Nanomaterials in Coatings Cal Poly State University Department of Chemistry and Biochemistry San Luis Obispo, CA www.polymerscoatings.calpoly.edu What is Nanotechnology It is a matter of scale 1 nm = 10-9 meter Nanometer is a billionth of a meter Average human hair is 100,000 nm or 100 micron or 0.1 mm in diameter 1
http://www.nano.gov/html/facts/the_scale_of_things.html Nano-Scale 100 500 nm: typical polymer latex particle size 10,000 nm: diatomaceous earth average size 250 nm: hiding grade TiO 2 particle size 50 100 nm: typical PUD particle size 2
Nano-Electronics COURTESY OF HEWLETT-PACKARD LABS http://pubs.acs.org/cen/coverstory/8039/803 9nanoelectronics1.html For more information.. National Nanotechnology Initiative (www.nano.gov) Vision 2020 Nanomaterials Roadmap (www.chemicalvision2020.org) Nanocoatings: Intellectual Property Landscape Conference June, 2003 Nanomaterial Technology Applications in Coatings, JCT CoatingsTech May, 2004 3
Initial Interest - Polymer Nano- composites Nylon/Clay Nanocomposites (Toyota, 1980 s) 70% higher tensile modulus 125% higher flexural modulus Heat distortion temperature increased from 65 o C to 152 o C Epoxy / Layered Silicate (Vaia Nanocomposites 2001 Conf.) Organo-Clays Dispersed Intercalated Exfoliated e.g. nylon/clay nanocomposite 4
Layered Structure of Vermiculite Clay X-ray diffraction pattern Interfacial Material Volume Particle Diameter (nm) 300 250 200 150 100 50 Interfacial Volume Fraction 0.03 0.04 0.05 0.06 0.10 0.22 10 nm Interfacial Layer Dispersed particle volume fraction is 0.3 in all cases 5
Key Nano-Attributes - 1 Polymer molecules at interface Surfactants at water/air interface Key Nano-Atributes - 2 Bulk material principles may not apply Non-Scalable Region 6
Key Nano Attributes (2) - Surface Material Content A particle of 10nm diameter has 20% surface atoms A particle of 2nm diameter has 80% surface atoms A particle of 1nm diameter has 100% surface atoms Single wall Carbon nanotube A capped single-wall carbon nanotube with a slight bend. http://www.thomas-swan.co.uk/pages/nano_images.html Key Nano Attributes (3) - Optical Clarity Nanoparticles are smaller than the wavelength of visible light, reducing the chance of light interacting with the particles This allows particles to be introduced into coatings without causing haze. 7
Barrier Property Improvements Path of Molecule Penetration Microcomposite Aspect Ratio 25:1 Nanocomposite Aspect Ratio 250:1 At the same loading level nanocomposites can display much better barrier properties Approaches to Making Nano-Composites (Inorganic/Organic) Dispersion of layered inorganics in polymer In-situ generation of nano-phases Incorporation of nano-particles 8
In-Situ Generation of Nanophases TEOS Hydrolysis/condensation Sol-gel derived silicon oxide networks 9
Sol-Gel Hybrid Nano-Composite Coatings OCH 3 C 2 H 5 O TEOS OC 2 H 5 Si OC 2 H 5 Si H 3 CO OCH 2 CH 2 CHCH 2 OCH 3 + + GPTMOS O O Cyclo-aliphatic Epoxy O C O H 2 C O OC 2 H 5 Inorganic / Organic Nanocomposite Potential Advantages of Nanocomposites Optical Clarity Mechanical Properties Increased scratch/mar resistance Reinforcing effect Barrier Properties Increased resistance to the diffusion of oxygen and/or other gases. 10
Nanomaterial Outlook Nanotechnolgy in Coatings: Realizing the Potential (FSCT ACSeries Event, Seattle, WA June 2005 Countless Companies and Other Entities 1200 start-ups (50% US) US Patent Applications (600 1992; 1200 1997; 3200 2002) Market Projections: US Nanomaterials will surpass $1billion in 2007 Nanomaterials to 2007, Freedonia Applications of Nanoparticles Coatings Plastics Drug Delivery Data Storage Cancer/Tumor Treatment Catalysts 11
