Can someone explain to me the science behind starch? Ive heard

>>9031443
What you're asking about has little to do with "starch" per se, but more to do with texture.

You want the potato to have a rough surface so that it becomes more crispy when you fry.

Both methods you described work. If you soak potatoes in water for a while then some of the starch on the outside will rinse away, leaving a rougher texture. Coating the potato in a starch powder achieves the same sort of rough texture, except instead of being created from the cellular structure of the potato it's now created by the particles of the powder you added. The starch coating also acts like a light breading.

>>9031443
>the science behind starch

It's a simple carbohydrate, a polymer of glucose.