Cwm Cees Bastiaansen

Preparation, structure and properties of uniaxially oriented polyethylene-silver nanocomposites

Uniaxially oriented composites of high-density polyethylene and silver nanoparticles were prepared using solution-casting, melt-extrusion and solid-state drawing techniques. The absorption spectrum in the visible wavelength range of the drawn nanocomposites was observed to strongly depend on the polarisation direction of the incident light. For instance, the nanocomposites appear bright yellow or red when the vibration direction of linearly polarised light is perpendicular or parallel, respectively, to the drawing axis. The optical anisotropy of the drawn nanocomposites originates from uniaxially oriented, pearl-necklace type of arrays of nanoparticles of high aspect ratios. The absorption spectrum of the nanocomposites can be shifted to higher wavelengths using appropriate annealing procedures. The annealing results in an increased size of the primary silver particles, due to Ostwald ripening, and consequently a range of polarisation-dependent colours can be generated in the drawn nanocomposites.

Solid-state replication of relief structures in semicrystalline polymers

The feasibility of structuring the surfaces of semicryst. polymers is explored using poly(tetrafluoroethylene-co-hexafluoropropylene) as a model material. Hot embossing was performed in the polymer melt at 330 Deg after which the samples were quenched at room temp. [on SciFinder (R)]

Studies on a new radiopaque polymeric biomaterial

A new radiopaque polymeric biomaterial has been synthesized. The material, which actually represents an entire family of analogous radiopaque materials, is composed of 2-(p-iodobenzoyl)-ethyl methacrylate (compound 1, 21 mol%), methyl methacrylate (MMA, 60 mol%), and 2-hydroxyethyl methacrylate (HEMA, 19 mol%). The terpolymer was synthesized in a radical polymerization reaction at elevated temperature in N,N-dimethylformamide (DMF). The product was subjected to a set of physicochemical characterization techniques (gel permeation chromatography, 500 MHz 1H NMR in deuterated dimethylsulphoxide (d6-DMSO) solution, differential scanning calorimetry, dynamic water contact angle measurements), as well as to an in vitro thrombogenicity assay. Furthermore, scanning electron microscopy was used to study interactions of the material with blood platelets. The most important findings are: (a) the material is a genuine polymer with excellent X-ray visibility, even in the form of thin (0.4 mm) drawn fibres. This was established under realistic conditions. (b) The material exhibits low in vitro thrombogenicity, i.e. comparable to polyvinyl chloride, which is known as a passive material. These observations lead us to the suggestion that this type of radiopaque polymer holds promise with respect to application as a construction material for a new type of endovascular stent. This could be relevant in particular to stents to be used in conjunction with percutaneous transluminal coronary angioplasty (PTCA), also known as Dottering. Currently there is a clear trend away from metallic stents towards all-polymeric stents, since the latter have superior biocompatibility.(ABSTRACT TRUNCATED AT 250 WORDS)

Surface-relief and polarization gratings for solar concentrators

Transmission gratings that combine a large diffraction angle with a high diffraction efficiency and a low angular and wavelength dispersion could be used to collect sunlight in a light guide. In this paper we compare the diffractive properties of polarization gratings and classical surface-relief gratings and explore their possible use in solar concentrators. It is found that polarization gratings and surface-relief gratings have qualitatively comparable diffraction characteristics when their thickness parameters are within the same regime. Relatively large grating periods result in high diffraction efficiencies over a wide range of incident angles. For small grating periods the efficiency and the angular acceptance are decreased. Surface-relief gratings are preferred over polarization gratings as in-couplers for solar concentrators.

Scattering birefringence polarizers based on oriented blends of poly(ethylene terephthalate) and core–shell particles

Here, we present the results on the optical characteristics of polymeric, linear polarizers produced from oriented, two-component, polymer blends. By a proper selection of materials and drawing conditions, the refractive index of the dispersed phase of the blend is matched with the ordinary refractive index of the birefringent continuous phase while, at the same time, a large refractive index mismatch is generated in the perpendicular direction. The films are, therefore, transparent or opaque, dependent on the polarization direction of the incident light and act as linear polarizers with a high contrast ratio (≈1000) between the transparent and opaque state. These polarizers are all-polymer-based linear polarizers that operate on the anisotropic scattering of light, instead of anisotropic absorption, which offers some unique features and advantages.

