Quantitative calculation of the orientation angles of adsorbed polyamides nanofilms Tamara Elzein * , Maurice Brogly, Jacques Schultz Institut de Chimie des Surfaces et Interfaces-CNRS, 15, rue Jean Starcky, 68057 Mulhouse, France Received 27 January 2003; received in revised form 18 March 2003; accepted 2 April 2003 Abstract 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, NH 2 and COOH functionalized substrates, and for the three PA. Twist angle of about 208 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. q 2003 Elsevier Science Ltd. All rights reserved. Keywords: Orientation; PM-IRRAS; Nanofilms 1. Introduction Interfacial characterization is of great interest for the understanding of the polymer adsorption in terms of chain orientation and conformation [1–7]. The creation of surfaces with specific applications could be done by adsorbing molecules with preferential orientation and, in some cases, different conformations relative to the bulk. In a recent work [8], we have showed that adsorbed polyamides (PA) PA66, 610 and 612, does not preserve their bulk conformations (Scheme 1). A twisted conformation between the diacid/diamine planes, initiated by adsorption, was evidenced. The quantitative calculation of these inter-planes orientation angles becomes possible by polarization modu- lation infrared reflection absorption spectroscopy (PM- IRRAS). In this work we will discuss PM-IRRAS results and calculated values of orientation angles of PA66, 610 and 612 adsorbed on gold, and OH, NH 2 and COOH functionalized gold substrates. 2. Experimental section 2.1. Materials The three PA were purchased from SIGMA ALDRICH Co. as 2 – 5 mm pellets. These PA are characterized by their T g ; T f ; T B ; and X c ; respectively, the glass transition temperature, melting and Brill temperatures and the degree of crystallinity [8]. Trichloroethanol (TCE) 99%, purchased from SIGMA ALDRICH, a common solvent of these three PA was used for the preparation of polyamide solutions (5 g/l). Thin films of PA were spin coated from solutions, with an acceleration of 10 3 rpm/s, a velocity of 2500 rpm and during 60 s, on the chosen substrates. For sample preparation, the detailed procedure was extensively described in a previous study [8]. Gold coated substrates were prepared by using glass slides cleaned with ethanol, and treated by Argon plasma for 3 min at a power of 80 W. 3-Mercaptopropyltriethoxysilane 0032-3861/03/$ - see front matter q 2003 Elsevier Science Ltd. All rights reserved. doi:10.1016/S0032-3861(03)00293-3 Polymer 44 (2003) 3649–3660 www.elsevier.com/locate/polymer * Corresponding author. Tel.: þ 33-3-89-60-87-78; fax: þ33-3-89-60-87- 99. E-mail address: tamara_elzein@yahoo.fr (T. Elzein).