Nanoporous (NP) metal foams combine desirable characteristics of metals with unique nanoarchitectural features to yield weight normalized properties far superior than either dense metals or bulk metal foams. Due to their high surface to volume ratios these structures show great promise as components of fuel cells, as sensors and have been suggested for use in biological applications, for example as antimicrobial scaffolds or as platforms on which to explore biological material behavior. While most NP metal foams are isotropic, structures with anisotropic features spanning different length scales can further extend applications. This work examines the parameters controlling the synthesis of transversely isotropic NP Platinum foam by dealloying an amorphous Pt-Si alloy. The structure that is examined in this work is hierarchical with Voronoi polyhedra that form on the free surface and under each polyhedral hyper-structure, nanocrystalline NP Pt foam forms with radial struts of length ~60 nm and grain size of 5 nm. The size of the polyhedra can be tailored by changing the dealloying potential. In turn, the mechanical properties of these structures as assessed by nanoindentation can range from 1 to 3GPa depending on the geometric arrangement of the struts. Finally, the initiation location of these structures and the relationship between electrochemical parameters and dealloying front evolution is examined.

Cellulose nanowhisker (CNW) prepared by acid hydrolysis of softwood Kraft pulp was incorporated as nanofiller in rigid polyurethane (PU) foam synthesis. The density, morphology, chemical structure, mechanical properties and thermal behavior of the products were characterized. The nanocomposites exhibited better performance especially at high CNW¡¯s content which was probably due to the high specific strength and aspect ratio of CNW, the hydrogen bonding and crosslinking between CNW and polymer matrix, a higher crosslinking density compared to the control, and the function of CNW as an insulator and mass transfer insulator. Lignin polyol was synthesized through oxypropylation and used for rigid PU foam preparation. The density, morphology, chemical structure, compressive property and thermal behavior of the product were characterized. Lingin-based rigid PU foam showed improved compressive property compared to its commercial counterpart. Ethanol organosolv lignin-based PU showed a slightly stronger compressive property than Kraft lignin-based PU. The enhancement was primarily attributed to the rigid phenolic structure and the high hydroxyl functionality of lignin. Lignin-based PU generated more char than common PUs which was possibly related to the better flame retardant property. This study provided an alternative way to valorize the two most abundant biopolymers and resulted in relatively environmentally benign rigid PU nanocomposite foam.

Beim fallenden Vollformguss mit Aluminiumlegierungen existiert wegen der vergleichsweise zu Gusseisen niedrigen Gießtemperatur, nahezu kein Gasspalt zwischen der Schmelze und dem Schaumstoffmodell. Durch die Variierung der Schmelzezufuhr konnten Vorteile des fallenden Vollformgießens gegenüber dem steigenden Vollformgießen verdeutlicht werden. Außer wirtschaftlichen Vorteilen erfordert das fallende Gießen deutlich geringere Formfüllzeiten, die sehr wichtig bei der Herstellung von Seriengussteilen sind. Eine Abhängigkeit der Porosität von der Schichtdicke der Schlichte wurde nachgewiesen. Bei der Versuchsreihe mit Entgasung, kombiniert mit dem Unterdruck, konnten sehr niedrige Porositätswerte erzielt werden. Die Argonspülung unmittelbar vor dem Gießen beeinflusst auch die Formfüllgeschwindigkeit positiv. Durch die mikroskopischen Untersuchungen konnten die Poren visualisiert und die zweidimensionalen Größen, wie Fläche, Durchmesser sowie minimale und maximale Querschnitte gemessen werden.

<p>Today’s rapid development of powerful tools for geneexpression analysis provides unprecedented resources forelucidating complex molecular events.</p><p>The objective of this workhas been to apply, combine andevaluate tools for analysis of differential gene expressionusing atherosclerosis as a model system. First, an optimisedsolid-phase protocol for representational difference analysis(RDA) was applied to two<i>in vitro</i>model systems. Initially, The RDA enrichmentprocedure was investigated by shotgun cloning and sequencing ofsuccessive difference products. In the subsequent steps,combinations of RDA and microarray analysis were used tocombine the selectivity and sensitivity of RDA with thehigh-throughput nature of microarrays. This was achieved byimmobilization of RDA clones onto microarrays dedicated forgene expression analysis in atherosclerosis as well ashybridisation of labelled RDA products onto global microarrayscontaining more than 32,000 human clones. Finally, RDA wasapplied for the investigation of the focal localisation ofatherosclerotic plaques in mice using<i>in vivo</i>tissue samples as starting material.</p><p>A large number of differentially expressed clones wereisolated and confirmed by real time PCR. A very diverse rangeof gene fragments was identified in the RDA products especiallywhen they were screened with global microarrays. However, themicroarray data also seem to contain some noise which is ageneral problem using microarrays and should be compensated forby careful verification of the results.</p><p>Quite a large number of candidate genes related to theatherosclerotic process were found by these studies. Inparticular several nuclear receptors with altered expression inresponse to oxidized LDL were identified and deserve furtherinvestigation. Extended functional annotation does not liewithin the scope of this thesis but raw data in the form ofnovel sequences and accession numbers of known sequences havebeen made publicly available in GenBank. Parts of the data arealso available for interactive exploration on-line through aninteractive software tool. The data generated thus constitute abase for new hypotheses to be tested in the field ofatherosclerosis.</p><p><b>Keywords:</b>representational difference analysis, geneexpression profiling, microarray analysis, atherosclerosis,foam cell formation</p>

