Scaling laws of entangled polysaccharides

Superchaotropic Nano-ion Binding as a Gelation Motif in Cellulose Ether Solutions

Nanometer-sized anions (nano-ions) like polyoxometalates and boron clusters exhibit so-called superchaotropic behavior, which describes their strong binding to hydrated non-ionic matter in water. We show here that nano-ions, at millimolar concentrations, dramatically enhance the viscosity and induce gelation of aqueous solutions of non-ionic cellulose ethers (CEs), a class of widely utilized polymers known for their thickening and gel-forming ability. These phenomena arise from an interplay of attractive forces and repulsive electrostatic forces between CE-chains upon nano-ion binding. The attractive forces manifest themselves as aggregation of CE-chains into a physically crosslinked polymer network (gel). In turn, the electrostatic repulsions hamper the viscosity increase and gelation. Superchaotropic nano-ion binding emerges as a novel and general physical crosslinking motif for CE-solutions and exceeds by far the conventional thickening effects of classical salts and ionic surfactants.

Role of Flaxseed Gum and Whey Protein Microparticles in Formulating Low-Fat Model Mayonnaises

Flaxseed gum (FG) and whey protein microparticles (WPMs) were used to substitute fats in model mayonnaises. WPMs were prepared by grinding the heat-set whey protein gel containing 10 mM CaCl₂ into small particles (10–20 µm). Then, 3 × 4 low-fat model mayonnaises were prepared by varying FG (0.3, 0.6, 0.9 wt%) and WPM (0, 8, 16, 24 wt%) concentrations. The effect of the addition of FG and WPMs on rheology, instrumental texture and sensory texture and their correlations were investigated. The results showed that all samples exhibited shear thinning behavior and ‘weak gel’ properties. Although both FG and WPMs enhanced rheological (e.g., viscosity and storage modulus) and textural properties (e.g., hardness, consistency, adhesiveness, cohesiveness) and kinetic stability, this enhancement was dominated by FG. FG and WPMs affected bulk properties through different mechanisms, (i.e., active filler and entangled polysaccharide networks). Panellists evaluated sensory texture in three stages: extra-oral, intra-oral and after-feel. Likewise, FG dominated sensory texture of model mayonnaises. With increasing FG concentration, sensory scores for creaminess and mouth-coating increased, whereas those of firmness, fluidity and spreadability decreased. Creaminess had a linear negative correlation with firmness, fluidity and spreadability (R² > 0.985), while it had a linear positive correlation with mouth-coating (R² > 0.97). A linear positive correlation (R² > 0.975) was established between creaminess and viscosity at different shear rates/instrumental texture parameters. This study highlights the synergistic role of FG and WPMs in developing low-fat mayonnaises.

Microrheological Approach for Probing the Entanglement Properties of Polyelectrolyte Solutions

The entanglement dynamics and viscoelasticity of polyelectrolyte solutions remain active research topics. Previous studies have reported conflicting experimental results when compared to Dobrynin's scaling predictions derived from the Doi-Edwards (DE) tube model for entangled polymers. Herein, by combining classical bulk shear rheometry with diffusing wave spectroscopy (DWS) microrheometry, we investigate how the key viscoelastic parameters (the specific viscosity η_sp, the plateau modulus G_e, and the ratio of the reptation time to the Rouse time of an entanglement strand τ_rep/τ_e) depend on the polymer concentration for semidilute entangled (SE) solutions containing poly(sodium styrenesulfonate) with high molecular weight. Our experimental measurements yield G_e ∝ c^1.51±0.04, in good agreement with the scaling of G_e ∝ c^1.5 predicted by Dobrynin's model for salt-free polyelectrolyte SE solutions, suggesting that the electrostatic interaction influences the viscoelastic properties of polyelectrolyte SE solutions. On the other hand, the deviation in the scaling exponent for η_sp ∝ c^2.56±0.04 and τ_rep/τ_e ∝ c^1.82±0.28 is observed between our DWS experiments and Dobrynin's model prediction (∝ c^1.5), likely due to the fact that Dobrynin's scaling model does not account for mechanisms such as the contour length fluctuation, the constraint release, and the retardation of solvent dynamics, which are known to occur for SE solutions of neutral polymers. Our results demonstrate that DWS serves as a powerful rheological tool to study the entanglement dynamics of polyelectrolyte solutions. The scaling relationships obtained in this study provide new insights to the long-standing debate on the entanglement dynamics of polyelectrolyte solutions.

Deconstruction and Reassembly of Renewable Polymers and Biocolloids into Next Generation Structured Materials

This review considers the most recent developments in supramolecular and supraparticle structures obtained from natural, renewable biopolymers as well as their disassembly and reassembly into engineered materials. We introduce the main interactions that control bottom-up synthesis and top-down design at different length scales, highlighting the promise of natural biopolymers and associated building blocks. The latter have become main actors in the recent surge of the scientific and patent literature related to the subject. Such developments make prominent use of multicomponent and hierarchical polymeric assemblies and structures that contain polysaccharides (cellulose, chitin, and others), polyphenols (lignins, tannins), and proteins (soy, whey, silk, and other proteins). We offer a comprehensive discussion about the interactions that exist in their native architectures (including multicomponent and composite forms), the chemical modification of polysaccharides and their deconstruction into high axial aspect nanofibers and nanorods. We reflect on the availability and suitability of the latter types of building blocks to enable superstructures and colloidal associations. As far as processing, we describe the most relevant transitions, from the solution to the gel state and the routes that can be used to arrive to consolidated materials with prescribed properties. We highlight the implementation of supramolecular and superstructures in different technological fields that exploit the synergies exhibited by renewable polymers and biocolloids integrated in structured materials.

