Hydrophobic / Hydrophilic surface
A hydrophobic surface is one that repels moisture. In contrast, a hydrophilic surface is one that absorbs moisture. The potential of a surface to absorb or repel moisture is based on many factors, including: temperature, relative humidity, material homogeneity, and static electricity. Surface roughness is also a major factor; the rougher the surface, the higher the spreading rate or attraction for water. The smoother the surface, the more repellent it is to moisture.
Contact angle measurement
A simplistic method to determine the level of surface protection is to observe the formation of large, closely spaced water droplets, which demonstrates that moisture is effectively prevented from being absorbed into the surface profile. The classification of water droplets on a hard surface is known as a water break test and is used to check surface cleanliness.
The size, shape, and height of the water droplets are measured by their contact angle. Contact angle is figured by a straight line that starts at the base of the droplet and travels along its outer surface to the break-off point. The measurement between this line and the surface determines the contact angle.
Beading is a surface interaction between water and the paint surface; dust or dirt particulates, oxidation, environmental pollutants, and etc interfere with the surface tension, thereby disrupting the beading. Beading that is left to evaporate on a car will lead to water marks; if there is acid or alkali contamination in the water.
Dependent upon the water source; ‘clean rainwater has no harmful effects; but cognizant that water beading whatever its aesthetic value doesn’t equate to surface protection. The average unprotected water-based paint absorbs approximately a pint of water; dependent upon what’s in the water this may be harmful.
Pros – the aesthetics of water beading are sought after by many detailers. Many detailers believe that if there is water beading on a paint surface the LSP is providing protection. Nothing could be further from the truth; water beading is primarily due to surface tension
Cons – dependent upon the water source; ‘clean rainwater has no harmful effects, acid rain is inert until heat is added and then it become corrosive, the water from a standard household supply usually contains minerals like calcium (Ca) magnesium (Mg) and alkaline.
The beads have a very small surface area, so the sun will increase the surface temperature very rapidly once these form a ‘bead’ reactivity ([: the chemical reactions of two or more substances that interact with each other]) starts (moisture, heat and an acid or alkaline) and once they are dried they will cause etching (a shallow indentation) of the paint surface
Be cognizant that (a) Dust and road soil will also have a negative impact on ‘water beading’; this is often mistaken as ‘wax / sealant failure. (b) Durability can fluctuate dependent upon environmental conditions and the products used between the application of a wax/sealant and the use of quick detailers (QD), car wash concentrate that contains a wax, spray wax, etc.)
Does water beading equate to durability or to actual surface protection?
Durability [: able to exist for a long time without significant deterioration] 
Beading is a surface interaction between water and the paint surface protection. Dust or dirt particulates, oxidation, environmental pollutants, and etc interfere with the surface tension, thereby disrupting the beading
Most waxes will bead until enough surface tension is created, and then it will sheet as the volume of water increases. Beading of rain water on the surface of a waxy surface, such as an automobile is due to surface tension. Water adheres weakly to wax and strongly to itself, so water clusters into drops. Surface tension gives them their near-spherical shape, because a sphere has the smallest possible surface area to volume ratio.
Nearly all wax and sealant products exhibit water beading or sheeting initially (in fact so does a clean paint surface without an applied protection) this is due solely to surface tension, once the protection breaks down (abrasion from water, road dirt/grime and other airborne pollutants) it will cause a reduction in the surface tension and the beading will revert to its former level
Slickness is also not an indicator of protection; as it comes from the (silicone) polymers and oils, once applied and exposed to the environment they start to evaporate / deteriorate. If your goal is maximum protection, don't use water beading/sheeting as an indicator; while it’s true that it is a visual indicator that a wax / sealant previously applied is still present it does not guarantee that it’s actually providing protection.
Hydrophobic beading on a paint surface is aesthetically pleasant, and many people equate beading with protection; there is a long standing myth “that as long as a paint surface maintains beading it’s being protected from the elements” (much like the myth that “the more soap produces suds the better the cleaning effect”) There are many things that will affect the ‘shape’ of a water bead on a surface; since gravity, surface tension and the surface energy of the coating all play a part.
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
Dust and road grime will have a very negative effect on surface beading than any other factor. The effect of this is often misconstrued as wax failure when this isn't the case.
Durability varies depending on various environmental factors, including but not limited to:
• Product is applied to a clean, cool and dry surface
• Product was allowed to cross-link and form a molecular bond with the paint system
• No oils or water (including moisture, dew, etc.) was introduced to the surface before it has formed a molecular bond
• What the environmental conditions (ambient temperature etc.) are where the vehicle is stored
• The kind of airborne contaminants the vehicle is regularly exposed to
• Frequency of washing and kind of car wash solution used (i.e. detergent strength, etc.)
[: 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?
• 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
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 with a diminished s 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
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 (hydrophilic) - 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 reactivity, which produces a highly concentrated acidic solution, causing concave indentations (acid etching) to the paint surface
Any product can be reformulated 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.
Always be willing to learn; because the more you learn, the more you’ll realize what you don’t know.
It is said that knowledge is power, with the caveat that it includes access to a reliable information sources. I would like to think that these articles become an asset to anyone who is new to detailing and to professional’s alike, as well as industry experts who seek to advance their knowledge.
I hope the article are informative. By having some understanding of the ‘What’ and ‘Why’ as well as the ‘How’ along with a little science to help you understand how the chemicals we use react, you can achieve the results you desire.
I would appreciate it if you would share these articles as it helps other detailers further their knowledge.
Questions and/ or constructive comments are always appreciated.
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