دانلود رایگان مقاله لاپونیت به عنوان رئولوژی از راه حل های آلژینات

ABSTRACT

The rheological behavior of alginate and Laponite/alginate solutions was studied. It was observed that the Cross viscosity model successfully describes the steady-state shear behavior of this polysaccharide. The scaling behavior analyzed for the entangled regime is in good agreement with polyelectrolyte solutions (Ge∼c 3/2 p ), with interactions generated between the alginate and the charged surfaces of the Laponite platelets. Therefore, the effect of Laponite as a rheology modifier is influenced by the alginate concentration. Higher alginate concentrations hindered the formation of the house of cards microstructure. Frequency sweep tests were performed to analyze the transition from solid-like to liquid-like behavior in a solid-like dominated domain. Soft physical gels were obtained at low alginate concentrations. The gel point was determined (1.65 wt.% of alginate and 2 wt.% of Laponite) through the Kramers–Krönig damping factor, and time sweep tests revealed the evolution of the storage (G ) and loss modulus (G) as functions of the waiting time (tw). The growing elasticity revealed that Laponite/alginate solutions undergo aging.

4. Conclusions

Rheological studies performed in alginate and Laponite/alginate solutions allowed the analysis of the mechanism that influences the transition from a shear-thinning behavior in alginate solutions to a pronounced shear-thinning behavior when Laponite is added. Electrostatic interactions between charged Laponite platelets generate a house of cards structure when the shear rate tends to zero. Therefore, at low shear rates, the entangled alginate chains and the house of cards structure contribute to increasing the viscosity considerably. In addition, a solid-like dominated behavior arises due to interactions between the alginate chains and Laponite platelets. As demonstrated, alginate solutions have a polyelectrolyte behavior (Ge∼c 3/2 p ). Therefore, taking into account that alginate is an anionic polysaccharide and the rim of the Laponite platelets is positively charged at pH ≤ 11, it is suggested that the alginate adsorbs on the positive surfaces of Laponite, which hinders the increase in viscosity at high alginate concentrations. Frequency sweep tests revealed that Laponite produces physical gelation in alginate solutions. Moreover, the damping factor from Kramers–Krönig allowed the determinationofthe gel point. This lastfactor defines the transition from solid-like to liquid-like behavior, which follows a similar route, as revealed by a superimposed curve. As observed, at the gel point, the damping factor has no dependence on the frequency. Finally, time sweep tests revealed a growing elasticity as a function of the waiting time. Hence, Laponite/alginate solutions undergo aging. Furthermore, it is anticipated that Laponite/alginate solutions together with AM processes have potential applications in tissue engineering. To crosslink the solutions to form hydrogels, the rheological characterizations of the chemical gelation will be included in future studies.