Dr. Charles Medom Hansen (born 1938 in Louisville, Kentucky) is an American-born scientist with Danish ancestry who is now a Danish citizen living in the Copenhagen area. After a degree (1961, Louisville) and Masters (1962, Wisconsin) in chemical engineering, Hansen worked for his Ph.D. at the Technical University of Denmark, initially on the problems of solvent retention in polymers, starting his lifetime interest in diffusion science. However, the problems of predicting the compatibility of solvents with polymers took over, leading him to overcome the problems of the then-popular Hildebrand solubility parameter by dividing Hildebrand's single parameter into three components: dispersion, polar and hydrogen bonding. His 1967 doctoral thesis (Dr. techn.) provided the basis for what came to