Spark, a Chicago-based media buying firm, is adding to its operations an arm of LiquidThread, a branded content and entertainment practice that is part of Spark parent media buying behemoth Starcom MediaVest Group. The new LiquidThread unit at Spark will be run by Eric Levin, who joins the Chicago media firm on Monday as a group client director. As the head of LiquidThread within Spark, Levin will work with Spark's client roster to introduce, build and execute a range of brand-content experiences. Noted…