**2. Formulation of the self-assembled polymer network (SAP)**

Several types of polymers commercially available were evaluated for the formulation of the SAP network with enhanced viscoelastic flow behavior. Xanthan gum (B), commercial food grade (Groupe Maison Cannelle Inc. (Richmond, QC, Canada)), a partly hydrolyzed polyacrylamide, HPAM, with a degree of hydrolysis ranging from 5 to 10 mol% and a molecular weight of approximately 5 × 10<sup>6</sup> daltons [41] (GelTech, Midland, TX, USA), and AP of low anionicity, low-molecular weight (8–12 million Dalton), and a high hydrophobic content [42–44] (SNF Floerger, Riceboro, GA, USA). Baseline polymers and polymer blends were initially prepared in brine solution of 2.1 wt% concentration (see **Table 1**). Polymer solutions were mixed using a magnetic stirrer under strong mixing conditions to prevent the formation of lumps (e.g., fish eyes) at room temperature. The viscoelastic behavior, DMA, and DTMA of the baseline polymers and SAP were characterized through oscillatory rheology at 25°C using a Bohlin Geminin HR Nano Rheometer manufactured by Malvern (Worcestershire, UK) equipped with a parallel-plate measuring geometry (gap: 1000 μm) and a solvent trap to prevent drying effects during measurements. The amplitude sweep was performed in the strain range from 1 to 1000% at a fixed frequency of 1 rad/s, while the frequency sweep was run from 0.01 to 100 rad/s at fixed strain within the linear viscoelastic (LVE) range as determined from the preceding amplitude sweep.

**Figure 2** displays the frequency sweeps as the curve functions of the loss factor (tan*δ*), storage modulus (*G*'), loss modulus (*G*"), and complex viscosity (|*η*\*|) for the baseline polymers B, HPAM, and AP at concentrations of 0.2, 0.2, and 0.1 wt%, respectively, prepared in 2.1 wt% brine.

The frequency sweeps (**Figure 2**) demonstrate that all polymers follow the characteristic shear-thinning flow behavior of polymers, thus viscosity decreases with increasing shear rate. At the same salinity (2.1 wt% brine), temperature, and angular frequency range, polymer B at 0.2 wt% solution concentration shows a significantly higher viscoelasticity than the HPAM at 0.2 wt% solution and the AP at 0.1 wt% solution. The behavior of polymer B (i.e., xanthan gum) results from its molecular-ordered aggregation behavior in saline solutions.

Regarding the loss factor (tan*δ*), which is useful to describe the viscoelastic behavior of materials in the low shear range (*ω* ≤ 1 s−1) [12, 45]; **Figure 2** shows that polymer B behaves different from the HPAM and AP polymer solutions. Polymer B exhibits a flow transition from a viscoelastic liquid behavior (tan*δ* > 1) to a viscoelastic weak-gel behavior (tan*δ* < 1) as angular frequency increases. At low angular frequencies (i.e., *ω* ≤ 1 rad/s), the polysaccharide molecules are entangled with neighboring macromolecules forming aggregates stabilized


**Table 1.** Brine compositions (wt%).

Hydrophobically modified polyacrylamides (HMPAMs) are water-soluble polymers containing both hydrophobic groups (e.g., methyl or ethyl acrylates, alkyl vinyl ethers, styrene comonomers, or alkyl acrylamides) and weakly charged pendant groups (e.g., carboxylic acid pendant groups) directly attached to the polymer backbone (**Figure 1(c)**). The hydrophobic groups can be distributed in a block-like fashion, randomly, or discretely distributed along the backbone. In aqueous solutions, these hydrophobic groups aggregate through intra- and intermolecular associations that increase the hydrodynamic volume of the polymer, which increases the viscosity of the polymer solution [36, 38]. The alkyl chain length and charge density determine the hydrophobicity of these polymers [39]. The presence of counter-ions in the aqueous media reduces the repulsion between charged groups within the polymer chain, which favors inter- and intrachain hydrophobic interactions [39, 40]. Benefits of HMPAM include salt tolerance and the enhancement in solution viscosity in the presence of low-molecular-weight electrolytes because of the shielding of intramolecular Coulombic attractions rather than the intermolecular hydrophobic interactions [36]. The inter- and intramolecular hydrophobic interactions are dynamic and reversible. Therefore, under high shear rate, these associations are interrupted and the viscosity of the solution decreases, but as soon as the high mechanical shear is removed, the hydrophobic

groups re-associate and the viscosity of the solution returns to its original value [36].

tion of the supramolecular system is beyond the scope of this work.

