James P. Lewicki

Encapsulated liquid sorbents for carbon dioxide capture

Drawbacks of current carbon dioxide capture methods include corrosivity, evaporative losses and fouling. Separating the capture solvent from infrastructure and effluent gases via microencapsulation provides possible solutions to these issues. Here we report carbon capture materials that may enable low-cost and energy-efficient capture of carbon dioxide from flue gas. Polymer microcapsules composed of liquid carbonate cores and highly permeable silicone shells are produced by microfluidic assembly. This motif couples the capacity and selectivity of liquid sorbents with high surface area to facilitate rapid and controlled carbon dioxide uptake and release over repeated cycles. While mass transport across the capsule shell is slightly lower relative to neat liquid sorbents, the surface area enhancement gained via encapsulation provides an order-of-magnitude increase in carbon dioxide absorption rates for a given sorbent mass. The microcapsules are stable under typical industrial operating conditions and may be used in supported packing and fluidized beds for large-scale carbon capture.

3D-Printing of Meso-structurally Ordered Carbon Fiber/Polymer Composites with Unprecedented Orthotropic Physical Properties

Here we report the first example of a class of additively manufactured carbon fiber reinforced composite (AMCFRC) materials which have been achieved through the use of a latent thermal cured aromatic thermoset resin system, through an adaptation of direct ink writing (DIW) 3D-printing technology. We have developed a means of printing high performance thermoset carbon fiber composites, which allow the fiber component of a resin and carbon fiber fluid to be aligned in three dimensions via controlled micro-extrusion and subsequently cured into complex geometries. Characterization of our composite systems clearly show that we achieved a high order of fiber alignment within the composite microstructure, which in turn allows these materials to outperform equivalently filled randomly oriented carbon fiber and polymer composites. Furthermore, our AM carbon fiber composite systems exhibit highly orthotropic mechanical and electrical responses as a direct result of the alignment of carbon fiber bundles in the microscale which we predict will ultimately lead to the design of truly tailorable carbon fiber/polymer hybrid materials having locally programmable complex electrical, thermal and mechanical response.

Shape-morphing composites with designed micro-architectures.

Shape memory polymers (SMPs) are attractive materials due to their unique mechanical properties, including high deformation capacity and shape recovery. SMPs are easier to process, lightweight, and inexpensive compared to their metallic counterparts, shape memory alloys. However, SMPs are limited to relatively small form factors due to their low recovery stresses. Lightweight, micro-architected composite SMPs may overcome these size limitations and offer the ability to combine functional properties (e.g., electrical conductivity) with shape memory behavior. Fabrication of 3D SMP thermoset structures via traditional manufacturing methods is challenging, especially for designs that are composed of multiple materials within porous microarchitectures designed for specific shape change strategies, e.g. sequential shape recovery. We report thermoset SMP composite inks containing some materials from renewable resources that can be 3D printed into complex, multi-material architectures that exhibit programmable shape changes with temperature and time. Through addition of fiber-based fillers, we demonstrate printing of electrically conductive SMPs where multiple shape states may induce functional changes in a device and that shape changes can be actuated via heating of printed composites. The ability of SMPs to recover their original shapes will be advantageous for a broad range of applications, including medical, aerospace, and robotic devices.

3D printed cellular solid outperforms traditional stochastic foam in long-term mechanical response

3D printing of polymeric foams by direct-ink-write is a recent technological breakthrough that enables the creation of versatile compressible solids with programmable microstructure, customizable shapes, and tunable mechanical response including negative elastic modulus. However, in many applications the success of these 3D printed materials as a viable replacement for traditional stochastic foams critically depends on their mechanical performance and micro-architectural stability while deployed under long-term mechanical strain. To predict the long-term performance of the two types of foams we employed multi-year-long accelerated aging studies under compressive strain followed by a time-temperature-superposition analysis using a minimum-arc-length-based algorithm. The resulting master curves predict superior long-term performance of the 3D printed foam in terms of two different metrics, i.e., compression set and load retention. To gain deeper understanding, we imaged the microstructure of both foams using X-ray computed tomography, and performed finite-element analysis of the mechanical response within these microstructures. This indicates a wider stress variation in the stochastic foam with points of more extreme local stress as compared to the 3D printed material, which might explain the latter’s improved long-term stability and mechanical performance.

The stability of polysiloxanes incorporating nano-scale physical property modifiers

Abstract Reported here is the synthesis and subsequent characterization of the physical and chemical properties of novel polysiloxane elastomers modified with a series of polyhedraloligomericsilsequioxane (POSS) molecular silicas. The physical properties of the formulated nanocomposite systems have been characterized with a combination of dynamic mechanical analysis (DMA), broadband dielectric spectroscopy (BDS) and confocal Raman microscopy. The results of the physical property characterization demonstrate that the incorporation of low levels (1–4% by wt.) of POSS particles into the polysiloxane network leads to significant improvements in the mechanical properties of the elastomer and significantly alters the motional chain dynamics of the system as a whole. The results of studies performed to assess the long-term stability of these novel nanocomposite systems have demonstrated that POSS physical property modifiers can significantly alter the thermal stability of polysiloxane elastomers. Physically dispersed POSS has also been shown in some cases to be both mobile and disruptive within the polysiloxane networks, agglomerating into domains on a micron scale and migrating to the surface of the elastomers. This work demonstrates both the potential of POSS nanoparticles as physical property modifiers and describes the effects of POSS on the physical and chemical stability of polysiloxane systems.

