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Quan Chen - One of the best experts on this subject based on the ideXlab platform.

  • conformation of dilute poly vinyl alcohol Borax complex by asymmetric flow field flow fractionation
    Journal of Chromatography A, 2020
    Co-Authors: Yonggang Liu, Quan Chen
    Abstract:

    ABSTRACT Complexation between poly(vinyl alcohol) (PVA) and Borax in aqueous solution yields a dynamic polyelectrolyte. Study of chain conformation of such a polyelectrolyte is challenging due to the difficulty in separating different macromolecular species. In this study, we investigated conformation of dilute PVA chains complexed with Borax in a wide concentration range between 0.02 and 78.6 mM using asymmetrical flow field-flow fractionation (AF4). We find that elution of the complexes is strongly influenced by the Borax concentration owing to (1) the charged complex is repelled electrostatically by the charged bottom membrane of the AF4 channel, and (2) the Debye screening length reduces with increasing a charge density. The chain conformation of PVA-Borax complexes depends on both polymer molar mass and Borax concentration. At low Borax concentrations of 0.02~0.5 mM, a transition from random coil to rod-like conformation is observed with increasing the chain size. At Borax concentrations of 1 mM and higher, all chains become random coil owing to a reduced screening length of the electrostatic repulsion.

  • thermorheological complexity of poly vinyl alcohol Borax aqueous solutions
    Journal of Rheology, 2020
    Co-Authors: Xiao Cao, Yonggang Liu, Quan Chen
    Abstract:

    Thermorheological behavior was examined for poly(vinyl alcohol) (PVA) and Borax aqueous solutions. The PVA content was fixed to be approximately four times the entanglement concentration, and the Borax concentration CBorax was varied in a wide range of 0–10.4 mM. In this system, borate ions yielded from the hydrolysis of Borax can crosslink the PVA chains to form a reversible network. At low CBorax = 2.5 mM, the network strands are larger than the precursor chains. The stress relaxation is governed by the effective breakup, and the time temperature superposition (tTs) fails only slightly. In contrast, at high Cborx ≥ 4.0 mM, the network strands are dense and each chain is divided averagely into several network strands. For this case, the stress relaxation is governed by chain relaxation activated by continuous ion dissociations, where tTs fails significantly. Analysis of the thermorheological behavior provides rich information on the temperature-dependent structural evolution. Particularly, analyzing the high frequency data attributed to the ion dissociation process indicates that the failure of tTs is owing to a reduction of the degree of gelation with increasing T, which leads to an acceleration of the chain relaxation with respect to the ion dissociation.

  • the role of electrostatic repulsion in the gelation of poly vinyl alcohol Borax aqueous solutions
    Soft Matter, 2018
    Co-Authors: Zhijie Zhang, Xiao Cao, Yonggang Liu, Quan Chen
    Abstract:

    This study examined linear viscoelasticity (LVE) of semidilute non-entangled poly(vinyl alcohol) (PVA) and Borax aqueous solutions: one Borax molecule dissociates into two B(OH)3 molecules and two B(OH)4- ions, and the latter can crosslink the PVA chains. Gelation was observed with increasing concentration of Borax in the solutions. Analysis of LVE with the reversible gelation model reveals that although the number density of crosslinking ions increases with increasing concentration of Borax, the fraction of the crosslinking ions decreases, which is attributed to the intensified electrostatic repulsion when more sites of the PVA chains are occupied by the ionic crosslinkers.

Yonggang Liu - One of the best experts on this subject based on the ideXlab platform.

  • conformation of dilute poly vinyl alcohol Borax complex by asymmetric flow field flow fractionation
    Journal of Chromatography A, 2020
    Co-Authors: Yonggang Liu, Quan Chen
    Abstract:

    ABSTRACT Complexation between poly(vinyl alcohol) (PVA) and Borax in aqueous solution yields a dynamic polyelectrolyte. Study of chain conformation of such a polyelectrolyte is challenging due to the difficulty in separating different macromolecular species. In this study, we investigated conformation of dilute PVA chains complexed with Borax in a wide concentration range between 0.02 and 78.6 mM using asymmetrical flow field-flow fractionation (AF4). We find that elution of the complexes is strongly influenced by the Borax concentration owing to (1) the charged complex is repelled electrostatically by the charged bottom membrane of the AF4 channel, and (2) the Debye screening length reduces with increasing a charge density. The chain conformation of PVA-Borax complexes depends on both polymer molar mass and Borax concentration. At low Borax concentrations of 0.02~0.5 mM, a transition from random coil to rod-like conformation is observed with increasing the chain size. At Borax concentrations of 1 mM and higher, all chains become random coil owing to a reduced screening length of the electrostatic repulsion.