<p>Today, the majority of materials used for single-use packaging are petroleum-based synthetic polymers. With increased concern about the environmental protection, efforts have been made to develop alternative biodegradable materials from renewable resources. Starch offers an attractive alternative since it is of low cost and abundant. However, the starch material is brittle without plasticizer and the mechanical properties of starch materials are highly sensitive to moisture.</p><p>In nature, the plant cell walls combine mechanical stiffness, strength and toughness despite a highly hydrated state. This interesting combination of properties is attributed to a network based on cellulose microfibrils. Inspired by this, microfibrillated cellulose (MFC) reinforced starch-based nanocomposites films and foams were prepared. Films with a viscous matrix and MFC contents from 10 to 70wt% were successfully obtained by solvent casting. The films were characterized by DSC, DMA, FE-SEM, XRD, mercury density measurements, and dynamic water vapor sorption (DVS). At 70wt% MFC content a high tensile strength together with high modulus and high work of fracture was observed. This was due to the nanofiber and matrix properties, favourable nanofiber-matrix interaction, a good dispersion of nanofibers and the MFC network.</p><p>Novel nanocomposite foams were obtained by freeze-drying aquagels prepared from 8wt% solutions of amylopectin starch and MFC. The MFC content was varied from 10 to 70wt%. For composite foam with MFC contents up to 40wt%, improved mechanical properties were observed in compression. The mechanical properties depended both on the cell wall properties and the cell-structure of the foam. The effect of moisture (20-80% RH) on the dynamical properties of composite foam with 40wt% MFC was also investigated and compared to those of neat starch foam. Improved storage modulus was noted with MFC content, which was a result of the nanofiber network in the cell-wall. In addition, the moisture content decreased with MFC content, due to the less hydrophilic nature of MFC.</p>

Within this paper recently developed mathematical tools for the modelling of contact problems on thin film structures [1] for multilayers and gradient coatings are adapted to allow the investigation of laminate structures of transversal isotropy. Applying series approaches using Bessel and Sinus functions complete three dimensional solutions can be found for relatively complex laminate structures allowing to model quasistatic contact, impact and bending loads. Worked into a small computer program the approach can be used to model laminate structures with up to 100 different layers on an ordinary personal computer in an acceptable calculation time. The new tool is applied to analyse a variety of load problems typically occurring in windsurfing and leading to damage of the boards consisting of a laminated shell and an polymer foam core. [1] N. Schwarzer: „Modelling of the mechanics of thin films using analytical linear elastic approaches“, habilitation thesis of the TU-Chemnitz 2004, department “Physics of solid bodies”, http://archiv.tu-chemnitz.de/pub/2004/0077

