The Effect of Salt on the Water Structure at a Charged Solid Surface: Differentiating Second- and Third-order Nonlinear Contributions
Bibliographic record
Abstract
We have used visible-infrared sum-frequency generation spectroscopy to reveal fundamental characteristics of water structure at the fused silica surface. By studying a wide range of ionic strengths, from 0.05 mM to 4 M, we are able to comment on the contributions of second- and third-order nonlinearities to the spectroscopic response. Spectra obtained from extremely dilute salt concentrations provide evidence of the previously sought increasing surface charge with ionic strength. This is followed by a screening regime where the extent to which the surface field penetrates into the bulk is limited by the electrolyte. Data from intermediate salt concentrations reveal a few strongly ordered layers of water immediately adjacent to the surface. At high concentrations, we observe a significant disruption of solvent ordering. Together, the observation of these four distinct regimes provides a unified understanding of interfacial water structure in the presence of salt that consolidates previous reports in the literature.
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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 | 0.001 |
| 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 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".