The goal of this exploratory research was to formulate a supramolecular polymer network with enhanced properties (i.e., viscoelasticity, mechanical stability, salt tolerance, and thermal stability), taking advantage of the synergistic combination of the beneficial properties of the individual polymers in the blend. The formation and characterization of the supramolecular polymer network was demonstrated through frequency (time) and temperature-dependent oscillatory rheology [4, 5]; the use of other analytical techniques for structural characteriza-

In this chapter, the formulation and characterization of the supramolecular self-assembled polymer network (SAP) is first described, and then the effect of ionic strength on the viscoelastic behavior of the SAP is discussed. The next section describes the structural strength of the SAP through dynamic mechanical analysis (DMA), followed by the evaluation of the SAP thermal stability by dynamic mechanical thermo-analysis (DMTA). In the following section, the long-term thermal stability of the SAP prepared in brines having different ionic strengths is discussed. Finally, the performance of the SAP in displacing heavy oil employing conven-

Several types of polymers commercially available were evaluated for the formulation of the SAP network with enhanced viscoelastic flow behavior. Xanthan gum (B), commercial food grade (Groupe Maison Cannelle Inc. (Richmond, QC, Canada)), a partly hydrolyzed polyacrylamide, HPAM, with a degree of hydrolysis ranging from 5 to 10 mol% and a molecular

anionicity, low-molecular weight (8–12 million Dalton), and a high hydrophobic content [42–44] (SNF Floerger, Riceboro, GA, USA). Baseline polymers and polymer blends were initially prepared in brine solution of 2.1 wt% concentration (see **Table 1**). Polymer solutions

daltons [41] (GelTech, Midland, TX, USA), and AP of low

tional sad-pack displacement tests at simulated oil reservoir conditions is presented.

**2. Formulation of the self-assembled polymer network (SAP)**

weight of approximately 5 × 10<sup>6</sup>

98 Polymer Rheology

by hydrogen bonds and intermolecular associations through acetate residues [15] that resist flow and therefore viscous behavior dominates [13, 14, 17, 19, 45]. As the angular frequency increases, progressive disentanglement of the macromolecules takes place aligning the molecules in the direction of shear and shear gradient, which offer less resistance to flow, and the viscoelastic flow behavior of polymer B solution transitions to an elastic-dominated state [11, 12, 17, 20, 45, 46]. This flow behavior at rest and/or low shear is different from the typical flow behavior of common polymer solutions [15–17, 19, 29].

Supramolecular systems can be formed via electrostatic interactions due to the high solubility of charged groups in water. Previous research has demonstrated that xanthan gum and HPAM form physical networks through ionic cross-linking using divalent cations (e.g., Ca2+) [2, 26]. More examples of network systems built up through electrostatic interactions are reported in Ref. [6]. Specifically, Ca2+ is an efficient binder for carboxylic acids that induce aggregation in aqueous polymer solutions through the formation of polyion/cation complexes. In these

Viscoelasticity of a Supramolecular Polymer Network and its Relevance for Enhanced Oil Recovery

http://dx.doi.org/10.5772/intechopen.77277

systems, "the focal point is the carboxylate moiety [that is an] excellent ligand" [52].

of many ordered supramolecular architectures" [54].

different concentrations of polymer B in the blends.

concentrations of HPAM and AP fixed at 0.2 and 0.1 wt%, respectively.

In this work, the anionic polymers were mixed in brine containing 3300 ppm of CaCl<sup>2</sup>

**Table 1**, brine 2.1 wt%). In this system, self-assembling is dominated by rapid cooperative electrostatic interactions in which the divalent cations, Ca2+, bridge the negative charges (i.e., carboxylic groups) in the polymer macromolecules causing complexation of a mixture of anionic polymers. In this case, the divalent cations act as the physical crosslink among the anionic polymer chains [6, 8]. The interpolymer associations driven by electrostatic interactions decrease the intra- and interpolymer electrostatic repulsion promoting the intra- and intermolecular hydrophobic interactions (i.e., van der Waals interactions) among the hydrophobic segments of the macromolecules forming a stronger network structure [36]. Therefore, the screening of the charged groups by divalent cations reduces the steric hindrance among polymer chains and aids the interpolymer association via hydrogen bonding and hydrophobic interactions [53]. Hydrogen bonding among side chains (e.g., carboxylic acids and amide groups) of polymers B, HPAM, and AP takes place, as previously demonstrated between HPAM and xanthan gum side groups [35, 51]. In solution, supramolecular networks are commonly controlled by strong intra- and intermolecular hydrogen bonds. "The double hydrogen bonding of two or more amides can work in a cooperative manner to drive the formation

