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Hydrophobic alkyl side chains steer water toward the charge-ion pair, giving rise to large interconnected water clusters that promote ion conduction.

The application of 3D printing of thermoplastics by Material Extrusion (MatEx) has commonly been limited by their poor mechanical strength that results from voids and weak interfaces between printed layers. Here, we demonstrate that core–shell structured filaments made of polycarbonate-based thermoplastics can achieve synergistic improvement in their interfacial bonding from the combination of high-glass transition temperature (T g)/high-viscosity core and low-T g/low-viscosity shell. Tensile strength along the printing direction was enhanced with the core–shell filaments. Layer-interfacial bonding strength as determined by Izod impact tests of the 3D printed parts is significantly improved by using filaments either with only a core–shell T g mismatch or both T g/viscosity core–shell mismatch. The mechanical behavior can be rationalized in terms of improved inter-layer molecule diffusion by a low T g/viscosity shell, better printability at higher temperature due to the core with higher melt strength, and better bulk mechanical strength of high-viscosity/T g core.

The local environment within a hydrogel influences the properties of water, including the propensity for ice crystallization. Water-swollen amphiphilic copolymers produce tunable nanoscale environments, which are defined by hydrophobic associations, for the water molecules. Here, the antifreeze properties for equilibrium-swollen amphiphilic copolymers with a common hydrophilic component, hydroxyethyl acrylate (HEA), but associated through crystalline (octadecyl acrylate, ODA) or rubbery (ethylhexyl acrylate, EHA) hydrophobic segments, are examined. Differences in the efficacy of the associations can be clearly enunciated from compositional solubility limits for the copolymers in water (2.6 mol % ODA vs ≤14 mol % EHA), and these differences can be attributed to the strength of the association. The equilibrium-swollen HEA-ODA copolymers are viscoelastic solids, while the swollen HEA-EHA copolymers are viscoelastic liquids. Cooling these swollen copolymers to nearly 200 K induces some crystallization of the water, where the fraction of water frozen depends on the details of the nanostructure. Decreasing the mean free path of water by increasing the ODA composition from 10 to 25 mol % leads to fractionally more unfrozen water (66-87%). The swollen HEA-EHA copolymers only marginally inhibit ice (13%) except with 45 mol % EHA, where nearly 60% of the water remains amorphous on cooling to 200 K. In general, the addition of the EHA leads to less effective ice inhibition than analogous covalently crosslinked HEA hydrogels (19.9 ± 1.8%). These results illustrate that fluidity of confining surfaces can provide pathways for critical nuclei to form and crystal growth to proceed.

Micelles formed within coacervate phases can impart functional properties, but it is unclear if this micellization provides mechanical reinforcement of the coacervate whereby the micelles act as high functionality crosslinkers. Here, we examine how sodium dodecyl sulfate (SDS) influences the structure and properties of Pluronic F108-polyacrylic acid (PAA) coacervates as SDS is known to decrease the aggregation number of Pluronic micelles. Increasing the SDS concentration leads to larger water content in the coacervate and an increase in the relative concentration of PAA to the other solids. Rheological characterization with small angle oscillatory shear (SAOS) demonstrates that these coacervates are viscoelastic liquids with the moduli decreasing with the addition of the SDS. The loss factor (tan

Additive Manufacturing (AM) enables the direct production of complex geometries from computer-aided designs (CAD). The AM fabrication process is often executed in a layer-by-layer manner, whereby minute printing errors in one layer can manifest significant defects in the final part. In-situ quality monitoring and control are currently limited for AM processes and cause low repeatability. Recently. advanced imaging is increasingly invested in AM and leads to the proliferation of layerwise imaging data, which provides an opportunity to transform quality control of AM from post-build inspection to in-situ quality monitoring. However, existing methodologies for in-situ inspection primarily focus on key characteristics of image profiles that tend to be limited in the ability to analyze the variance components, as well as root causes and failure patterns that are critical to process improvement. This letter presents an Additive Gaussian Process with dependent layerwise correlation (AGP-D) to model the spatio-temporal correlation of layerwise imaging data for AM quality monitoring. The AGP-D consists of three independent GP modules. The first GP approximates the base profile, whereas the second and third GP capture the correlation within the same layer and among layers, respectively. Based on posterior predictions of new layers, Hotelling ${{\boldsymbol{T}}^2}$ and generalized likelihood ratio (GLR) control tests are formulated to detect process shifts in the newly fabricated layer and analyze root causes. The proposed methodology is evaluated and validated using both simulation data and real-world case study of a cylinder build fabricated by a laser powder bed fusion (LPBF) machine. Experimental results show the proposed AGP-D is effective for real-time modeling and monitoring of layerwise-correlated imaging data.

