Pressure-enhanced dynamic heterogeneity in block copolymers of poly(methyl vinyl ether) and poly(isobutyl vinyl ether)

Abstract

The static structure factor and associated dynamics have been investigated in a series of block copolymers of poly(methyl vinyl ether) (PMVE) and poly(isobutyl vinyl ether) (PiBVE) using x-ray scattering and dielectric spectroscopy (DS). The origin of the dynamic arrest at the glass temperature (T(g)) of PiBVE has been explored by temperature- and pressure-dependent DS and pressure-volume-temperature measurements. Both temperature and volume are responsible for the segmental dynamics but temperature has a stronger effect. The copolymers display a minimal dynamic asymmetry (Delta T(g) approximately 7 K), nevertheless, are spatially and dynamically heterogeneous. Increasing pressure, unlike temperature, enhances the dynamic heterogeneity. This effect originates from the distinctly different pressure sensitivities of the homopolymers and can be traced back to differences in local packing.

The role of temperature and density on the glass-transition dynamics of glass formers

“…56 These results have also consequences with respect to the issue of dynamic heterogeneity in polymer blends and copolymers; the appropriate choice of monomers could result in drastically different T and P dependences for the two components, with consequences on their dynamic and possibly their thermodynamic miscibilities. 21 We also remark on the general form of the potential function; treating only the repulsive part of the potential may seem appropriate at high and high T ͑high-T approximation 57 ͒, however, the present results suggest that a general theory of liquid dynamics, applicable to all and T and for all glass formers, is necessary to include the effect of attractive forces that control the packing and the thermodynamic state.…”

“…20,21 This is made by coupling the relaxation times measured under isobaric ͑T͒ and isothermal ͑P͒ conditions with independent measurements of the equation of state V͑T , P͒. The result is shown schematically in Fig.…”

“…20,21 To facilitate the comparison of this ratio for the different glass-forming systems, we use its value at P = 0.1 MPa and at T g ͑defined at =1 s͒ and the known equation of state. 11,19,[21][22][23][24][25] The results ͑obtained mainly by dielectric spectroscopy and light scattering͒ are summarized in Table I. A seemingly unrelated property of amorphous systems is the presence of a degree of packing regularity reflected by the broad scattering peaks in the wide-angle x-ray or neutron-scattering curves. 22,26 For polymers, in particular, the peak at higher q values, with an equivalent Bragg spacing of about 0.5 nm, corresponds to the van der Waals ͑VDW͒ contacts of atoms and is known as the VDW peak.…”

Pressure-Dependent Dynamics of Polymer Melts from Arrhenius to Non-Arrhenius: The Cooperative Free Volume Rate Equation Tested against Simulation Data

“…Trends in the T , P dependence of E V / E P have been reported (e.g., via dielectric spectroscopy) for some experimental systems in the literature. Examples include results from Floudas and co-workers for poly­(2-vinylpyridine) (P2VP) and poly­(vinyl isobutyl ether) (PViBE) and from Naoki et al for poly­(vinyl chloride) (PVC) and the small molecule o -terphenyl (OTP). The trends in E V / E P for the experimental systems are diverse and system-specific.…”

Dispersion of the Structural Relaxation and the Vitrification of Liquids

“…These polymers include: polyvinylmethylether (PVME) [87]; poly(vinylacetate) (PVAc) [88]; poly(ethylene-co-vinyl acetate) (EVA, having 70 wt% vinyl acetate) [89]; polymethylphenylsiloxane (PMPS) [90]; poly(methyltolylsiloxane) (PMTS) [91]; 1,2polybutadiene (1,2-PBD, also referred to as polyvinylethylene, PVE) [92]; poly(phenyl glycidyl ether)-co-formaldehyde (PPGE) [93]; 1,4-polyisoprene (PI) [94]; poly(propylene glycol) (molecular weight: 4000 Da), PPG-4000 [95]; poly(oxybutylene), POB [96]; and poly(isobutyl vinylether), PiBVE [111]. Constant dispersions at a fixed value of t a independent of thermodynamic conditions (T and P) are shown for more than one t a in Fig.…”