Evaluation of hydrophylic montmorillonite nanofluids and xantane gum in saline environment

With an estimated increasing oil demand in the coming decades, the need to explore nonapplicable areas is intensified, and associated with them, before the high exploration costs, the need to improve available technologies. In this sense, in the last decade, the application of nanoparticles to improve drilling fluids has been intensified. In this scenario, montmorillonite nanoclays and xanthan gums were little explored for the development of nanofluids. In this work, the influence of hydrophilic nanoclay on the rheological parameters of xanthan, sodium and calcium chlorides solutions was verified. For this, first, the clay was characterized by XRD, XRF and TGA. Then, maintaining constant the salt and xanthan concentrations, the influence of the variation in the concentration of nanoclay on the rheology of the solution was evaluated. Then, keeping the components concentrations constant, the influence of temperature was verified and then the hydration time on the rheology of the mixture. Finally, to assess the interaction of the mixture, it was verified the Electrical Conductivity and the Potential Zeta, varying the concentration of the nanoclay and the hydration time. It was concluded that: for certain nanoclay concentrations, there is an improvement in the rheology of xanthan solutions; Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 an addition of nanoclay favors rheology in the mixture of xanthan with increased temperature; hydration time does not affect the rheology of the nanofluid; there is interaction between nanoclay and xanthan.

At the same time, the use of nanoparticles associated with polymer-based fluids is small compared to those of bentonite (Vryzas & Kelessidis, 2017;Aftab et al., 2017).
Usually associated with clay sludge, polymers accumulate multiple functions in drilling fluids, such as viscosifiers, filtrate tuners, well wall stabilizers, shale swelling inhibitors, etc., but their properties are sensitive to high temperatures (Caenn et al, 2014;Lucena et al., 2014). As an example of polymer-based nanofluids, Ismail et al. (2016) applied carbon nanotubes and nano-silicon associated with polyonic cellulose and polyacrylamide; Parizad et al. (2018) applied titanium nano-oxide in mud based on xanthan, polyacrylamide and carboxymethylcellulose; Sadeghalvaad and Sabbaghi (2015) applied titanium nano-oxide to polyacrylamide sludge; Fakoya and Shah (2013) used silica nano-oxide and a mixture of surfactant and guar gum.
In this context, xanthan gum (XG), applied since the 1960s in the oil sludge industry (Caenn et al. 2014;Reinoso et. al., 2014), has viscosifying properties, pseudoplastic behavior at low concentrations, reduced filtrate loss, resistance to bacterial degradation, resistance to a wide pH range and salt concentration (Caenn et al., 2014;Howard et al., 2015;Jang et al., 2015;Kelco, 2000). Associated with nanoparticles, XG has been applied to drug development (Kennedy et al., 2015;Pooja et al., 2014), in the food industry (Taheri and Jafari, 2019), biodegradable materials (Melo et al., 2011), porous barriers for environmental decontamination (Comba et. al., 2011), among other uses. However, in the development of nanofluids (Amanullah et al., 2011), they are still associated with bentonite sludge or are rarely applied as a major component of the sludge.
Hence, the interaction of NA and XG in saline solutions was studied, evaluating the rheological behavior, stress relationship and shear rate. For this, first, the nanoparticle was characterized. Then, by varying the NA concentration at a temperature of 25°C, the rheological interaction profile, the rheological parameters of these profiles and the influence of the NA concentration on the respective ones were determined. Then, selecting an NA concentration, the influence of temperature on the rheological profile and its parameters was evaluated. Then, maintaining the concentration of the components of the mixture, the hydration time of the samples and the effect on the reference parameters were varied. Finally, the interaction of the particles of NA and XG in saline environment was evaluated, verifying the influence of concentration and hydration time on the stability of these interactions.

