“…An early study on the role of parallel attraction in polymer crystallization was made by Bleha [46], who considered the enthalpic effect of parallel packing on the melting point of polymers. In addition, Mansfield [47] took parallel interactions into account in his Monte Carlo calculation of the chain-folding probability at the interphase zone between lamellar crystals and amorphous liquid.…”
Section: Implications Of Parallel Attractions In Polymer Systemsmentioning
“…An early study on the role of parallel attraction in polymer crystallization was made by Bleha [46], who considered the enthalpic effect of parallel packing on the melting point of polymers. In addition, Mansfield [47] took parallel interactions into account in his Monte Carlo calculation of the chain-folding probability at the interphase zone between lamellar crystals and amorphous liquid.…”
Section: Implications Of Parallel Attractions In Polymer Systemsmentioning
“…In this hypothetical entropy-separation process, the physical meaning of the γ value estimated at the transition point has been controversial in the literature. [29][30][31][32][33][34][35][36][37] In the present analysis, we have examined this subject in some detail (see the following).…”
Section: Analytical Procedures Of the Pvt Datamentioning
confidence: 99%
“…According to Mandelkern's book, , the volume-correction term Δ S V is defined as where γ (=α/β) is the thermal pressure coefficient at the transition, α the thermal expansion coefficient at constant pressure, and β the compressibility at constant temperature. In this hypothetical entropy-separation process, the physical meaning of the γ value estimated at the transition point has been controversial in the literature. − In the present analysis, we have examined this subject in some detail (see the following). 1 Volume vs temperature relations for MBBE-6 from 10 to 100 MPa.…”
Section: Analytical Procedures Of the Pvt Datamentioning
Thermodynamic characteristics of a dimer liquid crystal comprising a relatively long spacer -O(CH 2 -CH 2 O) 6were investigated. The contour length of the flexible spacer (∼25 Å) exceeds that of the hard segments (∼18 Å). The compound exhibits a nematic mesophase (N) between the crystal (C) and the isotropic melt (I) over a sizably wide temperature range (∼80 °C). Thermodynamic quantities such as thermal expansion coefficient R, isothermal compressibility β, thermal pressure coefficient γ ()R/β), and the volume change ∆V at the CN and NI interphase were carefully determined by the PVT measurements. The transition entropies due to volume expansion were estimated by the well-known relation ∆S V ) γ∆V. The latent entropies (∆S tr ) P for both CN and NI transitions were estimated according to the Clapeyron relation from the PVT and DTA data. The magnitude of the constant-volume entropy changes (∆S tr ) V calculated was found to be about 50-60% of the corresponding values of (∆S tr ) P . These results were consistent with the previous 2 H NMR observations that the chain segments adopt a nematic conformation in the LC state. The thermodynamic role of the flexible segment in determining the phase transitions has been critically discussed.
“…The entropy separation according to eqs 1 and 2 is a hypothetical process assuming that the volume of the isotropic fluid may be compressed to that of the solid state without affecting the configurational part of the entropy of chain molecules . The validity of such an assumption has been questioned by several authors. − Wunderlich et al pointed out that the volume dependence of γ during the compression from the liquid to the solid volume may not be negligible and thereby leads to a significant underestimate of the Δ S V term. They proposed to adopt an integration form such as to replace eq 1.…”
A conventional method of estimating conformational entropy change at the melting point of polymers has been set forth in Mandelkern's book. The entropy separation according to this method involves a hypothetical assumption that the volume of the isotropic fluid may be compressed to that of the solid state without affecting the configurational part of the entropy of molecules. In this work, we have extensively examined the volume dependence of thermal pressure coefficient γ ) (δP/δT) V ) (δS/δV)T of n-undecane. Molecular dynamic simulations were performed using the software package Insight II/Discover. In the standard calculation, a cubic box containing 30 n-undecane molecules was used under the conventional periodic boundary conditions. The experimental observations were well reproduced by the MD simulation performed as above, and accordingly the γ vs specific volume (vsp) relations derived from the simulation are favorably compared with those obtained from the experimental PVT data. The γ values remain quite insensitive to vsp over a wide range at given temperatures. Values of the trans fraction were found to decrease with an increase in temperature, while they tend to remain quite insensitive to pressure (0-200 MPa). It was concluded on this basis that the aforementioned treatment of the volume change at the phase transition seems to be supported by the present analysis.
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