Influence of the Thermomechanical Characteristics of Low-Density Polyethylene Substrates on the Thermoresistive Properties of Graphite Nanoplatelet Coatings

Ubaldo Coscia,Francesca Urban,Giuseppina Ambrosone,Angela Longo,Mariano Palomba,Andrea Sorrentino,Gianfranco Carotenuto,Antonio Di Bartolomeo,Gianni Barucca

doi:10.3390/coatings11030332

Abstract

Morphological, structural, and thermoresistive properties of films deposited on low-density polyethylene (LDPE) substrates are investigated for possible application in flexible electronics. Scanning and transmission electron microscopy analyses, and X-ray diffraction measurements show that the films consist of overlapped graphite nanoplatelets (GNP) each composed on average of 41 graphene layers. Differential scanning calorimetry and dynamic-mechanical-thermal analysis indicate that irreversible phase transitions and large variations of mechanical parameters in the polymer substrates can be avoided by limiting the temperature variations between −40 and 40 °C. Electrical measurements performed in such temperature range reveal that the resistance of GNP films on LDPE substrates increases as a function of the temperature, unlike the behavior of graphite-based materials in which the temperature coefficient of resistance is negative. The explanation is given by the strong influence of the thermal expansion properties of the LDPE substrates on the thermo-resistive features of GNP coating films. The results show that, narrowing the temperature range from 20 to 40 °C, the GNP on LDPE samples can work as temperature sensors having linear temperature-resistance relationship, while keeping constant the temperature and applying mechanical strains in the 0–4.2 × 10−3 range, they can operate as strain gauges with a gauge factor of about 48.

Highlights

Flexible electronics covers a wide range of applications including solar cells, piezoresistive sensors, strain gauges, displays, health care, industrial automation, robotics, smart textile and others [1,2,3,4,5]
Graphene layers and graphene/graphite nanoplatelets (GNP), for example, can be deposited by a top-down approach using the exfoliation of graphite, by mechanical methods [16,17,18,19], electrostatic deposition [20], chemical synthesis [7], electrochemical [21] and thermal expansions [22]
The aim of the present work is to explore the morphological, structural, and thermoresistive properties of graphite nanoplatelet films deposited by a micromechanical technique [19] on low-density polyethylene (LDPE) substrates for possible applications in flexible electronics [23]

Summary

Introduction

Flexible electronics covers a wide range of applications including solar cells, piezoresistive sensors, strain gauges, displays, health care, industrial automation, robotics, smart textile and others [1,2,3,4,5]. Carbon-based materials, such as carbon black [6], graphite [7], CNTs [8], graphene [9] and reduced graphene oxide [10], play an important role as conductive layers, in preparing effective electrical conductors. These materials can be used as fillers in ceramics and polymers to increase their electrical conductivity [8,11,12,13,14]. Graphene layers and graphene/graphite nanoplatelets (GNP), for example, can be deposited by a top-down approach using the exfoliation of graphite, by mechanical methods [16,17,18,19], electrostatic deposition [20], chemical synthesis [7], electrochemical [21] and thermal expansions [22]

Objectives

Methods

Results