Inverse microemulsion polymerization of acrylamide in the presence of N,N-dimethylacrylamide

The presence of N,N-dimethylacrylamide (NDA) influences the stability of initial, clear, single-phase Winsor IV inverse microemulsion composed of toluene/AOT (sodium salt of bis(2-ethylhexyl) sulfosuccinate)/NDA/water/acrylamide (AAm). For a molar fraction of NDA, n_NDA = [NDA]/([NDA] + [AAm]) = 0.200 a single-phase system turned to a milky one during polymerization initiated by oil-soluble dibenzoyl peroxide or water-soluble ammonium peroxodisulfate, and finally a two-phase system was formed. For n_NDA values greater than 0.200 also the precipitation of a polymeric product was observed during polymerization. The (co)polymerization rate of AAm and NDA exponentially decreases with increasing value of n_NDA, while the reverse is true for the (co)polymer particle diameter. The results support the idea of simultaneously proceeding free-radical polymerization initiated by free radicals in continuous oil and dispersed water phase of the inverse microemulsion system.     

Reactive processing of particulate filled polymers: m-phenylene bismaleimide modified polyethylene/magnesium hydroxide composites

Summary The influence of processing temperature and the presence of the reactive modifier, m-phenylene bismaleimide (BMI), on the formation of highly filled polyethylene/Mg(OH)₂ composites has been investigated using central composite design methods. Infrared spectroscopic and differential scanning calorimetric evidence produced suggests that maleimide C=C bonds are involved in a free radically induced process which leads to extended and crosslinked polyethylene chains being produced, some of which encapsulate the filler particles, resulting in formation of a crosslinked interphase. This effect resulted in increased tensile strength and reduced composite melt flow rate (MFR). Received: 17 February 1999/Accepted: 29 March 1999     

Single-channel response of hamster oocytes to fertilization with homologous spermatozoa.

Electrophysiological events occur early after fertilization, along with changes in intracellular Ca2+ concentration. Passive electrical parameters were determined in golden hamster oocytes by whole cell patch-clamp method. In separate experiments the effect of 4-aminopyridine on resting oocytes was tested. The single-channel patch clamp configuration was employed to assess the electrical response to fertilization with homologous sperm. Structure of oocytes submitted to patch clamp was evaluated with scanning electron microscopy and found to be preserved. Oocyte diameter was 70.2 +/- 2.2 microm; their resting parameters were: membrane potential 23.8 +/- 0.8 mV; total membrane specific resistance 519.1 +/- 94.6 ohms.cm2, and specific capacity 0.99 +/- 0.03 microF.cm(-2). Total membrane current was decreased by 42 % by 4-aminopyridine. Control oocytes and oocytes exposed to sperm differed in their membrane currents in response to a voltage ramp clamping membrane potential from - 100 mV to + 100 mV. In both cases, currents were largest at the most negative potentials, but sperm-exposed oocytes had larger currents. Additionally, while in control oocytes the current was inward at negative potentials but outward at positive potentials, in the presence of spermatozoa oocytes was inward within the whole voltage range tested. This latter current may represent Ca2+ entry.     

Experimental and Theoretical Determination of Phase Fraction in the Fe-B-V Alloys

In the present work the fraction of equilibrium phases in various Fe-B-V alloys was determined by various methods. Area fractions were determined from pictures of microstructures of alloys by means of software Gwyddion. Fractions were calculated also by lever rule from experimentally determined values. All experimentally determined fractions were compared with equilibrium fractions of phases calculated with software Thermo-Calc. Good agreement between theoretical and experimental values was found. The reason of the study was to verify the parameters for thermodynamics calculations for the Fe-B-V system Homolová et al. (J. Alloys Compd. 520:30-35, 2012).     

Efficient 2-$mu$m Continuous-Wave Laser Oscillation of Tm$^3 + $:KLu(WO$_4$)$_2$

Monoclinic crystals of Tm-doped KLu(WO₄)₂ were grown with high crystalline quality for several dopant concentrations. The relevant spectroscopic properties for the ³ F₄rarr³H₆ laser transition (cross sections, lifetime) were measured at room temperature. Laser oscillation in the 2-mum range was obtained both with Ti:sapphire and diode laser pumping near 800 nm using different setups. The maximum output powers achieved were 1.4 and 4 W, respectively, and the corresponding slope efficiencies with respect to the absorbed power were 60% and 69%, respectively. The novel monoclinic double tungstate thulium host KLu(WO₄)₂ was directly compared to KGd(WO₄)₂ and exhibited superior performance. The two laser polarization configurations for Tm:KLu(WO₄)₂ ,E//N_m and E//N_p, were also compared under identical conditions with pumping by the polarized Ti:sapphire laser. Tuning was studied for both of them using an intracavity Lyot filter and the tuning range achieved was from 1800 to 1987 nm. In the case of no polarization selective cavity elements the diode-pumped Tm:KLu(WO₄ )₂ laser naturally selected the E//N_m polarization