Page 102 - Handbook of Surface Improvement and Modification

7

Surface Tension and Wetting

7.1 METHODS AND MECHANISMS OF SURFACE TENSION
CHANGE

Much existing research contributes to the understanding of the influence of surface ten-
sion and wetting on properties of materials. These are the topics which will be discussed
here:
• surface tension decrease
• surface tension increase
• prediction of the surface tension of silanes
• effects on wetting
• adhesion of cells and organisms
• effect on compatibility
• effect on lubrication
• effect on conductivity
• performance of polymers
• performance of various products, such as blends, inks, medical applications,
nanofluids, natural fibers, ski gliding wax, and wood
• wettability control
This list does not include surface modifications by plasma, lasers, etc. because these
topics, although important for adhesion, are not related to the effect of additives on surface
tension and wetting processes. The above topics are discussed in the order of appearance
on the above list.
Cellulose nanocrystals and organophilic silica were used in poly(lactic acid) blends
1
with poly(lactic-co-glycolic acid). Cellulose nanocrystals acted as nucleating agents for
the crystallization of poly(lactic acid) but the best mechanical properties of blend were
obtained with a combination of both nanofillers because silica decreased surface tension
1
between polymeric components of the blend and cellulose nanofiller. In the next section
of this chapter, examples of additives are given which are useful in lowering the surface
tension of materials.
Bottlebrush polymers have been used as surface-active additives for chemically-
identical linear polymers because they spontaneously accumulate at surfaces through an
2
entropy-mediated process. Bottlebrush polymer macromolecules range in size from tens
2
to hundreds of nanometers. They may be spherical or elongated in shape. Bottlebrush
polymers having polydimethylsiloxane side-chains and bottlebrush copolymers having
PDMS and poly(lactic acid) side-chains were synthesized using ring-opening metathesis
2
polymerization (Figure 7.1). A spontaneous accumulation of these additives at the film