lennard Jones potential is often used as an approximate model for the isotropic part of a total repulsion plus attraction van der Waals force as a function of distance Van der Waals forces are responsible for certain cases of pressure broadening van der Waals broadening of spectral lines and the formation of van der Waals molecules The London van der Waals forces are related to the Casimir effect for dielectric media the former being the microscopic description of the latter bulk property The first detailed calculations of this were done in 1955 by E M Lifshitz 13 A more general theory of van der Waals forces has also been developed 14 15 The main characteristics of van der Waals forces are 16 They are weaker than normal covalent and ionic bonds The Van der Waals forces are additive in nature consisting of several individual interactions and cannot be saturated They have no directional characteristic They are all short range forces and hence only interactions between the nearest particles need to be considered instead of all the particles Van der Waals attraction is greater if the molecules are closer Van der Waals forces are independent of temperature except for dipole dipole interactions In low molecular weight alcohols the hydrogen bonding properties of their polar hydroxyl group dominate other weaker van der Waals interactions In higher molecular weight alcohols the properties of the nonpolar hydrocarbon chain s dominate and determine their solubility Van der Waals forces are also responsible for the weak hydrogen bond interactions between unpolarized dipoles particularly in acid base aqueous solution and between biological molecules London dispersion force EditMain article London dispersion force London dispersion forces named after the German American physicist Fritz London are weak intermolecular forces that arise from the interactive forces between instantaneous multipoles in molecules without permanent multipole moments In and between organic molecules the multitude of contacts can lead to larger contribution of dispersive attraction particularly in the presence of heteroatoms London dispersion forces are also known as dispersion forces London forces or instantaneous dipole induced dipole forces The strength of London dispersion forces is proportional to the polarizability of the molecule which in turn depends on the total number of electrons and the area over which they are spread Hydrocarbons display small dispersive contributions the presence of heteroatoms lead to increased LD forces as function of their polarizability e g in the sequence RI gt RBr gt RCl gt RF 17 In absence of solvents weakly polarizable hydrocarbons form crystals due to dispersive forces their sublimation heat is a measure of the dispersive interaction Van der Waals forces between macroscopic objects EditFor macroscopic bodies with known volumes and numbers of atoms or molecules per unit volume the total van der Waals force is often computed based on the microscopic theory as the sum over all interacting pairs It is necessary to integrate over the total volume of the object which makes the calculation dependent on the objects shapes For example the van der Waals interaction energy between spherical bodies of radii R1 and R2 and with smooth surfaces was approximated in 1937 by Hamaker 18 using London s famous 1937 equation for the dispersion interaction energy between atoms molecules 19 as the starting point by U z R 1 R 2 A 6 2 R 1 R 2 z 2 R 1 R 2 2 2 R 1 R 2 z 2 R 1 R 2 2 ln z 2 R 1 R 2 2 z 2 R 1 R 2 2 displaystyle begin aligned amp U z R 1 R 2 frac A 6 left frac 2R 1 R 2 z 2 R 1 R 2 2 frac 2R 1 R 2 z 2 R 1 R 2 2 ln left frac z 2 R 1 R 2 2 z 2 R 1 R 2 2 right right end aligned nbsp 1 where A is the Hamaker coefficient which is a constant 10 19 10 20 J that depends on the material properties it can be positive or negative in sign depending on the intervening medium and z is the center to center distance i e the sum of R1 R2 and r the distance between the surfaces z R 1 R 2 r displaystyle z R 1 R 2 r nbsp The van der Waals force between two spheres of constant radii R1 and R2 are treated as parameters is then a function of separation since the force on an object is the negative of the derivative of the potential energy function F V d W z d d z U z displaystyle F rm VdW z frac d dz U z nbsp This yields F V d W z A 6 64 R 1 3 R 2 3 z z 2 R 1 R 2 2 2 z 2 R 1 R 2 2 2 displaystyle F rm VdW z frac A 6 frac 64R 1 3 R 2 3 z z 2 R 1 R 2 2 2 z 2 R 1 R 2 2 2 nbsp 2 In the limit of close approach the spheres are sufficiently large compared to the distance