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RISS 인기검색어
- 검색키워드
- 저자 : van Ruymbeke, E. (검색결과 4 건)
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van Ruymbeke, E.,Lee, H.,Chang, T.,Nikopoulou, A.,Hadjichristidis, N.,Snijkers, F.,Vlassopoulos, D. The Royal Society of Chemistry 2014 SOFT MATTER Vol.10 No.27
<P>An emerging challenge in polymer physics is the quantitative understanding of the influence of a macromolecular architecture (<I>i.e.</I>, branching) on the rheological response of entangled complex polymers. Recent investigations of the rheology of well-defined architecturally complex polymers have determined the composition in the molecular structure and identified the role of side-products in the measured samples. The combination of different characterization techniques, experimental and/or theoretical, represents the current state-of-the-art. Here we review this interdisciplinary approach to molecular rheology of complex polymers, and show the importance of confronting these different tools for ensuring an accurate characterization of a given polymeric sample. We use statistical tools in order to relate the information available from the synthesis protocols of a sample and its experimental molar mass distribution (typically obtained from size exclusion chromatography), and hence obtain precise information about its structural composition, <I>i.e.</I> enhance the existing sensitivity limit. We critically discuss the use of linear rheology as a reliable quantitative characterization tool, along with the recently developed temperature gradient interaction chromatography. The latter, which has emerged as an indispensable characterization tool for branched architectures, offers unprecedented sensitivity in detecting the presence of different molecular structures in a sample. Combining these techniques is imperative in order to quantify the molecular composition of a polymer and its consequences on the macroscopic properties. We validate this approach by means of a new model asymmetric comb polymer which was synthesized anionically. It was thoroughly characterized and its rheology was carefully analyzed. The main result is that the rheological signal reveals fine molecular details, which must be taken into account to fully elucidate the viscoelastic response of entangled branched polymers. It is important to appreciate that, even optimal model systems, <I>i.e.</I>, those synthesized with high-vacuum anionic methods, need thorough characterization <I>via</I> a combination of techniques. Besides helping to improve synthetic techniques, this methodology will be significant in fine-tuning mesoscopic tube-based models and addressing outstanding issues such as the quantitative description of the constraint release mechanism.</P> <P>Graphic Abstract</P><P>By coupling and confronting results obtained with different characterization techniques, a detailed description of the sample architectural dispersity is obtained. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4sm00105b'> </P>
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Architectural Dispersity in Model Branched Polymers: Analysis and Rheological Consequences
Snijkers, Frank,van Ruymbeke, Evelyne,Kim, Paul,Lee, Hyojoon,Nikopoulou, Anastasia,Chang, Taihyun,Hadjichristidis, Nikos,Pathak, Jai,Vlassopoulos, Dimitris American Chemical Society 2011 Macromolecules Vol.44 No.21
<P>We combine state-of-the-art synthetic, chromatographic, rheological, and modeling techniques in order to address the role of architectural polydispersity in the rheology of model branched polymers. This synergy is shown to be imperative in the field and leads to several important results. Even the best available synthesis is prone to “contamination” by side-products. The exact targeted macromolecular structure can be analyzed experimentally and statistically and eventually fractionated. Temperature-gradient interaction chromatography proves to be an indispensible tool in this process. All techniques are sensitive to the various macromolecular structures, but in different ways. In particular, the presence of side-products may or may not influence the linear rheology, due to competing contributions of the different relaxation processes involved, reflecting different structures at different fractions. Hence, combination of all these techniques is the key for fully decoding the architectural composition of branched polymers and its influence on rheology.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2011/mamobx.2011.44.issue-21/ma2013805/production/images/medium/ma-2011-013805_0019.gif'></P>
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Anomalous Rheological Behavior of Dendritic Nanoparticle/Linear Polymer Nanocomposites
Goldansaz, Hadi,Goharpey, Fatemeh,Afshar-Taromi, Faramarz,Kim, Il,Stadler, Florian J.,van Ruymbeke, Evelyne,Karimkhani, Vahid American Chemical Society 2015 Macromolecules Vol.48 No.10
<P>We investigated the effects of soft dendritic polyethylene (dPE) nanoparticles on the rheological properties of a linear polystyrene (PS) matrix. The viscosity of PS–dPE nanocomposites is found to exhibit nonmonotonic dependence on the dPE concentration. In particular, with the addition of 1% dPE nanoparticles, we already observe more than 1 order of magnitude reduction in viscosity. The minimum viscosity was observed at 5% nanoparticles. At dPE concentrations higher than 5%, nanocomposite viscosity increases by addition of nanoparticles, yet it remains below the viscosity of PS. Addition of nanoparticles not only influences the terminal relaxation times of the nanocomposites but also affects their whole relaxation spectra. The viscosity of PS–dPE nanocomposites at high temperature is found to reversibly evolve with time, which proves the existence of supramolecular interactions between the PS matrix and the nanoparticles. Atomic force microscopy confirms that dPE nanoparticles are well distributed in the PS matrix, though each component of the nanocomposite exhibits its own glass transition. While the origin of viscosity reduction remains unknown, it cannot be attributed to confinement, free volume effect, change of entanglement density, surface slippage, shear banding, or particle induced shear thinning.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/mamobx/2015/mamobx.2015.48.issue-10/acs.macromol.5b00390/production/images/medium/ma-2015-003905_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ma5b00390'>ACS Electronic Supporting Info</A></P>
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Constraint Release Mechanisms for H-Polymers Moving in Linear Matrices of Varying Molar Masses
Lentzakis, Helen,Costanzo, Salvatore,Vlassopoulos, Dimitris,Colby, Ralph H.,Read, Daniel Jon,Lee, Hyojoon,Chang, Taihyun,van Ruymbeke, Evelyne American Chemical Society 2019 Macromolecules Vol.52 No.8
<P>We investigate the influence of the environment on the relaxation dynamics of well-defined H-polymers diluted in a matrix of linear chains. The molar mass of the linear chain matrix is systematically varied and the relaxation dynamics of the H-polymer is probed by means of linear viscoelastic measurements, with the aim to understand its altered motion in different blends, compared to its pure melt state. Our results indicate that short unentangled linear chains accelerate the relaxation of both the branches and the backbone of the H-polymers by acting as an effective solvent. On the other hand, the relaxation of the H-polymer in an entangled matrix is slowed-down, with the degree of retardation depending on the entanglement number of the linear chains. We show that this retardation can be quantified by considering that the H-polymers are moving in a dilated tube at the rhythm of the motion of the linear matrix.</P> [FIG OMISSION]</BR>
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