synopsisPoeitronium annihilation spectroscopy (PAS) has been used to study the microstructural properties of aminecured epoxy polymers. We have determined the free-volume "hole" sizes in these polymers by comparing the observed ortho-positronium lifetimes with the known lifetime-free volume correlation for low-molecular-weight systems. The free volumes for four epoxies with different crosslink densities are found to vary significantly over the temperature range between -7V and 250%. The free-volume holes for these polymers are found to range from 0.0% to 0.220 rims. Two important transition temperatures were found: one corresponds to the glass transition temperature T, determined by differential scanning calorimetry (DSC), and the other occurs about 80-130T below T,. The subT, transition temperature is interpreted tentatively as being where hole size reaches dimensions adequate for poeitronium trapping or else the onset temperature for local mode or sidechain motions. These two transition temperatures plus two additional onset temperatures are found to be correlated with crosslink densities calculated from stoichiometry.
The microwave spectra of cyclohexene, cyclohexene-d10, and 3,3,6,6-cyclohexene-d4 have been assigned. Subject to certain assumptions, the nine moments of inertia were least-squares fitted to obtain the structural parameters ∢C1–C2–C3 = 123.3°, ∢C2–C3–C4 = 111.6°, ∢C3–C4–C5 = 110.3°, ∢C–C–H (methylene) = 109.9°, ∢C–C–H (ethylene) = 119.5°, and θ=30.1°, where θ is the angle between the C1–us;C2 and C4–C5 bonds projected on the a–c principal axis plane. θ measures the deviation of the ring from planarity. The assumptions related to symmetry were (1) the molecular point group is C2; (2) the methylene groups are symmetric with equal C–C–H angles; and (3) the ethylene group and two adjacent carbons lie in a plane. The bond lengths were taken to be r(C1 –C2) = 1.34 Å, r(C2–C3) = 1.51 Å, r(C3–C4) = 1.53 Å, r(C4–C5) = 1.53 Å, r(C–H) (ethylene) = 1.09 Å, and r(C–H) (methylene) = 1.10 Å. Stark effect measurements yielded μb = 0.331 D for the common isotopic species and showed that μb is unchanged (within the experimental uncertainty) in the deuterated species. The Stark effect also confirmed the haclf-chair conformation and C2 symmetry by requiring μc to be less than 0.003 D.
would lead to separation factors of 13.5 in place of the observed values of 3.1 and 3.3.From the overvoltage data presented in this paper, separation factors of 3.0 to 3.2 are computed (Fig. 3). As has been pointed out, computed separation factors are based on the relative amounts of pure Ha and Da evolved at fixed overpotentials. The good agreement between these computed values and the experimental values for cases where Ha and HD were evolved, indicates that the separation factor is independent of the molecular form in which the hydrogen and deuterium atoms are evolved.These findings are incompatible with theories of hydrogen overvoltage which postulate as the slow step of the discharge process the combination of two or more entities on the electrode. These overvoltage and separation data can be interpreted only in terms of theories which postulate that only one particle is involved in the discharge process.
SummaryMeasurements of deuterium overvoltage on mercury cathodes at current densities from 10~6 to over 10"3 amp./sq. cm. and at temperatures from 4 to 70°are reported in this paper. These have been compared with previously reported measurements of hydrogen overvoltage made under similar conditions. 1 From these data, electrolytic separation factors for hydrogen and deuterium have been computed which agree very well with experimental separation data. These overvoltage and separation data appear to preclude the possibility that the slow step of the hydrogen discharge process, at mercury cathodes, involves more than one ion or atom. Brooklyn 2, N. Y.
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