Polymer nanocomposite foams have attracted tremendous interests due to their multifunctional properties in addition to the inherited lightweight benefit of being foamed materials. Polymer nanocomposite foams using high performance polymer and bio-degradable polymer with carbon nanotubes were fabricated, and the effects of foam density and pore size on properties were characterized. Electrical conductivity modeling of polymer nanocomposite foams was conducted to investigate the effects of density and pore size. High performance polymer Polyetherimide (PEI) and multi-walled carbon nanotube (MWCNT) nanocomposites and their foams were fabricated using solvent-casting and solid-state foaming under different foaming conditions. Addition of MWCNTs has little effect on the storage modulus of the nanocomposites. High glass transition temperature of PEI matrix was maintained in the PEI/MWCNT nanocomposites and foams. Volume electrical conductivities of the nanocomposite foams beyond the percolation threshold were within the range of electro-dissipative materials according to the ANSI/ESD standard, which indicates that these lightweight materials could be suitable for electro-static dissipation applications with high temperature requirements. Biodegradable Polylactic acid (PLA) and MWCNT nanocomposites and their foams were fabricated using melt-blending and solid-state foaming under different foaming conditions. Addition of MWCNTs increased the storage modulus of PLA/MWCNT composites. By foaming, the glass transition temperature increased. Volume electrical conductivities of foams with MWCNT contents beyond the percolation threshold were again within the range of electro-dissipative materials according to the ANSI/ESD standard. The foams with a saturation pressure of 2 MPa and foaming temperature of 100 °C showed a weight reduction of 90% without the sacrifice of electrical conductivity. This result is promising in terms of multi-functionality and material saving. At a given CNT loading expressed as volume percent, the electrical conductivity increased significantly as porosity increased. A Monte-Carlo simulation model was developed to understand and predict the electrical conductivity of polymer/MWCNT nanocomposite foams. Two different foam morphologies were considered, designated as Case 1: volume expansion without nanotube rearrangement, and Case 2: nanotube aggregation in cell walls. Simulation results from unfoamed nanocomposites and the Case 1 model were validated with experimental data. The results were in good agreement with those from PEI/MWCNT nanocomposites and their foams, which had a similar microstructure as modeled in Case 1. Porosity effects on electrical conductivity were investigated for both Case 1 and Case 2 models. There was no porosity effect on electrical conductivity at a given volume percent CNT loading for Case 1. However, for Case 2 the electrical conductivity increased as porosity increased. Pore size effect was investigated using the Case 2 model. As pore size increased, the electrical conductivity also increased. Electrical conductivity prediction of foamed polymer nanocomposites using FEM was performed. The results obtained from FEM were compared with those from the Monte-Carlo simulation method. Feasibility of using FEM to predict the electrical conductivity of foamed polymer nanocomposites was discussed. FEM was able to predict the electrical conductivity of polymer nanocomposite foams represented by the Case 2 model with various porosities. However, it could not capture the pore size effect in the electrical conductivity prediction. The FEM simulation can be utilized to predict the electrical conductivity of Case 2 foams when the percolation threshold is determined by Monte-Carlo simulation to save the computational time. This has only been verified when the pore size is small in the range of a few micrometers. / text

Carbon dioxide (CO₂) flooding is the second most common tertiary recovery technique implemented in the United States. Yet, there is huge potential to advance the process by improving the volumetric sweep efficiency of injected CO₂. Delivering CO₂ into the reservoir as a foam is one way to do this. Surfactants have traditionally been used to generate CO₂ foams for mobility control; however, the use of nanoparticles as a foam stabilizing agent provides several advantages. Surfactant-stabilized foams require constant regeneration to be effective, and the surfactant is adsorbed onto reservoir rocks and is prone to chemical degradation at harsh reservoir conditions. Nanoparticle-stabilized foams have been found to be tolerant of high temperature and high salinity environments. Their nano size also allows them to be transported through reservoir rocks without blocking pore throats. Stable CO₂-in-water foams were generated using 5 nm silica nanoparticles with a short chain polyethylene glycol surface coating. These foams were generated by the co-injection of CO₂ and a nanoparticle dispersion through both rock matrix and fractures. A threshold shear rate was found to exist for foam generation in both fractured and non-fractured Boise sandstone cores. The ability of nanoparticles to generate foams only above a threshold shear rate is advantageous; in field applications, high shear rates are associated with high permeability zones, where the presence of foam is desired. Reducing CO₂ mobility in these high permeability zones diverts CO₂ into lower permeability regions containing not yet swept oil. Nanoparticles were also found to be able to stabilize CO₂ foams by co-injection through rough-walled fractures in cement cores, demonstrating their ability to stabilize foams without matrix flow. Experiments were conducted on the ability of fly ash, a waste product from burning coal in power plants, to stabilize oil-in-water emulsions and CO₂ foams. The use of fly ash particles as a foam stabilizing agent would significantly reduce material costs for potential tertiary oil recovery and CO₂ sequestration applications. Nano-milled fly ash particles without surface treatment were able to generate stable oil-in-water emulsions when high frequency, high energy vibrations were applied to a mixture of fly ash dispersion and dodecane. Oil-in-water emulsions were also generated by co-injecting fly ash and dodecane, a low pressure analog to CO₂, through a beadpack. Emulsions generated by co-injection, however, were unstable and coalesced within an hour. A threshold shear rate was required for the emulsion generation. Fly ash particles were found to be able to stabilize CO₂ foam in a high pressure batch mixing cell, but not by co-injection through a beadpack. Dispersions of fly ash particles were found to be stable only at low salinities (<1 wt% NaCl). / text

