Search results for "CONDENSED MATTER"
showing 10 items of 13918 documents
Conformational studies of bottle-brush polymers absorbed on a flat solid surface.
2010
The adsorption of a bottle-brush polymer end-grafted with one chain end of its backbone to a flat substrate surface is studied by Monte Carlo simulation of a coarse-grained model, that previously has been characterized in the bulk, assuming a dilute solution under good solvent conditions. Applying the bond fluctuation model on the simple cubic lattice, we vary the backbone chain length $N_b$ from $N_b=67$ to $N_b = 259$ effective monomeric units, the side chain length $N$ from N=6 to N=48, and the grafting density $\sigma=1$, i.e., parameters that correspond well to the experimentally accessible range. When the adsorption energy strength $\epsilon$ is varied, we find that the adsorption tra…
Mechanism of anionic polymerization of (meth)acrylates in the presence of aluminium alkyls
1995
Summary Methyl methacrylate was polymerized with tert-butyl lithium in the presence of triethylaluminum or triisobutylaluminium at -78~ in toluene. As indicated by GPC and MALDI-TOF mass spectrometry, the polymerization is accompanied by side reactions. The lower oligomers were fractionated by distillation and characterised by NMR, FT-IR, UV and electron impact (EI) mass spectrometry. All these data show that part of the polymer chains are carrying exactly one tert-butyl isoprenyl ketone unit. In order to avoid the formation of tert-butyl isoprenyl ketone a molar ratio of A1/Li > 2 is necessary.
N-[Glycyl-(Z)-α,β-dehydrophenylalanylglycyl-(Z)-α,β-dehydrophenylalanyl]glycine trifluoroacetate methanol solvate
2007
The molecular conformation of the title dehydropeptide, H+-Gly1–ΔZPhe2–Gly3–ΔZPhe4–Gly5-OH·CF3COO−·CH3OH or C24H26N5O6+·CF3COO−·CH3OH, is characterized by the presence of two intramolecular N—H⋯O hydrogen bonds that stabilize two type III β-turns, at the ΔZPhe2 (ΔZPhe is the Z isomer of the α,β-dehydrophenylalanine residue) and Gly3, and Gly3 and ΔZPhe4 residues. As a result, the pentapeptide adopts a right-handed 310-helical conformation. All peptide units are linked trans to each other.
N‐[tert‐Butoxycarbonylglycyl‐(E)‐α,β‐dehydrophenylalanylglycylglycyl‐(E)‐α,β‐dehydrophenylalanyl]glycine
2006
In the molecule of the title hexapeptide, Boc0–Gly1–ΔEPhe2–Gly3–Gly4–ΔEPhe5–Gly6–OH, C31H36N6O9, there are two overlapping β-turns, one of type II on the ΔEPhe2 (ΔEPhe is isomer E of the α,β-dehydrophenylalanine residue) and Gly3 residues and the second of type III′ on the Gly3 and Gly4 residues. All amino acids in the peptide are linked trans to each other. Three relatively strong intramolecular N—H⋯O hydrogen bonds stabilize the crystal structure. Two of them, of the 4→1 type, are responsible for two β-turns in the peptide.
Impact of aggregates on excitation dynamics in transparent polymer films doped by dipolar molecules
2008
Abstract Optical properties of transparent polymer films of polymethylmethacrylate doped (up to 25 wt.%) by dipolar N , N -dimethylaminobenzylidene 1,3-indandione (DMABI) molecules were studied. Formation of DMABI nanocrystallites, increasing in their density and size with dopant concentration, was revealed by optical microscopy. Transformation of the fluorescence spectrum from the molecular-like emission (for the low dopant concentration below 1 wt.%) to highly red-shifted fluorescence corresponding to self-trapped excitons in the crystallites was observed. It was shown, that due to the resonant energy transfer in the blend, the DMABI nanocrystals can serve as efficient fluorescence marker…
Aggregation Processes and Formation of Silico-calco-alkaline Gels under High Ionic Strength
2002
This paper presents a systematic in situ study of the process of formation of silico-calco-alkaline gels starting from a liquid colloidal solution containing different alkaline ions and different calcium concentration until the final gel state. The combined use of X-ray and neutron small-angle scattering (SAS) and dynamical rheometry techniques lead to a consistent description of the structure of the aggregates and of the mechanisms of aggregation involved in gel formation. SAS results indicate that the aggregates are fractal objects, their structure strongly depending on calcium ion concentration. The differences in gelation kinetics for systems containing different alkaline ions were attr…
Universal glue for cells
2012
A dendritic polymer consisting of inversely oriented lipid head groups on a polyvalent polyglycerol scaffold makes an effective reversible biomembrane adhesive that may find use as a tissue sealant and a drug-delivery vehicle.
Characterization of oriented protein-ceramic and protein-polymer-composites for cartilage tissue engineering using synchrotron μ-CT
2007
Abstract In this paper we report on the synthesis of three different gelatine based scaffold materials for the reconstruction of articular cartilage defects. The first scaffold design is based on an unmodified, oriented gelatine network, while the second design further comprises an attached inorganic hydroxyapatite layer and the third design includes poly(l-lactide) microspheres as a model material for future drug-release applications. All three scaffold designs were characterized and imaged using synchrotron μ-CT, obtaining a complete volumetric reconstruction of a previously defined sample region. Furthermore, two unmodified scaffolds were cultivated for one week with porcine chondrocytes…
Scattering function and the dynamics of phase separation in polymer mixtures under shear flow
1988
The phenomenological mean-field theory describing concentration fluctuations and spinodal decomposition of binary mixtures of long flexible macromolecules is generalized to mixtures under steady shear flow. This shear flow leads to a partial orientation and stretching of the coils, as well as to an anisotropic deformation of concentration fluctuations. Generalizing the approach of Onuki and Kawasaki, we obtain the collective scattering function describing these concentration fluctuations in the mixture under shear flow. Both the steady-state situation in the one-phase region and the initial stages of spinodal decomposition for concentrations inside of the spinodal curve are considered.
Relaxation of electron-hole pairs and scintillation mechanism in alkali halide crystals
1997
Abstract The mechanism of the ionizing radiation energy transfer from host lattice to luminescence centers is discussed taking into account the results of the recent experimental investigations of electron-hole pair relaxation in alkali iodide crystals. The high scintillation yield in CsI-Tl, CsI-Na and partially in Nal-Tl crystals is explained by the process of the motion and capture of a one-center self-trapped exciton by impurity ions.