Methodology
Similar to previous authors (Amanullah et al., 2011;Ponmani et al., 2014;Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4. For sample preparation, the components were added in the following sequence: distilled water was added to the beaker in 50% of the total sample volume; XG was added and stirred for 10 minutes; then, NA was added and stirred for another 10 minutes; then, NaCl was added and the mixture was stirred for 5 minutes; finally, CaCl2 was added and the mixture was stirred for another 5 minutes. The sample volume was completed with distilled water and then the sample was stirred for 1 minute. In all stages, the mixtures were stirred between 1000 and 1500 rpm. The samples were kept at 4 ° C for 24 hours and then analyzed. The rheological model adopted for the tests was that of Herschel-Bulkley (Herschel and Bulkley, 1926), adopted for fluids that add Bingham's pseudoplastic and plastic properties, extensively applied in clay-based fluid modeling (Kelessidis et al., 2006;Kelessidis et al., 2007, Kelessidis andMaglione, 2008), but already adopted in studies of XG rheology in concentrations that show shear thinning (Holme et al., 1988;Khalil and Jan, 2012). The model follows the following equation: where 0 represents the Minimum Stress to the flow of the fluid, is the Behavior Index of the mixture and is the Consistency Index. The first parameter represents the resistance of the fluid to start the flow, the second parameter is associated with the thinning of the fluid with the increase of the shear rate, and the third parameter the apparent viscosity of the fluid (Herschel and Bulkley, 1926;Kelessidis et al., 2006;Kelessidis et al., 2007;Kelessidis and Maglione, 2008;Khalil and Jan, 2012). All tests were done in triplicate. To determine the rheological parameters, non-linear regression of Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 the results obtained on the viscometers was performed using the Origin Pro 2017® software.

Part 1
The XRD test was performed with a copper anode at 40kV and a current of 45mA, with a step of 1.2°/min under continuous scanning. The results are shown in Figure 1. The test shows peaks at 5. 95°, 26.99º, 41.99º, and the peaks between 70 and 80° belonging to Calcium Montmorillonite; the peaks of the order of 17º, 19.70º, 34.94º, 54.14 ° and 61.75° are from Sodium Montmorillonite; the other peaks of Beidellite. This composition shows that it is a so-called "natural" clay and considering that Beidellite is a sodium aluminosilicate, the analyzed clay has a higher sodium content than calcium, making it the sodium type (Santos, 1989;Grim and Güven, 1978). It is observed that the peak at 5.95°, corresponding to the basal layer with baseline reflection d001 (Santos, 1989), has an interlayer spacing of 14.85Å, meaning the existence of double layers of water (Sato et al., 1992;Laird, 2006), under a relative humidity of 40% for montmorillonites with calcium as free cation (Laird, 2006;Oueslati et al., 2015), confirming the identification of the mineral clay. Despite the possibility that the peaks detected between 20° and 30° are associated with the presence of quartz, mica and kaolinite (Souza, 1989;Morita et al., 2015;Menezes et al., 2008), the peak of the order of 29.04° and 40.24° is characteristic of Beidellite (Grim and Güven, 1978). Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 The chemical composition of the sample, obtained by FRX, is shown in Table 1.
The high concentration of SiO2 indicates the presence of free silica (Gaidzinski et al., 2009), and the concentration of Al2O3 is in agreement with montmorillonites (Santos, 2000). The low concentration of CaO associated with a high concentration of MgO points to the presence of carbonates (Monteiro and Vieira, 2004), and the high concentration of MgO confirms the classification of mineral clay (Santos, 2000). The ratio between Na2O and CaO concentrations is 1.88, indicating that sodium montmorillonite type (Santos, 2000). The low concentration of K2O preserves the rheological behavior of the clay by preventing the formation of crystalline structure under slight heating of the clay (Amorim, 2003). The low concentration of TiO4 shows that such an oxide does not interfere with the properties of the clay (Santos, 2000).
The thermigravimetric analysis is shown in Figure 2. Two endothermic peaks are observed at less than 100°C, corresponding to free adsorbed water (Santos, 1989;Xie et al., 2001;Mariani et al., 2013). There is an endothermic peak in the order of 260°C, which corresponds to dehydroxylation of amorphous aluminum hydroxides. The endothermic peak in the order of 700°C corresponds to the loss of structural hydroxyls (Santos, 1989 Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.

