Page 142 - Handbook of Surface Improvement and Modification

9

Water Repelling

(Hydrophobization)

9.1 METHODS AND MECHANISMS OF HYDROPHOBIZATION

In several previous chapters (Tack-free surface, Surface tension and wetting, and Easy sur-
face cleaning and stain inhibition), hydrophobization was broadly discussed as a part of
mechanisms involved in the development of these properties. Here, we will continue with
a discussion of specific cases of hydrophobization which are relevant to the formation of
properties of metals, ceramics, stones, glass, optical devices, cementitious materials, poly-
mers and their additives, fabrics, wood, and medicine.
Biomimetic (life-inspired) polydimethylsiloxane-hydroxyurethane-terminated with
catecholic moieties was used in chemical grafting on transition metal oxide-based surfaces
1
as an additive for inorganic and metallic surface modification. The additive was to be
capable of strong attachment onto metallic and inorganic substrates forming layers with
1
water-repellent surfaces. The cat-
echol terminal groups were
grafted by aminolysis reaction
onto a polydimethylsiloxane back-
1
bone. The product, PDMSUr-
Dopamine, presented high affinity
towards inhomogeneous alloy sur-
faces terminated by the native
1
oxide layers. The chemical com-
position was inspired by the termi-
nal peptides in adhesive proteins
Figure 9.1. Schematic representation of the PDMSUr-Dopamine
layer grafting on a titanium surface and exposing its hydrophobic of mussels (Mytilus edulis foot
PDMS segment. [Adapted, by permission, from de Aguiara, KR; protein), which bear catechol moi-
Rischka, K; Gatjen, L; Noeske, P-LM; Cavalcanti, WL; Rodrigues- eties and are strong adhesives even
Filho, UP, Appl. Surf. Sci., 427, 166-75, 2018.]
under natural and saline water. 1
The modifier facilitates functionalization of various substrates such as titanium alloy (Fig-
1
ure 9.1), steel, and ceramic surfaces.
Superhydrophobic coatings based on polytetrafluoroethylene and silica nanoparticles
2
were deposited on carbon steel surface by spraying. The inorganic (SiO ) and organic
2
(PTFE) nanoparticles were used for a comparative study on the performance of superhy-
2
drophobic coating on the carbon steel surfaces. Hydrophobized SiO -filled coating had
2
better uniformity than the raw SiO in spite of the fact that they had similar maximum
2