Deviation from time-composition equivalence in polymer solutions with selective cosolvents

Abstract

Time-composition superpositioning (tCS) permits determination of the mechanical properties of polymeric materials over a widely extended time (or frequency) domain by systematically varying composition under isothermal conditions. We have recently reported (Soft Matter, 6, 4331, 2010) the existence of such equivalence in technologically relevant triblock copolymers swollen with miscible, midblock-selective cosolvents differing in chemical constitution and viscosity. In this study, chemically homologous homopolymer and copolymer systems exhibiting rheological properties that deviate from tCS are investigated. With regard to the particular case of selectively solvated triblock copolymers, the source of deviation is explained in the context of endblock hopping

Ultrastretchable, cyclable and recyclable 1- and 2-dimensional conductors based on physically cross-linked thermoplastic elastomer gels

“…The rst temperature (denoted by an arrow near 130 C) corresponds to the maximum in the dynamic loss shear modulus (G 00 ) and (not shown) tan d, where d denotes the displacement angle. This temperature, noticeably above the glass transition temperature (T g ) of the polystyrene blocks in the SEBS copolymer, is attributed to lattice disordering, which results from endblocks migrating from one molten micelle to another (a relaxation mechanism commonly referred [43][44][45] to as endblock hopping) to relieve stresses in the copolymer nanostructure. At temperatures above T g , transient dangling endblocks (i.e., endblocks remaining in the incompatible matrix) become more numerous and weaken the network as they diffuse within the matrix in search of new molten micelles to join.…”

Factors affecting time–composition equivalence in ternary block copolymer/cosolvent systems

“…(Contributions from the glassy endblocks are omitted from this comparison as they undergo different dynamics 77,78 that are responsible for the upturns evident at low frequencies in some of the master curves. 79 ) Recall from Fig. 2b, however, that either the midblock can be plasticized by the cosolvent (at low w R ) or the midblock can plasticize the cosolvent (at high w R ), as discerned from examination of the ternary midblock/MO/resin T g .…”

Fundamental Principles and Emerging Opportunities for Selectively‐Solvated Block Copolymer Networks in Nonpolar Media: A Perspective

“…Such tCS behavior is achieved insofar as only one relaxation mechanism (due to entanglements) exists. Endblock hopping resulting from changes in composition‐adjustable solvent quality [ 112 ] is a second mechanism that compromises the quality of superpositioning, especially in G ″ at low ω, implying that tCS requires TPEs with sufficiently long endblocks in a strongly midblock‐compatible (co)solvent. Moreover, a C is found to scale with the zero‐shear viscosity of the MO/CR mixtures, with the scaling exponent varying linearly with respect to ϕ .…”