14 research outputs found
Influence of C60 fullerenes on the glass formation of polystyrene
AbstractWe investigate the impact of fullerene C60 on the thermal properties and glass formation of polystyrene (PS) by differential scanning calorimetry (DSC) and dielectric spectroscopy (DS), for C60 concentrations up to 30% mass fraction. The miscibility and dispersibility thresholds of PS/C60 nanocomposites are first estimated by a combination of microscopy, small angle neutron scattering (SANS) and wide-angle X-ray scattering (WAXS) experiments, and these thresholds were found to be â1 mass% and â4 mass% C60, respectively. The addition of C60 increases the glass-transition temperature (Tg) of rapidly precipitated PS composites, up to a âthresholdâ C60 concentration (â4 wt%, in agreement with the dispersibility estimate). Beyond this concentration, the Tg reverts gradually towards the neat PS value. We present a comprehensive study for composites based on PS of molecular mass 270 kg/mol, and demonstrate the generality of the impact of C60 on Tg for PS matrices of 2 and 20 kg/mol. Thermal annealing or slowly evaporated composites largely reverse these effects, as the dispersion quality decreases. The dynamic fragility m of the composite is found to increase in the presence of C60, but the scaling of m with Tg for PS is retained. Similarly, physical ageing experiments show a reduction of relaxation enthalpy in the glass regime, which is largely accounted for by the increase of Tg with C60. The slowing down of the PS α-relaxation with C60 contrasts with the local âsofteningâ indicated by former Debye-Waller measurements and increase in fragility m. This effect is opposite to that of antiplasticizer additives, which both stiffen the material in the glassy state and reduce Tg, and simulations suggest this could be due to an increase in packing frustration. Finally, we review observations on the effect of nanoparticles on the Tg of PS and discuss the non-universal nature of Tg shifts by various types of nanoparticles
2âMethyltetrahydrofuran (2âMeTHF) as a versatile green solvent for the synthesis of amphiphilic copolymers via ROP, FRP, and RAFT tandem polymerizations
2âmethyltetrahydrofuran (2âMeTHF) is a readily available, inexpensive, neoteric, bioâbased solvent. It has been adopted across a wide range of chemical processes including the batch manufacture of fine chemicals, enzymatic polycondensations and ring opening polymerizations. To reduce the environmental burden related to the synthesis of pharmaceuticalâgrade polymers based on lactide and caprolactone, we envisaged the use of 2âMeTHF. For the first time, we combined a series of metalâfree and enzymatic ROPs with free radical and controlled RAFT polymerizations (carried out separately and in tandem) in 2âMeTHF, in order to easily tune the chemistry and the architecture of the final polymers. After a simple purification, the amphiphilic polymers were formulated into nanoparticles and tested for their cytocompatibility in three model cell lines, to assess their application as potential polymeric excipients for nanomedicines
Functional initiators for the ring-opening polymerization of polyesters and polycarbonates:An overview
Functional ring-opening polymerization (ROP) initiators can instill a wide array of chemical, physical, and biological effects into a polymeric chain. Highlighting the versatility of this âactiveâ initiator approach, a broad range of characteristics can be achieved through the use of initiators with chemistries spanning from drugs and dyes (key in the case of drug delivery or nanoparticle applications) through to radically active monomers, polymerization transfer agents, and catalysts. The selection of a suitable âactiveâ initiator (monomers for tandem reactions, dyes, drugs, stereo-catalysts, etc.) can not only provide the final polymers with interesting application potential but also facilitate the implementation of ROP reactions in tandem with other polymerization techniques. Overall, this review will highlight that functionalities and properties can be effectively tuned by exploiting simple chemistry approaches, allowing readers to identify how these approaches could be of benefit to their own work in a range of applications including drug/gene delivery, amphiphilic bio/degradable carriers, drug/scent controlled release, and stereo-controlled polymers
Conformation and Interactions of Polystyrene and Fullerenes in Dilute to Semidilute Solutions
We
report the polymer conformation and fullerene aggregation in
a ternary system containing polystyrene, C<sub>60</sub>, and toluene
measured by small angle neutron, static, and dynamic light scattering.