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.

Acoustic/elastic metamaterials that rely on engineered microstructures instead of chemical composition enable a rich variety of extraordinary effective properties that are suited for various applications including vibration/noise isolation, high-resolution medical imaging, and energy harvesting and mitigation. However, the static nature of these elastic wave guides limits their potential for active elastic-wave guiding, as microstructure transformation remains a challenge to effectively apply in traditional elastic metamaterials due to the interplay of polarization and structural sensitivity. Here, a tunable, locally resonant structural waveguide is proposed and demonstrated for active vibration bandgap switching and elastic-wave manipulation between 1000–4000 Hz based on 3D printed building blocks of zinc-neutralized poly(ethylene-co-methacrylic acid) ionomer (Surlyn 9910). The ionomer exhibits shape memory behavior to enable rearrangement into new shape patterns through application of thermal stimuli that tunes mechanical performance in both space and time dimensions (4D metamaterial). The thermally induced shape-reorganization is programed to flip a series of frequency bands from passbands to bandgaps and vice versa. The continuously switched bandwidth can exceed 500 Hz. Consequently, altering the bandgap from “on” to “off” produces programmable elastic-wave propagation paths to achieve active wave guiding phenomena. An anisotropic cantilever-in-mass model is demonstrated to predict the self-adaptive dynamic responses of the printed structures with good agreement between the analytical work and experimental results. The tunable metamaterial-based waveguides illustrate the potential of 4D printed shape memory polymers in the designing and manufacturing of intelligent devices for elastic-wave control and vibration isolation.

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.

With increasing energy demands associated with portable electronics, routes to capture dissipated energy associated with everyday actions (energy harvesting) can be a key component in an integrated...

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.

Understanding the properties of water under either soft or hard confinement has been an area of great interest, but nanostructured amphiphilic polymers that provide a secondary confinement have garnered significantly less attention. Here, a series of statistical copolymers of 2-hydroxyethyl acrylate (HEA) and 2-(N-ethylperfluorooctane sulfonamido)ethyl methacrylate (FOSM) are swollen to equilibrium in water to form nanostructured physically cross-linked hydrogels to probe the effect of soft confinement on the dynamics of water. Changing the composition of the copolymer from 10 to 21 mol. % FOSM decreases the average size of the assembled FOSM cross-link, but also the spacing between the cross-links in the hydrogels with the mean distance between the FOSM aggregates decreasing from 3.9 to 2.7 nm. The dynamics of water within the hydrogels were assessed with quasielastic neutron scattering. These hydrogels exhibit superior performance for inhibition of water crystallization on supercooling in comparison to analogous hydrogels with different hydrophilic copolymer chemistries. Despite the lower water crystallinity, the self-diffusion coefficient for these hydrogels from the copolymers of HEA and FOSM decreases precipitously below 260 K, which is a counter to the nearly temperature invariant water dynamics reported previously with an analogous hydrogel [Wiener et al., J. Phys. Chem. B 120, 5543 (2016)] that exhibits nearly temperature invariant dynamics to 220 K. These results point to chemistry dependent dynamics of water that is confined within amphiphilic hydrogels, where the interactions of water with the hydrophilic segments can qualitatively alter the temperature dependent dynamics of water in the supercooled state.

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...

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.

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 (M

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.