The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform

Gyorgy Szekely - One of the best experts on this subject based on the ideXlab platform.

  • bio inspired robust membranes nanoengineered from interpenetrating polymer networks of polybenzimidazole polydopamine
    ACS Nano, 2019
    Co-Authors: Dan Zhao, Jeong F Kim, Gergo Ignacz, Peter Pogany, Young Moo Lee, Gyorgy Szekely
    Abstract:

    Marine mussel inspired polydopamine (PDA) has received increased attention due to its good thermal and chemical stability as well as strong adhesion on most materials. In this work, high-performance nanofiltration membranes based on interpenetrating polymer networks (IPN) incorporating PDA and polybenzimidazole (PBI) were developed for organic solvent nanofiltration (OSN). Generally, in order to obtain solvent stability, polymers need to be covalently cross-linked under harsh conditions, which inevitably leads to losses in permeability and mechanical flexibility. Surprisingly, by in situ polymerization of dopamine within a PBI support, excellent solvent resistance and permeance of polar aprotic solvents were obtained without covalent cross-linking of the PBI backbone due to the formation of an IPN. The molecular weight cutoff and permeance of the membranes can be fine-tuned by changing the polymerization time. Robust membrane performance was achieved in conventional and emerging green polar aprotic solvents (PAS) in a wide temperature range covering -10 °C to +100 °C. It was successfully demonstrated that the in situ polymerization of PDA-creating an IPN-can provide a simple and green alternative to covalent cross-linking of membranes. To elucidate the nature of the solvent stability, a detailed analysis was performed that revealed that Physical Entanglement along with strong secondary interaction synergistically enable solvent resistance with as low as 1-3% PDA content.

  • Bio-Inspired Robust Membranes Nanoengineered from Interpenetrating Polymer Networks of Polybenzimidazole/Polydopamine
    2019
    Co-Authors: Dan Zhao, Jeong F Kim, Gergo Ignacz, Peter Pogany, Young Moo Lee, Gyorgy Szekely
    Abstract:

    Marine mussel inspired polydopamine (PDA) has received increased attention due to its good thermal and chemical stability as well as strong adhesion on most materials. In this work, high-performance nanofiltration membranes based on interpenetrating polymer networks (IPN) incorporating PDA and polybenzimidazole (PBI) were developed for organic solvent nanofiltration (OSN). Generally, in order to obtain solvent stability, polymers need to be covalently cross-linked under harsh conditions, which inevitably leads to losses in permeability and mechanical flexibility. Surprisingly, by in situ polymerization of dopamine within a PBI support, excellent solvent resistance and permeance of polar aprotic solvents were obtained without covalent cross-linking of the PBI backbone due to the formation of an IPN. The molecular weight cutoff and permeance of the membranes can be fine-tuned by changing the polymerization time. Robust membrane performance was achieved in conventional and emerging green polar aprotic solvents (PAS) in a wide temperature range covering −10 °C to +100 °C. It was successfully demonstrated that the in situ polymerization of PDAcreating an IPNcan provide a simple and green alternative to covalent cross-linking of membranes. To elucidate the nature of the solvent stability, a detailed analysis was performed that revealed that Physical Entanglement along with strong secondary interaction synergistically enable solvent resistance with as low as 1–3% PDA content

Michel Moan - One of the best experts on this subject based on the ideXlab platform.

  • Rheological behavior of a hydrophobically associating water soluble polymer
    Journal of Rheology, 1994
    Co-Authors: Thierry Aubry, Michel Moan
    Abstract:

    We have investigated experimentally the behavior of a water soluble associating polymer system, hydrophobically modified (hydroxypropyl)guar, with very few randomly distributed hydrophobic substituents along the chains. We focus mainly on the rheological effects due to the superposition of the reversible hydrophobic interaction network on the Physical Entanglement network in dense macromolecular systems of that kind. Both linear and nonlinear response to transient, steady, and oscillatory shear flow prove that, in the semidilute and moderately concentrated regime, the hydrophobically associating polymer behaves like a classical dense macromolecular system whose long‐time dynamics can be described using only one long relaxation time, identified as a retarded disengagement time, much larger than the association lifetime. The temporary hydrophobically associating network can be destroyed when applying a critical shear stress τc, which is studied as a function of polymer concentration.

Cristian Micheletti - One of the best experts on this subject based on the ideXlab platform.

  • The elusive quest for RNA knots
    RNA biology, 2016
    Co-Authors: Aaron S. Burton, Marco Di Stefano, Niles Lehman, Henri Orland, Cristian Micheletti
    Abstract:

    Physical Entanglement, and particularly knots arise spontaneously in equilibrated polymers that are sufficiently long and densely packed. Biopolymers are no exceptions: knots have long been known to occur in proteins as well as in encapsidated viral DNA. The rapidly growing number of RNA structures has recently made it possible to investigate the incidence of Physical knots in this type of biomolecule, too. Strikingly, no knots have been found to date in the known RNA structures. In this Point of View Article we discuss the absence of knots in currently available RNAs and consider the reasons why knots in RNA have not yet been found, despite the expectation that they should exist in Nature. We conclude by singling out a number of RNA sequences that, based on the properties of their predicted secondary structures, are good candidates for knotted RNAs.

