The Relations between Surface pH, Ion Concentrations and Interfacial Tension. BY JAMES FREDERIC DANIELLI, Commonwealth Fund Fellow. The stronger the intermolecular forces of a liquid, the stronger its surface tension. Normally, the concentration of whatever substances H2O contains has nothing. sometimes the surface tension of nanofluid increases and sometimes decreases. with the nanoparticles concentration serii.info is no constant behavior.
For the sake of precision the peaks of the profiles are fitted with Gaussian curves.
The factor in the Gibbs equation for 1: The prevailing argument is factor 2, which is not appropriate. Besides the uncertainty dissociation of ionic surfactant molecules on the surface, one of well-founded grounds is factor 2 implying that the counter-ion contributes to the surface tension as much as the surface active ion though those two species have distinct surface activity and different sizes.
From this point, it does not need to revise the factor in the Gibbs equation. However, more experiments and theories should be developed in order to give a deeper insight into this topic.
Conclusions and outlook In the current work, we have investigated the dependence of surface tension on surface excess and surface concentration for two alkali dodecyl sulfate salts. Those three parameters are measured independently, and the comparisons are done without any extra assumptions.
The results evidence that the surface excess and surface concentration have different values as the surfactant solutions have identical bulk concentrations, reminding one of the fact that the surface excess is an excess quantity with respect to the bulk concentration. The surface excess can be approximated by the surface concentration when the bulk concentration is low, however, in case the bulk concentration is high the deviation between those two emerges and becomes significant.
Importantly, two series of solutions show the coincident linear dependencies of surface tension on surface concentration, but this case does not hold for their surface tension—surface excess relations. From this finding, an important conclusion can be drawn that the surface tension is decided by the surface concentration of the surface active ion, but not its surface excess which is just an excess quantity thermodynamically with respect to the bulk concentration.
This notion implies, when one investigates the topics like molecular orientation on the surface, which relates to the surface population of the adsorbed molecules, it is the surface concentration but not the surface excess that is more appropriate to be employed.
The present investigation on the structure of the electric double layer indicates as well that the same surface tension is not equivalent to the same distribution of hydrophilic counter-ions in the surface layer. It is necessary to explain further the definition of the surface—bulk phase boundary z B.
Emphatically, this is not a parameter chosen freely to fulfil the linearity between the surface tension and surface concentration. We have defined it in a vague way as the depth from where the surfactant begins to relax to its bulk concentration. Therefore, its value can be determined unambiguously through the shape of the concentration profile of the surfactant using eqn As a result, the surface concentration can be determined accurately by integrating the concentration profile until z B.
Due to the concentration profile levels off smoothly to the value in bulk, the depth of z B is a bit blurred. In the proceeding investigation, 4 the surface fraction of the outmost layer taken by the species has been related to the surface tension and a linear relationship among them has been found in several binary systems.
The current investigation is focused on the composition of the surface layer affecting the surface tension and the surface structure, for the pure solutions of two ionic surfactants. The forces of attraction acting between the molecules of same type are called cohesive forces while those acting between the molecules of different types are called adhesive forces.
When cohesive forces are stronger than adhesives forces, the liquid acquires a convex meniscus as mercury in a glass container. On the other hand, when adhesive forces are stronger, the surface of the liquid curves up as water in a glass. Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a spherical shape by the imbalance in cohesive forces of the surface layer. In the absence of other forces, including gravitydrops of virtually all liquids would be approximately spherical.
The spherical shape minimizes the necessary "wall tension" of the surface layer according to Laplace's law.
Water droplet lying on a damask. Surface tension is high enough to prevent floating below the textile Another way to view surface tension is in terms of energy. A molecule in contact with a neighbor is in a lower state of energy than if it were alone not in contact with a neighbor.
The interior molecules have as many neighbors as they can possibly have, but the boundary molecules are missing neighbors compared to interior molecules and therefore have a higher energy. For the liquid to minimize its energy state, the number of higher energy boundary molecules must be minimized.
The minimized number of boundary molecules results in a minimal surface area. Since any curvature in the surface shape results in greater area, a higher energy will also result.
Consequently, the surface will push back against any curvature in much the same way as a ball pushed uphill will push back to minimize its gravitational potential energy.
Effects of surface tension[ edit ] Water[ edit ] Several effects of surface tension can be seen with ordinary water: Beading of rain water on a waxy surface, such as a leaf. Water adheres weakly to wax and strongly to itself, so water clusters into drops.
Surface tension gives them their near-spherical shape, because a sphere has the smallest possible surface area to volume ratio.
Surface tension - Wikipedia
Formation of drops occurs when a mass of liquid is stretched. The animation below shows water adhering to the faucet gaining mass until it is stretched to a point where the surface tension can no longer keep the drop linked to the faucet. It then separates and surface tension forms the drop into a sphere.
If a stream of water was running from the faucet, the stream would break up into drops during its fall.