Entropy of polymer brushes composed of monodisperse flexible polymer chains regularly grafted
on a flat substrate plane with an equal “spacing” is numerically studied in the good solvent limit. We consider
systems of not only a free polymer brush but also a compressed polymer brush and two polymer brushes facing
each other at a “distance”. The total number of configurations, entropy, and force are calculated for various
chain lengths and graft densities by means of Monte Carlo simulations using an efficient enrichment algorithm
on a simple cubic lattice. We demonstrate that the effect of excluded volume plays an essential role. We find that
the entropy of a free polymer brush falls as −ΔS ∼ (spacing)-2.4±0.1, while the entropy of a compressed polymer
brush and two polymer brushes agrees very well with the analytical SCF theory by Milner, Witten, and Cates
[Macromolecules
1988, 22, 2610−2619]. The resulting interlayer force agrees also excellently well with the
recent experiments by Yamamoto et al. [Macromolecules
2000, 33, 5602−5607].
Generally, HTS coated conductor (CC) are hard to be quenched by local and transient disturbances during normal operation because of high temperature margin and high heat capacity of the conductor. However, the CCs still have possibilities of unexpected quenches originated by appearance of local defects due to repeated mechanical stresses and by temperature rise of long part of the CCs due to malfunction of cryogenic system, for example. In this work, hot spot temperature of CC with copper stabilizer during quench protection sequence is calculated by a numerical analysis for quenches by both of the origins mentioned above and practical amount of the stabilizer is discussed not to over-protect but for a coil system to surely survive from sever damages caused by quenches considering quench origins.
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