Page 35 - Handbook of Adhesion Promoters

28 Mechanisms of Adhesion

Figure 2.29. Adhesion mechanism of silver nanoparticles on substrate with 3-glycidoxypropyltrimethoxysilane at
the interface of the film. [Adapted, by permission, from Hong, JU; Kumar, ABVK; Han, HS; Koo, YH;
Kim, HW; Park, JH; Kang, HS; Lee, BC; Piao, L; Kim, S-H, Bull. Korean, Chem. Soc., 34, 8, 2539-42, 2013.]

Figure 2.28 shows the structure of painted TPO and its microscopic image. Adhesion pro-
51
moter diffuses 1 μm deep into TPO.
In polymer blends, adhesion is frequently a problem which causes reduction of their
mechanical properties. Application of compatibilizers is one of classical examples of how
to increase adhesion between polymer components by the formation of interphase
between them. The properties of interphase permit reaction or interaction of each compo-
nent polymer with functional groups on the surface of the compatibilizer (interphase).
This can also be achieved by the addition of inorganic materials (e.g., silica) to polymer
blends. The surface groups on silica can react (or interact) with component polymers to
52
increase interfacial adhesion and toughen the blend.
2.9 CHEMICAL BONDING

The mechanisms of adhesion by the participation of chemical bonding are the oldest and
the most frequently proposed because chemical bonding forms reliable, easy to explain
connections between substrate and adherent. The covalent bonds have high energy (e.g.,
C−C − 347, C−O − 358, C−N − 305, C−S − 259, N−O − 201, and O−O − 146 kJ/mol) and
they require substantial energy to break them. The adhesion promoters are widely avail-
able and common in use (properties of different groups of adhesion promoters are dis-
cussed in Chapter 7). Below we will discuss examples of silanes, maleic anhydride,
isocyanates, sulfur linkages, coordination linkages, and functionalized graphene com-
pounds as the most typical adhesion promoters in use.
Solar cells, memory devices and other flexible electronic elements are produced by
printing techniques using solution-based materials, as well as suspensions of metals (espe-
53
cially in nano-form), polymers, and carbon nanotubes. One of the major issues of these
53
processes is poor adhesion to substrates. For silver nano-ink used for printing on glass
and poly(ethylene terephthalate), 3-glycidoxypropyltrimethoxysilane was used as an
53
adhesion promoter. Figure 2.29 shows chemical mechanism of action of adhesion pro-