Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (57) (entfernen)
Schlagworte
- Polymer (57) (entfernen)
Organisationseinheit der BAM
- 1 Analytische Chemie; Referenzmaterialien (7)
- 1.2 Biophotonik (7)
- 6 Materialchemie (6)
- 6.5 Synthese und Streuverfahren nanostrukturierter Materialien (4)
- 5 Werkstofftechnik (2)
- 6.3 Strukturanalytik (2)
- 8 Zerstörungsfreie Prüfung (2)
- 8.5 Röntgenbildgebung (2)
- 5.2 Metallische Hochtemperaturwerkstoffe (1)
- 5.3 Polymere Verbundwerkstoffe (1)
Flexible, niedrigdichte Schäume aus Biokunststoffen im Extrusionsverfahren herzustellen war bisher industriell noch nicht möglich. Im Verarbeitungstechnikum Biopolymere des Fraunhofer IAP wurde in einem Projekt die Eignung von PBS-basierten Biokunststofftypen für Schaumanwendungen erforscht und weiterentwickelt.
Ablation experiments with ultrashort laser pulses (pulse duration 150 fs, wavelength 800 nm) on polymers (PC, PMMA) relevant for biomedical technology have been performed in air. The lateral and vertical machining precision was evaluated by optical, atomic force and scanning electron microscopy. The ablation threshold reaches values in the range of 0.52.5 J/cm2 and depends significantly on the number of laser pulses applied to the same spot. The hole diameters are influenced by the laser fluence and the number of laser pulses. The relation between the ablation threshold and the number of laser pulses applied to the same spot is described in accordance with an incubation model.
In order to develop simple and versatile procedures for the preparation of red emissive particles, various one-step swelling procedures for the loading of fluorophores into nanometer- and micrometer-sized polystyrene particles were systematically assessed. Parameters studied for model dyes from common dye classes include the composition of the swelling medium, dye charge and polarity, dye concentration, and particle surface chemistry. The dye loading procedures were compared based upon the efficiency of dye incorporation, fluorescence intensity, and colloidal stability of the resulting particles as well as the absence of dye leaking as determined by absorption and fluorescence spectroscopy, flow cytometry, and measurements of zeta potentials. In addition, for the first time, the influence of the amount of incorporated dye on the absolute fluorescence quantum yield and brightness of the fluorescent particles was investigated for selected chromophores in differently sized particles using a custom-made calibrated integrating sphere setup. Our results demonstrate the general suitability of these one-step loading procedures for efficient particle staining with neutral, zwitterionic, and charged fluorophores like oxazines, coumarines, squaraines, xanthenes, and cyanines emitting in the visible and near infrared. Dye polarity was identified as a suitable tool to estimate the loading efficiency of fluorophores into these polymer particles.
The thickness measurement of transparent layers with optical techniques is very problematic. The observed deviations can easily reach 100% of the layer thickness to be measured. In order to analyse these deviations, tactile reference measurements have been developed. The proposed method is based on contact mode measurements with low contact pressure. With stylus instruments, this can be realized either by using the recommended tip radius of 2 µm and very small probing forces in the micronewton range (and low scanning speeds of 50 µm s-1) or by using the recommended probing force of 750 µN, but a large probing tip radius. Three metal layers on silicon or silicon dioxide and two polymer resist materials on a thin chromium adhesive layer on silicon are used as artefacts. The comparison of the optical measurements with the tactile reference values disclosed deviations of the optical measurements of up to 195% of the layer thickness. Layer thicknesses were between 200 nm and 4 µm. This paper analyses the deviations of two white light interference microscopes, one phase shift interference microscope, one confocal microscope, one autofocus sensor, a chromatic sensor, an interferometric film thickness sensor and one spectroscopic ellipsometer. Simple and well-known expressions for the description of the observed deviations are presented and discussed. The order of magnitude of the observed deviations can be described well by these correction formulas but further investigations are necessary in order to better understand the systematic deviations of optical surface measuring instruments on non-cooperating surfaces.
A facile and convenient approach for the synthesis of core–shell particles via emulsion polymerization is presented. The shell consists of poly(vinylidene fluoride) (PVDF) and the core of poly(methyl methacrylate) (PMMA), poly(glycidyl methacrylate) (PGMA) or poly(methyl acrylate) (PMA). In a first step, a non-fluorinated (meth)acrylate monomer is polymerized in the emulsion to produce poly(meth)acrylate core particles. Secondly, vinylidene fluoride (VDF) is directly added to the reactor and polymerized for shell formation. Small-angle X-ray scattering (SAXS) was employed to characterize the structure of the core–shell particles. Interestingly, the particles’ core contains fluorinated and non-fluorinated polymers, whereas the shell of the particles consists only of PVDF. The resulting particles with a diameter of around 40 nm show a significantly higher PVDF β phase content than the PVDF homopolymer obtained by emulsion polymerization
We invented the first non-metallic, self-adhesive and dry biosignalling electrode. The PEDOT polymer electrode changes its aggregate state and conductivity by a light curing procedure. The electrode can be applied as a gel underneath hair without shaving. With the aid of blue light, the electrode can be hardened within a few seconds at the desired location on the scalp. The cured polymer electrode is highly conductive and can be applied on a very small location. Unlike other EEG electrodes, our electrode does not lose conductivity upon drying. Furthermore, our electrode strongly bonds to Skin and does not require any additional adhesive. Short circuits due to an outflow of gel are prevented with this technique. Therefore, the PEDOT polymer electrode is extremely well suited for applications that, up to now, have been challenging, such as non-invasive EEG recordings from awake and freely moving animals, EEG recordings from preterm babies in the neonatal intensive care unit or long-term recordings in the case of sleep monitoring or epilepsy diagnostics. We addressed two technical questions in this work. First, is the EEG recorded with polymer electrodes comparable to a standard EEG? Second, is it possible to record full-band EEGs with our electrodes?
