Direct printing of functional 3D objects using polymerization-induced phase separation.

3D printing has enabled materials, geometries and functional properties to be combined in unique ways otherwise unattainable via traditional manufacturing techniques, yet its adoption as a mainstream manufacturing platform for functional objects is hindered by the physical challenges in printing multiple materials. Vat polymerization offers a polymer chemistry-based approach to generating smart objects, in which phase separation is used to control the spatial positioning of materials and thus at once, achieve desirable morphological and functional properties of final 3D printed objects. This study demonstrates how the spatial distribution of different material phases can be modulated by controlling the kinetics of gelation, cross-linking density and material diffusivity through the judicious selection of photoresin components.

Enrichment of Semiconducting Single-Walled Carbon Nanotubes with Indigo-Fluorene-Based Copolymers and Their Use in Printed Thin-Film Transistors and Carbon Dioxide Gas Sensors.

High-purity semiconducting single-walled carbon nanotubes (sc-SWCNTs) are promising for portable and high-sensitivity gas sensors because of their excellent physical and electrical properties. Here, we describe the synthesis of a novel indigo-fluorene-based copolymer () that has been designed to selectively enrich sc-SWCNTs with excellent purity (>99.9%) yet contain a latent function in the form of a -butoxy (-BOC)-protected amine that can be later revealed and exploited for carbon dioxide (CO) gas sensing.

Full Spectrum Raman Excitation Mapping Spectroscopy.

A generalization of the Raman scattering (RS) spectrum, the Raman excitation map (REM) is a hyperspectral two-dimensional (2D) data set encoding vibrational spectra, electronic spectra and their coupling. Despite the great potential of REM for optical sensing and characterization with remarkable sensitivity and selectivity, the difficulty of obtaining maps and the length of time required to acquire them has been practically limiting. Here we show, with a simple setup using current optical equipment, that maps can be obtained much more rapidly than before (~ms to ~100 s now vs.

Polymer Encapsulants for Threshold Voltage Control in Carbon Nanotube Transistors.

Although carbon nanotube transistors present outstanding performances based on key metrics, large-scale uniformity and repeatability required in printable electronics depend greatly on proper control of the electrostatic environment. Through a survey of polymer dielectric encapsulants compatible with printing processes, a simple correlation is found between the measured interfacial charge density and the onset of conduction in a transistor, providing a rational route to control the electrical characteristics of carbon nanotube transistors. Smooth and continuous balancing of the properties between unipolar p-type and n-type transport is achieved using a molar fraction series of poly(styrene--2-vinylpyridine) statistical copolymers combined with an electron-donating molecule.

Dopant-Modulated Conjugated Polymer Enrichment of Semiconducting SWCNTs.

Conjugated polymer extraction (CPE) is a low-cost, scalable process that can enrich single-walled carbon nanotube (SWCNT) materials in organic media. For other separation methods in aqueous phases, redox chemistry and/or pH control dramatically affect the sorting process of the SWCNTs. We have previously determined that the CPE process can be fine-tuned by adjusting the pH on the tube surface.

Sorting of Semiconducting Single-Walled Carbon Nanotubes in Polar Solvents with an Amphiphilic Conjugated Polymer Provides General Guidelines for Enrichment.

Conjugated polymer extraction (CPE) has been shown to be a highly effective method to isolate high-purity semiconducting single-walled carbon nanotubes (sc-SWCNTs). In both literature reports and industrial manufacturing, this method has enabled enrichment of sc-SWCNTs with high purity (≥99.9%).

High-Purity Semiconducting Single-Walled Carbon Nanotubes: A Key Enabling Material in Emerging Electronics.

Semiconducting single-walled carbon nanotubes (sc-SWCNTs) are emerging as a promising material for high-performance, high-density devices as well as low-cost, large-area macroelectronics produced via additive manufacturing methods such as roll-to-roll printing. Proof-of-concept demonstrations have indicated the potential of sc-SWCNTs for digital electronics, radiofrequency circuits, radiation hard memory, improved sensors, and flexible, stretchable, conformable electronics. Advances toward commercial applications bring numerous opportunities in SWCNT materials development and characterization as well as fabrication processes and printing technologies.

Real Time Hyperspectroscopy for Dynamical Study of Carbon Nanotubes.

Photoluminescence excitation mapping used routinely to characterize semiconducting single-walled carbon nanotubes (sc-SWCNTs) is extended to provide time-dependent data. A hyperspectral method based on a supercontinuum light source and an imaging detector is demonstrated with excitation and emission wavelengths spanning 600-1000 and 1050-1650 nm, respectively, at time scales <100 ms. An example of a titration experiment is given to highlight the potential offered by the technique.

A hybrid enrichment process combining conjugated polymer extraction and silica gel adsorption for high purity semiconducting single-walled carbon nanotubes (SWCNT).

A novel purification process for the enrichment of sc-SWCNTs that combines selective conjugated polymer extraction (CPE) with selective adsorption using silica gel, termed hybrid-CPE (h-CPE), has been developed, providing a high purity sc-SWCNT material with a significant improvement in process efficiency and yield. Using the h-CPE protocol, a greater than 5 fold improvement in yield can be obtained compared to traditional CPE while obtaining sc-SWCNT with a purity >99.9% as assessed by absorption spectroscopy and Raman mapping.

Enrichment of large-diameter semiconducting SWCNTs by polyfluorene extraction for high network density thin film transistors.