Thermal Degradation Behavior and Product Speciation in Model Poly(dimethylsiloxane) Networks

The thermal degradation behavior of a series of well defined poly(dimethylsiloxane) (PDMS) model networks has been studied using a combination analytical thermal analysis techniques and multivariate statistical analysis in order to probe the influence of network architecture on degradation chemistry. The aim of this research has been to determine the effect differing network architectures: mono and bimodality, a range of crosslink density, inter-chain molar mass and percentage of free chain ends on the mechanisms of PDMS thermal degradation. A series of model PDMS networks have been formulated using of tin catalyzed condensation cure chemistry and a range of linear precursors to yield a matrix of model network systems. The thermal degradation chemistry of these model networks have been characterized in relation to their structure by means of pyrolysis gas chromatography mass spectrometry (Py-GCMS), thermal gravimetric analysis (TGA) and multivariate statistical analysis. The results clearly demonstrate that the structural architecture of (chemically similar) PDMS networks has a significant impact on the mechanisms of PDMS thermal degradation. Notability, with decreasing inter-crosslink chain length, larger cyclic siloxane species (>D5) become more abundant degradation products and that there is a relationship between inter-chain molar mass, degree of crosslinking and the thermal stability on the mechanisms of degradation. This work effectively demonstrates that quantifiable relationships exist between basic network architectures and the distributions of degradation derived species in PDMS networks.

Soft Materials with Recoverable Shape Factors from Extreme Distortion States.

Elastomeric polysiloxane nanocomposites with elongations of >5000% (more than 3× greater than any previously reported material) with excellent shape recovery are presented. Highly deformable materials are desirable for the fabrication of stretchable implants and microfluidic devices. No crosslinking or domain formation is observed by a variety of analytical techniques, suggesting that their elastomeric behavior is caused by polymer chain entanglements.

Advances in Modeling Sorption and Diffusion of Moisture in Porous Reactive Materials

Water-vapor-uptake experiments were performed on a silica-filled poly(dimethylsiloxane) (PDMS) network and modeled by using two different approaches. The data was modeled by using established methods and the model parameters were used to predict moisture uptake in a sample. The predictions are reasonably good, but not outstanding; many of the shortcomings of the modeling are discussed. A high-fidelity modeling approach is derived and used to improve the modeling of moisture uptake and diffusion. Our modeling approach captures the physics and kinetics of diffusion and adsorption/desorption, simultaneously. It predicts uptake better than the established method; more importantly, it is also able to predict outgassing. The material used for these studies is a filled-PDMS network; physical interpretations concerning the sorption and diffusion of moisture in this network are discussed.

The Influence of Polyhedral Oligomeric Silsequioxanes on Domain Microstructure in Polyurethane Elastomers

The influence of polyhedral oligomeric silsequioxanes (POSS) as covalently bound hybrid physical property modifiers on the segmental dynamics and morphology of segmented polyurethane elastomers has been studied by solid-state magic sandwich echo nuclear magnetic resonance (MSE-NMR), differential scanning calorimetry (DSC) and atomic force microscopy (AFM). A model system has been synthesized which incorporates diol functionalized POSS over a range of loadings into the hard-block of a methylene di-isocyanate - butane diol - poly(tetramethylene glycol) (MDI-BDO-PTMG) segmented PU elastomer. MSE-NMR has been employed to probe the segmental dynamics of the PU system as a function of POSS loading and it has been demonstrated that low levels of POSS as a substitute chain extender, both rigidify the hard-block phase of the PU and significantly alter both the phase morphology, mixing and structure of the inter-phase domains. These observations are supported by more classical AFM and DSC morphological characterization of the POSS-PU hybrid systems which show significant re-structuring of the phase domain structure of the PU and ordering of the crystalline hard-block domains. This work demonstrates the application of a multi-scaled experimental approach towards understanding the effects of three-dimensional, nano-scale cage moieties on the already complex phase structure of segmented polyurethanes. Through these efforts, new insight has been gained into the mechanisms by which low levels of a nano-material such as a cubic sesquioxane, can impact the phase separation and segmental dynamics of block ter-polymer polyurethanes.

An investigation of the nature and reactivity of the carbonaceous species deposited on mordenite by reaction with methanol

An investigation of the nature of the carbonaceous species deposited upon mordenite by reaction with methanol has been undertaken. The nature of the species has been shown to be a strong function of both temperature and time on stream. Upon reaction at 300 °C a range of alkyl and aromatic species, consistent with the development of an active hydrocarbon pool, are evident and time on stream studies have shown that these are developed within 5 min. Upon reaction at 500 °C, a narrower range of hydrogen deficient aromatic species is evident. Thermal volatilisation analysis (TVA), not previously applied to the study of coked zeolites, is shown to be complementary to the more commonly applied C analysis, 13C MAS NMR and TGA techniques.