Influence of gellan gum concentration on the dynamic viscoelasticity and transient flow of fluid gels (original) (raw)
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Rheology and microrheology of a microstructured fluid: The gellan gum case
Journal of Rheology, 2007
Particle tracking microrheology is used to study the effect of a constant applied shear during gelation of aqueous gellan gum with a monovalent salt. Shear modifies the gellan gum hydrogel microstructure and the bulk rheological properties of the system, depending on whether shear is applied during gelation or afterwards. The microstructure determines the linear elastic response of the gel, as well as the critical strain and stress above which the response becomes nonlinear. Bulk oscillatory rheology is used to study microstructured gellan gum hydrogels at different polymer and salt concentrations. The similarity between our system and concentrated microgel particle suspensions can be explained by considering the microstructured gellan system to be composed of microgel particles whose size is set by the applied shear stress magnitude during gelation. Polymer concentration and ionic strength control the individual microgel particles' elastic properties. We also find the gellan system exhibits an isoenergetic transition from the jammed to un-jammed state when sheared, similar to jammed colloidal systems ͓C.
Rheological characterization and activation energy values of binary mixtures of gellan
European Food Research and Technology, 2012
The present study determined the flow behavior and activation energy of high (HA) and low (LA) acyl gellan dispersions (0.2%) and their mixtures as a function of preparation temperature (25 and 90°C) and of the presence or absence of Ca 2? (30 mM). Heated gellan mixtures containing calcium were acidified with d-gluconolactone to obtain gels and determine linear viscoelasticity using the Kelvin-Voigt model. The studied dispersions showed non-Newtonian shear-thinning behavior. HA dispersions (with and without Ca 2? ) showed the highest activation energy values, 88.60 and 51.18 kJ/mol. Whereas, LA dispersions showed the lowest activation energy values, 3.73 and 9.19 kJ/mol. With respect to the rheological studies, it was observed that the relationships between HA and LA gellan did not affect the recovery percentages because similar values were obtained (86.90-90.00%), and this behavior along with the mean viscosity values obtained in the gel mixtures could indicate that the hydrogen bond formation between both gellan helix (HA, LA) is possible. These results can contribute to possible industrial applications of gellans in the development of new alimentary products.
Rheological analysis of emulsion-filled gels based on high acyl gellan gum
Food Hydrocolloids, 2013
Emulsion-filled gels are widely used in cosmetic, food, and pharmaceutical industry. As rheological properties of these systems are strongly dependent on the properties of the gelled polymer network, rheological characteristics of gels containing high and low acyl gellan gum were analyzed. Under the processing conditions low acyl emulsions were unstable, thus in the present work the influence of oil and hydrocolloid concentrations on the viscoelastic behavior of emulsion-filled gels containing high acyl gellan gum was studied. Increasing gellan concentration (from 0.1 g/100 g to 0.5 g/100 g) produced stronger gels, while oil fraction (10 g/100 ge30 g/100 g) slightly affected the elastic behavior of the emulsions reinforcing the structure and the elastic characteristics of the gellan matrix. Sauter diameter (d 32) was measured for all emulsions and an average value of 12 mm was obtained. Rheological data (oscillatory and creeperecovery tests) were successfully modeled to interpret the structural characteristics of the gelled emulsions. The broadened BaumgaerteleSchausbergereWinter spectrum was used to represent the linear viscoelastic behavior of the continuous phase and the emulsified system, showing that the rheological behavior of the systems was controlled by the highly structured continuous phase rather than the contribution of filler lipid droplet in the emulsion. Relaxation spectra were validated using creeperecovery experiments. Regardless of hydrocolloid concentration, creep compliance of the gel emulsions decreased compared with their respective gels, showing that the inclusion of oil droplets produced a reinforcement of the structure and the gel strength of the matrix.
Oscillatory and steady shear rheology of gellan/dextran blends
Journal of Food Science and Technology, 2014
Oscillatory and steady shear rheology of gellan (G) and dextran (D) solution individually, and in blends (G/D ratio 1:1, 1:2, and 1:3 w/v) with a total hydrocolloid concentration of 3 % (w/v) were studied at 25°C. Individually, 1.5 % dextran and 1.5 % gellan in solution exhibited Newtonian and non-Newtonian behavior, respectively. A blend of equal proportion of dextran and gellan (G/D=1:1) exhibits a distinct gel point (G′ = G″), and further addition of dextran in the blend (G/D=1:2 and 1:3) resulted predominating liquid-like (G″ > G′) behavior. A plot of G′ vs G″ distinctly showed the gradual transition of the blend. Shear stress (τ)-shear rate (γ ) data fitted well the Herschel-Bulkley model. The G/D blend exhibited shear thinning behavior with flow behavior index less than unity. The Cox-Merz rule did not fit well for the complex shear viscosity (η*) and apparent viscosity (η) of the blend.
