Reactive Inkjet Printing

A Chemical Synthesis Tool

Patrick J Smith, Aoife Morrin

• Publisher: Royal Society of Chemistry
• Year: 2017
• Print ISBN: 9781782627678
• eBook ISBN: 9781788013505
• Edition: 1
• Topic: Technology & Engineering
• Subtopic: Biotechnology
• Index: Technology & Engineering

Reactive inkjet printing uses an inkjet printer to dispense one or more reactants onto a substrate to generate a physical or chemical reaction to form a product in situ. Thus, unlike traditional inkjet printing, the printed film chemistry differs to that of the initial ink droplets. The appeal of reactive inkjet printing as a chemical synthesis tool is linked to its ability to produce droplets whose size is both controllable and predictable, which means that the individual droplets can be thought of as building blocks where droplets can be added to the substrate in a high precision format to give good control and predictability over the chemical reaction.

The book starts by introducing the concept of using reactive inkjet printing as a building block for making materials. Aspects such as the behaviour of printed droplets on substrate and their mixing is discussed in the first chapters. The following chapters then discuss different applications of the technique in areas including additive manufacturing and silk production, production of materials used in solar cells, printed electronics, dentistry and tissue engineering.

Edited by two leading experts, Reactive Inkjet Printing: A Chemical Synthesis Tool provides a comprehensive overview of this technique and its use in fabricating functional materials for health and energy applications. The book will appeal to advanced level students in materials science.

CHAPTER 1

Reactive Inkjet Printing—An Introduction

PATRICK J. SMITH*^a AND AOIFE MORRIN*^b

^a University of Sheffield, UK;

^b School of Chemical Sciences, National Centre for Sensor Research, Insight Centre for Data Analytics, Dublin City University, Ireland

*E-mail: [email protected], [email protected]

1.1 Introduction

‘Reactive inkjet (RIJ) printing’, or ‘reactive inkjet’ is a type of inkjet technique whose history in the research literature has been documented for less than ten years. Despite its recent beginnings, it has attracted much attention as a cost-effective and highly controllable method to fabricate patterns, where it elegantly combines the processes of material deposition and chemical reaction. The combination of these two processes creates boundless possibilities for the fabrication of 2-dimensional and indeed 3-dimensional structures whereby it allows functional materials to be synthesized in situ at the same time as their final device geometries are patterned.

The concept of micro-dispensation of reactants actually dates back to the 1990s when the first report of a solenoid-based inkjet chemical dispenser, ChemJet, was made for combinatorial library synthesis.¹ Since then, the field has grown from this application to become a combinatorial library synthesis tool for rational coating design, and a tool used for patterning materials directly within devices. Materials that have been reactively printed for direct device integration include conjugated polymers, fluorescent quantum dots, metallics and silk. It is the precursors to these materials that are dispensed (e.g., monomer and oxidant) and subsequently react in solution droplets (micro- or pico-litre sized) on a solid support. While performing chemistry in patterned droplets using this printing approach promises high controllability, technical challenges do still remain. Fundamental droplet analysis in terms of size, shape and kinetics must be understood in each application in order to design optimal precursor ink formulations and selection of appropriate print parameters.

A wide spectrum of reactive inks that have been reported allows one to fabricate various patterns that perform different functionalities. In terms of print resolution, RIJ will theoretically have the same resolution as inkjet printing. However, in practice, given the multi-head combinatorial approach often used, maintaining a resolution of single-layer, single-head inkjet printing, is more challenging. Nonetheless, patterning 2D structures at resolutions at the low micron-scale are easily achievable using RIJ.

As this book is concerned with RIJ, it seems prudent that the first chapter introduce to the reader what is meant by this term. By its nature, RIJ requires the use of an inkjet printer, the first chapter will, therefore, survey the various types of inkjet printing (such as piezo and thermal), as well as describing droplet ejection mechanisms and ink considerations. The following chapters will discuss a number of fundamental inkjet areas that will help inform the reader.

The second chapter discusses droplet behaviour from the moment a droplet impacts a surface to where it coalesces with a second or more to form a feature. The various drying phenomena, such as ‘coffee staining’ are discussed, as well as possible phase changes. The third chapter is fascinating; typically, RIJ involves two dissimilar droplets being joined, with their contained reactants meeting to form a product. Chapter 3 discusses how two droplets interact; what is intriguing is the observation that two droplets don’t appear to mix! What this chapter illustrates is the youth of the field of RIJ and that the early focus on applications has now opened up some fascinating physics to explore. The fourth chapter concludes the Fundamentals section with a discussion of the behaviour of high molecular weight polymers in ink. These polymers tend to break apart during jetting which offers the prospect that radical chemistry can be performed.

The third and largest section of the book is given over to a high level overview of many of the application areas that RIJ can be employed in. Alison Lennon illustrates the attraction of using RIJ in metallisation and the production of etchants for use in solar panel manufacture. The use of RIJ to generate HF in situ is a particularly compelling example. Ghassan Jabbour and co-authors continue the exploration of RIJ’s use in inorganic chemistry with the synthesis of gold nanoparticles, zinc oxide nanostructures and lead sulphide quantum dots. They begin their chapter by illustrating that RIJ offers organic chemistry applications in their modification of the sheet resistivity of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT : PSS) by selectively dispensing droplets of aqueous sodium hypochlorite onto the polymer, thereby tailoring the degree of oxidation.

The next two chapters move the focus on to biology with the preparation of silk by RIJ forming the core. The first of this duo looks at the preparation of dental barrier membranes. Here, the degradation rate of silk II can be tuned by RIJ. The second chapter looks at the preparation of Janus-particle like structures, silk micro-rockets, which could be employed in a range of applications such as environmental monitoring, Lab-on-a-Chip diagnostics, and in vivo drug delivery.

