Viscoelastic properties of physically crosslinked networks. 1. Transient network theory

摘要: A simple model is introduced to describe the dynamics of physically cross-linked networks in which junctions are sufficiently weak break and recombine thermal fluctuations. The time-evolution equation under arbitrary macrodeformation derived for creation annihilation junctions-and hence number elastically effective polymer chains with a fixed end-to-end vector. We focus our attention specifically on unentangled molecular weight M, between neighboring smaller than entanglement Me, so that each chain obeys Rouse modified by sticky trapping centers rather reptation. Stress-strain relation shear elonga- tional deformation detailed network made up polymers uniform length associating functional groups at their ends. On longer time scales junction breakage time, total decreases time-resulting an intranetwork flow. In most blends or solutions practical interest, carry specific interacting other associative forces capable forming bonds, description terms van der Waals type interaction-or x parameter lattice-theoretical termi- nology-is insufficient. These include hydrogen bonding, ionic association, stereocomplex formation, cross- linking crystalline segments, solvent complex- ation. common cases bonding energy comparable energy, bond formation reversible change temperature concentration. Thermodynamics multiphase competition were studied present authors1t2 phase behavior peculiar fluids via forces. paper concerns dynamic properties thermoreversible (or physical gels) study enhanced viscoelasticity due presence temporal junctions. There has been accumulation evidences exhibit highly viscoelastic quite different from ordinary melts. Typical examples exper- imental studies can be taken biological macro- molecule~~-~ formed bonding. It turned out mechanical spectrum dynamical moduli does not show any softening low frequencies but insensitive over wide range covering lo2 rad/s also relaxation stress seem obey exponential decay well described power law.4 was found complex viscosity larger stationary when compared frequency same as rate, thus suggesting failure Cox- Merz rule. Another example current research ther- moplastic elastmers6s7 synthetic groups. include, addition charge (electron) transfer, ion pairing, acid-base interaction, dipole-