Bubble Pressure Method
Encyclopedia
In physics
, the maximum bubble pressure method, or in short bubble measure method, is a technique to measure the surface tension
of a liquid
, with surfactant
s.
forms an interface with a gas
phase, a molecule
on the border has quite different physical properties
due to the unbalance of attracting forces by the neighboring molecules. At the equilibrium state
of the liquid, interior molecules are under the balanced forces with uniformly distributed adjacent molecules.
However, relatively fewer number of molecules in the gas phase above the interface than condensed
liquid phase makes overall sum of force
s applied to the surface molecule direct inside of the liquid and thus surface molecules tend to minimize their own surface area.
Such an inequality of molecular forces induce continuous movement of molecules from the inside to the surface, which means the surface molecules has extra energy
, which is called surface free energy
or potential energy
, and such an energy acting on reduced unit area is defined as surface tension
.
This is a frame work to interpret relevant phenomena which occurs surface or interface of materials and many methods to measure the surface tension
has been developed.
Among the various ways to determine surface tension, Du Noüy ring method
and Wilhelmy slide method
are based on the separation of a solid
object from the liquid surface, and Pendent drop method and Sessile drop or bubble method depend on the deformation
of the spherical shape of a liquid drop.
Even though these methods are relatively simple and commonly used to determine the static
surface tension
, in case that the impurities are added to the liquid, measurement of surface tension based on the dynamic equilibrium
should be applied since it takes more time to obtain a completely formed surface and this means that it is difficult to achieve the static equilibrium as a pure liquid does.
The most typical impurity to induce dynamic
surface tension measurement
is a surfactant molecule which has both of hydrophilic
segment, generally called “head group” and hydrophobic
segment, generally called “tail group” in a same molecule. Due to the characteristic molecular structure
, surfactant
s migrate to the liquid surface bordering gas phase until an external force disperse the accumulated molecules from the interface or surface is fully occupied and thus cannot accommodate extra molecules. During this process, surface tension decrease as function of time and finally approach the equilibrium surface tension (σequilibrium). Such a process is illustrated in figure 1. (Image was reproduced from reference)
Bubble pressure tensiometer
produces gas bubbles (ex. air) at constant rate and blows them through a capillary which is submerged in the sample liquid and its radius is already known.
The pressure
(P) inside of the gas bubble continues to increase and the maximum value is obtained when the bubble has the completely hemispherical shape whose radius is exactly corresponding to the radius of the capillary.
Figure 2 shows each step of bubble formation and corresponding change of bubble radius and each step is described below. (Image was reproduced from reference)
A, B: A bubble appears on the end of the capillary. As the size increases, the radius of curvature of the bubble decreases.
C: At the point of the maximum bubble pressure, the bubble has a complete hemispherical shape whose radius is identical to the radius of the capillary denoted by Rcap. The surface tension can be determined using the Laplace equation
in the reduced form
for spherical bubble shape within the liquid.
(σ: surface tension, ΔPmax: maximum pressure drop, Rcap: radius of capillary)
D, E: After the maximum pressure, the pressure of the bubble decreases and the radius of the bubble increases until the bubble is detached from the end of a capillary and a new cycle begins. This is not relevant to determine the surface tension.
Currently developed and commercialized tensiometers monitors the pressure needed to form a bubble, the pressure difference between inside and outside the bubble, the radius of the bubble, and the surface tension of the sample are calculated in one time and a data acquisition is carried out via PC
control.
Bubble pressure method is commonly used to measure the dynamic surface tension for the system containing surfactants or other impurities because it does not require contact angle measurement and has high accuracy even though the measurement is done rapidly. “Bubble pressure method” can be applied to measure the dynamic surface tension, particularly for the systems which contain surfactants. Moreover, this method is an appropriate technique to apply to biological fluids like serum
because it does not require a large amount of liquid sample for the measurements.
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
, the maximum bubble pressure method, or in short bubble measure method, is a technique to measure the surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
of a liquid
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
, with surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
s.
