| First, WD-40 is a petroleum product. What is the "micro" you speak of? It penetrates into the rust because of capillary effect. A material that enters the body through the skin is refered to as a systemic. These two phenomenon are not directly related. The first is a result of the reduction in gibbs free energy by replacing high surface energy interfaces with lower energy interfaces. Surface energy between air and metal is higher than between metal and oil. Thus the oil wets out the surface because doing so releases energy in the form of heat. The second does not occur because oil and water are immiscible. Water is polar, oil is not. Therefore they do not want to coalesce molecularly, because they are currently in a lower energy state. You can sleep at night... i promise. :)
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