36 research outputs found
Cross sectional nanoidentification as means of adhesion characterisation at the wood-adhesive bond line
Das Ziel dieser Arbeit war es, âcross sectional nanoindentationâ, eine Methode der AdhĂ€sionsmessung, an einer Holz-Klebstoff GrenflĂ€che anzuwenden. In einem ersten Schritt wurden die Proben verschiedenen OberflĂ€chenbehandlungen unterzogen um die AdhĂ€sion zum herabzusetzen. Eine Kontaktwinkelmessung zeigte signifikante Ănderungen aufgrund dieser Behandlungen. Gleichzeitig nahm fĂŒr alle Probentypen die maximale Zugspannung signifikant ab und lag fĂŒr einen Probentyp sogar bei fast Null. Somit waren gute Vorraussetzungen zur Messung der spezifischen AdhĂ€sion gegeben. Die Nanoindenter-Messungen wurden an der Holz-Leim-Grenzlinie durchgefĂŒhrt, an Stellen wo ein vollstĂ€ndiger Kontakt des Leims mit der Zellinnenwand gegeben war. Die Ergebnisse eines ersten Versuchs zeigten in Analogie zum Zugschertest eine Abnahme der AdhĂ€sion bei Proben mit höherem Kontaktwinkel. In einem zweiten Versuch wurden verschiedene Beladefunktionen fĂŒr die Indents verwendet, um deren Einfluss auf das Experiment zu untersuchen. Hierbei zeigte sich ein starker Hysterese-Effekt bei mehrstufigen weggesteuerten Beladefunktionen aufgrund zusĂ€tzlicher viskoelastischer Verformung. Das fĂŒhrte zu einer Zunahme der gemessenen spezifischen Indentationsarbeit als auch der spezifischen AdhĂ€sionsarbeit, wobei letztere Werte von 80-170J/mÂČ annahm. Alle Ergebnisse wiesen jedoch die erwartete signifikante Abnahme der AdhĂ€sion auf. Eine Charakterisierung der Materialeigenschaften von Zellwand und Leim zeigte keine Ă€hnlichen Trends, womit die Möglichkeit von Artefakten verworfen werden konnte. Die gefundenen Ergebnisse erlauben den Schluss, dass die Methode der âcross sectional nanoindentationâ an Holz-Leim-GrenzflĂ€chen eingesetzt werden kann. Sie sollte somit neue Einsichten in die Natur von adhĂ€siven Verbindungen in holz-basierten Verbunden ermöglichen.The aim of this work was to find a way to apply the method of cross sectional nanoindentation to wood-adhesive interfaces. Samples were subjected to various surface treatments to artificially lower the adhesion strength. Contact angle measurements showed significant changes for all treatments. In the following shear test, one set of samples displayed a shear strength close to zero, giving a good basis for measuring the specific adhesion was given. Nanoindentation experiments were performed directly at the wood-adhesive bond line, where the adhesive was in intimate contact with the inner cell wall of wood cells. Results from a first experiment displayed a clear trend of decreasing adhesion for increasing contact angles, in accordance with the shear test. In a second experiment, indents were performed using varying load functions, to analyse their influence on the experiment. Results showed a strong hysteretic behaviour of the force-displacement curve for displacement controlled multi-load functions due to additional visco-elastic deformation, causing an increase in the measured specific work of indentation as well as the specific work of adhesion, which varied between 80-170J/mÂČ. However, all results showed the expected significant decrease in adhesive strength. Material characterisation of the cell wall and the adhesive showed no similar trends for their respective mechanical properties, thus allowing to discard the possibility of artefacts. With these findings, it was concluded that cross sectional nanoindentation can indeed be applied to wood-adhesive interfaces and should provide new insights into the nature of adhesive bonds in wood-based composites
Nucleation and spreading of a heterochromatic domain in fission yeast
Outstanding questions in the chromatin field bear on how large heterochromatin domains are formed in space and time. Positive feedback, where histone-modifying enzymes are attracted to chromosomal regions displaying the modification they catalyse, is believed to drive the formation of these domains; however, few quantitative studies are available to assess this hypothesis. Here we quantified the de novo establishment of a naturally occurring âŒ20-kb heterochromatin domain in fission yeast through single-cell analyses, measuring the kinetics of heterochromatin nucleation in a region targeted by RNAi and its subsequent expansion. We found that nucleation of heterochromatin is stochastic and can take from one to ten cell generations. Further silencing of the full region takes another one to ten generations. Quantitative modelling of the observed kinetics emphasizes the importance of local feedback, where a nucleosome-bound enzyme modifies adjacent nucleosomes, combined with a feedback where recruited enzymes can act at a distance
