Synthesis and assessment of novel self-doped poly (5-nitro-orthanilic acid) as a multifunctional scaling inhibitor on controlling the precipitation and crystal growth of CaCO3 and CaSO4 in solution

: Self-doped-and nitro-polyanilines have become a widely used strategy to optimize the electronic and vibratory spectra of polymeric building blocks in various applications. We report the synthesis of poly (5-nitro-orthanilic acid) by an aniline-initiated oxidative polymerization reaction. The polymer is characterized by spectroscopic techniques, elemental shapes, cyclic voltammetry, electrical conductivity, microscopic and thermal measurements. The hydrophilic and hydrophobic nature of the supports provided the formation of amphiphilicity as judged by SEM. Thermo-gravimetric measurements reveal thermal stability up to 500  C and glass temperature (Tg) observed at 240  C. Electrical conductivity decreases as the temperature rises at the different frequencies used, reflecting the semiconducting nature in the extrinsic range, which is characterized by high carriers and low mobility. The presence of these electron residues causes a decrease in efficiency and increases the thermal conductivity. Dielectric measurements have shown that permittivity decreases gradually at lower levels, mainly due to the transport of charging carriers, resulting in higher performance. The testing of the copolymer as a new scale blocker has resulted in moderate to fairly high performance. This effect is attributed to the change in polymer geometry using intramolecular H-bonding group -SO 3 H and a chain polymer in an aqueous medium.


Introduction
Scale formation is commonly encountered and poses problems in water boilers coolers and oil well water, which cause a negative impact on operating systems and equipment, reducing heat transfer as an insulating layer and downhole completion equipment 1 .Among common encountered scaling cations in aqueous systems are Ca 2+ cations, which deposit calcium carbonate and/or calcium sulfate.Sulfate scales are often attributed to the mixing of the incompatible sea-and formation waters, where the concentrations of calcium ions are high in both 2 .Carbonate scale, on the other hand, is generally attributed to the process of self-scaling, where the loss of carbon dioxide gas from the water to the hydrocarbon phase as pressure falls 3 .Main carbonates scale are Calcite CaCO3, Vaterite CaCO3, Aragonite CaCO3, Siderite FeCO3, and Dolomite CaMg(CO3)2.Functionalized organic polymers are green scale inhibitors and have shown excellent properties in delaying, reducing, and/or preventing scale deposition 4 .The effectiveness of these inhibitors depends on the chain length of the polymers and thus, the efficiency order in most cases was a low chain- higher chain lengths, where the polymeric repeating units were nearly 10-15 5 .
The preparation of the self-doped polyaniline 6 has become a widely used strategy and the results clearly indicated that introducing the -SO3H (electron-attracting) group on the polyaniline backbone makes them promising building blocks for different directions in the applications 7 .In the meantime, the introduction of -NO2 group substitution into polyaniline chains modifies the electronic and vibrational spectra of the resultant polymer 8 .Generally, aniline derivatives containing weak electron-withdrawing groups form a stable free radical during polymerization and the reaction occurs slowly due to some decrease in the electron density on the aniline' nitrogen atom 9 .However, anilines containing a strong electron-withdrawing substituent, such as -NO2, produced an unstable radical intermediate, and thus, polymerization does not occur, and to solve this obstacle, a trace amount of aniline as an initiator/promoter improved the reaction rate and yield 10 .The readily synthesized poly (nitroaniline-co-aniline) in various molar ratios have been used as an effective green step for the removal of toxic by-products obtained from various dyes and textile industries 11 .Nevertheless, investigations concerning introducing -NO2 substituent onto self-doped polyaniline and the expected variation of physicochemical properties in the resultant polymers remain unexplored.In this work, poly (4-nitroaniline-2-sulfonic acid) catalyzed by aniline (10 mole %) was prepared by persulfate oxidative polymerization procedure and the resultant polymer was characterized by various techniques such as FTIR-and UV-visible spectroscopies, elemental analysis, scanning-and transmission electron microscopy (SEM, TEM), thermal analysis (TGA, DTG, DSC), electrochemical behavior and electrical and dielectric properties.Noteworthy, derivatives based (4-nitroaniline-2-sulfonic acid) were used, among many others, as sensing elements of optical sensors to determine sulfate in water and soil extracts 12 .As a continuation of our recent interests 13 , the assessment of the prepared poly (4-nitroaniline-2-sulfonic acid), for the first time, as a new scale inhibitor of CaCO3 and CaSO4 using slandered NACE, electrochemical tests and microscopic examinations was the main objective.The measurements were performed on as-synthesized samples, without the further re-doping procedure usually used in the literature.

