Research

Overview

Our group focuses on the use of advanced measurements and well-defined materials to provide fundamental insights into how to improve processing and properties of materials for a wide variety of applications. One underpinning concept is the importance of interfaces and that the properties at interfaces may dramatically deviate from the bulk. A wide variety of applications have been explored ranging from microelectronics to energy storage and generation to separations to additive manufacturing.

Additive Manufacturing

3D printing offers a disruptive platform that offers the potential to revolutionize manufacture through new part designs, massive customization without added costs, and inventory on-demand. One of the most cost effective methods for 3D printing of plastic objects is fused filament fabrication (FFF), which was initially commercialized by Stratasys as fused deposition modeling (FDM). This process relies on the melting of a thermoplastic filament to extrude the melt into the shape by rastering the hotend extruder of the FFF printer and then building up the object in a layer-by-layer manner. The ability to maintain the desired shape relies on the solidification of the polymer prior to significant flow under gravity that would deform the shape. However this requirement is orthogonal to the standard methodology to obtain mechanical properties for these 3D printed objects as diffusion of chains across the interface developed during printing provides the weld-strength. As these 3D printed parts are comprised of essentially a multitude of weld lines, it is unsurprising that the mechanical properties of these 3D printed materials is inferior to those obtained from more traditional polymer manufacture, like injection or compression molding. With the desire to evolve 3D printing from rapid prototyping to full blown additive manufacturing, there is a need to improve fundamental understanding of the processes involved with the printing to enable novel designs for filaments to provide performance to 3D printed objects for integration into products.


Taking inspiration from early work to understand injection molding process, we have fabricated filaments containing flow indicators (inorganic pigments) that allow for the flow out of the hot end to be visualized. As shown in the figure to the right, pigment was added to a polycarbonate (PC) and melt spun into 200-300 μm diameter fibers that were inserted into PC filaments. As the filament is fed into the hotend, the polymer melts and begins to flow. However this flow depends on the heat conduction through the polymer as the polymer must be melted. The filament is pressed through a narrow orifice that provides primary size for the polymer melt used to build the part. We have examined the solidified filament after extrusion through the hotend using both x-ray tomography and optical microscopy to quantify the shape of the flow indicator. These results indicate that one of the first assumptions of models for FFF is incorrect (isothermal flow). This platform provides an easy route to also quantify how the polymer flows within the printed part and how shape, size, and orientation change this flow for a variety of different objects.


From examination of the FFF process from a fundamental materials perspective, we have developed a novel core-shell architecture filament that allows the separation of the requirements for dimensional accuracy and formation of the weld interface. This geometry for the materials in the filament is translated into the printed part and has benefit of providing new mechanisms for energy dissipation in 3D printed parts that provide high toughness, in some cases comparable to injection molded PC. The selection of the polymer-polymer pair and its relative ratio in the filament can dramatically influence the performance of the 3D printed objects.

With the capabilities to fabricate our own filaments, functional polymers have been formed into filaments to provide added functionality or value-add to the part. For example, we have used a semicrystalline ionomer to provide shape memory behavior to a 3D printed part using standard FFF processing.

Representative publications:

  • J.-R. Ai, S. Li, B.D. Vogt. Increased strength in carbon-poly(ether ether ketone) composites from material extrusion with rapid microwave post processing. Additive Manufacturing, 2022, 60, 103209. https://doi.org/10.1016/j.addma.2022.103209
  • F. Peng, B.D. Vogt, M. Cakmak. Complex Flow and Temperature History during Melt Extrusion in Fused Deposition Modeling for Additive Manufacturing. Additive Manufacturing 2018, 22, 197-206. http://dx.doi.org/10.1016/j.addma.2018.05015

Material re-use, recycling and upcycling

Resource extraction, purification and processing all require extensive energy inputs to provide the materials that define the built environment and provide many of the conveniences of modern life. However, these investments in cost and energy are commonly discarded at the end of the service life with a linear materials economy that extracts resources to produce materials and disposes of the materials when their useful lifetime is complete. Although plastic waste  has become a key talking point, the energy use for construction and building materials is far greater and annually these industries produce nearly twice the amount of landfilled material than that from residential waste. These waste stream contain a variety of inorganic and plastic components, but their effective reuse is generally prohibited by the high costs associated with separations.  We are working to enable re-use of these materials and other difficult to recycle materials through the intrinsically low energy process of cold sintering. This process allows for the co-consolidation of ceramic and polymeric materials due to the low temperatures used for the sintering. In addition to the reprocessing of materials through cold sintering, we are also exploring other routes to transform plastic waste into higher value products as well as low cost routes to improve capability of commodity plastics to reduce sorting requirements.

