Modeling the growth processes of polyelectrolyte multilayers using a quartz crystal resonator

Area of Science:

• Materials Science
• Polymer Chemistry
• Biomaterials Engineering

Background:

• Layer-by-layer assembly is a key technique for fabricating functional polymer multilayers.
• Understanding the viscoelastic properties and growth dynamics of these multilayers is crucial for controlling their performance.
• Quartz Crystal Microbalance (QCM) is a sensitive tool for monitoring thin film deposition in real-time.

Purpose of the Study:

• To demonstrate a method for retrieving information from acoustically thick polymer layers during their buildup using QCM.
• To investigate the influence of ionic strength and temperature on the layer-by-layer assembly of chitosan/hyaluronan and poly(l-lysine)/hyaluronan multilayers.
• To develop a mathematical model to analyze the viscoelastic properties and growth parameters of the polymer layers.

Main Methods:

• Fabrication of chitosan/hyaluronan (CH/HA) and poly(l-lysine)/hyaluronan (PLL/HA) multilayers on a quartz crystal resonator (QCR).
• Monitoring of surface acoustic impedance during multilayer buildup under varying ionic strengths and temperatures.
• Analysis of QCR data by plotting surface acoustic impedance in the complex plane to obtain spiral patterns.
• Development and application of a mathematical model to fit the experimental spiral data and extract viscoelastic properties and growth parameters.

Main Results:

• The complex plane plots of surface acoustic impedance yielded single or double spirals, indicative of the layer's viscoelasticity and growth regularity.
• A mathematical model successfully represented the polymer layer as one or two zones with distinct viscoelastic properties.
• The growth process for all tested multilayers was predominantly exponential, with a growth exponent consistently between 0.250 and 0.275.
• The study successfully correlated the shape of the impedance spirals with the viscoelastic characteristics and growth modes of the polymer multilayers.

Conclusions:

• The QCR method, coupled with a two-zone viscoelastic model, provides valuable insights into the buildup of acoustically thick polymer multilayers.
• The observed exponential growth pattern suggests a consistent deposition mechanism across different polyelectrolyte systems and conditions.
• This approach offers a powerful tool for characterizing and optimizing multilayer fabrication for applications in biomaterials and nanotechnology.