Results and discussions
First trials to obtain pure poly (5-nitro-orthanilic acid) 2 failed and even if the reactants were stirred for 48 h produced only yellow precipitate contains an unreacted and probably dimeric mixture.Polymerization of aniline-2-sulfonic acid (orthanilic acid) was chemically achieved only at high pressure 14 to give the targeted polyorthanilic acid.Typical oxidative polymerization of orthanilic acid is not possible due to the -I and steric hindrances effects of the -SO3H group 15 .
In substrate 1 used in this investigation the presence of strong electron withdrawal effect exerted by the substituents -SO3H and -NO2 group inhibits the first initiating oxidation step.Therefore, using a little amount of aniline to initiate the polymerization reaction was our alternative 16 .The targeted poly (5-nitro-orthanilic acid) 2 was chemically prepared, according to standard procedure described in IUPAC technical report 17 , using 10 moles % aniline and ammonium persulfate as an oxidizing agent from the commercial 5-nitro-orthanilic acid 1 in low pH 1.5 aqueous HCl media, Scheme 1. Percentage yield (52 %, ηinh = 0.10) was calculated by using the formula 18 : [% Polymer yield = (Weight of polymer / Weight of substrate 1) x 100].The reaction rate depends mainly on the reactivity of the reactant substrate as well as any hindrance to reaction propagation which greatly affects the yield.The -SO3H and -NO2 substituents are present at the ortho and para positions with respect to the -NH2 group, respectively, would electronically direct the propagation taking place solely at the C3 position.During the propagation step, the ortho -SO3H group would reduce the nucleophilicity of the -NH2 group and also exerts a steric hindrance, nevertheless, further head-to-tail oxidative polymerization can be expected by the unsubstituted co-monomer aniline and thereby to fair polymerization yield.The postulated reaction mechanism is shown in Scheme 2.
Scheme 1: Chemical synthesis of aniline-catalyzed poly (5-nitro-2-orthanilic acid) The morphology of the synthesized polymers 2 investigated by SEM, Figure 1a, revealed that the polymer has a regular flower-leaf-like microstructure.However, the TEM image, Figure 1b, exhibited particle micro aggregates and clearly indicated the presence of both unsubstituted aniline units (dark nanospheres) and the substituted polymeric units (light gray micro aggregates).For comparison purposes, an SEM image of the product obtained from uncatalyzed polymerization trials is shown in Figure 1c.The morphology and the particles sizes are attributed to the nature of the substituent and thus the mechanism of the monomer unit's interactions 19 .The presence of monomer hydrophilic -SO3H group and a hydrophobic -NO2 on one aromatic ring gives the structure amphiphilicity or self-assembly nature, which are surrounded by the aromatic ring forming micelles 20 and the aggregation of such small micelles produces submicron groups that are templates for such morphology found.are in good agreement with the chemical formula of a modified polyaniline backbone.The total amounts of carbon, hydrogen and nitrogen in the resulting polymer were 90.94 %, indicating the contamination of the polymer with chlorine and/or ammonia as speculated doped emeraldine salt forms 21 .This could be attributed to the presence of ammonium hydrogen sulfate that was not possible to fully wash out during the working up of the product.The ratio of C/N was 1.76 (Calc.1.75)  and agrees with the theoretically predicted values for their analogues 22 .Worthy to note, the elemental data also indicated that ammonium species were incorporated into the polymer product during the polymerization.
Scheme 2: Proposed formation mechanism of the polymer 2

