Near-UV Reflective Structural Color via Layer-by-Layer Deposition

Technology #13678

Questions about this technology? Ask a Technology Manager

Download Printable PDF

Categories
Inventors
Professor Robert Cohen
Department of Chemical Engineering, MIT
External Link (cohengroup.mit.edu)
Debasish Banerjee
Toyota Motor Engineering and Manufacturing North America, Inc.
Masahiko Ishii
Toyota Motor Corporation
Pinar Kurt
Department of Material Science and Engineering, MIT
Professor Michael Rubner
Department of Material Science and Engineering, MIT
External Link (web.mit.edu)
Minjuan Zhang
Toyota Motor Engineering and Manufacturing North America, Inc.
Grinia Nogueira
Managed By
Jim Freedman
MIT Technology Licensing Officer - Chemicals, Instruments, Consumer Products
Patent Protection

UV-reflective structural color

US Patent 8,446,666

STRUCTURAL COLORS HAVING UV REFLECTANCE VIA SPRAY LAYER-BY-LAYER PROCESSING

US Patent 8,313,798
Publications
Structural color via layer-by-layer deposition: layered nanoparticle arrays with near-UV and visible reflectivity bands
J. Mater. Chem., 2009,19, pp. 8920-8927

Applications

This technology has applications in the development of pigments to prevent photodegradation of polymer coatings. Additionally, these pigments can be used in architectural, automotive, and aerospace coatings to repel birds and insects.

Problems Addressed

Unprotected polymer surface coatings, including those made of otherwise durable materials like polyesters, undergo rapid degradation when exposed to light due to the effect of energetic photons with wavelengths in the near ultraviolet (NUV) region. Conventional strategies to extend the lifetime of these polymers involve the incorporation of inorganic UV absorbers such as carbon black and titanium dioxide. This has a detrimental effect on the cosmetic appearance of these polymers. The NUV-reflective coatings described in this invention allows the mitigation of polymer photodegradation with minimal impact on appearance.

Coincidentally, the NUV radiation responsible for photodegradation of polymers is also involved in animal communication. This allows the proposed NUV-reflective coatings to address a multitude of problems caused by animal collisions with buildings and aircraft by emitting animal-repelling NUV signals.

Technology

The NUV reflective coating described in this invention is fabricated by alternately depositing nanoparticle layers made of high refractive index material (e.g., TiO2) and low refractive index material (e.g., SiO2) using an aqueous layer-by-layer (LbL) assembly scheme. The refractive index of each layer is a function of its nanoporosity and can, therefore, be tuned by varying assembly conditions.

A TiO2/SiO2 multilayer functions as a Bragg mirror which selectively reflects light at multiple bands depending on the relative thickness of its constituent layers. The location and width of these reflectance peaks can be tuned to suit specific applications. For the particular application of NUV-reflective coatings, secondary reflectance peaks in the visible wavelengths may alter the visible color of the coating. The effect of these secondary peaks can be mitigated by adding a half, high refractive index stack to the main stack, resulting in a NUV-reflective coating with minimal visible color interference.

Advantages

  • Tunable multiband NUV reflection behavior
  • Minimal impact on cosmetic appearance of polymer coatings possible
  • Aqueous LbL assembly is environmentally friendly, low-cost, and compatible with complex surface geometries