By:

Abubakar Yakubu (PhD)Wan Mahmud Mat Yunus

(PhD)

Outline

Introduction

Why Photo-Thermal Technique

Principle of P.T Technique.

Experimental (1), (2), (3)

Theory

Result and discussion

Bibliography

IntroductionWhat is Optical methods

Radiometry: the measurement of optical radiation or

electromagnetic radiation in the frequency range of 3 x

1011 – 3 x 1016 Hz.

Photometry: is the measurement of light. Light in this

case is defined as the electromagnetic radiation

detectable by the human eye. The range visible to the

human eye falls between 360 nm to 830 nm.

Parameters

Reflectance and Spectral reflectance

Transmittance and spectral transmittance

Abdorptance, spectral absorptance and absorption

coefficient

Thermal diffusivity

Why Photo-Thermal Method

Simple and reliable technique

Non-destructive, it is fast andsimple

Safe measurement

Sensitivity is very high

Inexpensive, very cost effective

Principle of P.T Technique

.

optical radiation usually starts from a source

Filtered to produce desired beam of light

Excitation reaches sample

Absorption, reflection, and transmission takes place

Signal is been amplified

Spectrum is displayed on the detector

Experimental 1

Measurement of thermal diffusivity of gold nano-fluids

Using Double beam thermal lens technique

All samples were prepared using γ-radiation method

Experimental Set-Up

Figure 1:Setup of Thermal Lens; C, Chopper; L1, L2, Lenses; S,

Sample; F, Filter; D, Detector (Shariari et al, 2013)

Theory

Signal using a diffraction approximation forGaussian beams is given as (Shariari et al, 2013);𝐼 𝑧, 𝑡= 𝐼0(1

− 𝜃𝑡𝑎𝑛−1(2𝑚𝑣

1 + 2𝑚)2 + 𝑉2𝑡𝑐2𝑡+ 1 + 2𝑚 + 𝑉2

)2 (1)

Where 𝑉 =𝑍1

𝑍2, 𝑚 = (

𝑤𝑝

𝑤𝑒)2, 𝑡𝑐 =

𝑤𝑒2

4𝐷(2)

𝜃 =𝑝𝑒𝛼𝑙

𝑘λ𝑝.𝑑𝑠

𝑑𝑇(3)

ResultFigure 2: UV-Vis Absorption spectra of fluids

Figure 3: Time evolution of the Thermal Lens

Result

TEM images and particles size histograms of Au particles

Thermal diffusivity of Au nano-fluid versus the particles size

Figure 4Figure 5

Discussion 1 Figure 2 shows an absorption peak at 525 nm

Decrease in size of gold particles shifts absorptionpeaks to higher wavelengths

TEM image in figure 4 shows a particles sizedistribution of 20.5 nm

The thermal lens signal in figure 3, shows agreementbetween calculated and experimental data.

Thermal diffusivity is calculated to be 2.51 x 10-3cm2/s

Thermal diffusivity increases with increase in particlesize

Experimental 2

Measurement of thermal diffusivity of Polyaniline

Using Photoflash technique

Materials used in the study were supplied by Zipperling Kessler & Co.

Experimental set-up

Figure 6: Schematic diagram of Photoflash technique

Theory For an Opaque material, the temperature at the rear is

expressed as (Josephine et al, 2002);

𝑇 𝐿, 𝑡 =𝑄

𝜌𝐶𝑝𝐿1 + 2

𝑛=1

∞

−1 𝑛𝑒𝑥𝑝 −𝑛2𝜋2𝑎𝑡

𝐿2(3)

Where Q is the energy of the light source, L is the sample thickness, t is the transient response time and Cp,

p and n are the specific heat capacity, density and integer (+).

THEORY The maximum temperature rise at the rear surface of

sample is expressed as;

𝑉 = 1 + 2

𝑛=1

∞

(−1)𝑛𝑒𝑥𝑝 −𝑛2𝜋2𝑎𝑡

𝐿2(4)

• The maximum temperature of the rear surface isexpressed as;

𝑇(𝐿, 𝑡)𝑚𝑎𝑥=𝑄

𝜌𝐶𝑝𝐿(5)

• Parker et al, 1961 derived an analytical

solution that can be used to calculate

thermal diffusivity if conditions are ideal.