Infrared Spectroscopy
The FTIR spectrum shows absorption at  3359-3425 cm -1 that corresponds to the NHvib bond, the peak in the region of  2925-3000 cm-1 is due to the vibrations of the C-Harom bonds.A band at 2707 cm -1 suggests the existence of ammonium salts 22 .Characteristic polymer structure peaks were found at  1500 and 1571 cm -1 corresponding to the vibrations of the benzenoid and quinoid moieties and their intensity ratio was 1.3, confirming the rapid equilibrium between the two forms 23,24 .The relative intensity of the quinoid / benzenoid bands reflects not only the degree of oxidation of the polymer chain 25 , but also confirms the formation of bipolaron in the initial oxidation stage.The absorption bands at 1321 cm -1 and  1254 cm -1 correspond to the C-N and C-N + stretching vibrations, respectively.The peak observed at  1221 cm -1 corresponds to N=O symmetric stretching vibration due to NO2 groups.The asymmetric stretching band of N=O group was not observed and could be buried under the C-N absorption.The presence of a peak at  1074-1131 cm -1 indicates the doped state of the polymer (-N + / N +• ).The absorption at  828 cm -1 corresponds to the bending vibrations of C-H in plane of the aromatic ring.The S-O stretching band appeared at  748 cm -l , and the peak at  620 cm -1 is for the C-S stretching vibrational 26 .

Ultraviolet-Visible Absorption Spectroscopy
The bandgap energy is calculated from the equation: E = hc / where E is band gab energy (eV), h = 6.625 x 10-34 JS, c = 3 x 108 m/s,  is the wavelength.The electronic spectra of the substituted polymer 2 show absorption bands at 255 nm, 380 nm and their band gab energies were 4.86 eV and 3.26 eV, respectively.The observed absorptions are assigned to bandgap and absorption data show bathochromic shifts.The increase in bandgap occurred because of increasing the torsion angle between C-N-C plane and the plane of the benzene ring, due to the electronic nature of the substituent and thus affecting the conjugation degree.Due to random substitution of the monomers of such polymerization, substituent causes entangling of polymer chains that disrupt the conjugation length that results in a hypsochromic shift of -* transition at 255 nm and polaron-* transition at 380 nm, respectively.