Representative publications:

Mechanics and structure of associating polymers

Non-covalent interactions between polymer chains provide effective crosslinks on the timescale of the lifetime of these interactions and thus can dramatically influence the dynamics and mechanical properties. The connectivity of polymers can  amplify the effective strength of these interactions, but the coordination number for the interactions can also play a key role. These cases of polymers are examined for a variety of applications including tough hydrogels for biomedical and ionomers for shape memory (see video above). Details about the connectivity and strength of the interactions can dramatically influence the properties of these materials. We use neutron and x-ray scattering to develop understanding of the associated nanostructure and how this evolves through deformation to provide insights into how to design polymers at a molecular level. The details of the polymer architecture and its composition translate to the mesoscale structure and ultimately macroscopic properties.


Amphiphilic statistical copolymers can form effective crosslinks through hydrophobic associations when immersed in water to form hydrogels. These associations are reversible and provide a mechanism for energy dissipation during deformation. From in-situ X-ray scattering measurements (SAXS) during tensile deformation, the primary mechanism for the energy dissipation through pull out of individual hydrophobic moieties from the nano-aggregates was determined. The observed deformation of the nanostructure, however, was strongly dependent on the deformation rate and was found to be directly related to the relaxation time spectra for the hydrogel. Through multiple associating species on a single polymer chain, the relative timescales for the rearrangement of the effective crosslinks can be tuned. Routes to modulate the relaxations to obtain challenging to obtain combinations of mechanical properties are being developed.

Representative publications:

  • K. Sadman, C. G. Wiener, R.A. Weiss, C.C. White, K. Shull, B.D. Vogt. Quantitative Rheometry of Thin Soft Materials using the Quartz Crystal Microbalance with Dissipation. Analytical Chemistry 2018, 90 (6), 4079-4088. http://dx.doi.org/10.1021/acs.analchem.7b05423
  • C. Wiener, C. Wang, R.A. Weiss, B.D. Vogt. Nanostructure evolution during relaxation from a large step strain in a supramolecular hydrogel crosslinked by hydrophobic aggregation: A SANS investigation. Macromolecules 2017, 50(4), 1672-1680. http://dx.doi.org/10.1021/acs.macromol.6b02680

Self assembled materials


Nature relies on specific interactions to assemble molecules into structures at multiple length scales. The precise control of these structures is dictated by the perfection in the macromolecules in both length and sequence. Synthetic methodologies to control polymerization have advanced in recent years to enable improved control and diversity in the chemical functionalities, but these tend to only assemble at a single length scale. Despite these limitations, simple block copolymer architectures provide routes to a wide variety of nanostructure. We have interests in developing routes to translate these well defined structures into inorganic materials and also improving the orientation/order of the self-assembly through novel processing. These methods can generally be applied to a wide variety of block copolymer (BCP) chemistries and BCP blends. Potential applications for these self-assembled materials can be divided into those that exploit the uniform size of the self-assembled structure such as porous materials for selective sensors and those that rely on their uniform periodic structure such as polarizers.

