polymer-films

name	polymer-films
description	Domain knowledge for polymer thin film reflectometry analysis. Covers common polymer SLD values, isotope labeling conventions, typical film thickness ranges, and contrast matching strategies. Use when the sample involves polymers, polystyrene, polymer brushes, block copolymers, or spin-coated films.
metadata	{"author":"aure","version":"1.0"}

Common Polymer SLDs (×10⁻⁶ Å⁻²)

Material	SLD
Polystyrene (h-PS)	1.4
d-Polystyrene (d-PS)	6.4
PMMA (h-PMMA)	1.06
d-PMMA	7.1
Polyethylene (h-PE)	-0.3
d-Polyethylene (d-PE)	7.0
Polyisoprene (h-PI)	0.27
d-Polyisoprene (d-PI)	6.7

Isotope Labeling

• Deuterium labeling replaces H with D to increase SLD contrast.
• A "d-" prefix indicates full deuteration; partial deuteration gives intermediate SLD values.
• When the sample mentions both h- and d- versions, the SLD difference provides the contrast mechanism.
• Be careful not to confuse protonated and deuterated variants — check if the description specifies the isotope labeling.

Typical Thickness Ranges

Film Type	Typical Thickness
Spin-coated thin film	100–2000 Å
Polymer brush (grafted)	50–500 Å
Block copolymer lamellae	100–500 Å per domain
Adsorbed polymer layer	10–100 Å
Self-assembled monolayer	10–30 Å

Contrast Matching Strategies

• Matching the SLD of one component to the solvent makes that component "invisible," revealing the other component's structure.
• Common contrast match points:
  • h-PS in d-toluene: PS becomes nearly invisible
  • d-PS in h-toluene: solvent SLD ≈ 0.94, d-PS stands out
  • Polymer in D₂O/H₂O mixture: tune to match specific component

Swelling and Solvent Penetration

• Polymer films may swell in solvent, changing thickness and SLD.
• The SLD of a swollen layer is a volume-weighted average of polymer and solvent SLDs.
• If fitting a swollen film, allow wider SLD and thickness bounds than the dry film values.

Refinement Strategy — Polymer Films

When refining polymer thin film models:

• Thickness drift: Polymer film thickness can vary from nominal due to processing conditions. Allow thickness bounds of ±50% around the nominal value for spin-coated films.
• SLD between isotope variants: If the fitted SLD falls between h- and d- values (e.g., 3.9 for PS where h-PS = 1.4 and d-PS = 6.4), this suggests partial deuteration or isotope blending. Adjust bounds to the appropriate intermediate range rather than forcing a pure-isotope SLD.
• Brush/grafted layers: These often have graded density profiles. If χ² is high and roughness is large relative to thickness, consider whether the single-slab approximation is adequate before adding sublayers.
• Swollen films: When the sample is measured in solvent, the layer SLD should be allowed to vary between the dry polymer SLD and the solvent SLD. Set SLD bounds accordingly.