Cyclic voltammetry
The electrochemical study of the substituted copolymer 2 obtained was conducted by measuring cyclic voltammogram, Figure 2. Polyaniline itself is known to be a redox polymer; therefore, incorporation of substituent into its structure affects the oxidation and reduction potentials observed on the cyclic voltammetry that are related to a change in its redox form.The cyclic voltammetry maxima correspond to transitions between the oxidation forms.The dielectric measurements carried out using a high analyzer technique could probe molecular fluctuations and charge transport in broad frequency and temperature ranges.The dielectric spectrum is separated to molecular dynamics at the molecular scale, i.e., charge carriers' transport, which is reflected in conductivity mechanisms.The permittivity (ε*) is the measure of resistance that is developed upon generating an electric field in a particular substance.The permittivity (ε*) was determined at five-spot frequency points and depicted against temperatures in the range of 40C to 100°C for the substituted polymer 2, Figure 5.In general, two distinguished trends of the real part of complex permittivity  vs frequency could be assigned.The lower frequency range (0.1Hz-10 kHz) shows a gradual decrease of  through six orders of magnitudes, mainly due to the charge carriers' transport causing expected high conductivity.At a higher range of frequencies (10 kHz  20 MHz), a slight effect was observed for frequency on decreasing the permittivity..The low conductivity of the copolymer 2 could be explained by both the reduced conjugation length in distorted chains and the decrease in interchain charge transport induced by bulky SO3H groups, and the electrostatic interactions between the sulfonate functional groups and main-chain cationic nitrogen or amine's hydrogens.The study of dielectric constant as a function of temperature and frequencies is one of the most convenient methods of studying the molecular orientation behavior and associated relaxation mechanism of polymer structure 31 .In Figure 7b, the dielectric constant decreases with increasing frequencies.At higher frequencies, the value of the dielectric constant nearly steadily decreases.However, at low frequency, the dielectric constant decreases between (20C-40C) temperature range, then maintain stable between (40C-60C) range and then continue decreasing.This nature is not observed at higher frequencies.The low-temperature dielectric dispersion is attributed to the dielectric response of the side groups which are more mobile or the small displacement of the dipoles near the frozen-in position and known as the secondary dispersion region or ß-relaxation 32 .To examine the synthesized copolymer 2 as new scale inhibitors of CaSO4, free calcium ions concentration was determined according to the NACE test in the absence and the presence of different polymer concentrations (ppm), and the results are compiled in Table 1.The concentration of free Ca +2 ions slightly increased with increasing polymer concentration, indicating inhibition of the calcium sulfate precipitation process.In the literature, the inhibition of the CaSO4 scale by inhibitor-containing sulfonate groups is usually explained by the interaction of calcium cations present in solution with sulfonate groups through Ca….SO3 interaction and thereby blocks crystal growth 13a .In general, while M-O interaction is weak in a single sulfonate moiety, each oxygen atom has the potential to bridge more than one metal center, and typically, the oxygen atoms of an SO 3-moiety will bridge a maximum to two metal ions 33 .The limited CaSO4 inhibition efficiency by polymer 2 is attributed, most probably, due to a change in polymer geometry because of the expected intramolecular hydrogen bonding interaction of the ortho-sulfonic group and the polymer chain in an aqueous medium, Figure 8, and thus retards the speculated calcium-sulfonate interaction.The buildup of the calcium carbonate layer on the metal surface is illustrated in Figure 9.As shown, the Chronoamperometry curve of the polarized steel electrode in the absence of the polymer decreases sharply, indicating to the fast formation of CaCO3 crystals which occupied parts of the steel surface and consequently decreases the current density.On the other hand, the addition of an inhibitor to the brine solution delays the scaling process and increases the residual current on the steel surface.Increasing the concentration of the polymer increases residual current values for steel electrode after polarization from 44 μA for a blank solution to 140 μA in presence of 150 ppm of the polymer, Figure 10.
