Beads Are Bad: Why water beads might be harming your finish
Everyone loves water beads on a protected car, but those beautiful beads can actually do some damage if they don't have a certain quality. Read more:
www.drbeasleys.com
Sliding angle
Talking about this concept is contrary to how coating brands frame hydrophobicity. Usually all they’ll mention is contact angle, implying that this metric is the sole determination of water repellency. But contact angle is only a static measure. A dynamic measure like sliding angle is what really tells you how easily a bead can leave your paint.So what accounts for low sliding angle? There are several metrics at play, but at the most basic level the answer lies in the slickness of your paintwork. The more slick the surface, the more easily a bead can roll off.
"The detailing crowd have really got the terminology confused - beading meaning hydrophobic and sheeting meaning... errrrr... hydrophobic. The worst of it is that many think that the 'sheeting' they are describing is hydrophillic. The problem comes in the 'sheet' definition. A drop of water on a hydrophobic surface forms a 'bead' - all good there. The same droplet on a hydrophilic surface forms a flat sheet (it spreads out flat) - but this isn't what detailers mean by a sheet. In detailing, a sheet is simply a collection of water droplets on a hydrophobic surface but a surface which is not hydrophobic enough to break that sheet up into droplets. In detailing, a bead and a sheet are manifestations of exactly the same surface chemistry.
It has got to the point that some now use the technical, hydrophilic, term to describe the detailers sheet - which is quite the opposite of fact. Worst of all, some of the brands, in a wonderful demonstration of their utter lack of technical expertise, are guilty of this!"
"Believe it or not, contact angle (what makes beads look impressive) and sliding angle (what makes them run off) are quite distinct and not necessarily linked. In fact, many high contact angle surfaces require quite high sliding angles to clear them. In automotive, contact angle is for show, sliding angle is what is actually best."