We investigate polymer concentrations across the dilute and semidilute
regime for five polymer molecular weights (<i>M</i><sub>w</sub> = 20 kg/mol to 1 Mg/mol), and fullerene concentrations below
and above its miscibility threshold in toluene. We find that the polymer
radius of gyration (<i>R</i><sub>g</sub><sup>poly</sup>), hydrodynamic radius (<i>R</i><sub>h</sub>), and the mixture correlation length (Ο) remain
unchanged upon addition of C<sub>60</sub>. The miscibility of C<sub>60</sub> in toluene, however, decreases upon addition of polystyrene
forming aggregates with a time-dependent radius on the order of 100
nm, and this effect is amplified with increasing polymer <i>M</i><sub>w</sub>. Our findings are relevant to the solution processing
of organic photovoltaics, which generally require the effective solubilization
of fullerene derivatives and polymer pairs in this concentration range
Structural Insight into Protective Alumina Coatings for Layered Li-Ion Cathode Materials by Solid-State NMR Spectroscopy
Layered transition metal oxide cathode materials can exhibit high energy densities in Li-ion batteries, in particular, those with high Ni contents such as LiNiO2. However, the stability of these Ni-rich materials often decreases with increased nickel content, leading to capacity fade and a decrease in the resulting electrochemical performance. Thin alumina coatings have the potential to improve the longevity of LiNiO2 cathodes by providing a protective interface to stabilize the cathode surface. The structures of alumina coatings and the chemistry of the coatingâcathode interface are not fully understood and remain the subject of investigation. Greater structural understanding could help to minimize excess coating, maximize conductive pathways, and maintain high capacity and rate capability while improving capacity retention. Here, solid-state nuclear magnetic resonance (NMR) spectroscopy, paired with powder X-ray diffraction and electron microscopy, is used to provide insight into the structures of the Al2O3 coatings on LiNiO2. To do this, we performed a systematic study as a function of coating thickness and used LiCoO2, a diamagnetic model, and the material of interest, LiNiO2. 27Al magic-angle spinning (MAS) NMR spectra acquired for thick 10 wt % coatings on LiCoO2 and LiNiO2 suggest that in both cases, the coatings consist of disordered four- and six-coordinate AlâO environments. However, 27Al MAS NMR spectra acquired for thinner 0.2 wt % coatings on LiCoO2 identify additional phases believed to be LiCo1âxAlxO2 and LiAlO2 at the coatingâcathode interface. 6,7Li MAS NMR and T1 measurements suggest that similar mixing takes place near the interface for Al2O3 on LiNiO2. Furthermore, reproducibility studies have been undertaken to investigate the effect of the coating method on the local structure, as well as the role of the substrate
Structural Insight into Protective Alumina Coatings for Layered Li-Ion Cathode Materials by Solid-State NMR Spectroscopy.
Layered transition metal oxide cathode materials can exhibit high energy densities in Li-ion batteries, in particular, those with high Ni contents such as LiNiO2. However, the stability of these Ni-rich materials often decreases with increased nickel content, leading to capacity fade and a decrease in the resulting electrochemical performance. Thin alumina coatings have the potential to improve the longevity of LiNiO2 cathodes by providing a protective interface to stabilize the cathode surface. The structures of alumina coatings and the chemistry of the coating-cathode interface are not fully understood and remain the subject of investigation. Greater structural understanding could help to minimize excess coating, maximize conductive pathways, and maintain high capacity and rate capability while improving capacity retention. Here, solid-state nuclear magnetic resonance (NMR) spectroscopy, paired with powder X-ray diffraction and electron microscopy, is used to provide insight into the structures of the Al2O3 coatings on LiNiO2. To do this, we performed a systematic study as a function of coating thickness and used LiCoO2, a diamagnetic model, and the material of interest, LiNiO2. 27Al magic-angle spinning (MAS) NMR spectra acquired for thick 10 wt % coatings on LiCoO2 and LiNiO2 suggest that in both cases, the coatings consist of disordered four- and six-coordinate Al-O environments. However, 27Al MAS NMR spectra acquired for thinner 0.2 wt % coatings on LiCoO2 identify additional phases believed to be LiCo1-xAlxO2 and LiAlO2 at the coating-cathode interface. 6,7Li MAS NMR and T1 measurements suggest that similar mixing takes place near the interface for Al2O3 on LiNiO2. Furthermore, reproducibility studies have been undertaken to investigate the effect of the coating method on the local structure, as well as the role of the substrate
Structural Insight into Protective Alumina Coatings for Layered Li-Ion Cathode Materials by Solid-State NMR Spectroscopy
Layered transition
metal oxide cathode materials can exhibit high
energy densities in Li-ion batteries, in particular, those with high
Ni contents such as LiNiO2. However, the stability of these
Ni-rich materials often decreases with increased nickel content, leading
to capacity fade and a decrease in the resulting electrochemical performance.
Thin alumina coatings have the potential to improve the longevity
of LiNiO2 cathodes by providing a protective interface
to stabilize the cathode surface. The structures of alumina coatings
and the chemistry of the coatingâcathode interface are not
fully understood and remain the subject of investigation. Greater
structural understanding could help to minimize excess coating, maximize
conductive pathways, and maintain high capacity and rate capability
while improving capacity retention. Here, solid-state nuclear magnetic
resonance (NMR) spectroscopy, paired with powder X-ray diffraction
and electron microscopy, is used to provide insight into the structures
of the Al2O3 coatings on LiNiO2.
To do this, we performed a systematic study as a function of coating
thickness and used LiCoO2, a diamagnetic model, and the
material of interest, LiNiO2. 27Al magic-angle
spinning (MAS) NMR spectra acquired for thick 10 wt % coatings on
LiCoO2 and LiNiO2 suggest that in both cases,
the coatings consist of disordered four- and six-coordinate AlâO
environments. However, 27Al MAS NMR spectra acquired for
thinner 0.2 wt % coatings on LiCoO2 identify additional
phases believed to be LiCo1âxAlxO2 and LiAlO2 at the
coatingâcathode interface. 6,7Li MAS NMR and T1 measurements suggest that similar mixing takes
place near the interface for Al2O3 on LiNiO2. Furthermore, reproducibility studies have been undertaken
to investigate the effect of the coating method on the local structure,
as well as the role of the substrate