Adhesives have been shown to have been used throughout
the last 6000 years. In about 1700 the first commercial
glue factory was started to manufacture animal glue from
hides. From about the 1750's, glues based on the following
materials: fish, animal bones, starch, rubber, and a protein
isolated from milk (casein) were patented. In the early
1900's plastic polymer glues were produced - allowing for
the creation of specialist glues that improve various properties
- such as flexibility, toughness, curing or setting time,
temperature and chemical (and water) resistance.
These modern glues are known as synthetic adhesives. Some
synthetic adhesives, such as the epoxy resins, are strong
enough to be used in construction in place of welding or
riveting. Adhesive tapes have a coating of pressure-sensitive
The following hyperlinks provide great resources for
teachers and students.
The following adhesives websites have very useful information,
along with links to other adhesives & sealants sites.
The Adhesives Mart site, linked below, advises website
users that they are "The Adhesives Matchmaker for Industry".
Answer a few questions and specific adhesive recommendations
will be provided along with detailed technical data for
each adhesive selected. AdhesivesMart claims to have "the
largest searchable industrial adhesives database on the
web, with many thousands of adhesives from over 50 suppliers".
The "About Woodworking" link, below, has
information on various woodworking adhesives and glues,
and also links to an article on understanding woodworking
Theories or Mechanisms of Adhesion should consider: 1)
Surface science 2) Polymer Characteristics 3) Interactions
between polymers and surfaces .
There is no unifying theory that describes all adhesive
bonds. There are, arguably, four mechanisms or theories
of adhesion. They are: 1. Mechanical Interlocking 2. Diffusion
Theory 3. Adsorption and Surface Reaction 4. Electrostatic
The bonding of two materials using an adhesive is the net
effect of the mechanical (physical) and chemical forces
involved. When discussing the theory of adhesion, it is
not possible to separate these forces from one another .
Mechanical interlocking forces: one aspect of adhesion
is the mechanical fastening of the adhesive in the surfaces
that are joined - even surfaces that look quite smooth have
pores and uneven regions.
Physical or electrostatic forces: is where one charged
particle exerts a force over another charged particle. The
transfer of electrons to or from the particle is what creates
Chemical forces: refers to intermolecular and chemical
bonding forces. There are three types.
a) Chemical adhesion is explained by adsorption
- which is adhesion of the molecules of liquids, gases,
and dissolved substances to the surfaces
of solids, as opposed to absorption, in which the
molecules actually enter the absorbing medium.
This theory is the most important mechanism
in achieving adhesion between two surfaces.
For more information on these forces search for information
on "van der Waals forces". Research indicates
that Geckos cling to surfaces using these forces .
The other commonly mentioned force that forms where
the adhesive and surface to be joined (adherend) meet
and is believed to impact on the intrinsic adhesion
strength is known as "acid-base interactions" .
To obtain good adsorption with commercially available
adhesives, sufficient adhesive must be applied to
achieve satisfactory "wetting" - meaning that enough
adhesive must be applied to the surface to spread
spontaneously when the join is formed.
gecko feet their incredibly strong, dry, reversible
adhesion. © PNAS 
b) Chemical interactions can be explained by the chemisorption
theory. Chemisorption is to take up and chemically bind
onto the surface of another substance. Chemical bonds are
strong and make a significant contribution to the intrinsic
adhesion in some cases.
c) Diffusion theory. This theory only applies to the bonding
of polymers. Most common polymers are made up of large chains
of carbon atoms. It is believed that the molecular chains
interpenetrate at the interface where the adhesive and surfaces
being bonded meet . In simple terms,
the two surfaces become interlocked at a molecular level,
and therefore, become one.
If exploring diffusion theory further, three key terms
that are worth to investigating are: entanglement coupling;
cooperativity; and reptation .
Also, if more detailed information is required, see the
two hyperlinks below (Citations).
Next >> Sealants
adhesive: a substance that unites or bonds.
absorption: the process of taking up
or sucking up (as a sponge absorbs
water, or charcoal absorbs gas).
adsorption: the adhesion in an extremely thin layer
of molecules to the surfaces of solid bodies or liquids
with which they are in contact.
sealant: a substance used to seal a surface to prevent
passage of a liquid or gas.
seta: (Biology) [plural: setae] a stiff hair,
bristle or part on an organism.
. SpecialChem S.A. (2002). Adhesives
& Sealants: Adhesion theory - Basics of adhesion. [WWW
Document] URL: www.specialchem4adhesives.com/techcenter/adhesionguide/index.aspx?id=theory
(visited October 2002).
. Gardner, Dr D.J. [Adhesion Research
Group, University of Maine] (2002, March). Theories or Mechanisms
of Adhesion. [Portable document format] URL: www.umaine.edu/adhesion/gardner/540lecture/adhesion%20lecture9.pdf
(visited October 2002).
. Autumn, Sitti et al. (August, 2002).
Proceedings of the National Academy of Sciences, published
online. "Evidence for van der Waals adhesion in gecko
setae". [WWW Document] URL: www.pnas.org/cgi/content/abstract/99/19/12252
(visited October 2002).
Note: This page is under
construction, and will be added to as time permits.
Copyright D. L. Christiansen [Last updated
Nov 2002] Images: respective copyright owners noted/cited.