Monomers and polymers in a centrifugal field: a new method to produce refractive-index gradients in polymers.

A new method is presented to generate and to fixate compositional gradients in blends of two miscible and amorphous polymers. A compositional gradient is introduced into a solution of a polymer in a monomer by use of a centrifugal field, and this gradient is subsequently fixated by polymerization of the solvent-monomer. It is shown that substantial compositional and refractive-index gradients can be generated in miscible, highly transparent, amorphous polymer blends by a proper selection of materials and processing conditions. Moreover, it is shown that these materials and processes are potentially useful for producing optical components such as self-focusing lenses.

Linear Polarizers Based on Polymer Blends: Oriented Blends of Poly(Ethylene-2,6-Naphthalenedicarboxylate) and a Poly(Styrene/Methylmethacrylate) Copolymer

The optical properties of linear polarizers based on blends of poly(ethylene-2,6-naphthalenedicarboxylate) and a poly(styrene/methylmethacrylate) copolymer are presented. In the oriented blends, the refractive index of the dispersed phase is matched with the ordinary refractive index of the birefringent continuous phase while, a large refractive index mismatch is simultaneously generated in the perpendicular direction. The films are therefore transparent or opaque depending on the polarization direction of the incident light and act as a linear polarizer. In the non transparent state, the incident light is mainly scattered in the backward direction (±80%), which potentially enhances the yield of transmitted polarized light if the backscattered light is recycled in a suitable device. This latter feature is useful, for instance, in display applications where a high brightness or energy efficiency is desired.

Linear polarizers based on oriented polymer blends

Traditionally, birefringent, double refracting crystals and, more commonly, sheet polarizers based on oriented polymers comprising dichroic additives are employed to generate linearly polarised light. Nowadays, these sheet polarizers are widely used in flat panel displays where they serve a dual purpose; a first polarizer is used to generate linearly polarised light and a second polarizer (analyser) generates visual perception of the switching of the polarisation direction of the light by electro-optical cells containing a twisted nematic or super twisted nematic material. A dichroic polarizer which generates perfectly, linearly polarised light absorbs at least fifty percent of the incident, unpolarized light and this light is transferred into thermal energy. Consequently, the brightness of flat panel displays is limited by the polarizers and the polarizers exhibit excessive heating when used in combination with high intensity light sources (e.g. in projection displays). These limitations of dichroic polarizers have triggered an extensive research effort into new optical components to produce linearly polarised light. Here we introduce uniaxially oriented, polymer blend sheet-polarisers that allow for the generation and analysis of polarised light through anisotropic scattering. By proper selection of materials and processing conditions, phase-segregated polymer blends are produced in which the refractive index of the dispersed phase matches the ordinary refractive index perpendicular to the orientation direction of a birefringent continuous phase, while, simultaneously, a large mismatch exists between the refractive indices parallel to that orientation direction. The refractive index mismatch leads to a scattering of light polarized in this direction and an opaque (white) appearance. The other polarization direction encounters equal refractive indices between the two phases and will therefore be transmitted resulting in a transparent appearance. Thus polarizers are produced based on the selective scattering of one polarization direction with contrast ratios exceeding 1750 in direct transmittance; which, in specific configurations, allow for the recycling of the unwanted (scattered) polarization direction to enhance the efficiency to produce linearly polarized light.

Diffractive flat panel solar concentrators of a novel design

A novel design for a flat panel solar concentrator is presented which is based on a light guide with a grating applied on top that diffracts light into total internal reflection. By combining geometrical and diffractive optics the geometrical concentration ratio is optimized according to the principles of nonimaging optics, while the thickness of the device is minimized due to the use of total internal reflection.

Novel Polarized-Light Emitting Polymer Systems

A novel, polymer bilayer illumination system is presented from which linearly polarized light is emitted. Separation of the two polarization directions is achieved by total internal reflection of the undesired light component at the polymer-polymer interface. Model systems comprising optically isotropic polystyrene (PS) sheets and oriented, birefringent poly(ethylene terephthalate) (PET) films with a relief structure to direct the light out of the systems displayed high polarizing capabilities: contrast ratios of over 10 for viewing angles between -10° and +20° were recorded in case of uncollimated incoming light. The use of a collimated light source resulted in contrast ratios of 20 up to over 40 over a viewing angle regime of -20° to +15°.