Quantitative calculation of the orientation angles of adsorbed polyamides nanofilms

Polyamides (PA) PA66, 610 and 612 were adsorbed as thin films on functionalized substrates. The conformational changes after adsorption are studied. New conformations due to the rotation of diamine/diacid planes were evidenced by infrared reflection absorption spectroscopy (IRRAS) and polarization modulation IRRAS (PM-IRRAS). The study of some infrared vibrators, which have a well defined transition moment direction with respect to the principal chain axis, allows us to access a qualitative information on the molecular orientation of PA chains. In this paper, we will discuss the possibility to obtain quantitative data on polyamide conformations on the basis of PM-IRRAS experiments. Values of orientation angles of diamine/diacid planes versus surface plane were determined. Similar angles are found in the four cases of gold, OH, NH2 and COOH functionalized substrates, and for the three PA. Twist angle of about 20° is found between diamine and diacid planes. The chain orientation angles and conformations obtained do not depend on the substrate functionality and thus suggest that they are only the consequence of an adsorption effect.