TABLE OF CONTENT

No. Title Pages

1 Abstract (Mechanism Of Adhesion) 2

2 Introduction 2

3 Chemical Bonding

Primary Bond/ Secondary Bond

3

4 Physical Bonding

Mechanical Interlocking

Diffusion Theory

Adsorption

Electrostatic

4

5 Conclusion 6

6 References 6

ABSTRACT

1

MECHANISM OF ADHESION

The analysis of adhesion uses various technique of thought, depending on one’s field of expertise,

and therefore treatment of the phenomena observed can be considerably different. This variety of

approaches is emphasized by the fact that many theoretical models of adhesion have been

proposed, which together are both complementary and contradictory. Adhesion is the action of

adhering to a surface or object. In the other word, it is the main application of adhesion in bonding

by adhesives, this technique replacing at least partially, more classical mechanical attachment

techniques such as bolting or riveting. Adhesion can be divided by two bond component; chemical

bond and physical bond. In chemical bond it is consist primary and secondary bond. For the physical

bond, it is consist four type bonding theory; mechanical interlocking, diffusion theory, adsorption

and electrostatic theory. In fact, the term ‘adhesion’ covers a wide variety concept of bonding ideas,

depending on whether the subject is broached from a molecular, microscopic or macroscopic point

of view about formation of the interface of failure of the formed system.

INTRODUCTION

Adhesion is a process of a substance bind or glued together to the surface of another

substance or substrate. The mechanism of adhesion has been explores for dotage. Many theories

have been introduced for adhesion phenomena. Nonetheless, there is no complete explanation of

what exactly adhesion mean. The briefly explanation of adhesion can be define as it is the bonding of

an adhesive to an object or a surface is the sum of a number of mechanical, physical, and chemical

forces that overlap and influence one another. It is requires two type of bonding; chemical bonding

and physical bonding. It is also can be defined as the tendency of same or different substrate which

is bind together by using adhesion.

On the other hand, according Benjamin E. Russ, adhesion is the binding force between two

different materials, whereas cohesion is the binding force between two similar materials. When two

materials are brought into contact with each other, the surface molecules interact, giving rise to

attractive forces that may be physical, chemical or electrostatic (corresponding to adsorption,

covalent bonding or van der Waals forces, respectively). When the molecules are similar, as in the

case of two 'glue molecules,' the cohesive force causes the glue to stick to itself. When the

molecules are dissimilar, as in the case of a glue molecule and a molecule of the substrate (the

surface the glue is sticking to), the adhesive force holds the glue to the substrate. Hence, the

'stickiness' of tape is caused by a combination of the molecular forces of the glue material sticking to

itself as well as holding onto the substrate.

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CHEMICAL BONDING

Chemical bonding is a form of adhesive bonding involving a reaction that results in covalent

bonds between the molecules of the adhesive and the surface material. The chemical bonding

mechanism suggests that primary chemical bonds may form across the interface. In chemical bond

consist two category of bond which is primary and secondary bond. Chemical bonds are strong and

make a significant contribution to the intrinsic adhesion in some cases.

PRIMARY/SECONDARY BONDING

Primary bond can be defined as a bond that forms between atoms and that involves the exchanging

or sharing of electrons. Whereas, secondary bond can be explain with it relies on the mechanical

linking of an adhesive to a material.

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PHYSICAL BONDING

Moreover, physical bond consist four types of theory; mechanical interlocking, diffusion

theory, adsorption and electrostatic. Adsorption theory is a form of adhesive bonding involving the

attraction between the molecules of an adhesive and a surface material. The bonding of an adhesive

to an object or a surface is the sum of a number of mechanical, physical, and chemical forces that

overlap and influence one another. As it is not possible to separate these forces from one another,

we distinguish between mechanical interlocking , caused by the mechanical anchoring of the

adhesive in the pores and the uneven parts of the surface, electrostatic forces, as regard to the

difference in electro negativities of adhering materials, and the other adhesion mechanisms dealing

with intermolecular and Chemical bonding forces that occur at the interfaces of heterogeneous

systems. This chemical adhesion mechanism is explained in the case of the intermolecular forces by

the adsorption theory, and in the case of chemical interactions by the chemisorption theory. The

processes that play a role in the bonding of similar types of thermoplastic high-polymer materials,

e.g. homogeneous systems, can be determined with the diffusion theory.

