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There are a lot of surface tensiometers with different measuring methods, made by different manufactories. And quality and working accuracy of these surface tensiometers are quite different from each other. How to choose the most suitable surface tensiometer for us is more important. This article will show you how to begin your surface tension measuring experience by choosing the most suitable surface tensiometer from different manufactories in worldwide.
Selecting surface tensiometer is easier than choosing suitable contact angle meter, because weighing sensor (main unit of meter) is almost fixed into balance made by such manufactory as METTLER TOLEDO and Sartorius. So, surface tensiometers made by different manufactories are homogenized very much. There are five main manufactories include KINO, KRUSS, Dataphysics, Biolin (Attension, KSV), Kyowa around world. All most all of them except KINO measured surface tension of liquid (or mixture liquid) using classWilhelmy plate method. (Refer http://www.uskino.com/news/55.html)
1, Startup choosing surface tensiometer (tension meter) from measuring method of surface tension?
Referring http://www.uskino.com/news/55.html for more information about method.
here are main commercial tensiometer includes max bubble pressure tensiometer, max drop volume (max drop weight) tensiometer, optical tensiometer (drop shape analysis system based on pendant drop method or sessile drop method) and force surface tensiometer based on weighing method. First two tensiometers are always used to measure dynamic surface tension (perhaps with poor measuring accuracy of surface tension). Among them, max bubble pressure tensiometer is more common. But recently, scholars start to use optical tensiometer based on oscillating method to measure dynamic surface tension and experiments show that better results can be achieved than first two. But measuring accuracy of optical tensiometer is about 1-2%. It is worse than force surface tensiometer ( About ±0.2mN/m or dyne/cm).
So, in this article, we discuss how to choose force surface tensiometer only. You can find how to choose tensiometer based on other methods in our web.
There are two main measuring methods including Du Noüy ring method and Wilhelmy plate method for force tensiometer.
1.1 Du Noüy ring method for measuring surface tension
Du Noüy ring method
Du Noüy ring method is so popular and almost all
manufactories consider this method as gift when they
sale tensiometer. Almost all manufactories can provide
this method in their tensiometer. And measuring process
or Du Noüy ring method is almost same. Nobody can
enhance measuring accuracy of Du Noüy as high as
Wilhelmy plate method due to such inborn defect as:
- Liable to be deformed
- Hard to keep levelness of ring for Du Noüy method.
- And more important disadvantage of Du Noüy ring method is
it cannot be used to measure surface tension of viscous
sample such as glycerol and adhesives.
Main reason of it is same as class Wilhelmy plate method as
shown below. More precise method for force tensiometer is
Wilhelmy plate method. If you want to choose tensiometer
just based on Du Noüy ring method, we think that it will
mislead you. But when you are budget shortfall for surface
tensiometer, you can choose Du Noüy ring tensiometer such as
surface tensiometer model A3 that is used balance from KINO
or tensiometer made by Fisher.
Cheaper tensiometer: left one is Classical Du Noüy ring
Tensiometer used torsion wire sensor, middle one is
tensiometer made by fisher and right one is tensiometer
model A3 made by KINO which used balance as sensor. Please
be noted that KINO is only one that provides tensiometer at
price about 1500USD using balance.
1.2 Wilhelmy plate method for measuring surface tension
1.2.1 Classical Wilhelmy plate method:
There are several variations of the Wilhelmy plate methods.
All are based on balancing the static forces of surface
tension, gravity, and buoyancy acting on a thin plate
(usually made of glass or platinum) suspended vertically in
the air-liquid interface.
Four variations of the Wilhelmy plate measurement are
commonly used:
- The zero-buoyancy method (Kawanishi et al. 1970; Lane and
Jordan 1970): plate was immersed and withdrew and was kept
stationary at zero depth of immersion. Then, measuring force
of tension and calculating surface tension from equation.
Generally, we will measure about 10 value of surface tension
versus time and average them, and we will consider this
averaged value as final value.
- The detachment method (Furlong and Hartland 1979): the
plate is quasi-statically pulled up
until it is entirely free from the liquid ( detachment
mode). As the instant of breaking loose is well-defined, the
force at that moment can be rather easily determined.
