Multifunctional hydrogels based on carbon nanomaterials

Resumen

The unique properties of graphene and graphene derivatives make them suitable for developing versatile materials for many different applications, from engineering to biological issues. In this context, the aim of this thesis is to design new smart materials based on graphene derivatives able to respond to external stimuli to be used in sensing and soft robotic applications attending to their features. The first chapter provides an overview of nanotechnology and carbon nanomaterials which deals mainly with graphene and graphene derivatives as precursors for the preparation of smart materials. The response of these smart materials to both chemical and physical stimuli are described. The second chapter is based on the preparation of graphene and graphene quantum dots following environmentally friendly methodologies. Firstly, an overview about the synthesis, properties and applications of both nanomaterials is provided. Secondly, the use of the mechanochemical approach, previously developed in our research group for the preparation of graphene, is described and the characterisation of the obtained nanomaterial is discussed. Finally, a modification of this method is described and applied to the preparation of graphene quantum dots. The structural and photoluminescent properties of the obtained nanomaterial are provided. Moreover, the reusability of the obtained by-product is considered and discussed. Both approaches permit stable dispersions of graphene and graphene quantum dots to be obtained in aqueous solutions, which is relevant for the development of the following chapters. The third chapter details the work developed using polyacrylamide-based hydrogels. Firstly, an overview describing important concepts about hydrogels and hydrogels which incorporate carbon nanomaterials on their structure is provided, mostly focusing on hydrogels based on graphene derivatives. Afterwards, the synthesis and characterisation of hydrogels is described and discussed, incorporating the graphene derivatives in two different manners. A comparison of the features of graphene, graphene oxide and graphene quantum dot-based hydrogels is performed in order to ascertain the structural role of the graphene derivatives into the polymeric network. The fourth chapter describes the use of graphene quantum dots as smart materials which response to chemical stimuli. Firstly, the stability of the photoluminescent properties of graphene quantum dots is studied in different media. Secondly, the incorporation of graphene quantum dots into cationic hydrogels is described in order to develop new materials for sensing applications. Synthesis and further characterisation are provided. Finally, the use of the graphene quantum dot-based hydrogel as a sensor for polyaromatic compounds in water media is described. The last chapter is based on the use of hydrogels in soft robotic applications. Firstly, an overview about the materials and methods commonly used in this field is provided, digging down on hydrogels as responsive materials used in the design of soft actuators. Secondly, the response to an electric field of the cationic hydrogels, previously described in chapter 4, is studied in different media (water, ionic liquid and ambient-air conditions) and incorporating graphene into the hydrogel. Attending to the response obtained, the use of these hydrogels in the development of grippers and modulable soft fingertips is discussed. In addition, the design of hydrogels following three-dimensional printing methodologies is considered.