Flexible electronics have demonstrated potential in a wide range of applications including wearable sensors, photovoltaics, medical devices and more, due to their properties of extreme adaptability while also being lightweight and highly robust. The main challenge standing in the way of progress in this field is the difficulty of large-scale manufacturing of these flexible electronics compared to their rigid counterparts. Microcontact printing is a form of soft lithography in which an elastomeric stamp is used to transfer sub-micron scale surface patterns onto a flexible substrate via ink monolayers. The integration of microcontact printing into a roll-to-roll (R2R) system will enable continuous printing of flexible electronics and scale it up for massive manufacturing. The proposed thesis outlines a novel mechanical design for a microcontact printer which utilizes flexural motion stages with integrated position and force sensors to control the print process on a R2R system. The printhead is designed to fit the available space on the pre-installed UMass Amherst Intelligent Sensing Laboratory test table and breadboard. The R2R system includes motorized rollers for winding/unwinding the PET (polyethylene terephthalate) web substrate, and idler rollers for guiding a web through the print system. As the central element to this design, two matching plate flexures are designed on the two ends of the printer roller to control the tilting and positioning of the print roller. Flexure mechanisms rely on bending and torsion of flexible elements: this allows them to achieve much higher precision in positioning compared to conventional mechanisms which rely on surface interaction between multiple moving parts. The print resolution target for this design is 500 nm (linewidth), based on current state-of-the-art designs [1, 2]. In the initial version of the printhead design, a total of 33 parts are custom fabricated for assembly and installation in the R2R system lab setup. These include everything from the components of the print roller, specially adapted air-bearing mounts, support structures, and connectors. The design and 4 fabrication process for every component is outlined here along with the functionality, as every component was designed with the system objectives and constraints in mind. Using SolidWorks simulation, FEA (finite element analysis) is performed for every part of the assembly that is subjected to stress in the real system, so that predictions can be made about the displacement of the motion stages and the frequency of vibration. These predictions are evaluated by comparation with the experimental results from tests conducted on the real system hardware and used to assess the quality of the fabricated assembly. The work performed in this thesis enables advancements in the assembly of an updated, optimized R2R system and has led to an experimentally functioning lab setup that is ripe for further improvements. Completion and calibration of this augmented R2R system will, in future, enable UMass Amherst in-house production of large-area flexible electronics which may be used in a wide range of applications, including medical sensors, solar cells, displays, and more. In addition to microcontact printing, this R2R system may also be applied to nanoimprint lithography, another contact-based print method, or integrated with inkjet printing, a non-contact method.

<p>Cellulose nanocrystals (CNCs) and its composite coatings may impart many benefits in packaging, electronic, optical, etc. applications; however, large-scale coating production is a major engineering challenge. To fill this knowledge gap, a potential large-scale manufacturing technique, roll-to-roll reverse gravure processing, has been described in this work for the manufacture of CNC and CNC-poly(vinyl alcohol) (PVA) coatings on a flexible polymer substrate. Various processing parameters which control the coating structure and properties were examined. The most important parameters in controlling liquid transfers were gravure roll, gravure speed, substrate speed, and ink viscosity. After successful fabrication, coating adhesion was investigated with a crosshatch adhesion test. The surface roughness and morphology of the coating samples were characterized by atomic force microscopy and optical profilometer. The Hermans order parameter (S) and coating transparency were measured by UV–Vis spectroscopy. The effect of viscosity on CNC alignment was explained by the variation of shear rate, which was controlled by the micro-gravure rotation. Finally, the CNC alignment effect was investigated for gas barrier and thermal management applications.</p> <p>In packaging applications, cellulose nanomaterials may impart enhanced gas barrier performance due to their high crystallinity and polarity. In this work, low to superior gas barrier pristine nanocellulose films were produced using a shear-coating technique to obtain a range of anisotropic films. Induction of anisotropy in a nanocellulose film can control the overall free volume of the system which effectively controls the gas diffusion path and hence, controlled anisotropy results in tunable barrier properties. The highest anisotropy materials showed a maximum of 900-fold oxygen barrier improvement compared to the isotropic arrangement of nanocellulose film. The Bharadwaj model of nanocomposite permeability was modified for pure nanoparticles, and the CNC data were fitted with good agreement. Overall, the oxygen barrier performance of anisotropic nanocellulose films was 97 and 27 times better than traditional barrier materials such as biaxially oriented poly(ethylene terephthalate) (BoPET) and ethylene vinyl alcohol copolymer (EVOH), respectively, and thus could be utilized for oxygen-sensitive packaging applications. </p> The in-plane thermal conductivity of CNC - PVA composite films containing different PVA molecular weights, CNC loadings and varying order parameters (S) were investigated for potential application in thermal management of flexible electronics. Isotropic CNC - PVA bulk films with 10-50 wt% PVA solid loading showed significant improvement in thermal conductivity compared to either one component system (PVA or CNC). Furthermore, anisotropic composite films exhibited in-plane thermal conductivity as high as ~ 3.45 W m-1 K-1 in the chain direction, which is higher than most polymeric materials used as substrates for flexible electronics. Such an improvement can be attributed to the inclusion of PVA as well as to a high degree of CNC orientation. The theoretical model was used to study the effect of CNC arrangement (both isotropic and anisotropic configurations) and interfacial thermal resistance on the in-plane thermal conductivity of the CNC-PVA composite films. To demonstrate an application for flexible electronics, thermal images of a concentrated heat source on both neat PVA and CNC-PVA composite films were taken that showed the temperature of the resulting hot spot was lower for the composite films at the same power dissipation.