Rheological and mechanical properties of acellular and cell-laden methacrylated gellan gum hydrogels
Journal of Biomedical Materials Research Part A, 2013
Tissue engineered hydrogels hold great potential as nucleus pulposus substitutes (NP), as they promote intervertebral disc (IVD) regeneration and re-establish its original function. But, the key to their success in future clinical applications greatly depends on its ability to replicate the native 3D micro-environment and circumvent their limitation in terms of mechanical performance. In the present study, we investigated the rheological/mechanical properties of both ionic-(iGG-MA) and photo-crosslinked methacrylated gellan gum (phGG-MA) hydrogels. Steady shear analysis, injectability and confined compression stress-relaxation tests were carried out. The injectability of the reactive solutions employed for the preparation of iGG-MA and phGG-MA hydrogels was first studied, then the zero-strain compressive modulus and permeability of the acellular hydrogels were evaluated. In addition, human intervertebral disc (hIVD) cells encapsulated in both iGG-MA and phGG-MA hydrogels were cultured in vitro, and its mechanical properties also investigated under dynamic mechanical analysis at 37 C and pH 7.4. After 21 days of culturing, hIVD cells were alive (Calcein AM) and the E' of ionic-crosslinked hydrogels and photo-crosslinked was higher than that observed for acellular hydrogels. Our study suggests that methacrylated gellan gum hydrogels present promising mechanical and biological performance as hIVD cells were producing extracellular matrix. V C 2013 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 101A: 3438-3446, 2013. How to cite this article: Silva-Correia J, Gloria A, Oliveira MB, Mano JF, Oliveira JM, Ambrosio L, Reis RL. 2013. Rheological and mechanical properties of acellular and cell-laden methacrylated gellan gum hydrogels. J Biomed Mater Res
Effect of Shear History on Rheology of Time-Dependent Colloidal Silica Gels
Gels
This paper presents a rheological study describing the effects of shear on the flow curves of colloidal gels prepared with different concentrations of fumed silica (4%, 5%, 6%, and 7%) and a hydrophobic solvent (Hydrocarbon fuel, JP-8). Viscosity measurements as a function of time were carried out at different shear rates (10, 50, 100, 500, and 1000 s −1), and based on this data, a new structural kinetics model was used to describe the system. Previous work has based the analysis of time dependent fluids on the viscosity of the intact material, i.e., before it is sheared, which is a condition very difficult to achieve when weak gels are tested. The simple action of loading the gel in the rheometer affects its structure and rheology, and the reproducibility of the measurements is thus seriously compromised. Changes in viscosity and viscoelastic properties of the sheared material are indicative of microstructural changes in the gel that need to be accounted for. Therefore, a more realistic method is presented in this work. In addition, microscopical images (Cryo-SEM) were obtained to show how the structure of the gel is affected upon application of shear.
Gelation of polymer solutions under shear flow
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2003
Gelling a polymer solution under constant shear rate was recently found to be an attractive procedure for preparing size-controlled microgels. In the theoretical approach developed in this paper, the microgels formed during gelling are modelled as non-covalent 'star' polymers. This approach provides scaling laws to predict the effects of the shear rate applied during gelation on: (1) the gelling kinetics in three flow regimes; (2) the microgel size dependence in weak and strong flows; and (3) the rheological and elastic properties of the microgel solutions. The reported experiments were carried out by gelling semi-dilute high molecular weight polymer solutions by a crosslinker small enough to diffuse inside macromolecules and thus able to form both intra and intermolecular cross-links. All available experimental results are in agreement with our theoretical predictions, but further experiments are needed for a complete validation of the proposed theory.
Understanding the rheology of novel guar-gellan gum composite hydrogels
Materials Letters, 2019
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International Journal of Food Engineering, 2008
Rheological behaviors of high acyl (HA) gellan are not well understood partially because of its relatively late commercialization compared to low acyl gellan. The objective of this study was to investigate the effect of temperature (5-30 °C), calcium (0, 1 and 10 mM) and gellan concentrations (0.0044-0.1000% w/v) on the flow behaviors of high acyl gellan aqueous solutions using rheological tests. Gellan solutions with 0 or 1 mM added Ca++ exhibited shear thinning behavior at gellan concentrations above 0.0125%. The influence of temperature on apparent viscosity (shear rate, 100 s-1) of gellan solutions can be described with an Arrhenius relationship. The apparent viscosity of gellan solution at low concentrations was more sensitive to temperature changes. The addition of Ca++ led to a decrease in flow resistance for a dilute gellan solution (<0.0125%), but an increased resistance for a relatively concentrated gellan solution (>0.0125%).
Food Hydrocolloids, 2007
The gelation mechanism and the change of the network structure during cooling of the mixed solution of high-acyl (HA) and low-acyl (LA) gellan (containing 0.5% HA gellan and 0.5% LA gellan; hereafter called ''mixed solution'') were elucidated on the basis of the results of dynamic viscoelasticity, circular dichroism (CD), and NMR measurements, which provide information about the network formation, the structural change due to random coil-double helix (C-H) transition, and the chain mobility of gellan, respectively. It was demonstrated that HA gellan chains in the mixed solution underwent C-H transition individually to form a network structure at the transition temperature for 1% HA gellan solution (75 1C), where storage modulus G 0 and loss modulus G 00 were steeply increased and the chain mobility of the HA gellan was restricted. The structural change of the HA gellan chains proceeded gradually with further cooling. At 25 1C, which is the C-H transition temperature for 1% LA gellan solution, LA gellan chains in the mixed solution formed a double helix, where G 0 and G 00 were slightly increased and the chain mobility of LA gellan was restricted. The results suggest that the double helix formation involves only the same kind of gellan chains even in the mixed solution, and that LA gellan chains decrease the mobility and promote the double helix formation of HA gellan chains, and vice versa. r