Invisible Glass

If you have ever watched television in anything but total darkness, used a computer while sitting underneath overhead lighting or near a window, or taken a photo outside on a sunny day with your smartphone, you have experienced a major nuisance of modern display screens: glare. Most of today’s electronics devices are equipped with glass or plastic covers for protection against dust, moisture, and other environmental contaminants, but light reflection from these surfaces can make information displayed on the screens difficult to see. Now, scientists at the Center for Functional Nanomaterials (CFN) — a U.S. Department of Energy Office of Science User Facility at Brookhaven National Laboratory — have demonstrated a method for reducing the surface reflections from glass surfaces to nearly zero by etching tiny nanoscale features into them.

Whenever light encounters an abrupt change in refractive index (how much a ray of light bends as it crosses from one material to another, such as between air and glass), a portion of the light is reflected. The nanoscale features have the effect of making the refractive index change gradually from that of air to that of glass, thereby avoiding reflections. The ultra-transparent nanotextured glass is antireflective over a broad wavelength range (the entire visible and near-infrared spectrum) and across a wide range of viewing angles. Reflections are reduced so much that the glass essentially becomes invisible.

This “invisible glass” could do more than improve the user experience for consumer electronic displays. It could enhance the energy-conversion efficiency of solar cells by minimizing the amount of sunlight lost to refection. It could also be a promising alternative to the damage-prone antireflective coatings conventionally used in lasers that emit powerful pulses of light, such as those applied to the manufacture of medical devices and aerospace components.

We’re excited about the possibilities,” said CFN Director Charles Black, corresponding author on the paper published online on October 30 in Applied Physics Letters. “Not only is the performance of these nanostructured materials extremely high, but we’re also implementing ideas from nanoscience in a manner that we believe is conducive to large-scale manufacturing.”

Our role in the CFN is to demonstrate how nanoscience can facilitate the design of new materials with improved properties,” concluded Black. “This work is a great example of that–we’d love to find a partner to help advance these remarkable materials toward technology.”


A Glass Of Milk So White…

The Project on Emerging Nanotechnologies (PEN) revealed a few weeks ago that there are over 1,600 nanotechnology-based products on the market today — and that the United States Food and Drug Administration (FDA) lacks the authority to regulate them.Some of these nanotechnological innovations — which refer to particles less than 100 nanometers wide, or approximately 1/800th the diameter of a strand of human hair — are likely harmless, such as embedded silver particles in athletic socks and underwear. According to SmartSilver Anti-Odor Nanotechnology Underwear, the microscopic silver particles are “strongly antibacterial to a wide range of pathogens, absorb sweat, and by killing bacteria help eliminate unpleasant foot odor.”

However, the PEN database also includes 96 nanotechnology-infused items currently stocked on grocery store shelves, and none of these items listed their nanotechnology among their ingredients. Included on the list are Dannon Greek Plain Yogurt, Hershey’s Bliss Dark Chocolate, Kraft’s American Cheese Singles, and Rice Dream Rice Drink, all of which contain nanoparticles of titanium dioxide.

Titanium dioxide — often referred to as “the perfect white” or “the whitest white” — is used as a pigment because its refractive index is extremely high. It has long been present in paints, plastics, paper, toothpaste, and pearlescent cosmetics, but researchers recently discovered the benefits of adding it to skim milk.

According to David Barbano, a professor at Cornell University’s Department of Food Science, “suspension of titanium dioxide in skim milk made the milk whiter, which resulted in improved sensory scores for appearance, creamy aroma, and texture… There is clearly a need to develop a whitener for fat-free milk other than titanium dioxide to provide processors with an ingredient option that would improve sensory properties and provide a nutritional benefit.”