BAHADIR C. BİRTÜRK

ADVISOR: AYHAN AYKARA

IŞILAY AYAN

Surface Tensiometer for Liquids

Contents:

● Surface Tension

● Methods of Measurement

● Device

∙ Parts of the Device

∙ Working Principle

● Findings

● Results and Discussion

● Suggestions

● Problem: Commonly used methods of surface tension

measurement, and the devices that required have high

costs.

● Goal: To design a new device for surface tension

measurement that is low cost.

Surface tension can be thought as the surface

behaving similarly to an elastic membrane. To

give a more scientific definition: the tension

caused by internal attractive forces on the

exposed fluid surfaces is called surface tension.

The most important factor that keeps liquid

molecules together is intermolecular attractive

forces between similar/identical particles. There

is also intermolecular attractive forces between

dissimilar particles.

Surface Tension

Surface Tension Formation in Liquids

The tension caused by these internal forces is called surface tension. This tension causes the

liquid surface to act like it has a membrane stretched on it. An object has to overcome surface

tension to break through the surface, whether it is going inside or outside. Surface tension is

equal at every point of surface.

Temperature (°C)

H2O CCl4 C6H6 C2H5OH CH3COOH

0 7,56 x10-4 2,90 x10-4 3,16 x10-4 2,40 x10-4 2,95 x10-4

25 7,19 x10-4 2,61 x10-4 2,82 x10-4 2,18 x10-4 2,71 x10-4

50 6,79 x10-4 2,31 x10-4 2,50 x10-4 1,98 x10-4 2,46 x10-4

75 6,35 x10-4 2,02 x10-4 2,19 x10-4 - 2,20 x10-4

Surface Tension Values of Various Liquids at Different

Temperatures (N/m)

Du Noüy Ring Method

In du Noüy Ring method(Figure 4), there are two ways

to measure the force required to separate the ring from the

surface or the liquid interface:

1. Hanging the ring from a scale.

2. Using du Noüy tensiometer.

Force required for separation, surface tenison or interfacial

tension is found with the following equation:

Using a platinum ring cleaned by a strong acid or flame is

necessary for ensuring a contact angle of zero. Also the surface

of the liquid is required to be calm, and the ring should be

parallel to the surface.

β: correction factor

F: Force required for

pulling the ring

r: Average radius of the

ring

Methods of Measuring Surface Tension

Parts of the Surface Tension

Measuring Device

Ultrasonic Ranging Sensor (HC-SR04)

HC-SR04 is a sensor that uses a 40 kHz sound wave,

which is not audible to human ear, and its echo to

determine the distance between itself and the closest

obstacle. However, it can only output the time past

between the initial sound wave and its echo, not the

actual range. ∆t·v/2 When the time interval is

multiplied by the speed of sound(in the air) and divided

by two(accounting for both the initial wave and the

echo) it gives us the distance between the sensor and

the obstacle.

.

Arduino UNO R3

Arduino is an open source, and easy to use hardware

and software development platform. Arduino boards

are devices that can read input from various sensors and

perform appropriate actions. How an Arduino board

reacts to different inputs can be determined by sending

various instructions to the board.

To achieve this, Arduino programming language and

Arduino IDE is used.

Stepper Motor (28BYJ-48) and Driver Board (ULN2003)

Stepper motors are brushless DC motors that have their one full rotation divided into equal

“steps”. Not only the motors only move in to “step” positions, as long as they are powered

on they also resist any external force that tries to move them out of their specified position.

28BYJ has 32 steps in full mode and 64 steps in half step mode. It also includes internal

gears with a factor of 1/64 which makes the motor effectively have 64 × 64 = 2048 steps.

Stepper motors are used in various number of applications because of mentioned features

and its low cost. ULN2003 is a driver board that makes controlling the stepper motor easier.

LCD (TC1602D-02WB0)

LCD we have used has 8 pins for data, 2 pins for power, 2 pins for

backlight, one pin for contrast, one pin for "Register Select", one

pin for Read/Write and finally one pin for startup.

Main reason that made us decide to use a display was to make the

device as independent and portable as possible.

Buttons and Buzzer

Buttons are used for calibrating the device and operating it during

the manual pre-measuring phase. Two buttons are used for

adjusting the position of the motor, and one is

used for starting the automated measuring phase.

A buzzer is used for notifying the user after the automated

measuring phase has ended.

