Scratch behavior of epoxy coating containing self-assembled zirconium phosphate smectic layers Fan Lei a, c , Marouen Hamdi b , Peng Liu b , Peng Li b , Michael Mullins b , Hongfeng Wang b , Jiang Li a, * , Ramanan Krishnamoorti c , Shaoyun Guo a , Hung-Jue Sue b, ** a State Key Laboratory of Polymer Materials Engineering, Polymer Research Institute of Sichuan University, Chengdu, Sichuan 610065, China b Polymer Technology Center, Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843, United States c Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, United States article info Article history: Received 15 November 2016 Received in revised form 30 January 2017 Accepted 4 February 2017 Available online 6 February 2017 Keywords: Scratch behavior Spray-coating Epoxy a-zirconium phosphate Smectic layer abstract A facile but efficient spray-coating method was recently developed to manufacture thin, flexible, and transparent epoxy films reinforced with well-exfoliated and highly-aligned a-zirconium phosphate (ZrP) nanoplatelets in smectic liquid crystalline order. Here, we investigate the scratch resistance of ZrP/epoxy nanocomposites prepared following the same spray-coating process. Comparison was made with neat epoxy coating to determine the impact of ZrP nanofillers. Tests were conducted with accordance to ASTM D7027/ISO 19252 scratch standard and scratch mechanisms were studied using different experimental tools. Results show that scratch resistance is considerably improved after introducing ZrP nanofillers to the epoxy coating. This was reflected by the delay in microcracking and plowing damages and the decrease of scratch coefficient of friction. This result is attributed to the significant role of exfoliated and aligned ZrP nanofillers in enhancing the mechanical properties of the epoxy matrix. The usefulness of the current study in developing new coating systems for high-performance applications is discussed. © 2017 Published by Elsevier Ltd. 1. Introduction Thanks to the emerging advanced materials with highly attractive properties, new devices and applications are being introduced in an ever-increasing pace. Many of these new devices and products contain significant polymeric components, such as electronic devices and energy efficient automobiles. These poly- meric components are subjected to tribological damages, thus reducing their functional and aesthetic performance. One of the most commonly challenging tribological damages for polymers is scratch damage. Consequently, improvement in scratch perfor- mance has become one of the most sought after desire among polymer producers and component manufacturers. Unfortunately, the time-dependent and non-linear constitutive behaviors, coupled by the complexity of polymer deformation and damage during scratch, make these efforts daunting. After significant concerted efforts between academia and polymer industry through an industrial consortium operation [1], an ASTM D7027/ISO 19252 standard was developed to perform consistent, straightforward, and meaningful scratch tests [2,3]. The standardized scratch test has since been increasingly adopted by industry and academic institutions globally. The new scratch test has now been used to study the effect of different surface proper- ties like roughness [4e6], friction [7], and perceptual attributes [7], mechanical properties like constitutive parameters [8,9], and test conditions like aging time [10,11], humidity [12], and test speed [13] on the scratch resistance of polymeric systems. Results show that scratch performance is generally related to friction, gloss, thermal treatment, surface roughness, yield stress, and strain hardening coefficient. Based on these findings, better scratch performance has been practiced by adding slip agents [7,14], increasing mold tem- perature [15], decreasing gloss level [7], and introducing surface texture [7]. Furthermore, better fundamental understanding of polymer scratch behavior is gained through finite element methods (FEM) modeling which provides mechanistic interpretations of scratch through extensive stress and parametric analysis [16e18]. This FEM modeling suggests that materials with greatly improved mechanical integrity and drop in friction coefficient are expected to exhibit significantly better scratch resistance. * Corresponding author. ** Corresponding author. E-mail addresses: li_jiang@scu.edu.cn (J. Li), hjsue@tamu.edu (H.-J. Sue). Contents lists available at ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer http://dx.doi.org/10.1016/j.polymer.2017.02.020 0032-3861/© 2017 Published by Elsevier Ltd. Polymer 112 (2017) 252e263