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Effect of Polymer Concentration on the Rheology and Surface Activity of Cationic Polymer and Anionic Surfactant Mixtures

This study examines how CHEC polymer concentration changes the rheology, surface tension, and electrical conductivity of CHEC–sodium lauryl sulfate mixtures, using pendant-drop surface-tension measurements to map surface activity across the composition range.

At-a-Glance Summary

Primary surface measurement reported

Surface tension of surfactant solutions and surfactant–polymer solutions, measured across CHEC concentrations of 1000–4000 ppm and surfactant concentrations of 0–500 ppm.

Dropometer attribution in the paper

The paper attributes surface-tension measurements to a “pendant drop tensiometer” manufactured by Droplet Lab, Markham, ON, Canada, with droplet profiles fit to the Young–Laplace equation.

How the surface-tension / contact-angle data were used in the study

The surface-tension data were used to compare pure polymer, pure surfactant, and polymer–surfactant mixtures, to locate minima versus surfactant concentration, and to track how those minima shifted as polymer concentration increased. The paper also compares the surface-tension minima with maxima in consistency index to interpret coupled changes in surface activity and rheology.

Replication / reliability statement

Surface tension was measured twelve times for each fluid and averaged; for the 2000 ppm CHEC series, the paper reports small standard deviations across the surfactant concentration sweep.

Paper Details

Title
Effect of Polymer Concentration on the Rheology and Surface Activity of Cationic Polymer and Anionic Surfactant Mixtures
Authors
Chung-Chi Sun and Rajinder Pal
Journal
Fluids
Year
2025
Volume
10
Pages / Article
253
DOI
10.3390/fluids10100253
License
CC BY 4.0

Journal context

What it is
Journal-level metrics for the publication venue (not a rating of this specific article).
How to read it
Compare metrics within category; updates are annual and lag current-year publications.

Scopus metrics (Elsevier / Scopus rating 2024)

CiteScore 2024

4.0

CiteScore subject ranks (CiteScore 2024)
  • Q2 - Mechanical Engineering (269/720)
  • Q2 - Fluid Flow and Transfer Processes (39/97)
  • Q2 - Condensed Matter Physics (195/443)
SJR 2024

0.432

Journal Impact Factor (Clarivate JCR)

Journal Impact Factor (JCR 2024)

1.8

5-Year Impact Factor

1.9

JCR category rank

Q3 - Physics, Fluids & Plasmas (24/40)

What Was Measured

Primary surface / interfacial measurement

Surface tension was measured for surfactant solutions and surfactant–polymer solutions at room temperature using the pendant droplet method. The study uses these measurements as its direct readout of surface activity across the CHEC/Stepwet composition sweep.

Supporting measurements

Steady rheological properties were measured and described with the power-law model through the consistency index K and the flow behavior index n. Electrical conductivity was also measured to compare ionic changes alongside rheology and surface activity.

Role of the Dropometer

For surface-tension measurements, the paper describes a pendant drop tensiometer manufactured by Droplet Lab, Markham, ON, Canada. A pendant droplet was generated, imaged at high resolution using a smartphone camera, and analyzed in specialized software by fitting the droplet profile with the Young–Laplace equation to estimate surface tension.

These measurements were used to show how surface activity changed with surfactant concentration, how that response depended on CHEC concentration, and where the surface-tension curves aligned with maxima in consistency index.

