Dynamic Light Scattering in Gels and Solutions

Dynamic light scattering (DLS) is a rich source of information in investigations of the frequency response of soft materials. Most commonly, however, it is underemployed, mainly for determining the size of suspended particles or macromolecules in solution. This article emphasizes some of the other aspects of the technique, how it acts as a frequency discriminator between mechanisms of differing relaxation rates, and how it can be used to determine directly the thermodynamic properties not only of simple solutions, but also of polymer gels and inhomogeneous solutions, as well as their large-scale structure. The method is illustrated with several detailed examples

Incompatible Liquids in Confined Conditions

In applications involving organic vapour, the performance of high surface area carbons is often challenged by water vapour in the atmosphere. Small angle neutron scattering (SANS), through its ability to distinguish between different components by means of contrast variation, is ideally suited to investigating the behaviour of adsorbed layers in simultaneous contact with a mixed vapour phase. Even at high relative humidity (RH), water alone forms a discontinuous film composed of clusters on the surface of the oxidized microporous carbon used for these studies. When toluene is also present, all the available carbon surface is wetted. Toluene and water adsorb as a single phase already at RH 11.5%, and the concentration of water present in the adsorbed phase is as high as 2.9 wt.%, far above its solubility in bulk toluene (0.033 wt.% at 25 deg C). At RH 87% the concentration of water in the adsorbed phase is four times higher, approximately 12 wt.%. The recently proposed mechanism of anchoring of the water by the aromatic molecules may provide an explanation for this phenomenon

TiO2-doped resorcinol–formaldehyde (RF) polymer and carbon gels with photocatalytic activity

Resorcinol-formaldehyde (RF) polymer gels offer a relatively easy and versatile route for incorporating metals into a carbon aerogel matrix. The hybrid materials thus obtained are ideal candidates for applications involving enhanced adsorption or catalysis. This paper presents a detailed study of Ti-doped RF and carbon aerogels. The metal was introduced into the system at three different stages of the preparation process: during polymerization, by impregnation of the RF gel, or by impregnation of the carbon gel. The structure and morphology of the samples are compared using low temperature N2 adsorption, SEM, and small and wide angle X-Ray scattering (SAXS/WAXS) methods. The TiO2-doped carbon aerogels display photocatalytic activity in breaking down aromatic compounds

Measurement of Dynamic Light Scattering Intensity in Gels

In the scientific literature little attention has been given to the use of dynamic light scattering (DLS) as a tool for extracting the thermodynamic information contained in the absolute intensity of light scattered by gels. In this article we show that DLS yields reliable measurements of the intensity of light scattered by the thermodynamic fluctuations, not only in aqueous polymer solutions, but also in hydrogels. In hydrogels, light scattered by osmotic fluctuations is heterodyned by that from static or slowly varying inhomogeneities. The two components are separable owing to their different time scales, giving good experimental agreement with macroscopic measurements of the osmotic pressure. DLS measurements in gels are, however, tributary to depolarised light scattering from the network as well as to multiple light scattering. The paper examines these effects, as well as the instrumental corrections required to determine the osmotic modulus. For guest polymers trapped in a hydrogel the measured intensity, extrapolated to zero concentration, is identical to that found by static light scattering from the same polymers in solution. The gel environment modifies the second and third virial coefficients, providing a means of evaluating the interaction between the polymers and the gel

