Orienting melt to produce on lab-microscale high performance and ultra thin foils

Efficient molecular orientation of polymers in the melt-or solution state requires concentric contraction flows, which result in single or multi-filament fiber shaped products. Directed molecular orientation in pipes, sheets, foils and films, like strip bi-axially, planar or tri-axial, are difficult to achieve and require complex multi-stage processing often supported by the addition of extra external magnetic, electric, or temperature gradient fields that put constraints to the materials to be processed. Here we aim at a simple continuous process to produce uni-axially oriented foils, by designing a special die in a standard miniaturized laboratory scale film casting process. The internal of the die consist of a fiber forming, and a fiber fusing part. The specific design of the fiber forming part allows the combination of the fibers formed, without them crossing, into a line that forms a sheet. Flow in the total volume around the slit ends up in molecularly oriented flow inside the slit. To preserve orientation, an air gap extrusion process follows the exiting slit flow, to allow for a strong draw down under high melt stress. Small air-gaps and a cold cooling nose, combined with a supporting carrying film, make the total process easy, clean and cheap, and the products unique. We will demonstrate that, mounted on the miniature Xplore MC 15 lab compounder, the device is able to produce not only high performance fully oriented foils based on a thermotropic liquid crystalline polyester (Vectra), but also extremely thin foils of polyamides and polyesters. In the last application, the melt orientation is used only to temporary obtain a high melt strength that allows a high draw-ability in the air gap.</p

Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures

Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo

Orienting melt to produce on lab-microscale high performance and ultra thin foils

Efficient molecular orientation of polymers in the melt-or solution state requires concentric contraction flows, which result in single or multi-filament fiber shaped products. Directed molecular orientation in pipes, sheets, foils and films, like strip bi-axially, planar or tri-axial, are difficult to achieve and require complex multi-stage processing often supported by the addition of extra external magnetic, electric, or temperature gradient fields that put constraints to the materials to be processed. Here we aim at a simple continuous process to produce uni-axially oriented foils, by designing a special die in a standard miniaturized laboratory scale film casting process. The internal of the die consist of a fiber forming, and a fiber fusing part. The specific design of the fiber forming part allows the combination of the fibers formed, without them crossing, into a line that forms a sheet. Flow in the total volume around the slit ends up in molecularly oriented flow inside the slit. To preserve orientation, an air gap extrusion process follows the exiting slit flow, to allow for a strong draw down under high melt stress. Small air-gaps and a cold cooling nose, combined with a supporting carrying film, make the total process easy, clean and cheap, and the products unique. We will demonstrate that, mounted on the miniature Xplore MC 15 lab compounder, the device is able to produce not only high performance fully oriented foils based on a thermotropic liquid crystalline polyester (Vectra), but also extremely thin foils of polyamides and polyesters. In the last application, the melt orientation is used only to temporary obtain a high melt strength that allows a high draw-ability in the air gap

Hierarchical and fractal structuring in polymer processing

The potential of structuring thermoplastic polymers by convection only, using a combination of static mixer elements, which easily produce stratified structures with thousands of layers, and the black box concept that serves to elegantly combine materials in standard co-extrusion technology is investigated. The aim is to obtain an alternative for routes that try to structure organic matter such as polymers down to submicrometer levels, usually via self-organization based on phase separation. Structure is characterized by its complexity, here defined by the level of hierarchy. Horizontal stratification, parallel to the surface, is level 0. Vertical stratification connected to horizontal surface layers, is level 1. A series of horizontal stratifications in distinct places vertically connected to the surface layers is level 2. Higher levels of hierarchy finally result in dendritic structures that are fractal. Applications of complex structures with a huge interface and guaranteed cocontinuity throughout the whole cross section of the products are found in, for example, membranes for fuel cells and gas separators, and in miniaturizing electronic and optical devices such as photovoltaic cells. (Figure presented.)

Sliding friction on particle filled epoxy: Developing a quantitative model for complex coatings

Epoxy resins represent an important class of thermosetting polymers that are extensively used in demanding applications like in scratch resistant coatings. Usually fillers, either hard (inorganic) or soft (rubbery), are added. Here we test hard and soft particle-filled epoxy systems in single asperity sliding friction experiments, and analyze the results with the hybrid numerical-experimental approach presented earlier. The focus is on the detailed modeling of the local deformation processes and it is confirmed that a rate-independent friction model proves appropriate to quantitatively model this complex process. The constitutive framework developed for amorphous thermoplastic polymers adequately describes also these thermoset systems. The materials response during scratching is likewise. Hard fillers decrease the penetration of the indenter into the surface, and consequently enhance scratch resistance; they cause the lateral friction force to decrease, since less material flows in front of the indenter tip. Soft fillers increase the penetration into the surface, according to expectations, but surprisingly also decrease the friction force. Simulations do not predict this, and suggest an alternative explanation. Migration of rubber particles during sample preparation to the surface could have occurred. Adding a thin rubbery layer to the surface makes the model quantitative, but SEM and TEM pictures of the cross-sections do not confirm this phase separation and instead show the presence of a large number of very small voids. Including these voids in the modeling allows to predict the penetration depth into the surface and lateral force quantitative for all sliding speeds