**Figure 4** displays the frequency sweep rheometry data that shows the effect of varying the concentration of polymer B in PB # 1 and # 4 from 0.1 to 0.3 wt%, while maintaining the

Increasing the concentration of polymer B significantly increases the elasticity and viscosity of both blends. However, the largest gain in viscoelasticity is shown by PB # 4. The rheological data suggest that increasing the concentration of polymer B encourages more intra- and interpolymer chain associations through cation bridging, hydrophobic interactions, and hydrogen bonding, which enhances the structural strength and viscosity of the SAP without compromising its solubility in brine solution [36]. Furthermore, PB # 4 exhibits the lowest

**Figure 4.** Frequency sweeps as curve functions of tan*δ*, *G*', *G*", and |*η*\*|for PB # 1 and PB # 4 in 2.1 wt% brine using

(see

101

The polymer blends (PBs) and respective concentrations evaluated were as follows:

PB̲#**1:B**[0.2 wt%] ↔ HPAM [0.2 wt%]―PB#̲**2 : B** [0.2 wt%] ↔ AP [0.1 wt%]

PB̲#**3 :**HPAM[0.2 wt%] ↔ AP [0.1 wt%]―PB̲#**4 :B**[0.2 wt%] ↔ HPAM[0.2 wt%] ↔ AP [0.1 wt%].

All polymer blend solutions were homogeneous as such phase separation was not observed. The dynamic rheological properties of PB #1, #2, and #4 (**Figure 3**) suggest polymer interactions with an enhanced viscoelasticity relative to the baseline polymers, except for PB # 3 (**HPAM** [0.2 wt%]↔**AP** [0.1 wt%]) that resulted in far inferior viscoelasticity (data not shown) and was rejected. Besides, it seems that polymer B directs the interactions among the mainand side chains of the blended polymers because PB # 1, # 2, and # 4 assume the rheological behavior of the baseline polymer B (see **Figures 2** and **3**).

Polymer blend # 4 -**B** [0.2 wt%]↔**HPAM** [0.2 wt%]↔**AP** [0.1 wt%] showed the highest elasticity and viscosity gain (**Figure 3**). At the angular frequency (*ω*) of 7.055 rad/s, the percentage increase in Δ*G*' was 43%, Δ*G*" was 41%, and Δ|*η*\*| was 42% relative to polymer B baseline. Δ*G,*' Δ*G*", and Δ|*η*\*|increase by more than an order of magnitude relative to the baseline of the HPAM and AP polymers at the same *ω* = 7.055 rad/s. Furthermore, the low loss factor, tan*δ* < 1, with *G*' > *G*" in the entire range of angular frequency; corresponds to a flow behavior that is characteristic of stable dispersions in the form of network-like structures built up through inter- and intramolecular interactions [3, 9, 45, 47–51]. Furthermore, the storage modulus, *G*', kept increasing at high angular frequencies, which "[verifies] the dynamic nature of the bonds within the network" [5]. This rheological behavior demonstrates that interchain self-association among the blended polymers forms a stronger polymer network of a larger hydrodynamic volume showing an enhanced solution viscosity. **Figure 3** also shows that PB # 1 displays the second larger gain in *G*', *G*", and |*η*\*|relative to their individual polymer constituents.

**Figure 3.** Frequency sweeps as curve functions of tan*δ*, *G*', *G*", and |*η*\*|for the polymer blends prepared in 2.1 wt% brine.

Supramolecular systems can be formed via electrostatic interactions due to the high solubility of charged groups in water. Previous research has demonstrated that xanthan gum and HPAM form physical networks through ionic cross-linking using divalent cations (e.g., Ca2+) [2, 26]. More examples of network systems built up through electrostatic interactions are reported in Ref. [6]. Specifically, Ca2+ is an efficient binder for carboxylic acids that induce aggregation in aqueous polymer solutions through the formation of polyion/cation complexes. In these systems, "the focal point is the carboxylate moiety [that is an] excellent ligand" [52].