  • thermorheological complexity of poly vinyl alcohol Borax aqueous solutions
    Journal of Rheology, 2020
    Co-Authors: Xiao Cao, Yonggang Liu, Quan Chen
    Abstract:

    Thermorheological behavior was examined for poly(vinyl alcohol) (PVA) and Borax aqueous solutions. The PVA content was fixed to be approximately four times the entanglement concentration, and the Borax concentration CBorax was varied in a wide range of 0–10.4 mM. In this system, borate ions yielded from the hydrolysis of Borax can crosslink the PVA chains to form a reversible network. At low CBorax = 2.5 mM, the network strands are larger than the precursor chains. The stress relaxation is governed by the effective breakup, and the time temperature superposition (tTs) fails only slightly. In contrast, at high Cborx ≥ 4.0 mM, the network strands are dense and each chain is divided averagely into several network strands. For this case, the stress relaxation is governed by chain relaxation activated by continuous ion dissociations, where tTs fails significantly. Analysis of the thermorheological behavior provides rich information on the temperature-dependent structural evolution. Particularly, analyzing the high frequency data attributed to the ion dissociation process indicates that the failure of tTs is owing to a reduction of the degree of gelation with increasing T, which leads to an acceleration of the chain relaxation with respect to the ion dissociation.

  • the role of electrostatic repulsion in the gelation of poly vinyl alcohol Borax aqueous solutions
    Soft Matter, 2018
    Co-Authors: Zhijie Zhang, Xiao Cao, Yonggang Liu, Quan Chen
    Abstract:

    This study examined linear viscoelasticity (LVE) of semidilute non-entangled poly(vinyl alcohol) (PVA) and Borax aqueous solutions: one Borax molecule dissociates into two B(OH)3 molecules and two B(OH)4- ions, and the latter can crosslink the PVA chains. Gelation was observed with increasing concentration of Borax in the solutions. Analysis of LVE with the reversible gelation model reveals that although the number density of crosslinking ions increases with increasing concentration of Borax, the fraction of the crosslinking ions decreases, which is attributed to the intensified electrostatic repulsion when more sites of the PVA chains are occupied by the ionic crosslinkers.

Antonio Palleschi - One of the best experts on this subject based on the ideXlab platform.

  • The Influence of pH on the Scleroglucan and Scleroglucan/Borax Systems.
    Molecules, 2017
    Co-Authors: Claudia Mazzuca, Gianfranco Bocchinfuso, Antonio Palleschi, Mario Grassi, Franco Alhaique, Chiara Di Meo, Paolo Conflitti, Tommasina Coviello
    Abstract:

    The effects that an increase of environmental pH has on the triple helix of scleroglucan (Sclg) and on the Sclg/Borax hydrogel are reported. Rheological experiments show that the hydrogel is less sensitive to pH increase than Sclg alone, while at pH = 14 a dramatic viscosity decrease takes place for both systems. This effect is evidenced also by the reduced water uptake and anisotropic elongation detected, at pH = 14, by the swelling behaviour of tablets prepared with the Sclg/Borax system. On the opposite, a different behaviour was observed with guar gum and locust bean gum tablets, tested as reference polysaccharides. The effect of pH on the structure of Sclg and Sclg/Borax was investigated also by means of spectroscopic approaches based on the interaction between Congo red (CR) and the Sclg triple helix. Obtained results indicated that the CR absorbance maximum is shifted as a function of pH and by the presence of Borax. Principal component analysis allowed very precise identification of the pH value at which the Sclg helix collapses. Molecular dynamics simulations of the Sclg/Borax–CR complex indicated that, at physiological pH, only a few ordered configurations are populated, according to the induced circular dichroism (CD) spectrum evidence.

  • Guar gum and scleroglucan interactions with Borax: Experimental and theoretical studies of an unexpected similarity
    Journal of Physical Chemistry B, 2010
    Co-Authors: Gianfranco Bocchinfuso, Chiara Sandolo, Silvia Margheritelli, Tommasina Coviello, Claudia Mazzuca, Franco Alhaique, Antonio Palleschi
    Abstract:

    Guar gum is a galactomannan that assumes a very flexible conformation in solution, while Scleroglucan is a very rigid polysaccharide that dissolves in water as triple helices. Both polymers can form gels in the presence of Borax. Despite their structural differences, the freeze-dried gel systems of both polymers, when compressed to form tablets, show a peculiar anisotropic swelling in water that reflects an amazing similarity in terms of their molecular properies. In this paper the behavior of the Guar/Borax gel is compared with that of Scleroglucan/Borax. The macroscopic properties of the two systems were characterized in terms of rheological measurements. Atomic force microscopy images and molecular dynamics simulation allowed to evaluate, at molecular level, the effect of Borax addition to the Guar polymer. Both experiments show that an increasing of the polymer rigidity is produced by Borax. The role played by galactose in the side chain was also discussed.

Xiao Cao - One of the best experts on this subject based on the ideXlab platform.

