Nanoindentation and wear behavior of thermally stable biocompatible polysulfone-alumina nanocomposites

The authors would like to acknowledge funding from the Spanish Ministerio de Economía y Competitividad under grant MAT2014-57557-R. R. Prof. Ozisik would like to acknowledge financial support from the U.S. National Science Foundation (CMMI-1538730). The authors also would like to thank I. Garc´ıa and A. Cervera from Euroortodoncia for their invaluable help in nanocomposite processing

Jet milling as an alternative processing technique for preparing polysulfone hard nanocomposites

This work describes how a solid-state blending method such as jet milling can be used to successfully prepare polysulfone (PSU)/-alumina nanocomposites. For comparison purposes, conventional melt extrusion was used as well. Morphological analysis revealed how jet mill blending allows obtaining well-dispersed -alumina nanoparticles within a polysulfone matrix without any surface treatment, with an important decrease of particle size promoted by the breakup of agglomerates and aggregates due to the particle-particle impacts during processing, which was not observed in the extruded nanocomposites. DSC analysis demonstrated that jet-milling processing promoted T-g enhancements with alumina addition, while TGA experiments confirmed the increment of thermal stability of the nanocomposites prepared by jet milling when compared with the composites prepared by extrusion. The tensile tests showed that ductility remains at a high value for milled nanocomposites, which agreed with the fracture surface images revealing large plastic deformation as a function of the alumina content. This comparative study indicates that the dispersion of nanoparticles in PSU was more homogeneous, with smaller nanoparticles when preparing nanocomposites using jet milling, showing a strong correlation with the enhanced final properties of the nanocomposites.The authors acknowledge funding from Spanish Ministerio de Economía y Competitividad under grant MAT2014-57557-R. R. Ozisik would like to acknowledge financial support from the US National Science Foundation (CMMI–1538730)

Interfacial characterization of epoxy/silica nanocomposites measured by fluorescence

Artículo publicado en papel: enero 2015 pero disponible online desde 10 noviembre 2014.Fluorescence labeling was used as a tool for the interfacial characterization of nanocomposites. The solvatochromic probe dansyl chloride was employed as interfacial reporter in epoxy/silica nanocomposites. Molecular spacers (organosiloxanes and polyetheramines) of different lengths were used to vary the location of the chromophore at the interface. The steady state and time resolved fluorescent responses reflect a rigid polar interface. Fluorescence changes during heating at a constant rate were analyzed for determining the local glass transition (Tg) at the interface region. The fluorescence results were then compared to the Tg obtained from differential scanning calorimetry and the results showed the existence of a gradient interface of a few nanometers thick having different properties than the bulk matrix. The thickness of this interface is small but its altered dynamics due to strong interactions with the nanofiller spreads its influence throughout the whole matrix.J.C. Cabanelas, C. Antonelli, J. Baselga and B. Serrano gratefully acknowledge Spanish Ministerio de Educación, Cultura y Deporte (MAT2010-17091) for financial support. R. Ozisik acknowledges support from the United States National Science Foundation under Grant No. 1200270

Functionalization of reduced graphene oxide with polysulfone brushes enhance antibacterial properties and reduce human cytotoxicity

The present study reports two routes to modify reduced graphene oxide (rGO) nanosheets with polysulfone (PSU) brushes via nitrene chemistry. The PSU polymer is bonded to rGO at the extremity (rGO-PSU end) and at the middle of the PSU chain (rGO-PSU mid). The resulting rGO-PSU synthetic products are carefully characterized by Raman and FTIR spectroscopy, XPS, TEM, and thermogravimetric analysis, evidencing the successful grafting of PSU onto rGO surfaces. The long-term stability of these nanosheets is also determined in common solvents. The antibacterial properties of polymer-functionalized rGO against the planktonic Bacilus subtilis and Escherichia coli are also investigated. It is established that the antimicrobial properties of these nanocomposites are due to the production of reactive oxygen species. The results also demonstrate that rGO-PSU mid presents better antimicrobial properties due to shorter polymer chains, which improves the contact of the microorganisms with the graphene surface.This work was financially supported by the Spanish Ministry of Economy and Competitiveness (MAT2014-57557-R), and partially supported by the U.S. National Science Foundation Career Award (NSF Award #104093). R.O. would like acknowledge support from U.S. National Science Foundation (CMMI-1538730 and DUE-CMMI-1538730/1003574). Janire Peña wants to acknowledge mobility grant from Carlos III University and Instituto Tecnológico de Química y Materiales “Alonso Barba”. Authors acknowledge Dr. A. Esteban-Arranz for giving access to ATR equipment

Molecular probe technique for determining local thermal transitions: The glass transition at Silica/PMMA nanocomposite interfaces

Local glass transition temperatures (Tg) have been measured in the interfaces of solution blended silica/poly(methyl methacrylate) (PMMA) nanocomposites using florescence spectroscopy and compared with Tg measured by differential scanning calorimetry (DSC). It was found that the two types of measurements yielded significantly different information. Combinations of silanes and poly(propylene glycol)-based molecular spacers bound to fluorophores were covalently linked to the surface of the nanoparticles, allowing for variation of the fluorophore response with respect to the distance from the nanofiller surface. Increases in the bulk Tg from the neat PMMA value were found upon the addition of nanofillers, but were independent of the nanofiller concentration when the filler concentration was above 2% by weight. Furthermore, as the size of the grafted molecular spacer was increased, Tg values were found to decrease and approach Tg of the neat PMMA. Owing to variable conformations of the spacers, an effective distribution of fluorophore-silica distances exists, which influences the fluorophores' response to the transition.This research was supported by the National Science Foundation under Grant No. 0500324. Authors from UC3M would like to acknowledge CICYT for financial support (MAT 2007-63722)

Controlling Foam Morphology of Poly(methyl methacrylate) via Surface Chemistry and Concentration of Silica Nanoparticles and Supercritical Carbon Dioxide Process Parameters

Polymer nanocomposite foams have received considerable attention because of their potential use in advanced applications such as bone scaffolds, food packaging, and transportation materials due to their low density and enhanced mechanical, thermal, and electrical properties compared to traditional polymer foams. In this study, silica nanofillers were used as nucleating agents and supercritical carbon dioxide as the foaming agent. The use of nanofillers provides an interface upon which CO2 nucleates and leads to remarkably low average cell sizes while improving cell density (number of cells per unit volume). In this study, the effect of concentration, the extent of surface modification of silica nanofillers with CO2-philic chemical groups, and supercritical carbon dioxide process conditions on the foam morphology of poly(methyl methacrylate), PMMA, were systematically investigated to shed light on the relative importance of material and process parameters. The silica nanoparticles were chemically modified with tridecafluoro-1,1,2,2-tetrahydrooctyl triethoxysilane leading to three different surface chemistries. The silica concentration was varied from 0.85 to 3.2% (by weight). The supercritical CO2 foaming was performed at four different temperatures (40, 65, 75, and 85°C) and between 8.97 and 17.93 MPa. By altering the surface chemistry of the silica nanofiller and manipulating the process conditions, the average cell diameter was decreased from 9.62±5.22 to 1.06±0.32 μm, whereas, the cell density was increased from 7.5±0.5×108 to 4.8±0.3×1011 cells/cm3. Our findings indicate that surface modification of silica nanoparticles with CO2-philic surfactants has the strongest effect on foam morphology

Jet Milling as an Alternative Processing Technique for Preparing Polysulfone Hard Nanocomposites

This work describes how a solid-state blending method such as jet milling can be used to successfully prepare polysulfone (PSU)/γ-alumina nanocomposites. For comparison purposes, conventional melt extrusion was used as well. Morphological analysis revealed how jet mill blending allows obtaining well-dispersed γ-alumina nanoparticles within a polysulfone matrix without any surface treatment, with an important decrease of particle size promoted by the breakup of agglomerates and aggregates due to the particle-particle impacts during processing, which was not observed in the extruded nanocomposites. DSC analysis demonstrated that jet-milling processing promoted Tg enhancements with alumina addition, while TGA experiments confirmed the increment of thermal stability of the nanocomposites prepared by jet milling when compared with the composites prepared by extrusion. The tensile tests showed that ductility remains at a high value for milled nanocomposites, which agreed with the fracture surface images revealing large plastic deformation as a function of the alumina content. This comparative study indicates that the dispersion of nanoparticles in PSU was more homogeneous, with smaller nanoparticles when preparing nanocomposites using jet milling, showing a strong correlation with the enhanced final properties of the nanocomposites