What is the difference between silica gels and bare silica?

Silica gel is commonly used in chromatography, functioning as the stationary phase through which the analyte and mobile phase move. Bonded phases can be attached through the silanol functional group and alter the surface chemistry of the silica, making them useful for modification of column selectivity or polarity. Some bonded phases include C18, cyano (which has intermediate polarity), and diol (which is more polar).

Bare silica is silica that does not have a bonded phase. Although bonded phases are at times preferred due to the possibility of analyte molecules interacting with metal or silanol groups on bare silica, bare silica may be better for separating structural isomers.