Steering surface topographies of electrospun fibers: understanding the mechanisms

A profound understanding of how to tailor surface topographies of electrospun fibers is of great importance for surface sensitive applications including optical sensing, catalysis, drug delivery and tissue engineering. Hereby, a novel approach to comprehend the driving forces for fiber surface topography formation is introduced through inclusion of the dynamic solvent-polymer interaction during fiber formation. Thus, the interplay between polymer solubility as well as computed fiber jet surface temperature changes in function of time during solvent evaporation and the resultant phase separation behavior are studied. The correlation of experimental and theoretical results shows that the temperature difference between the polymer solution jet surface temperature and the dew point of the controlled electrospinning environment are the main influencing factors with respect to water condensation and thus phase separation leading to the final fiber surface topography. As polymer matrices with enhanced surface area are particularly appealing for sensing applications, we further functionalized our nanoporous fibrous membranes with a phosphorescent oxygen-sensitive dye. The hybrid membranes possess high brightness, stability in aqueous medium, linear response to oxygen and hence represent a promising scaffold for cell growth, contactless monitoring of oxygen and live fluorescence imaging in 3-D cell models

Functional polymers from alternating aliphatic polyketones: synthesis and applications

Dit onderzoek focust zich op de synthese en toepassing van functionele polymere materialen afgeleid van alternerende alifatische polyketonen. Deze zijn, door de aanwezigheid van carbonylgroepen in de hoofdketen, geschikt voor een breed scala modificatiereacties, waardoor de thermische, morfologische en mechanische eigenschappen gemakkelijk gemoduleerd kunnen worden. In het bijzonder, de Paal-Knorr reactie van primaire amines met 1,4 dicarbonylen geeft pyrool ringen in de hoofdketen in een directe en gemakkelijke manier( d.w.z. zonder gebruik van oplosmiddelen of katalysatoren). De resulterende functionele materialen zijn toegepast om kleurstof aggregatie te voorkomen, een belangrijke eigenschap voor maximalisering van de opbrengst van dye sensitized solar cells. Verder behouden thermo-reversibele thermoharders geproduceerd door post modificatie van alifatische polyketonen dezelfde mechanische eigenschappen van vernette materialen maar tonen ook recycleerbaarheid (bijv. door simpelweg de temperatuur te verhogen) voor zeven cycli zonder enige degradatie van het materiaal. Thermoreversibiliteit is getest met twee verschillende systemen, welke in het eerste geval de productie van materialen met verschillende viscoelasticiteit verzekerde, en in het laatste geval een hoge thermische stabiliteit (tot 209°C). Chemisch gemodificeerde polyketonen zijn tevens efficient in het verwijderen van giftige metaalionen, als Cu(II), Ni(II), Co(II), Fe(III), Cr(III), Ag(I) en Hg(II) uit waterafval. Verschillende selectiviteit en adsorptie van specifieke metaalionen kon worden bereikt door het variëren van de functionele zijgroep. Tot slot zijn alifatische polyketonen getest in bad formulering voor elektro depositie voor toepassingen in de auto-industrie. De gevormde materialen toonden een excellente houdbaarheid en een stevig, groen-georiënteerd perspectief voor katalysator vrije en laag toxische depositie bad formulering

Compatibilizzazione reattiva di poli(acido lattico)(PLA) e poli(butilen-adipato-co-tereftalato)(PBAT)

Nel presente lavoro di tesi specialistica, saranno miscelati meccanicamente in miscelatori da laboratorio poliesteri provenienti da fonti rinnovabili e non, come il PLA (poli-acido lattico) e PBAT (poli-butilen adipato-co-tereftalato), allo scopo di ottenere nuovi materiali che conservino la loro caratteristica essenziale di biodegradabilità e abbiano proprietà termo-meccaniche modulabili. Per raggiungere quest’obiettivo, verranno utilizzate tecniche di compatibilizzazione reattiva delle miscele, che prevedono anche l’utilizzo di agenti di coupling e catalizzatori di transesterificazione. Le miscele così preparate verranno caratterizzate per esaminarne composizione chimica e proprietà attraverso l’uso di tecniche spettroscopiche (FT-IR, 1H e 13C-NMR), calorimetriche (DSC e TGA) e prove tensili. Il tutto rientra nel cosiddetto progetto europeo denominato Picus il quale ha l’obiettivo di sviluppare reti e sostegni per l’agricoltura in materiale di origine naturale o rigenerabile in modo da sostituire le poliolefine attualmente in uso

Compatible blends of biorelated polyesters through catalytic transesterification in the melt

The transesterification during the melt blending of polylactide (PLA) and poly(butylene adipate-coterephthalate) (PBAT) was investigated in presence of Ti(OBu)4 as a catalyst. Both the effect of catalyst concentration and reaction duration was considered. The process was studied by analyzing the molecular weight of the polyesters by size exclusion chromatography (SEC). The rheological, thermal and morphological properties of the blends were investigated by melt flow rate, DSC and SEM analyses, respectively. Evidences about the formation of PBAT-PLA copolymers were obtained and discussed. The tensile properties of compression moulded films were also determined and correlated to the structure and phase morphology development of the blends. In particular, the use of Ti(OBu)4 resulted in the improvement of compatibility. Moreover, the decrease in stiffness and the increase in elongation at break with the increase of mixing time was observed, in good agreement with the improved compatibility of the modified blend