• Thermal diffusivity of material can be

calculated from the Parker solution, which is

given as;

∝=𝟎. 𝟏𝟑𝟖𝟖𝑳𝟐

𝒕𝟏𝟐

(𝟔)

Where t1/2 is the time when temp at the rear

surfaces reaches one half its final temperature

Result Heat lost correction was calculated using Clark andTaylor rise curve (Magic and Taylor, 1992). Thecorrection factor, K was calculated from the ratio oft3/4/t1/4. the correction factor is thus calculated from;

𝐊𝐑 = −𝟎. 𝟑𝟒𝟔𝟏𝟒𝟔𝟕 + 𝟎. 𝟑𝟔𝟏𝟓𝟕𝟖𝐭𝟎.𝟕𝟓𝐭𝟎.𝟐𝟓

− 𝟎. 𝟎𝟔𝟓𝟐𝟎𝟓𝟒𝟑𝐭𝟎.𝟕𝟓𝐭𝟎.𝟕𝟓

𝟕

The corrected value of thermal diffusivity at half time isthus,

∝𝑐𝑜𝑟=∝0.5 𝐾𝑅0.13885

(8)

Thermal diff vs Pressure

Figure 7: Graph of Thermal diff vs Pressure

X Ray Diffraction

Figure 8: Emerald Base Figure 9: Emerald salt

Discussion 2 The measured thermal diffusivity of the emerald base

and salt were in the ranges of 1.52 – 1.79 cm/s and 1.37 -1.56 cm/s respectively.

Thermal diffusivity value for the emerald base and saltincreased in value as particle size of sample decreases.

Thermal diffusivity value of the emerald base washigher than the thermal diffusivity of the emerald salt.

The XRD profile shown in figure 8 and 9 show that thedegree of crystallinity of the emerald base is higherthan that of the emerald salt.

Experimental 3

Measurement of thermal diffusivity of Polypyrrole conducting polymer composite films

Using Photoacoustic technique

Four series of Ppy-PEG films used were prepared by Electrochemical polymerisation method

Experimental set-up

Figure 10: Experiment setup for OPC detection technique (Lim

et al, 2009)

TheoryPhotoacoustic technique was used to

measure thermal diffusivity of the

prepared conducting composite films.

Photoacoustic is the production of

acoustic waves by the absorption of

light.

In this experiment a heat transmission

configuration known as openphotoacoustic cell (OPC) was used.

Theory The photoacoustic signal for optical opaque samples at

low modulation frequency is given as (Lim, et al 2009);

𝑆 =𝐴

𝑓exp −𝑏 𝑓 9

Where, A is a constant and b is related to the thermaldiffusivity of sample with the expression;

𝑏 = 𝐼𝑠 𝜋𝛼 10

Fitting the experimental data to equation (9), thethermal diffusivity of the sample can be calculated.

ResultFigure 11: Signal fitting for PPy-

PEG Composite film

Figure 12: Thermal diffusivity vs

PEG concentration

Figure 13: Thermal diffusivity vs pyrrole

Figure 14: Thermal diffusivity vs p-toluene sulfonate concentration

Discussion 3 Thermal diffusivity of PPy-PEG composite films

prepared by electropolymerization was

investigated using open photoacoustic

technique.

The PPy-PEG composite films prepared at 0.20

M pyrrole monomer, 0.10 M p-toluene sulfonate

dopant and 1×10-3 M PEG at 1.20 volt gave thehighest thermal diffusivity of 7.88×10-7m2s-1.

Conclusion Three different photothermal techniques were used to

determine the thermal diffusivity of MUT.

The three techniques used are;

Photothermal lens technique

Photoflash technique

Photoacoustic technique

All techniques were successfully used to calculate the thermal diffusivity for materials under study. All three techniques can be classified under photometry or radiometry methods.

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