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Optimization of three-dimensional (3D) print conditions for material extrusion of plastics by fused filament fabrication typically involves trade-offs between mechanical properties and dimensional ...

Layer-by-layer (LbL) assembly facilitates controlled coatings on a variety of surfaces with the ability to manipulate the composition through the thickness by selection of the complementary pairs. However, the characterization of these composition profiles tends to be destructive and requires significant compositional differences that can limit their utility. Here, we demonstrate the ability to non-destructively quantify the depth dependence of the allyl content associated with the selective incorporation of poly(sodium acrylate-co-allylacrylamide) (84 : 16 mol : mol) (allyl-PAA) in LbL films based on the assembly of poly(diallyldimethylammonium chloride) (PDAC)/poly(acrylic acid) (PAA) and PDAC/allyl-PAA. Although the atomic composition of the film is not dramatically influenced by the change between PAA and allyl-PAA, the absorption in the IR near 1645 cm−1 by the allyl group provides sufficient optical contrast to distinguish the LbL components with spectroscopic ellipsometry. The use of IR spectroscopic ellipsometry can determine the thickness of layers that contain allyl-PAA and also gradients that develop due to re-arrangements during the LbL process. With multiple films fabricated simultaneously, the location of the gradient between the 1st and 2nd series of multilayers (e.g., first PDAC/PAA bilayers and then PDAC/allyl-PAA bilayers) can be readily assessed. The results from a variety of different multilayer architectures indicate that the gradient is located within the thickness expected for the 1st deposited bilayer stack (PDAC/PAA or PDAC/allyl-PAA). These results are indicative of a dynamic dissolution–deposition process (in- and out- diffusion) during the fabrication of these LbL films. These results provide additional evidence into the mechanisms for exponential growth in LbL assemblies. The ability to quantify a gradient with the low contrast system examined indicates that spectroscopic IR ellipsometry should be able to non-destructively determine compositional gradients for most polymer films where such gradients exist.

Thermoplastic elastomers based on ABA triblock copolymers are typically limited in modulus and strength due to crack propagation within the brittle regions when the hard end-block composition favors morphologies that exhibit connected domains. Increasing the threshold end-block composition to achieve enhanced mechanical performance is possible by increasing the number of junctions or bridging points per chain, but these copolymer characteristics also tend to increase the complexity of the synthesis. Here, we report an in situ polymerization method to successfully increase the number of effective junctions per chain through grafting of poly(styrene) (PS) to a commercial thermoplastic elastomer, poly(styrene)–poly(butadiene)–poly(styrene) (SBS). The strategy described here transforms a linear SBS triblock copolymer–styrene mixture into a linear-comb-linear architecture in which poly(styrene) (PS) grafts from the mid-poly(butadiene) (PBD) block during the polymerization of styrene. Through systematic variation in the initial SBS/styrene content, nanostructural transitions from disordered spheres to lamellar through reaction-induced phase transitions (RIPT) were identified as the styrene content increased. Surprisingly, maximum mechanical performance (Young's modulus, tensile strength, and elongation at break) was obtained with samples exhibiting lamellar nanostructures, corresponding to overall PS contents of 61–77 wt% PS (including the original PS in SBS). The PS grafting from the PBD block increases the modulus and the strength of the thermoplastic elastomer while preventing brittle fracture due to the greater number of junctions afforded by the PS grafts. The work presented here demonstrates the use of RIPT to transform standard SBS materials into polymer systems with enhanced mechanical properties.

Microwave heating provides an efficient method to rapidly heat materials through interaction of microwaves with the media. Here, we demonstrate the rapid synthesis of mesoporous cobalt oxide films through the heating of the silicon substrate by microwaves. A non-sol-gel approach based on cobalt nitrate-citric acid complex cooperative assembly with a poly[methoxy poly(ethylene glycol)methacrylate]-block-poly(butyl acrylate) (PMPEGMA-b-PBA) block copolymer was used to fabricate the cobalt oxide through a cobalt carbonate intermediate. The time required to convert cobalt carbonate to cobalt oxide with the full removal of the PMPEGMA-b-PBA template can be decreased by two orders of magnitude with microwaves in comparison to standard heating in a furnace at 350 °C. At the highest microwave power examined (1500 W), this can be accomplished within 2 s, while >5 min is required at 350 °C in a furnace. At a microwave power of

Poly(ethylene glycol) (PEG) tends to be considered low fouling, which has led to its use in a wide variety of applications. Amphiphilic polyols, such as Antifoam 204, are commonly used as surfactants in fermentation processes due to their limited toxicity and low cost, but these polyols in aqueous solutions can unexpectedly swell membranes. Here we examine the interactions of PEG or poly(propylene glycol) (PPG) with amphiphilic substituted norbornene copolymers through swelling in dilute aqueous solution. The effect of molecular mass (Mn) of the polyol (PEG and PPG) in aqueous (1 wt% butanol) solution on the swelling and mechanical properties of a series of poly(alkyl norbornene-co-hexafluoroisopropanol norbornene) is systematically investigated using a quartz crystal microbalance with dissipation. At 10 ppm of PEG, the swelling is less than 20% for all of the copolymers examined and the swelling is independent of PEG Mn. Although PPG at the lowest Mn examined leads to similar swelling to PEG, the swelling induced by PPG increases with Mn to reach a maximum at Mn = 3.1 kg mol-1. Pluronic L121 is similar compositionally to Antifoam 204, but the equilibrium swelling is decreased by nearly a factor of 2, which is attributed to the higher Mn of Pluronic L121. The limited dependence on the alkyl chain in the copolymer suggest that the interactions between the polyol and hexafluoroisopropanol moiety in the copolymer drive the uptake by the membrane through bound water with the unassociated ether in the PPG that increases swelling with increasing Mn, but a finite size effect limits the swelling for sufficiently large polymer additives.

