ISSN (Print): 2328-3777, ISSN (Online): 2328-3785, ISSN (CD-ROM): 2328-3793

American International Journal of Research in Formal, Applied & Natural Sciences

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The Optical Constants of Poly Methyl Methacrylate PMMA Polymer

Doped by Alizarin Red Dye Fadhil A. Tuma

Department of Physics,

College of Education for Pure Sciences,

University of Basrah, Basrah, Iraq

I. Introduction In recent years, polymeric materials has gained widespread attention by the scientific and technological

researchers, because of their important industrial applications. Such materials play today a very great role in

numerous fields of everyday life due to their unique advantages over conventional materials (e.g. wood, clay

and metals) like lightness, resistance to corrosion, ease of processing and low cost production. Furthermore, the

physical properties of polymers may be affected by doping using various materials as an additives. Such

additives are used in polymers for a variety of reasons, for example: improved processing, density control,

optical effects, thermal conductivity, control of the thermal expansion, electrical properties that enable charge

dissipation or electro-magnetic interference shielding, magnetic properties, flame resistance and improved

mechanical properties, such as hardness, elasticity and tear resistance [1-4]. Currently, the doped polymers have

been the subject of interest for both theoretical and experimental studies, because of the physical and chemical

properties needed for specific application may be obtained by adding or doping with some dopant [5]. Detailed

studies of doped polymer with different dopant concentrations allow the possibility of choice of the desired

properties [6]. General poly (methacrylates) are polymers of the esters of methacrylic acid. The most commonly

used among them is poly (methyl methacrylate) PMMA. Poly (methyl methacrylate) PMMA is one of the

earliest and best known polymers, with chemical formula (C5H8O2)n [7]. It is naturally transparent and colorless

polymer with density (1.15-1.19 g/cm3), and available on the market in both pellet (granules) and sheet form

under the names Plexiglas, Acrylite, Perspex, Plazcryl, Acryplast, Altuglas, Lucite etc. It is commonly called

acrylic glass or simply acrylic [8]. Table.1 shows some of optical characteristics of PMMA. Table.1 optical characteristics of PMMA

Optical property Value

Haze 1-96%

Transmission, Visible 80-93%

Refractive Index 1.49-1.489

PMMA is produced by free-radical polymerization of methyl methacrylate in mass (when it is in sheet form) or

suspension polymerization according to the following chart [9] Fig.(1).

Fig.(1) Preparation of the polymer PMMA

Abstract: In this work, the optical constants: refractive index (n), extinction coefficient (k), real and

imaginary parts of dielectric constants (εr ,εi) and the optical energy gap (Eg) of poly methyl methacrylate

PMMA doped by Alizarin red AR dye with thickness in the range ((40-60)µm have been investigated in the

wavelength range (190-900)nm. The AR dye was added by different concentrations (1,2 and 3) wt.%. The

study of the optical properties of the doped films have done in order to identify the possible change that

happen to the PMMA films due to doping. The results show that the optical constants change with

increasing dye doping concentration, and it has been found that optical energy gap (Eg) decreases with the

increasing of dye concentration.

Keywords: PMMA polymer, Alizarin red AR dye, Optical constants, Optical energy gap.

Fadhil A. Tuma, American International Journal of Research in Formal, Applied & Natural Sciences, 15(1), June-August, 2016, pp. 13-18

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Poly (methyl methacrylate) PMMA have been widely used due to its remarkable properties, such as, excellent

mechanical properties where it is one of the hardest thermoplastic and is also highly scratch resistant, very

suitable for electrical engineering purposes and it is dielectric properties is very good, thermal capability where

it is resistance to temperature changes is very good, exhibits unique optical properties, simple synthesis and low

cost, high transparency in the visible region, possible to use in nonlinear optics [10-14].

As a result of the above characteristics, PMMA has been extensively used in various industrial fields, like,

optical devices such as optical lenses and optical fiber [15], photonic of nanotechnology [16], as an optical

diffuser in a liquid crystal display backlighting unit (BLU) [17], humidity sensing after surface modification of

PMMA by argon-oxygen plasma processing [18], as a gas sensors [19], in memory materials [20].