Method Snapshot

Method Snapshot Table

System / series CHEC polymer concentration Sodium lauryl sulfate / Stepwet DF-95 concentration Surface-tension role in the paper Supporting measurements Instruments Conditions Notes
Polymer-only CHEC solutions 1000, 2000, 3000, 4000 ppm 0 ppm Establishes the polymer-only surface-tension baseline versus polymer concentration Electrical conductivity; shear stress, viscosity, and power-law parameters K and n Pendant drop tensiometer; Thermo Orion 3 Star conductivity meter; Fann 35A/SR-12 and Haake Roto-visco RV 12 with MV I viscometers Polymer solutions prepared in batches of about 1 kg at 22 ± 1 °C; mixed with Gifford-Wood homogenizer for nearly 1 h; measurements at room temperature (≈22 °C) Figure 3 shows surface tension almost independent of polymer concentration
Pure surfactant comparison 0 ppm 0–500 ppm Provides the surfactant-only surface-tension curve used for comparison against polymer–surfactant mixtures Pendant drop tensiometer Room temperature surface-tension measurement Pure surfactant surface-tension plots are shown in Figure 7 for comparison
CHEC–surfactant mixture sweep 1000 ppm 0–500 ppm Tracks how surface tension changes with surfactant concentration at the lowest CHEC level Electrical conductivity; power-law K and n Pendant drop tensiometer; Thermo Orion 3 Star conductivity meter; Fann/Haake viscometers Known surfactant added to polymer solution and mixed thoroughly for about 1 h at room temperature; air entrapment avoided Figures 7a and 8a
CHEC–surfactant mixture sweep 2000 ppm 0–500 ppm Tracks surface-tension minimum behavior at intermediate surfactant concentration Electrical conductivity; power-law K and n Pendant drop tensiometer; Thermo Orion 3 Star conductivity meter; Fann/Haake viscometers Known surfactant added to polymer solution and mixed thoroughly for about 1 h at room temperature; room-temperature measurement Figures 7b and 8a; Table 3 reports mean and standard deviation values
CHEC–surfactant mixture sweep 3000 ppm 0–500 ppm Tracks the higher-polymer surface-tension response across the surfactant sweep Electrical conductivity; power-law K and n Pendant drop tensiometer; Thermo Orion 3 Star conductivity meter; Fann/Haake viscometers Known surfactant added to polymer solution and mixed thoroughly for about 1 h at room temperature; room-temperature measurement Figures 7c and 8a
CHEC–surfactant mixture sweep 4000 ppm 0–500 ppm Tracks the highest-polymer surface-tension response across the surfactant sweep Electrical conductivity; power-law K and n Pendant drop tensiometer; Thermo Orion 3 Star conductivity meter; Fann/Haake viscometers Known surfactant added to polymer solution and mixed thoroughly for about 1 h at room temperature; room-temperature measurement Figures 7d and 8a
Reliability series for surface tension 2000 ppm 0, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500 ppm -Quantifies mean surface tension, standard deviation, and error bars for a full concentration sweep Pendant drop tensiometer Twelve measurements per fluid at room temperature; average value reported Table 3 and Figure 11

Key Findings

CHEC alone changed surface tension very little

For polymer-only CHEC solutions, surface tension was almost independent of polymer concentration and only slightly less than that of water. In the same series, conductivity increased with polymer concentration.

Polymer–surfactant mixtures were markedly more surface active

The surface tension of polymer–surfactant mixtures was substantially lower than that of the surfactant solution without polymer. The paper states that, at the same surfactant concentration, this indicates polymer–surfactant complexes were more surface active than surfactant molecules.

Surface-tension minima shifted with polymer concentration

At a given polymer concentration, surface tension dropped and passed through a minimum at intermediate surfactant concentration. The paper concludes that this minimum shifted to higher surfactant concentration as polymer concentration increased; for the 2000 ppm CHEC series, Table 3 shows a minimum mean surface tension of 27.058 mN/m at 250 ppm surfactant.

Surface and rheology extrema tracked together

The surface-tension plots were consistent with the rheological data in that the consistency index exhibited a maximum where surface tension was minimum. The consistency-index maximum shifted from 100–200 ppm surfactant at 1000 ppm CHEC to 400–500 ppm surfactant at 4000 ppm CHEC.

Higher polymer loading strengthened the mixture response

At any given surfactant concentration, increasing polymer concentration raised the consistency index and generally lowered the flow behavior index, making the mixtures more shear-thinning. In the same fixed-surfactant comparison, surface tension decreased substantially and conductivity increased with increasing polymer concentration.