Background
When the liquidLiquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
forms an interface with a gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
phase, a molecule
Molecule
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
on the border has quite different physical properties
Physical property
A physical property is any property that is measurable whose value describes a physical system's state. The changes in the physical properties of a system can be used to describe its transformations ....
due to the unbalance of attracting forces by the neighboring molecules. At the equilibrium state
Thermodynamic equilibrium
In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, radiative equilibrium, and chemical equilibrium. The word equilibrium means a state of balance...
of the liquid, interior molecules are under the balanced forces with uniformly distributed adjacent molecules.
However, relatively fewer number of molecules in the gas phase above the interface than condensed
Condensation
Condensation is the change of the physical state of matter from gaseous phase into liquid phase, and is the reverse of vaporization. When the transition happens from the gaseous phase into the solid phase directly, the change is called deposition....
liquid phase makes overall sum of force
Force
In physics, a force is any influence that causes an object to undergo a change in speed, a change in direction, or a change in shape. In other words, a force is that which can cause an object with mass to change its velocity , i.e., to accelerate, or which can cause a flexible object to deform...
s applied to the surface molecule direct inside of the liquid and thus surface molecules tend to minimize their own surface area.
Such an inequality of molecular forces induce continuous movement of molecules from the inside to the surface, which means the surface molecules has extra energy
Energy
In physics, energy is an indirectly observed quantity. It is often understood as the ability a physical system has to do work on other physical systems...
, which is called surface free energy
Specific surface energy
specific surface energy, also known as surface free energy, is the amount of increase of free energy when the area of surface increases by every unit area. It can be calculated using Stefan's formula. Specific surface energy is the same as surface tension for isotropic materials, but different...
or potential energy
Potential energy
In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...
, and such an energy acting on reduced unit area is defined as surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
.
This is a frame work to interpret relevant phenomena which occurs surface or interface of materials and many methods to measure the surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
has been developed.
Among the various ways to determine surface tension, Du Noüy ring method
Du Noüy ring method
The du Noüy ring method is one technique by which the surface tension of a liquid can be measured. The method involves slowly lifting a ring, often made of platinum, from the surface of a liquid...
and Wilhelmy slide method
Wilhelmy plate
A Wilhelmy plate is a thin plate that is used to measure equilibrium surface or interfacial tension at an air–liquid or liquid–liquid interface. In this method, the plate is oriented perpendicular to the interface, and the force exerted on it is measured...
are based on the separation of a solid
Solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...
object from the liquid surface, and Pendent drop method and Sessile drop or bubble method depend on the deformation
Deformation (mechanics)
Deformation in continuum mechanics is the transformation of a body from a reference configuration to a current configuration. A configuration is a set containing the positions of all particles of the body...
of the spherical shape of a liquid drop.
Even though these methods are relatively simple and commonly used to determine the static
Statics
Statics is the branch of mechanics concerned with the analysis of loads on physical systems in static equilibrium, that is, in a state where the relative positions of subsystems do not vary over time, or where components and structures are at a constant velocity...
surface tension
Surface tension
Surface tension is a property of the surface of a liquid that allows it to resist an external force. It is revealed, for example, in floating of some objects on the surface of water, even though they are denser than water, and in the ability of some insects to run on the water surface...
, in case that the impurities are added to the liquid, measurement of surface tension based on the dynamic equilibrium
Dynamic equilibrium
A dynamic equilibrium exists once a reversible reaction ceases to change its ratio of reactants/products, but substances move between the chemicals at an equal rate, meaning there is no net change. It is a particular example of a system in a steady state...
should be applied since it takes more time to obtain a completely formed surface and this means that it is difficult to achieve the static equilibrium as a pure liquid does.