  • The unknotted strands of life: knots are very rare in RNA structures
    2015
    Co-Authors: Cristian Micheletti, Marco Di Stefano, Henri Orland
    Abstract:

    The ongoing effort to detect and characterize Physical Entanglement in biopolymers has so far established that knots are present in many globular proteins and also abound in viral DNA packaged inside bacteriophages. RNA molecules, on the other hand, have not yet been systematically screened for the occurrence of Physical knots. We have accordingly undertaken the systematic profiling of the ~6,000 RNA structures present in the protein data bank. The search identified no more than three deeply-knotted RNA molecules. These are ribosomal RNAs solved by cryo-em and consist of about 3,000 nucleotides. Compared to the case of proteins and viral DNA, the observed incidence of RNA knots is therefore practically negligible. This suggests that either evolutionary selection, or thermodynamic and kinetic folding mechanisms act towards minimizing the Entanglement of RNA to an extent that is unparalleled by other types of biomolecules. The properties of the three observed RNA knotting patterns provide valuable clues for designing RNA sequences capable of self-tying in a twist-knot fold.

Hengti Wang - One of the best experts on this subject based on the ideXlab platform.

  • Flame-retarding nanoparticles as the compatibilizers for immiscible polymer blends: simultaneously enhanced mechanical performance and flame retardancy
    Journal of Materials Chemistry, 2019
    Co-Authors: Zhiang Fu, Xuewen Zhao, Hengti Wang, Xuan Li, Xiaoying Gu, Yongjin Li
    Abstract:

    Surface modified boehmite nanorods have been synthesized by binary grafting of reactive epoxide groups and long poly(methyl methacrylate) (PMMA) tails. The prepared nanoparticles have been incorporated into the immiscible poly(vinylidene fluoride)/poly(L-lactide) (PVDF/PLLA) blends. Unlike the traditional metal hydroxide flame retardants, a small amount of surface modified boehmite nanorods (5 wt%) can simultaneously enhance both the flame retardancy (with the LOI increasing 33%) and mechanical performance (with elongation at break increasing more than 10 times) of the PVDF/PLLA (70/30) blends. It is found that the boehmite nanorods are dominantly located at the interface between PVDF and PLLA phases. The reactive boehmite nanorods improve the compatibility of PVDF/PLLA blends by Physical Entanglement and in situ chemical reaction during melt blending. At the same time, the nanorods at the interface reduce the surface temperature and form a dense metal oxide layer which isolates the flame and oxygen through their thermal decomposition during combustion. Therefore, simultaneous enhancements in both mechanical properties and flame retardancy using flame-retarding metal hydroxides have been achieved for the first time.

  • enhanced interfacial adhesion by reactive carbon nanotubes new route to high performance immiscible polymer blend nanocomposites with simultaneously enhanced toughness tensile strength and electrical conductivity
    ACS Applied Materials & Interfaces, 2018
    Co-Authors: Xuewen Zhao, Hengti Wang
    Abstract:

    Physically anchoring carbon nanotubes (CNTs) onto the interface of immiscible polymer blends has been extensively reported; however, enhancement of Physical properties of the blends has seldom been achieved. Herein, we used CNTs with reactive epoxide groups and long poly(methyl methacrylate) (PMMA) tails as a thermodynamic compatibilizer for immiscible poly vinylidene fluoride/poly l-lactide (PVDF/PLLA) blends. The CNTs acted as an efficient compatibilizer and bridged the two phases through Physical Entanglement and chemical reaction. The sea–island structure of the blend transformed into a bicontinuous structure for CNT contents greater than 3 wt %. The mechanical properties, including ductility and tensile strength, thermal properties, and electrical conductivities were all enhanced by the CNTs compatibilizer. This strategy thermodynamically compatibilized by reactive nanofillers paves the way for advanced blend nanocomposites.

Alan N. Gent - One of the best experts on this subject based on the ideXlab platform.

  • slipping of carbon nanotubes in a rubber matrix
    Polymer International, 2011
    Co-Authors: Rajatendu Sengupta, Alan N. Gent
    Abstract:

    The interactions of carbon nanotubes (CNTs) and carbon black (CB) with rubber matrices are of great interest. Although both belong to the carbon filler family, their interactions are different. In this study the adhesion of CNTs, if any, with natural rubber (NR) was examined. Scanning electron microscopy examinations made on cryogenically fractured surfaces of a crosslinked NR sample containing 7% by weight of CNTs showed that the CNT bundles emerged from the side surface (narrowed by Poisson's ratio) and slowly slid back in when the deformation was removed. The protruded lengths were many times larger than the nanotube bundle diameters. This extensive slipping out of CNTs from the rubber matrix suggests that interfacial interactions between CNTs and NR are quite weak. In contrast, relatively strong interactions were found between CB and rubber, indicated by the large amount of bound rubber formation. Reinforcement of rubber by CNTs is therefore attributed to the large aspect ratio of CNT bundles. Physical Entanglement with rubber molecules is then able to generate effective load transfer, replacing the strong adhesion found with CB. Copyright © 2010 Society of Chemical Industry