Usually, the current density is inversely proportional to the quantity of CaCO3 scales formed on the metal surface.Thus, the observed inhibition order indicated that the presence of copolymer 2 significantly inhibits carbonate scale formation.The impedance spectra of the polymer show a typical feature of depressed semicircles followed by a low-frequency tail.The size of distorted semicircles decreases in the presence of the polymer due to the behavior of the double layer that led to a decrease in the charge transfer resistance due to the reduction of the insulation layer of the scale 13a .The equivalent circuit, Figure 12, that was used to fit the experimental data of impedance plots for the scale formation processes in brine solution was illustrated in Figures 13 and 14.    15.The cubic structure of calcium carbonate crystals is observed in absence of antiscalants.A low degree of crystals modification was observed in presence of the polymer, which may be due to change in polymer geometry because of the expected intramolecular hydrogen bonding interaction of the ortho-sulfonic group and the polymer chain in an aqueous medium and thus retards the speculated calciumsulfonate interaction which facilitates the attachment of polymer molecules on the metal surface and hinders crystal attachment.Measurements.Infrared spectra (IR, KBr pellets; 3 mm thickness) were recorded on a Perkin-Elmer Infrared Spectrophotometer (FTIR 1650).All spectra were recorded within the wave number range of 4000-600 cm -1 at 25 C.
Absorption spectra were measured with a UV 500 UV-Vis spectrometer at room temperature (rt) in DMSO with a polymer concentration of 2 mg/10 mL.Elemental analysis of as-synthesized copolymer was performed at the Microanalytical Unit, Cairo University.The sulfur content was determined by ASTM-D1552 technique at Middle East Oil Refinery Company (Midor), Alexandria, Egypt.Inherent viscosities (ηinh) were measured at a concentration of 0.5 g / dL in H2SO4 at 30 C by using an Ubbelohde viscometer.Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses were carried out in the temperature range from 20 C to 400 C in a steam of nitrogen atmosphere by Shimadzu DTG 60H thermal analyzer.The experimental conditions were platinum crucible, nitrogen atmosphere with a 30 mL/min flow rate and a heating rate10 C/min.Differential scanning calorimetry (DSC-TGA) analyses were carried out using SDT-Q600-V20.5-Build-15at the microanalytical unit, Cairo University.Cyclic voltammetry was performed using an eDAQ system (www.eDAQ.com),consisting of an E190 potentiostat connected to an e-corder which inputted to eChem software (running on a PC using Microsoft Windows 10).The working electrode was a 3 mm diameter glassy carbon electrode; the reference electrode was Ag/AgCl; the auxiliary electrode was a 0.25 mm diameter Pt wire.Applied potentials ranged from -500 to +500 mV, and the scan rate was 100 mV s -1 The volume of the voltametric cell was approximately 15 ml.The dielectric measurements of the polymeric materials were carried out using a high-resolution Alpha analyzer (Novo Control, Hundsangen, Germany) in parallel plate geometry over a frequency range from 10 −1 Hz to 10 7 Hz at different range of temperatures.In this geometry, the sample cell consists of two gold-coated brass disk electrodes.The upper one is 10 mm and the lower one is 20 mm diameter.The pressed sample with 12 mm diameter was sandwiched between the two electrodes.
The applied voltage was kept constant at 0.2 V to avoid any nonlinear effects.The empty sample capacitor is used as a reference to eliminate the additional contributions of the cables and the measurement cell.The temperature of the sample is controlled by a Quattro Novo control cryo-system with temperature stability better than 0.2 K, as described in references 34 .
The polymer powder was pressed to form discs of diameter 10 mm and thickness 1 mm.silver electrodes were deposited on both sides of the sample surface by thermal evaporation and two copper wires were fixed on the sample using conducting silver paint.The morphologies of polymers morphologies were observed by Scanning Electron Microscope (SEM) (JEOL-JSMIT 200) and Transmission Electron Microscopy (TEM) (JEOL-JTM-1400 plus), at the E-Microscope Unit, Faculty of Science, Alexandria University.The samples were sonicated in de-ionized water for 5 min and deposited onto carbon-coated copper mesh and allowed to air-dry before examination.
Synthesis of poly (5-nitro-orthanilic acid) 2. 5-Nitro-orthanilic acid 1 (5 g, 22.93 mmol) and aniline (0.5 g, 5.37 mmol; 10 mol % of 1) were dissolved in aqueous 1M HCl (100 ml) and a solution of ammonium persulphate (6.53 g, 28.65 mmol, 1.25x) dissolved in water (50 ml) was subsequently added over a period of 30 min.The mixture was mechanically stirred for 24 h at rt and the color change pattern during polymerization from yellow to light, then dark green to brownish black was observed from t = 10 min to 24 h.Polymerization was stopped by addition of methanol (50 ml).The resulting precipitate was subsequently washed with water, aqueous 1M HCl, water and acetone to remove the unreacted starting materials and short oligomers.Finally, the deep brown precipitate was dried in a vacuum oven at 50 ºC.Yield: 2.6 g (52 %).IR (cm -1 , ):  35 , calcium brine: 7.5g / L NaCl + 11.0 g / L CaCl2.2H2O and Sulfate brine: 7.5 g / L NaCl + 10.66 g / L NaSO4, 50 ml of each brine solutions were connected in the test cell with different concentration of sodium alginate and chitosan.Testing cells were placed in the water bath set at 71°C for 72 h.Then, the concentration level of calcium ions was determined in the solution by titration with EDTA and Murexide indicator.The scale inhibitor percent was calculated following the equation: % inhibition = 100 x (Ca-Cb) / (Cc -Cb), where Ca = Ca 2+ concentration in the treated sample after precipitation, Cb = Ca 2+ concentration in the blank after precipitation and Cc = Ca 2+ concentration in the blank before precipitation.

