Search results for "SPECTRA"

Relationship between structure of drawn polymers and molecular motion

1971

In order to study the relationship between structure and molecular motion, drawn polymers are more suitable than isotropic samples since their morphology can be characterized more easily by quantitative methods such as small angle X-ray scattering (SAXS) and electron microscopy (EM). The effects of changes in morphological structure on molecular motion are demonstrated by comparing the results of the SAXS and EM measurements with the dynamic mechanical behavior of drawn polyethylene. In addition the NMR broad line spectra of these samples were analyzed and the influence of annealing conditions and external stress was investigated.

The influence of mechanical damaging on the lifetime of positrons In ultrahigh-molecular polyethylene

2013

We study the influence of damaging of ultrahigh-molecular polyethylene [(PE-UHMW) Chirulen®1120] applied, among other materials, in the production of hip endoprostheses on the spectra of positrons lifetime in this material. Polyethylene samples were damaged by the impacts, rolling friction, and collisions with metal balls in a planetary mill. The changes in the parameters of the spectra of positrons lifetime related to the annihilation of orthopositronium (o-Ps) were analyzed depending on the mechanical energy transferred to the sample. On the basis of the Eldrup–Tao model, the changes in the radii of voids in which positroniums are formed and annihilated and the changes in the degree of fi…

Photosensitive properties of composite films based on copper chloride in polymer matrix

2013

The composite films based on PMMA and CuCl2 were prepared. Transmission spectra of the films before and after illumination by different laser lines (405, 448, 456 nm) were measured. The reversible character of the composite photosensitivity was fixed. The phenomenon of direct surface relief formation after laser beam illumination of composite films was described. The holographic gratings were recorded by different exposure (200 – 500 J/cm2) in the films with different concentration (8 and 20 wt. %) of copper salt. The film sensitivity dependence on polymer molecular weight was studied. Surface relief of the gratings was measured by AFM.

Visible polarized light transmission spectroscopy of the electro-optic switching behaviour of surface stabilized ferroelectric liquid crystal cells

1991

Abstract We present in this paper an experimental and theoretical modelling study of the switching characteristics and electro-optic behaviour of chevron surface stabilized ferroelectric liquid crystal cells with planar (low pre-tilt) and non-planar (high pre-tilt) surface conditions. The visible polarized light transmission spectra were taken of the cells with glass plates coated with films of either rubbed polymer or obliquely evaporated silicon monoxide (SiO) at various applied voltages and in various stages of switching and compared with the theoretical values calculated numerically based on our director-polarization structure model for the aforementioned cells. The results provide evid…

Excitons and nonlinear optical spectra in conjugated polymers.

1992

Excitons in conjugated polymers are studied theoretically in the Su-Schrieffer-Heeger model supplemented by long-range Coulomb interactions. The relationship between exciton energies and basic interaction parameters is clarified. Linear and third-order nonlinear optical susceptibilities (two-photon absorption, electroabsorption, and third-harmonic generation) have been calculated, elucidating the significance of singlet and triplet excitons and unbound electron-hole pairs. Using only moderate interaction strength, various experiments in polydiacetylene can be interpreted in a consistent way

Enhancement of metallo-supramolecular dissociation kinetics in telechelic terpyridine-capped poly(ethylene glycol) assemblies in the semi-dilute regi…

2019

The dynamics of supramolecular polymer assemblies is governed by that of their polymeric building blocks and that of the transient bonds between them. Entrapment of such bonds by topological crowding often causes renormalization of the bond lifetimes towards prolonging. In the present study, by contrast, we show that this effect can also be inverse in the case of telechelic metallo-supramolecular polymers in semi-dilute solution. We focus on linear poly(ethylene glycols) capped by terpyridine binding motifs at both ends that can form metal–ligand coordinative bonds with various transition metal ions, thereby creating transient metallo-supramolecular assemblies of varying length and binding …

ChemInform Abstract: Preparation and Structural Characterization of (Me3SiNSN)2Se, a New Synthon for Sulfur-Selenium Nitrides.

2010

The reaction of (Me(3)SiN)(2)S with SeCl(2) (2:1 ratio) in CH(2)Cl(2) at -70 degrees C provides a route to the novel mixed selenium-sulfur-nitrogen compound (Me(3)SiNSN)(2)Se (1). Crystals of 1 are monoclinic and belong the space group P2(1)/c, with a = 7.236(1) A, b = 19.260(4) A, c = 11.436(2) A, beta = 92.05(3) degrees, V = 1592.7(5) A(3), Z = 4, and T = -155(2) degrees C. The NSNSeNSN chain in 1 consists of Se-N single bonds (1.844(3) A) and S=N double bonds (1.521(3)-1.548(3) A) with syn and anti geometry at the N=S=N units. The N-Se-N bond angle is 91.8(1) degrees. The EI mass spectrum shows a molecular ion with good agreement between the observed and calculated isotopic distributions…

1990

New monomers are described for the synthesis of rod-like poly(1,4-phenyleneethynylene)s with long flexible aliphatic side chains. By palladium catalyzed polycondensation soluble polymers with melting points around 100°C could be obtained. The molecular weight was estimated by GPC, VPO and elemental analysis: GPC showed a multimodale distribution with Pn = 9–15. NMR spectra were found to be in agreement with the assumed polymer structure, but signals of the acetylenic carbons could not be detected. A broad, structureless absorption with a maximum at λ = 410 nm is seen in the UV-VIS-spectra. The thermal decomposition of the substituted PPE's starts at about 400°C and is comparable to that of …

Photon yields and decay times of cross luminescence in ionic crystals

1992

The authors report on the scintillation properties of the ternary inorganic crystals KMgF/sub 3/, KYF/sub 4/:Rb, K/sub 2/YF/sub 5/, KLuF/sub 4/, RbMgF/sub 3/, KZnF/sub 3/, BaTm/sub 2/F/sub 8/, LiYF/sub 4/:Nd, and BaF/sub 2/:Rb. The scintillation light output of these crystals was estimated from the X-ray-induced emission spectra. Optical absorption spectra and decay time spectra were also measured and are presented. The first four crystals produced cross-luminescence (CL) with a decay time of about 1.5 ns. CL was not observed for the other crystals. >

Shallow-donor impurities in indium selenide investigated by means of far-infrared spectroscopy.

1992

Shallow impurities in n-type indium selenide (InSe) have been investigated by means of Fourier-transform spectroscopy in the far-infrared region. Three electric dipole transitions have been identified: 1s-2${\mathit{p}}_{\ifmmode\pm\else\textpm\fi{}}$, 1s-2${\mathit{p}}_{0}$, and 1s-3${\mathit{p}}_{\ifmmode\pm\else\textpm\fi{}}$, corresponding to electrons bound to native donors and tin-, silicon-, and chlorine-related donors, whose ionization energies (17.6, 18.1, 18.8, and 19 meV, respectively) have been determined through the Guerlach-Pollmann model. That model was also used to calculate the oscillator strengths of those dipole transitions, and then to estimate the shallow-donor concentr…