Bewertungsverfahren des novellierten Fluglärmgesetzes

Die Entwicklung von modernen Gesellschaften führt zu immer distanzintensiveren Austauschbeziehungen. Die Globalisierung ist ein Ausdruck davon. Trotzdem diese Entwicklung auch mit der Telematisierung begleitet wird, steigt die Nachfrage nach weiten Ortsveränderungen von Personen und Gütern. Insbesondere die Bewegungen über Länder- oder sogar Kontinentgrenzen hinweg führt zum Anwachsen u.a. des Flugverkehrs. Allein 2005 nahmen die Fluggastzahlen in Deutschland um 7,5 Prozent und die Zahl der Flüge um 5,5 Prozent zu (DIW 2006: S. 34). Obwohl moderne Flugzeuge leiser als ältere sind, hat der Fluglärm in den letzten Jahrzehnten durch den rasanten Anstieg des Flugverkehrs immer mehr zugenommen. In der Wahrnehmung der Bevölkerung steht der Fluglärm auf Platz 2 der störenden Lärmquellen direkt hinter dem Straßenverkehr. Rund 37% der Bundesbevölkerung fühlt sich durch Fluglärm gestört (VCD 2005: S. 3). Das Besondere am Fluglärm sind die hohen, kurzen aber sehr lauten Maximalpegel. Die bisherigen Methoden zur Messung von Fluglärm, welche sich nicht wesentlich von der Messung anderer Lärmquellen wie beispielsweise Straßenverkehrslärm unterscheiden, werden aber dem besonderen Lärmpegelverlauf des Fluglärms nicht gerecht. Durch die Mittelung der gemessenen Pegel wird die tatsächliche Lärmbelästigung nur unzureichend erfasst. So kommt es, dass 200 tägliche Überflüge mit über 70 dB(A) und einer Geräuschdauer von jeweils rund 30 Sekunden den erlaubten täglichen Dauerschallpegel von 57 dB(A) noch nicht überschreiten (BUND 2006). Ein weiteres Problem des Fluglärms ist, dass konventionelle Lärmschutzmaßnahmen wie Schallschutzwände nicht helfen. Seit 1971, also seit mehr als 35 Jahren ist das Gesetz zum Schutz vor Fluglärm die wichtigste Rechtsgrundlage zur Fluglärmbekämpfung. Daraus leiten sich für alle Flughäfen Lärmschutzbereiche ab, welche mit Hilfe einer besonderen Rechenvorschrift prognostiziert werden. Die Lärmschutzbereiche sind Gebiete außerhalb des Flughafens, in denen der Dauerschallpegel mehr als 67 dB(A) beträgt. Diese Lärmschutzbereiche werden dann nochmals in 2 Schutzzonen (Dauerschallpegel mehr bzw. weniger als 75 dB(A)) eingeteilt. Hier gelten abgestufte Bauverbote und -beschränkungen. So müssen Wohnungen baulichen Schallschutzanforderungen (Schutzfenster) genügen. Aus Sicht der Lärmwirkungsforschung (Ortscheid, Wende 2001) sind die festgesetzten Grenzwerte von 1971 jedoch viel zu hoch. Ab 65 dB(A) Dauerschallpegel (tagsüber) sind Gesundheitsbeeinträchtigungen (Herz- Kreislauf-Erkrankungen) zu erwarten. In den letzten Jahren wurde verstärkt über ein neues Fluglärmgesetz debattiert und immer wieder wurden Novellierungsvorschläge eingebracht. Anfang 2006 fand die erste Lesung des aktuellen Novellierungsvorschlages im Bundestag statt, im Mai die öffentliche Anhörung. Es zeichnet sich ein Beschluss des Bundestages zur Novellierung des Fluglärmgesetzes von 1971 noch in dieser Legislaturperiode ab. Gleichzeitig ist es ein offenes Geheimnis, dass der geplante Flughafen BBI in Schönefeld als ein Modellflughafen im Sinne der Novelle fungiert, obwohl er bereits als Bestandsflughafen eingestuft ist und somit nur die abgeschwächten Lärmschutzwerte der Novelle beim Bau zu berücksichtigen sind. Dieser Bericht gibt einen Überblick zur Thematik Lärm im Allgemeinen und Fluglärm im Besonderen. Exemplarisch werden das geltende Gesetz zum Schutz gegen Fluglärm von 1971 mit der derzeit diskutierten Novellierung verglichen und die Auswirkungen dieser auf das Bauvorhaben BBI mit Hilfe der Unterlagen des Planfeststellungsverfahrens genauer untersucht

