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Polymer-based functional surface coatings are extensively used in advanced technologies, including optics, energy, and environmental applications. Surface thermodynamic properties profoundly impact the molecular interactions that control interfacial behaviors, such as adhesion and wettability, which in turn dictate coating processes and performance. Conventionally, contact angle measurements are used to assess the surface energy of polymer films and coatings, where the wettability of a surface is assessed using probe fluids (liquid drops). However, contact angle measurement oftentimes can be nontrivial due to the roughness or chemical heterogeneity of the solid surface, as well as the potential for the liquid drop to swell or even dissolve the material being measured. Alternatively, inverse gas chromatography (iGC) is a versatile technique to measure surface thermodynamics and Lewis acid–base properties while also providing environmental control such as temperature and humidity. Despite these benefits, the application of iGC has been limited to powders or fibers, while the direct measurement of supported thin films or coatings is still a nascent area of research. This creates a challenge when using iGC as a comprehensive platform for measuring the physicochemical properties of solid surfaces. Here, we demonstrate how to effectively use iGC to characterize the surface energy of supported polymer thin films by using a two-dimensional (2D) film holder and modifying operational controls, such as the concentration range of the injected gas probe molecules. This enables the precise control of surface coverage required for analyzing samples having minimal surface area, such as thin films. Poly(methyl methacrylate) (PMMA) was employed as a benchmark to determine suitable iGC parameters and to validate our approach on polymer thin films. The seminal work presented here expands the capability of state-of-the-art iGC to embrace supported thin films (2D iGC) that could either be smooth or display texture/roughness (patterned films) as well as coatings with heterogeneous chemical/structural composition.

The influence of polymer overlayers on the catalytic activity of Ag for electrochemical CO2reduction to CO is explored. Polystyrene and poly(4-vinylpyridine) films of varying thicknesses are applied as catalysis-directing overlayers atop Ag electrodes. For polystyrene, substantial suppression of CO2reduction activity is observed while the hydrogen evolution reaction (HER) increases. The addition of a nitrogen heteroatom into the phenyl groups of polystyrene (e.g., a pyridine ring) results in an increase in the conversion of CO2to CO and suppression of HER. Block copolymer variants containing both phenyl and pyridyl functionalities exhibit similar activity for CO evolution but appear to suppress HER further than the polymer layer containing only pyridine groups. The size of the blocks for the copolymer influences the catalytic output of the Ag electrode, suggesting that the hierarchical structure that forms in the block copolymer layer plays a role in catalytic activity at the electrode surface. Analysis of the polymer overlayers suggests that polystyrene significantly inhibits all ion transport to the metal electrode, while poly(4-vinylpyridine) enables CO2transport while modifying the electronics of the Ag active site. Therefore, the engineered application of polymer overlayers, especially those containing heteroatoms, enables new avenues of electrochemical CO2reduction to be explored.

The postcardiac injury syndrome (PCIS) includes the postmyocardial infarction syndrome, the postcommissurotomy syndrome, and the postpericardiotomy syndrome. Dressler reported a series of patients who developed a pericarditis-like illness days to [...]

As part of U.S. national efforts to combat the detrimental effect of global climate change, the National Institute of Standards and Technology (NIST) was recently tasked to support efforts in direct air capture (DAC) of carbon dioxide research and deployment. In order to develop test procedures, materials, and documentary standards, key characterization methods relevant to DAC materials have been investigated and used to identify desirable properties for a potential Standard Reference Material (SRM). Select amine-supported materials that previously showed potential for DAC applications have been characterized using commonly available laboratory methods. Further insights into the adsorption characteristics have been gained from developing and applying more specialized characterization tools ideal for probing low concentrations of carbon dioxide. A broad suite of capabilities that examine relevant properties under appropriate conditions gives the most profound insights into a material’s specific performance. We advocate for even more specialized capabilities to be developed and standardized to quantitatively monitor the interactions of CO2with molecular species in complex and often disordered systems to advance DAC and support carbon dioxide reduction (CDR) in general.