- The immersion method (Gaines 1966): Plate is immersed
below interface of liquid-gas or liquid-fluid at a constant
position such as 1mm, and correcting buoyancy from
calculating buoyancy by this height and side of plate.
- The maximum-pull method (La Mer and Robbins 1958; Loglio
et al. 1976; Gaonkar and Neuman 1984): Plate is pulled up
until max value is gotten. In this method, plate is not
pulled up quasi-statically and meniscus may be ruptured
before Wmax reached.
Referring http://www.uskino.com/news/55.html for more information
about method.
1.2.2 Modified Wilhelmy plate method
Recently, KINO proposed a new method name modified Wilhelmy
plate method. What separates them from four method described
above is we consider buoyancy and contact angle is always
existing during measuring process. Please be noted that
contact angle is not regard as 0°here
because we find out that contact angle is about 29-32° in
measuring process of surface tension (liquid-gas system).
This will reduce value of surface tension about 1-3mN/m for
measurement of surface tension.
Meniscus curve at interface of liquid-gas (fluid)-plate: 1,
alcohol-air-platinum/iridium plate;
2, water-air- platinum/iridium plate; 3, benzene-water-
platinum/iridium plate; 4, n-butyl alcohol-water-
platinum/iridium plate
And, there exists influential buoyancy due to liquid
enclosed at meniscus. So, how to correct this buoyancy is
more important. This value is about 0.59mN/m (using plate
with width 24mm and thickness 0.15mm, height of meniscus is
about 8mm). Changing of height about 1mm will affect surface
tension value about 0.07mN/m and it is about sensory force
for 0.1mg balance (0.1mg ≈ 0.02mN/m)
1.2.3 Different of classical and modified
Wilhelmy plate method
Main different of classical and modified Wilhelmy plate
method includes:
- Moving of sample stage: Classical Wilhelmy plate method
will immerse plate into liquid about a height and then
withdraw plate by same height, and measure surface tension
by averaging several surface tension versus time (usually
about 10 datas); But modified Wilhelmy plate method will not
immerse and withdraw the plate. In this method, sample stage
will stop once finding interface of liquid-gas or liquid-fluild.
- Calculating equation: Classical Wilhelmy plate method used
simplified equation without buoyancy and contact angle (this
value is assumed as 0°). But, in modified Wilhelmy plate
method, buoyancy and contact angle should be corrected by
Young-Laplace equation or elasticity coefficient.
Diagram of different measuring methods of surface
tensiometer
1.2.3.1
Modified Wilhelmy plate method
1.2.3.2 Classical Wilhelmy plate method (Max
pull)
1.2.3.3 Classical Wilhelmy plate method (Zero
buoyance method)
Note:This method is used in surface tensiometer made by
Kruss, KSV, KYOWA. And it cannot used to measure surface
tension of cationic surface active agent and sample with
viscosity due to its immersing and drawing out process.
1.2.3.4 DuNouy ring method
Note: Sometimes, we will repeat process 2, 3 after process 3
by rising stage and lowering stage several times, and
calculate surface tension by average measured data.
You can visit youtube to watch videos of surface tensiometer
from different manufactory by click address below:
Surface tensiometer model K100 from Kruss:
http://www.youtube.com/watch?v=-R24A5KaCuc
surface tensiometer model sigma 700 from Attension
http://www.youtube.com/watch?v=mwUBemTAHj0
surface tensiometer model DY300 from Kyowa
http://www.youtube.com/watch?v=MkKlJ-2YrqA
surface tensiometer model A601 from KINO
http://www.youtube.com/watch?v=yTpWg-btpAE
1.2.4 Advantage and disadvantage of
Wilhelmy plate method
1.2.4.1 Both Wilhelmy plate method and Du
Noüy ring method is not suitable to measure interface
tension between liquid-fluid system.
Measurement of the interfacial tension between two
immiscible liquids can present special difficulties.
