Effectiveness of Low-Field NMR to Assess the Molecular Dynamics of Fatty Esters around the Glass Transition
Bibliographic record
Abstract
The molecular dynamics involved in the emergence of solidity in glass-forming organic esters are poorly understood. Some branched esters are examples of organic materials that do not crystallize under typical thermal protocols but form glasses at low temperatures. The present work investigates the solid-to-liquid phase transition of three fatty branched esters, which are synthetic mimics of compounds found in jojoba oil (so-called jojoba-like esters or JLEs), using low-field 1H NMR and differential scanning calorimetry (DSC). Spin–lattice and spin–spin relaxation times (T1 and T2, respectively) measured from the solid-arrested state to the fluid state provided information about the dynamics and structures of the JLEs below and above the glass transition temperature (Tg). The T1 and T2 state diagrams indicated that the transition involves an intermediary viscoelastic state similar to that observed in polymers. 1H NMR detected the transition because the backbone is “arrested” at the viscoelastic–fluid transition. Tg measured by DSC recorded the “arrest” of the molecules when the branches enter the glassy state deep in the viscoelastic state matching the lowest temperature singularity in the T1 and T2 state diagrams. The rotational correlation time determined using the Bloembergen–Purcell–Pound (BPP) theory indicated an Arrhenius function for T > Tg with an activation energy of 26.1 kJ·mol–1 similar to those of other organic glass formers. The minimum of the coupling constant × T1 (KT1) technique and simultaneous solution of the BPP expressions showed that the distance between neighboring protons remains constant in the glassy state (rg = 2.09 Å) and increases almost linearly in the viscoelastic and fluid states.
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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 | 0.003 | 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 | 0.001 |
| 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".