  • thermorheological complexity of poly vinyl alcohol Borax aqueous solutions
    Journal of Rheology, 2020
    Co-Authors: Xiao Cao, Yonggang Liu, Quan Chen
    Abstract:

    Thermorheological behavior was examined for poly(vinyl alcohol) (PVA) and Borax aqueous solutions. The PVA content was fixed to be approximately four times the entanglement concentration, and the Borax concentration CBorax was varied in a wide range of 0–10.4 mM. In this system, borate ions yielded from the hydrolysis of Borax can crosslink the PVA chains to form a reversible network. At low CBorax = 2.5 mM, the network strands are larger than the precursor chains. The stress relaxation is governed by the effective breakup, and the time temperature superposition (tTs) fails only slightly. In contrast, at high Cborx ≥ 4.0 mM, the network strands are dense and each chain is divided averagely into several network strands. For this case, the stress relaxation is governed by chain relaxation activated by continuous ion dissociations, where tTs fails significantly. Analysis of the thermorheological behavior provides rich information on the temperature-dependent structural evolution. Particularly, analyzing the high frequency data attributed to the ion dissociation process indicates that the failure of tTs is owing to a reduction of the degree of gelation with increasing T, which leads to an acceleration of the chain relaxation with respect to the ion dissociation.

  • the role of electrostatic repulsion in the gelation of poly vinyl alcohol Borax aqueous solutions
    Soft Matter, 2018
    Co-Authors: Zhijie Zhang, Xiao Cao, Yonggang Liu, Quan Chen
    Abstract:

    This study examined linear viscoelasticity (LVE) of semidilute non-entangled poly(vinyl alcohol) (PVA) and Borax aqueous solutions: one Borax molecule dissociates into two B(OH)3 molecules and two B(OH)4- ions, and the latter can crosslink the PVA chains. Gelation was observed with increasing concentration of Borax in the solutions. Analysis of LVE with the reversible gelation model reveals that although the number density of crosslinking ions increases with increasing concentration of Borax, the fraction of the crosslinking ions decreases, which is attributed to the intensified electrostatic repulsion when more sites of the PVA chains are occupied by the ionic crosslinkers.

Gianfranco Bocchinfuso - One of the best experts on this subject based on the ideXlab platform.

  • The Influence of pH on the Scleroglucan and Scleroglucan/Borax Systems.
    Molecules, 2017
    Co-Authors: Claudia Mazzuca, Gianfranco Bocchinfuso, Antonio Palleschi, Mario Grassi, Franco Alhaique, Chiara Di Meo, Paolo Conflitti, Tommasina Coviello
    Abstract:

    The effects that an increase of environmental pH has on the triple helix of scleroglucan (Sclg) and on the Sclg/Borax hydrogel are reported. Rheological experiments show that the hydrogel is less sensitive to pH increase than Sclg alone, while at pH = 14 a dramatic viscosity decrease takes place for both systems. This effect is evidenced also by the reduced water uptake and anisotropic elongation detected, at pH = 14, by the swelling behaviour of tablets prepared with the Sclg/Borax system. On the opposite, a different behaviour was observed with guar gum and locust bean gum tablets, tested as reference polysaccharides. The effect of pH on the structure of Sclg and Sclg/Borax was investigated also by means of spectroscopic approaches based on the interaction between Congo red (CR) and the Sclg triple helix. Obtained results indicated that the CR absorbance maximum is shifted as a function of pH and by the presence of Borax. Principal component analysis allowed very precise identification of the pH value at which the Sclg helix collapses. Molecular dynamics simulations of the Sclg/Borax–CR complex indicated that, at physiological pH, only a few ordered configurations are populated, according to the induced circular dichroism (CD) spectrum evidence.

  • Guar gum and scleroglucan interactions with Borax: Experimental and theoretical studies of an unexpected similarity
    Journal of Physical Chemistry B, 2010
    Co-Authors: Gianfranco Bocchinfuso, Chiara Sandolo, Silvia Margheritelli, Tommasina Coviello, Claudia Mazzuca, Franco Alhaique, Antonio Palleschi
    Abstract:

    Guar gum is a galactomannan that assumes a very flexible conformation in solution, while Scleroglucan is a very rigid polysaccharide that dissolves in water as triple helices. Both polymers can form gels in the presence of Borax. Despite their structural differences, the freeze-dried gel systems of both polymers, when compressed to form tablets, show a peculiar anisotropic swelling in water that reflects an amazing similarity in terms of their molecular properies. In this paper the behavior of the Guar/Borax gel is compared with that of Scleroglucan/Borax. The macroscopic properties of the two systems were characterized in terms of rheological measurements. Atomic force microscopy images and molecular dynamics simulation allowed to evaluate, at molecular level, the effect of Borax addition to the Guar polymer. Both experiments show that an increasing of the polymer rigidity is produced by Borax. The role played by galactose in the side chain was also discussed.