Representative publications:

  • Z. Qiang, Y. Xia, X. Xia, B.D. Vogt. Generalized Synthesis of a Family of Highly Heteroatom Doped Ordered Mesoporous Carbons. Chemistry of Materials 2017, 29 (23), 10178-10186. http://dx.doi.org/10.1021/acs.chemmater.7b04061
  • Z. Qiang, Y. Zhang, Y. Wang, S.M. Bhaway, K.A. Cavicchi, B.D. Vogt. Highly aligned, large pore ordered mesoporous carbon films by solvent vapor annealing with soft shear. Carbon 2015, 82, 51-59. https://doi.org/10.1016/j.carbon.2014.10.025

Modified properties in nanoconfinement


When dimensions approach those of the molecule itself, there is a tendency to observe properties that can deviate substantially from the bulk material. These changes are sometimes a result of the intrinsic size, but in many cases are directly related to the changes induced by the interfaces. This is especially true for polymers where their intrinsic size can be readily varied by degree of polymerization, but the properties in nanoconfinement tend to be independent of molecular weight (when supported). We have been particularly interested in the mechanical properties of nanoconfined polymers due to their significance in microelectronics as photoresists. As the size of the features in the transistors is continuously decreasing to enable scaling following Moore’s law, the features that need to be generated in the photoresist have decreased to <10 nm. These features must be stable through the processing to allow for their transfer into the underlayer, so understanding their mechanical properties at these length scales provides insights into potential for pattern collapse. The size dependence of elastic modulus in polymers can be in general avoided through the incorporation of an appropriate anti-plasticizer or through selection of a polymer with an intrinsically stiff backbone.

More recently, the confinement of water within hydrophobically-crosslinked hydrogels has been investigated through examination of the dynamics of water within the hydrogels (through quasi elastic neutron scattering) and the crystallization of water (ice) within the hydrogel. Interestingly with appropriate sizes, almost all crystallization of water can be suppressed within the hydrogel with the size corresponding to the critical water cluster size for ice that has been previously reported.

Representative publications:

  • C. Wang, C.G. Wiener, R. Li, M. Fukuto,R.A. Weiss, B.D. Vogt. Antifreeze Hydrogels from Supramolecular Copolymers. Chemistry of Materials 2019, 31, 135-145. https://doi.org/10.1021/acs.chemmater.8b03650
  • J.M. Torres, C.M. Stafford, B.D. Vogt. Elastic Modulus of Amorphous Polymer Thin Films: Relationship to the Glass Transition Temperature. ACS Nano 2009, 3(9), 2677-2685. http://dx.doi.org/10.1021/nn9006847

Beyond Li ion batteries

Although Li ion batteries dominate the consumer energy storage market today, the demands for energy density grow along with sensitivity to cost as new technologies are developed. There has been substantial efforts to increase the energy density through alternative storage strategies of alloying and conversion instead of the commercial intercalation mechanism. However to achieve substantial increases in performance, lithium metal electrodes are required. The non-uniform deposition of Li through charge-discharge cycling leads to the growth of dendrites that represent a serious safety hazard. We have been exploring scalable routes to control dendrite growth through passivation of the Li metal surface using low cost precursors and novel processing. Combining these advances in a metal anode with sulfur as the active cathode material provides the potential for high performance batteries with also low cost due to the availability of sulfur.

However the increasing use of lithium challenges the future supply and thus there are concerns about the long term prices for lithium. To overcome these cost challenges, alternative chemistries are being explored. We have interests in sodium and magnesium as the ions for rechargeable batteries. Control of the nanostructure of the electrodes, surface chemistry and details of the electrolyte are all critical to the performance and potential lifetime of the battery. We use a variety of structural and electrochemical measurements to understand the interplay of these characteristics.

Representative publications:

  • Z. Qiang, Y.-M. Chen, Y. Xia, W. Liang, M. Gao, Y. Zhu, B.D. Vogt. Ultralong Cycle Life Sodium-Sulfur Batteries using Highly Doped (N,S) Nanoporous Carbon. Nano Energy, 2017, 32, 59-66. https://doi.org/10.1016/j.nanoen.2016.12.018
  • S.M. Bhaway, Z. Qiang, Y. Xia, B. Lee, K.G. Yager, L. Zhang, K. Kisslinger, Y.-M. Chen, K. Liu, Y. Zhu, B.D. Vogt. Operando Grazing Incidence Small-Angle X-ray Scattering/X-ray Diffraction of Model Ordered Mesoporous Lithium-Ion Battery Anodes. ACS Nano 2017, 11(2), 1443-1454. http://dx.doi.org/10.1021/acsnano.6b06708