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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>
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>
Pankaj Kumar Jha,Md. Golam Shahi Alam,Md. Abdullah Al Mansur,Mohammad Rafiqul Islam Talukder,Nazmun Naher,A. K. M. Anisur Rahman,David C. Hall,Farida Yeasmin Bari 한국동물생명공학회(구 한국동물번식학회) 2020 Journal of Animal Reproduction and Biotechnology Vol.35 No.2
The effects of the number of frozen-thawed ram sperm per single and double intra-cervical artificial insemination (AI) on fertility in ewes were studied. A total of 89 non-pregnant ewes were synchronized for oestrus with two doses of 100 μg PGF2α (Cloprostenol) 9 days apart. The ewes were randomly assigned to one of four groups; D200 (n = 23; double AI with 200 × 106 sperm), S200 (n = 24; single AI with 200 × 106 sperm), D100 (n = 24; double AI with 100 × 106 sperm) and S100 (n = 18; single AI with 100 × 106 sperm). Ewes were inseminated within 12 to 18 h for single AI and, within 10 to 12 h and 16 to 18 h for double AI after the onset of oestrus. The onset of oestrus ranged from 28 to 76 h (54.33 ± 1.28 h). The high percentage (29.2%) of ewes showed oestrus between 51 to 60 h. The non-return rates were highest in group D200 (56.5%) and differed significantly (p < 0.05) from group S100 (11.1%). No ewes were pregnant in group S100, and the pregnancy rates among the remaining groups did not differ. The mean gestation period was 152.8 ± 0.5 days and no difference was observed among the groups. The lambing and multiple birth rates were 100% in group D200. The single and twin lambing was highest in group D100 (33.3%) and group D200 (83.3%), respectively. Only one triplet lambing and the highest lambing size (2.2 ± 0.2) was recorded in group D200. In conclusion, double AI with 200 × 106 sperm showed comparatively most practical for achieving high pregnancy rates and lambing performances in Bangladeshi ewes under field conditions.
Pankaj Kumar Jha,Md. Golam Shahi Alam,Md. Abdullah Al Mansur,Mohammad Rafiqul Islam Talukder,Nazmun Naher,A K M Anisur Rahman,David C. Hall,Farida Yeasmin Bari 사단법인 한국동물생명공학회 2020 한국동물생명공학회지 Vol.35 No.2
The effects of the number of frozen-thawed ram sperm per single and double intra-cervical artificial insemination (AI) on fertility in ewes were studied. A total of 89 non-pregnant ewes were synchronized for oestrus with two doses of 100 μg PGF2α (Cloprostenol) 9 days apart. The ewes were randomly assigned to one of four groups; D200 (n = 23; double AI with 200 × 106 sperm), S200 (n = 24; single AI with 200 × 106 sperm), D100 (n = 24; double AI with 100 × 106 sperm) and S100 (n = 18; single AI with 100 × 106 sperm). Ewes were inseminated within 12 to 18 h for single AI and, within 10 to 12 h and 16 to 18 h for double AI after the onset of oestrus. The onset of oestrus ranged from 28 to 76 h (54.33 ± 1.28 h). The high percentage (29.2%) of ewes showed oestrus between 51 to 60 h. The non-return rates were highest in group D200 (56.5%) and differed significantly (p < 0.05) from group S100 (11.1%). No ewes were pregnant in group S100, and the pregnancy rates among the remaining groups did not differ. The mean gestation period was 152.8 ± 0.5 days and no difference was observed among the groups. The lambing and multiple birth rates were 100% in group D200. The single and twin lambing was highest in group D100 (33.3%) and group D200 (83.3%), respectively. Only one triplet lambing and the highest lambing size (2.2 ± 0.2) was recorded in group D200. In conclusion, double AI with 200 × 106 sperm showed comparatively most practical for achieving high pregnancy rates and lambing performances in Bangladeshi ewes under field conditions.