Domain: Natural Science — Chemistry
Target concept: Solid particles gradually swell, soften, and eventually dissolve, resulting in a homogeneous and transparent liquid system.

Video generation prompt: A dilute hydrochloric acid solution is placed in a test tube, and an appropriate amount of solid aliphatic polyester (e.g., PLA) particles is added. The test tube is heated, and changes in the particle morphology are recorded.

Evaluation guide:
(i) Target concept: Acid-catalyzed hydrolytic degradation of an aliphatic polyester (e.g., PLA) in aqueous HCl under thermal activation.
Minimum mechanism: Presence of H+ ions and elevated temperature must jointly enable nucleophilic water attack on the carbonyl carbon of the ester linkages; chain scission increases solubility and reduces the polymer's glass transition temperature, enabling macroscopic swelling and softening prior to full solvation. Because the hydrolysis monomers of an aliphatic polyester (e.g., lactic acid from PLA) are water-soluble, the end state is a clear, homogeneous solution; this outcome is specific to aliphatic polyesters and would not hold for an aromatic polyester such as PET, whose hydrolysis product (terephthalic acid) is essentially water-insoluble and would instead leave a cloudy precipitate.
(ii)Storyline: [Frame 0–2] Static shot: upright test tube containing transparent liquid, empty space above meniscus. [Frame 3–4] Polyester particles released from tweezers/spoon, falling vertically into liquid under gravity. [Frame 5–6] Particles rest at bottom, angular and discrete. [Frame 7–12] Flame appears beneath tube base; particles begin increasing in apparent size while retaining shape (swelling). [Frame 13–18] Particle edges blur, corners round, surfaces smooth (softening); no fragmentation. [Frame 19–24] Particles lose all discrete silhouette, fading uniformly into background liquid clarity (dissolution). [Frame 25+] Final state: motionless, fully transparent, homogeneous liquid; no bubbles, haze, or sediment. All phases occur within fixed viewpoint, no camera movement, no cuts, no occlusion of reaction zone.

Manual:
Experimental Procedure
1. Place dilute hydrochloric acid solution in a clear test tube.
2. Add solid aliphatic polyester (e.g., PLA) particles to the solution.
3. Heat the test tube uniformly at the base using a flame or hot plate.
4. Record continuous visual changes in particle morphology.
Observation of Experimental Phenomena
Solid polyester particles gradually swell in volume, lose angular edges and become rounded (softening), then fully disappear, yielding a homogeneous transparent liquid with no residue.
Summary of Experimental Principles
Aliphatic polyester (e.g., PLA) undergoes acid-catalyzed hydrolysis in warm dilute HCl: ester bonds cleave, breaking the polymer chain into water-soluble monomers and oligomers (e.g., lactic acid) — causing progressive swelling, softening, and eventual dissolution into a homogeneous, optically clear solution. (This clear outcome depends on the polyester being aliphatic; an aromatic polyester such as PET would instead hydrolyze to insoluble terephthalic acid and leave a cloudy precipitate rather than dissolve.)

Prompt Grounding rubric:
level_1: No test tube is shown, no dilute hydrochloric acid is visible, no solid polyester particles appear, no heating action is depicted, and no change in particle shape is observable anywhere in the clip.
level_2: A test tube holding some liquid appears, but the liquid does not read as a dilute aqueous acid (wrong color, cloudy, or no supporting context); the added solid is not recognizable as polyester particles (e.g., it looks like sugar, salt, or a metal shaving); no flame or hot plate is visible beneath the tube; and the particles are never shown contacting the liquid.
level_3: A test tube holds a transparent liquid; solid polyester (e.g., PLA) particles are dropped into it; a flame or hot plate is visibly applied to the tube's base; the particles are confirmed present before heating begins, but no gradual change in particle shape is shown, only a static before-and-after with no visible swelling or softening in between.
level_4: All required elements are present and identifiable: a clear cylindrical test tube, a transparent liquid consistent with dilute aqueous acid, white or off-white granular polyester (e.g., PLA) particles, and a visible flame or hot plate heating the tube's base; the particles are shown entering and settling in the liquid, and heating begins while they are submerged; at least two distinct states are visible (intact angular particles, then visibly swollen/rounded particles), but one later transition (softening into full dissolution) is unclear due to motion blur, occlusion, or low contrast.
level_5: Every element is unambiguous and in context: an identifiable test tube; a transparent, colorless liquid filling roughly the lower third to half of the tube; discrete, opaque white granular polyester (e.g., PLA) particles fully submerged; a visible flame or hot plate beneath the tube; and a single continuous shot showing the particles start angular and separate, gradually swell and lose their sharp edges, become rounded and semi-deformed, and finally disappear from view with no residue left behind, all without a cut or camera reposition.