An Early Transcriptional Analysis of Fracture Hematoma in Rat

Among other stressors, age and mechanical constraints significantly influence regeneration cascades in bone healing. Here, our aim was to identify genes and, through their functional annotation, related biological processes that are influenced by an interaction between the effects of mechanical fixation stability and age. Therefore, at day three post-osteotomy, chip-based whole- genome gene expression analyses of fracture hematoma tissue were performed for four groups of Sprague-Dawley rats with a 1.5-mm osteotomy gap in the femora with varying age (12 vs. 52 weeks - biologically challenging) and external fixator stiffness (mechanically challenging). From 31099 analysed genes, 1103 genes were differentially expressed between the six possible combinations of the four groups and from those 144 genes were identified as statistically significantly influenced by the interaction between age and fixation stability. Functional annotation of these differentially expressed genes revealed an association with extracellular space, cell migration or vasculature development. The chip-based whole-genome gene expression data was validated by q-RT-PCR at days three and seven post-osteotomy for MMP-9 and MMP-13, members of the mechanosensitive matrix metalloproteinase family and key players in cell migration and angiogenesis. Furthermore, we observed an interaction of age and mechanical stimuli in vitro on cell migration of mesenchymal stromal cells. These cells are a subpopulation of the fracture hematoma and are known to be key players in bone regeneration. In summary, these data correspond to and might explain our previously described biomechanical healing outcome after six weeks in response to fixation stiffness variation. In conclusion, our data highlight the importance of analysing the influence of risk factors of fracture healing (e.g. advanced age, suboptimal fixator stability) in combination rather than alone

Small angle neutron scattering study of globular proteins confined in porous carbons

International audienceThis article reports measurements of the concentration distribution of two model proteins adsorbed from aqueous solution by two different high surface area carbons, using small angle neutron and X-ray scattering (SANS and SAXS). The proteins investigated were bovine serum albumin (67 kDa), and bovine pancreatic trypsin inhibitor (BPTI), also known under the name aprotinin (6.5 kDa). The two carbon substrates were C1, an open structured carbon aerogel derived from a resorcinol– formaldehyde polymer aerogel, and C2, a commercial nanoporous carbon from MAST Carbon (UK). Although both C1 and C2 possess a high proportion of pores that are either closed or inaccessible to low temperature nitrogen vapour, the size distribution of the accessible pores is broad enough to accommodate BSA molecules. In C1, which is hydrophobic, the BSA molecules migrate individually into pores that are compatible with their size, whereas BPTI forms clusters having the same size as BSA. With C2, the hydrophilic internal surface limits the adsorption efficiency. The strong adhesion of proteins to hydrophilic surfaces prevents diffusion of either molecule into the micro-and nanopores. In this sample both BSA and BPTI form large clusters. These observations have relevance in biomedical applications, such as haemoperfusion or as a medium for protein storage

Search for the Origin of Discrepancies in Osmotic Measurements of the PNIPAM - Water System

Major, still unelucidated, inconsistencies exist in the literature among measurements of the thermodynamic properties of poly(N-isopropylacrylamide) (PNIPAM) solutions and gels. This paper looks for evidence of intrinsic ionic behaviour in cross-linked PNIPAM homopolymer hydrogels synthesized in water under standard conditions. Systematic measurements are made of the swelling and osmotic properties of lightly cross-linked PNIPAM hydrogels, as well as of their potentiometric titration and DSC response, over a wide range of pH and ionic strength conditions, in order to distinguish the effects of the latter two parameters on putative intrinsic ions. The intrinsic ion content of the gel is found to be vanishingly small, and consequently unlikely to be the source of the divergences among past measurements. By contrast, a major finding of this study is that comparison of the present results with the literature reveals that frustrated equilibrium can be a source of substantial discrepancies