Najafi Q&A: Al-Zihar

If a man makes ẓihār (a form of divorce by comparing the wife to the sister or mother) against his wife without witnesses present, does the ẓihār take effect or not?

Does the Zihar (a husband is referring to his wife as his mother or by uttering that, “you are, to me, like my mother” and vice-versa.) occur for the young wife and the barren woman?