by hydrogen bonds and intermolecular associations through acetate residues [15] that resist flow and therefore viscous behavior dominates [13, 14, 17, 19, 45]. As the angular frequency increases, progressive disentanglement of the macromolecules takes place aligning the molecules in the direction of shear and shear gradient, which offer less resistance to flow, and the viscoelastic flow behavior of polymer B solution transitions to an elastic-dominated state [11, 12, 17, 20, 45, 46]. This flow behavior at rest and/or low shear is different from the typical flow

The polymer blends (PBs) and respective concentrations evaluated were as follows:

PB̲#**1:B**[0.2 wt%] ↔ HPAM [0.2 wt%]―PB#̲**2 : B** [0.2 wt%] ↔ AP [0.1 wt%]

PB̲#**3 :**HPAM[0.2 wt%] ↔ AP [0.1 wt%]―PB̲#**4 :B**[0.2 wt%] ↔ HPAM[0.2 wt%] ↔ AP [0.1 wt%].

All polymer blend solutions were homogeneous as such phase separation was not observed. The dynamic rheological properties of PB #1, #2, and #4 (**Figure 3**) suggest polymer interactions with an enhanced viscoelasticity relative to the baseline polymers, except for PB # 3 (**HPAM** [0.2 wt%]↔**AP** [0.1 wt%]) that resulted in far inferior viscoelasticity (data not shown) and was rejected. Besides, it seems that polymer B directs the interactions among the mainand side chains of the blended polymers because PB # 1, # 2, and # 4 assume the rheological

Polymer blend # 4 -**B** [0.2 wt%]↔**HPAM** [0.2 wt%]↔**AP** [0.1 wt%] showed the highest elasticity and viscosity gain (**Figure 3**). At the angular frequency (*ω*) of 7.055 rad/s, the percentage increase in Δ*G*' was 43%, Δ*G*" was 41%, and Δ|*η*\*| was 42% relative to polymer B baseline. Δ*G,*' Δ*G*", and Δ|*η*\*|increase by more than an order of magnitude relative to the baseline of the HPAM and AP polymers at the same *ω* = 7.055 rad/s. Furthermore, the low loss factor, tan*δ* < 1, with *G*' > *G*" in the entire range of angular frequency; corresponds to a flow behavior that is characteristic of stable dispersions in the form of network-like structures built up through inter- and intramolecular interactions [3, 9, 45, 47–51]. Furthermore, the storage modulus, *G*', kept increasing at high angular frequencies, which "[verifies] the dynamic nature of the bonds within the network" [5]. This rheological behavior demonstrates that interchain self-association among the blended polymers forms a stronger polymer network of a larger hydrodynamic volume showing an enhanced solution viscosity. **Figure 3** also shows that PB # 1 displays the second larger gain in *G*', *G*", and |*η*\*|relative to their individual

**Figure 3.** Frequency sweeps as curve functions of tan*δ*, *G*', *G*", and |*η*\*|for the polymer blends prepared in 2.1 wt% brine.

behavior of common polymer solutions [15–17, 19, 29].

100 Polymer Rheology

behavior of the baseline polymer B (see **Figures 2** and **3**).

polymer constituents.

In this work, the anionic polymers were mixed in brine containing 3300 ppm of CaCl<sup>2</sup> (see **Table 1**, brine 2.1 wt%). In this system, self-assembling is dominated by rapid cooperative electrostatic interactions in which the divalent cations, Ca2+, bridge the negative charges (i.e., carboxylic groups) in the polymer macromolecules causing complexation of a mixture of anionic polymers. In this case, the divalent cations act as the physical crosslink among the anionic polymer chains [6, 8]. The interpolymer associations driven by electrostatic interactions decrease the intra- and interpolymer electrostatic repulsion promoting the intra- and intermolecular hydrophobic interactions (i.e., van der Waals interactions) among the hydrophobic segments of the macromolecules forming a stronger network structure [36]. Therefore, the screening of the charged groups by divalent cations reduces the steric hindrance among polymer chains and aids the interpolymer association via hydrogen bonding and hydrophobic interactions [53]. Hydrogen bonding among side chains (e.g., carboxylic acids and amide groups) of polymers B, HPAM, and AP takes place, as previously demonstrated between HPAM and xanthan gum side groups [35, 51]. In solution, supramolecular networks are commonly controlled by strong intra- and intermolecular hydrogen bonds. "The double hydrogen bonding of two or more amides can work in a cooperative manner to drive the formation of many ordered supramolecular architectures" [54].