Unmodified multi-wall carbon nanotubes in polylactic acid for electrically conductive injection-moulded composites
Tailoring the properties of natural polymers such as electrical conductivity is vital to widen the range of future applications. In this article, the potential of electrically conducting multi-wall carbon nanotube (MWCNT)/polylactic acid (PLA) composites produced by industrially viable melt mixing is assessed simultaneously to MWCNT influence on the compositeâs mechanical strength and polymer crystallinity. Atomic force microscopy observations showed that melt mixing achieved an effective distribution and individualization of unmodified nanotubes within the polymer matrix. However, as a trade-off of the poor tube/matrix adhesion, the tensile strength was lowered. With 10 wt% MWCNT loading, the tensile strength was 26% lower than for neat PLA. Differential scanning calorimetric measurements indicated that polymer crystallization after injection moulding was nearly unaffected by the presence of nanotubes and remained at 15%. The resulting composites became conductive below 5 wt% loading and reached conductivities of 51 S mâ1 at 10 wt%, which is comparable with conductivities reported for similar nanocomposites obtained at lab scale. </jats:p
Chromosomal barcoding as a tool for multiplexed phenotypic characterization of laboratory evolved lineages
Cellulose nanofibrils as filler for adhesives: effect on specific fracture energy of solid wood-adhesive bonds
Analysis methods in wood and natural fibre science applying nanoindenter and atomic force microscope
Das Ziel dieser Doktorarbeit war die Entwicklung und Implementierung neuer Methoden zur Mikro- und Nanocharakterisierung im Bereich der Naturfaserforschung. Als Instrumente standen hierbei speziell Nanoindenter und Rasterkraftmikroskop zur VerfĂŒgung. In Paper 1 wird eine neue Methode zur AdhĂ€sionsmessung mittels Nanoindenter direkt an der GrenzflĂ€che zwischen Zellwand und Leim prĂ€sentiert. Diese Methode wird in Paper 2 angewendet, um Unterschiede im AdhĂ€sionsverhalten zweier Leimtypen an der S2- und S3-Zellwandschicht von Fichtenholz zu untersuchen. Der Zusammenhang zwischen Nanorauheit gemessen mit dem Rasterkraftmikroskop und dem optischen Erscheinen von LignozelluloseoberflĂ€chen wird in Paper 3 undersucht. Paper 4 untersucht zeitabhĂ€ngige nderungen der OberflĂ€chenchemie der S2- und S3-Schicht der Holzzellwand mittels Kraftscans. In Paper 5 wird die richtungsabhĂ€ngige WĂ€rmeleitfĂ€higkeit von Holzproben mittels Scanning Thermal Microscopy untersucht. Weitere Arbeiten an dieser Methode mit dem Ziel einer quantitativen Messung werden im Experimentalteil der Arbeit prĂ€sentiert.The aim of this doctoral thesis was the development and implementation of new methods for micro- and nano-characterisation in natural fibre science. The main experimental devices for this were nanoindenter and atomic force microscope. A new method for measuring the cell wall-adhesive interaction directly at the interface by means of nanoindentation is presented in Paper 1. This method is applied in Paper 2 to analyse dfferences in the bonding behaviour of two types of adhesives to the S2 and S3 cell wall, respectively, of spruce wood. Measuring nanoscale roughness with the AFM, Paper 3 investigates the influence of roughness on the optical appearance of ligno-cellulosic fibres. Paper 4 examines temporal changes in surface chemistry of the S2- and S3 cell wall layer by applying a mechanical mapping mode. Paper 5 introduces scanning thermal microscopy to evaluate the direction-dependent thermal conductivity of wood samples on the cell wall level. Further work on this method with the aim of obtaining quantitative results for fibrous materials is presented in the experimental section of this thesis.submitted by Michael ObersriebnigAbweichender Titel laut Ăbersetzung der Verfasserin/des VerfassersZsfassung in dt. SpracheWien, Univ. fĂŒr Bodenkultur, Diss., 2014OeBB(VLID)193166