Nano-Binders Smaller particle acrylic Better pigment binding ability Better film formation PUDs Urethane/Acrylic Hybrids Available Nanomaterials and Their Properties in Coatings Aluminum Oxide Mechanical properties Zinc Oxide UV / light stability Anti-microbial Indium / Antimony Tin Oxide Antistatic IR-absorption Titanium Dioxide UV / light stability Anti-microbial Copper Oxide Anti-microbial Silicon Dioxide Mechanical properties Cerium Oxide UV / light stability Mechanical properties Iron Oxide UV / light stability Magnetism 12
Nanoparticles in Coatings Scratch resistant coatings can be advantageous for: Wood floors Automotive finishes Safety glasses Electronic displays Inorganic nanoparticles (alumina and silica) can reinforce the coating matrix, increasing resistance to scratches 13
Photocatalytic TiO 2 Nanoparticles Self-cleaning surface Antibacterial Activity Super hydrophilicity Anti-fogging activity Contact Angle Wetting θ θ - Contact Angle Zero Contact Angle Spontaneous Wetting & Spreading 14
Titanium Dioxide Pigments Chalking: loose pigment particles form on the surface from the erosion of the binder as a result of photodegradation. Type I Anatase Type II Rutile Type III Rutile Type IV Rutile Product Name TiO 2 min.% Chalking Surface treatment LW 94 free none R-900 92 medium resistant Al 2 O 3 R-900, R-901 80 medium resistant SiO 2 +Al 2 O 3 R-960 80 medium resistant SiO 2 +Al 2 O 3 Complete encapsulation to protect TiO2 from UV free radical reaction Photocatalytic TiO 2 Nanoparticles Super hydrophilicity Anti-fogging activity Self-cleaning surface http://www.nano-pac.com/en/jj/na02.htm 15
Nano-Particles in Coatings: Challenges Dispersion and Dispersant Demand Rheology Functionalization Application Specific? Characterization Cost/Performance Balance Health Effects Nanosafe2.org Nanoparticles: health impacts?, David Warheit (DuPont), Materials Today, Feb. 2004, p32 Nanoscience and nanotechnologies: opportunities and uncertainties, http://www.nanotec.org.uk/finalreport.htm, July 2004 Dispersant Demand Particle Diameter (nm) 300 250 200 150 100 50 Interfacial Volume Fraction 0.03 0.04 0.05 0.06 0.10 0.22 10 nm Interfacial Layer Dispersed particle volume fraction is 0.3 in all cases 16
Effect of Dispersed Phase on Viscosity Viscosity % Volume Solids 64 Cubic Packing Critical Volume Fraction - 0.5236 Hexagonal Packing Critical Volume Fraction - 0.7405 For Random Packing, Critical Volume Fraction - 0.64 Experimental Coating System 2K Polyurethane automotive refinish formulation. Nanoparticle Dispersions: Nanoparticles Solvent % Solids Avg. Particle Size(nm) Alumina-A Dipropyleneglycol mono-n-butyl ether 38 30-40 Alumina-B Alumina-C Silica-A Tripropylene glycol diacrylate Methoxypropyl acetate Methoxypropyl acetate / methoxypropanol 40.9 32 32 30-40 30-40 >100 17
Experimental Nanoparticles were incorporated into coating at various levels. Formulated Coatings were applied at 3 mil thickness onto steel panels. The samples were cured in an oven at 70 C for 30 minutes. Tests were performed on the cured samples. Initial Results-Scratch Resistance Milligrams Coating Removed After 50 Double Rubs 0000 Steel Wool vs. Dry Wt% Nanoparticles Mass Removed (mg) 14 12 10 8 6 4 2 0 0 2 4 6 8 10 Dry Wt. % Nanoparticles Alumina-A Alumina-B Alumina-C Silica-A 18
Haze Samples Haze Rating No Nanoparticles 0 1% Alumina- A 0 2.5% Alumina- A 1 5% Alumina- A 2 1% Alumina- B 1 2.5% Alumina- B 2 5% Alumina- B 3 0.75% Alumina- C 0 1.75% Alumina- C 0 3% Alumina- C 0 Haze Rating: 0 = Clear 10 = Opaque 2% Silica- A 0 4% Silica- A 0 6% Silica- A 0 8% Silica- A 0 Atomic Force Microscopy Figure 9. AFM Images of coatings containing nanoparticles: (a) Alumina-B at 2.67 wt.% loading scan area 5x5 micron, (b) Silica-A at 0.67 wt.% loading scan area 10x10 micron 19