Newtonian fluid means viscosity ("internal friction") is constant  relative to the shearing stress and this is unrelated to tension forces, which surface tension depends on.So surface tension is about the balance of forces on the surface, while these forces may not behave like "friction" /viscosity

As a "conviction" check super-fluid helium which has "zero" viscosity, yet exhibits surface tension

Newtonian fluid means viscosity ("internal friction") is constant  relative to the shearing stress and this is unrelated to tension forces, which surface tension depends on.So surface tension is about the balance of forces on the surface, while these forces may not behave like "friction" /viscosity

As a "conviction" check super-fluid helium which has "zero" viscosity, yet exhibits surface tension

That was very helpful. Thank you!

To follow up on Yannis' excellent answer. When we speak of two immiscible liquids we speak of interfacial tension rather than surface tension (which is usually reserved for describing liquid/gas systems). The phenomena that interfacial tension or surface tension give rise to are: capillary pressure effects, surface tension gradients and the force of capillarity at contact lines. Of course, if the liquids are perfectly miscible then by definition there is no interfacial tension, but Korteveg stresses may exist leading to interesting phenomena. The ability to achieve ultralow interfacial tensions in immiscible liquid-liquid systems using surfactants is a well known technology used in enhanced oil recovery.

Surface tension is a contractive tendency of the surface of a liquid that allows it to resist an external force.It is an inherent property of  liquids. So What ever may be the liquid is , surface tension will  exist.

Agree with Koveos. Newtonian fluid is a fluid having constant viscosity. Viscosity and Surface Tension are two different properties of fluids. While viscosity is related to the resistance offered by the fluid against its deformation and thereby its motion against the force applied on it, the surface tension refers to the net force developed at the surface of two fluids or a fluid and a solid in contact due to the difference in their respective inter-molecular forces. So not only the Newtonian fluid, but also the ideal fluid or inviscid  fluid will also have the surface tension. But if the fluids in contact have the same inter-molecular force then there will not be any surface tension and thereby will not have any existence of boundary surface between those two fluids and thus they can mix to form a solution, if they do not undergo any chemical reaction.

Hi,

Newtonian fluid are class of fluids which obeys newton's law of viscosity.  The ratio of shear stress to shear strain rate is a constant, for a given temperature and pressure, and is defined as the viscosity. for Newtonian fluid the viscosity is independent of the shear rate but for Non-Newtonian fluids viscosity is not constant and is dependent on the shear rate.

but surface tension is different concept and nothing to do with Viscosity or Newtonian fluid.

The concept of surface tension comes in to picture only when two immiscible fluid(Two non-mixing liquids, could be liquid and gas) have interface(Surface of separation) between them.  Across this interface there exist a discontinuity in density.  This interface behaves like a stretched membrane under tension. hence surface tension is tensile force per unit length exist at the thin interface between two non mixing fluids.

Important point about surface tension is that, it is not a property of single fluid, its binary property

Ex. The surface tension of water with respect to air is 0.073 N/m

All fluids (Newtonian / non newtonian) do have surface tension between them. And one should talk about the surface tension between two fluids not surface tension with respect to one fluid which is non sense.

Water is a Newtonian fluid - and nobody doubts that there is surface tension when water is in contact with solids, other liquids and/or gases!

A Newtonian fluid is a fluid which obeys the newton's law of viscosity. All the fluids have viscosity up to some degree. The surface tension has nothing to do with the viscosity; it is a tensile force per unit length acting at the interface of liquid and surrounding gas/air. As Heinz Herwig mentioned about water; it is a newtonian fluid as well as has surface tension when is in contact with solids,liqids or gas.

To begin with, liquid surface tension and viscosity share a common trait: they both involve properties of fluids. After that, things start to get murky.

Let us start with surface tension. This relates Surface Tension - FloatingPaper Cilpto the property of a liquid’s surface that resists force; it serves as a barrier to foreign materials as well as keeping the liquid together. This ever-present property is caused by unbalanced forces on surface molecules that pull toward the main part of the liquid.

Viscosity, on the other hand, is related toviscosity shear rate a liquid’s resistance to being deformed or moved. This is caused by the friction between molecules.

Compared to viscosity, surface tension is a simpler phenomenon. It is basically stable, changed mostly by temperature and chemicals that modify the bonding characteristics of the molecules. As temperature decreases, surface tension increases. The effects of adding an unrelated substance is illustrated by the example of putting soap (a surfactant) in water to reduce the surface tension, which allows the dirt on your hands to more easily mix with the water.

Regarding viscosity, knowing the type of liquid is essential. For example, there are Newtonian fluids that react to forces (sometimes called shear rate) that move the liquid (sometimes called shear stress) in a straight-forward, linear manner.

However, non-Newtonian fluids follow different sets of rules. Shear-thinning fluids decrease in viscosity as the Ketchuppressure or force increases. Thixotropic fluids change viscosity over time -- Example gels and colloids, and yes ketchup are stable at rest, but become fluid when agitated.

Thus we see that finding the true value of viscosity [which some of us may think of as simply thickness] is a complex process. Viscosity, unlikeViscosity Thick to Thin surface tension [which tends to be a static phenomenon], is all about movement. All that should concern us in regard to measuring surface tension is whether to use a Wilhelmy Plate or a duNouy Ring. (That is enough to keep me entertained.)

The last question, which perhaps should have been the first, is about the correlation between surface tension and viscosity. You would think that thick fluids would translate to a high surface tension and that thin fluids would produce lower surface tension. Not true. In fact, my research has shown that there is no conclusive correlation.

This got into a lot more theoretical entanglement than I expected when I first considered taking on what seemed like a international Nosimple comparison. The answer, however, is clear: no correlation. The reasons are not so simple. I guess a good summary would be that surface tension is about steady state and viscosity is about movement.

By Art Gatenby

ideal fluids are just a model and like each model simpify certain aspects, here the  absence of viscosity. There are not such fluids per se but certain physical situations in which the fluid behavior can be described by this model.