Many studies have been carried out using different materials as an additive in PMMA such as methylene blue,

methyl orange and methyl red [21-23] as a pigments (dyes), and many of other studies which using metal

chloride such as MgCl2 and CrCl2 [5,6], or Kaolinte [12], and Erbium and Erbium/Ytterbium [13]. All the

above studies reveal that the optical constants change with increasing dopant concentrations.

In this study an attempt was introduced to obtain the effect of Alizarin red AR dye as additive on the optical

constants of PMMA.

Alizarin is an organic compound is known since ancient times an important red pigment. Anthraquinone, a

compound derived from the roots of the madder plant. It is the first natural pigment produced industrially in

1869 [24]. Alizarin red (AR) is a solid appearing reddish-orange as crystals and brownish-yellow as powder,

with chemical formula (C14H8O4), and used chiefly in the synthesis of other dyes [25]. Fig.(2) illustrates in (a)

Sample of AR and (b) Skeletal formula of AR.

(a)

(b)

Fig.(2) (a) Sample of AR. (b) Skeletal formula of AR

It must be noted that alizarin name is derived from the Arabic word al-usara [26]. Table. 2 shows some

properties of AR [25].

Table.2 The main characteristics of AR dye Quantity Value

Molecular Weight 240.21 g/mol.

Exact Mass 239.93 g/mol.

Density 1.540 g/cm3

Purity 98.97

II. Materials and Methods

Materials:

The materials used in this work are Poly (methyl methacrylate) PMMA, Alizarin red dye AR and

Tetrahydrofuran THF, which is an organic compound with the chemical formula C4H8O, and is a versatile

solvent [27].Table. 3 shows some properties of the solvent THF.

Table. 3 Some properties of the solvent THF Quantity Value

Molar Mass 72.11 g/mol.

Density 0.89 g/cm3 at 20oC

Appearance Colorless Liquid

Purity 99.96 %

Films Preparation: Poly (methyl methacrylate) PMMA films doped with AR dye were prepared using solution casting technique.

Poly (methyl methacrylate) solution was prepared by dissolving PMMA granules in glass beaker (30ml) by

Tetrahydrofuran THF solvent using magnetic stirrer in mixing process for more than an hour until the polymer

granules became completely soluble, and AR dye was dissolved easily in another glass beaker by water.

The chosen weight percentages of AR dye relative to pure PMMA (1, 2 and 3) wt.% were added and mixed for

(30min) to get homogeneous solution. The mixture was poured into clean flat glass dishes placed on a platform

which can be leveled with the aid of spirit level fixed on the platform, and then kept inside dry-oven under

temperature (40oC ) for at least (24hr) to ensure removal of solvent traces, then left to cool slowly to room

temperature (25oC ). Several similar films have been prepared in order to ensure dried samples without bubbles

and thermal damage. The thickness of the prepared films were measured with the help of digital micrometer and

was found to be in the range (40-60)µm, these films were clear, without any remarkable defects and showing

light brownish color.

Fadhil A. Tuma, American International Journal of Research in Formal, Applied & Natural Sciences, 15(1), June-August, 2016, pp. 13-18

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Optical Measurements:

The absorbance and transmittance spectra were recorded utilizing double beam UV/VIS-7200 (England)

spectrophotometer in wavelength range (190-900) nm, all the measurements were carried out at room

temperature.

The optical constants are very important because they characterize the optical behavior of the materials. The

spectroscopic behavior of materials is utilized to determine their optical constants refractive index (n), extinction

coefficient (k), real and imaginary parts of dielectric constants (εr,εi). Such constants could be determine by

using the following procedure which include measurements of absorbance (A), reflectance (R) and transmittance

(T). The relationship between absorbed light intensity (I) by material and the intensity of incident light (Io) is given

by [28]

(1)

Where (t) is the thickness of the matter and (α) is the absorption coefficient.

(2)

Where the amount of log( I/Io) represents the absorbance (A).

The absorption coefficient (α) is defined as the ability of material to absorb light of the given wavelength can

be calculated by [29]

(3)

The relation between the optical energy gap (Eg), absorption coefficient (α) and the photon energy (h𝜐) can be

written as [28,29]

(4)

Where (B) is a constant related to the properties of the valance band and conduction band, the exponent (r) is an

empirical index which determines the type of optical transition and can be assumed to have values of (1/2, 3/2, 2

and 3) depending on the nature of the electronic transition responsible for the absorption. r = 1/2 and 3/2 for

direct allowed and forbidden transition respectively, r = 2 and 3 for indirect allowed and forbidden transition

respectively [28,30].

The refractive index (n) of a material is the ratio of the velocity of light in vacuum to that of the specimen, and

can be measured by using the following equation [1,29]

(5)

(6)

The extinction coefficient (k) can be defined as the amount of energy losing as a result of interaction between

the light and the charge of medium, and can be calculated by the following relation [31]

(7)

Where (λ) is the wavelength. The extinction coefficient (k) is directly proportional to the absorption coefficient

as seen from Eq.(7).

The complex dielectric constant (ε*= εr + i εi) characterizes the optical properties of the solid material, where (εr)

real part and (εi) imaginary part of the dielectric constant, and can be calculated by the following relations [31]

(8)

(9)

The real (εr) and imaginary (εi) parts of the dielectric constant are related to (n) and (k) values as seen from Eq.

(8) and Eq. (9). The calculation of these two parts supply information about the loss factor.

III. Results and Discussion

Optical characterization: The optical measurements of absorbance for doped PMMA films by AR dye in different concentrations

deposited on glass substrate have been studied through recording the absorption spectrum in the range (190-

900)nm as shown in Fig.(3). It can be observed that all the doped PMMA films showed two absorption bands at

the same position nearly, the first one in the UV region, and the other in the visible region, which are related to

energy absorption [32].

Fadhil A. Tuma, American International Journal of Research in Formal, Applied & Natural Sciences, 15(1), June-August, 2016, pp. 13-18

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0

0.1

0.2

0.3

0.4

0.5

0.6

0 200 400 600 800 1000

PMMA+3% AR

PMMA+1% AR

PMMA+2% AR

Ab

sorb

ance

(nm) Fig.(3) Absorption spectrum of PMMA doping with AR at different concentrations

The absorption increase with increasing concentration of AR dye. The best absorption was for the doped PMMA

film by 3% weight percentage of dye, which is attributed to the localized state of doping material in the energy

gap. The localized state causes decrease in energy gap, then increasing in absorption value [33].

Refractive index and extinction coefficient:

Fig.(4) shows the variation of refractive index (n) for doped PMMA films with different concentrations of AR

dye with the photon energy, the values of (n) are increased with increasing each of the photon energy and dye

concentration, this due to increase the density of doped PMMA films [22].

0

0.5

1

1.5

2

2.5

3

0 1 2 3 4 5

PMMA+3%AR

PMMA+2%AR

PMMA+1%AR

(eV)

Fig.(4) Variation in refractive index (n) as a function of photon energy of doped PMMA with AR dye

Fig.(5) shows the variation of the extinction coefficient (k) with the photon energy. It is noticed that (k) values

has reduced, this behavior has systematic with photon energy, where decrease with increasing photon

energy[21].

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0 1 2 3 4 5

PMMA+3%AR

PMMA+2%AR

PMMA+1%AR

(eV)

Fig.(5) Variation in extinction coefficient (k) as a function of photon energy of doped PMMA with AR dye

Determination of the dielectric constant:

The variation of the real (εr) and imaginary (εi) parts of the dielectric constant for doped PMMA films by AR

dye with photon energy are shown in Fig.(6) and Fig.(7) respectively. They almost indicate the same pattern

curves but the values of real part are higher than those of the imaginary part. On the other hand the increase of

the real and imaginary parts of the dielectric constant with increasing the weight percentages of AR dye

attributed to increase the density of doped PMMA films and number of carries charges [22].