Lithium ion capacitors (LICs) are energy storage devices integrating the complementary features of both supercapacitors and lithium ion batteries to simultaneously reach high energy and power densities. One of the major challenges in LIC technology is the kinetic imbalance between the faradaic insertion anode and capacitive cathode. Therefore, the design of electrode materials is crucial to enhance the rate performance of anode and the capacitance of the cathode in LIC devices. In this work, novel LICs were demonstrated with nanostructured cathode and anode. A vertically-aligned carbon nanoflakes (VACNFs) cathode provided high electrochemically active surface area and excellent conductivity, while a metal organic framework (MOF) derived carbonized nickel cobalt oxide (cNiCo2O4) anode ensured fast conversion reactions and remarkable cyclability. Electrochemical characterization of individual electrode confirmed that both electrodes exhibited good electron and ion transport capability. The LICs were fabricated with optimized electrode active materials loading to deliver high energy densities at desired charge/discharge rates. The devices exhibited energy density up to 136.9 W h/kg (at 200 W/kg). At higher power density of 40 kW/kg, under which a full charge-discharge can be finished within 4 s, the LICs could still deliver an energy density of 26.44 W h/kg. The devices also showed a good cycle stability (≈90% capacitance retention after 9000 cycles, under current density of 4 A/g) within the voltage range of 1–4.2 V.

One key limitation of lithium metal electrodes is their propensity for dendrite formation that limits their use in commercial batteries. Here, a simple surface modification method was demonstrated ...

The cooperative assembly of functional precursors with block copolymers (BCPs) is a powerful, general route to fabricate ordered mesoporous materials, but the precise tuning of the mesopore size generally requires trial and error to obtain the correct BCP template or appropriate swelling agent. Here, we demonstrate the ability to effectively modulate both expansion and contraction of the ordered cylindrical mesopores relative to those obtained from cooperatively assembled Pluronic F127, resol, and tetraethylorthosilicate. The two key physical parameters for the swelling agents are their hydrophobicity, as quantified by the octanol-water partition coefficient (Kow), and Hansen solubility parameters that describe the interactions of the solvent with the different components of the BCP template. Four low volatility solvents are examined that span a wide Kow with up to 90 wt % solvent relative to the Pluronic F127. Glycerol triacetate (Kow < 1) can decrease the average mesopore size from 5.9 to 4.8 nm due to segmental screening of the interactions in the Pluronic F127 to decrease chain stretching at intermediate loadings. A modest increase in mesopore size to 8.1 nm can be achieved with trimethylbenzene (TMB, Kow = 3.42). Dioctyl phthalate (DOP), which is slightly more hydrophobic (Kow = 8.1), is more effective than TMB at expanding the pore size (maximum: 13.5 nm) without loss of ordered structure. A more hydrophobic solvent, tris (2-ethylhexyl) trimellitate (Kow = 12.5), is less effective at increasing the pore size (maximum: 8.2 nm). The Hansen solubility parameters for DOP most closely match those of the hydrophobic segment in the Pluronic F217 template. We attribute this similarity, which is related to the solvent quality, to the improved efficacy of DOP in increasing the pore size. These results illustrate that both the Hansen solubility parameters (relative to the hydrophobic segment of the template) and relative hydrophobicity of the swelling agent determine the obtainable pore sizes in cooperatively assembled ordered mesoporous materials.

Nanoparticle-functionalized 2D material networks are promising for a wide range of applications, but in situ formation of nanoparticles is commonly challenged by rapid growth. Here, we demonstrate controlled synthesis of small and dispersed iron oxide nanoparticles on reduced graphene oxide (rGO) networks through rapid localized heating with microwaves with low-cost iron nitrate as the precursor. The strong coupling of the microwave radiation with the rGO network rapidly heats the network locally to decompose the iron nitrate and generate iron oxide nanoparticles, while cessation of microwaves leads to rapid cooling to minimize crystal growth. Small changes in the microwave reaction time (

High porosity and surface areas of ordered mesoporous materials provide substantial capacity for loading of guest molecules and the well-defined morphology of such materials can control their transport for controlled release. Here, the loading and release of mitoxantrone from unmodified ordered mesoporous carbon films is monitored using UV/Vis spectroscopy. Organic-organic self-assembly of Pluronic F127 with phenolic resin leads to interconnected elliptical pores (≈2 nm) in the film after carbonization. Interestingly, the total loading (2.6 ± 0.4 μg/cm(2)) and release of mitoxantrone is independent of film thickness (50–400 nm), suggesting diffusion limitations in pore filling. With alternative template, the pore size increases to ≈5 nm and the mitoxantrone loading increases to 3.5 ± 0.9 μg/cm(2), but the loading still remains thickness independent. Using phosphate buffered saline at 37 °C, less than 60 % of the loaded mitoxantrone is readily released from the mesoporous carbon films over a two-week period. The release profile includes an initial burst with a modest fraction (< 20 %) of the loaded drug released within the first day, followed by a near linear release over the subsequent 5–9 days. Interestingly, the smaller pores (ca. 2 nm) release nearly 50 % more mitoxantrone over 2 weeks than the larger pores (ca. 5 nm), despite the lower initial loading. These results illustrate potential limitations as well as opportunities for the use of highly hydrophobic porous materials for the controlled release of hydrophobic biologically active compounds as drug delivery systems.

Polymer membranes represent a low cost, low energy solution to separating biologically derived chemicals from fermentation. However, the performance of these membranes is commonly limited by fouling caused by biological components, but additives are also included in typical fermentation broths that can interact with the polymer membrane. Here, we examine how a common polyol antifoam agent (Antifoam 204) dramatically swells and plasticizes a high performing biobutanol membrane copolymer of hydroxyhexafluoroisopropyl and n-butyl substituted norbornene. When equilibrated against 1 wt % (aq) butanol, the solvent in the copolymer increases from 40 vol % at 1 ppm of antifoam and >80 vol % at 100 ppm of antifoam. The effect of the antifoam on the properties of the copolymer as determined by QCM-D is much more significant than that of the butanol concentration. Even with 4 wt % butanol (greater than typically viable for biobutanol), the copolymer swells

To prevent brittle failure, tough hydrogels rely on energy dissipation, which can be manifested through sacrificial covalent bonds or reversible, noncovalent cross-links. However, these noncovalent...

