Instead of divorcing a difficult wife, can I just take another wife?

Polygyny is not a way to punish a wife or avoid solving problems; it still demands full justice to both sides. If the intention is to pressure or retaliate, that is wrongdoing and goes against the purpose of the religion. Face the real problem first: talk, get counselling, or a sulh officer if needed. If the relationship truly cannot be repaired, Islam also allows separating with kindness as an honest option, rather than keeping two families in suffering. Polygyny entered out of resentment will leave one wife neglected and another wronged. Choose the path with the least harm and the most honesty. See counselling.