Dense
poly(N-isopropylacrylamide) (
PIPAAm) brushes were created on
silica bead surfaces by surface-initiated atom transfer radical polymerization (ATRP). Interfacial properties of
PIPAAm brushes were characterized by thermoresponisve interaction with biomolecules. The grafted amounts of
PIPAAm on
silica bead surfaces exceeded that from previously reported
polymer-
hydrogel-modified
silica beads prepared by conventional radical polymerization by nearly 1 order of magnitude. Temperature-dependent chromatographic interactions with soluble analytes were modulated by changing the grafted
PIPAAm chain lengths. Short
PIPAAm-grafted
silica beads produce insufficient
dehydration and chain aggregation to separate
steroids using weak hydrophobic interactions. In contrast, broad unresolved peaks were observed on
silica beads column grafted with long
PIPAAm chains due to
steroid partitioning into thick, densely grafted
PIPAAm brush layers. Thus,
silica beads column grafted with
PIPAAm chains of proper length can demonstrate baseline separation of
steroids with relatively high resolution among the tested columns. Relatively longer retention times for
steroid analytes were observed on all columns compared to those previously reported for other
PIPAAm-grafted
silica beads. This indicates that densely
PIPAAm-grafted chains enable control of strong hydrophobic interactions with
steroids by changing the column temperature. Densely grafted
PIPAAm columns were also successful in separating two
peptides into two peaks as the column temperature was increased to 40 degrees C. This provides an effective separation alternative for
peptides using substantial hydrophobicity without modification of hydrophobic surfaces and/or low mobile phase pH. In conclusion, densely
PIPAAm-grafted surfaces exhibit strong, reversible temperature-modulated hydrophobic interactions, facilitating baseline separations of
steroids and
peptides in aqueous milieu without changes in the mobile phase pH and high ionic strength.