Block copolymer templating enables the generation of well-defined pore sizes and geometries in a wide variety of frameworks, typically through evaporation-induced self-assembly (EISA). Here, we systematically modulate the solvent quality with mixtures of tetrahydrofuran-ethanol (THF-EtOH) to manipulate the unimer/micelle ratio in the precursor solution to explore how the associated solution structure influences the final pore morphology. A bottlebrush block copolymer (BBCP) with poly(ethylene oxide) and poly(

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 st...

Prevention of ice formation is a critical issue for many applications, but routes to overcome the large thermodynamic driving force for crystallization of water at significant supercooling are limited. Here, we demonstrate that supramolecular hydrogels formed from statistical copolymers of 2-hydroxyethyl acrylate (HEA) and 2-(N-ethylperfluorooctane sulfonamido)ethyl methacrylate (FOSM) exhibit a degree of ice formation suppression unprecedented in a synthetic material. The mechanisms of ice prevention by these hydrogels mimic two methods used by nature: (1) hydrogen bonding of water to highly hydrophilic macromolecular chains and (2) nanoconfinement of water between hydrophobic moieties. From systematic variation in the copolymer composition to control the nanoscale (

The hydrothermal synthesis of Co3O4 particles using cobalt nitrate as the precursor and citric acid as a weak chelating agent was modulated using poly(vinyl pyrrolidone) (PVP) to control the shape and size of the resulting particles. The molar ratio of PVP to the cobalt in the precursor solution was key to controlling the particle morphology. In the absence of PVP, large truncated cube-like particles with a bimodal size distribution (200 and 1450 nm) are formed. When the molar ratio of PVP/Co is less than ≈ 0.5, the particle size is generally invariant. As the molar ratio of PVP/Co is increased from 0.5 to nearly 2, the cubes with rounded edges are formed, but the hydrodynamic diameter decreases from nearly 1.4 μm to 800 nm at a molar ratio of 1.8. At PVP/Co > 2, there is a significant decrease in the particle size down to 142 nm at PVP/Co = 3.5 and the shape becomes spherical, but the particles remain crystalline, characteristic of Co3O4. The size of Co3O4 particles was also determined using scanning electron microscopy. This size is consistent with the particle size obtained from dynamic light scattering. A competitive growth mechanism between free cobalt ions and PVP-bound cobalt ions in the solution was proposed to explain the influence of PVP on the size and shape of the Co3O4 particles. Due to heavy metal specificity for the binding with PVP and the crystal space group for metal oxides, the evolution in particle shape is not universal with no apparent change in the shape obtained over a similar PVP concentration range for iron oxide.

The uniaxial mechano-optical behavior of a series of amorphous l-valine-based poly(ester urea) (VAL-PEU) with varying diol lengths was studied to elucidate the molecular mechanism associated with their thermal shape memory properties. A custom, real-time measurement system was used to capture the true stress, true strain, and birefringence during the temporary shape programming at stretching temperatures above the glass transition temperature (Tg). The mechano-optical response of VAL-PEUs exhibits an initial photoelastic behavior related to enhanced segmental correlation at low temperatures above the Tg. A characteristic temperature, defined as the liquid–liquid (Tll) transition (rubbery–viscous transition), was found at about 1.05 Tg (K) (at Tg + 15 °C) at strain rate of 0.017 s–1, above which the segmental contacts largely “melt” and the initial slope of the stress-optical curves becomes temperature independent. This temperature corresponds to the temperature where mean relaxation time for the polymer i...

Zone annealing, a directional crystallization technique originally used for the purification of semiconductors, is applied here to crystalline polymers. Tight control over the final lamellar orientation and thickness of semicrystalline polymers can be obtained by directionally solidifying the material under optimal conditions. It has previously been postulated by Lovinger and Gryte that, at steady state, the crystal growth rate of a polymer undergoing zone annealing is equal to the velocity at which the sample is drawn through the temperature gradient. These researchers further implied that directional crystallization only occurs below a critical velocity, when crystal growth rate dominates over nucleation. Here, we perform an analysis of small-angle X-ray scattering, differential scanning calorimetry, and cross-polarized optical microscopy of zone-annealed poly(ethylene oxide) to examine these conjectures. Our long period data validate the steady-state ansatz, while an analysis of Herman's orientation function confirms the existence of a transitional region around a critical velocity, v(crit), where there is a coexistence of oriented and isotropic domains. Below v(crit), directional crystallization is achieved, while above v(crit), the mechanism more closely resembles that of conventional isotropic isothermal crystallization. This work was supported by grants DE-SC0018182, DE-SC0018135, and DE-SC0018111, funded by the U.S. Department of Energy, Office of Science. A.A.K. acknowledges funding from the Gates Millennium Scholars program under Grant No. OPP1202023 from the Bill & Melinda Gates Foundation. A.J.M. acknowledges funding from the Basque Government through grant IT1309-19. We are grateful to Dr. Andrew J. Lovinger for critically reviewing the manuscript and offering multiple comments that have helped us to significantly improve our paper. We would also like to thank Beatrice Bellini for experimental assistance.

Hydrophobically associating hydrogels based on copolymers of a water-soluble monomer with a fluoroacrylate or fluoromethacrylate possess microphase-separated morphologies that provide unique properties. Physical crosslinks in these hydrogels involve hydrophobic bonds between fluoro(meth)acrylate groups that associate into 2–6-nm-diameter core–shell nanodomains that represent multifunctional crosslinks. These hydrogels exhibit exceptional mechanical properties and fracture toughness values approaching 104 J/m2, are extrudable, and show self-healing behavior of the microstructure. This chapter reviews the characteristics of these microphase-separated, hydrophobically associating hydrogels and discusses potential applications of these materials as injectable in situ forming hydrogels, electrospun fiber mats suitable for tissue scaffolds, controlled drug release, antifreeze materials, and shape memory hydrogels.

