Rheological Characterization of Alginate Microbead Gels and Suspensions
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Date
2009-06-29
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Abstract
As the use of microgel beads in food, pharmaceutical, and other industries becomes more prevalent, additional data is needed regarding the rheology of suspensions and gels composed of microgel beads. The goal of this work was to evaluate the rheological properties of alginate microbead gels and suspensions.
The microgel beads used in this research were produced by an air-assisted atomization process that was designed for this work. The process was based on disintegration of alginate solution jet by exposure to high-velocity air, and yielded alginate microgel beads ranging in size from several microns to several hundred microns. The bead diameter was a function of solution viscosity and air velocity. Decreasing solution viscosity and increasing air velocity contributed to the disintegration of the atomized liquid jet and produced smaller beads. A correlation between the bead mean diameter and the Weber and Reynolds numbers was obtained by dimensional analysis: D∠(We×Re)^(-0.25). The beads produced were used for construction of the “microbead gels†and suspensions.
The mechanical properties of the microbead gels were investigated as a function of bead mechanical properties and particle size distribution. Bulk gels were used to evaluate the mechanical properties of the beads, which depended on alginate type and concentration. The microbead gels were constructed from different bead types and the viscoelastic properties of the microbead gels were related to the viscoelastic properties of the bulk gels. While higher modulus beads contributed to the modulus of the microbead gel, they were also less deformable and therefore decreased interparticle contact. As smaller particles were introduced into the system, the importance of particle deformability and interparticle interactions increased.
The rheology of suspensions composed of viscoelastic particles was investigated as a function of shear rate, volume fraction, particle size distributions, and mechanical properties of the beads. The viscoelastic properties of the beads proved to be very important in the analysis of the effects shear rate, particle volume fraction, and particle size distribution had on suspension viscosity. The diverse flow behavior could not be fully explained by the models presented in literature; therefore, several mechanisms were proposed to explain suspension rheology. The proposed mechanisms were based on the hydrodynamic forces, interactions between the particles, and the beads viscoelastic properties.
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Keywords
Rheology, suspension, viscoelastic, alginate, microbeads
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Degree
PhD
Discipline
Food Science
