Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering Center

The Interfacial Tension Of Colloidal Suspensions

Lichun Dong, Xusheng Wu and Dr.Duane JohnsonMINT Center and Department of Chemical Engineering

The University of Alabama

This work supported by Alabama Space Grant Consortium (SUB2002-036) and the University of Alabama Albert

Simmons Endowment Fund

Center For Materials For Information TechnologyAn NSF Materials Research Science and Engineering Center

• Colloidal dispersion are ubiquitous • Magnetic recording materials• Printing inks• Inorganic and organic pigments• Paper Coating

• Interfacial tension plays a very important role in determining the properties and processing of the colloidal suspensions.

Motivation

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Literature Data

•Surface tension of aqueous silica suspension•Suspension structures are liquid –like or gas-like•Particle size is from 6 nm to 60 nm.

T.Okubo, J. Coll. Int. Sci. 171, 55-62 (1995)

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Current Experiments

• Measure the surface tension of SiO2 and TiO2 suspension at various concentrations using pendant drop method and DeNuoy ring method

• Measure interfacial tension of the suspensions in silicone oil.

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Zeta Potential of Titania Dispersion

The zeta potential of titania dispersion as a function of pH and concentration of aluminum nitrate.

R. O. James et al. J. Coll. Int. Sci., 59, 381-385 (1977)

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Interfacial Tension of Silica DispersionUsing Pendant Drop Method

Note: the size of the particles is from 100µm to 600 µm

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35Weight Percent (%)

Inte

rfac

ial T

ensi

on (d

yne/

cm)

In AirIn Silicone Oil

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Interfacial Tension of Titania DispersionUsing Pendant Drop Method

0

10

20

30

40

50

60

0 5 10 15 20 25 30 35Weight Percent(%)

Inte

rfac

ial T

ensi

on (d

yne/

cm

In AirIn Silicone Oil

Note: The size of the particles is from 50µm to 300µm

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Surface Tension of Titania Dispersion Using Ring Method

50

55

60

65

70

75

0 5 10 15 20Weight Percentage(%)

Surf

ace

Ten

sion

(dyn

e/cm

Note: the size of the titania particles is from 50µm to 300µm

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Schematic representation of colloidal particles at the interface.

AG

∂∂

=γ

Physical Explanation

G = Gibbs free energy at the interface.A = The interfacial area.

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The particles at the interface

Schematic of two particles placed at an interface. The interactive energy between two particles ∆W is:

( )qLKQW 02πγ2=∆Plot of the interaction energy between two immersed colloidal particles of the same radius, r. The plot was calculated using the values: γ = 72 dyne/cm, ∆ρ = 1 g cm-3, ψ = 60o.

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Physical Explanation (cont.)

•For pendant drop method, the curvature is large, fewer particles can be packed at the interface

•For ring method, the interface is flat, more particles can be packed at the interface

~20mm

~1mm

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Questions for Future Work

• How important is the electric double layer (pH value) in determining the surface tension?

• How does the size and polydispersity of the particles affect the surface tension?

• How would the addition of surfactants change the surface tension?

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Conclusions

• Interfacial tension of a colloidal dispersion can be a strong function of the particle concentration- decreases with the increase of the

concentration at low weight percents- increases with the increase of the

concentration at higher weight percents.- Pendant drop and DeNuoy ring can give

different results.

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Pendant Drop Method

The pedant drop method determines the profile of the bubble at hydrostatic And interfacial equilibrium, calculate the surface tension from the measurement of the shape of he drop.

RHI 2001 Imaging Goniometer System

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Ring Method

σ = real surface tension value P = maximum force at the ringσ* = measured surface tension value Ri = radius at inner side of the ringF = correction factor Ra= radius at outside side of the ringThe correction factor F include the weight of the liquid is lifted by the ring.

FRR

PFai

⋅+⋅

=⋅=)(2

*π

σσ

The Interfacial Tension Of Colloidal SuspensionsMotivationLiterature DataCurrent ExperimentsZeta Potential of Titania DispersionInterfacial Tension of Silica DispersionUsing Pendant Drop MethodInterfacial Tension of Titania DispersionUsing Pendant Drop MethodSurface Tension of Titania Dispersion Using Ring MethodPhysical ExplanationThe particles at the interfacePhysical Explanation (cont.)Questions for Future WorkConclusionsPendant Drop MethodRing Method