Nanotech for waterproofing |

best_waterproof_phones_thumb800 Background

Nanotechnology is becoming increasingly important in modern times, and already has many uses in medical applications and technology.

What is nanotechnology exactly? Nanotechnology is the use and control of structures and materials that are on the nanoscale (between 1-100 nm), and only a tens or hundreds atoms in size. 1 nm is 1 billionth of a metre, i.e. 0.000 000 001 m (nano = 1 x 10^-9m). If we take a human hair, there are 100,000 nm across its diameter.

A nanomaterial, is any material that has one of its dimensions on the nanoscale, such as nanoparticles, which particles that are 1-100 nm in diameter. Nanomaterials can be very long in one direction, such as DNA; DNA is only a few nanometres across, but can stretch into centimetres long. Nanomaterials can also be much larger than the nanometre is 2 dimensions, such as nanosheets, like graphene.

volsaratio — As materials get smaller, the surface-area:volume ratio increases

Nanomaterials are all around us, and can occur naturally, for example in volcanic ash. Many, however, are designed and produced by scientists. Nanomaterials often behave quite differently to their bulk materials, merely due to the nanoscale dimensions of the material; nanomaterials have a very large surface areas, and are often more reactive.

The experiment

A pdf version of this experiment is available here. There is no safety card for this experiment. Details for teachers or technicians can be found here.

AIM

To observe the effect of a natural functional nanomaterial with water, and compare it with flat surfaces of paper and foil

YOU WILL NEED

a plastic Pasteur pipette
1-2 mL of tap water
a sheet of paper
a small square of aluminium foil (~ 6 x 6 cm)
a square of a dried lotus leaf (~ 6 x 6 cm)

PROCEDURE

Firstly take a sheet of paper, and drop a droplet of water onto the paper. Look at the droplets side-on, and draw the shape that you see. Tilt the paper and see if the droplet likes to ‘stick’ to the paper. Repeat this with foil. Finally, take a dried lotus leaf and try this.

QUESTIONS

Which material repels the water the most? Which material attracts the water the most?
If you wanted to make a water-repellant surface, which surface would you try to replicate?
Do both sides of the lotus leaf behave the same?

paper

aluminium foil

lotus leaf

Nanotechnology

The lotus leaf is an example of a functional nanosurface that exists in nature. The surface of a lotus leaf is ‘ultrahydrophobic’; when water is dripped onto its surface it does not wet the leaf at all, but rolls off. Not only are the leaves extremely water-repellent, they are also ‘self-cleaning’, due to the surface structure of the leaves. The lotus leaf has a series of protrusions that are roughly 10 μm (1.0 x 10^– ⁵ m) high covering its upper surface, these can be seen in the microscope images shown below:

Dried lotus leaf imaged from the top under a microscope

Dried lotus leaf imaged from the side under a microscope

This ‘rough’ surface structure with microscale bumps has a second smaller structure as each protrusion is itself covered in bumps of a hydrophobic, waxy material that are roughly 100 nm (1 x 10^-7 m) in height. This means that water droplets sit lightly on the tips of hydrophobic protrusions as if on a bed of nails. This combined structure traps a layer of air in between the surface of the leaf and the water droplet. Hence, the water is not allowed to wet the surface and is easily displaced. This ultra-hydrophobicity gives rise to the self-cleaning process on the surface because as the droplets travel along the leaves, they pick up any dirt or other matter they encounter along the way. This process keeps the lotus leaves dry, clean and free of pathogens such as bacteria and fungi.

lotus_schematic

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In the research lab

best_waterproof_phones_thumb800 Chemists at the University of Durham have developed methods of creating similar surface-structures artificially, that can be sprayed onto devices and protect them from water damage. The invention has been commercialised by the British company, P2i, which is the world leader in liquid repellent nanocoating technology and was named ‘most innovative company in Europe’ in the 2012 International Business Awards. Customers include household names such as Nokia, Motorola and Alcatel (mobile phones), Timberland and Hi-Tec (footwear) and HLT (hearing aids).

Other uses of functional nano-surfaces:

Researchers at the University of Birmingham, including Professor Paula Mendez in Chemical Engineering, and Dr John Fossey (School of Chemistry) create functional nanosurfaces to make sensors to detect diseases, such as prostate cancer. Sensors are one of the many areas of technology that rely on the development of new nanomaterials, and their manufacturing techniques. Information about our health can be extracted from biological material in our saliva, blood, urine and sweat, in order to detect the onset of disease. Many of these ‘disease markers’ include proteins and DNA, which are tens of nanometers in size, and hence interact selectively with materials on the nanoscale. The sooner a disease is diagnosed, the more likely it can managed or cured. To learn more about these sensors, take a look at the video below, published April 2016: