Graphene quantumdots: In the crossroad of graphene, quantum dots and carbogenic nanoparticles

The scientific and technological importance of graphene quantum dots (GQDs) is directly related to their nanoscopic nature that endows remarkable photo-physical properties and colloidal stability in a variety of solvents. GQDs combine characteristics arising from their graphitic structure, their carbogenic origin and their quantum nature. They are considered as the environmentally benign alternatives of heavy metal based quantum dots, given that not only are they synthesized following green strategies, but they also exhibit minimal toxicity. GQDs are systematically explored in printing, energy harvesting, bioimaging, catalysis, optoelectronics and sensing applications

Adaptation of pharmaceutical excipients to FDM 3D printing for the fabrication of patient-tailored immediate release tablets

This work aims to employ fused deposition modelling 3D printing to fabricate immediate release pharmaceutical tablets with various model drugs. It investigates the addition of non-melting filler to methacrylic matrix to facilitate FDM 3D printing and explore the impact of (i) the nature of filler, (ii) compatibility with the gears of the 3D printer and, and iii) polymer: filler ratio on the 3D printing process. A specially developed filament based on pharmaceutically approved methacrylic polymer (Eudragit E) and thermally stable filler, TCP (tribasic calcium phosphate) was optimised. Four model drugs with different physicochemical properties were included into ready-to-use mechanically stable tablets with immediate release properties. Amongst the investigated fillers in this work, directly compressible lactose, spray-dried lactose and microcrystalline cellulose showed a level of degradation at 135°C whilst talc and TCP allowed consistent flow of the filament and a successful 3D printing of the tablet. Following the two thermal processes (hot melt extrusion (HME) and fused deposition modelling (FDM) 3D printing), drug contents were 94.22%, 88.53%, 96.51% and 93.04% for 5-ASA, captopril, theophylline and prednisolone respectively. XRPD indicated that a fraction of 5-ASA, theophylline and prednisolone remained in the crystalline form whilst captopril was in amorphous form. By combining the advantages of thermally stable pharmaceutically approved polymers and fillers, this unique approach provides a low cost production method for on demand manufacturing of individualised dosage forms

Fouling Release Nanostructured Coatings based on PDMS-polyurea Segmented Copolymers

http://www.elsevier.com/wps/find/journaldescription.cws_home/30466/description#descriptionThe bulk and surface characteristics of a series of coatings based on PDMS-polyurea segmented copolymers were correlated to their fouling release performance. Incorporation of polyurea segments to PDMS backbone gives rise to phase separation with the extensively hydrogen bonded hard domains creating an interconnected network that imparts mechanical rigidity. Increasing the compositional complexity of the system by including fluorinated or POSS-functionalized chain extenders or through nanoclay intercalation, confers further thermomechanical improvements. In analogy to the bulk morphology, the surface toporgraphy also reflects the compositional complexity of the materials, displaying a wide range of motifs. Investigations on settlement and subsequent removal of Ulva sporelings on those nanostructured surfaces indicate that the work required to remove the microorganisms is significantly lower compared to coatings based on standard PDMS homopolymer. All in all, the series of materials considered in this study demonstrate advanced fouling release properties, while exhibiting superior mechanical properties and thus, long term durability. (C) 2010 Elsevier Ltd. All rights reserved.This publication is based on work supported by the Office of Naval Research. This publication is also based on work supported in part by Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST). We acknowledge facility support through the Cornell Center for Materials Research (CCMR) and the Nanobiotechnology Center (NBTC)

Mechanism of enhancement of intumescent fire retardancy by metal acetates in polypropylene

The effects of cobalt acetate (CoAc), manganese acetate (MnAc), nickel acetate (NiAc) and zincacetate (ZnAc) as fire retardant additive in intumescent polypropylene (PP) formulations containing PP/ammonium polyphosphate (APP)/pentaerythritol (PER) are reported. The limiting oxygen index (LOI) and vertical burning (UL94) tests and cone calorimetry were used to quantify the enhancement. Environmental chamber rheometry, thermal gravimetric analysis and the morphology of the residual char were used to investigate the mechanism of enhancement. The incorporation of small quantities of metal acetates had a significant influence on the fire behaviour. As an example, 0.7 wt% MnAc improved the UL 94 rating of PP/APP+PER (mass ratio 100/25, with APP/PER=3/1) sample from V-2 to V-0, while 1 wt% MnAc reduced the peak heat release rate and the total heat release by 18% and 12% in the cone calorimeter. Rheological data, cone calorimetry, and photographs of the residual char showed how the fire retardancy of the systems were affected by the melt viscosity, which depended on the loading of metal acetate. During thermal decomposition, the metal acetates promote the crosslinking of the polymer and the fire retardant, reinforcing the protective intumescent layer. While, the effect is most potent at the optimal metal loadings. At higher MnAc loadings, the benefit of a stronger char is overwhelmed by the adverse effect of crosslinking on the transition char layer. Thus, this paper offers a new insight into the mechanism of the intumescent fire retarded PP system

Dramatic photoluminescence quenching in carbon dots induced by cyclic voltammetry

This study focuses on the structural rearrangements and the photoluminescent behavior of pyrolytically derived carbon dots when subjected to a series of cyclic voltammetry sweeps. Although the electrical signals involved are not pronounced, multiple electrochemical cycling results in a progressive suppression of the photoluminescence, so that after 42 sweeps the intensity is reduced by one order of magnitude. At the same time, the fluorescence component stemming from the organic fluorophores is blue-shifted, while the contribution of the carbogenic cores is red-shifted. XPS and FTIR spectra reveal that the voltammetric field induces an extensive formation of C-O and C[double bond, length as m-dash]O at the expense of the C[double bond, length as m-dash]C bonds. Our findings indicate a close relationship between the electrochemical response and the structure of C-dots and, thus, have direct implications on the development of C-dot based electroluminescent materials, electrochemical sensors and solar cells

Optical transparency in a polymer blend induced by clay nanofillers

The effect of added nanoclays to the morphological characteristics and the macroscopic properties in a blend of isotactic polypropylene (iPP) and poly(ethylene oxide) (PEO) is examined in this study. It is shown that strong interactions between the surfactant used for clay modification and the binary matrix can effectively control the spatial organization of the suspended polymer droplets. It is also shown that the emulsifying efficiency of nanoclays to the polymer blend has a critical effect on the macroscopic properties of the nanocomposites. In this study, we present a unique case in which the incorporation of a small amount of organically modified nanoclay induces a dramatic transformation from an opaque to a transparent system. © 2008 Elsevier Ltd. All rights reserved

Nafion-clay hybrids with a network structure

http://www.elsevier.com/wps/find/journaldescription.cws_home/30466/description#descriptionNafion-clay hybrid membranes with a unique microstructure were synthesized using a fundamentally new approach. The new approach is based on depletion aggregation of suspended particles - a wellknown phenomenon in colloids. For certain concentrations of clay and polymer, addition of Nafion solution to clay suspensions in water leads to a gel. Using Cryo-TEM we show that the clay particles in the hybrid gels from a network structure with an average cell size in the order of 500 nm. The hybrid gels are subsequently cast to produce hybrid Nafion-clay membranes. Compared to pure Nafion the swelling of the hybrid membranes in water and methanol is dramatically reduced while their selectivity (ratio of conductivity over permeability) increases. The small decrease of ionic conductivity for the hybrid membranes is more than compensated by the large decrease in methanol permeability. Lastly the hybrid membranes are much stiffer and can withstand higher temperatures compared to pure Nafion. Both of these characteristics are highly desirable for use in fuel cell applications, since a) they will allow the use of a thinner membrane circumventing problems associated with the membrane resistance and b) enable high temperature applications (C) 2009 Elsevier Ltd. All rights reserved.We acknowledge the financial support of the Cornell Fuel Cell Institute funded by DOE. EPG acknowledges the support of Award No. KUS-C1-018-02, made by King Abdullah University of Science and Technology (KAUST)

Aqueous gels of diblock oxyethylene-oxypropylene copolymers

Aqueous solutions of diblock copolymers E102P37 and E92P55 (E=oxyethylene unit, P=oxypropylene unit) were investigated by rheometry. Storage (G′) and loss (G″) modulus and yield stress (σy) were used to detect and characterise hard and soft gels in experiments which covered the concentration range 4-28 wt.-% copolymer and the temperature range 5-85°C. Comparison is made with phase diagrams reported for other diblock copoly-(oxyalkylene)s, and it is shown that the mesophase behaviour of these systems depends on the effective thickness of the E-block corona and the stability of the micelles at low temperatures

Effect of ethanol on the rheological properties of water-rich gels of diblock copolymer E43B11

The effect of added ethanol on the Theological behaviour of aqueous solutions of diblockcopolymerE43B11 (E = oxyethylene unit, B = oxybutylene unit) has been investigated. Thermally reversible sol-gel transitions were observed for concentrated solutions of the copolymer in solutions containing 0-30 wt.-% ethanol. Storage (G') and loss (G″) moduli and yield stress (oσγ) were used to define hard and soft gel phases. The introduction of 10 wt.-% ethanol did not alter the phase behaviour greatly, whereas higher ethanol concentrations had a large effect, which differed in kind from that reported for triblock copolymers of ethylene oxide and propylene oxide, type EPE