Atherosclerosis (Heart Disease) is an inflammatory disease caused by the formation of plaque within the arterial wall. In response to inflammation, monocytes enter the artery wall, differentiate into macrophages and take up altered low-density-lipoprotein (such as oxidised-LDL). This oxLDL is taken up into the phagocytotic macrophages via the action of the scavenger receptors. If more oxLDL is engulfed than the cell can process, they further differentiate into lipid-loaded foam cells. These are the main cell type found in atherosclerotic plaques. The scavenger receptor CD36 is responsible for 70% of oxLDL uptake by macrophages. Previous studies show that CD36 expression can be down regulated by the antioxidant, 7,8-dihydroneopterin. This research focuses on the effect of CD36 down regulation by 7,8-dihydroneopterin on foam cell formation. Human macrophages prepared from monocytes purified from human blood were incubated with copper oxidised LDL for up to 48 hours. Macrophage accumulation of the sterols was measured using a high performance chromatograph (HPLC) method developed as part of this project. The HPLC analysis measured: cholesterol, cholesteryl-oleate and -palmitate and 7-ketocholesterol accumulation within human macrophages. A flow cytometry procedure was developed where the strongly adherent macrophages could be lifted from the tissue culture plates before immuno staining for CD36. Effect of incubating macrophages with 7,8-dihydroneopterin on the formation of foam cells was studied by measuring the lipid content by HPLC and flow cytometry measurement of CD36. HPLC analysis showed non-cytotoxic levels of oxLDL produced a large accumulation of cholesterol and cholesteryl esters in the macrophages. Cholesterol, 7-ketocholesterol and cholesteryl-oleate and -palmitate concentrations in the cells rose significantly over the first 24 hours and stayed at a steady level for the following 24 hours. CD36 levels was further analysed on human macrophages. This study shows that foam cell formation can be measured using human macrophages. 7,8-Dihydroneopterin treatment resulted in a reduction of cholesterol and oxysterol uptake back to basal levels. It also reduced CD36 cell surface expression by a third. These results suggest that even a small reduction in CD36 cell surface expression may have a large effect on foam cell formation. This is another mechanism by which 7,8-dihydroneopterin protects against atherosclerosis developing.

While hollow glass microspheres are commonly used in syntactic foam, their abrasive and brittle properties usually result in poor processability and have adverse effects on the foam performance. Therefore, a number of attempts have been made in the industry to replace hollow glass microspheres with polymeric foamed microspheres. Among many choices, expandable thermoplastic (ETP) microspheres filled syntactic foam has shown its high potential to become a novel class of engineering materials, especially for lightweight structural applications. However, conventional processing techniques for syntactic foam usually experience difficulties such as high processing viscosity, low loading of foam fillers, and ineffective microsphere expansion. To address these emerging issues, a microwave expansion process to produce thermoset-matrix syntactic foam containing thermoplastic foam beads was developed in this thesis work. In this process, unexpanded ETP microspheres were directly foamed in uncured thermoset matrix via microwave heating. Expandable polystyrene (EPS) microspheres and epoxy resin were chosen as a model material system. The resin viscosity and specific microwave energy are found to be the two primary control parameters determining the process window. Mechanical characterization showed that the syntactic foam can outweigh neat polymer in lightweight structural applications and was effectively toughened by foamed EPS. Furthermore, the microwave expansion process was found to be capable of molding syntactic foam parts of relatively sophisticated geometry with smooth surfaces. In order to broaden its impact, the microwave expansion process was extended to produce composite EPS foam. This process converts an expandable suspension into a composite foam with a honeycomb-like barrier structure. The suspension viscosity was found to highly influence the foam morphology. Results from mechanical tests showed that the existence of the barrier structure can considerably improve the mechanical performance of the composite foam. Fire-retardation tests demonstrated that the barrier structure can effectively stop the fire path into the foam, suppress toxic smoke generation, and maintain foam structure integrity. A general formulation was developed to model the EPS expansion to optimize the microwave expansion process. A semi-analytical solution was first obtained based on the case of a single bubble expansion in an infinite matrix. The dimensionless bubble radius and pressure are defined and found to be as exponential functions of dimensionless expansion time. The semi-analytical solution can qualitatively predict the radial expansion of EPS microsphere observed in a real-time experiment. To have an accurate prediction, a numerical solution was obtained to the model that couples the nucleation and expansion of multiple bubbles in a finite matrix. The results show that the numerical solution can quantitatively predict the radial expansion of EPS. A parameter sensitivity study was performed to examine the effect of each parameter over the expansion process.