Thermal transitions in hydrated layer-by-layer assemblies observed using electrochemical impedance spectroscopy

Choonghyun Sung; Katelin Hearn; Jodie Lutkenhaus

doi:10.1039/C4SM01269K

Thermal transitions in hydrated layer-by-layer assemblies observed using electrochemical impedance spectroscopy

Choonghyun Sung,^a Katelin Hearn^a and Jodie Lutkenhaus*^a

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^a Artie McFerrin Department of Chemical Engineering, Texas A&M University, College Station, USA
E-mail: jodie.lutkenhaus@tamu.edu

Abstract

Layer-by-layer (LbL) assemblies have been of great interest due to their versatile functionality and ease of fabrication, but their response to temperature is not completely understood. It has been recently shown that hydrated LbL assemblies of poly(diallyldimethylammonium chloride) (PDAC) and poly(styrene sulfonate) (PSS) under go a thermal transition much like a “glass-melt” transition. This thermal transition is of great interest because many LbL applications are found in water. Here, we report upon the nature of this thermal transition as probed using electrochemical impedance spectroscopy (EIS) as a function of assembly salt concentration, film thickness, and outermost layer. EIS reveals that the transition is signified by a structural rearrangement of virtual pores, resulting in increased conductivity and decreased surface coverage of the electrode. Two separate thermal transitions are obtained from changes in the film resistance (T_{tr,R_f}) and the charge transfer resistance (T_tr,_{R_ct}). Only T_{tr,R_ct} is strongly dependent on film thickness, salt concentration, and outermost layer, for which values ranging from 50 to 64 °C were observed. As the assembly salt concentration increases from 0.5 M to 1.0 M NaCl, T_tr,_{R_ct} increases by about 10 °C. Below 20 layers, deviations of T_{tr,R_ct} with respect to outermost layer appear, in which PSS-capped LbL films tend to show elevated T_tr,_{R_ct} values. These results suggest that extrinsic charge compensation plays a large role in the value of T_{tr,R_ct} in which a large degree of extrinsic charge compensation drives T_{tr,R_ct} towards higher values. On the other hand, T_{tr,R_f} is largely unaffected by assembly parameters, and closer in value to prior reports via calorimetry and quartz crystal microbalance with dissipation.

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Publication details

The article was received on 12 Jun 2014, accepted on 08 Jul 2014 and first published on 23 Jul 2014

Article type: Paper

DOI: 10.1039/C4SM01269K

Author version available: Download Author version (PDF)

Citation: Soft Matter, 2014,10, 6467-6476

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Thermal transitions in hydrated layer-by-layer assemblies observed using electrochemical impedance spectroscopy

C. Sung, K. Hearn and J. Lutkenhaus, Soft Matter, 2014, 10, 6467
DOI: 10.1039/C4SM01269K
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Soft Matter

Thermal transitions in hydrated layer-by-layer assemblies observed using electrochemical impedance spectroscopy

Abstract

Supplementary files

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Thermal transitions in hydrated layer-by-layer assemblies observed using electrochemical impedance spectroscopy

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