Dynamics Of Miscible Blends Research Articles

Dynamic Heterogeneity in Fully Miscible Blends of Polystyrene with Oligostyrene

Binary blends of polystyrene with oligostyrene are perfectly miscible (χ=0) yet dynamically heterogeneous. This is evidenced by independent probing of the dipole relaxation perpendicular to the backbone by dielectric spectroscopy and molecular dynamics. The self-concentration model with a single intramolecular length scale qualitatively describes the slower segmental dynamics. A quantitative comparison based on MD, however, requires a composition-dependent length scale. The pertinent dynamic length scale that best describes the slow segmental dynamics in miscible blends relates to both intra- and intermolecular contributions.

Polypropylene and Polyethylene−Copolymer Blend Miscibility: Slow Chain Dynamics in Individual Blend Components near the Glass Transition

We systematically evaluate the slow conformational reorientations of polypropylene (PP) and polyethylene-co-1-butene (PEB) chains at temperatures near Tg before and after formation of a miscible blend with chain specific experiments. Solid-state 13C CODEX and static 129Xe NMR experiments reveal that aPP and PEB66 (PEB copolymer with 66 wt % 1-butene) are intimately mixed at the chain level. The two pure polymers, differing in Tg by ca. 50 K, exhibit large differences in the central correlation time constant τc for slow chain segmental motion (1–1000 ms) at any temperature but have equal correlation time distributions at/near Tg. In the miscible blend, slow chain dynamics are characterized by essentially equal central correlation time constants τc (ca. 15 ms) at a common temperature corresponding to the maximum exchange intensity for segmental rearrangement in the CODEX experiment, but the widths of the correlation time distributions diverge dramatically at any temperature, including at/near Tg. On the basis of comparisons of quantitative Arrhenius vs WLF models, and using an Adams−Gibbs treatment of the data, we determine that the overall configurational entropy Sc in the aPP/PEB66 blend exceeds that of the unmixed components by 15%, in agreement with previous work (Macromolecules 2007, 40, 5433). On the basis of the experimental data, general conclusions regarding driving forces for polyolefin miscibility and slow chain dynamics in miscible blends are discussed in the context of recent proposals in the literature, recognizing that polyolefins represent a limiting case of macromolecular thermodynamics due to their nonpolar structure. Importantly, all data are measured on individual signals from each polymer component in the solid blend.

Effect of Pressure on the Dynamic Heterogeneity in Miscible Blends of Poly(methyl methacrylate) with Poly(ethylene oxide)

The poly(methyl methacrylate) (PMMA) segmental dynamics in miscible blends of PMMA with poly(ethylene oxide) (PEO) were studied as a function of pressure by means of dielectric spectroscopy (DS). This facilitates a test of the predictions of the self-concentration model proposed by Lodge and McLeish, at elevated pressures. We find that pressure increases the glass temperature and slows down the segmental dynamics but does not affect the length scale or the self-concentration associated with the dynamic glass transition. This is in agreement with the expectations borne out from the model.

Locally heterogeneous dynamics in miscible blends of poly(methyl methacrylate) and poly(vinylidene fluoride)

Comparative measurements of specific heat capacities (temperature interval between 2 and 500 K), and of low frequency mechanical spectroscopy (temperature interval between 120 and 400 K) in poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) amorphous blends show the existence of single calorimetric and mechanical glass transition temperatures, as a clear indication of the existence of homogeneous single-state structures. Below Tg, the experimental data reveal distinct local relaxation processes within the backbone of the individual components, while the heat capacities below 15 K can be explained in terms of a two-phase model (i.e., a simple linear overlap of the contributions from wholly amorphous PMMA and PVDF, weighted by their proportions). These findings are associated with locally heterogeneous relaxation and vibrational motions, and are regarded as experimental evidence for the existence of a nanoscopic length scale where the dynamics of a blend exhibits a heterogeneous regime.

Dynamics in Miscible Blends of Polystyrene and Poly(vinyl methyl ether)

We report results on the linear viscoelasticity (oscillatory shear in the temperature range Tg (glass-transition temperature) ≤ T ≤ Tg + 90 K) of miscible blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) and segmental relaxations, measured by dielectric spectroscopy. The Flory−Huggins interaction parameter of this blend is weakly negative, and the glass transitions of the pure components are quite disparate (ΔTg = 125 K). PS/PVME blends have been found to be consistently thermorheologically complex at both the segmental and terminal levels: the empirical time−temperature superposition (tTS) principle applies to neither their oscillatory shear response nor their dielectric response. Using the tube model, we quantitatively compare dielectric and mechanical results. At low temperatures, the effective time scale for motion of a Kuhn segment (the shortest Rouse mode) is near the long-time end of the distribution of segmental relaxation times of PVME, in both the pure and blended states. The slow...

Component Dynamics in Miscible Blends: Equally and Unequally Entangled Polyisoprene/Polyvinylethylene

Miscible blends of 1,4-polyisoprene (PIP) and polyvinylethylene (PVE) are studied using rheo-optical methods to extract the dynamics of each component in the blend. Since orientational coupling contributes to the birefringence, but not the stress, simultaneous analysis of these observables for bidisperse blends is used to determine the coupling coefficient, e. No systematic dependence of e on composition or temperature was detected. The dynamics of the blend components extracted using the mean value of e are in good agreement with those observed previously for equally entangled blends: blending causes only small changes in the component entanglement molecular weights but dramatically alters the species' friction coefficients, with the dynamics of the high T_g species (PVE ) being more sensitive to both temperature and composition.

Component Dynamics in Miscible Blends of 1,4-Polyisoprene and 1,2-Polybutadiene

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTComponent Dynamics in Miscible Blends of 1,4-Polyisoprene and 1,2-PolybutadieneJeffrey A. Zawada, Gerald G. Fuller, Ralph H. Colby, Lewis J. Fetters, and Jacques RooversCite this: Macromolecules 1994, 27, 23, 6861–6870Publication Date (Print):November 1, 1994Publication History Published online1 May 2002Published inissue 1 November 1994https://doi.org/10.1021/ma00101a026RIGHTS & PERMISSIONSArticle Views312Altmetric-Citations46LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Rheo-Optiics for Multicomponent Liquids

AbstractThe application of techniques in optical rheometry for the study of multicomponent systems is reviewed. Small angle light scattering (SALS) patterns are related to the structure of concentration fluctuations with length scales of the order of the wavelength of light. Scattering techniques such as SALS and scattering dichroism have been applied to monitor the transient evolution of anisotropic concentration fluctuation enhancement during simple shear induced phase separation in a semi-dilute solution of polystyrene (PS) in dioctyl phthalate(DOP). Furthermore, the Onuki- Doi theory relating scattering dichroism and structure factor has been used to verify the consistency between scattering dichroism and anisotropy in structure factor. Infrared polarimetry is a useful technique in probing the transient microstructural orientation of individual chemical species in multicomponent systems. The simultaneous measurement of intrinsic infrared dichroism and birefringence is particularly effective and has been employed to monitor component relaxation dynamics in miscible blends of poly(ethylene oxide) and poly(methyl methacrylate). Polarization Modulated Laser Raman Scattering (PMLRS) has been successfully employed to study the orientation dynamics of a polymer melt subjected to transient uniaxial extension. PMLRS provides quantitative information about the time evolution of both the second and fourth moments of the orientation distribution function of molecular segments.