Fadhil A. Tuma, American International Journal of Research in Formal, Applied & Natural Sciences, 15(1), June-August, 2016, pp. 13-18

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0

1

2

3

4

5

6

7

8

9

0 1 2 3 4 5

PMMA+3%ARPMMA+2%ARPMMA+1%AR

(eV)

Fig.(6) Variation of real part (εr) of dielectric constant for doped PMMA by AR dye with photon energy

0

0.001

0.002

0.003

0.004

0.005

0.006

0 1 2 3 4 5

PMMA+3%ARPMMA+2%ARPMMA+1%AR

(eV)

Fig.(7) Variation of imaginary part (εi) of dielectric constant for doped PMMA by AR dye with photon energy

It is conclude that the variation of(εr) mainly depends on (n2) because of small values of (k2), while (εi) mainly

depends on (k) values which are related to the variation of absorption coefficients.

The real part of the dielectric constant is associated with the term that shows how much it will slow down the

speed of light in the material and the imaginary part shows how a dielectric absorbs energy from an electric field

due to dipole motion [34].

Optical energy gap:

The absorption coefficient helps to know the nature of electronic transition, when the values of the above

coefficient is high (α > 104 cm-1) at high energies, it is expected that direct transition of electron occur, the

energy and moment are preserved by the electrons and photons. On the other hand when the values of the

absorption coefficient is low (α < 104 cm-1) at low energies, it is expected that indirect transition of electron

occur, and the momentum of electron and photon are preserved with the assistance of a phonon [35]. The

findings indicated that the values of the absorption coefficient is less than (104 cm-1) , that is clear how the

electronic transition is indirect.

The optical energy gap (Eg) for the doped PMMA films with AR dye can be estimated by plotting (αh𝜐)1/2

versus photon energy (h𝜐), then extrapolating the straight line part of the curve to a point ((αh𝜐)1/2 = 0) on the

photon energy axis. Fig.(8) shows the variation of the optical energy gap for doped PMMA films.

0

10

20

30

40

50

0 1 2 3 4 5

PMMA+3%ARPMMA+2%ARPMMA+1%AR

(eV)

( ℎ

)1/2

(c

m-1

eV)1

/2

Fig.(8) The optical energy gap (Eg) for the doped PMMA films with AR dye

Fadhil A. Tuma, American International Journal of Research in Formal, Applied & Natural Sciences, 15(1), June-August, 2016, pp. 13-18

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The calculation of (Eg) of doped PMMA films showed which decreased with increasing of AR concentration,

this is ascribed to increase in absorption coefficient as a result of introducing dopant atoms and hence (Eg) will

be decreasing [21].The values of (Eg) for doped PMMA with AR dye are listed in Table.4.

Table.4 The values of (Eg) for doped PMMA Sample Eg (eV)

PMMA + 1% AR 1.6

PMMA + 2% AR 1.4

PMMA + 3% AR 0.8

IV. Conclusions

1. The absorbance of prepared films of doped PMMA with AR dye is increased with increasing the AR

concentration.

2. The optical constants: refractive index, extinction coefficient, real and imaginary parts of dielectric constants

are changed with increasing weight percentages of AR dye.

3. The doped PMMA with AR dye have indirect energy band gap (optical energy gap) which decrease with

increasing the AR concentration.

References

[1] J. F. Gerard, "Fillers and Filled Polymers", Wiley-VCH, Weinheim, 2001.

[2] Z. M. Huang, Y. Z. Zhang, M. Kotaki and S. Ramarkrishna, Composites Sci. & Tech., 63(15), 2223-2253, 2003.

[3] S. Glushanin, V. Y. Topolov and A. V. Krivoruchko, Materials Chem. & Phys., 97(2-3), 357-364, 2006. [4] P. Hine, V. Broome and I. Ward, Polymer, 46(24), 10936-10944, 2005.

[5] E. Abdelrazek, Physica B Condensed Matter, 351(1-2), 83-89, 2006.

