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Microviscoelasticity of soft repulsive sphere dispersions: Tracer particle microrheology of triblock copolymer micellar liquids and soft crystals
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10.1063/1.3578183
/content/aip/journal/jcp/134/17/10.1063/1.3578183
http://aip.metastore.ingenta.com/content/aip/journal/jcp/134/17/10.1063/1.3578183
View: Figures

Figures

Image of FIG. 1.
FIG. 1.

Colloidal sphere thermal motion in an aqueous 20 wt. % Pluronic F108 solution-effect of temperature. The mean squared displacement of 420 nm diameter polystyrene spheres diffusing in an aqueous 20 wt. % Pluronic F108 solution at the following temperatures increasing from left to right: 22, 25, 28, 30, 30.12, 30.25, 30.38, 30.5, 30.62, 30.75, and 31 °C. Probe motion was measured by diffusing wave spectroscopy in an ∼4.5 mm path length temperature cell. The probe sphere concentration was ∼1 vol. %.

Image of FIG. 2.
FIG. 2.

Colloidal sphere thermal motion in aqueous Pluronic F108 solutions-effect of concentration. The mean squared displacement of 966 nm diameter polystyrene spheres diffusing in 23 °C aqueous Pluronic F108 solutions at the following concentrations increasing from left to right: 5, 10, 15, 21, 22, 23, 24, and 25 wt. %. Probe motion was measured by diffusing wave spectroscopy in 10 mm path length optical cells. The probe sphere concentration was ∼1 vol. %.

Image of FIG. 3.
FIG. 3.

Microscopic creep of aqueous Pluronic F108 solutions. The microscopic creep of 10 (top-left), 15 (top-right), 17.5 (bottom-left), and 20 (bottom-right) wt. % aqueous Pluronic F108 solutions as determined from Eq. (1) are shown. The corresponding temperatures from left to right are as follows: 10 wt. %—23, 30, 35, 45, and 40 °C; 15 wt. %—25, 30, 35, 40, and 45 °C; 17.5 wt. %—25, 30, 35, 35.5, 36, 36.5, 36.55, 36.6, 36.61, and 36.63 °C; and 20 wt. %—22, 25, 28, 30, 30.12, 30.25, 30.38, 30.5, 30.62, 30.75, and 31 °C.

Image of FIG. 4.
FIG. 4.

Zero-shear microviscosity determined from colloidal sphere thermal motion. The zero shear viscosity as determined from Eq. (7) in the text. For all four concentrations considered here the viscosity initially increases with temperature, owing to increasing micellization with the two highest concentrations, 17.5 and 20 wt. %, eventually forming soft micellar polycrystals at 36.7 and 31 °C, respectively. The subsequent viscosity decrease in the two noncrystallizing solutions primarily owes to dehydration of the micelle corona.

Image of FIG. 5.
FIG. 5.

Normalized loss component of the complex microviscosity of a 20 wt. % Pluronic F108 aqueous solution. The loss component of the complex viscosity as determined from Eqs. (3)–(5) in the text. From left to right the curves correspond to (▪) 30.6, (□) 30.5, (●) 30.4, (◯) 30.2, (▲) 30.1, and (△) 30 °C.

Image of FIG. 6.
FIG. 6.

Normalized storage component of the complex microviscosity of a 20 wt. % Pluronic F108 aqueous solution. The storage component of the complex viscosity as determined from Eqs. (3)–(5) in the text. The symbols denote the following temperatures: (▪) 30.6, (□) 30.5, (●) 30.4, (◯) 30.2, (▲) 30.1, and (△) 30 °C.

Image of FIG. 7.
FIG. 7.

Crossover of the microscopic viscoelastic storage and loss moduli in a 20 wt. % Pluronic F108 aqueous solution. The viscoelastic storage and loss moduli as determined from Eqs. (3)–(5) and the relations G′ = ωη′′ and G′′ = ωη′ The symbols denote the storage and loss moduli, respectively, at the following temperatures: (▲, △) 29, (●, ◯) 30.12, and (▪, □) 30.75 °C.

Image of FIG. 8.
FIG. 8.

Dynamic phase diagram for aqueous Pluronic F108 solutions. The symbols denote the following: (▪) a micellar liquid with G′′ > G′; (×) micellar dispersions exhibiting a crossover from a G′′ dominated low-frequency region to a G′ dominated high-frequency region; and (◯) a polycrystalline solid with G′ > G′′. The frequency dependence of the viscoelastic moduli for each of these typical cases is illustrated in Fig. 7.

Image of FIG. 9.
FIG. 9.

Storage modulus of a 20 wt. % Pluronic F108 aqueous solution. The microviscoelastic storage modulus as determined from colloidal sphere thermal motion. The symbols denote the following temperatures: (▪) 31, (□) 30.75, (●) 30.62, (◯) 30.5, (▲) 30.38, (△) 30.25, (◆) 30.12, (◊) 30, (◂) 27, and (◃) 23 °C.

Image of FIG. 10.
FIG. 10.

Loss modulus of a 20 wt. % Pluronic F108 aqueous solution. The microviscoelastic loss modulus as determined from colloidal sphere thermal motion. The symbols denote the following temperatures: (▪) 31, (□) 30.75, (●) 30.62, (○) 30.5, (▲) 30.38, (△) 30.25, (◆) 30.12, (◊) 30, (◂) 27, and (◃) 23 °C.

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/content/aip/journal/jcp/134/17/10.1063/1.3578183
2011-05-05
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Microviscoelasticity of soft repulsive sphere dispersions: Tracer particle microrheology of triblock copolymer micellar liquids and soft crystals
http://aip.metastore.ingenta.com/content/aip/journal/jcp/134/17/10.1063/1.3578183
10.1063/1.3578183
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