Not sure what the chemicals do or how they are injected, but "The Expanse" gets gravity correct. The ships' decks are laid out like skyscrapers, not cruise ships or airplanes. So when they are under thrust, the force of gravity holds them to the deck.
The other thing "The Expanse" gets correct is just how much time you have to spend decelerating. So a ship goes roughly halfway to its destination, then does a 180-degree flip so the drive engine can begin slowing the ship. And that's where the magnetic boots come in; they keep you attached to the deck. Otherwise, you'd be glued to the ceiling.
These issues (and others) are discussed at Atomic Rockets:
Seal of Approval - Atomic Rockets