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Thermal transitions in hydrated layer-by-layer assemblies observed using electrochemical impedance spectroscopy
Choonghyun Sung1, Katelin Hearn, Jodie Lutkenhaus
1Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, Texas 77843, USA. jodie.lutkenhaus@tamu.edu.
Soft Matter
|July 24, 2014
Summary
This study investigates the thermal transitions in layer-by-layer (LbL) assemblies using electrochemical impedance spectroscopy (EIS). We found that the charge transfer resistance transition (Ttr,Rct) is influenced by salt concentration and film properties, revealing insights into LbL assembly behavior in aqueous environments.
Area of Science:
- Materials Science
- Physical Chemistry
- Polymer Science
Background:
- Layer-by-layer (LbL) assemblies offer versatile functionality and ease of fabrication.
- The thermal response of hydrated LbL assemblies, particularly poly(diallyldimethylammonium chloride) (PDAC) and poly(styrene sulfonate) (PSS), is not fully understood.
- Understanding thermal transitions is crucial as many LbL applications are utilized in aqueous environments.
Purpose of the Study:
- To investigate the nature of the thermal transition in hydrated PDAC/PSS LbL assemblies.
- To explore the influence of salt concentration, film thickness, and outermost layer on this thermal transition.
- To elucidate the underlying mechanisms of the observed thermal transitions using electrochemical impedance spectroscopy (EIS).
Main Methods:
- Fabrication of PDAC/PSS LbL assemblies with varying salt concentrations, film thicknesses, and outermost layers.
- Electrochemical impedance spectroscopy (EIS) was employed to probe the thermal transitions.
- Analysis of film resistance (Ttr,Rf) and charge transfer resistance (Ttr,Rct) as a function of temperature and assembly parameters.
Main Results:
- EIS revealed a structural rearrangement of virtual pores during the thermal transition, leading to increased conductivity and decreased electrode surface coverage.
- Two distinct thermal transitions were identified: Ttr,Rf and Ttr,Rct.
- Ttr,Rct showed significant dependence on film thickness, salt concentration, and outermost layer, with values ranging from 50 to 64 °C.
- Increasing NaCl concentration from 0.5 M to 1.0 M elevated Ttr,Rct by approximately 10 °C.
- PSS-capped LbL films exhibited higher Ttr,Rct values below 20 layers, suggesting a role for extrinsic charge compensation.
Conclusions:
- The thermal transition in PDAC/PSS LbL assemblies is characterized by a significant structural rearrangement.
- Ttr,Rct is strongly influenced by extrinsic charge compensation, film thickness, and salt concentration, while Ttr,Rf remains largely unaffected.
- These findings provide critical insights into the thermal behavior and stability of LbL assemblies in aqueous environments, relevant for their application development.
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