Effect of Structure of Polymers Grafted from Graphene Oxide on the Compatibility of Particles with a Silicone-Based Environment and the Stimuli-Responsive Capabilities of Their Composites.

Monika Zygo,Miroslav Mrlik,Joanna Pietrasik,Jaroslav Mosnáček,David Skoda,Michal Sedlacik,Barbora Hanulikova,Lukas Munster,Marketa Ilcikova,Martina Hrabalikova,Pavel Urbánek,Martin Cvek,Josef Osicka

doi:10.3390/nano10030591

Abstract

This study reports the utilization of controlled radical polymerization as a tool for controlling the stimuli-responsive capabilities of graphene oxide (GO) based hybrid systems. Various polymer brushes with controlled molecular weight and narrow molecular weight distribution were grafted from the GO surface by surface-initiated atom transfer radical polymerization (SI-ATRP). The modification of GO with poly(n-butyl methacrylate) (PBMA), poly(glycidyl methacrylate) (PGMA), poly(trimethylsilyloxyethyl methacrylate) (PHEMATMS) and poly(methyl methacrylate) (PMMA) was confirmed by thermogravimetric analysis (TGA) coupled with online Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Various grafting densities of GO-based materials were investigated, and conductivity was elucidated using a four-point probe method. Raman shift and XPS were used to confirm the reduction of surface properties of the GO particles during SI-ATRP. The contact angle measurements indicated the changes in the compatibility of GOs with silicone oil, depending on the structure of the grafted polymer chains. The compatibility of the GOs with poly(dimethylsiloxane) was also investigated using steady shear rheology. The tunability of the electrorheological, as well as the photo-actuation capability, was investigated. It was shown that in addition to the modification of conductivity, the dipole moment of the pendant groups of the grafted polymer chains also plays an important role in the electrorheological (ER) performance. The compatibility of the particles with the polymer matrix, and thus proper particles dispersibility, is the most important factor for the photo-actuation efficiency. The plasticizing effect of the GO-polymer hybrid filler also has a crucial impact on the matrix stiffness and thus the ability to reversibly respond to the external light stimulation.

Highlights

Particle surface chemistry is a crucial factor that influences the performance of two-phase systems, where the particles create a discontinues phase dispersed in a continues one
In our previous research using surface-initiated atom transfer radical polymerization (SI-ATRP) for preparation of hybrid particles, we proved that graphene oxide polymer hybrids with tailored polymer chain architecture, possessing good affinity to silicone oil, and with controlled electrical conductivity to fit parameters needed for ER applications can be efficiently prepared
The degree of polymerization (DP) was expected to increase in the following order: poly(n-butyl methacrylate) (PBMA) < poly(glycidyl methacrylate) (PGMA) < poly(methyl methacrylate) (PMMA) < PHEMATMS

Summary

Introduction

Particle surface chemistry is a crucial factor that influences the performance of two-phase systems, where the particles create a discontinues phase dispersed in a continues one. Photomechanical actuators belong to the class of stimuli-responsive materials as they can provide mechanical motion as a response to external light stimuli Such materials find utilization in engineering applications such as robots [4], pens for molecular printing [5], smart curtains, light-driven motors [6], or treating of amphiphilic nano-objects by light-induced charge separation [7]. They contain hard and soft phases, where the hard phase provides the shape stability, and the soft phase enables the shape changes [8]. The properties of the polymer matrix network play an important role, since it determines the stability of the materials during actuation. Systems based on both chemical and physical cross-linking have been studied. Compared to previously mentioned matrix materials, poly(dimethyl siloxane) is easy to process, is nontoxic and provides the ability for sufficient photo-actuation [14,21,22,23]

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Conclusion