between them i e r R 1 displaystyle r ll R 1 nbsp or R 2 displaystyle R 2 nbsp so that equation 1 for the potential energy function simplifies to U r R 1 R 2 A R 1 R 2 R 1 R 2 6 r displaystyle U r R 1 R 2 frac AR 1 R 2 R 1 R 2 6r nbsp 3 with the force F V d W r A R 1 R 2 R 1 R 2 6 r 2 displaystyle F rm VdW r frac AR 1 R 2 R 1 R 2 6r 2 nbsp 4 The van der Waals forces between objects with other geometries using the Hamaker model have been published in the literature 20 21 22 From the expression above it is seen that the van der Waals force decreases with decreasing size of bodies R Nevertheless the strength of inertial forces such as gravity and drag lift decrease to a greater extent Consequently the van der Waals forces become dominant for collections of very small particles such as very fine grained dry powders where there are no capillary forces present even though the force of attraction is smaller in magnitude than it is for larger particles of the same substance Such powders are said to be cohesive meaning they are not as easily fluidized or pneumatically conveyed as their more coarse grained counterparts Generally free flow occurs with particles greater than about 250 mm The van der Waals force of adhesion is also dependent on the surface topography If there are surface asperities or protuberances that result in a greater total area of contact between two particles or between a particle and a wall this increases the van der Waals force of attraction as well as the tendency for mechanical interlocking The microscopic theory assumes pairwise additivity It neglects many body interactions and retardation A more rigorous approach accounting for these effects called the macroscopic theory was developed by Lifshitz in 1956 23 Langbein derived a much more cumbersome exact expression in 1970 for spherical bodies within the framework of the Lifshitz theory 24 while a simpler macroscopic model approximation had been made by Derjaguin as early as 1934 25 Expressions for the van der Waals forces for many different geometries using the Lifshitz theory have likewise been published Use by geckos and arthropods Edit nbsp Gecko climbing a glass surfaceFurther information Arthropod adhesion The ability of geckos which can hang on a glass surface using only one toe to climb on sheer surfaces has been for many years mainly attributed to the van der Waals forces between these surfaces and the spatulae or microscopic projections which cover the hair like setae found on their footpads 26 27 There were efforts in 2008 to create a dry glue that exploits the effect 28 and success was achieved in 2011 to create an adhesive tape on similar grounds 29 i e based on van der Waals forces In 2011 a paper was published relating the effect to both velcro like hairs and the presence of lipids in gecko footprints 30 A later study suggested that capillary adhesion might play a role 31 but that hypothesis has been rejected by more recent studies 32 33 34 A 2014 study has shown that gecko adhesion to smooth Teflon and polydimethylsiloxane surfaces is mainly determined by electrostatic interaction caused by contact electrification not van der Waals or capillary forces 35 Among the arthropods some spiders have similar setae on their scopulae or scopula pads enabling them to climb or hang upside down from extremely smooth surfaces such as glass or porcelain 36 37 See also Edit nbsp Chemistry portal nbsp Biology portalArthropod adhesion Cold welding Dispersion chemistry Gecko feet Lennard Jones potential Noncovalent interactions Synthetic setae Van der Waals molecule Van der Waals radius Van der Waals strain Van der Waals surface Wringing of gauge blocksReferences Edit Woodford Chris 2 July 2008 How do microfiber cloths work The science of cleaning Explain that Stuff Retrieved 11 February 2022 IUPAC Compendium of Chemical Terminology 2nd ed the Gold Book 1997 Online corrected version 2006 van der Waals forces doi 10 1351 goldbook V06597 Garrett Reginald H Grisham Charles M 2016 Biochemistry 6th ed University of Virginia pp 12 13 Tschumper Gregory S 20 October 2008 Reliable Electronic Structure Computations for Weak Noncovalent Interactions in Clusters In Lipkowitz Kenny B Cundari Thomas R eds Reviews in Computational Chemistry Vol 26 John Wiley amp Sons pp 39 90 doi 10 1002 9780470399545 ch2 ISBN 9780470399545 Mahan Gerald D 2009 Quantum mechanics in a nutshell Princeton Princeton University Press ISBN 978 0 691 13713 1 OCLC 226037727 A A Abrikosov L P Gorkov I E Dzyaloshinsky 1963 1975 Methods of Quantum Field Theory in Statistical Physics Dover Publications ISBN 978 