Search results for "Composites"
showing 10 items of 1905 documents
E-beam curing of epoxy based blends in order to produce high performance composites
2007
In this work, blends of a difunctional epoxy monomer and a thermoplastic toughening agent are E-beam irradiated at two different dose rates and two different total absorbed doses. The influence of the processing conditions on the thermal properties and on the morphology of the obtained matrices has been investigated. In particular, it is shown how the increase of the dose rate causes an increase of the temperature during irradiation, thus inducing a simultaneous thermal and radiation curing. On the contrary, at low-dose rate the system mainly undergoes to radiation curing, thus making the cured material very sensible to a post-irradiation thermal treatment with a significant improvement of …
Residual order in amorphous dry films of polymer latices: indications of an influence of particle interaction
2002
Abstract We report small angle X-ray scattering and atomic force microscopy measurements on macroscopically thick, dry films of polymer latex particles. While the surface of dried droplets has long range order due to layering effects, the overall bulk structure is amorphous. This holds for both low charge polymethylmetacrylate particles and for highly charged polystyrene particles with additional stabilisation with sodiumdodecylsurfate. In the latter case, however, considerable amounts of residual crystal-like order is observed.
Polysarcosine-containing copolymers: Synthesis, characterization, self-assembly, and applications
2018
Although the first polysarcosine (pSar) synthesis by Wesseley et al. was reported almost a century ago, it was only recently that pSar gained broader attention and is considered a potential alternative of poly(ethylene glycol) (PEG). In contrast to polyethers, such as PEG, pSar is a polypeptoid based on the amino acid sarcosine, i.e. N-methylated glycine. As a polymer, pSar combines PEG-like properties, e.g., excellent solubility in water, protein resistance, low cellular toxicity and a non-immunogenic character, while being based on endogenous material. Sarcosine can be obtained in a simple one-step reaction of bromoacetic acid and methylamine, easily transferred into the sarcosine N-(thio…
Self-diffusion in polymer solutions using the bond-fluctuation MC-algorithm
1991
Abstract A lattice Monte Carlo study of the self-diffusion of polymer chains in an athermal solution of equal chains is presented. The examined chain lengths, N (= 20–200), and volume fractions, φ (= 0.025-0.5), cover the range from dilute solution to concentrated solution, respectively. The dynamics show a gradual crossover from Rouse to reptation-like behaviour. Analysing the data according to a scaling theory and taking into account the density dependence of the microscopic length and time-scales, an almost perfect scaling of the self-diffusion coefficient is achieved. The high statistical accuracy of the data (103–104 chains per parameter combination) was obtainable by using a transpute…
From orientational glasses to structural glasses: What computer simulations have contributed to understand experiments
2002
Abstract Orientational glasses, produced by random dilution of molecular crystals, exhibit a freezing transition of the quadrupole moments. Monte Carlo simulations of lattice models (generalization of the Edwards–Anderson spin glass model) have been used to elucidate this behavior. While short range models exhibit a static glass transition at zero temperature only, the infinite range Potts glass exhibits a transition where a glass order parameter appears discontinuously. At higher temperature, a dynamical transition occurs, described by mode-coupling theory (MCT). MCT has also been tested by Monte Carlo and molecular dynamics simulations of coarse-grained models of glass-forming polymers. W…
Structural study of NaNdGa4S8, a luminescent material with low-concentration quenching
1988
Abstract Single-crystal X-ray diffraction analysis and optical investigations of NaNdGa 4 S 8 show that Nd 3+ ions are essentially distributed in two of the three square antiprismatic sites of a CaGa 2 S 4 -type lattice. The NdS 8 polyhedra are isolated (minimum NdNd distance: 6.07 A) so the interactions responsible for concentration quenching of the luminescence are considerably reduced
Mode I interlaminar fracture toughness of thin-ply laminates with CNT webs at the crack interface
2019
Abstract Pristine and functionalized carbon nanotube (CNT) webs were introduced at the interlaminar region of two different thin-ply carbon fibre reinforced polymer systems (NTPT 402 prepreg, and TeXtreme/SE84LV). The Mode I interlaminar fracture toughness (ILFT) for the NTPT 402 material was substantially lower. In contrast when SE84LV resin was used, the resistance curves were virtually unchanged and with no depreciation in the steady state value of the ILFT. This demonstrates that a careful choice of the resin is essential to permit the embedding of CNT webs in thin-ply laminates without compromising structural performance and opens a new way towards the development of multifunctional th…
Discrete bond model (DBM) of sodium silicate glasses derived from XPS, Raman and NMR measurements
1993
In sodium silicate glasses, the fraction of differently bound Si species Q[i] (i = 0−4), depending on the number i of bridging oxygens bound to the quarternary silicon, is a function of stoichiometry and the Na/Si ratio. Sodium silicate glasses were investigated by high resolution X-ray photoelectron spectroscopy. To explain the differences in chemical shifts and linewidths of the O 1s signal of the bridging and the non-bridging oxygen as a function of alkali concentration, and extended glass model was developed. This new model takes into account the influence of the alkali concentration on the Q[i] distribution and on the appearance and concentrations of differently bound bridging oxygens …
The cyclic [N(PiPr2E)2]+ (E = Se, Te) cations: a new class of inorganic ring system.
2006
The two-electron oxidation of [(tmeda)NaN(PiPr2E)2] with iodine produces the cyclic [N(PiPr2E)2]+ (E = Se, Te) cations, which exhibit long E–E bonds in the iodide salts. peerReviewed
Sterically controlled self-assembly of tetrahedral M(6)L(4) cages via cationic N-donor ligands.
2014
Tripodal cationic N-donor ligands exhibit sterically controlled self-assembly of tetrahedral M6L4 coordination cages that promote selective anion encapsulation (PF6(-)OTf(-)) in the solid state. The described method is a potential template for stepwise assembly of hetero-ligand coordination cages and polymers.