Material Synthesis and Additive Manufacturing


Additive Manufacturing through Interference Lithography

Collaboration with Professor Andrei Faraon's group (Caltech).

Personnel: Andrew Friedman (Ph.D. student in Chemical Engineering) and Dr. Luizetta Elliott (Alumna)

Developments in additive manufacturing have revealed numerous applications for three-dimensional (3D) micro- and nano-architected materials such as microfluidic filters, photonic crystals, advanced structural materials, catalysts, and high-velocity projectile impact absorption. Proper realization of these applications requires manufacturing techniques that allow for rapid, high-throughput 3D patterning with structural feature resolution on the order of nanometers. The rate-limiting aspect of standard techniques such as multi-photon and electron-beam lithography is the rastered voxel size, and that of holographic interference lithography is the spot size of a single exposure. We present a visible light interference lithography technique that utilizes a 2x2 cm metasurface mask composed of Si nanopillars on quartz capable of enabling patterning without index-matching fluids or direct contact with the photoresist or substrate. We use this technique to expose arbitrarily large areas (>10x10) cm in 20-60 um-thick films of commercial negative-tone photoresist SU-8 and in >20 um films of custom glycidyl-methacrylate-derived alternatives via serialized raster exposures to produce a fully continuous and homogenous nano-architected material.

additive manufacturing

Utilization of (meth)acrylate chemistry in custom photoresists allows for incorporation of functional monomers directly into the photoresist backbone, rendering it amenable to post-processing surface functionalization via pendant amine incorporation. The combination of our metasurface-enabled large-scale 3D patterning technique with customizable photoresist chemistry provides a new pathway for scalable production of architected materials with nanometer feature resolution and advanced properties such as shape memory effects, localized surface functionalization, and impact absorption.

Additive Manufacturing of Novel Materials

Creating materials with a suite of designed properties is one of key challenges in our society. Solving this grand challenge will open pathways to create entirely new classes of materials, whose properties are determined a priori and attained through a multi-scale physically informed approach. These new material classes will offer breakthrough advances in almost every branch of manufacturing and technology: from ultra lightweight and damage-tolerant structural materials to safe and efficient energy storage, biomedical devices, biochemical and micromechanical sensors and actuators, nanophotonic devices, and textiles.

Additive manufacturing (AM) has enabled advances in various fields of science and technology due to its unique ability to fabricate architected materials — materials with topologically defined features that result in unprecedented and unique material properties. Vat photopolymerization (VP) stands out amongst all the AM techniques available due to its high resolutions and throughputs achievable, and have been used to fabricate materials with unique mechanical and optical properties.

Hydrogel-derived Metals and Ceramics

Personnel: Dr. Kai Narita (Alumnus), Max Saccone (Ph.D. student in Chemical Engineering), and Dr. Daryl Yee (Alumnus)

The materials that are compatible with VP are largely limited to polymers, with ceramics and metals being challenging to fabricate. We developed a process that combines in-situ solution combustion synthesis with VP to fabricate metals and ceramics from hydrogels. This process is facile, compositionally versatile, and compatible with any VP technique.

Microlattices of zinc oxide (ZnO) with features sizes of ~250nm were fabricated using two photon lithography using this process. Using characterization techniques such as X-ray diffraction, energy-dispersive spectroscopy, thermogravimetric analysis and transmission electron microscopy, we show that these structures were composed of monolithic polycrystalline ZnO with an average grain size of 5nm. In situ compressions of these architected ZnO structures using a custom-build electromechanical setup also indicated that these structures had electromechanical capabilities.

additive manufacturing

We have also used this technique to explore the AM of materials for lithium-ion battery applications. 3D architected lithium cobalt oxide (LCO) materials fabricated using digital light processing printing with our process had resolutions ~100µm. These free-standing, binder- and conductive additive-free LCO structures were integrated as cathodes into LIBs, and exhibited electrochemical capacity retention of 76% over 100 cycles at C/10.

Our novel ceramic and metal fabrication process enables the facile synthesis of advanced materials for AM, and has direct implications in a variety of fields, from nanoelectromechanical systems to chemical catalysis, energy storage, and new material synthesis, and could enable the production of previously impossible 3D smart devices.

We developed a general method for the fabrication of a wide variety of metals and alloys with complex shapes, mesoscale resolution, and overall cm-scale dimensions via digiltal light processing (DLP) AM and subsequent post-processing and thermal treatment. This streamlined technique makes use of a single resin composition and a single set of processing conditions during the DLP process, followed by infusion of appropriate metal precursors into a hydrogel structure. Heat treatment in oxidizing followed by reducing atmospheres converts the polymer/precursor matrix into the target metal. Unlike previous vat photopolymerization strategies which have target materials or precursors incorporated into the resin during the printing process, this method does not require re-optimization of resins and resin curing parameters when the target material is changed; relevant process control parameters are shifted to the hydrogel infusion and heat treatment steps. This experimental work opens the door to an entirely new class of metal AM methods based on conventional polymer-processing AM techniques such as DLP.

additive manufacturing

DLP Printing of Compliant Materials

Personnel: Amylynn Chen (Ph.D. student in Materials Science) and Dr. Daryl Yee (Alumnus)

With the rapid advancements in additive manufacturing (AM) and 3D printing technologies, an increasing demand on versatile material properties of the photoresins arises to accommodate the broad range of applications enabled by AM. Majority of the materials obtained from commercially-available VP photoresins are tend to the brittle and inert which limit their range of applications.

Polyelectrolyte complexes (PECs) are a class of materials containing supramolecular interactions such as electrostatic crosslinks, which display mechanical compliance, self-healing, and stimuli responsivity with applications in soft-robotics, recyclable materials, reparable systems and sensors. Our search aims to develop a PECs-based photoresin, which allows the 3D fabrication of materials that displays high compliance, stimuli-response, and rapid self-healing. These properties arise from the presence of physical entanglement and dynamic electrostatic crosslinking as opposed to conventional covalent crosslinking, which allow PECs to untangle, change configuration, and reform bonds once broken.

3D Nano-architected Metals

Personnel: Dr. Andrey Vyatskikh (Alumnus)

Nano-architected materials enable de-coupling properties that have historically been linked together, for example strength and density, thermal conductivity and modulus, which shifts the material creation paradigm to properties -> architecture -> fabrication. When the characteristic dimensions of solid constituents that comprise architected materials are reduced to the nano-scale, many new phenomena emerge. Nearly all materials exhibit different properties when reduced to nano-scale – for example, in terms of mechanical properties where smaller can be stronger or weaker, can suppress brittle failure and induce ductility, couple into light to create 3D photonic crystals and negative refraction materials, and activate phonon scattering-driven thermal processes.

We use novel chemical syntheses and two-photon lithography, as well as 3D printing, to create nano- and micro-architected materials, which represent a class of new "meta-materials" that can utilize the optimized nanometer-sized induced material properties, high surface area, and 3D architectures, to enable distinct departure from existing material systems. We focus on exploring the combination of hierarchical design and nanoscale dimensions of different materials classes – glasses, metals, polymers, semiconductors, shape-memory, photonic and piezoelectric materials, etc. - that enable de-coupling historically linked properties like strength and density through architectural control.

additive manufacturing