Nonequilibrium Liquid–Liquid Phase Separation of Poly(<i>N</i>-isopropylacrylamide) in Water/Methanol Mixtures
Bibliographic record
Abstract
At room temperature, poly( N -isopropylacrylamide) (PNIPAM) is soluble in water and in methanol. Within intermediate mixing ratios of the two solvents, the PNIPAM coils collapse into insoluble globules, a phenomenon known as co-nonsolvency. Visual observation of mixed PNIPAM/water/methanol systems (polymer concentration ≥10 g L –1, M n 80 000 g L –1 ) revealed that mixtures of methanol volume fractions (ϕ M ) ranging from 0.57 to 0.65 undergo macroscopic liquid–liquid phase separation (MLLPS) at 21 °C. MLLPS took place over a wider composition range (0.25 < ϕ M < 0.60) for water/methanol mixtures containing a polymer sample bearing n -butyl end-groups (PNIPAM-45K (10.0 g L –1, M n 44 500 g mol –1 ), but systems containing a polymer with chloroethyl end-groups (PNIPAM-Cl) (10.0 g L –1, M n 44 500 g mol –1 ) did not undergo MLLPS over the entire mixing ratio span. Observation by fluorescence microscopy of a demixed PNIPAM-45K/water/methanol sample containing trace amounts of pyrene-labeled PNIPAM revealed that the rim of the heavy phase droplets is enriched in PNIPAM, which may affect the stability/coalescence of the droplets. 1 H NMR spectroscopy analysis of the heavy and light phases formed in demixed PNIPAM-45K/water/methanol samples indicated that the heavy liquid phase is enriched in PNIPAM and in water compared to the nominal composition of mixtures as prepared. A temperature/composition map (−40 °C < T < +45.5 °C) of PNIPAM-45K/water/methanol is reported, based on visual observations of samples prepared and stabilized at 21 °C. Interestingly, the macroscopically demixed samples were never transparent: one or both liquid phases remained cloudy or opaque independently of their history over experimentally undefined long times, implying that the samples reached metastability. The equilibrium state of lowest free energy that corresponds to the coexistence of two transparent phases was never attained.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".