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									Protective sol-gel nanocoatings for enhanced surface properties

 Protective sol-gel
 The sol-gel technique involves the evolution of
 inorganic nanoscale networks in a continuous
 liquid phase through the formation of colloidal
 suspension and the following gelation of the
 sol. Controlled hydrolysis and condensation
 reactions are the keys for the formation of
 the sol-gel matrix. Due to these reactions the
 sol-gel technique offers a great opportunity to
 produce for example functional and premium
 transparent thin films. In addition monoliths,
 powders, fibres, composites, porous gels
 and membranes can be fabricated by sol-gel
 technology. Polymer materials compounded,
 milled or otherwise mixed with nanosized
 organic or inorganic filler materials form new
 material combinations. With proper planning
 these new materials can have enhanced
 properties due to the interaction of the
 individual material components at nanolevel.

 The sol-gel coatings can be deposited using different
                                                              Properties obtained by sol-gel coatings:
 application techniques, for example dip, spill or spin
 coating, spraying, brushing or roll coating. Coat-       •    Anti-fouling and easy-to-clean
 ing thickness ranges from 0.1 to 10 µm depending         •    Abrasion and scratch resistance
 on the coating chemistry and the coating technique       •    Corrosion protection
 used.                                                    •    Barrier and moisture control
                                                          •    Modification of surface free energy
 A wide range of materials can be coated with sol-        •    Photocatalytical
 gel technique. Substrate material can be metallic,       •    Hygienic coating
 ceramic, polymeric or even organic materials like
 wood, paper and fibres.
 The surface hardness as well as                                        Abrasion resistant sol-gel
 scratch and wear resistance can be                                     coating on stainless steel.
 improved with thin hybrid sol-gel
 coating materials. Ceramic network
 gives hardness to the coatings and
 organic components make coatings
 more flexible and tough.

                             Improved abrasion resistance,
                             modification of surface topogra-
                             phy and photoactive properties
                             can be achieved by nanoparticle

                             Functional properties for                 Surface energy of wood
                             sol-gel coatings by nano-                 modified with sol-gel coating.
                             particle additions.

                                                                       Surface energy of stainless
                                                                       steel modified with sol gel

 Anti-fouling phenomenon is based usually on surface                  Sol-gel coated Nylon PA6.
 energy and topography of the surfaces. The surface
 can be hydrophilic, when water easily spreads on
 the surface, or hydrophobic, when water forms a
 spherical drop. The surfaces can also be oleophilic or
 oleophobic, when oil either wets the surface or forms
 droplets. Dirt can be carried on the surface by water
 or oil and the hydro- or oleophobicity of the coating
 can be tailored according to the application.

Additional information
Funktional surfaces and structures
Juha Mannila                       Juha Nikkola                 Anne Pahkala             Amar Mahiout
Tel. +358 20 722 3702              Tel. +358 20 722 3672        Tel. +358 20 722 3706    Tel. +358 20 722 5415      

VTT Technical Research Centre of Finland
P.O. Box 1000, FI-02044 VTT, Finland

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