Polyolefins dominate the market for commodity plastics due to their low cost and suitable properties, but polyolefins are rarely used in 3D printing due to issues with deformation of the printed structure during crystallization from the large volume change. Here, we demonstrate that filaments containing approximately 50% of either high density or low density polyethylene (HDPE/LDPE) as a shell with a polycarbonate (PC)/acrylonitrile-butadiene-styrene (ABS) blend core can be printed using standard fused filament fabrication methods with adequate to good dimensional accuracy, improved impact resistance, and enhanced elongation at break relative to samples printed with PC/ABS alone. The combination of lower crystallinity (28%) of LDPE in comparison to HDPE (62%) and lower crystallization temperature of LDPE (89 degrees C) than HDPE (117 degrees C) leads to improved dimensional accuracy of the printed part. However, the elastic modulus of the composite containing LDPE is only 48% of the part printed with only PC/ABS for flat (XY) orientations, whereas the reduction in modulus with the HDPE shell is significantly less. The mechanical behavior can be rationalized in terms of aligned fiber composite theory where anisotropic modulus is expected to be dependent on the angle between stretching direction and fiber axis. The low cost of LDPE and HDPE along with the ability to increase impact strength and extensibility of printed parts further demonstrate the promise of composite core-shell filaments for additive manufacturing.

A fused filament fabrication process is used for conversion of polyimide aerogels into bicontinuous gyroid structures to obtain enhanced elasticity. A sacrificial hollow mold in an inverse gyroid shape is first fabricated from high impact polystyrene and is filled with the polyimide sol. After the sol-gel transition, the mold is dissolved in a solvent to yield the gel structure of a gyroid shape. The gel is supercritically dried to recover a free-standing aerogel structure with ultrahigh porosity (98.9%) and low bulk density (0.0146 g/cm(3)). The bicontinuous gyroid structure of the aerogel offers significant elasticity and high elongation at break compared to an otherwise brittle monolithic aerogel of polyimide. The ability to create intricate aerogel structures opens up a large potential in applications such as sensor housing and acoustic barriers of arbitrary shape and size and load-bearing porous thermally insulating structures that allow breathing.

A photocurable triple shape memory polymer (TSMP) resin based on acrylic monomers and an ion-pair comonomer (IPC) has been formulated and successfully 3D printed with a digital light processing (DLP) printer. The ion-rich and ion-poor domains produced by polymerization-induced microphase separation (PIMS) generate two well-separated glass transition temperatures and an excellent triple shape memory effect in the material, which is systematically studied by dynamic mechanical analysis (DMA) and atomic force microscopy (AFM). With the TSMP resin, an intermediate shape can be set to distinguish and program different shape evolution pathways (SEPs). To visualize the sequential shape shifting, several 3D models are printed and transform through distinct pathways. A potential application of shape memory microfluidics is also demonstrated as a proof-of-concept.

A methodology for the preparation of porous scaffolds for tissue engineering using co-extrusion is presented. Poly(ε-caprolactone) is blended with poly(ethylene oxide) in a twin-screw extruder to form a two-phase material with micrometer-sized domains. Selective dissolution of the poly(ethylene oxide) with water results in a porous material. This method of polymer extrusion permits the preparation of scaffolds having continuous void space and controlled characteristic length scales without the use of potentially toxic organic solvents. A range of blend volume fractions results in co-continuous networks of polymer and void spaces. Annealing studies demonstrate that the characteristic pore size may be increased to larger than 100 μm. The mechanical properties of the scaffolds are characterized by a compressive modulus on the order of 1 MPa at low strains and approximately 10 MPa at higher strains. The results of osteoblast seeding suggest it is possible to use co-extrusion to prepare polymer scaffolds without the introduction of toxic contaminants.

The effect of lower critical solution temperature (LCST) phase separation on the crystallization of poly(ε-caprolactone) PCL in PCL/poly(D,L-lactide) (PDLA) blends is studied by simultaneous small-angle x-ray scattering (SAXS) and wide-angle x-ray scattering (WAXS). Phase separation is induced by controlled temperature jumps into the LCST (two-phase) region, which is above the melting temperature (60 °C) of PCL and the glass transition temperature (50 °C) of PDLA. We have followed the nanoscale structural changes (< 100 nm) during subsequent crystallization at 45 °C of critical (0.36 PCL) and off-critical (0.50 PCL) blend compositions in both one-phase and two-phase melts. The spherulite morphology (1–100 μm) is examined with optical microscopy. When crystallization follows LCST phase separation, the shape, size and distribution of the spherulites depends on the extent of melt phase separation. In our x-ray measurements, the WAXS crystallinity of PCL is less than 40 % for the temperature range of interest. We perform a correlation function and intensity model analysis of our SAXS data to obtain morphological variables that characterize the intraspherulitic morphology. These morphological variables are relatively constant during crystallization and are also independent of melt phase separation. On the other hand, the ultimate crystallinity and the crystallization rate depend on the extent of melt phase separation.