Measurement by the capillary rise, Du Noüy ring, or Wilhelmy
plate method is problematic in that the contact angle is
often nonzero (from 20-120°). The pendant drop and drop
weight methods can both be applied, provided the densities
of the two liquids are sufficiently different. The pendant
drop method, in particular, is widely used for interfacial
tension measurement. Ultralow values of interfacial tension
can be measured by the spinning drop or pendant drop
methods. (Refer “Measurement, Instrumentation, and Sensors
Handbook, Second Edition, Spatial, Mechanical, Thermal, and
Radiation Measurement, Edited by Halit Eren, CRC Press 2014,
Pages 1–14, Print ISBN: 978-1-4398-4888-3, eBook ISBN:
978-1-4398-4889-0, DOI: 10.1201/b15474-52.”)
1.2.4.2 Both classical Wilhelmy plate
method and Du Noüy ring method cannot be used to measure
surface tension of viscous sample such as glycerol and
adhesives.
Because when plate or ring immersed and withdrew from
viscous sample, adhesive force will affect at probe during
movement of plate or ring and this force cannot be corrected
by any way. So, usually when we used tensiometer based on
classical Wilhelmy plate method or Du Noüy ring method,
measured result will larger than actual value.
Secondary, it is difficult to immerse plate or ring into
sample with high viscosity. So, measurement cannot be
carried out at this case.
But with modified Wilhelmy plate method, you can measure
surface tension or viscous sample and max viscosity can
reach 10,000CP.s.
1.2.4.3 Both classical Wilhelmy plate
method and Du Noüy ring method is not suitable to measure
surface tension of surfactant especially cationic surface active agent.
When measuring surface tension of surfactant based on
classical Wilhelmy plate method, contact line between liquid
and plate is keeping moving and will age new surface of
surfactant. So, when we used classical Wilhelmy plate method
to measure surface tension, if moving time and total
measuring time is not agree with adsorbing time of
surfactant to contact line, we may not achieve real value of
sample’s surface tension. And usually, measured value is
higher than actual one.
Red line means changing value of weighing during measuring
process and green line means changing value of surface
tension during adsorbing process. So, if at time T3,
surfactant has not adsorbed totally to contact line between
liquid-plate, measured values will be entirely higher than
actual one.
By contrast, in modified Wilhelmy plate method, surfactant
will adsorb at interface between liquid and gas at first and
adsorbs to contact line once plate touching interface, and
will keep on adsorbing until contact line is full of
surfactant as shown above. You can find out measuring
process is quite agree with adsorbing process of surfactant.
We have measured value of some surfactant, and find out that
when measuring surfactant with longer adsorbing time,
measured value used classical Wilhelmy plate method or Du
Nouy ring method is much higher than modified Wilhelmy plate
method. And we check out measured value measured by modified
Wilhelmy plate method using pendant drop method and spinning
drop method, all values are agree with each other.
Unit: mN/m
No. |
name |
type |
Classical
Wilhelmy plate |
Du Nouy ring |
Modified
Wilhelmy plate |
Pendant drop |
Spinning
drop |
1 |
Diallyldimethylammonium chloride(1827) |
cationic |
38.6 |
37.5 |
29.1 |
31.5 |
31.8 |
2 |
Dimethyldioctadecylammonium chloride(1821) |
cationic |
39.4 |
36.5 |
19.5 |
21.6 |
22.3 |
And more over, as KRUSS proposed, when measuring surface
tension using Wilhelmy plate method, Langmuir monolayers
made at surface of plate during measuring process.
Especially when measuring surface tension of cationic
surface active agent, this new surface of monolayers will
change surface of probe into hydrophobic surface, and this
is not suitable for measurement of surface tension because
contact angle here is no longer 0°. (Refer application
article “Influences to Plate measurements” from KRUSS.)
1.2.4.4 Both Classical Wilhelmy plate
method and Du Noüy ring method need more volume of liquid
than 1mL except Modified Wilhelmy plate method
Because probe should be immersed into liquid in Classical
Wilhelmy plate method or Du Noüy ring method, you must keep
a height of liquid (such as 5mm?) to carry out measurement
of surface tension. But in modified Wilhelmy plate method,
plate should not be immersed in and we have invented a
sample vessel made of PTFE to measure surface tension of
liquid using volume about 1mL.
