Primary surface measurement reported
Surface tension of polymer–surfactant solutions measured at room temperature (reported as surface tension vs. surfactant concentration plots).
Client Citation Analysis
Steady Shear Rheology and Surface Activity of Polymer–Surfactant Mixtures
This study investigates how five surfactants affect steady-shear rheology and “surface activity” by tracking electrical conductivity and pendant-drop surface tension in two polymer systems (LR-400 and Praestol 2540TR) in water.
At-a-Glance Summary
How the paper credits the instrument
Section 2.4, verbatim: "The surface tension of the solutions was measured at room temperature using a smartphone-based tensiometer and the ADSA (Axisymmetric Drop Shape Analysis) method. The instrument was supplied by Droplet Lab, Markham, ON, Canada."
How the surface-tension data were used in the study
Surface tension vs. surfactant concentration curves (paired with conductivity curves) were used to discuss surface activity and to estimate approximate CAC (critical aggregation concentration) and PSP (polymer saturation point) based on slope changes.
Replication / reliability statement
Each solution’s surface tension was measured 12 times and averaged; the authors describe the measurements as “very consistent” and use this to support method reliability.
What the Droplet Lab instrument did and did not do
The Droplet Lab tensiometer measured surface tension only. The paper's headline result (how five surfactants change the steady shear rheology of two polymers) came from a Fann 35A/SR 12 coaxial cylinder viscometer, and the paired conductivity data came from a Thermo Orion 3 Star meter. Of the paper's 25 figures, 2 show chemical structures (Figures 1 and 2), 11 are rheology only (Figures 3 to 13), 10 plot surface tension and conductivity together on shared axes, and 2 panels (19b and 25b) are surface tension alone.
Paper Details
Title
Steady Shear Rheology and Surface Activity of Polymer-Surfactant Mixtures
Authors
Qiran Lu; Rajinder Pal (corresponding author)
Journal
Polymers
Year
2025
Volume
17
Pages / Article
364
License
Open access; Creative Commons Attribution (CC BY) license (CC BY 4.0)
9.7
Scopus metrics (Elsevier / Scopus rating 2024)
Scopus metrics (Elsevier / Scopus rating 2024)
CiteScore subject ranks (CiteScore 2024)
- Q1 - Chemistry (all) (58/404)
- Q1 - Materials Science: Polymers and Plastics (25/167)
1.227
Scopus metrics (Elsevier / Scopus rating 2024)
0.918
Scopus metrics (Elsevier / Scopus rating 2024)
4.9
Journal Impact Factor (Clarivate JCR)
5.2
Journal Impact Factor (Clarivate JCR)
Q1 - Polymer Science (19/94)
Journal Impact Factor (Clarivate JCR)
What Was Measured
Primary surface / interfacial measurement
Surface tension of aqueous polymer–surfactant solutions at room temperature, obtained from pendant-drop measurements analyzed using ADSA with a smartphone-based tensiometer
Supporting measurements
Electrical conductivity of polymer–surfactant solutions (used alongside surface tension to interpret concentration-dependent behavior).
Steady-shear rheology (shear stress vs. shear rate and viscosity vs. shear rate), including power-law model parameters K (consistency index) and n (flow behavior index).
Surface tension
Smartphone-based tensiometer (Droplet Lab, Markham, ON, Canada) using ADSA (Axisymmetric Drop Shape Analysis)
Rheology
Fann 35A/SR 12 coaxial cylinder viscometer (Fann Instrument Company, Houston, TX, USA)
Electrical conductivity
Thermo Orion 3 Star conductivity meter (Thermo Fischer Scientific Inc., Beverly, MA, USA)
Role of the Droplet Lab instrument
The paper reports surface tension measured with "a smartphone-based tensiometer and the ADSA (Axisymmetric Drop Shape Analysis) method," with the instrument "supplied by Droplet Lab, Markham, ON, Canada" (Section 2.4). The paper does not name a product model. A pendant droplet is formed at the tip of a needle or capillary, back-illuminated, imaged at high resolution using a smartphone camera, and analyzed with specialized software that calculates surface tension numerically from the droplet geometry.
These surface-tension outputs are used throughout the “surface activity” results to compare surfactant effectiveness and to estimate approximate CAC and PSP values from changes in slope of surface-tension–concentration plots (often considered alongside conductivity plots).
Bring This Measurement Into Your Lab
If you need surface tension across a surfactant concentration series in polymer solutions, we can show you the same pendant drop workflow on your samples.
Key Findings
Surface tension decreases, then levels off at higher surfactant concentration
In the LR-400 mixtures (and for Amphosol and Alfonic in Praestol 2540TR), the surface tension decreases as surfactant concentration increases and tends to level off at higher concentrations. The authors interpret the initial decrease as adsorption at the air–water interface and the leveling behavior as saturation of the interface by surfactant–polymer complexes and surfactant molecules.
Amphosol is the most effective surface-tension reducer in both polymer systems
In the cross-surfactant comparisons (LR-400: Figure 19b; Praestol 2540TR: Figure 25b), Amphosol is identified as the most effective surfactant in reducing surface tension at a given concentration.