A systematic study on the use of 9,9-dialkylfluorene homopolymers (PFs) for large-diameter semiconducting (sc-) single-walled carbon nanotube (SWCNT) enrichment is the focus of this report. The enrichment is based on a simple three-step extraction process: (1) dispersion of as-produced SWCNTs in a PF solution; (2) centrifugation at a low speed to separate the enriched sc-tubes; (3) filtration to collect the enriched sc-SWCNTs and remove excess polymer. The effect of the extraction conditions on the purity and yield including molecular weight and alkyl side-chain length of the polymers, SWCNT concentration, and polymer/SWCNT ratio have been examined.

Type- and species-selective air etching of single-walled carbon nanotubes tracked with in situ Raman spectroscopy.

The thermal oxidation of carbon nanotubes in air is investigated by in situ Raman spectroscopy. Etching rates are directly seen to be diameter, chirality, and type dependent. We directly track the evolution of bundled nanotube networks that undergo air etching from 300 to 600 °C.

Photoinduced band gap shift and deep levels in luminescent carbon nanotubes.

Individual air-suspended single-walled carbon nanotubes are imaged both spatially and spectrally in photoluminescence. At low excitation power, photoluminescence is bright and stable with high quantum efficiency; however, higher power initially causes a gradual red shift and then more severe changes. Blinking, the loss of quantum efficiency, and the appearance of new deep levels are all seen and can be explained by the introduction of defects.

Charge contrast imaging of suspended nanotubes by scanning electron microscopy.

A method of rapidly identifying and imaging suspended nanotubes by scanning electron microscopy is reported. Nanotubes are visible in high contrast and even at low magnification. The contrast can be explained by considering the effect that the charge on the nanotube has on the substrate.

Excited excitonic states in single-walled carbon nanotubes.

Polarized photoluminescence excitation spectroscopy on individual SWNTs reveals not only the longitudinal and transverse E 11, E 22, and E 12 ground-state excitons but also excited excitonic states including the continuum. When heated, SWNTs are known to undergo a bandgap shift transition (BST), which effectively changes the nanotube dielectric environment. Here, we show that the entire spectrum of excitonic resonances blue shifts under this transition, with excited states showing larger shifts, approaching 100 meV for a 1 nm diameter nanotube.

Reduced number of homogalacturonan domains in pectins of an Arabidopsis mutant enhances the flexibility of the polymer.

Pectins are a family of highly complex multifunctional cell wall polysaccharides. Little is known on the relation between pectin structure, hydrodynamic properties, and cellular function. In this study, we took advantage of the Arabidopsis pectin mutant quasimodo2 (qua2), which specifically lacks half of its homogalacturonan blocks, to study the relationship between the amount of homogalacturonan blocks and the hydrodynamic properties of pectins.

Photoluminescence imaging of suspended single-walled carbon nanotubes.

Single-walled carbon nanotubes (SWNTs) suspended in air over trenches are imaged using their intrinsic near-infrared (NIR) photoluminescence (1.0-1.6 microm).

Swelling behavior and controlled release of theophylline and sulfamethoxazole drugs in beta-lactoglobulin protein gels obtained by phase separation in water/ethanol mixture.

Physically cross-linked beta-lactoglobulin (BLG) protein gels containing theophylline and sulfamethoxazole low molecular weight drugs were prepared in 50% ethanol solution at pH 8 and two protein concentrations (6 and 7% (w/v)). Swelling behavior of cylindrical gels showed that, irrespective of the hydrated or dehydrated state of the gel, the rate of swelling was the highest in water. When the gels were exposed to water, they first showed a swelling phase in which their weight increased 3 and 30 times for hydrated and dehydrated gels, respectively, due to absorption of water, followed by a dissolution phase.

Structure determination of the 1/1 alpha/beta mixed lactose by X-ray powder diffraction.

The mixed form of alpha/beta lactose was obtained by heating amorphous alpha-lactose at 443 K. NMR spectroscopy determined the stoichiometry of this mixed compound to be 1/1. The X-ray powder diffraction pattern was recorded at room temperature with a sensitive curved detector (CPS 120).

Ab initio structure determination of the high-temperature phase of anhydrous caffeine by X-ray powder diffraction.

The high-temperature phase I of anhydrous caffeine was obtained by heating and annealing the purified commercial form II at 450 K. This phase I can be maintained at low temperature in a metastable state. A powder X-ray diffraction pattern was recorded at 278 K with a laboratory diffractometer equipped with an INEL curved position-sensitive detector CPS120.

Structure determination of the stable anhydrous phase of alpha-lactose from X-ray powder diffraction.

The stable anhydrous form of alpha-lactose has been obtained by the dehydration of alpha-lactose monohydrate in methanol. An X-ray powder diffraction pattern was recorded at room temperature with a laboratory diffractometer equipped with an INEL curved sensitive detector CPS120. The starting structural model of this form was found by a Monte-Carlo simulated annealing method.

Structure determination of forms I and II of phenobarbital from X-ray powder diffraction.

From pure powders of forms I and II of phenobarbital, X-ray diffraction patterns were recorded at room temperature. The starting crystal structural models were found by a Monte-Carlo simulated annealing method. The structures of the two forms were obtained through Rietveld refinements.

Ab initio structure determination of the hygroscopic anhydrous form of alpha-lactose by powder X-ray diffraction.

Annealing of alpha-lactose monohydrate at 408 K yielded a mixture of this compound with hygroscopic anhydrous alpha-lactose. A powder X-ray diffraction pattern of this mixture was recorded at room temperature. The starting structural model of hygroscopic alpha-lactose was found by a Monte Carlo simulated-annealing method.