**Figure 4** displays the frequency sweep rheometry data that shows the effect of varying the concentration of polymer B in PB # 1 and # 4 from 0.1 to 0.3 wt%, while maintaining the concentrations of HPAM and AP fixed at 0.2 and 0.1 wt%, respectively.

Increasing the concentration of polymer B significantly increases the elasticity and viscosity of both blends. However, the largest gain in viscoelasticity is shown by PB # 4. The rheological data suggest that increasing the concentration of polymer B encourages more intra- and interpolymer chain associations through cation bridging, hydrophobic interactions, and hydrogen bonding, which enhances the structural strength and viscosity of the SAP without compromising its solubility in brine solution [36]. Furthermore, PB # 4 exhibits the lowest

**Figure 4.** Frequency sweeps as curve functions of tan*δ*, *G*', *G*", and |*η*\*|for PB # 1 and PB # 4 in 2.1 wt% brine using different concentrations of polymer B in the blends.

crossover point (*G*' = *G*" and tan*δ* < 1 at *ω* = 0.1 rad/s), which indicates the formation of a more stable supramolecular system [4]. For this reason, PB # 4 was selected as the optimum SAP formulation. Hereafter, PB # 4 is designated as SAP, while PB # 1 is designated as the baseline system for comparison purposes.

On the basis of the results obtained from oscillatory rheology in this exploratory research, a hypothetical structure of the optimum supramolecular polymer network is proposed in **Figure 5**, which shows the plausible reversible interactions taking place during self-aggregation of the SAP network.

Forthcoming research will characterize the structure of the optimum SAP system in depth, employing several analytical techniques (i.e., 1 H Nuclear Magnetic Resonance (1 H-NMR), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrometry (FTIR), and Size Exclusion Chromatography, among others) to test the proposed hypothetical SAP structure shown in **Figure 5**. In the succeeding section, a qualitative characterization of the polymers and SAP morphologies was conducted through optical microscopy. However, a more comprehensive characterization of these systems is required. This information will be provided in the upcoming work, which is beyond the scope of this chapter.

In the photomicrographs presented in **Figure 6(a)** is possible to qualitatively observe the morphology of the different polymer systems despite light interference [55]. The micrograph of the AP polymer in distilled water (**Figure 6(a1)**) reveals well-separated ramifications of aggregated macromolecules or clusters as previously reported for hydrophobically modified polyacrylamides [6, 40], while polymer B (**Figure 6(a2)**), HPAM (**Figure 6(a3)**), and the SAP (**Figure 6(a4)**) display extended macromolecular configurations. The polymer blend in **Figure 6(a4)** exhibits a more dense, well-aligned, and extended configuration of polymer structures. This macromolecular configuration results from the reciprocal charge repulsion among the anionic polymers stretching out the chains, which occupy a larger hydrodynamic volume because, minimum interchain interactions take place in distilled water [13, 26].

**Figure 6.** Polarized light micrographs of samples of baseline polymers and SAP system. (a) in distilled water and (b) in brine (8.4 wt%). Micrographs (1)–(4) correspond to polymers AP, B, HPAM, and the SAP system, respectively.

Viscoelasticity of a Supramolecular Polymer Network and its Relevance for Enhanced Oil Recovery

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103

**Figure 6(b1)**–**(b4)** demonstrate that in brine solution, the screening of the negative charges in the polymer chains causes the increase of intra- and interchain interactions among the anionic polymers. For instance, dense intra- and interchain hydrophobic interactions are visible for the associating polymer, AP, in **Figure 6(b1)**, in the form of a dense network that was not observed in distilled water (**Figure 6(a1)**). Micrographs in **Figure 6(b2)** and **(b3)** display branch-like fractal structures for polymer B and HPAM, which agree with previous research [56]. The screening of the negative charges in the polymer side chains causes the coiling/folding of the polymer chains that decreases the hydrodynamic volume of the macromolecules and the viscosity of the polymer solutions [13, 26]. By contrast, **Figure 6(b4)** exposes a network of fully entangled macromolecules. This high-density thread-like net reveals a homogeneous

web of intra- and interchain interactions among the anionic polymers.

of the curve functions of tan*δ*, *G*', *G*", and |*η*\*|.