Additive manufacturing provides an opportunity to redefine sustainability for plastic products, as polyolefins, which dominate traditional plastics manufacturing, are generally unsuitable for 3D printing. One of the most widely used 3D printing technologies is fused filament fabrication (FFF), where a thermoplastic filament is melted and extruded to build the object layer-by-layer. The printing performance can be quantified in terms of mechanical properties and dimensional accuracy of the part. Here we demonstrate the ability to print high-quality parts via FFF using a biorenewable polyamide-11 (PA-11). The PA-11 monomer, 11-aminoundecanoic acid, is derived directly from castor beans by hydrolysis, methylation, and heat treatment of its oils. The elastic modulus and dimensional accuracy can be further improved by the incorporation of a natural nanofiller, sepiolite. The role of print orientation and filler content are systematically investigated, with elastic moduli greater than 1.1 GPa obtained for the o...

3D printing using the materials extrusion additive manufacturing (ME-AM) process is highly nonisothermal. In this process, a solid polymer filament is mechanically drawn into a heated hot end (liquefier) where the polymer is ideally melted to a viscous liquid. This melt is extruded through an orifice using applied pressure of the solid filament that is continuously being drawn into the extruder. The extruded filament melt is deposited to build up the desired part. The poor thermal conductivity of most polymers inevitably leads to temperature gradients, in both the radial and axial directions. Here we quantify the temperature evolution of the polymer filament in axial direction using embedded fine thermocouples as a function of process parameters. Information about the radial gradients is obtained by introducing dye markers within the filament through understanding the flow behavior through the extruder by the deformation of the dye from a linear to pseudo parabolic profile. The polymer is heated above the glass transition temperature for less than 30 s for reasonable print conditions with the center of the filament remaining cooler than the liquefier temperature throughout the process. These process measurements provide critical data to enable improved simulation and modeling of the ME-AM process and the properties of the printed parts.

A self-assembled Manganese (Mn) based metal organic complex (Mn-MOC) with spherical structure was synthesized via a solvothermal reaction. The Mn-MOC precursor materials were converted to hierarchical porous Mn3O4/C nanospheres through thermal annealing treatment. These nanospheres exhibited a high reversible specific capacity (1237 mAh/g at 200 mA/g), excellent ratability (425 mAh/g at 4 A/g), and extremely long cycle life (no significant capacity fading after 3000 cycles at 4A/g) as an anode in lithium ion batteries. The notable capability for lithium storage is attributed to the unique porous hierarchical structure of the Mn3O4/C nanospheres, which consist of homogeneously distributed Mn3O4 nanocrystals with thin carbon shells. Such a desired nanostructure not only provided large reaction surface area and enhanced electrical conductivity, but also promoted the formation of a stable solid electrolyte interphase (SEI) and accommodated the volume change of the conversion reaction type electrode.

Hydrophobically modified copolymers provide a versatile platform of hydrogel materials for diverse applications, but the influence of salts on the swelling and material properties of this class of hydrogels has not been extensively studied. Here, we investigate model hydrogels with three different sodium salts with anions chosen from the classic Hofmeister series to determine how these counterions influence the swelling and mechanical properties of neutral hydrogels. The gel chosen was based on a statistical copolymer of dimethylacrylamide and 2-(

The low intrinsic conductivity of sulfur necessitates conductive additives, such as mesoporous carbons, to the cathode to enable high-performance metal-sulfur batteries. Simultaneous efforts to address polysulfide shuttling have introduced nitrogen-doped carbons to provide both conductivity and suppressed shuttling because of their strong interaction with sulfur. The strength of this interaction will impact the ability to fill the mesopores with sulfur via melt infusion. Here, we systematically investigate how nitrogen doping influences the rate that molten sulfur can infiltrate the mesopores and the overall extent of pore filling of highly ordered mesoporous doped carbons using in situ small angle X-ray scattering (SAXS). The similarity in electron density between molten sulfur and the soft carbon framework of the mesoporous material leads to a precipitous decrease in the scattered intensity associated with the ordered structure as voids are filled with sulfur. As the nitrogen doping increases from 1 to 20 at. %, the effective diffusivity of sulfur in the mesopores decreases by an order of magnitude (2.7 × 10

The unusually large film thickness at which confinement effects manifest themselves in surface fluctuations of unentangled four-arm star polymers has been defined using film thicknesses from 10Rg to 107Rg. For 15k four-arm star polystyrene (SPS), confinement appears at a thickness between 112 nm (40Rg) and 72 nm (26Rg), which is remarkably larger than the thicknesses at which confinement appears for unentangled 6k linear (

The swelling and deswelling of a cross-linked polydimethylsiloxane (PDMS) pad adhered to a block copolymer (BCP) film during solvent vapor annealing (SVA) provides sufficient shear force to produce highly aligned domains over macroscopic dimensions in thin films. Here, we examine how far this alignment can propagate through the thickness of a BCP film to understand the limits for efficacy of the SVA-S (SVA with shear) process. Films of cylinder-forming polystyrene-block-polyisoprene-block-polystyrene (SIS) ranging from 100 nm to more than 100 μm are examined using the same processing conditions. The SIS surface in contact with the PDMS is always well-aligned, with Herman’s orientation parameter (S) exceeding 0.9 as determined from AFM micrographs, but the bottom surface in contact with the silicon wafer is not aligned for the thickest films. The average orientation through the film thickness was determined by transmission small-angle X-ray scattering (SAXS), with S decreasing gradually with increasing thi...

Lithium ion battery electrodes are highly engineered, but their performance can be impacted by the properties of the polymeric binder in the electrode. Here, the swelling and plasticization of PVDF, PAA, BPEI and SEPDM by common carbonate-based electrolytes is probed using quartz crystal microbalance with dissipation (QCM-D). The swelling of the PVDF increased with increasing temperature and decreased slightly with addition of Li salt. The composition of ethylene and propylene carbonate in the electrolyte impacts the swelling more significantly than salt selection. Despite the large differences in the swelling (25%–75%), the high frequency shear modulus of the swollen PVDF remains nearly invariant for all conditions examined, which is attributed to its semi-crystalline network. In contrast, BPEI, SEPDM, and PAA are marginally swollen by carbonate electrolytes. These measurements provide insight into the electrolyte-binder interactions to help select pairs for emerging high-performance electrodes.

