Short versus long chain polyelectrolyte multilayers: a direct comparison of self-assembly and structural properties

Area of Science:

• Materials Science
• Polymer Chemistry
• Surface Science

Background:

• Layer-by-layer (LbL) assembly is a versatile technique for fabricating multilayer films.
• Polyelectrolyte multilayers (PEMs) are widely studied for various applications.
• The influence of polymer chain length on PEM stability and growth is not fully understood.

Purpose of the Study:

• To investigate the successful LbL growth of short-chain polyelectrolyte multilayers (PEMs) for the first time.
• To compare the growth and stability of short-chain PEMs with their high molecular weight counterparts.
• To elucidate the role of preparation conditions, particularly salt concentration, in overcoming stability limitations.

Main Methods:

• Quartz crystal microbalance with dissipation (QCM-D) was used for detailed analysis.
• Three key processes were identified: initial mass uptake, adsorption-desorption during equilibration, and desorption during rinsing.
• Mechanical properties were extracted from frequency and dissipation shifts.

Main Results:

• Short-chain poly(sodium styrene sulfonate) (PSS)-poly(diallyl dimethylammonium chloride) (PDADMAC) multilayers exhibit layer degradation, unlike stable high molecular weight (HMW) PEMs.
• Instability phenomena include mass decrease during PDADMAC adsorption equilibration and significant mass loss during salt-free PSS rinsing.
• Increased salt concentration significantly enhances layer growth and reduces mass loss during rinsing for both short and long chain PEMs.

Conclusions:

• Successful LbL assembly of very short polyelectrolyte chains is achievable, expanding the scope of PEM fabrication.
• Short-chain PEMs display inherent instability, characterized by degradation and mass loss.
• Optimizing preparation conditions, specifically increasing salt concentration, is crucial for enhancing the growth and stability of short-chain PEMs.