The most typical impurity to induce dynamic
Dynamics (mechanics)
In the field of physics, the study of the causes of motion and changes in motion is dynamics. In other words the study of forces and why objects are in motion. Dynamics includes the study of the effect of torques on motion...
surface tension measurement
Measurement
Measurement is the process or the result of determining the ratio of a physical quantity, such as a length, time, temperature etc., to a unit of measurement, such as the metre, second or degree Celsius...
is a surfactant molecule which has both of hydrophilic
Hydrophile
A hydrophile, from the Greek "water" and φιλια "love," is a molecule or other molecular entity that is attracted to, and tends to be dissolved by water. A hydrophilic molecule or portion of a molecule is one that has a tendency to interact with or be dissolved by, water and other polar substances...
segment, generally called “head group” and hydrophobic
Hydrophobe
In chemistry, hydrophobicity is the physical property of a molecule that is repelled from a mass of water....
segment, generally called “tail group” in a same molecule. Due to the characteristic molecular structure
Molecular structure
The molecular structure of a substance is described by the combination of nuclei and electrons that comprise its constitute molecules. This includes the molecular geometry , the electronic properties of the...
, surfactant
Surfactant
Surfactants are compounds that lower the surface tension of a liquid, the interfacial tension between two liquids, or that between a liquid and a solid...
s migrate to the liquid surface bordering gas phase until an external force disperse the accumulated molecules from the interface or surface is fully occupied and thus cannot accommodate extra molecules. During this process, surface tension decrease as function of time and finally approach the equilibrium surface tension (σequilibrium). Such a process is illustrated in figure 1. (Image was reproduced from reference)
- Figure 1 – Migration of surfactant molecules and change of surface tension (σt1 > σt2 > σequilibrium)
Maximum bubble pressure method
One of the useful methods to determine the dynamic surface tension is measuring the “maximum bubble pressure method” or, simply, bubble pressure method.Bubble pressure tensiometer
Tensiometer
A Tensiometer as it applies to physics is an instrument used to measure the surface tension of liquids.-Goniometer/Tensiometer:...
produces gas bubbles (ex. air) at constant rate and blows them through a capillary which is submerged in the sample liquid and its radius is already known.
The pressure
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...
(P) inside of the gas bubble continues to increase and the maximum value is obtained when the bubble has the completely hemispherical shape whose radius is exactly corresponding to the radius of the capillary.
Figure 2 shows each step of bubble formation and corresponding change of bubble radius and each step is described below. (Image was reproduced from reference)
- Figure 2 – Change of pressure during bubble formation plotted as a function of time.
A, B: A bubble appears on the end of the capillary. As the size increases, the radius of curvature of the bubble decreases.
C: At the point of the maximum bubble pressure, the bubble has a complete hemispherical shape whose radius is identical to the radius of the capillary denoted by Rcap. The surface tension can be determined using the Laplace equation
Laplace's equation
In mathematics, Laplace's equation is a second-order partial differential equation named after Pierre-Simon Laplace who first studied its properties. This is often written as:where ∆ = ∇² is the Laplace operator and \varphi is a scalar function...
in the reduced form
Reduced form
In statistics, and particularly in econometrics, the reduced form of a system of equations is the result of solving the system for the endogenous variables. This gives the latter as a function of the exogenous variables, if any...
for spherical bubble shape within the liquid.
(σ: surface tension, ΔPmax: maximum pressure drop, Rcap: radius of capillary)
D, E: After the maximum pressure, the pressure of the bubble decreases and the radius of the bubble increases until the bubble is detached from the end of a capillary and a new cycle begins. This is not relevant to determine the surface tension.
Currently developed and commercialized tensiometers monitors the pressure needed to form a bubble, the pressure difference between inside and outside the bubble, the radius of the bubble, and the surface tension of the sample are calculated in one time and a data acquisition is carried out via PC
Personal computer
A personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
control.
Bubble pressure method is commonly used to measure the dynamic surface tension for the system containing surfactants or other impurities because it does not require contact angle measurement and has high accuracy even though the measurement is done rapidly. “Bubble pressure method” can be applied to measure the dynamic surface tension, particularly for the systems which contain surfactants. Moreover, this method is an appropriate technique to apply to biological fluids like serum
Serous fluid
In physiology, the term serous fluid is used for various bodily fluids that are typically pale yellow and transparent, and of a benign nature, that fill the inside of body cavities. Serous fluid originates from serous glands, with secretions enriched with proteins and water. Serous fluid may also...
because it does not require a large amount of liquid sample for the measurements.