Chemistry Letters
Online ISSN : 1348-0715
Print ISSN : 0366-7022
ISSN-L : 0366-7022
Volume 41 , Issue 10
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  • Thomas W. Healy, Peter J. Scales
    2012 Volume 41 Issue 10 Pages 1020-1022
    Published: October 05, 2012
    Released: September 29, 2012
    JOURNALS OPEN ACCESS
    The great Dutch school of colloid science of Kruyt, Overbeek, and others developed theoretical and experimental models of the silver halide–water interface. Potentiometric titrations, electrokinetic measurements, and coagulation kinetics set high standards of experimentation. They, further, led to the development of theoretical models, mostly thermodynamic, of the silver halide–aqueous electrolyte interface, which allowed quantitative understanding of experimental results. The fundamental step was to recognize that silver and halide ions, as potential-determining ions, controlled the Nernst potential of the interface. At ca. 25 °C, as the concentration of silver ions in the bulk solution changed by a factor of 10, the potential of the silver halide–water interface changed by 59 mV. Colloid scientists across the globe in the post-1948 era, additionally wished to understand the properties of colloidal dispersions of simple inorganic oxides such as silica, hematite, and alumina, and more recently, the properties of “latex” particles. In short, it became difficult to apply the theories that allowed understanding of the silver halide–water interface to the understanding of the properties of latex, oxides, and similar colloidal dispersions. Finally, a very recent resurgence in the interest in the electrical double layer (e.d.l.) at the air–water and oil–water interface has fuelled the discussion on the ubiquitous role of protons as potential-determining ions (p.d.i.’s) on interfaces ranging from oxides, to lattices, close packed monolayers, and oil–water and air–water interfaces. We explore the new thinking on all of these aqueous interfaces.
    Colloid scientists across the globe in the post 1948 world also wished to understand the properties of colloidal dispersions of simple inorganic oxides such as silica, hematite, alumina, and the like or more recently, the properties of “latex” particles. In short it became difficult to transpose the thinking that allowed understanding of the silver halide–water interface to make sense of the properties of latex, oxide, and similarim colloidal dispersions. Finally a very recent resurgence in interest in the electrical double layer at air–water and oil–water interfaces has provoked problems in understanding the ubiquitous role of protons as potential-determining ions for interfaces from oxides, to lattices, to close-packed monolayers and to oil and air–water interfaces. We explore the new thinking of all of these aqueous interfaces. Fullsize Image
     
  • Tharwat Tadros
    2012 Volume 41 Issue 10 Pages 1023-1028
    Published: October 05, 2012
    Released: September 22, 2012
    JOURNALS OPEN ACCESS
    The interaction forces between adsorbed layers of two graft copolymers were directly measured using surface force apparatus and atomic force microscopy. Two types of graft copolymers that were adsorbed on hydrophobic surfaces were used: (i) a graft copolymer consisting of poly(methyl methacrylate)/poly(methacrylic acid) backbone (the B chain) on which several poly(ethylene oxide) chains are grafted (to be referred to as PMMA/PEOn) and (ii) a graft copolymer consisting of inulin (linear polyfructose with degree of polymerization greater than 23) (the A chain) on which several C12 chains are grafted (INUTEC SP1). In the first case, adsorbed layers of the graft copolymer were obtained on mica sheets and the interaction forces were measured using the surface force apparatus. In the second case, the interaction forces were measured using atomic force microscopy (AFM). For this purpose, a hydrophobically modified glass sphere was attached to the tip of the cantilever of the AFM and the glass plate was also made hydrophobic. Both the sphere and the glass plate contained an adsorbed layer of INUTEC SP1. The curves of energy E(D) versus distance D for the graft copolymer of PMMA/PEOn between mica surfaces bearing the graft copolymer could be used to estimate the interaction energy between flat surfaces, by using Derjaguin approximation for cross cylinders. The results were compared with the theoretical calculations using de Gennes scaling theory. The agreement between experimental results and theoretical calculations was satisfactory. The same graft copolymer was used in latex dispersions, and the high frequency modulus G was measured as a function of the volume fraction φ of the dispersion. This high-frequency modulus could be related to the potential of mean force. In this way, one could compare the results obtained from rheology and those obtained from direct measurement of interaction forces. In the AFM method, the interaction forces are measured in the contact area between two surfaces, i.e., the surfaces of a spherical glass particle and a glass plate. The glass spheres and plates were hydrophobized using dichlorodimethylsilane. Results were obtained for adsorbed layers of INUTEC SP1 in water and in the presence of various concentrations of Na2SO4 (0.3, 0.8, 1.0, and 1.5 mol dm−3). All results showed a rapid increase in force with a decrease in the separation distance, and the forces were repulsive up to the highest Na2SO4 concentration. This explains the high stability of dispersions when using INUTEC SP1 as the stabilizer.
    The interaction forces between adsorbed layers of two graft copolymers were directly measured using surface force apparatus and atomic force microscopy.
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