Showing papers by "Christoph Weder published in 2000"

Single-Molecule Imaging Revealing the Deformation-Induced Formation of a Molecular Polymer Blend

Abstract: Photoluminescence microscopy of conjugated polymer molecules in a polyethylene host has been applied to monitor the transition of a phase-separated polymer blend into a molecular dispersion induced by solid-state tensile deformation. Statistical analysis of conjugated polymer cluster sizes as a function of the degree of matrix deformation shows that phase-separated domains of conjugated polymer transform into smaller clusters and single molecules as the degree of matrix deformation increases. Concomitantly, the conjugated guest molecules tend to adopt the preferential orientation of the surrounding matrix. We demonstrate that single-molecule detection can be readily extended and applied to probing molecular dispersion, orientation, and morphology in polymer−polymer blends.

Synthesis and optical properties of novel poly(p-phenylene ethynylene)s

Abstract: In order to explore the influence of chemical modifications on the photophysical properties of poly(p-phenylene ethynylene)s (PPEs), a series of PPE-copolymers was synthesized employing Heck-type cross-coupling reactions. UV/Vis absorption and photoluminescence experiments clearly demonstrate that the design of PPE-copolymers which comprise conjugated segments of well-defined length and (aliphatic) spacers in a strictly alternating fashion allows to tune the bandgap to higher energies, and thus the absorption and emission maxima to shorter wavelengths. The derivatization of the PPE backbone with electron-withdrawing substituents, by contrast, is found to be significantly less effective and only leads to comparably small shifts in the absorption and emission spectra.

Poly(p‐phenylene alkylene)s – A forgotten class of polymers

Abstract: Within the wealth of hydrocarbon polymers, poly(p-phenylene alkylene)s (“alkarotics”) hold a special position since they have been a long forgotten class of hydrophobic polymers. This is somewhat surprising, since the cornerstones of this polymer family cover extremely broad materials properties and the few known representatives attract attention with very favorable characteristics. In the course of this article, four new representatives of this family are presented. Whereas poly(p-phenylene octylene) (PPPO; 90°C), poly(p-phenylene hexylene) (PPPH; 120°C) and poly(p-phenylene propylene) (PPPPr; 110–130°C) have surprisingly low melting temperatures, the highly crystalline poly(p-phenylene butylene) (PPPB), melting between 200 and 225°C, meets many of the requirements that are essential for a novel, hydrophobic, processable, engineering polymer. In connection with the efforts to tailor the melting temperature of these polymers, a simple, semi-empirical methodology to estimate melting temperatures of unknown representatives of homologous series of polymers was developed and verified. By means of this approach, the melting temperatures of PPPH and PPPB could be predicted with remarkable accuracy. In addition, it was shown that the method is not restricted to the present alkarotic polymers, but it seems to have a rather broad range of applications as shown by the successful description of the polymer series, including various liquid-crystalline hydrocarbon polymers and different polyamides.

Photoluminescent display devices having a photoluminescent layer with a high degree of polarization in its absorption, and methods for making the same

Abstract: Display devices are disclosed of a high brightness, high contrast and large viewing angle that comprise at least one thin, photoluminescent layer that is characterized in a high degree of polarization in its absorption. Also disclosed are methods for making same.

Polarizing energy transfer in photoluminescent polymer blends

Abstract: The occurrence of polarizing energy transfer in uniaxially oriented polymer blend films is investigated. A poly(2,5-dialkoxy-p-phenylene ethynylene) derivative (EHO-OPPE) and poly[2-methoxy-5-[2′-ethyl-hexyloxy]-p-phenylene vinylene] (MEH-PPV) were used as the acceptors, and various sensitizers were used as donors. Some of the properties of the chromophores required for polarizing energy transfer to occur efficiently are elucidated, such as form-isotropy and thermal characteristics. The energy transfer efficiency is quantified, and for the present, optimized systems, values as high as 85% were demonstrated.

Phase behavior and anisotropic optical properties of photoluminescent polarizers

Abstract: The phase behavior and anisotropic optical properties of tensile deformed blends of a photoluminescent polymer guest in an ultra-high molecular weight polyethylene matrix were studied on the level of single molecules by means of scanning confocal optical microscopy It is shown that upon tensile deformation of the blends, the system transforms from a phase-separated system into a quasi-molecular solid solution The influence of this phase transition on the anisotropic optical properties of oriented blend films was also investigated with polarized steady-state photoluminescence spectroscopy We show that well-dissolved guest molecules tend to reach higher degrees of orientation at lower draw ratios of the blend films compared to guests that phase-separate from the matrix polymer Dichroic ratios in emission in the range of 50 were observed in optimized blend films based on photoluminescent oligomers and linear low density polyethylene

Process for forming photoluminescent polarizers

Abstract: A process for the manufacture of PL polarizers that exhibit a high dichroic ratio in absorption, and which preferably have been produced by applying minimal mechanical deformation is disclosed. The invention also discloses a process for the manufacture of PL polarizers that exhibit a high dichroic ratio in absorption and emission, and which preferably have been produced by applying minimal mechanical deformation. The process comprises the steps of a) providing a blend comprising at least one photoluminescent dye and at least one carrier polymer by melt-mixing, and b) melt-processing said blend into a body having a first shape, and c) anisotropically distorting the first shape of the body to yield said photoluminescent polarizer.