Practical Application of Intermolecular Forces A Study of Adhesives By Babi Hijau (Photo taken by own) [Public domain], via Wikimedia Commons

Intermolecular Forces Forces between molecules Permanent dipoles Induced dipoles van der Waals or London Dispersion forces Hydrogen bonds

Applications Determines various physical properties of a molecular solid Melting point Boiling point Vapor pressure Adhesive force of glue

An adhesive is a substance that sticks to the surface of an object such that two surfaces become bonded. In order for an adhesive to bond (hold together) to the substrate, there must be several types of molecular interaction between the adhesive and both substrates. By Amirreza Saharkhiz (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons

The adhesive will “wet” or cover the substrate, when the Intermolecular forces between the glue and the substrate are stronger than the Intermolecular forces between the glue and glue. Why does the Elmer’s glue stick to this piece of paper? Glue hardens when there is a loss of water from the formula. Exposure to the atmosphere will cause the water to evaporate and make the glue harden. By Mk2010 (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

For an adhesive to wet a surface, the adhesive should have a lower surface tension, than the solid’s surface energy (or critical surface tension), A shows a fluid with very little wetting, while C shows a fluid with more wetting. A has a large contact angle, and C has a small contact angle. By MesserWoland (own work created in Inkscape) [GFDL (http://www.gnu.org/copyleft/fdl.html), CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/) or CC BY-SA 2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/2.5-2.0-1.0)], via Wikimedia Commons

Adhesive Curing Theilr’s Flickr account – Creative Commons Attribution Once the adhesive is applied to the substrate, it will begin to cure, or form a permanent bond Different Adhesives have different mechanisms in which the curing takes place

So HOW do glues compare? In the following lab you will investigate the differences in the adhesive ability of some different types of glues By Selena Wilke (Own work) [Public domain], via Wikimedia Commons