Effect of temperature on surface tension

AI Thread Summary
Surface tension is significantly influenced by temperature, typically decreasing as temperature rises and nearing zero at the critical temperature. The discussion involves using Carnot's theorem to derive the relationship between surface tension and temperature, with a focus on adiabatic expansion and its effects on liquid films. Participants seek guidance on proving a linear relation between surface tension and temperature, referencing the Carnot cycle's principles. The conversation also touches on the efficiency of a heat engine driven by surface tension, suggesting that this relationship could reveal the dependence of surface tension on temperature. Overall, the thread emphasizes the need for a mathematical approach to solidify these concepts.
AmanWithoutAscarf
Messages
22
Reaction score
1
Homework Statement
According to the Eötvös rule, the surface tension is a linear function of the temperature, but I cannot find any theoretical proof of the function, except for the following excersise.
Relevant Equations
##F=\sigma .L##
The translated version is:
Surface tension is temperature-dependent. Therefore, it is essential to specify the temperature when providing the surface tension value of an interface. Typically, surface tension decreases with increasing temperature and approaches zero at the critical temperature. This excersise will explore these concepts in detail.
1.
a) Use Carnot's theorem to find the variation of surface tension ##σ## with temperature ##T##.
b) Calculate the temperature change of the liquid film during adiabatic expansion.
2.
Inside a soap bubble of radius ##\displaystyle r_{0}## contains air (ideal gas) at temperature ##\displaystyle T_{0}## and pressure ##\displaystyle p_{0}##. The surface tension of the soap solution at this temperature is ##\displaystyle \sigma _{0}##. The specific heat of formation of a unit of soap film surface in an isothermal process is ##\displaystyle q_{0}##. Find the derivative of bubble radius with respect to temperature ##\displaystyle \frac{dr}{dT}## when ##\displaystyle T_{0}##. The outside pressure remains constant.

I did research on the topic and the Eötvös rule, but most of the results are just qualitative explanations or experiment-based proofs of the temperature-dependent function of surface tension.

Can anyone give me some hints on how to prove that linear relation (using Carnot's theorem)? And the following questions, if possible, please.
 
Physics news on Phys.org
AmanWithoutAscarf said:
Can anyone give me some hints on how to prove that linear relation (using Carnot's theorem)?
To quote from here: https://phys.libretexts.org/Bookshelves/Thermodynamics_and_Statistical_Mechanics/Thermodynamics_and_Statistical_Mechanics_(Nair)/03:_The_Second_Law_of_Thermodynamics/3.01:_Carnot_Cycle
“The processes involved in the Carnot cycle may refer to compression and expansion if the material is a gas ... But any other pair of thermodynamic variables will do as well. We can think of a Carnot cycle utilizing magnetization and magnetic field, or surface tension and area …”

So I’d guess you are meant to conceive of some design of heat-engine based on a liquid being heated/cooled so that surface tension and area cyclically change and the driving 'force' is surface tension. Presumably the efficiency can be shown to be some function of surface tension, then the dependence of surface tension on temperature should emerge.

Just a guess though.
 
So if I apply Carnot cylcle with the driven force from surface tension, the efficiency will be:
$$\eta =1-\frac{T_{2}}{T_{1}} =\frac{W}{Q_{H}} =\frac{\int _{S1}^{S2} \sigma ( T) .dS}{\int _{T1}^{T2} C.dT}$$
Suppose the system witnesses a minimal change in temperature ##dT## when it is stretched by ##dS##. We have:
$$ \begin{array}{l}
T_{1} -T_{2} =dT\\
W=\sigma ( T) .dS\\
Q_{H} =C.dT
\end{array}$$
Substituting the variables, I think the result would be: $$\frac{\sigma ( T) .dS}{C.dT} =\frac{dT}{T} $$
but I don't know how to cancel out ##dS## and ##dT## to have a linear function of ##\sigma ( T)## T.T
 
Thread 'Minimum mass of a block'
Here we know that if block B is going to move up or just be at the verge of moving up ##Mg \sin \theta ## will act downwards and maximum static friction will act downwards ## \mu Mg \cos \theta ## Now what im confused by is how will we know " how quickly" block B reaches its maximum static friction value without any numbers, the suggested solution says that when block A is at its maximum extension, then block B will start to move up but with a certain set of values couldn't block A reach...
TL;DR Summary: Find Electric field due to charges between 2 parallel infinite planes using Gauss law at any point Here's the diagram. We have a uniform p (rho) density of charges between 2 infinite planes in the cartesian coordinates system. I used a cube of thickness a that spans from z=-a/2 to z=a/2 as a Gaussian surface, each side of the cube has area A. I know that the field depends only on z since there is translational invariance in x and y directions because the planes are...
Thread 'Calculation of Tensile Forces in Piston-Type Water-Lifting Devices at Elevated Locations'
Figure 1 Overall Structure Diagram Figure 2: Top view of the piston when it is cylindrical A circular opening is created at a height of 5 meters above the water surface. Inside this opening is a sleeve-type piston with a cross-sectional area of 1 square meter. The piston is pulled to the right at a constant speed. The pulling force is(Figure 2): F = ρshg = 1000 × 1 × 5 × 10 = 50,000 N. Figure 3: Modifying the structure to incorporate a fixed internal piston When I modify the piston...
Back
Top