Molecular Interactions of a Polyaromatic Surfactant C5Pe in Aqueous Solutions Studied by a Surface Forces Apparatus
Bibliographic record
Abstract
Studies on molecular mechanisms of polyaromatic surfactants in stabilizing water-in-oil (W/O) or oil-in-water (O/W) emulsions are of great scientific and practical importance. A polyaromatic surfactant N-(1-hexylheptyl)-N'-(5-carboxylicpentyl) perylene-3,4,9,10-tetracarboxylic bisimide (C5Pe) with well-defined molecular structure containing fused aromatic rings and heteroatoms similar to asphaltene molecules, was used in this study in an attempt to understand molecular interaction mechanisms of heavy oil components in aqueous solutions. A surface forces apparatus (SFA) was used to directly measure the molecular interactions of C5Pe. Solution pH, salt concentration and Ca(2+) addition showed a strong impact on molecular interactions between C5Pe adsorbed on mica surfaces. The repulsion observed between the two adsorbed C5Pe molecular layers was shown to have a steric and electrosteric origin. The force-distance profiles at short separation distances under high compression force were well fitted with the Alexander-de Gennes (AdG) model. At pH ≥ 4, the repulsive forces measured over a long separation distance under low compression force were shown to deviate from the AdG model but could be fitted with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, indicating an electrostatic origin of the observed repulsion due to ionization of -COOH groups. Adhesion between two C5Pe surfaces was shown to decrease sharply with increasing solution pH and salt concentration, being attributed to the decrease in surface hydrophobicity and hence hydrophobic attraction. Addition of Ca(2+) ions induced the formation of large C5Pe aggregates due to strong bonding of Ca(2+) with -COOH groups, leading to a longer range steric repulsion. Our results provide a new insight into the molecular interactions of polyaromatic surfactants at oil-water interfaces and in complex aqueous solutions.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".