科研之友
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摘要
The equilibrium surface pressure (Pi(e)) and electric surface potential (Delta chi(e)) vs. concentration (c) isotherms of n-decanoic acid (DA) in 5 x 10(-3) mol/dm(3) HCl were concurrently measured at the air/solution interface - the Pi with a platinum Wilhelmy plate, the Delta chi with the vibrating plate method (named also the dynamic condenser). The Pi(e)-Delta chi(e) dependence was used by us for calculating the surface charge' density basing on the Lippmann first electrocapillary equation. It was applied under the assumption that: (i) the surface charge is solely formed by orientation of the adsorbate, and (ii) the changing DA bulk concentration does not deprive the Pi(e)-Delta chi(e) dependence of consistency with the Lippmann equations. The charge (Q(e)) expressed per the adsorbate molecule (basing on the Gamma-c dependence predicted by the best fit of Frumkin model to the experimental Pi(e)-c results) increases with the adsorption coverage (Theta) within a fraction of electron per the adsorbate molecule - the reasonable result for a non ionic surfactant. The Q(e) vs. Theta course shows a great analogy to that of quotient of the effective dipole moment to the interface's permittivity, mu(1)/epsilon(s) vs. Theta, derived from the Delta chi(e)-Gamma dependence. The two dependencies: (Q(e) vs. Theta and mu(1)/epsilon(s) vs. Theta, show a plateau within the coverage range of 20 < Theta <80% and a steep increase above it. Recalculation of the (Q(e) vs. Theta dependence for the equivalent dipole moment, under the assumption that the dipole length is comparable to length of a polar bond of the head group (ca. 1.2 A) implies the bond's inclination to the interface of 12 degrees. Such low inclination is reasonable in view of an angular deviation of molecular dipole moment from amphiphile molecule' long axis.
- 出版日期2014-5-1
