Surface Forces between Silica Surfaces in CnTACl Solutions and Surface Free Energy Characterization of Talc

In general, the stability of suspension can be studied using two methods. <i>One</i> is to directly measure the forces between two interacting surfaces in media. <i>The other</i> is to study the interfacial surface free energies of the particles in suspension. Direct surface force measurements were conducted between silica surfaces in octadecyltrimetylammonium chloride (C₁₈TACl) solutions using an Atomic Force Microscope (AFM). The results showed that the hydrophobic force existed in both air-saturated and degassed C₁₈TACl solutions. The attraction decreased with NaCl addition, and was the strongest at the point of charge neutralization (p.c.n.) of silica substrate. The force measurement results obtained in C_nTACl solutions showed that the attractions decayed exponentially and became the maximum at the p.c.n.'s. The decay lengths (<i>D</i>) increased with surfactant chain length. The measured forces were fitted to a charged-patch model of Miklavic <i>et al</i>. (1994) with rather large patch sizes. It was also found that the decay length decreased linearly with the effective concentration of the CH2/CH3 groups raised to the power of -1/2. This finding is in line with the model of Eriksson <i>et al</i>. (1989). It suggested that the long-range attractions are hydrophobic forces originating from the changes in water structure across a hydrophobic surface-solution interface. For the TiO₂/water/TiO₂ system, the Hamaker constant was found to be 4±1×10^-20 J. The force curves obtained in the TiO₂/C_nTACl system showed a repulsion-attraction-repulsion transition with increasing surfactant concentration. The long-range attraction observed between TiO₂ surfaces in C_nTACl solutions reached maximum at the p.c.n., and the decay length increased with chain length. In present work, the thin-layer wicking technique was used to determine the surface free energy (γ_s) and its components of talc samples. The results showed that the basal surfaces of talc are weakly basic while the edge surfaces are acidic. The effect of chemicals on the surface free energies of talc was systemically studied. The results showed that CMC (carboxymethyl cellulose sodium salt) and EO/PO (ethylene oxide/propylene oxide) co-polymers made talc surface hydrophilic by increasing the surface free energies, especially γ^LW and γ^-. SOPA (sodium polyacrylate) increased greatly the zeta-potentials instead of the surface free energies.

Name thesis:degree_name

Ph. D.

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Mining and Minerals Engineering

Department dc:contributor.department

Mining and Minerals Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2006

Author dc:creator

• Zhang, Jinhong

Chair dc:contributor.committeechair

• Yoon, Roe-Hoan

Committee members dc:contributor.committeemember

• Vlachos, Pavlos P.
• Luttrell, Gerald H.
• Davis, Richey M.
• Telionis, Demetri P.

• talc
• long range attraction
• adhesion force
• surface force
• surface free energy
• thin-layer wicking
• extended DLVO
• hydrophobic force

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Dc Identifier Other

etd-12082006-132335

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/29997