Page 63 - Handbook of Adhesion Promoters

56 Substrates - Surface Condition and Treat-

create highly adherent thin poly-
mer films on the surface to com-
pletely change adhesion between
4
two surfaces.
Some of these findings can
be illustrated in more depth by the
nanotribological behavior of
5
amorphous polystyrenes. The
question to answer in these studies
was how asperities of surface
affect adhesion force on contact
and what role is played by molec-
5
ular weight of polymer. Figure
4.1 shows interaction between
polymer chains in the sample’s
Figure 4.2. Adhesion forces and corresponding capillary forces and surface and tip of silicon nitride
(VdW/acid-base) forces histograms of PS-26, PS-118, PS-245 and probe of atomic force micro-
PS-385 (the number is equivalent to thousands in molecular
5
weight). [Adapted, by permission, from Ghorbal A; Brahim, AB, scope. With molecular weight
Polym. Testing, 32, 1174-80, 2013.] increase a greater density is
observed in contact with AFM
5
tip.
Figure 4.2 shows the effect
of the polystyrene molecular
5
weight on adhesion force. The
adhesion force increases with the
molecular weight of polystyrene
increase as do van der Waals and
5
acid-base forces. When the AFM
tip and the polystyrene film sur-
faces are brought into contact with
air, surfaces adhere to each other
because of van der Waals interac-
tions, acid-base interactions
Figure 4.3. Bacterial adhesion (%) to various materials as a func- between π-ring electrons of poly-
tion of time: () aged Zn; () aged aluminium brass; () aged Cu; styrene and polar groups on the tip
(O) bare Cu; () bare aluminium brass; and (+) PE. 100% of adhe- surface, and the Laplace pressure
2
sion = 325 adhered bacteria/100 μm . Results are indicated as mean
value standard deviation (n = 10). [Adapted, by permission, from of the capillary condensed water
Valcarce, MB; Busalmen, JP; de Sanchez, SR, Int. Biodet. Biodeg., at the periphery of the contact
50, 61-6, 2002.] 5
zone. The capillary force is con-
stant but the van der Waals and acid-base forces increase when the molecular weight of
5
polystyrene is increased.
Still another example of the effect of surface condition comes from studies on adhe-
6
sion of bacteria (Pseudomonas fluorescens) to metal surface. Figure 4.3 shows the bacte-
6
rial adhesion to various metal substrates as a function of time. What happens during this
6
time is the formation of zinc oxide on the surface of metals. The presence of ZnO in the