[alancalverd]

If that happened then the detergent would be doing its job as a wetting agent and the water would spread out, rather than beading up in droplets.

I visualised the problem as the formation of inverted micelles, with water droplets surrounded by detergent molecules that stick to the plastic.

[alancalverd]

Hmm...so I've been washing & drying stuff incorrectly ever since.
😑

If you have been washing up by hand with cold water, you have been wasting water, detergent, and your own time.

[Bored chemist]

If that happened then the detergent would be doing its job as a wetting agent and the water would spread out, rather than beading up in droplets.

I visualised the problem as the formation of inverted micelles, with water droplets surrounded by detergent molecules that stick to the plastic.

And, because they stick to the plastic, they spread out so that as many of them as possible are stuck to it.
That's how detergents and wetting agents work.

[alancalverd]

So here's a development of the hypothesis.

Agreed we see water droplets on the surface of washed plastics because the residual water doesn't wet the plastic. I also note that detergents are less effective at removing grease from plastics than from inorganic materials: could just be that used plastics have more microscopic scratches but arguably the lyophilic end of the detergent molecule has some affinity for the plastic and sticks to it rather than dissolving in the grease. So during the washing phase the surfactant doesn't form the desired micelles, and the rinsing phase removes it because the hydrophilic end preferentially dissolves in the large excess of water leaving the hydrophobic plastic plus grease to form droplets.

On the other hand clean metals and ceramics have a low contact angle with water even in the absence of surfactant, so if they are degreased they will sustain a thin coating which evaporates easily.

[Bored chemist]

The grease sticks preferentially to the ("oily")  plastic for essentially the same reasons that it sticks to the "oily" end of the detergent molecule.
That's why the detergents struggle to get plastic clean.

However, with or without a layer of grease, the water beads up on the plastic.
It doesn't do so on clean  ceramic or metal.

[Zer0]

Hmm...so I've been washing & drying stuff incorrectly ever since.
😑

If you have been washing up by hand with cold water, you have been wasting water, detergent, and your own time.

I've done Worse!
😑
I use a Washing Machine.

So i wasted Electricity which I'm aware comes from a Coal Plant, thereby polluting the environment.

Wasted bucket loads of non drinking water, which might have been useful for gardening or atleast drinkable for other animals.

Wasted gel liquid & detergent resources, almost like i made it rain on my dumbness.

Perhaps i should have just bought new clothes.
With covid19 there are boards up on shopping windows offering 50% discount.
Even like buy 2 & get 1 free.

Query - Is there any line of clothing that does not require cleaning & ironing?
(Except for raincoats & banana leaves)

[wolfekeeper]

To be honest, I'm not finding that plastic dries significantly worse than ceramics. I find that if the object is set so the water flows off, it dries very well, or if there's a place for the water to collect, it will still be there at the end, and that's irrespective of the material.

I did have a big problem previously, but this went away when I started using rinse aid. AFAIK dishwashers usually have a setting for adjusting the amount of rinse aid used. If you're getting excessive drying marks then increase this. Also make sure you set things on a tilt so that the water rolls off.

[ygengineering]

A very counterintuitive main reason is that plastics don't dry well because they are hydrophobic. That's right: they let water stick to them because they're waterproof (but not completely).