Impact of drying on the sodium alginate obtained after polyphenols ultrasound-assisted extraction from Ascophyllum nodosum seaweeds

Ultrasound-assisted extraction (UAE) of polyphenols from the brown seaweeds Ascophyllum nodosum leaves a solid phase where alginates can be extracted. This study characterizes alginates extracted after the UAE process, with and without an intermediate drying stage at different temperatures (50 and 90 °C) producing sequentially two bioactive compounds from a unique raw material. FT-IR and 1H NMR analyses showed the high purity of alginates with features in the range of commercial alginates. Drying at high temperature decreased average block length and viscosity average molecular weight (Mv) of alginate from 428 to 133 kg/mol. Steady-shear curves (shear-thinning behaviour) and viscoelasticity (liquid like character) features depended clearly on Mv. Solutions of alginates with high Mv were more viscous and the elastic character was more relevant. Cox-Merz rule was only accomplished within the semi-dilute regimes of alginate concentration. Tested process conditions allow the production of alginates with different properties.

Quantifying Properties of Polysaccharide Solutions

We apply a scaling theory of semidilute polymer solutions to quantify solution properties of polysaccharides such as galactomannan, chitosan, sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, xanthan, apple pectin, cellulose tris(phenyl carbamate), hydroxyethyl cellulose, hydroxypropyl cellulose, sodium hyaluronate, sodium alginate, and sodium κ-carrageenan. In particular, we obtain the molar mass of the chain segment inside a correlation blob M _g = B̂ ^3/(3ν-1) c ^1/(1-3ν) as a function of concentration c, interaction parameter B̂, and exponent ν. Parameter B̂ assumes values B̂ _g, B̂ _th and M ₀/N _A ^1/3 l for exponents v = 0.588, 0.5 and 1, respectively, where M ₀ is the molar mass of a repeat unit, l is the projection length of a repeat unit, and N _A is the Avogadro number. In the different solution regimes, the values of the B̂-parameters are extracted from the plateaus of the normalized specific viscosity η_sp (c)/M _w c ^1/(3ν-1), where M _w is the weight-average molecular weight of the polymer chain. The values of the B̂-parameters are used in calculations of the excluded volume v, Kuhn length b, and crossover concentrations c*, c _th, and c** into a semidilute polymer solution, a solution of overlapping thermal blobs and a concentrated polymer solution, respectively. This information is summarized as a diagram of states of different polysaccharide solution regimes by implementing a v/bl ² and c/c** representation. The scaling approach is extended to the entangled solution regime, allowing us to obtain the chain packing number, P̃ _e. This completes the set of parameters {B̂ _g, B̂ _th, P̃ _e} which uniquely describes the static and dynamic properties of a polysaccharide solution.

Glyceraldehyde as an Efficient Chemical Crosslinker Agent for the Formation of Chitosan Hydrogels

The rheological changes that occur during the chemical gelation of semidilute solutions of chitosan in the presence of the low-toxicity agent glyceraldehyde (GCA) are presented and discussed in detail. The entanglement concentration for chitosan solutions was found to be approximately 0.2 wt.% and the rheological experiments were carried out on 1 wt.% chitosan solutions with various amounts of GCA at different temperatures (25 °C and 40 °C) and pH values (4.8 and 5.8). High crosslinker concentration, as well as elevated temperature and pH close to the pKa value (pH ≈ 6.3-7) of chitosan are three parameters that all accelerate the gelation process. These conditions also promote a faster solid-like response of the gel-network in the post-gel region after long curing times. The mesh size of the gel-network after a very long (18 h) curing time was found to contract with increasing level of crosslinker addition and elevated temperature. The gelation of chitosan in the presence of other chemical crosslinker agents (glutaraldehyde and genipin) is discussed and a comparison with GCA is made. Small angle neutron scattering (SANS) results reveal structural changes between chitosan solutions, incipient gels, and mature gels.

Rheological and NMR Studies of Cellulose Dissolution in the Ionic Liquid BmimAc

Solutions of two types of cellulose in the ionic liquid 1-butyl-3-methyl-imidazolium acetate (BmimAc) have been analyzed using rheology and fast-field cycling nuclear magnetic resonance (NMR) spectroscopy, in order to analyze the macroscopic (bulk) and microscopic environments, respectively. The degree of polymerization (DP) was observed to have a significant effect on both the overlap (c*) and entanglement (c_e) concentrations and the intrinsic viscosity ([η]). For microcrystalline cellulose (MCC)/BmimAc solutions, [η] = 116 mL g^-1, which is comparable to that of MCC/1-ethyl-3-methyl-imidazolium acetate (EmimAc) solutions, while [η] = 350 mL g^-1 for the commercial cellulose (higher DP). Self-diffusion coefficients (D) obtained via the model-independent approach were found to decrease with cellulose concentration and increase with temperature, which can in part be explained by the changes in viscosity; however, ion interactions on a local level are also important. Both Stokes-Einstein and Stokes-Einstein-Debye analyses were carried out to directly compare rheological and relaxometry analyses. It was found that polymer entanglements affect the microscopic environment to a much lesser extent than for the macroscopic environment. Finally, the temperature dependencies of η, D, and relaxation time (T₁) could be well described by Arrhenius relationships, and thus, activation energies (E_a) for flow, diffusion, and relaxation were determined. We demonstrate that temperature and cellulose concentration have different effects on short- and long-range interactions.