title: Measuring molecular order in poly(3-alkylthiophene) thin films with polarizing spectroscopies.
abstract: We measured the molecular order of poly(3-alkylthiophene) chains in thin films before and after melting through the combination of several polarized photon spectroscopies: infrared (IR) absorption, variable angle spectroscopic ellipsometry (SE), and near-edge X-ray absorption fine structure (NEXAFS). The data from the various techniques can be uniformly treated in the context of the dielectric constant tensor epsilon for the film. The combined spectroscopies allow determination of the orientation distribution of the main-chain axis (SE and IR), the conjugated pi system normal (NEXAFS), and the side-chain axis (IR). We find significant improvement in the backbone order of the films after recrystallization of the material at temperatures just below the melting temperature. Less aggressive thermal treatments are less effective. IR studies show that the changes in backbone structure occur without significant alteration of the structure of the alkyl side chains. The data indicate that the side chains exhibit significant disorder for all films regardless of the thermal history of the sample.
authors.affiliation: Surface and Microanalysis Science Division, Chemical Science and Technology Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, Mail Stop 8372, Gaithersburg, Maryland 20899, USA.
authors.forename: Marc C
authors.initials: MC
authors.lastname: Gurau
authors.forename: Dean M
authors.initials: DM
authors.lastname: Delongchamp
authors.forename: Brandon M
authors.initials: BM
authors.lastname: Vogel
authors.forename: Eric K
authors.initials: EK
authors.lastname: Lin
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Fischer
authors.forename: Sharadha
authors.initials: S
authors.lastname: Sambasivan
authors.forename: Lee J
authors.initials: LJ
authors.lastname: Richter
mesh_terms: D000465:Algorithms; D003460:Crystallization; D008956:Models, Chemical; D015233:Models, Statistical; D008968:Molecular Conformation; D017785:Photons; D011108:Polymers / Q000737:chemistry*; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013379:Substrate Specificity; D013696:Temperature; D013876:Thiophenes / Q000737:chemistry*; D014965:X-Rays
chemical_list: D011108:Polymers; D013876:Thiophenes