Paal-Knorr kinetics in waterborne polyketone-based formulations as modulating cross-linking tool in electrodeposition coatings

Novel cationic resins were synthesized for a direct application in automotive industry. A previous patent protocol with lower bath toxicity (i.e. no catalyst neither harmful compounds were employed), as compared to the current industrial methods based on polyurethane chemistry, was implemented. This includes the use of aliphatic polyketones as cross-linking agents for epoxy-based resins in electro-deposition (EPD) processes. Cross-linking takes place through the Paal-Knorr reaction of the amino groups on the epoxy-based materials with 1,4-dicarbonyl groups present on the polyketone backbone. The reaction kinetics can be finely tuned by the steric hindrance on both components. This was preliminarily investigated by using 2,5,8-nonanetrione as model compound. The used amines (i.e. 4-aminopiperidine (AP) and 4-aminomethyl piperidine (AMP)) display higher steric hindrance with respect to the primary ones used in the original protocol. Application of these components during electro-deposition coating yields the desired high-quality coating layers on several metallic substrates as shown by optical microscopy and image processing. All the produced coatings scored higher adhesion and chemical resistance rating than the amine-based ones used in the previous protocol (i.e. diethylenetriamine, DETA). Afterwards, the same electro-deposition baths showed to have stable performance even after being reused 21 and 56 days later. (C) 2016 Published by Elsevier Ltd

Properties of Reversible Diels–Alder Furan/Maleimide Polymer Networks as Function of Crosslink Density

Thermally reversible thermosets are synthesized based on furan functionalized polyketones crosslinked with (methylene-di-p-phenylene)bis-maleimide. The number of furan groups present along the backbone and the crosslinker/furan molar ratio are varied. According to DSC measurements the de-crosslinking temperature does not change signifi cantly as function of furan intake and its molar ratio with the crosslinker. All samples show an almost complete recovery of storage and loss modulus. The crosslinked samples are recycled up to seven times without signifi cant quality loss. This suggests that a change in conformation does not result in different visco-elastic behavior. The most crosslinked sample is able to fully repair itself within 1 hour. A number of low crosslink density materials additionally show a shape memory effect.

Metal‐Textile Laser Welding for Wearable Sensors Applications

Electronic textile (E‐textile), an emerging technology, has the potential to revolutionize consumer electronics by transforming them into wearable devices. Highly conductive, textile conductors, suitable for commercialization, have yet not been developed. Here, a new metal‐textile laser welding method is presented for a rapid one‐step, stable, and cost‐efficient manufacturing of electrically conductive textiles. This method is a direct on‐textile approach for customized 2D nanothick metal coatings with flexible design. Different metals, like palladium, silver, or copper can be welded on functional membranes and textiles containing polymers. As shown by bonding a copper 2D pattern on a polyamide textile, the resistivity does not vary if compared to the bulk material. The generated interlocking bonding ensures strong physical adhesion between the partly molten polyamide fibers and a copper layer, resisting up to 10 000 abrasion cycles using the standardized Martindale test and up to 42 000 flexion cycles using the industrial standardized Schildknecht test. A promising application for textile integrated conductors is body monitoring sensors. The feasibility of a laser welded resistance temperature sensors on a functional membrane is demonstrated without impairing its mechanical stability. This technology presents suitable properties and variabilities for a wide range of application in E‐textiles and its commercialization.ISSN:2199-160

Reversible Oxygen Sensing Based on Multi-Emission Fluorescence Quenching

Oxygen is ubiquitous in nature and it plays a key role in several biological processes, such as cellular respiration and food deterioration, to name a few. Currently, reversible and non-destructive oxygen sensing is usually performed with sensors produced by photosensitization of phosphorescent organometallic complexes. In contrast, we propose a novel route of optical oxygen sensing by fluorescence-based quenching of oxygen. We hereby developed for the first time a set of multi-emissive purely organic emitters. These were produced through a one-pot hydrothermal synthesis using p-phenylenediamine (PPD) and urea as starting materials. The origin of the multi-emission has been ascribed to the diversity of chemical structures produced as a result of oxidative oligomerization of PPD. A Bandrowski’s base (BB, i.e., trimer of PPD) is reported as the main component at reaction times higher than 8 h. This indication was confirmed by electrospray-ionization quadrupole time-of-flight (ESI-QTOF) and liquid chromatography-mass spectrometry (LC-MS) analysis. Once the emitters are embedded within a high molecular weight poly (vinyl alcohol) matrix, the intensities of all three emission centers exhibit a non-linear quenching provoked by oxygen within the range of 0–8 kPa. The detection limit of the emission centers are 0.89 kPa, 0.67 kPa and 0.75 kPa, respectively. This oxygen-dependent change in fluorescence emission is reversible (up to three tested 0–21% O2 cycles) and reproducible with negligible cross-interference to humidity. The cost-effectiveness, metal-free formulation, cross-referencing between each single emission center and the relevant oxygen range are all appealing features, making these sensors promising for the detection of oxygen, e.g., in food packaged product