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A benchmark study on the thermal conductivity of nanofluids
Buongiorno, Jacopo,Venerus, David C.,Prabhat, Naveen,McKrell, Thomas,Townsend, Jessica,Christianson, Rebecca,Tolmachev, Yuriy V.,Keblinski, Pawel,Hu, Lin-wen,Alvarado, Jorge L.,Bang, In Cheol,Bishnoi, American Institute of Physics 2009 JOURNAL OF APPLIED PHYSICS - Vol.106 No.9
DIFFUSION OF ORGANIC SOLVENTS IN ISOBUTYLENE : BASED POLYMERS
Hong, Seong Uk,Duda, J Larry,Venerus, David C. 한국화학공학회 1996 Korean Journal of Chemical Engineering Vol.13 No.3
Diffusion behavior of several organic solvents in polyisobutylene (PIB) and in poly(p-methylstyrene-co-isobutylene) (PMS-BR) with different monomer ratios has been studied. The experiments have been conducted over a temperature range of 50 to 100℃ using a conventional gravimetric sorption technique. The PMS-BR copolymers contained 2, 7, and 15 weight percent p-methylstyrene, respectively. Although employing temperatures were far above the glass transition temperatures of polymers, the diffusion coefficients are correlated well with the Vrentas-Duda free-volume theory. For all the solvents, the PIB shows the highest diffusivity while the copolymer with the 15% p-methylstyrene gives the lowest value. This behavior can be explained by the amount of fractional free-volume present in a system.
Diffusion of Organic Solvents in Isobutylene - Based Polymers
Hong, Seong Uk,Duda, J Larry,Venerus, David c 한국화학공학회 1996 NICE Vol.14 No.4
Diffusion behavior of several organic solvents in polyisobutylene (PIB) and in polyp-methylstyrene-co-isobutylene (PMS-BR) with different monomer ratios has been studied. The experiments have been crmducted over a temperature range of 50 to 100℃ using a conventional gravimetric sorption technique. The PMS-BR copolymers contained 2, 7, and 1S weight percent p-rnethylstyrene, respectively. Although employing tempetahues were afar above the glass transition temperatures of polymers, the diffusion coefficients are correlated well with the VrentasDuda free-volume theory. For all the solvents, the PIB shows the highest diffusivity while the copolymer with the 15% p-methylstyrene gives the lowest value. This behavior can be explained by the amount of fractional free-volume present in a system.
Hall, Ryan,Kang, Beom-Goo,Lee, Sanghoon,Chang, Taihyun,Venerus, David C.,Hadjichristidis, Nikos,Mays, Jimmy,Larson, Ronald G. American Chemical Society 2019 Macromolecules Vol.52 No.4
<P>We determine experimentally the “dilution exponent” α for entangled polymers from the scaling of terminal crossover frequency with entanglement density from the linear rheology of three 1,4-polybutadiene star polymers that are blended with low-molecular-weight, unentangled linear 1,4-polybutadiene at various star volume fractions, ϕ<SUB><I>s</I></SUB>. Assuming that the rheology of monodisperse stars depends solely on the plateau modulus <I>G</I><SUB><I>N</I></SUB>(ϕ<SUB>s</SUB>) ∝ ϕ<SUB><I>s</I></SUB><SUP>1+α</SUP>, the number of entanglements per chain <I>M</I><SUB><I>e</I></SUB>(ϕ<SUB><I>s</I></SUB>) ∝ ϕ<SUB><I>s</I></SUB><SUP>-α</SUP>, and the tube-segment frictional Rouse time τ<SUB><I>e</I></SUB>(ϕ<SUB><I>s</I></SUB>) ∝ ϕ<SUB><I>s</I></SUB><SUP>-2α</SUP>, we show that only an α = 1 scaling superposes the <I>M</I><SUB><I>e</I></SUB>(ϕ<SUB><I>s</I></SUB>) dependence of the terminal crossover frequency ω<SUB><I>x</I>,<I>t</I></SUB> of the blends with those of pure stars, not α = 4/3. This is the first determination of α for star polymers that does not rely on any particular tube model implementation. We also show that a generalized tube model, the “Hierarchical model”, using the “Das” parameter set with α = 1 reasonably predicts the rheological data of the melts and blends featured in this paper.</P> [FIG OMISSION]</BR>
Desai, Priyanka S.,Kang, Beom-Goo,Katzarova, Maria,Hall, Ryan,Huang, Qifan,Lee, Sanghoon,Shivokhin, Maksim,Chang, Taihyun,Venerus, David C.,Mays, Jimmy,Schieber, Jay D.,Larson, Ronald G. American Chemical Society 2016 Macromolecules Vol.49 No.13
<P>We compare predictions of two of the most advanced versions of the tube model, namely the 'Hierarchical model' by Wang et al. [J. Rheol. 2010, 54, 223] and the BoB (branch-on-branch) model by Das et al. [J. Rheol. 2006, SO, 207], against linear viscoelastic G' and G '' data of binary blends of nearly monodisperse 1,4-polybutadiene 4-arm star polymer of arm molar mass 24 000 g/mol with a monodisperse linear 1,4-polybutadiene of molar mass 58 000 g/mol. The star was carefully synthesized and characterized by temperature gradient interaction chromatography and by linear rheology over a wide frequency region through time temperature superposition. We found large failures of both the Hierarchical and BoB models to predict the terminal relaxation behavior of the star/linear blends, despite their success in predicting the rheology of the pure star and pure linear polymers. This failure occurred regardless of the choices made concerning constraint release, such as assuming arm retraction in 'fat' or 'skinny' tubes. Allowing for 'disentanglement relaxation' to cut off the constraint release Rouse process at long times does lead to improved predictions for our blends, but leads to much worse predictions for other star/linear blends described in the literature, especially those of Shivokhin et al. [Macromolecules 2014, 47, 2451]. In addition, our blends and those of Shivokhin et al. were also tested against a coarse-grained slip-link model, the 'clustered fixed slip-link model (CFSM)' of Schieber and co-workers [J. Rheol. 2014, 58, 723], in which several Kuhn steps are clustered together for computational efficiency. The CFSM with only two molecular-weight- and chain-architecture-independent parameters was able to give very good agreement with all experimental data for both of these sets of blends. In light of its success, the CFSM slip-link model may be used to address the constraint release issue more rigorously and potentially help develop improved tube models.</P>
Hall, Ryan,Desai, Priyanka S.,Kang, Beom-Goo,Huang, Qifan,Lee, Sanghoon,Chang, Taihyun,Venerus, David C.,Mays, Jimmy,Ntetsikas, Konstantinos,Polymeropoulos, George,Hadjichristidis, Nikos,Larson, Ronal American Chemical Society 2019 Macromolecules Vol.52 No.20
<P>We blend newly synthesized nearly monodisperse four-arm star 1,4-polybutadienes with various well-entangled linear polymers, confirming the conclusions in Desai et al. [<I>Macromolecules</I>201649 (13)49644977] that advanced tube models, namely, the hierarchical 3.0 and branch-on-branch models [Wang, Z.; <I>J. Rheol.</I>201054 (2)223260], fail to predict the linear rheological data when the pure linear polymers have shorter relaxation times, but within 3-4 orders of magnitude of the star polymer. However, when the linear polymer has a longer relaxation time than the star, our new work, surprisingly, finds that non-monotonic dependence of terminal relaxation behavior on composition is both observed experimentally and captured by the models. Combined with previous data from the literature, we present results from over 50 1,4-polybutadiene star-linear blends, suitable for thorough testing of rheological models of entangled polymers.</P> [FIG OMISSION]</BR>