Scale-up of green nanoscience pathway for optically transparent nanocomposites
A technology to deposit multi-layered thin films with discrete refractive indices over wide areas and onto highly flexible substrates simply does not exist. Vision Dynamics LLC (VDL) has developed andcommercialized inorganic-organic nanocomposite coatings systems for the ophthalmic industry that maintain high transparency even though the inorganic nanoparticles occupy over half of the volume of the nanocomposite. Enormous commercial opportunities exist for this technology as anti-reflective coatings on consumer electronic displays ($24B annually), solar cells with improved transmission ($10B annually), UV-protection coatings for organic solar cells, and thermal management coatings for architectural windows. In this SBIR phase I project, the team set out to prove feasibility of extending deposition of familiar nanocomposite chemistry over wide-areas using a roll-to-roll manufacturing technique. The team approached this project by generalizing tasks into three different hubs: 1) implementation of green design principles, 2) synthesis and formulation of nanoparticle dispersions, and 3) implementing roll-to-roll process and conducting spray-coating feasibility studies. The team has successfully prepared dispersions of titania nanoparticles with average particle size of 15 nm and narrow size distributions. The particles have been functionalized with methacryloxylpropyltrimethoxysilane and formulated with dipentaeurythritol dipentaacrylate monomer and 1 hydroxycyclohexylphenyl ketone as a photo-initiator. With the aid of collaborators at the University of Kentucky, the team developed a hydroxide audita to assess the number of available hydroxyl groups present on a variety of metal oxide nanoparticles as a function of measured surface area (from BET measurements) and overall hydroxide content (from TGA measurements). The developed procedure can be used for future optimization of the silanization procedure. In addition, the team has shown that nanoparticles with selectively adjusted surface energies can be separated during the deposition process. Titania and silica nanoparticles were functionalized with hydrophobic and hydrophilic surface groups and formulated with monomer and photo-initiator. The formulations were spin-coated onto polycarbonate substrates and analyzed for phase separation using transmission electron microscopy and electron dispersive X-ray analysis (EDX) on the outermost area of the coating. The team assembled a 3-axis spray-coater to simulate roll-to-roll process and optimized spray-deposition parameters such as wetting of substrate, spray width, spray height, line speed, air pressure, liquid pressure, and droplet size. The optimized parameters were used to generate uniform nanocomposite films (less than 5% average surface roughness) with variable film thicknesses on glass and poly(ethylene terephthalate) (PET) substrates as radiation-curable organic-inorganic nanocomposites. The refractive index of the films were modeled to be 1.81 - 1.83 from physical thickness measurements and optical response (reflectance measurements) through the visible range. The titania high index formulation was deposited into a three layer stack between two low index layers with discrete refractive index of 1.46 for an anti-reflective effect. These samples are evident that these nanocomposites can be deposited using a roll-to-roll manufacturing technique to allow constructive and destructive interferences for reflective and anti-reflective coatings, with adhesion to polymer substrates. Further optimization is required for more sophisticate stack designs which would allow superior optical response through the visible spectrum.
- Research Organization:
- Vision Dynamics, LLC
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0003276
- OSTI ID:
- 1009122
- Report Number(s):
- DOE/SC0003276-1
- Country of Publication:
- United States
- Language:
- English
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