One-step creation of hierarchical fractal structures

Relatively recently, we advanced a route to create, in a controlled fashion, combined horizontal and vertical stratified structures by simple and energy-efficient processing operations employing static mixing elements. While in state-of-the-art static mixing the focus is on layer multiplication, here the aim is to create hierarchical fractal structures. Therefore, the main question addressed in this article is how structures, rather than layers, can be multiplied. The key aspect is the addition of layers on the sides or in the midplane of the flow during the process; every addition step increases the hierarchy by one level. This article derives the general formalism for forming fractal structures with controlled hierarchy, and we develop the language required to design and construct the dies. The main part of the article addresses this main topic and is based on the splitting serpentine static mixer geometry that can be easily made on the parting surfaces of a mold on both the micro- and the macroscale. The second part of the article addresses the strategy to minimize the number of mirroring steps, eventually avoiding mirroring completely, and is based on the rotation-free multiflux static mixer geometry. With the design language derived, complex hierarchical fractal structures can be generated simply by changing the number and sequence of operators within extrusion dies or molds, providing a one-step solution to produce material structures for potential use in diverse applications ranging from advanced mechanical systems to photovoltaic devices, where controlled assembly of dissimilar materials, and the realization of huge interfaces and genuine cocontinuity throughout the cross section, is critical.</p

Electrospun poly(ε-caprolactone) scaffold for suture-free solder-mediated laser-assisted vessel repair

Background and Objective: The addition of poly(lactic-co-glycolic) acid (PLGA) scaffolds to liquid solder-mediated laser-assisted vascular repair (sLAVR) has been shown to increase soldering strength significantly. Unfortunately, the fast degradation of PLGA is associated with adverse effects such as acidity of the degradation products. This study investigated the possibility of using electrospun poly(ε-caprolactone) (PCL) as reinforcement material in scaffold and solder-mediated LAVR (ssLAVR). Materials and Methods: In vitro sLAVR of 10-mm arteriotomies (n = 62) was performed on 0.3-to 0.6-cm diameter porcine carotid arteries with a 670-nm diode laser. The solder contained 50% bovine serum albumin (BSA) and 0.1-0.7% methylene blue (MB) as a chromophore. The soldering strength was studied as a function of PCL-scaffold thickness, scaffold-fiber diameter, MB concentration, number of laser passes, and different sLAVR techniques. Leaking-point pressures (LPPs) were measured with a fluid-infusion technique. Results: The highest mean ± SD LPP (749 ± 171 mm Hg) was produced by the ssLAVR modality that included the sheathing of the arteriotomy with 30 μL solder containing 50% BSA and 0.5% MB, followed by application of the PCL scaffold (mean ± SD thickness of 187 ± 9 μm and 14-μm fiber diameter) and irradiation with two consecutive continuous-wave laser passes. Conclusions: The study demonstrated the potential applicability of an electrospun PCL scaffold as reinforcement material in ssLAVR. Soldering strength was dependent on the scaffold physical properties, chromophore concentration, the number of laser passes, and the ssLAVR technique.</p

Search for intermediate-mass black hole binaries in the third observing run of Advanced LIGO and Advanced Virgo

International audienceIntermediate-mass black holes (IMBHs) span the approximate mass range 100−105 M⊙, between black holes (BHs) that formed by stellar collapse and the supermassive BHs at the centers of galaxies. Mergers of IMBH binaries are the most energetic gravitational-wave sources accessible by the terrestrial detector network. Searches of the first two observing runs of Advanced LIGO and Advanced Virgo did not yield any significant IMBH binary signals. In the third observing run (O3), the increased network sensitivity enabled the detection of GW190521, a signal consistent with a binary merger of mass ∼150 M⊙ providing direct evidence of IMBH formation. Here, we report on a dedicated search of O3 data for further IMBH binary mergers, combining both modeled (matched filter) and model-independent search methods. We find some marginal candidates, but none are sufficiently significant to indicate detection of further IMBH mergers. We quantify the sensitivity of the individual search methods and of the combined search using a suite of IMBH binary signals obtained via numerical relativity, including the effects of spins misaligned with the binary orbital axis, and present the resulting upper limits on astrophysical merger rates. Our most stringent limit is for equal mass and aligned spin BH binary of total mass 200 M⊙ and effective aligned spin 0.8 at 0.056 Gpc−3 yr−1 (90% confidence), a factor of 3.5 more constraining than previous LIGO-Virgo limits. We also update the estimated rate of mergers similar to GW190521 to 0.08 Gpc−3 yr−1.Key words: gravitational waves / stars: black holes / black hole physicsCorresponding author: W. Del Pozzo, e-mail: [email protected]† Deceased, August 2020