In the inertial limit, the resonance frequency of the quartz crystal microbalance (QCM) is related to the coupled mass on the quartz sensor through the Sauerbrey expression that relates the mass to the change in resonance frequency. However, when the thickness of the film is sufficiently large, the relationship becomes more complicated and both the frequency and damping of the crystal resonance must be considered. In this regime, a rheological model of the material must be used to accurately extract the adhered film's thickness, shear modulus, and viscoelastic phase angle from the data. In the present work we examine the suitability of two viscoelastic models, a simple Voigt model ( Physica Scripta 1999, 59, 391-396) and a more realistic power-law model ( Langmuir 2015, 31, 4008-4017), to extract the rheological properties of a thermoresponsive hydrogel film. By changing temperature and initial dry film thickness of the gel, the operation of QCM was traversed from the Sauerbrey limit, where viscous losses do not impact the frequency, through the regime where the QCM response is sensitive to viscoelastic properties. The density-shear modulus and the viscoelastic phase angle from the two models are in good agreement when the shear wavelength ratio, d/λ

Confinement of water to nanoscale dimensions enables substantial supercooling through disruption of the hydrogen bonding network. However, there remain questions associated with the importance of the nature of the water-surface interactions relative to physical confinement defined by the pore geometry on the dynamics of supercooled water. Here, a simple route to tune the surface wetting properties through nitrogen doping of carbon is reported. This method leads to nearly indistinguishable mesopore sizes to enable separation of surface wettability and pore size effects. Quasielastic neutron scattering (QENS) is used to probe the proton dynamics of water confined within the mesopores with an average diameter of 4.85 ± 0.05 nm as a function of temperature from 267 K to 189 K. The motions of water in the mesopores follow jump-diffusion. For the temperatures examined, the diffusivity of water in the mesopores decreases with increasing nitrogen doping of the carbon framework. The activation energy associated with proton dynamics increases by approximately 30% with N-doping when compared to the undoped carbon surface, which is attributed to the enhanced surface wettability (favorable interactions between water and pore surface). This acts to provide an energy barrier for the water motions. This work suggests that the influence of surface chemistry on the dynamics of supercooled water confined in mesopores is less than the influence of nanopore size.

Fe2O3 and carbon nanofiber (Fe2O3@CNFs) composite anodes for lithium ion batteries (LIBs) were fabricated by electrospinning and electrodeposition of naturally abundant, environmentally friendly, and cost effective materials to provide a simple route for modulating the morphology of the anodes and their performance. These anodes offer the advantage of being self-supporting to avoid increased mass of the electrodes from the binder, carbon black and the current collector, so the performance is reported on the basis of the full mass of the electrode (0.5–0.8 mg cm−2). Anodes consisting of nanofibers with a flat morphology without nanoscale roughness exhibit a superior cyclic stability (692 mA h g−1 in the 2nd cycle vs. 518 mA h g−1 after 100 cycles at 0.05 A g−1) compared with an anode with nanoscale roughness, where the capacity faded by 36.6% under the same conditions. The improvement in the cyclic performance for the flat morphology was attributed to the formation of a stable solid–electrolyte interface layer on the smooth sample combined with the enhanced contact between Fe2O3 and the CNFs, which inhibited degradation from the volume change of Fe2O3 during the successive charge and discharge. The Fe2O3@CNFs with flat morphology also exhibit reasonable performance (232 mA h g−1) at a high current density of 2.5 A g−1. These studies provide insights about how morphology impacts performance, namely the flat morphology at the nanoscale can stabilize the interfaces between the electrolyte and electrode composed of carbon and high performance active materials to promote long cycle life.

High concentrations of heteroatom can be doped into ordered mesoporous carbon by infiltration of molten dopants into silica-reinforced mesoporous cross-linked polymer (resol) and subsequent carbonization. The high concentration of dopants relative to polymer enables a high probability of heteroatoms to be dynamically integrated into the framework through carbonization, while the silica in the framework prevents loss of the ordered structure. This method is demonstrated to generate ordered mesoporous carbons with high heteroatom content (up to 26 atom % N, 15 atom % B, 7 atom % P, or 4 atom % S) for a wide variety of elements through melt infusion of the appropriate dopant (melamine, boric anhydride, ammonium dihydrogen phosphate, or dibenzyl sulfide). The ratio of the solid dopants to mesoporous silica–resol in a physical mixture during the melt infusion provides a simple methodology to precisely tune the doping content in the carbonized material. Etching of the silica postcarbonization generates addition...

Confinement of polymers to nanoscale dimensions can dramatically impact their physical properties. Substantial efforts have focused on the glass transition temperature (Tg) of polymers confined to thin films, but their mechanical properties are less studied despite their technological importance. In this review, challenges with mechanical measurements of polymer thin films are discussed along with novel metrologies that provide insight into their mechanical properties. A comparison of experimental measurements, simulations and theory provide several general conclusions about the mechanical properties under confinement. Confinement impacts the elastic modulus, rubbery compliance and viscosity of polystyrene, the archetypal polymer for confinement, but the confinement effect appears to depend on the measurement technique. This effect may be due to the details of averaging of gradients in properties that are dependent on the measurement details. Routes to minimize confinement effects are addressed. Despite progress in the measurements of mechanical properties of polymer thin films, there remain unresolved questions about the impact of confinement, which we highlight at the end of this review. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

The isothermal structural relaxation (densification) of a family of glassy polynorbornene films with high glass transition temperatures (Tg > 613 K) is assessed via spectroscopic ellipsometry. Three polymers were examined: poly(butylnorbornene) (BuNB), poly(hydroxyhexafluoroisopropyl norbornene) (HFANB), and their random copolymer, BuNB-r-HFANB. The effective aging rate, β(T), of thick (∼1.2 μm) spun cast films of BuNB-r-HFANB is approximately 10−3 over a wide temperature window (0.49

Complex coacervation of polymers can be a route to the compartmentalization of aqueous solutions. Presented here is a study of the hydrogen-bonded complex coacervation of poly(acrylic acid) and poly(ethylene glycol) or Pluronic block copolymers and the ability of these coacervates to encapsulate various ionic and nonionic dyes as well as a pharmaceutical compound within them. The formation of complex coacervate driven by hydrogen bonding is studied as a function of both pH and salt content with turbidimetry and isothermal calorimetry. Small-angle X-ray scattering shows the presence of micelles within Pluronic containing coacervate materials formed with a Pluronic block copolymer concentration higher than its critical micelle concentration. Although dyes generally partition to the coacervate phase, in the absence of salt, dyes that are able to hydrogen bond with the coacervate components are better incorporated into the coacervate. It is observed that the addition of salt to the polymer solutions increases...

