2. Formulation of self-assembling systems

The associating polymers (APs) were provided by SNF Holding Co. (Riceboro, Georgia, USA). Two of these APs, designated as AP1 and AP2, display high grade of anionicity (hydrolysis degree: 25 – 30 mol% at room temperature) and high molecular weights (≈16 – 20 million Dalton). AP1 has a low hydrophobic content, while AP2 has a medium hydrophobic content. The third associating polymer, designated as AP3, has low anionicity (hydrolysis degree: 15 mol%), low molecular weight (8 – 12 million Dalton), and high hydrophobic content [6, 13, 14]. The relative hydrophobic contents of AP1, AP2, and AP3 are 1, 2, and 5 – 6, respectively [13]. APs are tolerant to high salinities at moderate temperatures [14]. The anionic surfactant, a primary alcohol alkoxy sulfate 30% active, was supplied by Sasol North America (Houston, Texas) [15]. β-Cyclodextrin (β-CD) Technical Grade Trappsol® was acquired from Cyclodextrins Technology Development Inc. (CDT, Inc. Alachua, Florida, USA). The assay of the β-CD powder was 98% (molecular weight: 1135 g/mol).

The SAP-AP systems were formulated in synthetic reservoir brines [16] and the effect of different concentrations of brine on the rheological properties of the SAP-AP systems was determined. Table 1 shows the compositions of the synthetic brines.

The formulation of the SAP-AP systems was based on a molar ratio of surfactant to β-CD of 2:1 established from our previous research [17–20]. In the initial formulation of the SAP-AP system, the concentration of polymer was kept fixed at 0.5 wt% in 2.1 wt% brine. Table 2 presents the experimental design applied for the SAP-AP formulation. All the experiments were duplicated or even triplicated, and the results presented are the average of several measurements.

Self-assembly was monitored through rheology by observing the changes in the elastic (G<sup>0</sup> ) and viscous behavior (G00), loss factor (tanδ = G00/G<sup>0</sup> ), and complex viscosity, |η\*|, relative to the baseline associating polymers [8–10, 12, 21]. The rheological analysis was conducted using a Bohlin Gemini HR Nano Rheometer manufactured by Malvern (Worcestershire,


Table 1. Synthetic brine compositions.

This work evaluated the generation of advanced polymer-surfactant systems built via noncovalent and host-guest interactions based on β-cyclodextrin that would be stable under harsh reservoir conditions. The aim was to formulate efficient, chemically stable, and cost-effective systems as an

Self-assembly allows the coassembly of two or more types of building blocks, resulting in increasingly structurally complex nanoassemblies that may have physical and chemical properties that are distinct from those of the original monostructures [7]. Host-guest interactions refer to the formation of supramolecular inclusion complexes based on macrocyclic molecules (i.e. host molecules) consisting of two or more entities connected via noncovalent interactions in a highly controlled and cooperative manner. These host-guest inclusions are relatively stable and provide reliable and robust connections for the fabrication of stimuli-responsive supramolecular systems [8]. Cyclodextrins (CDs) are the most used and affordable hosts in the field of

Supramolecular β-CD-based polymer systems retain their structural stability and functionality (i.e. self-healing) after exposure to externally applied stimuli or shear forces increasing the life span of these materials [8, 7]. The self-healing capability is highly dependent on the noncovalent connections in the polymer backbone and on the decomplexation and complexation of the supramolecular system [7, 8, 11, 12]. Therefore, supramolecular chemistry built on weak and reversible noncovalent interactions has emerged as a powerful and versatile strategy to design and fabricate materials with extraordinary reversibility and adaptivity

In this chapter, we first discuss the steps followed during the formulation of the SAP-AP systems and their rheological analysis. Secondly, we explore the effect of ionic strength on the rheological properties of the SAP-AP systems. Next, we discuss the combined effect of shear and ionic strength on the structural stability of the self-assembling systems. Finally, we summarize the short- and long-term thermal performance of the SAP-AP systems.

The associating polymers (APs) were provided by SNF Holding Co. (Riceboro, Georgia, USA). Two of these APs, designated as AP1 and AP2, display high grade of anionicity (hydrolysis degree: 25 – 30 mol% at room temperature) and high molecular weights (≈16 – 20 million Dalton). AP1 has a low hydrophobic content, while AP2 has a medium hydrophobic content. The third associating polymer, designated as AP3, has low anionicity (hydrolysis degree: 15 mol%), low molecular weight (8 – 12 million Dalton), and high hydrophobic content [6, 13, 14]. The relative hydrophobic contents of AP1, AP2, and AP3 are 1, 2, and 5 – 6, respectively [13]. APs are tolerant to high salinities at moderate temperatures [14]. The anionic surfactant, a primary alcohol alkoxy sulfate 30% active, was supplied by Sasol North America (Houston, Texas) [15]. β-Cyclodextrin (β-CD) Technical Grade Trappsol® was acquired from Cyclodextrins Technology Development Inc. (CDT, Inc. Alachua, Florida, USA). The assay of the β-CD

alternative to expensive chemical synthesis.

with potential applications in diverse fields [8].

2. Formulation of self-assembling systems

powder was 98% (molecular weight: 1135 g/mol).

inclusion chemistry [7, 9, 10].

202 Cyclodextrin - A Versatile Ingredient


\* AP: associating polymer: AP1, AP2, or AP3 mixed at a fixed concentration of 0.5 wt%.

\*\*S: surfactant.

\*\*\*SAP-AP: self-assembling polymeric system.

Table 2. Experimental design: SAP-AP formulations.

UK) equipped with parallel-plate measuring geometry (gap between the plates of 1000 μm) and solvent trap to avoid evaporation and/or drying effects. First, amplitude sweeps were run to determine the limit of the linear viscoelastic (LVE) range of the samples at 25�C; followed by frequency sweeps to establish the time-dependent deformation behavior [22]. G0 , G00, tanδ (G00/G<sup>0</sup> ), and |η\*| were plotted as a function of the angular frequency (ω) in logarithmic scales on both axis.

2.2. Effect of surfactant addition

2.1 wt% brine.

70 ppm, and for surfactant-AP3 ranged from 30 to 90 ppm.

2.3. Effect of the simultaneous addition of surfactant and β-CD

Figure 2(a–c) demonstrates the effect of the addition of surfactant on the viscoelastic properties of polymers AP1, AP2, and AP3. These plots reveal interactions (noncovalent associations) among the surfactant and polymers AP1, AP2, and AP3. The addition of surfactant increases the elasticity (tanδ decreases and G<sup>0</sup> increases) and viscosity of the samples (G<sup>00</sup> and |η\*| increase) relative to the respective baseline polymers. However, these plots also indicate that there is no a clear relationship between surfactant concentration and the improvement of the viscoelastic properties. For instance, the surfactant concentrations that render the best viscoelastic properties for surfactant-AP1 ranged from 30 to 70 ppm; for surfactant-AP2 was

Advanced Polymer-Surfactant Systems via Self-Assembling

http://dx.doi.org/10.5772/intechopen.74618

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Figure 3(a–c) demonstrates that the simultaneous addition of surfactant and β-CD produces strong noncovalent interactions and robust self-assembling. Self-aggregation significantly increases the viscoelastic properties of the different systems, specifically for the SAP-AP systems formulated using polymers AP2 (Figure 3(b)) and AP3 (Figure 3(c)). Furthermore, the

Figure 2. Oscillatory tests for surfactant/AP blends at different surfactant concentrations at 0.5 wt% polymer solution in
