Conformation of chemisorbed oleate at a calcite surface

The surface chemistry of the calcite/oleate flotation system was examined b y in situ FT-NIR/IRS. Spectra of combination and overtone bands of aliphati c stretching vibrations revealed gauche/trans conformational changes that o ccurred solely as a function of temperature. The conformational changes wer e attributed to the simple "melting" behavior associated with phase transit ions. It was concluded that chemisorbed oleate at calcite surfaces is gel-l ike at temperatures below 22 degreesC, resembles a coagel between 22 degree sC and 31 degreesC, and becomes micelle-like at temperatures above 31 degre esC. By comparison, chemisorbed oleate at fluorite surfaces also undergoes these phase transitions but is additionally dependent on adsorption density . The conformational changes were observed at high chemisorption densities (>2.0x10(-10) mol/cm(2)) and attributed to molecular forces, primarily van der Waal's interactive forces, among neighboring chemisorbed oleate molecul es. Similar analysis of in situ FT-NIR/IRS spectra of surface-precipitated calcium dioleate at calcite surfaces did not exhibit this behavior thereby confirming that surface-precipitated calcium dioleate remains in an all-tra ns conformation. The results help explain why surface polymerization is not observed at calcite surfaces but is observed at fluorite surfaces.