Single pot, multi-component assembly of resol (carbon source), Pluronic F127, tetraethylorthosilicate (TEOS), dicyandiamide (nitrogen source) and iron nitrate (iron oxide source) yields nitrogen-doped ordered mesoporous carbon/iron oxide nanocomposites on carbonization. Etching the silica derived from the TEOS generates micropores in the carbon framework. The incorporation of iron oxide and nitrogen doping of the carbon tends to decrease the surface area; at approximately 3.7 wt% nitrogen and 21 wt% iron oxide (OMC-3.7-21), the surface area decreases from 2162 m 2 /g for the undoped ordered mesoporous carbon (OMC) to 974 m 2 /g and the pore volume decreases from 1.62 cm 3 /g to 0.6 cm 3 /g due to deformation of the nanostructure by crystallization of γ-Fe 2 O 3 nanoparticles and N-doping of the carbon. Despite the decreased surface area, the reversible capacity when used as anodes in a sodium ion battery is increased from 110 mAh/g (undoped OMC) to 275 mAh/g (OMC-3.7-21) due to high capacity from the γ-Fe 2 O 3 nanoparticles and the improved capacity associated with nitrogen doping of carbon. These nitrogen-doped ordered mesoporous carbon/iron oxide nanocomposites exhibit good cycle stability with almost 99% capacity retention after 350 charge/discharge cycles. The combination of low-cost and excellent electrochemical performance makes these mesoporous nanocomposites promising anode materials for sodium-ion batteries.

The nanostructure changes associated with stress dissipation in a tough, supramolecular hydrogel were determined by small-angle neutron scattering (SANS) and compared with stress-relaxation measurements to understand the molecular origin of the toughness. The hydrogels were formed from random copolymers of N,N-dimethylacrylamide (DMA) and 2-(N-ethylperfluorooctane sulfonamido)ethyl acrylate (FOSA), which exhibit a microphase-separated morphology with physical cross-links formed by the FOSA nanodomains connected by DMA chains. The stress relaxation behavior following a step strain was fit using seven exponentials with relaxation times that spanned 5 orders of magnitude. The deformation and relaxation of the FOSA nanodomains and network chains were independently resolved using two different contrasts with SANS experiments. Stretching of the hydrogel produced anisotropic scattering at both contrasts examined. The DMA network chains relaxed to an isotropic state at a fast rate that corresponded to the shorter...

Efficiency, cost, and lifetime are the primary challenges for stationary energy storage with vanadium-redox flow and sodium-sulfur batteries as promising options. In particular, room temperature sodium-sulfur battery systems offer the potential for safe, simple, low-cost and high energy density storage, but the high reactivity or solubility of sodium polysulfides in common liquid electrolytes for carbonates or glycols, respectively, leads to rapid performance loss on cycling. Herein, we demonstrate a robust route to inhibit reactivity of the sulfides with carbonate electrolytes (and also inhibit the diffusion of polysulfides dissolved in TEGDME) and prevent performance loss on cycling using highly doped (≈40 atom%) nanoporous carbon from low-cost raw materials infused with sulfur as the cathode. This cathode design leads to an ultra-stable room temperature sodium-sulfur battery with less than 3% decay in the discharge capacity after 8000 cycles at a high current density of 4.6 A/g. At 0.23 A/g, the discharge capacity is approximately 400 mAh/g and stable over 350 cycles. This combination of low cost and excellent cycle stability is promising for stationary, grid-level energy storage.

A binary Ni/Co metal organic framework (Ni–Co-MOF) with a hollow-sphere structure that is decorated with cone-shaped protrusions was prepared via a facile solvothermal reaction. Carbonization and sulfurization of the Ni–Co-MOF produced a Ni3S2/Co9S8/N-doped carbon composite that retained the hierarchical structure. The final composite material presents exceptional electrochemical performance when used as an anode in sodium-ion batteries. A reversible specific capacity of 419.9 mA h g−1 at a current density of 0.1 A g−1 was achieved after 100 cycles, with an exceptional capacity retention of 98.6%. Furthermore, superior rate capability was also demonstrated: an average capacity of 323.2 mA h g−1 at a current density of 2 A g−1 can be achieved. This exceptional performance can be attributed to the unique nano-architecture derived from the MOF precursor, as the resultant material possesses an ideal profile for an excellent anode material: ultrafine Ni3S2 and Co9S8 particles (∼7 nm), a hollow, porous structure, and an ultrathin N-doped carbon coating.

Soft templating using block copolymers provides a generalized synthetic strategy to fabricate mesoporous materials, but it is generally challenging to obtain highly crystalline frameworks without significant deformation or loss of the mesoporous structure. Here, we demonstrate a simple route to generate ordered mesoporous crystalline manganese oxide films by block copolymer templating through microwave processing to convert carbonate precursors to oxides, remove the polymeric template and crystallize the Mn3O4, all within 1 min. The microwave heating in this case is driven primarily by the high microwave cross-section of the substrate (silicon wafer), but manganese oxide also absorbs microwaves to provide energy locally for promoting nucleation/crystallization. Conversely, conventional heating in a muffle furnace at an analogous surface temperature leads to either significant residual copolymer or nanostructure collapse with low crystallinity. This difference in the behavior is attributed to the rapid and local heating of the manganese oxide by microwaves to crystallize the oxide. Microwaves rapidly generate the crystals as evidenced by the invariance in the refractive index of the films after 45 s on further microwave heating. Additionally, the microwave processing leads to nearly twice the specific surface area for the films than that of mesoporous films fabricated by calcination in the furnace. Microwave energy appears to be an attractive alternative to enable the fabrication of a highly crystalline framework in soft-templated ordered mesoporous materials when the microwaves can be absorbed by the framework of interest.

