What is PA?
Parking area (PA) is the average surface area containing one functional group, calculated from the diameter of the particles (in microns) and the titrated milli-equivalents (of acid, sulfate, hydroxyl, or amino groups) per gram of polymer solids. The higher the PA value, the fewer functional groups will be found on a given area of particle surface. For particles with carboxyl groups, a low PA (below about 30) indicates a hydrophilic surface with many COOH groups available for covalent coupling. A high PA (above about 60) means a more hydrophobic surface with less coupling capability.