Part 2
For the second part, the concentrations of XG, NaCl and CaCl2 were maintained at 0.51% w/v, 12.86% w/v and 0.414% w/v, respectively. At this concentration, above the limit concentration, XG in water is salt-free and has a tangle conformation (Wyatt et  Research, Society and Development, v. 9, n. 8, e75985305, 2020(CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 al., 2011, characterized by the prevalence of hydrogen bonds between the disordered anionic chains of biopolymer in the aqueous environment, given the repulsion of these (Wyatt et al., 2011;Zhong et al., 2013). With the addition of salt, there is the screening effect of the added ions and the consequent balance of the charges of the biopolymer molecules, promoting the reduction of the repulsion between them, however the availability of polymers and the consequent proximity due to the high concentration of the gum enables the formation new connections between molecules in the environment (Wyatt et al., 2011;Zhong et al., 2013;Wyatt and Liberatore, 2010). In addition, the small divalent ions, as in the case of calcium cations, enter the intramolecular spaces of the polymer chains and act as a non-covalent lattice, favoring the formation of bonds between the particles dispersed in the environment, increasing the viscosity (Wyatt and Liberatore, 2010). In this scenario, the addition of salt increases the viscosity of the XG solution (Wyatt et al., 2011;Wyatt and Liberatore, 2010). In parallel, in view of a possible sedimentation of XG molecules with a high concentration of salts, despite the turbidity in XG solutions with concentrations greater than 0.1% (m/v) under the addition of NaCl (Morariu et al., 2018), there are records of sedimentation of the polymer by adding this salt (Morariu et al., 2018;García-Ocho et al., 2000). Xie and Lecourtier (1992) demonstrated stability of XG solutions in concentrations greater than 0.2% (m/v) for the addition of up to 2% (m/v) of CaCl2, at 25°C. In addition, to preserve the flow according to the proposed rheological model, Wyatt and Liberatore (2009) determined that salt-free XG solutions, with concentrations between 20 and 70ppm, presented shear thinning, and concentrations above 70ppm presented minimal stress with proportional growth increased XG concentration. In addition, Melo (2008) Table 2. It is observed that the first sample does not present the addition of NA, exactly to serve as a reference for the increase of rheological parameters. Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 Table 3 shows the shear stress values obtained in the tests for each sample. It is observed that, for a wide range of NA concentrations, only the concentration range between 0.05%, 0.1%, 0.125% and 0.15% (m/v) shows an increase in shear stresses, when compared to the sample free of nanoparticle. For example, the shear stress for 19.44s -1 of the NA-free sample (sample I) is 7.560Pa and increases to 10.017Pa in sample III (0.05% w/v), an increase of 32.5%. Samples IV, XI and XII show an increase for this same shear rate of 22.5%, 47.50% and 50.0%, respectively. It is also observed that, for sample III, the stress increase is negative by 1.14% for 1574.4s -1 , meaning that the NA-free sample, with a final stress of 24.854Pa, changes to 24.570Pa, however this difference corresponds at 284mPa, which can be considered irrelevant. The same occurs with the increase in sample IV, which adds the same 1.14% in stress to the respective shear rate. Therefore, it can be considered that such samples practically alter the initial stresses of XG, preserving the final stress of the fluid. Samples XI and XII, on the other hand, show a greater increase in shear stress in all shear rates, the most significant being 0.15% (m/v) of NA. It is also observed, in this scenario, that the main contribution to the flow was the increase of the initial stresses, which means a greater resistance to flow for fluid at rest, characteristic of Bingham plastics, a model widely foreseen for drilling fluids based on clay (Kelessidis et al., 2006;Kelessidis et al., 2007;Kelessidis and Maglione, 2008), but less present in XGbased fluids (Borges et al., 2009;Speers and Tung, 1986;Khalil and Jan, 2012). Figures 3A, 3B and 3C show, respectively, the shear rate curves by shear stress for samples whose concentrations vary from 0.0% to 0.025% (m/v), 0.05% to 0.125% (m/v) and 0.15% to 1.0%. Figure 3D shows the shear rate curves by shear stress for samples I, III, IV, XI and XII, to highlight the increment on the stresses recorded from the addition of NA. Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305   It is also observed that, with the increase in the shear rate, the increase in shear stresses decreases, following the shear thinning phenomenon, common for pseudoplastic fluids, expected for XG solutions (Holme et al., 1988;Khalil and Jan, 2012;Wyatt and Liberatore, 2009). Such decrease follows a logarithmic relationship for each measured concentration. Although the increase in stress is perceived for the respective concentration range, a law was not observed that links the concentration of NA with the increase in stress. Table 4 shows the percentage increase for each measured stress, relative to samples III, IV, XI and XII. Figure 4 shows the evolution of the percentage increase on shear stresses for samples III, IV, XI and XII: it is verified that, by the trend line, the logarithmic behavior of the phenomenon. Frame 1 shows the equations for the respective curves in Figure 4.  Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305  Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 Still with a view to increasing the shear stress of XG solutions, the rheological parameters of the samples in question were evaluated. Table 5 shows the values obtained for the rheological parameters of samples III, IV, XI and XII. Again, a law was not observed that would associate the values of the calculated parameters with the variation of the NA mass. It is observed that the Behavior Index remains practically constant with the addition of NA: the average of the values obtained was 0.4173, with an amplitude of 4.25% over the average, a standard deviation of 1.39%; when compared to the value of the parameter for an NA-free sample, the difference between the average value and the respective is 1.71%. Therefore, it can be concluded that the value of this parameter is preserved with the addition of the nanoparticle, that is, the addition does not interfere with the pseudoplastic behavior of the sample, meaning the prevalence of the rheological properties of XG before NA, as already verified by other authors (Xie and Lecourtier, 1992;Benyounes et al., 2010). Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 The Consistency Index changed with the addition of NA. It was found that the addition reduced the parameter by 20% for samples with 0.05% and 0.125% (m/v), and by less than 10% for samples with 0.1% and 0.15% (m/v). The viscosity of the polymer in a nanoparticle-free solution comes from its concentration in the environment as well as from the crosslinking effect caused by the cations dispersed in the solution (Wyatt et al., 2011;Zhong et al., 2013;Wyatt and Liberatore, 2010). This phenomenon can be justified by the presence of the silanol group on the surface of the nanoparticle (Rojtanatanya and Pongjanyakul, 2010;Rongthong et al., 2013) which, in addition to being the link with the hydroxyls of the biopolymer, forms links with the water in the environment (Maghzi et al., 2014), which facilitates the mobility between the particles during the stress of shearing, which is interesting for drilling fluids as it ensures less mechanical effort to raise the gravel to the surface (Caenn et al., 2014;Abu-Jdayil, 2011;Vryzas et al., 2016).
The Minimum Stress of the samples increased to 50% or more in relation to the value of the initial parameter, reaching double the value for samples XI and XII. This characteristic was required in XG solutions, precisely because of thixotropy, a property associated with gravel support when the drilling fluid is at rest (Caenn et al., 2014;Abu-Jdayil, 2011;Vryzas et al., 2016). XG solutions free of polyvalent cations and in low concentration, do not present a network formation because of the great electrostatic repulsion of the macromolecules; this repulsion is mitigated by the high concentration of cations in the environment and by the high concentration now worked out experimentally (Wyatt et al., 2011;Zhong et al., 2013;Wyatt and Liberatore, 2010), however, it cannot be admitted that, even if mitigated, this repulsion does not exist in these conditions. This perspective is ratified by the change in parameter values after the addition of the nanoparticle: due to the large surface area, which is essentially formed by silanol groups (Santos, 1989;Rojtanatanya and Pongjanyakul, 2010;Rongthong et al., 2013), a the presence of NA enhances the formation of hydrogen bonds between the particles of the biopolymer, and of these with the water, intensifying the formation of a network.

Part 3
In this step, the concentrations of XG, NaCl and CaCl2 in the mixture were maintained. Also, in view of the concentrations that showed an increase over the rheological parameters, sample IV was adopted as a reference, whose NA concentration Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 was 0.10% (m/v). The temperatures worked were 25°C, 42°C, 59°C and 72°C. The temperature ceiling adopted was intended to prevent water loss through evaporation.
