Means of control over poly(4-vinylpyridine)–CoBr2 complex functional thin film formation in static and dynamic conditions

Abstract

We provide a detailed study on the formation kinetics of the poly(4-vinylpyridine)–CoBr₂ complex (P4VP–CoBr₂) – a novel material combining the advantages of polymers and Single Ion Magnets that exhibit magnetic relaxations, which has promising potential applications in e.g. high-density data storage, or plastic electronics. The P4VP–CoBr₂ compound was previously proven to form in the top layer of thin spin coated P4VP films after dipping them in CoBr₂ solution, developing a wrinkled topography. However, the kinetics of this process have never been studied until now. Two approaches to control the Co(II) concentration in the thin film were employed: dynamic (varying time spent in solution) and static (varying the solution concentration). The dynamic approach revealed two consecutive breakthrough increases in Br₂Co(py)₂ concentration within the layer vs. time spent in solution, both of which can be described by the Yoon–Nelson model of adsorption. We also confirmed an interplay between the said complex concentration and the development of the wrinkled topography. The static approach found a non-monotonous dependence between the Co(II) concentration in the layer and CoBr₂ concentration in solution that conforms to two modified Langmuir–Freundlich isotherms: a Langmuir-type isotherm in the low concentration regime with flat topography, and a Langmuir–Freundlich type for higher concentrations, caused by simultaneous adsorption and formation of wrinkles.