Domain: Engineering — Materials Science & Engineering
Target concept: Cationic dyes adsorbed on negatively charged textile fibers

Video generation prompt: The fabric samples of natural cotton and synthetic polyester were placed side by side in water containing cationic dye, then lifted together and rinsed under running tap water.

Evaluation guide:
(i) Target concept: Selective adsorption of cationic dyes driven by electrostatic attraction to anionic sites on cellulose.
Minimum mechanism: Cotton must present a net negative surface charge in water, arising mainly from preferentially adsorbed hydroxide ions and trace carboxyl groups introduced during fiber processing, rather than from deprotonation of cellulose's hydroxyl groups (whose pKa lies far above neutral pH); cationic dye must be present as solvated cations; polyester must remain inert due to its non-ionic, hydrophobic surface.
(ii)Storyline: Frame 0–2: Two distinct fabric samples (visually distinguishable by texture/label) placed adjacent in colored liquid inside static container. Frame 3–5: Both fabrics lifted upward together, maintaining fixed lateral spacing, emerging coated with liquid. Frame 6–9: Continuous stream of clear water flows over both fabrics; cotton retains color, polyester sheds all dye visibly. Perspective: Fixed frontal view, full-frame composition showing container base, fabric pair, and rinse zone; no cuts or viewpoint shifts; all causal transitions (immersion → lift → rinse → outcome) must be temporally contiguous and spatially unbroken.

Manual:
Experimental Procedure
1. Place one natural cotton fabric sample and one synthetic polyester fabric sample side-by-side in a transparent container filled with colored cationic dye solution.
2. Lift both samples together vertically out of the solution.
3. Rinse both samples simultaneously under continuous running tap water.
Observation of Experimental Phenomena
After rinsing, cotton fabric retains strong, uniform dye color; polyester fabric remains undyed and unchanged in appearance.
Summary of Experimental Principles
Cationic dyes carry positive charge and adsorb strongly onto cotton's negatively charged fiber surface — a charge that comes mainly from adsorbed hydroxide ions and minor carboxyl groups picked up during processing, not from deprotonation of cellulose's hydroxyl groups; polyester lacks ionizable surface groups and exhibits negligible electrostatic affinity for cationic dyes.

Prompt Grounding rubric:
level_1: Neither a cotton swatch nor a polyester swatch is visible, or only one fabric type appears; no water/dye container is shown; the liquid in the container doesn't read as a colored dye bath (looks like plain clear water or an unrelated tint); no lifting of the fabrics out of the liquid occurs; no rinsing under water occurs; or the two swatches are never shown next to each other in the liquid.
level_2: A cotton-like and a polyester-like swatch both appear in the liquid, but something is off: they aren't placed next to each other; they look identical in texture and sheen so there's no way to tell which is which; the two swatches aren't submerged in the dye bath at the same time; the lift shows only one swatch coming out of the liquid; or rinsing water appears without the swatches ever having been immersed and lifted first.
level_3: Both swatches sit side by side, fully submerged together in a container of visibly colored dye liquid; both are lifted out together as a pair; both then pass under a stream of running water; the side-by-side placement holds through immersion, lifting, and rinsing.
level_4: Everything true at the 3-point level still holds, and neither swatch drifts apart from, rotates away from, or overlaps the other during the full lift or the full rinse; the dye liquid visibly wets both swatches evenly as they come out; the rinse stream reaches both swatches at the same time rather than one first.
level_5: Everything true at the 4-point level still holds, and the gap between the two swatches never changes (no tilting, sliding, overlapping, or blocking that would hide how they sit relative to each other) from the moment they enter the dye bath to the end of the rinse; both swatches travel the same vertical path in and out of the liquid; the rinse water touches both continuously and at the same time, with neither one getting a head start or a gap in coverage.

Scientific and Causal Correctness rubric:
level_1: No color difference shows up between the two swatches after rinsing; or both end up equally colored or equally plain; or the dye's behavior contradicts what a cationic dye should do: for instance the polyester swatch ends up more strongly colored than the cotton swatch.
level_2: A difference appears but it points the wrong way or shows up at the wrong moment: the polyester swatch retains more color than the cotton swatch; or the cotton swatch shows no color at all until the rinse itself is underway, as though the rinse water is coloring it fresh rather than the fabric having carried dye over from the earlier soak; or dye washes off the cotton swatch faster or more completely than it does off the polyester swatch; or the two swatches still look the same color once the rinse ends, despite clearly being different fabrics.
level_3: After the rinse, the cotton swatch shows an even, visible dye color across its surface (a clear change from its original pale shade), while the polyester swatch has returned to, or stayed at, its original undyed look; cotton keeps the color and polyester does not, and this direction is unambiguous.
level_4: Everything true at the 3-point level still holds, and the cotton swatch's color stays on the fabric itself rather than clouding the rinse water as it passes over; the polyester swatch shows no hue change anywhere on its surface, including at its edges or folds.
level_5: Everything true at the 4-point level still holds, and the color retained by the cotton swatch visibly matches the shade of the original dye bath rather than looking washed-out or shifted; the polyester swatch shows no dye pickup at all (no tint, no change in sheen, no staining at seams or edges) under the same lighting as the rest of the scene; the water leaving the rinse area looks clear rather than carrying color away from the cotton.

Spatiotemporal Consistency rubric:
level_1: One of the fabric swatches jumps to a different spot in the frame with no motion shown; the container disappears and reappears; the scene's brightness suddenly switches between bright and dim with no visible transition; or a swatch's edge tears, melts, or warps in a way real fabric wouldn't.
level_2: One clear break in continuity occurs somewhere in the clip: a swatch briefly disappears during the lift and then reappears; the container flickers in and out; the rinse water starts or stops instantly with no tap or hand shown turning it on or off; the shadows the swatches cast suddenly swing to the opposite side even though nothing about the light source changes; or one swatch spins on its own while the other stays still during the lift.
level_3: The container stays in the same spot and orientation for the whole clip; the two swatches keep their side-by-side arrangement and orientation as they move together; the lift out of the liquid is smooth, without freezing or warping; the rinse water flows steadily without cutting in and out; the light's position and the direction of the shadows the swatches cast stay the same from beginning to end.
level_4: Everything true at the 3-point level still holds, and neither swatch nor the container suddenly looks bigger or smaller unless the camera is actually shown moving closer or farther; the fabric edges stay crisp during motion rather than smearing; the rinse stream keeps a steady thickness and clarity from one moment to the next; no swatch appears to pass through the container wall or through the other swatch.
level_5: Everything true at the 4-point level still holds, and neither the fabrics nor the container show any bending or stretching that a real camera wouldn't produce; the lift and the rinse both play out smoothly with no freezing or blur that would make it hard to tell the two swatches apart; if one swatch sits slightly in front of the other from this angle, it consistently occludes it that way rather than flickering back and forth; light reflecting off the wet cotton shifts naturally as it moves rather than staying static or flickering.