0 486 63228 5 Chapter 6 Electromagnetic Radiation in an Absorbing Medium Batsanov S S 2001 Van der Waals Radii of Elements Inorganic Materials 37 9 871 885 doi 10 1023 A 1011625728803 S2CID 52088903 Hirschfelder Joseph O 1954 Molecular theory of gases and liquids Charles F Curtiss R Byron Bird University of Wisconsin Naval Research Laboratory New York Wiley ISBN 0 471 40065 3 OCLC 534717 Wang Shiyi Hou Kaiyi Heinz Hendrik 10 August 2021 Accurate and Compatible Force Fields for Molecular Oxygen Nitrogen and Hydrogen to Simulate Gases Electrolytes and Heterogeneous Interfaces Journal of Chemical Theory and Computation 17 8 5198 5213 doi 10 1021 acs jctc 0c01132 ISSN 1549 9618 PMID 34255965 S2CID 235823673 Heinz Hendrik Lin Tzu Jen Kishore Mishra Ratan Emami Fateme S 12 February 2013 Thermodynamically Consistent Force Fields for the Assembly of Inorganic Organic and Biological Nanostructures The INTERFACE Force Field Langmuir 29 6 1754 1765 doi 10 1021 la3038846 ISSN 0743 7463 PMID 23276161 Halgren Thomas A September 1992 The representation of van der Waals vdW interactions in molecular mechanics force fields potential form combination rules and vdW parameters Journal of the American Chemical Society 114 20 7827 7843 doi 10 1021 ja00046a032 ISSN 0002 7863 Heinz Hendrik Vaia R A Farmer B L Naik R R 6 November 2008 Accurate Simulation of Surfaces and Interfaces of Face Centered Cubic Metals Using 12 6 and 9 6 Lennard Jones Potentials The Journal of Physical Chemistry C 112 44 17281 17290 doi 10 1021 jp801931d ISSN 1932 7447 For further investigation one may consult the University of St Andrews levitation work in a popular article Science Journal New way to levitate objects discovered and in a more scholarly version Leonhardt Ulf Philbin Thomas G 2007 Quantum levitation by left handed metamaterials New Journal of Physics 9 8 254 arXiv quant ph 0608115 Bibcode 2007NJPh 9 254L doi 10 1088 1367 2630 9 8 254 S2CID 463815 which relate the Casimir effect to the gecko and how the reversal of the Casimir effect can result in physical levitation of tiny objects Dzyaloshinskii I E Lifshitz E M Pitaevskii Lev P 1961 General theory of van der waals forces Soviet Physics Uspekhi 4 2 153 Bibcode 1961SvPhU 4 153D doi 10 1070 PU1961v004n02ABEH003330 Zheng Y Narayanaswamy A 2011 Lifshitz Theory of van der Waals Pressure in Dissipative Media Phys Rev A 83 4 042504 arXiv 1011 5433 Bibcode 2011PhRvA 83d2504Z doi 10 1103 PhysRevA 83 042504 S2CID 64619547 Sethi M S Satake M 1992 Chemical bonding New Delhi Discovery Publishing House ISBN 978 81 7141 163 4 OCLC 912437861 Schneider Hans Jorg 2015 Dispersive Interactions in Solution Complexes Accounts of Chemical Research 48 7 1815 1822 doi 10 1021 acs accounts 5b00111 PMID 26083908 H C Hamaker Physica 4 10 1058 1072 1937 F London Transactions of the Faraday Society 33 8 26 1937 R Tadmor March 2001 The London Van der Waals interaction energy between objects of various geometries Journal of Physics Condensed Matter 13 9 L195 L202 Bibcode 2001JPCM 13L 195T doi 10 1088 0953 8984 13 9 101 S2CID 250790137 Israelachvili J 1985 2004 Intermolecular and Surface Forces Academic Press ISBN 978 0 12 375181 2 V A Parsegian 2006 Van der Waals Forces A Handbook for Biologists Chemists Engineers and Physicists Cambridge University Press ISBN 978 0 521 83906 8 E M Lifshitz Soviet Phys JETP 2 73 1956 D Langbein Phys Rev B 2 3371 1970 B V Derjaguin Kolloid Z 69 155 64 1934 Russell Anthony P Higham Timothy E 2009 A new angle on clinging in geckos incline not substrate triggers the deployment of the adhesive system Proceedings of the Royal Society B Biological Sciences 276 1673 3705 3709 doi 10 1098 rspb 2009 0946 ISSN 0962 8452 PMC 2817305 PMID 19656797 Autumn Kellar Sitti Metin Liang Yiching A Peattie Anne M Hansen Wendy R Sponberg Simon Kenny Thomas W Fearing Ronald Israelachvili Jacob N Full Robert J 2002 Evidence for van der Waals adhesion in gecko setae Proceedings of the National Academy of Sciences 99 19 12252 6 Bibcode 2002PNAS 9912252A doi 10 1073 pnas 192252799 PMC 129431 PMID 12198184 Steenhuysen Julie 8 October 2008 Gecko like glue is said to be stickiest yet Reuters Retrieved 5 October 2016 Quick Darren 6 November 2011 Biologically inspired adhesive tape can be reused thousands of times New Atlas Retrieved 5 October 2016 Hsu Ping Yuan Ge Liehui Li Xiaopeng Stark Alyssa Y Wesdemiotis Chrys Niewiarowski Peter H Dhinojwala Ali 24 August 2011 Direct evidence of phospholipids in gecko footprints and spatula substrate contact interface detected using surface sensitive spectroscopy Journal of the Royal Society Interface 