Scientific and Causal Correctness rubric:
level_1: The liquid is colored, opaque, or visibly viscous from the start; the particles stay rigid and unchanged the whole time; the particles dissolve the instant they touch the liquid with no visible swelling or softening; the particles vanish before any heating begins; or the liquid turns cloudy or forms a precipitate after heating.
level_2: The liquid looks aqueous but takes on an unexpected color or turbidity as it heats; the particles shrink or break apart instead of swelling; the particles melt into rounded droplets (a sign of simple thermoplastic melting rather than acid hydrolysis); dissolution happens with no visible swelling or shape change beforehand; or the final liquid is cloudy, layered, or still holds visible undissolved bits.
level_3: The particles visibly swell (grow larger while still recognizable as separate granules) and then soften (lose their sharp corners and round off) as they heat, and only dissolve after both of those stages; the final liquid is clear and uniform, but one stage is misrepresented, e.g., the swelling looks instantaneous rather than gradual, the softening stage is skipped (angular particles going straight to gone), or a faint haze or speck remains after dissolution.
level_4: Swelling shows up as a gradual, visible increase in particle size while the particles stay opaque and separate; softening shows up as a gradual rounding-off of edges with no fragmentation; dissolution shows up as the particles' outlines fading away completely with no lingering specks, streaks, or cloudiness; the final liquid is fully clear and uniform, but either one particle skips the swelling stage before dissolving, or a brief patch of bubbling or steam mist momentarily obscures part of the sequence without otherwise breaking the causal order.
level_5: Every particle goes through an unbroken sequence: starts as a sharp-edged granule, visibly grows in apparent volume while staying opaque and distinct (swelling), gradually rounds off and blurs at the edges with no breakage (softening), and finally loses its outline entirely with no leftover texture or haze (dissolution), ending in a still, uniform, fully transparent liquid consistent with an aliphatic polyester's (e.g., PLA) acid hydrolysis into water-soluble monomers, with nothing resembling melting, charring, foaming, layering, or an unexpected color change.

Spatiotemporal Consistency rubric:
level_1: The test tube abruptly appears in a different spot or orientation with no motion shown getting there; a particle appears or disappears with no visible path into or out of the liquid; the liquid's surface level changes abruptly with no gradual transition; the flame's brightness swings wildly, with intensity changes more than 3 times per second; the lighting shifts from warm to cool partway through the clip; or the tube tilts more than 15° with nothing visibly holding or supporting it.
level_2: The test tube wobbles hard or tilts more than 20° without any visible cause; a particle appears to rise upward against gravity before settling; the liquid's surface ripples in a way that doesn't match where the flame is (e.g., agitation at the top while the flame heats the bottom); the flame's shadow jumps sideways by more than a quarter of the tube's width between one moment and the next; or background elements visibly warp or shear.
level_3: The test tube stays upright and in place; particles fall smoothly into the liquid under gravity; the heat source stays fixed relative to the tube's base; the liquid surface shows gentle, natural-looking ripples as it heats; the flame or hot plate's glow stays steady aside from ordinary flicker; nothing blocks the reaction zone for more than a moment, but one small flaw remains, such as a particle briefly freezing in place for an instant amid otherwise continuous motion, or a brief loss of focus on the particles.
level_4: The tube stays centered and steady in frame; particles descend straight down into the liquid with no sideways drift; the heat source stays fixed beneath the tube's base; the liquid's surface motion matches the heating physically; the flame's size and brightness vary only within ordinary flicker; there is no warping, stretching, or shearing of any object, but one subtle flaw remains, such as a brief lens flare over the particles, or the tube appearing to drift very slightly in position for an instant.
level_5: The test tube stays in the same position, orientation, and scale across the entire clip; particles follow a smooth, gravity-consistent path down into the liquid with no motion blur that looks faster or slower than their actual speed; the liquid's surface ripples spread naturally outward from the heated zone; the flame flickers only in the ordinary, natural way with no strobing or sudden shape collapse; and nothing in the shot drops a frame, loses focus, shifts perspective, or has a lighting discontinuity.