February 2011

My wife calls it a midlife crisis. I was hoping to save my midlife crisis for a BMW sports car but fear it may be used up now on my new Kawasaki Versys (shown below). After a twenty-year hiatus I decided last summer to get back on two wheels.

Motorcycling can be a lot of fun - especially on a warm sunny summer day. Even if all rides began under such agreeable circumstances, they don't always end that way. Eventually you hit rain which not only makes for a slippery road surface to stay up on but also decreases visibility. Unlike a the driver of a car who benefits from a glass windshield and a pair of wipers, a motorcyclist's first line of defense is a small windshield - if he's lucky enough to have one. The second line of defense is a plastic face shield affixed to the helmet - assuming he's wearing one (in NJ it's required by law). In my case, I have a small windshield which primarily is designed to push some of the wind off the chest in normal driving conditions. However, in a pinch, you can crouch behind it in a rain storm and it offers some very limited protection. As it turns out, the windshield as well as the face shield are both made of a polycarbonate resin thermoplastic known by its trademarked name Lexan.

Lexan is an amazing material: strong, impact resistant, temperature resistant, easily extruded and formed, and exhibits good optical qualities. Lexan has long been used to make aircraft windows, CD's and DVD's, and more recently, automotive headlight covers. Lexan is an ideal material for motorcycle windshields and face shields: it's shatter resistant, hard, and can be easily molded into any unique shape that may be required. On the downside, Lexan is susceptible to scratching and is not easy to see through when wet.

So, our question became: "How can we improve the visibility for motorcyclists who, when caught in a rainfall, contend with looking through one or more polycarbonate surfaces?" And this turned into a small research project which we just concluded. We began by making a lists of cleaning compounds and treatments that would be expected to decrease wetting which in turn would increase visibility by allowing the rain to roll off and take with it any contaminants which may further foul the surface. We began by visiting a number of forums to see what other bikers are using and recommending to clean and treat their face shields and windshields. We shortly found that any alcohol-based cleaner, such as Windex, should be avoided as it can compromise the integrity of the surface and lead to spider web cracks and a white cloudy haze. We also found a number of unconventional techniques including the use of peanut butter, toothpaste, a diaper, reverse osmosis and sheepskin. In the end, we narrowed our contestants down to (6) commercially available products: Pledge, Rain-x, PlastX, Scrubbing Bubbles, Plexus, and Simple Green. Of the contestants, only two of them, PlastX and Plexus, are specifically formulated for cleaning and treating plastics and are specifically recommended for use on polycarbonates.

I should point out that one of the most important metrics used to determine a successful cleaner for Lexan is its ability to remove small scratches and to certainly not add new scratches. To this extent, a microfiber finishing towel is the recommended applicator. This is what we used in conjunction with following each manufacturer's cleaning or application instructions. However, our study focuses on not on scratch reduction but rather on how successful each treatment is at increasing hydrophobicity and maintaining a hydrophobic surface after being exposed to a rainstorm. The more hydrophobic a surface is, the greater the tendency for water drops to roll off naturally - or with the help of the wind.

To begin we measured the static contact angle on each of (6) samples of flat Lexan using a ramé-hart Model 200 Standard Goniometer (s/n 110127). For each sample, we took at least (5) readings on separate 4µL water drops. The values reported below are averages of these readings. Next, we treated each of these samples using the proscribed methods detailed by the manufacturer and then measured again a number of times on each sample. Finally, we rinsed the samples in a shower of cold water for five minutes (simulating five minutes of heavy rain) and then measured the contact angles one last time. The table below shows the results on each of the (6) samples Before treatment, After treatment, the improvement in contact angle (BA Delta), the contact angle after being Rinsed, and the difference between the original Before contact angle and the one after the rinse (BR Delta).

We found that after treatment, Pledge produced the most improvement in contact angle with a gain of 12.66°. However, most of the gain was lost after exposure to five minutes of rain. Three of the treatments, Rain-x, PlastX, and Simple Green, actually lowered the contact angle. However, in every case, the contact angle improved after being rinsed. In the case of PlastX, the rinsed sample exhibited a contact angle of 7.15° higher than before treatment, the highest of the (6) treatments. Rain-x performed poorly but in fairness to the makers of Rain-x, the bottle does say to use on glass windshields and not on plastics.

Conclusion: None of the treatments tested make Lexan superhydrophobic. Pledge improves the contact angle the most but those gains are short-lived once it starts to rain. In the long run, Plexus might be the best choice since the contact angle improves by 8.20°, the second best of the (6), and half of that gain is maintained after five minutes in a rain storm. In the end, the best way to improve visibility is to check the weather before taking off and take the car when the forecast calls for rain.
 

Each coaxial needle is really a needle in a needle allowing a variety of liquid/liquid and liquid/gas drop and bubble combinations to be made in a gas or liquid phase. See the diagram below. The inner drop could be an oil, the outer drop could be water, and the external phase could be hexadecane or any other liquid which is immiscible in water. Either the inner or outer could also be a gas.

If you have a present or future need for a coaxial or any other type of custom needle, please send us a copy of your sketch or specifications and we would be happy to work up a quotation. For a detailed guide to our standard dispensing needles including needle dimensions and part numbers, see: http://www.ramehart.com/pdf/needles.pdf.