In situ α-alumina hydrophobization dynamics at acid pH: effectiveness limitations of short-chain amphiphilic molecules

Abstract

The present work highlights that α-alumina hydrophobicity (attained by the in situ modification of its surface properties with water soluble organic monoacids) cannot be increased by using molecules with low acidity (pKa) values due to the alumina zeta potential profile at pHs below approximately 4. In order to certify this statement, the effects of short-chain fatty acids and fluorinated ones on the alumina contact angle (θe) with water were analyzed. It is also pointed out that the θe values derived from the experiments carried out using fluorinated acids are the highest possible when monoacid surfactants are added in α-alumina suspensions in acidic pH. This result indicates that there is another constraint to the in situ hydrophobization procedure, which was not previously elucidated or fully settled in literature.