The orientation of polyamide thin films on non-porous substrates was investigated using Fourier transform infrared (FTIR) spectroscopy and corroborated by near-edge X-ray absorption fine structure (NEXAFS) measurements. Polyamide films composed of m-phenylene diamine and trimesoyl chloride were synthesized via a layer-by-layer deposition process on both gold and silicon substrates, where the number of sequential monomer deposition steps (cycles) determines the overall polyamide film thickness. These films represent model materials for metrology development that can be applied to understand the selective polyamide layers in reverse osmosis (RO) membranes. Using the fingerprint region in the infrared spectrum for the m-phenylene diamine-trimesoyl chloride (MPD-TMC) system, peaks were identified that could be used as diagnostic modes for molecular orientation analysis. At extremely low cycle numbers, FTIR measurements suggest that the MPD-derived aromatic rings exhibited a tilt angle of ∼6° from the surface parallel, while the carbonyl group of the amide was similarly oriented with an average tilt angle of ∼17°. The FTIR insights are in agreement with NEXAFS results, which indicate that the aromatic rings in the first-half layer-by-layer cycle are oriented parallel to the surface. Both FTIR and NEXAFS measurements further show high anisotropy in the materials at low cycle numbers. As the films approach 60 cycles (∼13 nm films), the films become isotropic and no orientation was detected.

Soft elastomers are critical to a broad range of existing and emerging technologies. One major limitation of soft elastomers is the large friction of coefficient (COF) due to inherently large adhesion and internal loss. In applications where lubrication is not applicable, such as soft robotics, wearable electronics, and biomedical devices, elastomers with inherently low dry COF are required. Inspired by the low COF of snakeskins atop soft bodies, this study reports the development of elastomers with low dry COF by growing a hybrid skin layer with a strong interface with a large stiffness gradient. Using a solid–liquid interfacial polymerization (SLIP) process, hybrid skin layers are imparted onto elastomers, which reduces the COF of the elastomers from 1.6 to 0.1, without sacrificing the bulk compliance and ductility of elastomer. Compared with existing surface modification methods, the SLIP process offers spatial control and ability to modify flat, prepatterned, curved, and inner surfaces, which is essential to engineer multifunctional skin layers for emerging applications.

Reduced graphene oxide (r-GO) membranes with narrow channels exhibit salt rejections comparable to conventional nanofiltration (NF) membranes. However, their water permeances are much lower because of the high tortuosity for water permeation. Herein, we report a facile solution-processable approach to create in-plane nanopores on GO nanosheets before reduction, dramatically decreasing the tortuosity and increasing water permeance while retaining the salt rejection. Specifically, holey GO (HGO) nanosheets were prepared via chemical etching using hydrogen peroxide followed by the deposition on a porous support by vacuum filtration and then reduction via exposure to hydriodic acid solutions to generate the reduced HGO (r-HGO) membrane. The generation of nanopores increases the water permeance from 0.4 L m–2h–1bar–1(LMH/bar) to 6.6 LMH/bar with Na2SO4rejection greater than 98.5%, and the membranes were robust under strong cross-flow shearing force for 36 h. Both water permeance and Na2SO4rejection of these r-HGO membranes for the first time simultaneously reach the level of the commercial polyamide-based NF membranes. Given their good antibacterial properties and resistance to aggressive chemical washing, the r-HGO membranes show promise as next-generation NF membranes for desalination.

A compressive strain applied to bilayer films (e.g., a thin film adhered to a thick substrate) can lead to buckled or wrinkled morphologies, which has many important applications in stretchable electronics, anticounterfeit technology, and high-precision micrometrology and nanometrology. A number of buckling-based metrology methods have been developed to quantify the residual stress and viscoelastic properties of polymer thin films. However, in some systems (e.g., solvent-induced swelling or thermal strain), the compressive strain is unknown or difficult to measure. We present a quantitative method of measuring the compressive strain of wrinkled polymer films and coatings with knowledge of the “skin” thickness, wrinkle wavelength, and wrinkle amplitude. The derived analytical expression is validated with a well-studied model system, e.g., a stiff, thin film bonded to a thick, compliant substrate. After validation, we use our expression to quantify the applied swelling strain of previously reported wrinkled poly(styrene-alt-maleic anhydride) brush surfaces. Finally, the applied strain is used to rationalize the observed persistence length of aligned wrinkles created during atomic force microscopy lithography and subsequent solvent exposure.