In the absence of salt, the XG in an aqueous environment, at a temperature below 51°C, dispersed by electrostatic repulsion and has a disordered fractured helix conformation; with increasing temperature, there is a conformational change from XG to a coil-like structure, which disrupts the XG structure (Rocheford and Middleman, 1987;Choppe et al., 2010;Luporini and Bretas, 2011). This conformational change reduces the viscosity and shear thinning of XG solutions, bringing their rheological behavior closer to Newtonian fluids (Speers and Tung, 1986;Borges et al., 2009). The addition of salt minimizes the electrostatic repulsion of the trisaccharide chains, making the molecules adopt a double-helix structure ordered in the form of rods; minimizing electrostatic repulsion allows the interaction between molecules by XG hydrogen bonds (Rocheford and Middleman, 1987;Choppe et al., 2010;Luporini and Bretas, 2011); this interaction allows the conformational transition temperature to be greater than 51°C (Luporini and Bretas, 2011). For example, Luporini and Bretas (2011) determined that there was no conformational transition for temperatures below 86°C. Xie and Lecourtier (1992) verified in suspensions of 1% XG (m/v) with bentonite, for concentrations of 2% NaCl (m/v) or 1% CaCl2 (m/v), conformational transition temperature 125ºC -it should also be considered that bentonite does not interfere with XG's conformational transition temperature (Xie and Lecourtier, 1992). Consequently, the rheological properties in XG saline solutions are less influenced by the increase in temperature (Xie and Lecourtier (1992); Rocheford and Middleman, 1987;Choppe et al., 2010). Figure 5 shows the shear stress rate curves of the samples with 0.1% NA, for each measured temperature. Table 6 presents the results of stress by shear rate adopted for each temperature. Table 7 shows the proportion of the shear stress reduction for each temperature range and in relation to the initial temperature. It is observed that, at a temperature lower than the conformational change of salt-free XG solutions, there is a reduction in the shear stress for higher shear rates. For example, between temperatures 25°C and 42°C, there is no stress reduction to 19.44s -1 , but there is a 2% reduction for the following shear rates; the reduction progresses to the shear rate of 1574.4s -1 , on the order of 11.3%. When the phenomenon is observed between 42°C and 59°C, it can be seen that the reduction is more significant over the whole range, but marked in the initial and final shear rates -between 12.62% to 15.82% -, and for the other shear rates, varying between 8.83% and reaching 10.97%. For the transition between 59°C and 76°C, the phenomenon Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 remains, with more marked reductions for the higher shear rates -in the order of 7.54% to 10.56% -, an average reduction of 5.49% between 32.4s -1 and 291.6s -1 , and a negligible reduction for first stress, less than 1%. It is also observed that, when compared to the shear stress at 25°C, the reduction is more pronounced: the reduction for the initial stresses, at 19.44s -1 , are of the order of 15% for 59°C and 76°C; stress in the intermediate rates are already rising to 10.53%, reaching 16.36% to 59°C, and growing even more to 76°C, reaching almost 22%; for final rate stresses, the reduction varies between 18.04% to 59°C, reaching 28.57% to 76°C. These results can be justified by the high concentration of XG in the environment which, even under the presence of a large amount of salts, and considering the independence of NA over the rheological effects suffered by XG in the face of temperature variation, ends up suffering a partial degradation as an increase temperature, even if in a reduced form. Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 The previous analysis should be extended to the rheological parameters of the mixtures, shown in Table 8. In the transition between 25°C and 42°C, a 5.58% decrease in the Consistency Index is observed, a 5.61% increase over the Minimum Stress , and a 4.20% reduction in the Behavior Index. This phenomenon can be interpreted as a greater availability of biopolymer molecules dispersed in the environment, caused by the increase in temperature; this provides a greater interaction between the particles when at rest, but less resistance to flow when in motion, causing even greater shear thinning. This phenomenon is similar to what happened with lamellar structures, such as those of bentonite, which, with the increase in temperature, suffers from these structures due to the release of adsorbed water, causing sedimentation (Santos, 1989;Xie and Lecourtier, 1992); this sedimentation causes greater mechanical resistance to flow at rest, but less resistance to shear (Xie and Lecourtier, 1992 Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 reduction in the Consistency Index, an increase of 39.13% in the Minimum Stress and an increase of 15.44% in the Behavior Index. This can be justified in analogy to bentonite suspensions (Santos, 1989;Xie and Lecourtier, 1992): with the increase in temperature, there are more disordered molecules and a greater energy of water molecules on the surface of the nanoparticles given the temperature of the environment, which decreases the ability to resist shear and consequently offer less thinning by thinning; at rest, there is greater availability of dispersed particles, but interactions are weak, especially due to Van der Walls (Luporini and Bretas, 2011), since hydrogen bridges are no less viable by agitating water molecules and the disordered structure of molecules of XG.
