Mechanical properties of polydopamine (PDA) thin films
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.52
Mechanical properties of polydopamine (PDA) thin films Haoqi Li, Jiaxin Xi, Yao Zhao, Fei Ren Department of Mechanical Engineering, College of Engineering, Temple University, Philadelphia, PA 19122, U.S.A.
ABSTRACT Polydopamine (PDA) is a biopolymer, which can form uniform thin films on almost all solid substrates as well as at the liquid/air interface. Carbonized polydopamine possesses graphitelike structure and exhibits high electrical conductivity, which makes it a potential carbonbased thin film conductor. However, studies on mechanical behavior of PDA and its derived materials are very limited. In this study, PDA samples were synthesized through selfassembly of dopamine in aqueous solution. Elastic modulus of thin films was measured using the nanoindentation technique. It is shown that the Young’s modulus of PDA thin film increased with increasing heat treatment temperature (up to 600˚C). Doping with Cu ions also increased the Young’s modulus of PDA. Furthermore, all PDA thin films, with and without Cu, exhibited creep behavior.
INTRODUCTION Polydopamine (PDA) is a biopolymer inspired by mussel chemistry [1]. It has attracted much attention owing to its interesting properties and ease of synthesis. An auto-oxidation process under mild conditions in dopamine solution [2] can yield nanoscale PDA powder with controllable size [3], smooth, crack-free, and thin coatings on solid substrates, or free-standing films at the solution/air interface [4]. Multiple function groups give PDA the ability to interact with other molecules and metal ions through secondary bonding or coordination bonding [5]. PDA is proposed to be used in surface modification with tailored hydrophobicity, target drug delivery, and capture of heavy metal ions for water treatment [6-9]. In addition, thin PDA films can also be converted to a graphite-like phase via heat treatment under protective atmosphere. Carbonized PDA (cPDA) is found to have an electrical conductivity [10] as high as 1.2 x 105 S/m which is comparable to reduced graphene oxide (rGO) [1, 11]. Such founding may open up the possibilities for cPDA to be used in various electronic applications, such as sensors, flexible electrodes, and protective shielding coatings. However, the mechanical behavior of PDA and cPDA thin films, which is essential for design and fabrication of devices based on this material, is not well
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understood. Lin et al [12] has built in-silico models to simulate the mechanical properties of PDA with different crosslinking schemes. The results from simulation showed the Young’s modulus of covalently linked PDA range from 4.1 GPa to 4.4 GPa. This result also matched the lower bound of their experimental results obtained from nanoindentation, which range
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