Effect of postgrafted alkyl chains on the wettability of hydrophilic poly(amidoamine)-grafted nano-sized silica

In order to control the surface wettability of hyperbranched hydrophilic poly(amidoamine) (PAMAM)-grafted nano-sized silica, hydrophilic alkyl chain (C n H2n+1) with different chain lengths (n = 4, 8, 15) were postgrafted onto PAMAM-grafted silica by the reaction of terminal amino groups of PAMAM grafted on the silica surface with alkyl acid chlorides (C n H2n+1-COCl). The postgrafting of C n H2n+1-COCl increased with increasing PAMAM grafting and alkyl chain length of C n H2n+1-COCl. However, the terminal amino groups of PAMAM-grafted silica used for the postgrafting of C n H2n+1-COCl decreased with increasing chain length. This may be due to the steric hindrance between terminal amino groups of PAMAM-grafted silica and C n H2n+1-COCl: the steric hindrance is considered to increase with increasing chain length of C n H2n+1-COCl. The surface wettability was estimated by contact angle measurement for water and methanol wettability. As a result, it was found that contact angle and methanol wettability incre...