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Electrical Properties and Relaxation Behavior of TOPO Monolayers Formed at the Air/Water Interface

Wydro P., Hąc-Wydro K.

Polish Journal of Chemistry

2007

Vol. 81, nr 1

115-127

The properties of the Langmuir monolayer formed by tri-n-octylphosphine oxide (TOPO) have been analyzed. The investigations were based both on traditional (surface potential measurements) and more advanced (the relative reflectivity using Brewster angle microscopy BAM) experimental techniques and, for better analysis, the semiempirical computation using HyperChem programme has been done. Moreover, detailed characteristics of the relaxation behaviour of TOPO monolayers have been performed. It has been found that with the increase of the surface pressure () the film thickness increases, and TOPO monolayer becomes denser; however its state does not change. Upon film compression, the reorientation of TOPO molecules occurs in this way that they become progressively more perpendicular to the surface until the collapse of the monolayer. The relaxation of TOPO monolayers formed both on water subphase as well as on NaCl solution of various concentrations were analyzed according to two-steps desorption mechanism. As it turned out, the stability of TOPO monolayer decreases with the surface pressure. At lower the loss of the monolayer material is controlled both by dissolution and diffusion mechanism, while at higher surface pressure the monolayer relaxation is controlled by two dissolution steps of different rates and the monolayer does not achieve a steady-state. Moreover, the monolayer stability increases with ionic strength.

The phase structure and relaxation phenomena in blends of a poly(ether-ester) elastomer with a liquid crystalline polyester (Vectra)

Majszczyk J., Rosłaniec Z., Pietkiewicz D., Pakuła T.

Polimery

2002

T. 47, nr 1

34-42

Poly(ether-ester) (PEE) Elitel 4450 - liquid crystalline polyester (LCP) Vectra RD 501 blends extruded (L/D = 20, D = 19mm) with a homogenizing head at 225degreesC, were studied by differential scanning calorimetry (DSC), dynamical mechanical thermal analysis (DMTA), dielectric spectroscopy, and scanning electron microscopy (SEM). The blends exhibited a multiphase microstructure. Two mechanical relaxation temperatures were found to occur, and similarly two glass transition temperatures were recorded by DSC. There is a glass transition in the PTMO soft phase (ca. - 60degreesC) and in Vectra (+ 107degreesC). For the PBT hard phase (ca. +35degreesC), T-g2, is weakly pronounced because of the high crystallinity. The blend showed only one m.p., close to the m.p. of the PEE. Three dielectric relaxation processes were found to occur in PEE and three others in Vectra. In the blends, the dielectric spectra are seen to be superimposed. These blends are immiscible in terms of thermodynamics. Vectra modified the molecular mobility of the PEE rigid segments, as evident from nonisothermal crystallization of the PBT hard phase and degree of crystallinity as also from changes of the PTMO content in the soft phase. SEM disclosed either a spherical or a fibrousstructure in the blends, depending on Vectra content.

Otrzymano szereg różniących się składem mieszanin: poli(eter/ester)/ciekłokrystaliczny poliester "Vectra" (PEE/LCP) i zbadano je metodami DSC (rys. 1, 2, tabela 1), DMTA (rys. 3, tabela 1), spektroskopii dielektrycznej (rys. 6-8, tabela 2) oraz mikroskopii elektronowej SEM (rys. 11). Jako PEE zastosowano "Elitel 4450" złożony z 50% mas. sztywnych segmentów poli(tereftalanu butylenu) (PBT) i 50% giętkich segmentów polioksatetrametylenu (PTMO). Mieszaniny te wykazują strukturę wielofazową. Badania wskazują na niemieszalność obu składników z termodynamicznego punktu widzenia. Obecność LCP "Vectra" modyfikuje jednak ruchliwość molekularną sztywnych segmentów PEE, a wpływ ten jest widoczny podczas nieizotermicznej krystalizacji PBT (zmiany stopnia krystaliczności, rys. 2 i 5a) oraz w postaci zmian zawartości PTMO w fazie miękkiej (rys. 5b). Metodą SEM stwierdzono występowanie zarówno sferycznej, jak i fi-brylarnej struktury badanych mieszanin (rys. lla-c). Właściwości dielektryczne tych mieszanin zależą przede wszystkim od matrycy PEE; wpływ zawartości LCP na te właściwości jest mały.