Composite hydrogels containing graphene oxide (GO) offer advantageous mechanical properties, but tuning these properties generally requires the synthesis of new hydrogels or if the hydrogel is thermally responsive, utilization of a chemistry determined temperature window. Here, we demonstrate a simple route to generate a family of GO-based hydrogels from aqueous solution based assembly of GO with polycationic poly(ethylenimine), PEI, without any secondary chemical crosslinking. Tuning the ratio of GO : PEI during the assembly produces a family of hydrogels that responds to mechanical compression by irreversibly altering their equilibrium water content and mechanical properties in a controllable manner. Despite the lack of chemical crosslinks, the hydrogels are stable when stored in an excess of water or NaCl solutions (up to 1 M) and exhibit a tunable swelling ratio (mass hydrogel : mass solid) between 44 and 162 based on both composition and compression history. Consequently, the storage modulus from shear rheology can be increased by more than 3 orders of magnitude from this irreversible mechanical compression of the hydrogel. This stiffening of the hydrogels in response to mechanical stimuli enables the prior compression loading of the hydrogel to be determined. We demonstrate that this strategy is generalizable to other anionic 2D materials such as clay (cloisite). This family of mechanically adaptive hydrogels enables facile fabrication and tuning of physical properties that could be advantageous for sensing, energy dissipation, and other applications.

The in situ recovery of n-butanol from conventional batch fermentation is an effective strategy to overcome cytotoxic titer limitations. Here, we demonstrate efficient butanol recovery using magnetically responsive micro/mesoporous carbon adsorbents. Although large surface areas (>1400 m2/g) promote adsorption, inclusion of magnetic Ni nanoparticles enables direct and facile magnetic retrieval of spent adsorbents, bypassing the need for column configurations (e.g., packed or expanded bed). Butanol loading capacities of a family of mesoporous powders (4–10 wt %Ni content) are not significantly impacted by Ni content, performing comparably to commercial resins and activated carbons (e.g., up to 0.26 g/g at 12.5 g/L equilibrated butanol). Magnetic recovery of the mesoporous powder is dependent on the Ni content, with up to 89 wt % recovery achieved in 6 min with 10 wt % Ni. Desorption studies using retrieved adsorbents demonstrated an average of 93% recovery of the total adsorbed butanol. Biocompatibility st...

The effects of polyelectrolyte charge density, polyelectrolyte-to-surfactant ratio, and micelle species on coacervation were studied by turbidity, dynamic light scattering, and zeta potential measurements to examine the coacervation of the weak polyelectrolyte branched polyethylenimine (BPEI) and oppositely charged sodium dodecyl sulfate (SDS) micelles as well as BPEI and mixed micelles composed of SDS and poly(ethylene glycol) 4-nonylphenyl 3-sulfopropyl ether potassium salt (PENS). The results of dynamic light scattering and zeta potential measurements are discussed in terms of pH and BPEI-to-surfactant ratio. An intrapolymer-dominant to interpolymer-dominant association model for the BPEI–micelle coacervates was proposed based on the variation of size and zeta potential of coacervate particles by their BPEI-to-surfactant ratio. The partition coefficient of solutes into BPEI–micelle coacervates was determined using UV-vis measurements as a function of pH, BPEI-to-surfactant ratio, and mixed micelle composition. Both the hydrophobicity of solutes and micelles, as well as the association mode of coacervates, impact the solute uptake efficiency. Dynamic rheological measurements on the coacervates suggest that the rheological properties of the complex coacervates are impacted by the association mode of the coacervates as well as the charge density on BPEI chains during coacervation.

Hydrogels are used widely for exploratory tissue engineering studies. However, currently, no hydrogel systems have been reported which exhibit a wide range of elastic modulus without changing precursor concentration, identity, or stoichiometry. Herein, ester- and amide-based poly(ethylene glycol) (PEG)–oxime hydrogels with tunable moduli (∼5–30 kPa) were synthesized with identical precursor mass fraction, stoichiometry, and concentration by varying the pH and buffer concentration of the gelation solution, exploiting the kinetics of oxime bond formation. The observed modulus range can be attributed to increasing amounts of network defects in slower forming gels, as confirmed by equilibrium swelling and small-angle neutron scattering (SANS) experiments. Finally, human mesenchymal stem cell (hMSC) viability was confirmed in these materials in a 24-h assay. While this was only an initial demonstration of the potential utility, the controlled variation in defect density and modulus is an important step forward in isolating system variables for hypothesis-driven biological investigations.

Highly doped porous carbons are highly promising for a variety of applications, but it is challenging to obtain high heteroatom content with well-defined pore morphology without using an inorganic template. Here, we describe a simple microwave accelerated approach to generate high surface area, ordered mesoporous carbons with controllable nitrogen content directly on a nickel foam framework. Cooperative assembly of phenolic resin (resol) and Pluronic F127 coated on the nickel foam provides a route to hierarchically structured composites to promote efficient transport, while melamine provides the nitrogen source. The strong interaction of microwaves with nickel rapidly and locally heats the precursors to yield nitrogen doped mesoporous carbon with high surface areas attached to the nickel foam within 3 min. As the microwave power is increased, the total nitrogen incorporated into the framework increases with a preference for pyridinic nitrogen. With this microwave assisted synthesis, the nitrogen content within the mesoporous carbons can approach 20 at%, while a relatively large average pore size (~7.5 nm) is obtained from the Pluronic template without any swelling agents or inorganic scaffold. To illustrate their potential, these nitrogen-doped mesoporous carbons are demonstrated as electrocatalysts for the oxygen reduction reaction (ORR) with stable performance over 5000 cycles. This solid state microwave fabrication methodology produces highly nitrogen doped ordered mesoporous carbons with characteristics difficult to obtain with traditional soft templating and this methodology should be extendable to a wide range templates and heteroatom dopants.