MECHANICAL INTERLOCKING

The mechanical interlocking theory of adhesion can briefly explain that proper adhesion occurs only

when an adhesive penetrates into the pores, holes and crevices and other distortion of the substrate

and locks mechanically to the substrate. The adhesive must not only wet the substrate, but also have

the right rheological properties to penetrate pores and openings in a reasonable time.

DIFFUSION THEORY

The diffusion model explains the concept of adhesion by the compatibility between polymers and

the movements that occur in the polymer chains. When two polymers are compatible, its polymer

chains are able to mix up between them, resulting in partial penetration between the 2 materials, as

a result of these penetrations anchorage areas and adhesion points take place. The mobility and

degree of penetration of the polymers is determined directly by their molecular weight, so that short

polymer chains have high mobility and penetrate into the other material before the long polymer

chain. Rouse model and reptation model give a detailed explanation of the movements that occur

between the polymer chains which produce the diffusion. Using this theory can explain the

phenomenon of adhesion that occurs between polymeric materials, plastic welding, plastic binding

with adhesives, etc...

4

ADSORPTION THEORY

The adsorption mechanism theory suggests that bonding is the process of intermolecular attraction

(van der Waals bonding or permanent dipole, for example) between the adhesive and the adherend

at the interface. An important factor in the strength of the bond according to this theory is the

wetting of the adherend by the adhesive. Wetting is the process in which a liquid spreads onto a

solid surface and is controlled by the surface energy of the liquid-solid interface versus the liquid-

vapor and the solid-vapor interfaces. In a practical sense, to wet a solid surface, the adhesive should

have a lower surface tension than the adherend. The adsorption theory or model explains the

phenomenon of adhesion based on concepts such as contact angle, wet ability and surface tension.

When the adhesive has a lower surface tension compared to the substrate surface energy, it is

capable of wetting the surface, generating a contact angle less than 90 °, thus generating the

adhesion between the adhesive and substrate. Against the mechanical model and the model of

diffusion, adsorption model explains the phenomenon of adhesion without penetration by the

adhesive to the substrate; the adhesion is generated by the contact between the adhesive and

substrate.

ELECTROSTATIC THEORY

Electrostatic forces may also be a factor in the bonding of an adhesive to an adherent. These forces

arise from the creation of an electrical double layer of separated charges at the interface and are

believed to be a factor in the resistance to separation of the adhesive and the adherend. Adhesives

and adherends that contain polar molecules or permanent dipoles are most likely to form

electrostatic bonding according to this theory.

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CONCLUSION

The stronger adhesion of bonds between mechanically or chemically roughened surfaces is based on

the enlargement of the effective surface (contact surface between the adhesive and the substrate),

and an increase in the number of active centres, e. g. edges, corners, and faulty parts which, as in

the heterogeneous catalysis, increase the interactive forces in the interface adhesive/surface.

REFERENCES

Scientific American tm online journal; http: //www.specialchem4adhesives.com /resources

/adhesionguide/index.aspx?id=factors

http://www.adhesiveandglue.com/adhesive-definition.html

http://solutions.3m.com/wps/portal/3M/en_US/Adhesives/Tapes/Support/Technical-News-

Articles/?PC_7_U00M8B1A00NI60IDFIPS8T3HR2000000_assetId=1319232951956

http://www.toolingu.com/definition-670120-41242-chemical-bonding.html

http://www.scientificamerican.com/article.cfm?id=what-exactly-is-the-physi

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