Effects of chain flexibility on polymer conformation in dilute solution studied by lattice Monte Carlo simulation

Effects of chain flexibility on the conformation of homopolymers in good solvents have been investigated by Monte Carlo simulation. Bond angle constraint coupled with persistence length of polymer chains has been introduced in the modified eight-site bond fluctuation simulation model. The study about the effects of chain flexibility on polymer sizes reveals that the orientation of polymer chains under confinement is driven by the loss of conformation entropy. The conformation of polymer chains undergoing a gradual change from spherical iso-diametric ellipsoid to rodlike iso-diametric ellipsoid with the decrease of polymer chain flexibility in a wide region has been clearly illustrated from several aspects. Furthermore, a comparison of the freely jointed chain (FJC) model and the wormlike chain (WLC) model has also been made to describe the polymer sizes in terms of chain flexibility and quasi-quantitative boundary toward the suitability of the models.

The effect of chain flexibility and chain mobility on radiation crosslinking of polymers

Radiation crosslinking of polymers mainly depends on the structure of polymer chain. The flexibility and mobility of chain directly influence the possibility of the reactive radicals recombination. Flexible chain is easier to crosslink than rigid-chain polymer. The latter must be crosslinked at high temperature, as most polymers can only crosslink above their melting point. Structural effect also influences the mechanism of radiation crosslinking of polymers. We find from the results in literature and in our laboratory that, the flexibility chain polymer mainly crosslinked with H type, but the rigid chain polymer mainly crosslinked with Y type. (C) 2001 Published by Elsevier Science Ltd.

Metabolic characteristics of sea cucumber Apostichopus japonicus (Selenka) during aestivation

Metabolic characteristics of the sea cucumber Aposticholpus japonicus (Selenka) during aestivation were studied in the laboratory. The effects of water temperature on oxygen consumption rate (OCR) and ammonia-N excretion rate (AER) in A. japonicus were determined by the Winkler and Hypobromite methods, respectively. Mature (large, 148.5 +/- 15.4 g, medium 69.3 +/- 6.9 g) and immature (small, 21.2 +/- 4.7 g) individuals aestivated at water temperatures of 20 and 25 degrees C, respectively. The metabolic characteristics of mature individuals were different from immature individuals during this period. The OCR of mature sea cucumbers peaked at 20 degrees C, and then dropped significantly at higher temperatures, whereas the OCR of the immature animals continued to increase slightly, even beyond the aestivation temperature. The AER of mature individuals peaked at 20 T, while that of the immature animals peaked at 25 degrees C. The relationships between dry weight (DW) and absolute oxygen consumption (R) and absolute ammonia-N excretion (N) could be described by the regression equation R or N=aW(b). With the exception of 15 degrees C, the O/N ratios (calculated in atomic equivalents) of large size sea cucumbers was close to 20 across the temperatures used in this study, indicating that their energy Source was a combination of lipid and protein. Oil the other hand, apart from small individuals maintained at 10 degrees C, the O/N ratios of the medium and small sea Cucumbers were close to 10, indicating that protein was their major energy source. The O/N ratios in all size groups remained unchanged after aestivation was initiated. (c) 2005 Elsevier B.V. All rights reserved.