Another relevant analysis occurs on the variations of the parameters in relation to those determined at 25°C: in the transition to 42°C, the variation of the parameters was in the order of 4% to 5%. Comparing the parameters determined at 25°C and 59°C, there is an increase of 93.41% in the Consistency Index, in addition to reductions of 27.31% in the Behavior Index and 40.69% in the Minimum Stress, showing the effect of the conformational change (Rocheford and Middleman, 1987;Choppe et al., 2010;Luporini and Bretas, 2011) and, consequently, weaker interactions between particles dispersed in the environment, greater mechanical impediment to flow and greater resistance to shear thinning. When comparing the parameters obtained at 25°C and 76°C, there is an increase of 10.47% for the Consistency Index, and reductions of 16.09% for the Behavior Index and 17.48% for the Minimum Stress, therefore, milder changes compared to the changes observed at 59°C. Certainly, due to the proximity to the temperature of conformational change, the disorganized particles must be closer and, consequently, they must offer greater mechanical impediment to shear than at higher temperatures, where there is certainly less interaction with water, more spacing between macromolecules and greater mobility between scattered particles. For this reason, the increase over the parameters is greater when close to the transition temperature and milder when moving away. Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4. Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305  Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 and 65°C, there was a reduction of 66%, 9.8% and 16% for the respective parameters.
Comparing the two studies, considering the proximity of the temperatures of 42 and 45°C and both being below the temperature of conformational change, a smaller reduction of the parameters is observed for the samples with NA; for an average range of 60°C, this relationship is reversed, with more significant reductions in the Behavior Index and Minimum Stress for samples with NA, but an increase of 104% over the Consistency Index for the nanofluid compared to a reduction of 27% for the sample of Melo (2008).
In addition, the reductions in the rheological parameters between 55°C and 65°C are more pronounced for the study by Melo (2008) than those observed in the transition of the nanofluid parameters both between 42 and 59°C, and between 59 and 76°C. Therefore, it can be concluded that the increase in temperature causes a disorganization of the XG particles, but the presence of nanoclay in the mixture allows the recovery of the interactions of these particles, and consequently, the recovery of the rheological properties of the fluid. Therefore, samples with NA are less sensitive to temperature variation over their rheological parameters.

Part 4
In this step, the same concentrations of the components of the mixture as in the previous step were adopted. The influence of the hydration time of the samples on the shear stresses and on the rheological parameters of the Herschel-Bulkley model was evaluated. To this end, it is emphasized that Melo (2008) separately verified the effect on XG solutions and bentonite suspensions, attesting that XG solutions stabilize their rheological parameters within 24 hours of hydration, but the bentonites did not do so in 120h of evaluation. Santos (1989) points out that the effect on bentonite comes from the great hygroscopic capacity of the clays, which incorporate abundant water to their structure, given the presence of the silanol group (Santos, 1989). This effect occurs mainly in the clays of the montmorillonite group, the same clay from the nanoparticle adopted in this study. Table 9 shows the variation in shear stresses under the hydration time of the samples.