9 69 657 664 doi 10 1098 rsif 2011 0370 ISSN 1742 5689 PMC 3284128 PMID 21865250 Huber Gerrit Mantz Hubert Spolenak Ralph Mecke Klaus Jacobs Karin Gorb Stanislav N Arzt Eduard 2005 Evidence for capillarity contributions to gecko adhesion from single spatula nanomechanical measurements Proceedings of the National Academy of Sciences 102 45 16293 6 Bibcode 2005PNAS 10216293H doi 10 1073 pnas 0506328102 PMC 1283435 PMID 16260737 Chen Bin Gao Huajian 2010 An alternative explanation of the effect of humidity in gecko adhesion stiffness reduction enhances adhesion on a rough surface Int J Appl Mech 2 1 9 Bibcode 2010IJAM 02 1C doi 10 1142 s1758825110000433 Puthoff Jonathan B Prowse Michael S Wilkinson Matt Autumn Kellar 2010 Changes in materials properties explain the effects of humidity on gecko adhesion J Exp Biol 213 21 3699 3704 doi 10 1242 jeb 047654 PMID 20952618 Prowse Michael S Wilkinson Matt Puthoff Michael Mayer George Autumn Kellar February 2011 Effects of humidity on the mechanical properties of gecko setae Acta Biomaterialia 7 2 733 738 doi 10 1016 j actbio 2010 09 036 PMID 20920615 Izadi H Stewart K M E Penlidis A 9 July 2014 Role of contact electrification and electrostatic interactions in gecko adhesion Journal of the Royal Society Interface 11 98 20140371 doi 10 1098 rsif 2014 0371 PMC 4233685 PMID 25008078 We have demonstrated that it is the CE driven electrostatic interactions which dictate the strength of gecko adhesion and not the van der Waals or capillary forces which are conventionally considered as the main source of gecko adhesion Kesel Antonia B Martin Andrew Seidl Tobias 19 April 2004 Getting a grip on spider attachment an AFM approach to microstructure adhesion in arthropods Smart Materials and Structures 13 3 512 518 Bibcode 2004SMaS 13 512K doi 10 1088 0964 1726 13 3 009 ISSN 0964 1726 S2CID 250841250 Wolff Jonas O Gorb Stanislav N 7 January 2012 The influence of humidity on the attachment ability of the spider Philodromus dispar Araneae Philodromidae Proceedings of the Royal Society B 279 1726 139 143 doi 10 1098 rspb 2011 0505 PMC 3223641 PMID 21593034 Further reading EditBrevik Iver Marachevsky V N Milton Kimball A 1999 Identity of the van der Waals Force and the Casimir Effect and the Irrelevance of These Phenomena to Sonoluminescence Physical Review Letters 82 20 3948 3951 arXiv hep th 9810062 Bibcode 1999PhRvL 82 3948B doi 10 1103 PhysRevLett 82 3948 S2CID 14762105 Dzyaloshinskii I D Lifshitz E M Pitaevskii Lev P 1961 Obshaya teoriya van der vaalsovyh sil General theory of van der Waals forces PDF Uspekhi Fizicheskikh Nauk in Russian 73 381 English translation Dzyaloshinskii I D Lifshitz E M Pitaevskii L P 1961 General theory of van der Waals forces Soviet Physics Uspekhi 4 2 153 Bibcode 1961SvPhU 4 153D doi 10 1070 PU1961v004n02ABEH003330 Landau L D Lifshitz E M 1960 Electrodynamics of Continuous Media Oxford Pergamon pp 368 376 Langbein Dieter 1974 Theory of Van der Waals Attraction Springer Tracts in Modern Physics Vol 72 New York Heidelberg Springer Verlag Lefers Mark Van der Waals dispersion force Life Science Glossary Holmgren Lab Archived from the original on 24 July 2019 Retrieved 2 October 2017 Lifshitz E M 1955 Russian title is missing The Theory of Molecular Attractive Forces between Solids Zhurnal Eksperimental noĭ i Teoreticheskoĭ Fiziki in Russian 29 1 94 English translation Lifshitz E M January 1956 The Theory of Molecular Attractive Forces between Solids PDF Soviet Physics 2 1 73 Archived from the original PDF on 13 July 2019 Retrieved 8 August 2020 London force animation Intermolecular Forces Western Oregon University Lyklema J Fundamentals of Interface and Colloid Science p 4 43 Israelachvili Jacob N 1992 Intermolecular and Surface Forces Academic Press ISBN 9780123751812 External links EditSenese Fred 1999 What are van der Waals forces Frostburg State University Retrieved 1 March 2010 An introductory description of the van der Waals force as a sum of attractive components only Robert Full Learning from the gecko s tail TED 1 February 2009 Retrieved 5 October 2016 TED Talk on biomimicry including applications of van der Waals force Wolff J O Gorb S N 18 May 2011 The influence of humidity on the attachment ability of the spider Philodromus dispar Araneae Philodromidae Proceedings of the Royal Society B Biological Sciences 279 1726 139 143 doi 10 1098 rspb 2011 0505 PMC 3223641 PMID 21593034 Retrieved from https en wikipedia org w index php title Van der Waals force amp oldid 1181373300, wikipedia, wiki, book, books, library,

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