Sub-nanometer scale investigation of polyelectrolyte adsorption and desorption processes using etched fiber Bragg...

Area of Science:

• Materials Science and Nanotechnology
• Optical Sensing
• Surface Chemistry

Background:

• Polyelectrolyte multilayer (PEM) thin films are fabricated using Layer-by-Layer (LbL) self-assembly for various nanotechnology applications.
• Accurate in-situ thickness monitoring is essential for controlling PEM film growth and properties.
• Existing methods may lack the precision or real-time feedback needed for nanoscale control.

Purpose of the Study:

• To present a novel optical measurement technique for in-situ analysis of PEM film buildup.
• To utilize Etched Fiber Bragg Gratings (EFBG) as sensors for quantifying deposited thickness.
• To investigate the adsorption and desorption dynamics of polyelectrolytes at varying pH conditions.

Main Methods:

• Fabrication of PEM films via LbL self-assembly using weak polyelectrolytes Poly(allylamine hydrochloride) (PAH) and Poly(acrylic acid) (PAA).
• Deposition of PEM films directly onto EFBG-based optical sensors.
• In-situ monitoring of thickness changes during alternative deposition steps and desorption phases.

Main Results:

• EFBG sensors successfully quantified the deposited thickness of PEM films during LbL assembly.
• Sub-nanometer scale observation of desorption revealed distinct behaviors: linear for PAA and exponential for PAH.
• The results validate inter-diffusive behavior of low molecular weight polyelectrolytes during both adsorption and desorption.

Conclusions:

• EFBG-based sensors provide a precise tool for real-time monitoring of PEM layer-by-layer buildup.
• The technique allows extraction of fundamental information on adsorption/desorption kinetics at the nanoscale.
• This enables fine-tuning of multilayer nano-scale architecture for advanced nanotechnology applications.