It is observed that the shear stress variations were small, under a standard deviation that ranged from 1,767% to 4,246%, meaning the predominance of XG rheology over NA (Xie and Lecourtier, 1992;Benyounes et al., 2010) and a certain stability in the rheological behavior of the mixture over the measured period. This can be Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 justified by the nanoparticulate state of the clay, which does not cause the effect of water incorporation over time (Santos, 1989;Melo, 2008): the nanoparticle, for being under a lamellar structure (Santos, 1989;Golubeva et al., 2013;Uddin, 2008;Hoidy et al. 2009) and by the interaction with the other components of the mixture, its particles end up being kept apart from each other, which prevents the incorporation of water between the valleys formed between the lamellae. The nanoparticle interaction occurs mainly with the biopolymer trisaccharides by hydrogen bonding with the NA silanol group, and by this type of bonding with the solution's free water (Santos, 1989;Rojtanatanya and Pongjanyakul, 2010;Rongthong et al., 2013;Maghzi et al., 2014).
The same behavior is observed for the evaluated rheological parameters, shown in Table 10. It is noticed that the Behavior Index varies between 0.3758 and 0.4112, under an average of 0.3949 and a standard deviation of 3.6%, a certain stability for the interval of measured time. The Minimum Stress fluctuated between 5.9944 and 7.4238Pa, an average of 6.6430Pa and a standard deviation of 7.84%, which can be explained by the dynamic interaction between the particles that form hydrogen bonds and their Brownian motion in the environment. The Consistency Index varied more significantly, between 834.5 and 1188.9mPa.s n , an average of 991.7mPa.s n and standard deviation of 14.9%, but which can also be justified in analogy to the Minimum Stress. Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4. Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305

Part 5
In Considering that Electrical Conductivity is a measure of free ion distribution in the environment subject to electrical conduction, it can be inferred that they would be in dynamic balance of interaction between ions and counterions dispersed in the aqueous environment (Rao et al., 2005), which makes it an indirect measure of interaction between the particles in the mixture. In parallel, it should be considered that, in polyelectrolyte saline solutions, the electrical conductivity of the environment is practically independent of the polyelectrolyte concentration for high salt concentrations (Sagou et al., 2015;Bordi and Carnetti, 1986). From the results presented in the two evaluations, it is observed that the concentration of electrolytes in equilibrium is practically stable: the conductivity values for the samples showed a maximum difference of 6%, which means that this balance does not depend on the variation of NA in the environment; for variation of hydration time, the results vary by 5% between 24 and 120h, with only a discrepancy in these values in the 144h sample; the values for this hydration time can be considered null, since they vary between zero and -1.0mS/cm. Research, Society and Development, v. 9, n. 8, e75985305, 2020 (CC BY 4. Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 It is important to mention that Electrical Conductivity attests only to the concentration of electrolytes with sufficient electrophoretic mobility to conduct electric current, therefore it does not discriminate the charge or the type of electrolyte (Roa et al., 2005;Show, 1992); the stability measured in the experiment points to a stability in the ionic concentration in the environment, but not to the dynamics of the interactions. For this, the Zeta Potential was measured, which corresponds to the electrophoretic mobility of the particles dispersed in the environment and also adopted as a measure of stability between the particles; this property is sensitive to the concentration and charge of the electrolytes in the environment (Shaw, 1992). For XG solutions, the Zeta Potential varies between -20 and -74mV, in proportion to the increase in the concentration of the biopolymer, since it is anionic (Thonart et al., 1985). In parallel, it should be noted that the instability interval between flocculation and deflocculation occurs between ± 50mV (Salopek et al., 1992).
Evaluating the results of the samples with different concentrations of NA, it is observed that the sample IV presents electrophoretic stability, even with great variations of Zeta Potential. However, the same was not verified for samples II and IX, whose transitions of the parameter values between positive and negative suggest instability in the interactions of the particles of the environment (Shaw, 1992;Salopek et al. 1992). It is also verified that the increase in the concentration of NA negatively interferes in the interaction between the cations and the biopolymer molecules, which is reflected in the values of Zeta Potential varying from negative to positive with the increase in NA concentration, pointing to a greater availability of cations with mobility in the mixture.
