Q. Why do onions, potatoes, etc. stick to my new chef's knife when slicing, and what can be done to prevent it?
A. The surface tension in the water in vegetables is what causes them to stick to any flat, non-porous surface. This may be more evident with your new, sharp knife, because it allows you to cut a very flat surface that will stick like mad to your blade. Cut with a dull or uneven knife, the surface of the vegetable would be rougher, and less able to form a tight seal with the knife.
Drying potatoes and other vegetables before you cut them may help, but there’s nothing you can do about the moisture inside the vegetables. The wetter the vegetable, the more likely it will be to stick. Zucchini and summer squash are more sticky than the relatively dry carrot. Waxy potatoes are more sticky than russets or other low-moisture varieties.
Now, how good are your knife skills? If you are reasonably adept at the up-and-down rocking motion favored by chefs (in which the tip of the knife doesn’t leave the cutting surface), the slice of potato you are currently cutting will dislodge the slice you just cut that is stuck to the blade.
We actually spent a little time looking through a number of cooking school textbooks to see if they offered any tips for keeping foods from sticking (they don’t), and were amused to see that they use perfectly clean (apparently sanitized) knives in all their photos, and that all the vegetables are lying in perfectly ordered piles just to the side of the knife. Don’t believe it! Watch any cooking show on TV where they’re actually cutting (as opposed to removing previously chopped vegetables from a bowl), and you’ll see vegetables stick to the blade, roll around the cutting board, and misbehave just as they do in your kitchen.