2, Choosing your surface tensiometer
according to your sample that wants to measure (viscous
sample or surfactant?), accuracy requirement and your budget
based on measuring method
2.1 First consider measuring surface
tension for viscous sample.
If viscosity of your sample is higher than 500CP.s,
classical Wilhelmy plate method and Du Nouy ring method is
not your suitable choice. You can choose KINO’s tensiometer
used modified Wilhelmy plate method or optical tensiometer
based on pendant drop method or constrained sessile drop
method. A simply way to adjusting whether your sample is
suitable for using modified Wilhelmy plate method to measure
surface tension is checking out if liquid is movable by
inclining sample bottle. If sample is easy to move, you can
use modified Wilhelmy plate method to get more accurate
value of surface tension. If not so, this sample can only be
considered as solid and using method of calculating surface
free energy of it based on equation of state method.
Contact us for comparing value of different viscosity that
measured by different method.
2.2 Measuring surface tension and critical
micelle concentration (CMC) of surfactant
If your budget is enough to buy automatic critical micelle
concentration measuring system (syringe pump system and
corresponding controlling software), you can purchase one
for you. But, using effect may be not as good as you
supposed. We suggest you choosing measuring CMC by manual to
find a proper concentration and then allocating several
sample with concentration nearby CMC measured by manual to
measure CMC more accurately. Such operations described above
is instead more convenient and timesaving.
For most cases of measuring surface tension of surfactant,
all of three methods can be used, except measuring surface
tension of surfactant with long adsorption time.
Another phenomenon that we must pay attention is when
measuring surface tension of surfactant, measured value will
be reduced at about 0.2-0.5mN/m each step. This is caused by
Langmuir monolayers described above. So, when measuring
surface tension of surfactant using tensiometer based on
Wilhelmy plate method or Du Nouy ring method, repeating
measurement more than 5 time is not proper. We advise you to
measure surface tension by repeating about 3 time. Or, you
can stir sample and clean plate or ring, then measure
surface tension. Value of surface tension will return to
value you just measured.
2.3 Your budget?
As you known, you get what you pay for.
No. |
Range of
budget |
type |
Manufactory |
Note |
1 |
About
1,000-2,500 |
Model A3 |
KINO |
Balance
1mN/m |
CSC |
CSC |
torsion wire |
K6 |
Kruss |
torsion wire |
2 |
About
4,000-16,000 |
A101 |
KINO |
Balance
0.1mg |
A601 |
KINO |
Balance
0.1mg |
Sigma 702 |
Biolin |
torsion wire |
DCAT11 |
Dataphysics |
balance |
K11 |
Kruss |
balance |
DY-300 |
Kyowa |
torsion wire |
3 |
20,000-60,000 |
A801 |
KINO |
Balance
0.01mg |
Sigma 700 |
Biolin |
Balance
0.01mg |
K100 |
Kruss |
Balance
0.1mg (K100C) and 0.01mg (K100MK2) |
DCAT21 |
Dataphysics |
Balance
0.01mg |
3, Difference of surface tensiometer made
by different manufactory.
Note:
1, Test method of update speed of balance is acquiring data
from balance versus times about several seconds, and at same
time, we used stopwatch to record times; after then,
calculating speed of data updating by dividing number of
data by time. And we find out that data update speed of
Sartorius’s balance model WZA215 can only reach’s speed
about 8-10 data/s when we using code “print: 1B 50 0D 0A”.
If we used function of “Auto output on” at Sartorius’s
balance model WZA215, update speed is about 20data/s, but we
cannot control balance such as stop data outputting or power
off, balance will continue to outputting data without
control.
2, Max capability depends on max load of balance. So real
range of max value is higher than 1000 or 2000mN/m. But when
we used torsion wire sensor in tensiometer, max reload of
sensor is just max capability in this sensor.
3, Pre-wetting is very useful when measuring surface tension
of organosilicone surfactant or fluorine surfactant.
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