Compensated Arrhenius formalism applied to a conductivity study in poly(propylene glycol) diacrylate monomers.

The temperature dependence of the ionic conductivity is studied in a series of poly(propylene glycol) diacrylate monomers. The experimental data are analyzed by means of the approach recently proposed by Petrowsky et al. [J. Phys. Chem. B. 113, 5996 (2009)10.1021/jp810095g]. This so-called compensated Arrhenius formalism (CAF) approach takes into account the influence of the dielectric permittivity on the exponential prefactor in the classical Arrhenius equation. The experimental data presented in this paper show a good agreement with the CAF; this means that the exponential prefactor is principally dielectric permittivity dependent. The compensated data revealed two conduction processes with different activation energies; they correspond to low and high temperature ranges, respectively.

FT-IR and FT-Raman spectra of 2-hydroxyethyl methacrylate--A conformational and vibrational analysis.

A conformational search of the flexible 2-hedroxyethyl methacrylate molecule by semi-empirical AM1 and B3LYP formalisms leads to six stable conformations. Four of them are in the s-trans conformation. The optimized geometries at DFT using 6-311+G(∗∗) basis set are in good agreement with experimental electron diffraction data of the methyl methacrylate molecule, thereby the s-trans is the most stable form. The harmonic frequencies at the fully optimized geometries of all conformers have been performed at the DFT//B3LYP/6-311+G(∗∗) level of theory. Infrared and Raman intensities and potential energy distributions of the scaled harmonic frequencies are used for the assignment of the observed IR and Raman bands. We noticed a good agreement between the experimental and the computed spectra. The strong band at 1081 cm(-1), in the infrared spectrum, maybe used as a characteristic band of the s-trans conformation. Henceforth, the less stable structure contribute alone for reproducing the Raman bands located at 276 (sh) and 3020 (vw) cm(-1).

MM and QM: conformational and vibrational spectra analysis of 2-hydroxyethyl acrylate.

2-Hydroxyethyl acrylate is generally used with other acrylic and methacrylic products in order to get the desired characteristics of the final product. In this work we are about to make an assignment of experimental infrared bands with the help of a theoretical quantum chemistry calculations. The exact knowledge of some bands which are not characteristics of acrylic materials will enable us to make a quick analysis with available techniques of low costs for mixtures of polymers based on acrylate and methacrylate molecules. In the experimental part, the infrared spectrum of 2-hydroxyethyl acrylate is obtained by using a FTIR Perkin Elmer model 2000. In the computational part and as first step, the theoretical calculations are performed by the semi-empirical AM1 method for excluding similar structures of 2-hydroxyethyl acrylate molecule by a meticulous conformational analysis. As a second step the obtained structures are optimized using DFT. The simulated frequencies are then scaled and a tentative assignment is made based on band intensities and PED percentages. The theoretical calculations predict the existence of thirteen conformations two of them represent the majority of experimental bands in the infrared spectrum. Two neighbor experimental bands located at 1301 and 1207 cm(-1) maybe used as characteristic bands to locate and distinguish the existence of one or both conformations.

Spectrophotometric investigation of interaction between iodine and pentadentate Schiff base ligands.

The interaction between iodine as an electron acceptor (A), and three pentadentate Schiff bases, 1,3-bis(salicylideneamino)-2-propanol (SB1), 1,3-bis(2-hydroxy-1-naphthylideneamino)-2-propanol (SB2), and 1,3-bis[1-(pyridine-2-yl)methylideneamino]-2-propanol (SB3), as electron donor systems (D), was studied spectrophotometrically in methanol at 28 °C. Equilibrium constants K(AD) and molar extinction coefficients ε(AD) of the donor-acceptor complexes (AD) were determined using the modified Benesi-Hildebrand equation in conjunction with the non linear fit analysis. The method shows the formation of 1:1 type complexes as major species in solution. The free energy changes ΔG° and the energy of the charge transfer band E(CT) were also calculated for all complexes. The iodine complex derived from SB2 seems to be more stable than those derived from SB3 and SB1. On the other hand, the ionization potential I(D) of each Schiff base was estimated from the corresponding complex band energy, using an empirical equation. An inverse relationship between I(D) and K(AD) values was found. Blue and red shift observed for the 445 nm band of iodine were also discussed on the basis of theoretical considerations.

