The Orientation of Semifluorinated Alkanes Attached to Polymers at the Surface of Polymer Films

Abstract

The surface molecular orientation of a liquid crystalline (LC) layer made up of semifluorinated (SF) single side groups [−CO−(CH2) x - 1−(CF2) y F] (single SF groups) attached to polyisoprene homopolymer or the isoprene block of a styrene−isoprene diblock copolymer was determined by analyzing the partial electron yield C-edge NEXAFS signal. The results show that the surfaces of thin SF polymer films are covered with a uniform layer, consisting of the SF−LC groups whose average −CF2− tilt angle with the surface normal lies in the range 29−46°. This is in direct contrast to the bulk, where the directors of the SF−LC mesogens are aligned parallel to the polystyrene/SF−polyisoprene interface of the block copolymers. This average tilt angle increases with increasing the length of the −(CH2) x - 1− group (x increases) but decreases with increasing the length of the −(CF2) y − part of the molecule (y increases) at constant x.

Interrogation of “surface,” “skin,” and “core” orientation in thermotropic liquid‐crystalline copolyester moldings by near‐edge X‐ray absorption fine structure and wide‐angle X‐ray scattering

“…Details of the technique as applied to semifluorinated polymers appear elsewhere. [15][16][17] The PEY spectra for the carbon K edge were obtained for each sample over the incident angles relative to the sample surface of 208, 308, 408, 558, 608, 708, 808, and 908, normalized in the energy range of 280-315 eV, and the relative intensities, I(y), for the 1s?p* peak for the C¼ ¼C bonds were recorded. Figure 5 Data analysis procedure used to extract azimuthal intensity scans describing the scattering contributions due to shear (''skin'') and extension (''core'').…”

“…8 This convention is based upon a configuration in which the perpendicular relationship for the coordinates of the analysis is taken relative to the normal to the sample surface. This convention has been used by several authors, [15][16][17]20 including previous work on the surface orientation in TLCPs. 7 Under this convention, an average uniaxial orientation parameter, S a , is defined as:…”

Characterization of the skin orientation of thermotropic liquid‐crystalline copolyester moldings with near‐edge X‐ray absorption fine structure

“…The capabilities of this beam line have been described elsewhere. 15 The beam-line soft X-rays had a degree of polarization of about 85% and an incident energy photon resolution and approximate intensity of 0.1 eV and 5 ϫ 10 10 photons/s, respectively. The NEXAFS PEY signal was collected with a channeltron electron multiplier fitted with an electrostatic three-grid high-pass electron kinetic energy filter.…”

“…Details of the technique as applied to semifluorinated polymers appear elsewhere. [15][16][17] The PEY spectra for the C K edge were obtained for each sample over the values with respect to the sample surface of 20, 30, 40, 55, 60, 70, 80, and 90°, normalized in the energy range of 280 -315 eV, and the relative intensities, I(), for the 1s 3 * peak for the CAC bonds were recorded. With the technique of Stö hr and Samant, 13 the PEY I() value is predicted to take the following form, regardless of the degree of orientation:…”

Self‐Organized Buffer Layers in Organic Solar Cells

“…This hypothesis is also supported by previous studies of the surface orientation of perfluoroalkyl groups in copolymer films. [26] Figure 5b shows the PYS results of the P3HT:PCBM-blended films with and without F-PCBM. The IP of P3HT is approximately 4.7 eV, which is close to the reported values (4.65-5.1 eV).…”