Non-destructive determination of functionalized polyelectrolyte placement in layer-by-layer films by IR ellipsometry

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Layer-by-layer (LbL) assembly allows for controlled coating fabrication with tunable composition.
• Characterizing composition profiles in LbL films is often destructive and requires significant compositional differences.
• Existing methods limit the utility of LbL films due to characterization challenges.

Purpose of the Study:

• To demonstrate a non-destructive method for quantifying depth-dependent composition in LbL films.
• To investigate the incorporation of poly(sodium acrylate-co-allylacrylamide) (allyl-PAA) in LbL assemblies.
• To understand compositional gradients and their impact on LbL fabrication mechanisms.

Main Methods:

• Fabrication of LbL films using poly(diallyldimethylammonium chloride) (PDAC)/poly(acrylic acid) (PAA) and PDAC/allyl-PAA.
• Utilized infrared (IR) spectroscopic ellipsometry to detect the allyl group's absorption at 1645 cm⁻¹.
• Analyzed multiple film architectures to assess gradient location and thickness.

Main Results:

• IR spectroscopic ellipsometry successfully distinguished LbL components with low optical contrast.
• Quantified the thickness of allyl-PAA containing layers and identified compositional gradients.
• Determined that gradients are primarily located within the first deposited bilayer stack, indicating dynamic dissolution-deposition processes.

Conclusions:

• Non-destructive IR spectroscopic ellipsometry can effectively quantify compositional gradients in LbL films.
• The findings provide evidence for dynamic dissolution-deposition mechanisms driving exponential growth in LbL assemblies.
• This technique offers a versatile tool for analyzing compositional variations in various polymer films.