Our device's method has been inspired by the du

Noüy Ring method. A circular plate of sufficient

size is slowly lowered parallel to the substance-

to-be-measured. After the plate has been caught

by the surface, automatic measurement phase

begins.

Through the automatic measurement phase,

stepper motor slowly turns and

starts wrapping the elastic string around the

pulley, causing it to stretch. The stretched length

is directly proportional to the force stored.

How Our Surface Tension Measuring Device Works

When the force applied by the elastic string

overcomes the force applied by the surface

tension, the plate breaks free and leaps

vertically. This sudden movement is

detected by the ultrasonic ranging sensor

and system stops.

Number of the steps taken since the

automatic phase has begun is then

multiplied with a predetermined factor.

Measuring range of device is 0-100 dyn/cm which is why were unable to measure the surface tension of mercury.

Comparisons between theoretical surface tension values and ones measured at 20°C by the device we’ve developed are

given in Table 2.

Table 2: Comparison Table

No. Sample Theoretical Values (dyn/cm) Measured Valuesi (dyn/cm)

1 Acetik Acid 27,60 26,49 ± 0,15456

2 Acetone 23,70 23,90 ± 0,13272

3 Ethanol 22,27 22,26 ± 0,12471

4 Glyserol 63,00 62,92 ± 0,3528

5 Isopropanol 21,70 21,61 ± 0,12152

6 Methanol 22,60 21,91 ± 0,12656

7 n-Hexane 18,40 18,39 ± 0,10304

8 Distilled Water 72,80 72,80 ± 0,40768

9 Diethyl Ether 17,00 17,02 ± 0,0952

10 Mercury 485 Unable to measure

Findings

After comparing measurements that have been taken using the device with theoretical values,

we concluded the device has a fairly low margin of error. Observed reasons of this is

• initial reference value being slightly off due to temperature

• slight lagging caused by the ultrasonic sensor

Advantages and disadvantages are given in Table 3.

Advantages Disadvantages

Low cost Faulty values in noisy environments

High accuracy measurements in low time

Portability

Convenient usage

Open to development

Compatible with computers

0-100 dyn/cm range

Conclusion

There are quite a few ways of improving the device.

• Using a more efficient source of power.

• It is possible to make hardware and software changes which will provide more reliable mea-

surements.

• Using more resistant material for the plate, in case of deailng with caustic substances.

• Automating the entire process.

Suggestions

● Bolat, M., Y. Aydoğdu, and İ. Evgi. Ortaöğretim 9. Sınıf Fizik Ders Kitabı . Ankara: Mega Yayıncılık,

2013.

● Dean, John A, and others. “Lange’s Handbook of Chemistry, 1999.” McGraw-Hill, Inc. New York,

n.d.

● DÜZYOL, Selma. “CEVHER Hazirlama Işlemlerinde Yüzey Gerilimi Ve Temas Açisi ölçümünün

Genel Bir Değerlendirmesi.” Soma MYO Teknik Bilimler Dergisi , 2016, 21.

● Freaks, Elec. “HC-Sr04 User Guide,” 2015. http://elecfreaks.com/estore/download/EF03085-HC-

SR04_Ultrasonic_Module_User_Guide.pdf.

● ———. “Ultrasonic Ranging Module Hc-Sr04,” 2011. http://www.electroschematics.com/wp-

content/uploads/2013/07/HCSR04-datasheet-version-1.pdf.

● Gönül, Dr. Nurşin. ÇOK Fazli Sistemler I Yüzey Kimyasi Ve Kolloidler . Ankara Üniversitesi

Basımevi: ANKARA ÜNİVERSİTESİ ECZACILIK FAKÜLTESİ YAYINLARI, 2000.

Bibliography

Bibliography● Kiatronics. “28BYJ-48 – 5V Stepper Motor,” 2012. http://www.sensors.co.nz/datasheet/28BYJ-

48%20Stepper%20Motor.pdf.

● ———. “4 Phase Uln2003 Stepper Motor Driver Pcb,” 2012.

http://www.sensors.co.nz/datasheet/942102570285.pdf.

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● ———. “Arduino - Introduction,” 2017. https://www.arduino.cc/en/Guide/Introduction.

● Noüy, P Lecomte du. “An Interfacial Tensiometer for Universal Use.” The Journal of General

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● Serway, R. A. Fen Ve Mühendislik Için Fizik . Ankara: Palme Yayıncılık, 1996.