The determination method of critical beam concentration (CMC) is introduced.

Original title: The determination method of critical beam concentration (CMC) introduces the conceptual critical beam concentration of the critical beam concentration (CMC, glue beam, test method, aggregation state) (English expression: critical micelle concentration, abbreviated to CMC).
1925 since Mcbain first proposed the concept of glue beam (group), it is believed that when the concentration rises to a certain value, soap molecules in the water solution from monomer to "glue aggregation state", and called "glue beam" or "glue" (Figure 1), the formation of these bundles are thermodynamically stable, thus forming the concentration of the glue beam when known as the concentration of the gel beam, known as CMC concentration.
once a beam or group of the solution containing the surfactant is formed, a series of properties of the solution body phase change (Figure 2), such as molar conductivity, surface tension (bound), decontamination, osmosis pressure, and dissolution, adsorption and other mutations in the solution In the body phase, the surfactant aggregation state, these properties of variation usually occur in a narrow concentration range, and this narrow concentration range is defined as the critical beam concentration, the method of acquisition is to extend the CMC solution properties of the continuous change of the curve extended to intersect, the intersection corresponding to the concentration of CMC.
the critical beam concentration of the test method in the solution phase of the glue beam, continue to increase the concentration, the concentration of monomer in the body phase will no longer rise, so in theory, all the use of beam formation and the nature of discontinuous changes can be used to determine The CMC, but it is important to note that some properties are sensitive to monomer concentration, some are sensitive to the beam, so the same surface active agent with different methods to determine the CMC value is a small difference. There are many methods
to test critical beam concentration, such as surface tension method, conductivity method, dye method, dissolving method, osmotic pressure method, pulse dispensing method, fluorescence method, ultrasonic adsorption method, turbidity method, pH method, rheological method, ion selective electrode method and circulating voltamp method.
, surface tension test principle solution surface tension mainly depends on the concentration of the surfactant monomer in the solution, when the plastic beam is formed, the concentration of the monomer is almost unchanged, so the surface tension on the concentration will appear a significant turn.
are generally the concentration of log coordinates, the resulting curve becomes the gamma-log-log curve, the inflection point on the curve can be sought out CMC, if the inflection point is not obvious, the inflection point can be extended on both sides of the straight line, from the intersection to find the CMC. the surface tension of the
(Figure 3) surfactant water solution decreases sharply with the increase of concentration at a very low concentration, and changes slowly or no more after reaching a certain concentration (CMC).
characteristics: the test method is simple and easy to operate, can be suitable for the solution containing various types of surfactant critical beam concentration test, its sensitivity is not affected by the type of surfactant, activity, the presence of inorganic salts and concentration.
instrument selection: surface tension analyzer, the market to choose from more commercial surface tension tester, based on the principle of testing can be divided into bubble method, drop weight method, force measurement method, rotary dropmethod method.
force measurement is a surface tension analyzer which is more widely used.
, the principle of conductivity: the use of conductivity meter to determine the different concentrations of surfactant water solution conductivity (can also be converted to molar conductivity).
for ion-type surfactants, when the solution concentration is very thin, the change law of the conductivity is similar to the general strong electrolyte, the surfactant completely dissociated as ions, with the concentration rise, conductivity K nearlinear rise but when the concentration of the solution reaches the critical bundle concentration, with the formation of the beam, the beam directional movement rate slows down, K still increases with the concentration, but the change is small.
the molar conductivity of m also dropped sharply, using the turning point of the K-C curve to find the cmc value (Figure 4).
characteristics: conductivity is a classic method to determine the concentration of critical beam, with the advantages of easy operation.
but this test method can only be applied to ion-type surfactants, which have high accuracy with ion-type surfactants called high surfactivity, and less sensitive for critical beam concentrations.
and the presence of organic salts in the solution will affect the determination.
instrument selection: conductivity analyzer three, dye principle: the use of certain optical properties of oil-soluble substances as a probe to detect the solution began to form a large number of bundle concentrations.
are usually preceded by the addition of a small number of dyes to a higher concentration of the surfactant solution.
the dyes used can be dissolved with the glue beam to give the solution a special color.
then use the titration method to gradually dilute the solution with water until the color changes significantly, the concentration of the solution is its critical bundle concentration.