Electrochemical test for CaCO3 scaling
Monitoring the buildup of calcium carbonate layers on the metal surface was studied by the electrochemical method including chronoamperometry and electrochemical impedance spectroscopy 13a .
Chronoamperometry test.Cathodic polarization of steel electrode initializes scaling process by forcing few nuclei of CaCO3 to be precipitated on steel surface according to the following equations: Ca 2+ + HCO3 -+ OH -→ CaCO3 + H2O In chronoamperometry test, cathodic polarization was applied to steel electrode surface which increases the local pH at the cathode as illustrated in equation 1, while increasing the hydroxyl ion concentration enables calcium carbonate to precipitate as given in equation 2. The electrochemical measurements were carried out in a cell with three-electrode mode using platinum sheet and saturated calomel electrode (SCE) as counter and reference electrodes, respectively.The material used for constructing the working electrode was steel that had the following chemical composition (wt.%):C, 0.

Conclusions
We report the synthesis of poly (5-nitro-orthanilic acid), a new type of polyaniline containing two types of functionalities by an aniline-initiated oxidative polymerization reaction.The nitro-orthanilic acid monomer itself did not polymerize under similar reaction conditions.The obtained polymer, as synthesized without further doping, was characterized with IR and UV spectroscopic techniques, elemental composition, cyclic voltammetry, viscosity, electrical conductivity, and dielectric measurements.SEM, TEM, TGA, DSC measurements were also investigated for additional analysis.Elemental analysis of carbon and nitrogen present is in good agreement with the given chemical formula of a modified polyaniline backbone.Analysis of sulfur contents resulted in an S/N ratio = 0.66 indicating a high content of substituted units in the resulted polymer backbone.The observed moderate reaction yield was expected because of the presence of electron-withdrawing groups which form a stable radical intermediate and the reaction occurs slowly due to electron density decreasing on the aniline' nitrogen atom.The presence of the hydrophilic -SO3H and a hydrophobic -NO2 groups on one aromatic ring gave the structure amphiphilicity or self-assembly nature and therefore the polymer morphology has a regular flower-leaf like microstructure as judged by SEM.The electronic spectra show absorption bands at 255 nm, 380 nm, and their bandgap energies were 4.86 eV and 3.26 eV, respectively.Because of the random substitution of the monomers in such polymerization, substituents disrupt the conjugation length that results in a hypsochromic shift of -* and polaron-* transitions.The voltammogram wave showed cathodic and anodic peaks corresponding to the quinoid and benzenoid structures, respectively, in the polymer main chain.Thermogravimetric measurements revealed high thermal stability up to 500C and the degradation curves showed subsequent weight-losses within four steps in which the third-(major peak) and fourth ones from 281C -346C and 345C -466C, respectively, are likely due to decomposition and/or elimination processes of the side-chain substituents.The oxidative thermal decomposition of polymer backbones was suggested above 500C for the polymeric remaining residues (31%) as final weight loss.Differential thermogravimetric analysis unambiguously pointed out the glass temperature (Tg) at 240C.The electrical conductivity decreases as the temperature increases at different applied frequencies.This behavior is indicative of semi-conducting nature in the extrinsic range which is characterized by high carriers and low mobility.The presence of such electron withdrawing residues causes a decrease of conductivity and increases the steepness of temperature dependence of conductivity.The dielectric measurements indicated that the permittivity, the measure of resistance, gradually decreased at the lower frequency range, up to 10 kHz, mainly due to the charge carriers' transport causing expected high conductivity.At a higher frequency range, up to 20 MHz, a slight effect was observed for frequency on decreasing the permittivity.Assessment of the copolymer as a new scale inhibitor of CaSO4, using the NACE test, indicated moderate CaSO4 inhibition efficiency, and this result is attributed to the change of polymer geometry via intramolecular H-bonding interaction of the -SO3H group and the polymer chain in an aqueous medium.On the other hand, the copolymer exerted good CaCO3 inhibition with increasing inhibitor concentration despite the observed anomalous behavior.Thus, the above-mentioned features achieved by polymerization of (5-nitro-orthanilic acid) make the obtained polymer highly potential for application as a new multifunctional scaling inhibitor of CaSO4 and CaCO3 precipitation, the common problem in the industry.The noteworthy, derivatives-based monomer used in this work were actively used as sensing elements of optical sensors to determine sulfate in water and soil extracts.

