Functional group quantification of polymer nanomembranes with soft x-rays

Area of Science:

• Materials Science
• Nanotechnology
• Analytical Chemistry

Background:

• Polyamide nanomembranes are crucial for water desalination and clean water production.
• Understanding the chemistry and network structure of ultrathin films (<100 nm) is key to improving membrane efficiency.
• Existing techniques often lack the compositional information needed for these ultrathin films.

Purpose of the Study:

• To quantify functional group concentrations in polyamide nanomembranes using resonant soft x-ray reflectivity (RSXR).
• To establish a relationship between functional group density, crosslink density, and permselectivity.
• To demonstrate the capability of RSXR for depth-dependent analysis in thin films.

Main Methods:

• Utilized resonant soft x-ray reflectivity (RSXR) to probe chemical bonds in polyamide nanomembranes.
• Employed reference materials to calibrate optical constants with functional group density.
• Calculated crosslink density from amide carbonyl and carboxylic acid group concentrations.

Main Results:

• RSXR successfully quantified functional group concentrations in polyamide nanomembranes.
• Crosslink density varied significantly across different polyamide chemistries.
• A direct correlation was found between higher functional group density and increased permselectivity (α).
• RSXR demonstrated depth-dependent quantification in a polyamide/poly(acrylic acid) bilayer.

Conclusions:

• RSXR is a powerful tool for characterizing the chemistry of ultrathin polyamide films.
• Crosslink density, determined by functional group analysis, is a critical factor in desalination performance.
• This technique advances the understanding and design of high-performance water purification membranes.