We combine in situ heated atomic force microscopy (AFM) with automated line-by-line spectral analysis to quantify the relaxation or decay phenomenon of nanopatterned composite polymer films above the glass-transition temperature of the composite material. This approach enables assessment of pattern fidelity with a temporal resolution of ≈1 s, providing the necessary data density to confidently capture the short-time relaxation processes inaccessible to conventional ex situ measurements. Specifically, we studied the thermal decay of nanopatterned poly(methyl methacrylate) (PMMA) and PMMA nanocomposite films containing unmodified and PMMA-grafted silica nanoparticles (SiO2NP) of varying concentrations and film thicknesses using this new approach. Features imprinted on neat PMMA films were seen to relax at least an order of magnitude faster than the NP-filled films at decay temperatures above the glass transition of the PMMA matrix. It was also seen that patterned films with the lowest residual thickness (34 nm) filled with unmodified SiO2NP decayed the slowest. The effect of nanoparticle additive was almost negligible in reinforcing the patterned features for films with the highest residual thickness (257 nm). Our in situ pattern decay measurement and the subsequent line-by-line spectral analysis enabled the investigation of various parameters affecting the pattern decay such as the underlying residual thickness, type of additive system, and temperature in a timely and efficient manner.

Polymeric membranes are ubiquitous in transport applications including gas separation, water desalination, solid-state batteries, and fuel cells. The transport mechanism in certain classes of membranes is well understood. It is generally believed that polymeric membranes used in gas separation follow the solution–diffusion model. However, the transport mechanism in other membranes such as the ones used in water desalination is less clear as both the solution–diffusion and hydrodynamic models have been proposed. In this contribution, we study the structure as well as the water and polymer dynamics of several polymeric membranes using small-angle and quasi-elastic neutron scattering. We demonstrate that on the scale of a few nanometers, water appears to diffuse through a desalination membrane at a rate comparable to bulk water, while water diffuses at a rate that is a factor of 2 slower in an anion-exchange membrane. These results illustrate the importance of studying both the structure and dynamics of membrane materials and have important implications in understanding the transport mechanisms that differentiate the different types of polymeric membranes.

Polymers with high permeability and strong size-sieving ability are needed for H2/CO2separation at temperatures ranging from 100 to 300 °C to enable an energy-efficient precombustion CO2capture process. However, such polymers usually suffer from a permeability/selectivity tradeoff, that is, polymers with high permeability tend to exhibit a weak size-sieving ability and thus low selectivity. Herein, we demonstrate that carbonization of a suitable polymer precursor (i.e., polybenzimidazole or PBI) generates microcavities (leading to high H2permeability) and ultramicroporous channels (leading to strong size-sieving ability and thus high H2/CO2selectivity). Specifically, carbonization of PBI at 900 °C (CMS@900) doubles H2permeability and increases H2/CO2selectivity from 14 to 80 at 150 °C. When tested with simulated syngas-containing equimolar H2and CO2in the presence of water vapor for 120 h, CMS@900 exhibits stable H2permeability of ≈36 barrer and H2/CO2selectivity of ≈53 at 150 °C, above Robeson’s 2008 upper bound and demonstrating robustness against physical aging and CO2plasticization.

