Water beading
[: convex beads that have a small, tight symmetrical shape due to cohesion]
Although you cannot equate a products beading ability to protection and durability, if an applied product continues to `bead' water, one wash after another, then that would prove that whatever it is that is causing high surface tension is not washing off.
How can you tell when a paint surface protection has diminished to a point that it is no longer being protected?
Scientific explanation
? Water (H2O) is a polar molecule, composed of two hydrogen (H2) atoms bonded to a single oxygen (O2) atom. Water molecules adhere to each other, this is called cohesion.
? Water molecules also can be attracted to other substances, such as metal or dirt, especially if they have some static charge on them, this is called adhesion.
? Some substances are not attracted to water, and even repel it. These include oils, fats and waxes; these are called non-polar substances.
? When water falls on an un-waxed paint surface, the forces of adhesion and cohesion are almost in equilibrium, and the water spreads out
A wax or sealant, when applied properly to a clean paint surface, fills in the larger surface fissures and layers the whole surface. The chemical structure of the wax prevents water from penetrating to the surface of the car. Because the wax itself is hydrophobic (literally repels water), the forces of adhesion are much less than the forces of cohesion. So, water is more likely to bead higher and rounder than on a surface without wax / sealant
Non-scientific explanation
a) If the paint surface feels dry (your hand or a cloth drags), it?s an indication that there?s nothing left between you and the paint finish. Glazes, waxes and polymer?s create a finish with less friction (surface tension) than the paint itself.
b) A suggestion from a polymer product manufacturer [To test your wax / sealant you must measure the water beading of your paint (height, contact angle and diameter) without any polish/wax applied Next, measure the water beading of your paint (height, contact angle and diameter) within 24 hours after initially applying your polish/wax. This is your starting point. This will also be the gauge for determining the water beading (longevity, duration and changes) for that specific product. As the water beads start to diminish (get wider and shallower and loses contact angle), the polish/wax and its film protection factor is going away, Once the water beading is the same as before you apply your product, the polish/wax and its protection are gone] [Sal Zaino]
Conclusion- water beading is indicative but not conclusive proof of protection
Note - durability can fluctuate dependent upon environmental conditions and the products used between waxing/sealing (quick detailer (QD) car wash concentrate that contains a wax, spray wax, etc)
c)
Indications that the products durability may be diminishing- (contact angle varies) when the water beads become noticeably larger in diameter with a flat, concave or an irregular shape usually indicate that the surface tension of the wax or sealant is diminishing. Or when dust, dirt or bug residue becomes more difficult to wipe off with a quick detailing spray are indications that it may be time to renew the protection
d)
Slickness- slide a micro fibre towel across a horizontal surface to see how much resistance there is, if there has been a significant reduction from what you experienced previously the durability is probably diminishing
e)
Sheeting or water beading- the self cleaning (sheeting) ability of the hydrophilic polymer seems to be much better than the hydrophobic organic wax (beading) effect, as it may accelerate the oxidation when drying after rain.
There are some disadvantages to water beading (hydrophobic) as opposed to the sheeting effect (hydrophilic) of a polymer, when they are dried by ambient temperature they cause ?spotting? (if the rain contains calcium it will leave a white residue) The other is there could be over a pint of liquid trapped within the beads over the paint film surface area, if they contain acid from industrial fall out (IFO) this could increase the time the acidic solution remains on the paint surface compared to ?water sheeting?.
The beads have a very small surface area, so the sun will increase the surface temperature very rapidly; many chemical compounds react to slight heating and an oxidizing process. Now you have acid + water + oxygen + ozone + heat; all of which equates to a highly concentrated acidic solution, which causes a concave indentation (acid etching) to the paint surface
Any product can be reformulated by a Chemist or product formulator with active surface agents (surfactants) either ionic (?sheeting?) or non-ionic (?beading?) that alters the surface tension and causes water to ?sheet? or ?bead? to satisfy consumer demand. But if a product beads on initial application and after a period of time starts to sheet water (or vice-versa) it is normally indicative that the wax/sealant protection has diminished.
Note- Dust and road soil will also have a negative impact on ?water beading?. This is often mistaken as ?wax / sealant failure
Contact Angle
[: the angle at which a liquid/vapour interface meets the solid surface].
[The contact angle is specific for any given system and is determined by the interactions across the three interfaces. Consider a liquid drop on a solid surface. If the liquid is very strongly attracted to the solid surface (for example water on a strongly hydrophilic solid) the droplet will completely spread out on the solid surface and the contact angle will be close to 0?.
Less strongly hydrophilic solids will have a contact angle up to 90?. On many highly hydrophilic surfaces, water droplets will exhibit contact angles of 0? to 30?. If the solid surface is hydrophobic, the contact angle will be larger than 90?. On highly hydrophobic surfaces the surfaces have water contact angles as high as 150? or even nearly 180?. On these surfaces, water droplets simply rest on the surface, without actually wetting to any significant extent.] [1]
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