Friday, 1 April 2016

Applied Nanotechnology for Cleaning Optics - Silica Nanoparticle Microfiber Cloths.

Microfiber cloths are now fairly ubiquitous for glass/plastic optics cleaning applications in many fields and industries.

Cleaning with microfiber products is fast, easy and environmentally friendly. Microfiber cloths are attractive in their ability to lift away even difficult forms of dirt without the use of chemical solvents.

Microfiber cloths are also soft and do not scratch the surface they are cleaning, but at the same time they are effective for all cleaning applications.

We can examine the differences between microfiber cloths and natural fibers by looking at their micro-structure (fig-1) and comparing their effects.

Fig-1 - Microstructure of an Artificial Micro-Fiber and a Natural Fiber (i.e. Cotton)

Natural single fibers, such as cotton, more or less simply move or push dirt and dust from one place to another.

Microfibers, owing to their microscopic structure, actually ‘scrape’ the dirt or stain from the surface, and then store the dirt particles in the fabric until it is washed.

Microfibers then trap dirt and dust inside the cloth, and do not spread dust or dirt around. The user can clean the cloths with either a polar (i.e. water) or non-polar (i.e. acetone or ethanol) later.

The scheme of cleaning dirt by natural fibres and microfibres are shown in below (fig-2).

Fig-2 - Cleaning Scheme of a Natural Fiber vs a MicroFiber. The Natural Fiber merely sweeps a dirt layer whereas a MicroFiber sweeps and scoops up the fine nano-sized dust/dirt particles

By treating microfiber cloths with SiO2 (Silica) nanoparticles in solution we can "trap" a concentration of nanoparticles inside the structure of each microfiber (Fig-3) which is then replicated throughout the superstructure of the cloth.

Fig-3: Nano-Treatment of MicroFiber with SiO2 (Silica) Nanoparticles

This allows us to create, among other things, superhydrophobicity ("water-fearing") and oleophobicity ("oil fearing") cloths, often displayed as the so-called "Lotus Effect" -i.e. suspending a condensed droplet on the surface of the material (Fig-4)

Fig-4: "Lotus Effect" of water droplet on a Superhydrophic MicroFiber Cloth

Owing to their fine, compact structure, microfibre textiles offer excellent filtration effects for air filtration. Hence, although we have hydrophobicity and oleophobicity, air molecules can still pass through the cloth unencumbered.

The trapped silica nanoparticles within the microfiber cloth can then be used to buffer conventional silica glass or polymer plastic surfaces to remove fine dirt and create a high optical transparency without creating erosion.

Moreover, by buffering with the silica nanoparticle-saturated cloth we can in-effect deposit a fine layer of silica nanoparticles on top of lightweight polymer plastic optics (Fig-5).

Fig-5: Lightweight and Cheap to Produce Polymer Plastic Optics have a wide range of uses today

In practice this layer may not be even, however it may help either fill in some grooves in the uneven surface or perhaps create a few droplet seeding points on the surface of the polymer optics where a water drop can form and roll off much more easily instead of the water vapor fogging up the optics which greatly mitigates visibility.

In any case, this can in principle give otherwise ordinary polymer optics the effect of having a thin layer of what is effectively nanoparticulate glass which can reduce fogging and increase durability with polymer optics which fog and corrode much more easily than glass.

The process can be accomplished by spraying an ordinary microfiber cloth with silica nanoparticles in a water suspension until the cloth is completely saturated and is dripping and then leaving the cloth to dry in air.

We can then, by simply sweeping the cloth across the optic surface, use the saturated cloth to buffer a layer of nanoparticulate silica on a polymer optic's surface (Fig-6). The buffering procedure is represented in the diagram below

Fig-6: Silica Nanoparticle Treatment of Conventional Optic Surface

The saturation treatment process is then repeated before each buffering to ensure that the cloth is laden with as many silica nanoparticles as possible so that we get the most amount deposited on the surface of the optics, leading to the most even distribution of the layer as possible.

This can give us, in principle, a new way to easily optimize polymer-based optics, which are relatively cheap and lightweight, to the best of our abilities in applications where weight and expense of conventional glass optics can be a problem for our goals.

Video demonstration:

Video and Project Designed and Developed by MuonRay Enterprises Ireland.