"So tell the people of Israel, 'I am the Lord. I will throw off the heavy load the Egyptians have put on your shoulders. I will set you free from being slaves to them. I will reach out my arm and save you with mighty acts when I judge Egypt.
... Moses reported those things to the Israelites. But they didn't listen to him. That's because they had lost all hope and had to work very hard.
Then the Lord said to Moses, "Go. Tell Pharaoh, the king of Egypt, to let the people of Israel leave his country."
But Moses spoke to the Lord. "The people won't listen to me," he said. "So why would Pharaoh listen to me? After all, I don't speak very well."
... "But I will make Pharaoh's heart stubborn. I will multiply my miraculous signs and wonders in Egypt. In spite of that, he will not listen to you. So I will use my powerful hand against Egypt. When I judge them with mighty acts, I will bring my people Israel out like an army on the march.
"Then the Egyptians will know that I am the Lord. I will reach out my powerful hand against Egypt. I will bring the people of Israel out of it."(New International Reader's Version)
The 10 plagues were not really for Pharaoh. Not really to make him give in. God could have done that without any plagues with just one word. The Lord had his view on eternity and his audience was larger than just Pharaoh. The plaques were designed to display the power of God to Moses, Aaron, the Israelites, the Egyptian people, and ultimately everyone throughout history who would learn of what happened.