에탄올 없이 콜로이드 실리카와 물만을 사용하여 제조된 S4의 코팅 용액도 안정하고 침전물이 없음을 확인하였다.
It was confirmed that the coating solution of S4 produced by using only colloidal silica and water without ethanol was also stable and had no precipitate.