The conventional quantitative method for the analysis of inorganic elements in polymer matrices is a complex and time consuming process that presents a significant risk for error. Typically, polymers are digested in a microwave oven or other devices under high temperature and pressure for several hours while employing different mixtures of high purity acids. In many cases, particularly when high concentrations of doped elements are present, the digestion is often incomplete and therefore the reproducibility depends strongly on the type of polymer and additives used. A promising alternative technology that allows for the direct analysis of these polymers without digestion is laser ablation ICP-MS. Due to a lack of available reference materials and the presence of matrix dependent effects, a precise calibration cannot be obtained. In order to compensate for the matrix dependent effects the use of internal standardization is necessary. In this study the correlation between the carbon released during the ablation process and the 13C signal detected by ICP-MS and its use as an internal standard are investigated. For this purpose, twenty-one virgin polymer materials are ablated; the released carbon is determined and correlated with the corresponding integrated 13C signal. The correlation resulted in a direct relationship between the ablated carbon and 13C signal demonstrating the potential ability to neglect at least some of the matrix dependent and transport effects which occur during the laser ablation of virgin polymers.
For analysis of the gaseous thermal decomposition products of polymers, the common techniques are thermogravimetry, combined with Fourier transformed infrared spectroscopy (TGA–FTIR) and mass spectrometry (TGA–MS). These methods offer a simple approach to the decomposition mechanism, especially for small decomposition molecules. Complex spectra of gaseous mixtures are very often hard to identify because of overlapping signals. In this paper a new method is described to adsorb the decomposition products during controlled conditions in TGA on solid-phase extraction (SPE) material: twisters. Subsequently the twisters were analysed with thermal desorption gas chromatography mass spectrometry (TDS–GC–MS), which allows the decomposition products to be separated and identified using an MS library. The thermoplastics polyamide 66 (PA 66) and polybutylene terephthalate (PBT) were used as example polymers. The influence of the sample mass and of the purge gas flow during the decomposition process was investigated in TGA. The advantages and limitations of the method were presented in comparison to the common analysis techniques, TGA–FTIR and TGA–MS.
From simple homopolymers to functionalized, 3-dimensional structured copolymers, the complexity of polymeric materials has become more and more sophisticated. With new applications for instance in the semiconductor or pharmaceutical industry, the requirements for the characterization have risen with the complexity of the used polymers. For each additional distribution, an additional dimension in analysis is needed. Small, often isomeric heterogeneities in topology or microstructure can usually not be simply separated chromatographically or distinguished by any common detector, but affect the properties of materials significantly. For a drug delivery system for example, the degree of branching and branching distribution is crucial for the formation of micelles. Instead of a complicated, time consuming and/or expensive 2d-chromatography or ion mobility spectrometry (IMS) method, that also has its limitations, in this work a simple approach using size exclusion chromatography (SEC) coupled with electrospray ionization mass spectrometry (ESI) is proposed. The online coupling allows the analysis of reconstructed ion chromatograms (RIC) of each degree of polymerization. While a complete separation often cannot be achieved, the derived retention times and peak widths lead to information on the existence and dispersity of heterogeneities. Although some microstructural heterogeneities like short chain branching can for large polymers be characterized with methods such as light scattering, for oligomers where the heterogeneities just start to form and their influence is at the maximum, they are inaccessible with these methods. It is also shown, that with a proper calibration even quantitative information can be obtained. This method is suitable to detect small differences in e. g. branching, 3d-structure, monomer sequence or tacticity and could potentially be used in routine analysis to quickly determine deviations.
Statistical ethylene oxide (EO) and propylene oxide (PO) copolymers of different monomer compositions and different average molar masses additionally containing two kinds of end groups (FTD) were investigated by ultra high pressure liquid chromatography under critical conditions (UP-LCCC) combined with electrospray ionization time-of flight mass spectrometry (ESI-TOFMS).
Theoretical predictions of the existence of a critical adsorption point (CPA) for statistical copolymers with a given chemical and sequence distribution1 could be studied and confirmed. A fundamentally new approach to determine these critical conditions in a copolymer, alongside the inevitable chemical composition distribution (CCD), with mass spectrometric detection, is described. The shift of the critical eluent composition with the monomer composition of the polymers was determined. Due to the broad molar mass distribution (MMD) and the presumed existence of different end group functionalities as well as monomer sequence distribution (MSD), Gradient separation only by CCD was not possible. Therefore, isocratic separation conditions at the CPA of definite CCD fractions were developed. Although the various present distributions partly superimposed the separation process, the goal of separation by end group functionality was still achieved on the basis of the additional dimension of ESI-TOF-MS. The existence of HO-H besides the desired allylO-H end group functionalities was confirmed and their amount estimated. Furthermore, indications for a MSD were found by UPLC/MS/MS measurements. This approach offers for the first time the possibility to obtain a fingerprint of a broad distributed statistical copolymer including MMD, FTD, CCD, and MSD.