Surface-tension measurements were repeatable

Surface tension was measured twelve times per fluid and averaged. For the 2000 ppm CHEC series, the paper reports small variability around the mean across the full surfactant concentration sweep, and Figure 11 shows correspondingly small error bars.

Thresholds / Regimes

The paper identifies surfactant-concentration windows where the mixture response changes direction, expressed as maxima in consistency index and corresponding minima in surface tension. These response windows move to higher surfactant concentration as CHEC concentration increases.
CHEC polymer concentration (ppm) Response feature reported by authors Stepwet concentration (ppm) How determined in the paper Surface-tension context reported Figure / table
1000 Maximum in consistency index 100–200 Stated in the Figure 5 discussion and in the Conclusions Low-polymer series described as showing a minimum at intermediate surfactant concentration Figure 5a, Figure 7a, Conclusions
2000 Maximum in consistency index 200–300 Stated in the Figure 5 discussion and in the Conclusions Table 3 reports a minimum mean surface tension of 27.058 mN/m at 250 ppm Figure 5b, Figure 7b, Table 3, Figure 11, Conclusions
3000 Maximum in consistency index 300 Stated in the Figure 5 discussion and in the Conclusions The low-surface-tension response is shifted toward higher surfactant concentration Figure 5c, Figure 7c, Conclusions
4000 Maximum in consistency index 400–500 Stated in the Figure 5 discussion and in the Conclusions The low-surface-tension response is shifted toward the highest surfactant concentrations in the sweep Figure 5d, Figure 7d, Conclusions

Figures & Visuals

Figure 3 — baseline surface activity of CHEC solutions

What it shows

Shows conductivity and surface tension for polymer-only CHEC solutions, establishing that surface tension changes little with polymer concentration before surfactant is added.

Figure 7 — composition sweep within each polymer level

Why it matters

Shows conductivity and surface tension versus surfactant concentration for 1000, 2000, 3000, and 4000 ppm CHEC, alongside the pure surfactant comparison curve.

Figure 8 — cross-comparison across polymer concentrations

What it shows

Shows that, at a given surfactant concentration, surface tension decreases substantially as polymer concentration increases.

Figure 11 — reliability of the 2000 ppm CHEC surface-tension series

What it shows

Shows error bars on the 2000 ppm CHEC surface-tension data, matching the mean and standard deviation values reported in Table 3.

Why It Matters

The paper frames polymer–surfactant interactions as important to applications such as enhanced oil recovery, hydraulic fracturing and drilling fluids, and formulated products. In that context, surface tension served as the study’s direct measure of surface activity alongside rheology and conductivity.

Here, the pendant-drop data did more than show that mixtures lowered surface tension. They helped locate the composition ranges where behavior changed, showed that the low-surface-tension response moved as CHEC concentration changed, and reinforced the paper’s conclusion that surface-active and rheological changes were linked across the formulation sweep. The authors discuss charge neutralization and entanglement at lower surfactant addition, and recharging and disentanglement at higher surfactant addition, as a possible explanation for these coordinated trends.

Practical Takeaways

Use surface tension to locate composition windows

In this study, surface-tension minima marked the same composition region where the consistency index reached a maximum.

Expect the surfactant window to move with polymer loading

As CHEC concentration increased from 1000 to 4000 ppm, the response shifted to higher sodium lauryl sulfate concentrations.

Keep polymer-only and surfactant-only baselines in view

The paper used both baselines to show that CHEC alone had little effect on surface tension, while polymer–surfactant mixtures were much more surface active.

Read surface tension together with rheology and conductivity

The authors used all three measurements to interpret how mixture behavior changed across composition.

Build repeat measurements into the workflow

Each fluid was measured twelve times for surface tension and averaged, and the 2000 ppm series showed small standard deviations across the sweep.

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