XPS and FTIR surface characterization of TiO2 particles used in polymer encapsulation

The surfaces of hydrophilic (P25) and hydrophobic (T805) TiO2 particles wer e characterized by X-ray photoelectron spectroscopy (XPS) and Fourier trans form infrared spectroscopy (FTIR) to gain a better understanding of the ads orption mechanism of OLOA 370 (polybutene-succinimide pentamine) on TiO2 pa rticles dispersed in styrene monomer prior to miniemulsion encapsulation po lymerizations. XPS analysis revealed that both the P25 and T805 TiO2 partic les had significant amounts of hydroxyl groups on their surfaces. The XPS r esults showed that the surface hydroxyl concentration on the hydrophilic (P 25) particles was 3.3 OH/nm(2), whereas the trimethoxy octyl silane (TMOS)- surface-modified hydrophobic (T805) particles unexpectedly contained 6.6 OH /nm(2). This apparent increase in the hydroxyls was attributed to hydrolysi s of -OCH3 on the TMOS. The majority of these groups, however, were apparen tly either not acidic or not accessible to the OLOA 370 in adsorption studi es, where the concentration of reactive hydroxyls on the T805 particles was estimated to be 1.8 OH/nm(2). FTIR analysis showed the existence of reacti ve hydroxyl groups on the surfaces of both the hydrophilic and hydrophobic TiO2 particles. Exposure of the particles to ammonia indicated a large redu ction in the hydroxyl groups as detected by in situ FTIR measurements. New peaks characteristic of N-H stretching bands indicated strong interactions between the ammonia and hydroxyl groups on the surface of the TiO2 particle s.