Now I know there is the dark eldar but that's not chaos is there any eldar who were ever taken by chaos?
In the ancient lore, there were Chaos Eldar, although it was noted that there were very few. They were Eldar who were not consumed in The Fall but voluntarily surrendered
There are probably chaos Eldar on the craftworld Lu'nasad
Eldar as a whole shy away from Chaos since Slaanesh constantly hunts them thru her minions and occasional direct action.
Even if one of them chose to foolishly embrace Chaos, they could never truly serve any of the powers because their souls are already Slaanesh's property from birth. Throwing aside their mental discipline would simply make it that much easier for Slaanesh and her minions to find and then consume them.
The Dark Eldar might not be Chaos worshippers but they are basically tied into Slaanesh's creation and all of his/her/its major likes. They are hedonist, drug abusing, torturous, sex fiend, artistic genius/psychopaths. Everything they do and say keeps Slaanesh happy. It's just that, unlike those foolish humans who follow Chaos wholeheartedly, the Dark Eldar are smart enough to know that they're doomed to be a soulfood snack to She Who Thirsts. But they're not about to modify their behaviour because being bad is too much fun.
The Eldar psyche is also fundamentally tied into Slaanesh, so it's difficult for the other aspects of Chaos to get a look into their souls. Khorne, Nurgle and Tzeentch have claws into many races but they're indebted most powerfully to humanity as a gestalt, psychically burgeoning race that numbers far more than the rest of the galactic races by many factors (not counting Orks who are usually too dumb to be corrupted, being Mushrooms with big guns effectively).
Falling to Chaos would be a death sentence to an Eldar, as they would eventually be claimed by Slaanesh and their souls consumed to sate her unending hunger.
What do you think?