**3. Effect of ionic strength on the viscoelasticity of the SAP system**

Three brine concentrations 2.1, 4.2, and 8.4 wt% (see **Table 1**) were employed to establish the effect of ionic strength on the viscoelasticity of the SAP system. **Figure 7** presents the frequency sweep of the SAP and baseline solutions in different brine concentrations in terms

The morphology of the baseline polymers samples and the optimum SAP was observed using a polarized light optical microscope (Olympus model GX41), equipped with an M Plan N 10×/0.25 ∞/-FN22n objective (Olympus), digital camera, and image analysis software (Lumenera model Infinity 2-2C). **Figure 6(a)** and **(b)** display the micrographs of the baseline polymers and SAP dissolved in distilled water and in brine (8.4 wt%), respectively. In these micrographs, **Figures 1**–**4** correspond to polymers AP, B, HPAM, and SAP respectively.

**Figure 5.** Proposed hypothetical structure of the SAP network.

Viscoelasticity of a Supramolecular Polymer Network and its Relevance for Enhanced Oil Recovery http://dx.doi.org/10.5772/intechopen.77277 103

crossover point (*G*' = *G*" and tan*δ* < 1 at *ω* = 0.1 rad/s), which indicates the formation of a more stable supramolecular system [4]. For this reason, PB # 4 was selected as the optimum SAP formulation. Hereafter, PB # 4 is designated as SAP, while PB # 1 is designated as the baseline

On the basis of the results obtained from oscillatory rheology in this exploratory research, a hypothetical structure of the optimum supramolecular polymer network is proposed in **Figure 5**, which shows the plausible reversible interactions taking place during self-aggrega-

Forthcoming research will characterize the structure of the optimum SAP system in depth,

Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrometry (FTIR), and Size Exclusion Chromatography, among others) to test the proposed hypothetical SAP structure shown in **Figure 5**. In the succeeding section, a qualitative characterization of the polymers and SAP morphologies was conducted through optical microscopy. However, a more comprehensive characterization of these systems is required. This information will be provided in the

The morphology of the baseline polymers samples and the optimum SAP was observed using a polarized light optical microscope (Olympus model GX41), equipped with an M Plan N 10×/0.25 ∞/-FN22n objective (Olympus), digital camera, and image analysis software (Lumenera model Infinity 2-2C). **Figure 6(a)** and **(b)** display the micrographs of the baseline polymers and SAP dissolved in distilled water and in brine (8.4 wt%), respectively. In these micrographs, **Figures 1**–**4** correspond to polymers AP, B, HPAM, and SAP respectively.

H Nuclear Magnetic Resonance (1

H-NMR),

system for comparison purposes.

employing several analytical techniques (i.e., 1

**Figure 5.** Proposed hypothetical structure of the SAP network.

upcoming work, which is beyond the scope of this chapter.

tion of the SAP network.

102 Polymer Rheology

**Figure 6.** Polarized light micrographs of samples of baseline polymers and SAP system. (a) in distilled water and (b) in brine (8.4 wt%). Micrographs (1)–(4) correspond to polymers AP, B, HPAM, and the SAP system, respectively.

In the photomicrographs presented in **Figure 6(a)** is possible to qualitatively observe the morphology of the different polymer systems despite light interference [55]. The micrograph of the AP polymer in distilled water (**Figure 6(a1)**) reveals well-separated ramifications of aggregated macromolecules or clusters as previously reported for hydrophobically modified polyacrylamides [6, 40], while polymer B (**Figure 6(a2)**), HPAM (**Figure 6(a3)**), and the SAP (**Figure 6(a4)**) display extended macromolecular configurations. The polymer blend in **Figure 6(a4)** exhibits a more dense, well-aligned, and extended configuration of polymer structures. This macromolecular configuration results from the reciprocal charge repulsion among the anionic polymers stretching out the chains, which occupy a larger hydrodynamic volume because, minimum interchain interactions take place in distilled water [13, 26].

**Figure 6(b1)**–**(b4)** demonstrate that in brine solution, the screening of the negative charges in the polymer chains causes the increase of intra- and interchain interactions among the anionic polymers. For instance, dense intra- and interchain hydrophobic interactions are visible for the associating polymer, AP, in **Figure 6(b1)**, in the form of a dense network that was not observed in distilled water (**Figure 6(a1)**). Micrographs in **Figure 6(b2)** and **(b3)** display branch-like fractal structures for polymer B and HPAM, which agree with previous research [56]. The screening of the negative charges in the polymer side chains causes the coiling/folding of the polymer chains that decreases the hydrodynamic volume of the macromolecules and the viscosity of the polymer solutions [13, 26]. By contrast, **Figure 6(b4)** exposes a network of fully entangled macromolecules. This high-density thread-like net reveals a homogeneous web of intra- and interchain interactions among the anionic polymers.