Figure 2 : 1 Copolymer 2
Figure 2: Cyclic voltammogram of substituted the prepared polymer 2. Scan rate of 100 mV s-1Copolymer 2 was subjected to electrochemical tests to study the electron transferred behavior.The experiment (one cycle) was conducted at concentration 5 mg in 20 ml DMSO solution.The voltammogram wave shape showed only one broadly cathodic peak at 0.056 V, assumed for the reduction of quinoid structure in the polymer chain, and one broadly anodic peak at -0.090 V, respectively.This electrochemical behavior could be attributed to the presence of electron-withdrawing, -SO3H and -NO2 groups which can be oxidized to quinone and vice versa at different potentials27 , Figure3.The cyclic voltammogram of copolymer 2 exhibited good reversibility.

Figure 3 :
Figure 3: Reduced and resonating oxidized structures of the functionalized monomeric moiety in the copolymer 2

Figure 5 :
Figure 5: Effect of temperature on permittivity (*) at different frequency for the polymer 2The variation of conductivity ' vs frequency (DC-conductivity) and the dissipation factor tan  vs frequency at a temperature ranging (40C -100C) are illustrated graphically in Figures6a and 6bfor polymer 2, respectively.Figures show a clear sharp peak followed by a small shoulder at lower limit points of frequency.At higher frequencies, it follows the power law: [σ' (ω) = Aω 5 ], in which A is constant and s characterizes the rate of change of AC-conductivity with increasing frequency.The intermediate range of frequency shows a plateau-like behavior that represents the dcconductivity, dc.It is affected vary slightly between 1 and 2 mS/cm by the variation of the irradiation dose, which confirms the fact that the contribution of the conductivity plays the main role of the permittivity values at the lower frequencies.The accumulation of charge carriers is the origin of the electrode polarization, the ubiquitous phenomenon which takes place at the interface between a metallic and an ionic conductor and thus, increases by many orders of magnitude the net dielectric response of the sample cell.Since Coulombic interactions take place here, ion mobility is drastically slowed down at the interfaces.

Figure 6 :Figure 7
Figure 6: a) Conductivity (`) vs frequency-and b) Dissipation factor (tan ) vs frequency for polymer 2 at temperature range 40 C-100 C

Figure 8 :
Figure 8: Proposed intramolecular interaction of the ortho-sulfonic group and the polymeric chain

Figure 9 :
Figure 9: Chronoamperometry curves for polarized steel electrode in CaCl2 brine solution in the absence and presence of different concentrations of studied polymer at -1 V vs SCE and 40 ○ C.

Figure 11 represents
Figure 11 represents Nyquist plots for steel after cathodic polarization in a brine solution in the absence and presence of different concentrations of copolymer 2. The impedance spectra of the polymer show a typical feature of

Figure 10 :
Figure 10: Variation of residual current for steel electrode after 3 h of polarization in CaCl2 brine solution in in the absence and presence of different concentrations of studied polymer at -1 V vs SCE and 40 ○ C.

Figure 11 :Figure 12 :Figure 13 :Figure 14 :
Figure 11: Impedance spectra of polarized steel in brine solution in the absence and presence of different concentrations of the copolymer 2 at 40 C

Figure 15 :
Figure 15: SEM images of CaCO3 crystals: (a) in absence, and (b) in presence of copolymer 2

Table 2 :
Computer fit results of the impedance spectra obtained for the steel electrode that was cathodically polarized in CaCl2 brine solution containing different concentrations of copolymer 2 after 3h 4lectrochemical impedance spectroscopy.EIS measurements were done at −1.0 V (vs SCE) after scale deposition process.The frequency range for EIS measurements was 0.1 to 1×104Hz with applied potential signal amplitude of 10 mV.All the measurements were done at 40.0 ± 0.1°C in solutions open to the atmosphere without stirring.To test the reliability and reproducibility of the measurements, triplicate experiments were performed in each case at the same conditions.