Cryo-Imaging of Hydrogels Supermolecular Structure

Marmorat, Clement; Arinstein, Arkadii; Koifman, Naama; Talmon, Yeshayahu; Zussman, Eyal; Rafailovich, Miriam

doi:10.1038/srep25495

Cited by 52 publications

(32 citation statements)

References 25 publications

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“…The parts of the skeleton inside one mesh are very rigid, but at some points they form sharp kinks due to the presence of short flexible macromolecular segments-"melted" xanthan helices, which join rigid double helix segments together. Recently, similar structure was observed for other stiff polysaccharides [20].…”

Section: Introductionsupporting

confidence: 81%

pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions

et al. 2020

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Cross-linking of polysaccharides by metal ions provides polymer gels highly required by industrial applications. In this article, we study the rheological properties and microstructure of solutions of a stiff anionic polysaccharide xanthan cross-linked by chromium (III) ions, and we demonstrate that their properties are highly sensitive to the preparation pH. Stable gels are obtained in a wide range of pH from 2.4 to 7.8. The maximum elastic modulus is observed for the gels made at pH 6.3, and by freeze-fracture transmission electron microscopy it is shown that they are characterized by the most dense network structure. However, out of this pH interval, no gelation is observed. At low pH (< 2.4) it is due to high protonation of carboxylic groups of xanthan preventing their interaction with chromium ions, and to the disappearance of oligomeric ions, which are effective in cross-linking. At high pH (> 7.8) the absence of gelation is caused by the transformation of reactive chromium ions into insoluble chromium hydroxide. At the same time, for the gels initially formed at pH 6.3, subsequent change of pH to strongly acidic (1.4) or basic (8.9) medium does not affect appreciably their properties, meaning that chromium cross-links are stable once they are formed. These observations open a reliable route to produce polysaccharide gels with required mechanical properties in a wide pH range where they initially cannot be prepared. It is also shown that the increase of pH to 6.3 of the initially ungelled solution prepared at pH 1.5 results in gelation. This effect offers a facile way for delayed gelation of polysaccharides, which is especially required by oil industry.

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Section: Introductionsupporting

confidence: 81%

pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions

et al. 2020

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“…Unfortunately, currently, it can only be estimated by theoretical calculation (e.g., tree-like approximation, real space renormalized effective medium approximation) [1,2]. Experimentally, many different sizes have been used as mesh size, including correlation blob (ξc) by scattering experiments [3,4], elastic blob (ξel) by rheological measurements [3,5], and mesh-like structure observed in scanning transmittance electron microscopes (STEM) [6,7].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of Mesh Size in Model Polymer Networks Consisting of Tetra-Arm and Linear Poly(ethylene glycol)s

Tsuji

Shibayama

2018

Gels

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The structure and mechanical properties of model polymer networks consisting of alternating tetra-functional poly(ethylene glycol)s (PEGs) and bis-functional linear PEGs were investigated by dynamic light scattering and rheological measurements. The sizes of the correlation blob (ξc) and the elastic blob (ξel) were obtained from these measurements and compared to the theoretical mesh size, the geometric blob (ξg), calculated by using the tree-like approximation. By fixing the concentration of tetra-PEGs and tuning the molecular weight of linear-PEGs, we systematically compared these blob sizes in two cases: complete network (Case A) and incomplete network (Case B). The correlation blob, ξc, obtained by dynamic light scattering (DLS) was found to obey the well-known concentration dependence for polymer solutions in semidilute regime (ξc~ϕ−3/4) irrespective of the Cases. On the other hand, the G′ was strongly dependent on the Cases: For Case A, G′ was weakly dependent on the molecular weight of linear-PEGs (G′~Mc0.69) while G′ for Case B was a strong increasing function of Mc (G′~Mc1.2). However, both of them are different from the geometric blob (theoretical mesh) of the gel networks. In addition, interesting relationships between G′ and ξc, G′~ξc, G′~ξC−2, were obtained for Cases A and B, respectively.

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“…The mesh size describes the average pore size in the network and is an important parameter that can dictate diffusion and swelling characteristics of the material . Based on elasticity theories, the higher the mesh size, the lower the crosslink density ( C D or ρ) . In eq.…”

Section: Introductionmentioning

confidence: 99%

“…38 Based on elasticity theories, the higher the mesh size, the lower the crosslink density (C D or q). 39 In eq. (5), R is the molar gas constant, T is the temperature, N A is the Avogadro's number, and G 0 is the storage modulus of the hydrogels.…”

Section: Introductionmentioning

confidence: 99%

Gelation studies on acrylic acid‐based hydrogels via in situ photo‐crosslinking and rheology

Magami

Williams

2018

J of Applied Polymer Sci

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The gelation characteristics of acrylic acid (AA)‐based hydrogels were investigated using real time in situ photocrosslinking and rheological measurements. The gel point and gelation times were established using Winter–Chambon criteria. Frequency independence of tan δ was observed in all cases, such that G′ and G″ scaled as ∼ωn. The Flory–Stockmayer theory was used alongside other indices in order to probe the gelation and the post‐gelation characteristics of the critical gels and the fully formed hydrogels. Network relaxation exponents (n) were influenced by the concentrations of AA and methylene bis‐acrylamide. The gel stiffness (S) decreased with an increase in the concentration of the monomer and of the concentration of the crosslinker, while network branching decreased (lower fractal dimensions) at the gel point. The conversion at the gel point was found to be iso‐conversion with respect to the intensity of the UV irradiance used in the photocrosslinking reactions (1–20 mW/cm2). Thus, network clusters and the crosslinking reaction mechanism were the same irrespective of radiation intensity, although the rates of the reactions were affected. Having sufficient amounts of reactive species at the time of cure drive the crosslinking reactions beyond the gel point to greater crosslink density and smaller mesh sizes. The effects of auto‐acceleration and free‐volume were observed and shown to have key effects on the gelation mechanisms and the branching topographies of the network, when the concentration of the known polyacrylamide medium were not controlled. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46691.

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Cryo-Imaging of Hydrogels Supermolecular Structure

Cited by 52 publications

References 25 publications

pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions

pH-Dependent Gelation of a Stiff Anionic Polysaccharide in the Presence of Metal Ions

Evaluation of Mesh Size in Model Polymer Networks Consisting of Tetra-Arm and Linear Poly(ethylene glycol)s

Gelation studies on acrylic acid‐based hydrogels via in situ photo‐crosslinking and rheology

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