Aminopolymer sorbents are leading candidates for extracting CO2directly from the atmosphere under ambient conditions. For effective carbon capture, this requires not only that the CO2actively binds with amine groups of the polymer under low gas concentrations but also that it readily diffuses through the sorbent media to access as many of the amine binding sites as possible. Unfortunately, high reactivity and diffusivity tend to be mutually exclusive properties when it comes to small molecule transport within a polymer, posing a significant materials design challenge. While many reports to date focus on chemical additives or engineering strategies to tackle this trade-off, only a few studies have seriously investigated the underlying chemical and physical properties of the sorbent polymer as a function of its interaction with the relevant sorbate molecules. In this study, we investigate the interplay of polymer-sorbate reactivity and diffusive dynamics of both H2O and CO2in branched polyethylenimine (PEI) using quasielastic neutron scattering (QENS), infrared spectroscopy, gravimetric uptake, and mechanical dissipation measurements as a function of atmospheric dosing conditions. We uncover an intriguing and previously unreported discrepancy in the diffusive dynamics of PEI dosed with CO2and H2O vapor at the microscopic and macroscopic length scales. At the macroscopic scale, our mechanical dissipation measurements show that while the exposure to H2O vapor alone always plasticizes the dynamics of PEI, the absorption of CO2, either in the presence of H2O or not, leads to a mechanical stiffening of the PEI. Interestingly, this response differs at the microscopic scale where the diffusive dynamics of the H2O- and/or CO2-dosed samples as quantified by QENS are always enhanced relative to the undosed PEI. This dynamic facilitation is greatest in the presence of H2O vapor alone, consistent with H2O strongly plasticizing the dynamics of PEI. However, the simultaneous exposure to both H2O and CO2leads to a stiffening of the QENS dynamics at the microscopic scale relative to the hydrated state, signifying local interactions between the CO2and the polymer. Under these conditions, we also observe a greater amount of CO2absorbed into the PEI film that is simultaneously exposed to both H2O and CO2as compared to the film exposed to just CO2, further evidencing a complicated three-way interaction between the H2O, CO2, and PEI. These results are discussed in terms of an absorption process that involves the formation of carbamate ions, the generation of ionic cross-link junctions in the PEI, and changes in the local hydration level of the polymer around the ions. To establish the importance of the carbamate ions in this process, we utilize a methylation reaction to modify the PEI and convert all of the primary and secondary amines into tertiary amines that are incapable of forming carbamates. This considerably diminishes the role of hydrogen bonding in the PEI, enhances the microscopic dynamics of the undosed PEI, and results in diffusive dynamics that do not depend heavily on dosing with H2O and/or CO2. The observations reported here provide insights into the design of next-generation aminopolymer sorbents where both reactivity and diffusive dynamics can be optimized.

Metal–organic frameworks (MOFs) are renowned for their tunable structure, porosity, and internal chemistry, with demonstrated applications in molecular separations, storage, and conversion. While they are widely usable, the powdery characteristics of MOF materials can be limiting for large-scale processing and implementation in devices. Incorporating MOF particles into polymer supports affords engineering solutions to overcome these issues, yet the nature of the resulting composites is difficult to assess. In this work, we present spectroscopic and calorimetric methods that we believe help establish a holistic physicochemical picture of the composite structure using a series of Zr MOFs with different pore sizes as a testbed. Power law decays are observed in X-ray scattering profiles in low q-space ranging between 2.4 and 3.3, which we interpret as changes in scattering due to polymer infiltrating MOF particles. This interpretation is supported by solid-state nuclear magnetic resonance spectroscopy and differential scanning calorimetry measurements that identify populations of the MOF-associated polymer. Additionally, positron annihilation lifetime spectroscopy measurements collected on a series of composites with different MOF-polymer ratios show multiple decay constants, each correlated to a different free volume elements. In combination with the spectroscopic, calorimetric, and scattering results, we utilize the trends in decay constants as a function of polymer mass fraction to hypothesize a polymer infiltration mechanism whereby large pores are preferentially filled, followed by small pores and, later still, interstitial spaces between particles. Even with vigorous investigation of polymer, MOF, and interface characteristics, the complex and heterogeneous nature of the composites makes absolute structural assertions difficult. We envision that the approaches demonstrated here will be a useful foundation to assess and ultimately guide the design of future MOF-polymer composites.

