Page 35 - Handbook of Adhesives and Sealants

An Introduction to Adhesives and Sealants 5

Other important definitions may be illustrated by considering the
schematic of the joint in Fig. 1.2 where two substrates are bonded
together with an adhesive or sealant. The substrate is the material to
be bonded. After bonding, the substrate is often referred to as an ad-
herend (although sometimes these two terms are used synonymously).
The area between the adhesive and adherend is referred to as the
interphase region. This interphase region is a thin region near the
point of adhesive—adherend contact. The interphase region has dif-
ferent chemical and physical characteristics than either the bulk ad-
hesive or the adherend. The nature of the interphase region is a crit-
ical factor in determining the properties and quality of an adhesive
bond.
Different from the interphase is the interface, which is contained
within the interphase. The interface is the plane of contact between
the surface of one material and the surface of the other. The interface
is often useful in describing surface energetics. The interface is also
at times referred to as a boundary layer. Between the adhesive and
adherend there can be several interfaces composed of layers of differ-
ent materials. The boundary layers will be discussed in detail in the
following chapters.
Sometimes a primer is used with adhesives or sealants. A primer is
applied to a surface prior to the application of an adhesive or sealant,
usually for improving the performance of the bond or protecting the
surface until the adhesive or sealant can be applied. The joint is the

Interphase Regions

Adherends Adhesive or Sealant Primer

Figure 1.2 Components of a typical adhesive or sealant joint.