The final three chapters continue to portray the breadth of application areas where RIJ can make a contribution. Christopher Tuck and colleagues describe the use of RIJ in additive manufacture, whilst Paul Calvert looks at the use of RIJ to form conductive features of either copper or nickel. The use of copper is of particular interest since it is a cheaper alternative to silver. Finally, the focus returns to biology with a discussion of the use of RIJ in the production of alginate- and fibrin-based systems for tissue engineering.

1.2 Reactive Inkjet Printing—The Concept

In simple terms, the concept of reactive inkjet printing (RIJ) describes the process where an inkjet printer deposits a droplet of reactant that changes due to a chemical reaction with material on the substrate or with a subsequent printed second reactant (Figure 1.1). Reactive inkjet printing can be used to deposit systems that cannot be deposited in ink form, such as some polyurethanes or to prepare purer forms of systems, such as nanoparticles that no longer require surfactants to stabilise them in suspension.

Figure 1.1 Reactive inkjet printing involves adding one reactant to another to form a product.

Inkjet printing is an essential component of RIJ because it produces droplets of uniform, controllable size. The second feature of inkjet is that the produced droplets can be positioned accurately on a substrate in pre-determined locations. The ability to consistently produce droplets whose volume can be predicted allows the droplets to be treated as building blocks, thereby allowing inkjet to be employed as an additive manufacturing technique as well as a synthesis tool. Moreover, this faculty of uniform droplets that are accurately positioned allows inkjet to be widely employed in the field of graphics.

From an RIJ point of view it is the fact that an inkjet printer can be employed as a synthesis tool that is of the greatest interest. In traditional chemical synthesis, the chemist seeks to have a high degree of precision with the aliquots of solution that they mix, as this ensures that the correct stoichiometry is obtained. In RIJ, the inkjet printer is treated as a precise pipette.

RIJ can be compared to micro-fluidic chips, (‘Lab-on-a-Chip’), in which networks of channels have been etched in to the substrate. Typically, two or more channels each containing a reactive species meet in a chamber where the reactants mix forming a product. In terms of comparison, the channels in micro-fluidic chips are in the region of 300 to 3000 micron wide whereas an inkjet printer typically produces droplets that have contact diameters on the substrate of 100 microns. Due to improved mixing, micro-fluidic chips offer increased reaction yields and decreased consumption of material; these advantages are also enjoyed by RIJ. However, a further advantage of RIJ is that reaction products can also be placed such that the final device geometry is obtained.

Two types of RIJ have been defined.¹ These types are ‘Single RIJ’ and ‘Full RIJ’. Single RIJ involves an inkjet printer dispensing an ink, typically a solution, that reacts with a species that has been deposited on the substrate by another deposition technique, such as spin-coating or spraying. Although an argument could be made for expanding the concept of single RIJ to involve etching of the substrate, this approach isn’t covered in this book. Etching, or chemical machining, is typically several orders of magnitude smaller than RIJ such as the etching of silicon to form integrated chips or several of orders of magnitude larger such as in bulk cleaning or smoothing. RIJ, whether Single or Full, requires a substrate that does not take part in the reaction.

The main advantage of Single RIJ is that most research laboratories possess inkjet printers that allow the jetting of one ink only. Although, inkjet printer manufacturers are making machines that dispense more than one ink these tend to be more expensive and complex than single ink systems. Another advantage of Single RIJ is that one reactant can be deposited in bulk which increases the speed of the overall process. The second patterning step forms the desired product and the unreacted material can be removed.

Full RIJ is where an inkjet printer deposits two or more reactants, usually in separate passes from independent printheads. The advantage of Full RIJ is that less waste is generated when compared to Single RIJ and direct patterning is obtained. However, Full RIJ can be more time consuming and in some cases, depending on the solvents used, the drying out of the first reactant may be an issue.

1.3 Types of Inkjet Printer

Inkjet printing can be divided into two types: continuous inkjet and drop-on-demand ink. A further division can be made with drop-on-demand (DoD) into piezo DoD and thermal DoD, with the divisor being the actual method of actuation employed. Regardless of the type of inkjet method used, the in-flight diameters of the produced droplets range from 150 micron down to 10 micron.²

1.3.1 Continuous Inkjet Printing

There are a number of ways droplets are produced in continuous inkjet (CIJ), however all methods involve the droplets passing between a set of electrodes. Domino’s A-Series SureStart print head contains a vibrating drive rod, which creates ultrasonic pressure waves in the ink, breaking it up into individual droplets.³ Linx CIJ technology involves ...

Table of contents

• Cover
• Title Page
• Copyright Page
• Preface
• Contents
• Chapter 1 Reactive Inkjet Printing—An Introduction
• Chapter 2 From Inkjet Printed Droplets to Patterned Surfaces
• Chapter 3 Droplet Mixing
• Chapter 4 Unwanted Reactions of Polymers During the Inkjet Printing Process
• Chapter 5 Reactive Inkjet Printing for Silicon Solar Cell Fabrication
• Chapter 6 Reactive Inkjet Printing: From Oxidation of Conducting Polymers to Quantum Dots Synthesis
• Chapter 7 Reactive Inkjet Printing of Silk Barrier Membranes for Dental Applications
• Chapter 8 Reactive Inkjet Printing of Regenerated Silk Fibroin as a 3D Scaffold for Autonomous Swimming Devices (Micro-rockets)
• Chapter 9 Reactive Inkjet Printing for Additive Manufacturing
• Chapter 10 Reactive Inkjet Printing of Metals
• Chapter 11 The Use of Reactive Inkjet Printing in Tissue Engineering
• Subject Index