Determination of Molecular Orientation in Biaxially Oriented Ultrathin Films

Abstract

Biaxial orientation in ultrathin films is characterized by a preferential orientation of the main molecular axis in the plane of the film in addition to its orientation with respect to the normal of the film. In this paper, analytical expressions allowing the calculation of the molecular orientation in biaxially oriented films from their anisotropic optical constants are presented for the first time. These expressions have been used to calculate the molecular orientation in multilayers of poly(γ-benzyl-L-glutamate) and to determine the angles between the main molecular axis and the different transition moments used (R angles). Using the optical constants determined by Buffeteau et al.1 for PBG multilayers, we have found that the tilt angle of the PBG helices with respect to the monolayer normal is 89°and that the azimuthal angle in the plane is 57°. The calculated R angles for the carbonyl stretching mode of the ester group and the amide I and amide II modes of the amide group are 49, 34 and 74°, respectively. The analytical expressions presented in this paper have also been used to calculate the molecular orientation in Langmuir-Blodgett monolayers of an equimolar blend of poly(D-lactide) and poly(L-lactide). The optical constants of a monolayer of the polylactide mixture determined using p-and s-polarized transmittance and p-polarized reflection-absorption infrared spectra have shown that the polylactide helices have a tilt angle of 81°and an azimuthal angle of 56°.

Water Barrier Properties in Biaxially Drawn Poly(lactic acid) Films

“…In opposition the WAXS pattern obtained from flat-on view (SB3e) shows an anisotropic structure as revealed by the presence of the two intensity reinforcements around the equator. Since these two equatorial arcs are ascribed to the (200)/(110) diffraction planes, this indicates a preferential orientation of the crystals in the plane of the film . As a consequence, these results obtained for the SB drawing mode show that a strain-induced crystallization phenomenon occurs above λ = 2, the crystallinity degree increasing with increasing strain, and that the strain-induced crystals have an orthotropic orientation.…”

Structure and Orientation of Interfacial Proteins Determined by Sum Frequency Generation Vibrational Spectroscopy

“…7.3 (Pelletier, Laurin, Buffeteau, & Pézolet, 2004). 7.3 (Pelletier, Laurin, Buffeteau, & Pézolet, 2004).…”

Understanding Factors Affecting Alignment of Self-Assembling Nanofibers Patterned by Sonication-Assisted Solution Embossing

“…f φ can be thought of as a two-dimensional order parameter quantifying the in-plane alignment of directors along the x axis and is used here as the primary figure of merit. The orientation parameters cannot be determined exactly from the three polarized spectra alone, but upper and lower bound values of f φ can be calculated assuming cylindrical symmetry about the nanofiber axis and specific values of α and θ (see the Supporting Information): f normalφ , min = K x − K y K x + K y f normalφ , max = K x − K y K x + K y − 2 K z The spectroscopic model assumes that the material is optically isotropic and that variations in reflectance and refractive index with wavelength are negligible, , but the calculated values of f φ are useful as figures of merit by which the effects of different experimental parameters may be compared within the realm of the proposed molecular model.…”