309 1. IntroductIon Ultrathin ilms are becoming important from the point of view of both basic physics and technology. Among the family of environmental friendly biodegradable polymers, poly (L lactic acid), PLLA (-[CH 2 CH(CH 3 )COO] n -) - has been attracting much attention because of many advantages in its intrinsic properties. For example, the polymer exhibits biocompatibility 1-3 , and so has importance in medical industry for applications such as drug delivery systems, implant materials for bone ixation 4 , nuclear oncology and surgical suture 5-15 . But the main reason behind its debut in large-scale production is found in its tremendous potential in traditional applications where thermoplastics are employed, such as the production of disposable products for the packaging and ilm industries 16 . PLLA is also melt-spinable and has very good iber- and ilm-forming properties. Recently, applications involving high-strength ibers and ilms were reported 17 . But there is no detail of information prevalent in the literature on the role of annealing on the morphological state with reference to the vibration spectroscopic features. The objective of this study is to investigate the effect of annealing on the structural variation in the PLLA ilm. The morphology is observed by Fourier transform infrared (FTIR) and Raman measurement. The former is utilized to study the structural variation and the latter is to investigate the conformation of crystallite form with the effect of temperature. FTIR and Raman measurements on PLLA ilms mainly focused on the identiication of characteristic bands 19-21 . 2. ExpErImEnt PLLA was procured from Sigma Aldrich and used in as- received form. The ultra thin ilms of PLLA (Mw-125, 000) were prepared by spin coating technique. Prior to deposition Si wafer was ultrasonically cleaned in acetone followed by iso-propanol and Milli-Q water (ca. 15 MΩcm). PLLA was dissolved in chloroform to make a uniform solution (70 mg/10 ml). After that PLLA thin ilm of different thicknesses were prepared by spin deposition technique by means of varying concentration and rpm rate. All ilms were grown under identical conditions in air on Si (100) substrate. Films of various thicknesses were prepared as 15 nm, 25 nm, 30 nm, and 40 nm ilms are designated as S 1 , S 2 , S 3 and S 4 respectively. For the purpose of study the effect of temperature on PLLA ilms, similar ilm of thickness circa 40 nm was also drawn on cleaned Si wafer coated with Au buffer layer. Film was grown under identical conditions in air (4000 rpm, 60 s) and is designated as S 5 . To meet the requirement of standardization of surface analysis of the ilm, x-ray relectivity experimental measurements have Inluence of Temperature on the Conformational Guided Physical Properties of Ultrathin Films of PLLA Pallavi Pandit, Mandira Banerjee * , G.S. Mukherjee # , Rakesh Parikh @ , U.P. Deshpanday ! , and Ajay Gupta $ School of Physics, Devi Ahilya University, Indore-452 001, India # Defence Scientiic Information and Documentation Centre, DRDO, New Delhi-110 054, India @ Raja Ramanna Centre for Advanced Technology, Indore-452 013, India ! UGC-DAE, Consortium for Scientiic Research, Indore-452 001, India $ Center for Spintronic Materials, Amity University, Noida-201 303, India * E-mail: mandira_bm@rediffmail.com AbsTrACT Poly (L lactic acid) (PLLA) ultrathin ilms of various thicknesses were prepared by spin coating method and investigated by using vibrational spectroscopic techniques such as FTIR and Raman. The analysis has been done in two parts: irst one is veriication of structural mode to understand the visibility of characteristic band to conirm the PLLA structure; where interestingly, as the thickness of the ilm increased, the structural features were found to be more explicit. The second part of the study was to observe the features of the ilm having been annealed for 1 h in two separate temperatures, one at speciic annealing temperature 120 °C and the other at 160 °C to enable PLLA chains to reorient to get crystallized from its soften state at two such speciic temperatures. The isothermal crystallization behavior of PLLA ilm at 120 °C and 160 °C from the melt was monitored by FTIR as well as Raman spectroscopies. More importantly, the band at 921 cm -1 corresponds to α crystalline phase of PLLA has been observed even in this ultrathin ilm with the effective application of temperature as selected in this study. Keywords: Ultrathin ilm, biopolymer, X-ray relectivity, PLLA Received 1 November 2013, revised 3 March 2014, online published 20 May 2014 Defence Science Journal, Vol. 64, No. 3, May 2014, pp. 309-313, DOI : 10.14429/dsj.64.7329  2014, DESIDOC