Phase diagrams and morphology of polymer dispersed liquid crystals based on nematic-liquid-crystal-monofunctional-acrylate mixtures

Phase diagrams of unpolymerized and UV-polymerized 2-ethyl hexyl acrylate (EHA) mixtures with the liquid crystal E7 are established using optical microscopy and differential scanning calorimetry. Both diagrams show upper critical solution temperature behavior. From 50 to 90 wt % liquid crystal (LC), the (I+I) phase located between the (N+I) and (I) phases was clearly shown. The nematic phase inside the droplets exhibits a twisted radial structure indicating that homeotropic anchoring occurs at the polymer interface. The experimental phase diagrams were successfully analyzed using a model based on the Flory-Huggins theory of isotropic mixing supplemented with the Maier-Saupe theory of nematic order. The LC solubility limit in the polymer matrix and the fractional amount of LC contained in the droplets were deduced from the calorimetric measurements. For the specific composition EHA/E7 (50:50), the scattering and morphological properties of the films were studied as a function of time elapsed after UV exposure. Drastic changes in the size, shape, spatial distribution, and number density of nematic droplets were observed and analyzed in terms of coalescence/diffusion phenomena.

Phase Behavior of Blends of Polymers and Smectic-A Liquid Crystals.

The phase behavior of blends of polymers and smectic-A liquid crystals (LCs) is investigated using Flory-Huggins and Maier-Saupe-McMillan theories. Various examples are considered to depict the effects of the architecture and the size of the polymer together with the nature of anisotropic ordering forces on the phase diagram. The strength of these forces is characterized by a parameter alpha which is directly related to the temperature of the smectic-nematic transition. Three cases are considered depending on the value of alpha, and the corresponding phase diagrams are constructed. Substantial differences are observed in these diagrams, and the reasons for these differences are discussed. A comparative study is performed between mixtures of polymers and LCs, where the polymer is made of linear and crosslinked chains. The LC consists either of molecules with nematic ordering only or of molecules presenting both nematic and smectic-A ordering. Blends where polymer matrices are cross-linked networks are also examined. Remarkable properties are found in the nature of the phase diagrams for such mixtures. In general, it is observed that the ordering forces favor unmixing with a stronger effect for the higher smectic-A ordering. Spinodal curves are also reported for these mixtures. The effects of fluctuations near the transition temperatures are briefly discussed.

Effects of α-tocopherol (Vitamin E) on the Ultrastructure of Human Platelets In Vitro.

Washed human platelets were incubated with increasing concentrations of α-tocopherol. Spontaneous aggregation was induced by tocopherol (0.5 mM or above). Aggregation was inhibited by ethylenediaminetetraacetate and platelet activation was reduced by prostaglandin E(1). Using electron microscopy, it was confirmed that tocopherol caused platelet disruption to some extent and the released components may have generated aggregation. These effects were not observed in platelet-rich plasma. Spontaneous activation was not observed when the concentration of tocopherol was 0.03 mM or lower. Concentrations of tocopherol between 0.075 mM and 0.0075 mM had inhibiting influences on activation of washed platelets by thrombin. Tocopherol (between 0.1 mM and 0.005 mM) changed activation of washed platelets by cationized ferritin in that it facilitated the first phase of aggregation but reduced the second phase in an indirect proportional manner. The results show that the effects of tocopherol in washed platelet preparations are not comparable to those observed in plasma and that the platelet membrane must be regarded as a crucial target for vitamin E.