characteristics: test ingle concentration of CMC a method, a disadvantage of dye method is that sometimes the color change is not obvious enough, so that the critical beam concentration is not easy to accurately determine. Another important disadvantage of
dye method is that the addition of dyes may have an effect on the critical beam concentration of the system, and the wrong results are uncertain.
test equipment: titration tube IV, turbidity principle: the probe compound used is not a dye, but insoluble hydrocarbons, detection is not a spectral or color change, but a change in system turbidity.
due to the hydrocarbon seine solution in the surfactant (characteristic: the turbidity method has the problem of the hydrocarbon solubility affecting the concentration of the surfactant critical bundle.
although the impact is not very large due to the small amount of dosage, but the impact is there.
is generally to reduce the concentration of critical beams, the degree of reduction varies depending on the type of hydrocarbon used.
required equipment: turbidity analyzer five, fluorescent probe method principle: water-repellent probecommon in water media has radon and its derivatives.
solubility in water is very small, about 0mol/L. the I1/I3 values of
in aqueous solution, cyclhexane solution and SDS bond are approximately 1.8, 0.7 and 0.87, respectively.
therefore, the cmc of the surfactant can be determined by the mutation (beam formation) of the i1/I3 value after the electron beam. After
exceeds cmc, there is a mutation in the solution's dissolving capacity.
at the same time I1/I3 The concentration at the point of change is similar to the titration curve, the concentration at the sudden point of the curve is cmc (critical beam concentration).
features: fluorescent probe method is simple to operate, no special requirements for the system, the amount of probe is small, the interference to the system is small, but the disadvantage is the need to configure the benzene solution, because the benzene is toxic, the operation process is more cumbersome, and the accuracy is not as accurate as the surface tension method test.
required equipment: fluorescent photophotometer vi, light scattering principle: light through the surfactant solution, if there are glue beam particles in the solution, then a part of the light will be scattered by the beam particles, therefore, the determination of scattered light strength is turbidity, can reflect the formation of the surfaceactive agent glue beam in the solution.
the concentration of the liquid c is x axis, and the light scattering intensity I is the Y axis, making the I-c relationship curve.
when the surfactant reaches or exceeds a certain concentration in the solution, it will synthesize the gel agglomeration from the monomer (a single ion or molecule), that is, the formation of a glue beam, its size conforms to the range of the size of the gel particles, so there is the scattering phenomenon of light.
with the increase of the concentration of surfactants, the increasing number of connectivity and molecules, and the increasing number of bundles, the light scattering intensity of the liquid is increasing. When
CMC, the light scattering intensity increases dramatically, and the CMC can be identified by the mutation point of the curve.
characteristics: light scattering method as a method to determine the concentration of critical bundles can be tested CMC can also be used to test the aggregation of the bundle, the size and shape of the glue beam and the charge of the glue beam, etc., but this method requires the solution is very clean, can not have dust spots, so this method to test the critical bundle of the solution is more limited.
required equipment: dynamic light scattering analyzer summary: critical beam concentration (CMC) as a measure of the surfactant of the surfactant, is an important nature parameter, can choose to test The CMC method more, we can according to the nature of the tested sample and the relevant equipment available in the surrounding laboratory to select the appropriate method to test the critical beam concentration.
can be seen by comparing various methods, the light scattering method as a determination of critical beam concentration needs to test the solution clean, more restricted factors.
and conductivity is only applicable to the testing of CDCs containing osmotic surfactants.
the fluorescent probe method to test the CMC, although the restriction smaller factors, but the need to configure the benzene solution of the xenon probe, and benzene is toxic and the operation process is cumbersome.
the dye method to test the CMC required equipment is simple, but because the color change is not obvious enough, will affect the accuracy of The CMC, turbidity method as also easy to use hydrocarbon solubility affect the surfactant critical bundle concentration of the problem affects the accuracy of the test CMC.
surface tension method compared to the above other methods to test the critical beam concentration when affected by external factors less, the test obtained the CMC value is accurate, the operation process is relatively simple, at the same time the market to choose from more commercial surface tension analyzers, we can choose according to their respective needs, generally can choose a force-based surface tension analyzer.
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computer software controls the measurement, storage and processing of surface tension data.
Finland's Kibron is an innovative, high-tech company focused on developing equipment related to surface tension testing.
recently introduced a portable probe-type surface tension analyzer (EZ-PLUS) is a very suitable for enterprise or university research platform for the study of surfactants beam concentration determination, because of its portable, test inglises required for small sample size, simple operation process, by many users and related institutions alike.
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