The previous results demonstrate the total interaction between nanoparticles and biopolymer. This perspective can be associated with the rheological parameters of the samples in question: for 24h of hydration, the sample with 0.01% (m/v) of NA presents, even in the interval of instability, negative values of the parameter, demonstrating an anionic predominance of the solution; the sample with 0.025% (m/v) shows values that change between positive and negative, and the sample with 0.1% (m/v) shows positive values. This fact justifies the transition observed in the rheological parameters of the samples in question: for the sample with 0.01% NA, with little availability of nanoparticles, there is a predominance of fragile interactions naturally promoted between the polymer molecules (Wyatt et at., 2011;Zhong et al., 2013;Wyatt and Liberatore, 2010), reflected in the high value of the Consistency Index and the low value of the Minimum Stress; in the sample with 0.025% NA, with greater availability of Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 nanoparticles in the environment, the formation of hydrogen bonds and reduction of the interaction between the polymer molecules during the stress application given the connection with water is favored (Rojtanatanya and Pongjanyakul, 2010;Rongthong et al., 2013;Maghzi et al., 2014), which explains the decrease in the Consistency Index and the increase in Minimum Stress; in the sample to 0.1% (m/v), for intermediate values to those presented between the previous and the following sample.
The increase in the hydration time reduces the values of Zeta Potential: initially varying between 9.89 and 98.9mV, the values tend to change between positive and negative in 48h of hydration already, a fact that intensifies at the end of the period, whose amplitude reduces ± 10mV in the penultimate of close to zero in the last period. This result can be interpreted as a lower availability of ions with mobility in the environment over time, justified by the possible interaction of cations with nanoparticles (Santos, 1989) and/or with XG molecules still with free anionic regions (Wyatt et at., 2011;Zhong et al., 2013;Wyatt and Liberatore, 2010), to the point of almost exhausting them from the environment. It is observed that the value of Electrical Conductivity is also close to zero, which would correspond to almost total interaction of the dispersed ions, in the absence of conductivity or ion mobility. This justification is confirmed by the stability of the rheological parameters of the samples for the measured hydration interval, allowing to conclude that the available cations do not interfere in the binding of NA with XG molecules.

Final Considerations
It was concluded that, for an analyzed concentration range, the nanoclay increases the shear stresses of saline solutions of XG in the concentrations 0.05%, 0.10%, 0.125% and 0.15% (m / v). There was a certain reduction in dynamic viscosity (Consistency Index) of a maximum of 20%, but there was a substantial increase in viscosity at rest (Minimum Tension), increases that even doubled this parameter. It was also observed that the main increases in shear stress occur in the initial shear rates, tending to decrease with increasing rate. These results allow us to conclude that the nanoparticles positively interfere in the ability to form bonds between the XG macromolecules when at rest, increasing their binghanian characteristic, even improving the thixotropy of the solution.
The addition of the nanoparticle does not interfere with the pseudoplastic profile of the mixture, characteristic of XG solutions. Development, v. 9, n. 8, e75985305, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i8.5305 The temperature continues to act negatively on the properties of the solution, as it reduces the shear stresses, Behavior Index and Minimum Stress. These parameters even reduce 30% at 76ºC, showing that, even in the presence of salt, certainly due to the high concentration of XG, part of the particles undergo conformational change. The temperature also interferes with the Behavior Index, which fluctuates with its increase, however is not far from the pseudoplastic behavior. Comparing the parameters with previous studies, it is observed that the nanoparticle contributes positively to the preservation of the rheological parameters of the mixture.
It was also observed stability of the rheological parameters for the hydration time between 24h and 144h, meaning that the clay's dependence on hydration was already resolved. Therefore, it is concluded that the addition of NA favored the evaluated parameters, as well as their preservation with increasing temperature and their stability over the hydration time. For future studies, it is interesting to evaluate the rheology of nanoclay and xanthan mixtures in saline solutions with trivalent ions, especially due to the sensitivity of xanthan the presence of high ionization ions (Kelco, 2000). Another suggestion is the evaluation of the rheology of the mixture worked in this research under high pressure at high temperature. Another, the evaluation of the filtrate of the mixture adopted in this work.