The primary alpha and the secondary Johari-Goldstein (JG) beta relaxations of supercooled glass-forming neat epoxy resin and 2-picoline in mixture with tristyrene are monitored by broadband dielectric relaxation spectroscopy at ambient pressure and elevated pressures. For different combinations of pressure and temperature that maintain the alpha-relaxation time constant, the frequency dispersion of the alpha relaxation is unchanged, as previously found in other glass-formers, but remarkably the JG beta-relaxation time remains constant. This is more clear evidence of a strong connection between the alpha- and JG beta-relaxation times, a fact that should be taken into account in the construction of a viable theory of glass transition.

The conductivity relaxation dynamics of the room-temperature ionic liquid 1-methyl-3-trimethylsilylmethylimidazolium tetrafluoroborate ([Si-MIm][BF(4)]) have been studied by broadband conductivity relaxation measurements at ambient pressure and elevated pressures up to 600 MPa. For the first time, several novel features of the dynamics have been found in a room-temperature ionic liquid. In the electric loss modulus M″(f) spectra, a resolved secondary β-conductivity relaxation appears, and its relaxation time τ(β) shifts on applying pressure in concert with the relaxation time τ(α) of the primary α-conductivity relaxation. The spectral dispersion of the α-conductivity relaxation, as well as the fractional exponent (1 - n) of the Kohlrausch-Williams-Watts function that fits the spectral dispersion, is invariant to various combinations of pressure and temperature that keep τ(α) constant. Moreover, τ(β) is unchanged. Thus the three quantities, τ(α), τ(β), and n, are coinvariant to changes in pressure and temperature. This strong connection to the α-conductivity relaxation shown by the β-conductivity relaxation in [Si-MIm][BF(4)] indicates that it is the analogue of the Johari-Goldstein β-relaxation in nonionically conducting glass-formers. The findings have fundamental implications on theoretical interpretation of the conductivity relaxation processes and glass transition in ionic liquids. It is also the first time such a secondary conductivity relaxation or the primitive conductivity relaxation of the coupling model has been fully resolved and identified in M″(f) in any ionically conducting material that we know of.

We investigate the linear viscoelastic response of model telechelic linear and star (of varying functionality) polyisoprene melts with different molar masses above the entanglement limit in relation to their structure. We find that these systems self-assemble as a result of the strong dipolar interactions and form clusters that seem to depend primarily on the number of dipolar groups per star. The dynamics is rather complex, but some pertinent features are observed: the segmental dynamics is affected by the telechelic functionalization, especially for short arm lengths; this reflects the change of microstructure (and thus glass-transition temperature) with functionalization. The terminal relaxation is much slower compared to similar nonionic stars, reflecting the relaxation of clusters. Linear semitelechelic polymers (with only one end functionalized) aggregate in a star-like fashion. We further develop a tube model based on the time-marching algorithm for stars and linear chains, where we incorporate the association status of the chains via the dipolar interactions at each time step. The agreement of the predictions with the data, using two adjustable parameters (the average times when two dipolar pair remain associated or free, respectively), is remarkable and suggests design criteria for forming desired supramolecular assemblies.

Atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT) process, and the conventional radical polymerization (RP) were applied to the copolymerization of methyl methacrylate (MMA) and methacrylate-terminated poly(dimethylsiloxane) macromonomer (PDMS-MA). They resulted in PMMA-g-PDMS graft copolymers with various branching and molecular weight distributions. By applying appropriate conditions, ATRP led to homogeneously branched copolymer and RAFT to gradient branched copolymer. The RP process gave heterogeneously branched copolymer with large polydispersity. The structure and mechanical properties in these copolymers were analyzed.

Dielectric relaxation spectra of two closely related glass formers, dipropylene glycol [H-(C3H6O)2-OH] and dipropylene glycol dimethyl ether [CH3-O-(C3H6O)2-CH3], were measured at ambient and elevated pressures in the supercooled and the glassy states are presented. Hydrogen bonds formed in dipropylene glycol are removed when its ends are replaced by two methyl groups to become dipropylene glycol dimethyl ether. In the process, the primary relaxation, the excess wing, and the resolved secondary relaxation of dipropylene glycol are all modified when the structure is transformed to become dipropylene glycol dimethyl ether. The modifications include the pressure and temperature dependences of these relaxation processes and their interrelations. Thus, by comparing the dielectric spectra of these two closely related glass formers at ambient and elevated pressures, the differences in the relaxation dynamics and properties in the presence and absence of hydrogen bonding are identified.

In this letter, we report that an essentially extended scaling version of the Avramov model leads to a consistent relation between dynamic scaling and thermodynamic properties in the thermodynamic scaling regime, which is valid for a considered herein ionic liquid 1-butyl-1-methylpyrrolidinium bis[oxalate]-borate (BMP-BOB), although the thermodynamic scaling works imperfectly for the tested ionic liquid. Taking into account that the relation is suggested to be well-grounded by an effective intermolecular potential based on the inverse power law, this finding is meaningful because it shows that benefits originating from the thermodynamic scaling idea and the newly developed Avramov model can concern a wider class of materials than only supercooled van der Waals liquids, and consequently the theoretical approach presented herein can play an important role in the description of molecular dynamics near the glass transition.

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