We review recent advances in the development of combinatorial methods for polymer characterization. Applied to materials research, combinatorial methodologies allow efficient testing of structure–property hypotheses (fundamental characterization) as well as accelerated development of new materials (materials discovery). Recent advances in library preparation and high-throughput screening have extended combinatorial methods to a wide variety of phenomena encountered in polymer processing. We first present techniques for preparing continuous-gradient polymer “libraries” with controlled variations in temperature, composition, thickness, and substrate surface energy. These libraries are then used to characterize fundamental properties such as polymer-blend phase behavior, thin-film dewetting, block-copolymer order–disorder transitions, and cell interactions with surfaces of biocompatible polymers.

Combinatorial methods were used for studying dewetting of thin hydrophobic polystyrene (PS) and hydrophilic poly( DL -lactic acid) (PDLA) films on chemically modified gradient energy surfaces. Substrate libraries were prepared by immersing passivated Si (Si-H surface functionality) in Piranha solution (H 2 SO 4 /H 2 O 2 /H 2 O) at acontrolled rate, yielding a systematic variation of solvent contact angles across the surface. Additionally, chlorosilane-treated Si surfaces were exposed to UV radiation in a gradient fashion under ozone atmosphere such that a range from hydrophobic to hydrophilic conditions was obtained across the surface (≈ 3 cm). Solvent droplet contact angles of water and diiodo methane were used to quantify the spatial variation of surface energy along one axis across the surface. Libraries of thin films of PS or PDLA coatings on gradient energy surfaces orthogonal to gradients in film thickness were screened for dewetting behavior using automated optical microscopy. Contrasting trends in the wettability of PS and PDLA were visibly apparent as a function of surface energy of the substrate. The number density of polygons of the dewet PS films was found to obey a power law relationship with both film thickness and substrate surface hydrophilicity.

Presentation describes United Technologies Research Center's recent work in green energy systems, including APRA-E project content to create a synthetic analogue of the carbonic anhydrase enzyme and incorporate it into a membrane for CO2 separation from the flue gas of a coal power plant.

A peptide sequence SVSVGMKPSPRP that selectively recognizes hydroxyapatite (HA) is identified by using a phage display approach. The engineered sequence exhibits chemical and structural specificity for HA over calcium carbonate and HA's amorphous calcium phosphate precursor. In situ binding to HA in a tooth cross section further demonstrates the sequence specificity and utility in nondestructive imaging applications.

Microfluidic devices were developed that integrate the synthesis of well defined block copolymers and dynamic light scattering (DLS) measurement of their micelle formation. These metal devices were designed to operate in contact with organic solvents and elevated temperatures for long periods, and thus were capable of continuous in-channel atom transfer radical polymerization (ATRP) of styrene and (meth) acrylate homopolymers and block copolymers. These devices were equipped with a miniaturized fiber optic DLS probe that included several technology improvements, including a measurement volume of only 4 microlitres, simple alignment, and reduced multiple scattering. To demonstrate the integrated measurement, poly(methyl methacrylate-b-lauryl methacrylate) and poly(methyl methacrylate-b-octadecyl methacrylate) block copolymers were processed on the device with a selective solvent, dodecane, to induce micelle formation. The in situ DLS measurements yielded the size and aggregation behavior of the micelles. For example, the block copolymer solutions formed discrete micelles (D-H approximate to 25 nm) when the corona block was sufficiently long (f(MMA) < 0.51), but the micelles aggregated when this block was short. This study demonstrates the utility of these new devices for screening the solution behavior of custom synthesized polymeric surfactants and additives.

Self-assembly is a promising route for controlling the nanoscale structure and material properties of coatings, yet it remains difficult to control the microstructure of these systems. In particular, self-assembling materials typically have complex and delicate energy landscapes, which are sensitive to defects, making it difficult to control morphology or orientation. We present a simple and robust strategy for modulating the film-substrate interaction, which can bias the self-assembly energy landscape and thus enforce a desired microstructure. The technique uses nanoparticles with tunable surface energy to generate a rough interface with controlled properties. The intentionally disordered interface is tolerant to variation in substrate preparation. We apply this technique to block-copolymer lamellae, and demonstrate a remarkable thickness-dependence of the induced orientation, consistent with theoretical predictions. The simultaneous control of substrate energy and topography enables expression of the vertical lamellae state without rigorous control of the preparation conditions. We measure an 8-fold increase in surface energy tolerance compared to flat substrates.