[6] K. Al-Ammar, A. Hashim and M. Husaien, Chemical & Materials Eng., 1(3), 85-87, 2013. [7] Stevens and P. Malcolm, "Polymer Chemistry: An Introduction", Oxford University Press, USA, 1998.

[8] Harper, A. Charles and M. Petrie Edward, "Plastic Materials and Processes", John Wiley and Sons, 2003.

[9] Harper and A. Charles, "Handbook of Plastic Processes", John Wiley and Sons, 2005. [10] Van Krevelen, "Properties of Polymers", Elsevier, 2003.

[11] T. Tsai, C. Lin, G. Guo and T.Chu, , Materials Chem. & Phys., 108, 382, 2008.

[12] Y. Li, B. Zhang and X. Pan, Composites Sci. & Tech., 68,1954, 2008.

[13] V. Prajzler, V. Jerabek, O. Lyutako, I. Huttel, J. Spirkova, V. Machovic, J. Oswald, D. Chvostostova and J. Zavadil, Act Poly

Technica, 48(5), 14, 2008.

[14] J. E. Klemberg-Sapieha, L. Martinu, N. L. Yamasaki and C.W. Lantman, Thin Solid Films, 476,101, 2005. [15] J. M. Yu, X. M. Tao, H. Y. Tam and M. S. Demokan, Applied Surface Science, 252, 1283, 2005.

[16] M. Nakajima, T. Yoshikawa, K. Sogo and Y. Hirai, Micro Electron Eng., 83(4-9).876, 2006.

[17] G. Kim, European Polymer J., 41,1729, 2006. [18] R. V. Dabhade, D. S. Bodas and S. S. Gangal, Sensors Actuators B: Chemical, 98(1), 37, 2004.

[19] S. Shang, L. Li, X. Yang and Y. Wei, Composites Sci. & Tech., 69,1156, 2009.

[20] K. Beev, K. Temelkov, N. Vuchkov, T. Petrova, V. Dragostinova, R. Stoycheva-Topalova, S. Sainov and N. Sabotinov, J. Optoelectronics & Advanced Materials, 7, 3, 1315, 2005.

[21] Tariq J. Alwan, Malaysian Polymer J., 5(2), 204-213, 2010.

[22] A. H. Ahmad, A. M. Awatif and N. Zeid Abdul-Majied, Eng. &Tech. J., 25(4), 558-568, 2007. [23] Z. T. Khodair, M. H. Saeed and M. H. Addul-Allah, Iraqi J. Phys.,12(24), 47-51, 2014.

[24] R. Shanker, D. Mahanta and S. C. Tiwari, Dyes and Pigments, 76(1), 207–212,2008.

[25] H. Bien, J. Stawitz and K. Wunderlich, "Anthraquinone Dyes and Intermediates", in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.

[26] Alizarin, Dictionary.com, Dictionary.com Unabridged (v 1.1), Random House,

Inc. http://dictionary.reference.com/browse/alizarin

[27] Herbert Müller, "Tetrahydrofuran" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2002.

[28] J. Tauc, "Amorphous and Liquid Semiconductors", Plenum Press, New York, 1979. [29] N. Mott and E. Davis, "Electronic Process in Non-Crystalline Materials", 2nd Edition, University Press, Oxford, 1979.

[30] S. M. Sze,"Semiconductor Devices Physics and Technology", 3rd Edition, John Wiley and Sons, Canada, 2007.

[31] J. H. Nahida and R. E. Marwa, Eng. &Tech. J., 29(4), 2011. [32] K. M. Abd El-Kader and A. S. Orbi, Polymer Testing, 21, 591-595, 2002.

[33] J. H. Almashhadani, Ph. D. Thesis, University of Baghdad, College of Science, 2004.

[34] K. Rtintu, K. Saurav, K. Sulakshnab, V. Nampoori, J. Non-Oxide Glasses, 2(4), 167-174, 2010. [35] B. L. Deng, Y. S. Hu, Y. S. Chiu and L. W. Chen, Polym. Degrade. Stab, 57, 269,2003.