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Rheological complexity in simple chain models
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Image of FIG. 1.
FIG. 1.

Analysis of the second Legendre polynomial of the end-to-end vector for ten-site FR-R at , , and . (A) vs ln(t). The lower thick line is really the overlapping points of the raw data which would obscure the curve passing through them. This curve is reproduced shifted to the right where the solid line is the Kohlrausch function; and the dashed, the single-exponential tail. (B) The Lindsey–Patterson plot. The points are the data. The dashed line is the single exponential tail; and the solid line has a slope of . (C) The modified Lindsey–Patterson plot. The points are the data. The dashed line shows a slope of one; and the solid, a slope of . (D) The Lindsey and Patterson cross-plot. The points are the data. The solid line has a slope of one and an intercept of with . In all cases, the vertical dashed lines denote the intermediate time regime. Logarithms are base .

Image of FIG. 2.
FIG. 2.

Examples of the determination of the KWW stretching exponent for a number of packing fractions for FR chains. [The are from top to bottom (1.6, 0.612, 0.318, 0.758)-R; (2.2, 0.944, 0.471, 0.681)-R; (2.0, 1.06, 0.536, 0.660)-R; (1.6, 1.06, 0.551, 0.656)-R; (1.6,1.06, 0.563, 0.650)-A]. In (A) are shifted Lindsey and Patterson cross-plots with lines of a slope of 1. In (B) are unshifted, modified Lindsey–Patterson plots with lines of slope .

Image of FIG. 3.
FIG. 3.

Chain center of mass diffusion coefficient for freely jointed chains [in (A) and (C)] and for freely rotating chains [in (B) and (D)]. The squares are for attractive FJ chains and the circles are for repulsive FJ chains. The triangles are for attractive FR chains and the inverted triangles are for repulsive FR chains. In (A) and (B), in Lennard–Jones units is plotted in Arrhenius fashion against inverse temperature. In (C) and (D), the reduced diffusion coefficient, , is plotted against packing fraction . In (C) and (D), the repulsive and attractive results have been shifted, as indicated by the arrows. The lines are powerlaw fits9 to : For FJ, ; for FR, . Logarithms are base 10.

Image of FIG. 4.
FIG. 4.

Variation of the KWW stretching exponent as a function of packing fraction in (A) and as a function of the inverse of the logarithm of the KWW relaxation time in (B) and (C). The circles correspond to FJ-R, the squares to FJ-A; the inverted triangles to FR-R, and the triangles to FR-A. In (A), a representative error bar of is shown to the left and vertical lines at the location of the packing fractions at the ideal glass transition are shown to the right [ and ]. In (B) is shown the results of Paluch et al. [Ref. 39(c)] for the fragile glass former [poly(bisphenol A-co-epichlorohydrin), glycidyl end capped] at a variety of pressures (symbols representing different pressures) and the line is a guide to the eye. The boxed area in (B) is reproduced in (C); the line is duplicated and the simulation results are plotted instead of experimental results. The relaxation times used to reduce the data in (B) and (C) are for experiment, and in Lennard–Jones time units, for the FR and for the FJ simulations. Logarithms are base 10.

Image of FIG. 5.
FIG. 5.

Variation of relaxation times. In (A), both and for FJ chains are plotted against the distance to the glass transition where . Circles are -R; squares, -R; triangles, -A; and inverted triangles, -R. The line has a slope of 2.2, In (B) the ratio of to is plotted against . Circles are FJ-R; squares, FJ-A; triangles, FR-A; and inverted triangle, FR-R. (C) is identical to (A) except for FR chains, , and the line has slope 3.0. In (D) is plotted against . Circles are FJ-R; squares, FJ-A; triangles, FR-A; and inverted triangle, FR-R. Logarithms are base 10.


Generic image for table
Table I.

State points simulated. Temperature in units of . Density in units of . Pressure in units of .


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Rheological complexity in simple chain models