Structural Mechanism for Viscosity of Semiflexible Polymer Melts in Shear Flow

The viscosities of semiflexible polymers with different chain stiffnesses in shear flow are studied via nonequilibrium molecular dynamics techniques. The simulation reproduces the experimentally observed results, giving a complete picture of viscosity as chain stiffness increases. Analysis of flow-induced changes in chain conformation and local structure indicates two distinct mechanisms behind a variety of viscosity curves. For polymers of small stiffnesses, it is related to flow-induced changes in chain conformation and, for those of large stiffnesses, to flow-induced instabilities of nematic structures. The four-region flow curve is confirmed for polymers of contour length close to persistence length and understood by combining the two structural mechanisms. Thus, these findings clarify the microscopic structures indicated by the macroscopic viscosity

Conformation and Dynamics of Individual Star in Shear Flow and Comparison with Linear and Ring Polymers

How polymers with different architectures respond to shear stress is a key issue to develop a fundamental understanding of their dynamical behaviors. We investigate the conformation, orientation, dynamics, and rheology of individual star polymers in a simple shear flow by multiparticle collision dynamics integrated with molecular dynamics simulations. Our studies reveal that star polymers present a linear transformation from tumbling to tank-treading-like motions as the number of arms increases. In the transformation region, the flow-induced deformation, orientation, frequency of motions, and rheological properties show universal scaling relationships against the reduced Weissenberg number, independent of the number and the length of arms. Further, we make a comprehensive comparison on the flow-induced behaviors between linear, ring, and star polymers. The results indicate that distinct from linear polymers, star and ring polymers present weaker deformation, orientation change, and shear thinning, either contributed by a dense center or without ends

Conformation and Dynamics of Individual Star in Shear Flow and Comparison with Linear and Ring Polymers

How polymers with different architectures respond to shear stress is a key issue to develop a fundamental understanding of their dynamical behaviors. We investigate the conformation, orientation, dynamics, and rheology of individual star polymers in a simple shear flow by multiparticle collision dynamics integrated with molecular dynamics simulations. Our studies reveal that star polymers present a linear transformation from tumbling to tank-treading-like motions as the number of arms increases. In the transformation region, the flow-induced deformation, orientation, frequency of motions, and rheological properties show universal scaling relationships against the reduced Weissenberg number, independent of the number and the length of arms. Further, we make a comprehensive comparison on the flow-induced behaviors between linear, ring, and star polymers. The results indicate that distinct from linear polymers, star and ring polymers present weaker deformation, orientation change, and shear thinning, either contributed by a dense center or without ends

Conformation and Dynamics of Individual Star in Shear Flow and Comparison with Linear and Ring Polymers

How polymers with different architectures respond to shear stress is a key issue to develop a fundamental understanding of their dynamical behaviors. We investigate the conformation, orientation, dynamics, and rheology of individual star polymers in a simple shear flow by multiparticle collision dynamics integrated with molecular dynamics simulations. Our studies reveal that star polymers present a linear transformation from tumbling to tank-treading-like motions as the number of arms increases. In the transformation region, the flow-induced deformation, orientation, frequency of motions, and rheological properties show universal scaling relationships against the reduced Weissenberg number, independent of the number and the length of arms. Further, we make a comprehensive comparison on the flow-induced behaviors between linear, ring, and star polymers. The results indicate that distinct from linear polymers, star and ring polymers present weaker deformation, orientation change, and shear thinning, either contributed by a dense center or without ends

Conformation and Dynamics of Individual Star in Shear Flow and Comparison with Linear and Ring Polymers

How polymers with different architectures respond to shear stress is a key issue to develop a fundamental understanding of their dynamical behaviors. We investigate the conformation, orientation, dynamics, and rheology of individual star polymers in a simple shear flow by multiparticle collision dynamics integrated with molecular dynamics simulations. Our studies reveal that star polymers present a linear transformation from tumbling to tank-treading-like motions as the number of arms increases. In the transformation region, the flow-induced deformation, orientation, frequency of motions, and rheological properties show universal scaling relationships against the reduced Weissenberg number, independent of the number and the length of arms. Further, we make a comprehensive comparison on the flow-induced behaviors between linear, ring, and star polymers. The results indicate that distinct from linear polymers, star and ring polymers present weaker deformation, orientation change, and shear thinning, either contributed by a dense center or without ends

Highly Efficient Epoxidation of Allylic Alcohols with Hydrogen Peroxide Catalyzed by Peroxoniobate-Based Ionic Liquids

This work reports new kinds of monomeric peroxoniobate anion functionalized ionic liquids (ILs) designated as [A⁺]­[NbO­(O-O)­(OH)₂] (A⁺ = tetrapropylammonium, tetrabutylammonium, or tetrahexylammonium cation), which have been prepared and characterized by elemental analysis, HRMS, NMR, IR, TGA, etc. With hydrogen peroxide as an oxidant, these ILs exhibited excellent catalytic activity and recyclability in the epoxidation of various allylic alcohols under solvent-free and ice bath conditions. Interestingly, subsequent activity tests and catalyst characterization together with first-principles calculations indicated that the parent [NbO­(O-O)­(OH)₂]⁻ anion has been oxidized into the anion [Nb­(O-O)₂(OOH)₂]⁻ in the presence of H₂O₂, which constitutes the real catalytically active species during the reaction; this anion has higher activity in comparison to the analogous peroxotungstate anion. Moreover, the epoxidation process of the substrate (allylic alcohol) catalyzed by [Nb­(O-O)₂(OOH)₂]⁻ was explored at the atomic level by virtue of DFT (density functional theory) calculations, identifying that it is more favorable to occur through a hydrogen bond mechanism, in which the peroxo group of [Nb­(O-O)₂(OOH)₂]⁻ serves as the adsorption site to anchor the substrate OH group by forming a hydrogen bond, while OOH as the active oxygen species attacks the CC bond in substrates to produce the corresponding epoxide. This is the first example of the highly efficient epoxidation of allylic alcohols using a peroxoniobate anion as a catalyst

The average end-to-end distance (<i>R</i>_<i>f</i>) of backbone for MCLCP and SCLCP.

<p>The average end-to-end distance (<i>R</i>_<i>f</i>) of backbone for MCLCP and SCLCP.</p

The average simulation cost per step of GALAMOST (GALA) and LAMMPS (LAMM) with the GB (+GB) or the MGB (+MGB) interaction as a function of the number of particles in simulation systems.

<p>The average simulation cost per step of GALAMOST (GALA) and LAMMPS (LAMM) with the GB (+GB) or the MGB (+MGB) interaction as a function of the number of particles in simulation systems.</p

The phase diagram of mesogens in small molecular LC obtained by GPU-accelerated simulation equipped with coarse grained GB potential.

<p>Solid circles mark our simulation results and lines are plotted for guide only. The X-axis is converted to number density for the comparison with de Miguel’s report.</p

The orientational order parameter <i>S</i>, the probability of the local orientation <i>P</i> (a, b), and the second virial coefficient <i>A</i>₂ (c, d) as a function of temperature for mesogens in small molecular, SCLCP and MCLCP systems.

<p>Insert in (c) illustrated the multi-domain nematic phase for SCLCP system.</p