LR-400 system: surface-tension ranking across surfactants at fixed concentration
For surfactant/LR-400 polymer solutions, at any given surfactant concentration, the surface tension order reported is: Stepwet > Stepanol > HTAB > Alfonic > Amphosol.
Praestol 2540TR system: surface-tension ranking across surfactants at fixed concentration
For surfactant/Praestol 2540TR polymer solutions, at any given surfactant concentration, the surface tension order reported is: HTAB > Stepanol ≥ Stepwet > Alfonic > Amphosol.
CAC/PSP values are treated as approximate based on slope changes
The authors use changes in slope of surface tension vs. concentration plots (and paired conductivity plots) to estimate CAC and PSP values, and note that the plots do not show “sharp enough breaks” to draw definite conclusions; they also mention alternative methods (e.g., calorimetry or spectroscopy) as possible validation approaches.
Anionic surfactants strongly thicken the cationic polymer
Stepanol WA-100 and Stepwet DF-95 sharply raise the consistency index and lower the flow behaviour index of cationic LR-400 solutions above 100 ppm, making them more viscous and more shear-thinning. The authors attribute this to charge neutralisation and polymer chain entanglement between the oppositely charged pair.
Surfactants barely affect the anionic polymer
None of the five surfactants strongly influences the rheology of anionic Praestol 2540TR. Interaction strength runs HTAB > Amphosol > Stepanol = Stepwet = Alfonic. The authors attribute the negligible effect of the anionic surfactants to electrostatic repulsion between like-charged species, which hinders changes in the entanglement and network structure.
Figures & Visuals
What it shows
Shows electrical conductivity and surface tension versus Stepanol concentration in surfactant + LR-400 solutions, with CAC/PSP indicated in the plotted trends.
What it shows
Compares surface tension behavior across the five surfactants at matched concentration in the LR-400 polymer solution, including the reported surface-tension ordering and identification of Amphosol as most effective.
What it shows
Shows electrical conductivity and surface tension versus Stepanol concentration in surfactant + Praestol 2540TR solutions, illustrating the concentration dependence used for CAC/PSP estimation.
What it shows
Compares surface tension behavior across the five surfactants at matched concentration in the Praestol 2540TR polymer solution, including the reported surface-tension ordering and identification of Amphosol as most effective.
Why It Matters
The paper frames polymer–surfactant interactions as important for designing advanced fluid systems used in applications such as enhanced oil recovery, drilling, and chemical processing. Within that scope, the surface-tension measurements, together with conductivity, provide the “surface activity” component of the study, enabling direct comparison of how surfactant type influences the air–water interface behavior across the two polymer systems.
By pairing surface tension with conductivity versus surfactant concentration, the authors use the Droplet Lab smartphone-based tensiometer (ADSA) to interpret adsorption/saturation behavior and to read approximate CAC and PSP regime markers from paired surface tension and conductivity curves. The authors are explicit that this pairing did not resolve the transitions cleanly: "The break points... are not sharp enough to estimate the critical aggregation concentration (CAC) and polymer saturation point (PSP) accurately," and they suggest calorimetry or spectroscopy as possible validation methods.
Expert Perspective
Practical Takeaways
Most effective surfactant in these tests
Amphosol CG is identified as the most effective surfactant for reducing surface tension at a given concentration in both LR-400 and Praestol 2540TR polymer solutions.
Common concentration-response shape
The paper describes surface tension curves that drop sharply at low surfactant concentration and level off at higher concentration, interpreted as interface saturation behavior.
Use CAC/PSP values as approximate regime markers
The authors state the plots do not exhibit sharp enough breaks for definite CAC/PSP determination and present CAC/PSP values as approximate, with calorimetry/spectroscopy mentioned as potential validation approaches.
Surfactant-dependent response differences in Praestol 2540TR
The paper notes that for Amphosol and Alfonic the surface tension drops sharply then levels off, while for Stepanol, Stepwet, and HTAB the decrease is more gradual in the Praestol 2540TR system.
Frequently Asked Questions
What did the Droplet Lab tensiometer measure in this study?
The authors measured the surface tension of aqueous polymer and surfactant solutions at room temperature with a smartphone based tensiometer supplied by Droplet Lab, using pendant drops analyzed by Axisymmetric Drop Shape Analysis (ADSA). Five surfactants were tested with two polymers, cationic LR-400 at 5000 ppm and anionic Praestol 2540TR at 500 ppm, and each solution was measured 12 times and averaged.
What were the key surface tension results?
With LR-400, surface tension dropped sharply at first and then levelled off as surfactant concentration increased, which the authors attribute to saturation of the air and water interface by surfactant and polymer complexes and surfactant molecules. With Praestol 2540TR the same pattern was seen for Amphosol and Alfonic, while Stepanol, Stepwet and HTAB lowered surface tension more gradually. In both polymer systems, Amphosol was the most effective surfactant at reducing surface tension at a given concentration.
What did the paper conclude about CAC and PSP?
The authors used changes in slope of the surface tension and conductivity plots to estimate approximate critical aggregation concentration (CAC) and polymer saturation point (PSP) values, for example CAC = 50 ppm and PSP = 350 ppm for Stepanol with LR-400. They state the breaks were not sharp enough to determine these points accurately and suggest that methods such as calorimetry or spectroscopy could be used to validate them.