The immersion of poly(n-propyl methacrylate), PPMA, films (ca., 425 nm) in water induces swelling that is measured in-situ using spectroscopic ellipsometry. Unexpectedly, the end group of the PPMA resulting from the reversible addition-fragmentation chain transfer (RAFT) polymerization impacts the temperature dependence of swelling, despite their relatively high molecular weights (ca., 30 kDa). At 25 °C, dithiobenzoate terminated PPMA (PPMA-DB) leads to significantly less swelling (5.6 vol %) than the dodecylsulfanylthiocarbonyl terminated PPMA (PPMA-DD, 9.0 vol %). These PPMA films swell significantly more than expected due to a common carboxylic acid end group. As temperature is increased, the swelling for PPMA-DB increases and that for PPMA-DD decreases, with a crossover at approximately 35 °C–40 °C where the swelling is indistinguishable between the two polymers. The swelling kinetics exhibit two stages: an initial rapid swelling within the first minute of immersion and then a slow increase in thickness over multiple hours. The water contact angle of PPMA-DB increases on heating, while the water contact angle of PPMA-DD is invariant. This difference in the temperature dependence of the hydrophobicity is consistent with that for swelling. These results illustrate the potential unexpected consequences of residual RAFT fragment end groups on physical properties of polymers even at relatively high molecular weights. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016

Development of smart regenerative surface is a highly challenging but important task for many scientific and industrial applications. Specifically, very limited research efforts were made for surface regeneration between bio-adhesion and antifouling properties, because bioadhesion and antifouling are the two highly desirable but completely opposite properties of materials. Herein, we developed salt-responsive polymer brushes of poly(3-(1-(4-vinylbenzyl)-1H-imidazol-3-ium-3-yl) propane-1-sulfonate) (polyVBIPS), which can be switched reversibly and repeatedly between protein capture/release and surface wettability in a controllable manner. PolyVBIPS brush has demonstrated its switching ability to resist both protein adsorption from 100% blood plasma/serum and bacterial attachment in multiple cycles. PolyVBIPS brush also exhibits reversible surface wettability from ∼40° to 25° between in PBS and in 1 M NaCl solutions in multiple cycles. Overall, the salt-responsive behaviors of polyVBIPS brushes can be interpreted by the “anti-polyelectrolyte effect”, i.e. polyVBIPS brushes adopt a collapsed chain conformation at low ionic strengths to achieve surface adhesive, but an extended chain conformation at high ionic strength to realize antifouling properties. We expect that polyVBIPS will provide a simple, robust, and promising system for the fabrication of smart surfaces with biocompatible, reliable, and regenerative properties. Statement of Significance Unlike many materials with “one-time switching” capability for surface regeneration, we developed a new regenerative surface of zwitterionic polymer brush, which exhibits a reversible salt-induced switching property between a biomolecule-adhesive state and a biomolecule repellent state in complex media for multiple cycles. PolyVBIPS is easily synthesized and can be straightforward coated on the surface, which provides a simple, robust, and promising system for the fabrication of smart surfaces with biocompatible, reliable, regenerative properties.

A facile method to fabricate hierarchically structured fiber composites is described based on the electrospinning of a dope containing nickel and manganese nitrate salts, citric acid, phenolic resin, and an amphiphilic block copolymer. Carbonization of these fiber mats at 800 °C generates metallic Ni-encapsulated NiO/MnOx/carbon composite fibers with average BET surface area (150 m(2)/g) almost 3 times higher than those reported for nonporous metal oxide nanofibers. The average diameter (∼900 nm) of these fiber composites is nearly invariant of chemical composition and can be easily tuned by the dope concentration and electrospinning conditions. The metallic Ni nanoparticle encapsulation of NiO/MnOx/C fibers leads to enhanced electrical conductivity of the fibers, while the block copolymers template an internal nanoporous morphology and the carbon in these composite fibers helps to accommodate volumetric changes during charging. These attributes can lead to lithium ion battery anodes with decent rate performance and long-term cycle stability, but performance strongly depends on the composition of the composite fibers. The composite fibers produced from a dope where the metal nitrate is 66% Ni generates the anode that exhibits the highest reversible specific capacity at high rate for any composition, even when including the mass of the nonactive carbon and Ni(0) in the calculation of the capacity. On the basis of the active oxides alone, near-theoretical capacity and excellent cycling stability are achieved for this composition. These cooperatively assembled hierarchical composites provide a platform for fundamentally assessing compositional dependencies for electrochemical performance. Moreover, this electrospinning strategy is readily scalable for the fabrication of a wide variety of nanoporous transition metal oxide fibers.

Large-scale (multigram-to-kilogram) fabrication of soft-templated ordered mesoporous carbon (OMC) is enabled by roll-to-roll (R2R) processing via evaporation induced self assembly of Pluronic F127, oligomeric phenolic resin (resol), and tetraorthosilicate (TEOS) from ethanolic solution. The solution concentration, TEOS loading (etchable for microporous framework), and crosslinking temperature impact the pore structure. Here we demonstrate that mesoporous carbons with surface areas up to 2455 m2/g can be obtained under the proper processing conditions. Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS) and nitrogen adsorption–desorption isotherms reveal (i) suppressed framework shrinkage with increasing solution concentration during casting, (ii) improved long range order and higher surface area with increasing TEOS content up to 3:1 TEOS:resol, and (iii) enhanced porosity with crosslinking at 100 °C. These differences can be explained on the basis of block copolymer thermodynamics and mechanical reinforcement by silica. This family of OMCs are effective adsorbents for bulky aqueous organic dyes, such as methylene green (MG) and methyl blue (MB), with high adsorption capacities of 0.436 g MG/g OMC and 0.378 g MB/g OMC obtained. This R2R method provides a facile method to generate significant quantities of OMCs with tunable pore textures.