An optical study of phase transitions of poly (ethylene terephthalate-co-p-hydroxybenzoic acid) liquid crystal

The copolyester containing 40 mol % ethylene terephthalate (PET) and 60 mol % p-hydroxybenzoate (HB) units has been reported by several investigators to be biphasic in the solid and the liquid states. The reported thermal transitions in the two phases, however, are in part contradictory, perhaps partly due to different polymerization conditions. The present work is a study of the transitions in each of the two phases of this copolyester by polarized light microscopy and by light transmission measurements. By light transmission measurements, the two phases were found to have two different glass transition temperatures for the onset of segmental motion, consistent with two assignable temperatures (T.). Cold crystallization and melting in each of the two different phases was also detected. The results help clarify the nature of transitions and agree with the results of dynamic mechanical analysis on the same thermotropic liquid crystalline copolyester.     

A new approximation method for scattering by long finite arrays

The scattering of water waves by a long array of evenly spaced,rigid, vertical circular cylinders is analysed under the usualassumptions of linear theory. These assumptions permit the reductionof the problem to that of solving the Helmholtz equation intwo dimensions, with appropriate circular boundaries. Our primarygoal is to show how solutions obtained for semi-infinite arrayscan be combined to provide accurate and numerically efficientsolutions to problems involving long, but finite, arrays. Theparticular diffraction problem considered here has been chosenboth for its theoretical interest and for its applicability.The design of offshore structures supported by cylindrical columnsis commonplace and understanding how the multiple interactionsbetween the waves and the supports affect the field is clearlyimportant. The theoretical interest comes from the fact that,for wavelengths greater than twice the geometric periodicity,the associated infinite array can support Rayleigh–Blochsurface waves that propagate along the array without attenuation.For a long finite array, we expect to see these surface wavestravelling back and forth along the array and interacting withthe ends. For particular sets of parameters, near-trapping haspreviously been observed and we provide a quantitative explanationof this phenomenon based on the excitation and reflection ofsurface waves by the ends of the finite array.     

Eisenuntersuchungen

Ohne Zusammenfassung     

Relation between steady shear flow and dynamic rheology

Summary The relationships between steady shear flow and dynamic rheology are investigated at relatively high shear rates and frequencies. A useful empirical relationship in this region predicts that the magnitude of the complex dynamic viscosity | ^*| should be compared with the shear viscosity at equal values of frequency and shear rate (Cox-Merz-rule). Polystyrenes (PS) and Polyacrylamides (PAAm) have been investigated over a wide range of concentration and molecular weight. Only in case of PAAm/H₂O solutions we have found that the results do not coincide with Cox-Merz-rule. As far as we know this is the first time that deviations from Cox-Merz-rule were observed in a homogeneous system. A molecular interpretation is given.

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Zusammenfassung Die Beziehung zwischen der Scherviskosität und der komplexen (dynamischen) Viskosität bei relativ hohen Schergeschwindigkeiten und Frequenzen wurde untersucht. Eine geeignete empirische Beziehung in diesem Bereich sagt aus, daß der Betrag der komplexen Viskosität | ^*| mit der Scherviskosität bei gleichen Werten von Frequenz und Schergeschwindigkeit vergleichbar ist (Cox-Merz-Regel). Polystyrole (PS) and Polyacrylamide (PAAm) wurden über einen weiten Bereich der Konzentration und des Molekulargewichts untersucht. Nur im Fall der PAAm/H₂O-Lösungen wurden Abweichungen von der Cox-Merz-Regel gefunden. Soweit uns bekannt, ist es das erste Mal, daß Abweichungen von der Cox-Merz-Regel in einem homogenen System gefunden wurden. Eine molekulare Erklärung wird gegeben.

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Presented at the IUPAC 26^th International Symposium on Macromolecules, Mainz, September 17–21, 1979.

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With 4 figures and 1 table     

Marine mammal blubber reference and control materials for use in the determination of halogenated organic compounds and fatty acids

The National Institute of Standards and Technology (NIST) has a diverse collection of control materials derived from marine mammal blubber, fat, and serum. Standard Reference Material (SRM) 1945 Organics in Whale Blubber was recertified for polychlorinated biphenyl (PCB) congeners, organochlorine pesticides, and polybrominated diphenyl ether (PBDE) congeners. SRM 1945 has also been assigned mass fraction values for compounds not frequently determined in marine samples including toxaphene congeners, coplanar PCBs, and methoxylated PBDE congeners which are natural products. NIST also has assigned mass fraction values, as a result of interlaboratory comparison exercises, for PCB congeners, organochlorine pesticides, PBDE congeners, and fatty acids in six homogenate materials produced from marine mammal blubber or serum. The materials are available from NIST upon request; however, the supply is very limited for some of the materials. The materials include those obtained from pilot whale blubber (Homogenates III and IV), Blainville’s beaked whale blubber (Homogenate VII), polar bear fat (Homogenate VI), and California sea lion serum (Marine Mammal Control Material-1 Serum) and blubber (Homogenate V).