Asymmetric Bias Effects of Polyelectrolyte Brushes: A Systematic Electrochemical Impedance Spectroscopy Study

Polyelectrolyte brushes are promising surface modifications, and it is known that their properties are affected by environmental conditions. For electrical applications, it is crucial to know the effect of these environmental conditions on the electrical properties of the brushes. Here, we systematically evaluate the role of the ion concentration and bias voltage on the electrical properties of negatively charged polyelectrolyte brushes through probe-free electrochemical impedance spectroscopy. We interpret the response using an equivalent electrical circuit and find that the values of the equivalent circuit elements are affected by environmental conditions. We attribute these effects to structural and compositional changes in the brush layers. Because of the charged nature of the brush, the response displays an asymmetry between positive and negative biases, which inverts if the charge of the brush is inverted. These results reveal that brush charge and environmental conditions deserve critical consideration when charged polymer brushes are used in electronic or iontronic applications.