Page 32 - Handbook of Surface Improvement and Modification

2.2 Additives used 27

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tions formed in the vicinity of POSS cages. The addition of POSS did not have a nega-
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tive effect on the optical quality of clearcoat.
A typical POSS nanoparticle has a cubic inorganic Si O core surrounded by eight
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8
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organic corner groups and has a particle size of about 1.5 nm. The eight organic corner
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groups can be functionalized with a variety of organic substituents. Usually, one of them
is functionalized with a polymerizable or reactive group (e.g., acrylate group), while the
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others are designed to have identical nonreactive groups (e.g., isobutyl group). A UV-
curable sol-gel coating was formulated from methacrylate silane precursor, in which a
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hard POSS had an acrylic function. The mechanical properties and pencil scratch resis-
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tance of the coating were greatly improved.
POSS-modified UV-curable coatings had improved scratch hardness and hydropho-
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bicity. The significant increase of the surface hydrophobicity (by 60%) and scratch hard-
ness (even by 400%) was obtained using only small amounts (1.5-3 wt%) of the
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investigated POSS compounds. The improvement of the scratch resistance was
explained by the formation of a sliding layer by the diffusion of the fluoroalkyl POSS
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molecules to the surface of the coating.