Polymer films provide a versatile platform in which complex functional relief patterns can be thermally imprinted with a resolution down to few nanometers. However, a practical limitation of this method is the tendency for the imprinted patterns to relax (“slump”), leading to loss of pattern fidelity over time. While increasing temperature above glass transition temperature (Tg) accelerates the slumping kinetics of neat films, we find that the addition of polymer-grafted nanoparticles (PGNP) can greatly enhance the thermal stability of these patterns. Specifically, increasing the concentration of poly(methyl methacrylate) (PMMA) grafted titanium dioxide (TiO2) nanoparticles in the composite films slows down film relaxation dynamics, leading to enhanced pattern stability for the temperature range that we investigated. Interestingly, slumping relaxation time is found to obey an entropy–enthalpy compensation (EEC) relationship with varying PGNP concentration, similar to recently observed relaxation of strain-induced wrinkling in glassy polymer films having variable film thickness. The compensation temperature, Tcompwas found to be in the vicintity of the bulk Tg of PMMA. Our results suggest a common origin of EEC relaxation in patterned polymer thin films and  nanocomposites.

Carboxylic acid groups impart hydrophilicity and ionizable moieties to polyamide membranes for desalination, hence influencing water and ion transport through the material. Model polyamide films were synthesized via molecular layer-by-layer (mLbL) deposition on planar substrates to study the formation process of these materials and overcome the chemical and topological inhomogeneity inherent to conventional interfacially polymerized polyamide membranes. The carboxylic acid content in these model films was characterized using Fourier transform infrared (FTIR) spectroscopy by quantifying the C═O band at 1718 cm–1. The concentration of carboxylic acid groups decreased as the thickness of the membrane increased, suggestive of an increase in cross-link density as the polyamide network develops. For the thinnest molecular layer-by-layer samples, the carboxylic acid concentration for films on gold was 0.35 mmol g–1, whereas analogous films on silicon had an acid content of 0.56 mmol g–1, indicating a clear influence of the substrate on the initial network formation. As the thickness of the membrane increased, the influence of the substrate and initial layer growth became less significant as the carboxylic acid concentration on both substrates reached a value of 0.12 mmol g–1. We demonstrate that FTIR spectroscopy is a practical and accessible way to quantify the carboxylic acid content in these types of extremely thin polyamide membranes to help quantify network formation in these materials.

We report a first-order like sharp surface wettability transition with varying film thickness dependent morphology in cast films of an amphiphilic triblock copolymer. Films composed of poly(2-(N-ethylperfluorooctanesulfonamido) ethyl methyl acrylate), poly(FOSM), and poly(N,N′-dimethyl acrylamide), poly(DMA), with thickness (h) in the transition-range, 200 < h< 300 nm, exhibited an abrupt hydrophobic to hydrophilic dynamic water contact angle transition. After an induction time, ti≈ 40 to 180 s, water contact angle varied as θc≈ 116° to 40° with an ultrafast contact angle decay time constant, dθcdt≈ −18°/s. This behavior is a result of competing heterogeneous and antagonistic effects of bumpy poly(DMA) wetting domains against a nonwetting planar poly(FOSM) background, with a “jump percolation” wetting transition when the poly(DMA) domain density reaches unity. Outside of this film thickness range, relatively shallow decreasing water contact angle gradients were observed with a monotonically increasing poly(DMA) domain area coverage with increasing film thickness in the overall range of 40 nm (hydrophobic, θc≈ 118°) < h< 500 nm (hydrophilic, θc≈ 8°). The optical diffuse reflectance properties of these rough surfaces exhibit an onset of diffuse reflectance maxima correlated to the transition morphology film thickness.

Perfluorinated ionomers, in particular, Nafion, are a critical component in hydrogen fuel cells as the ion conducting binder within the catalyst layer in which it can be confined to thicknesses on the order of 10 nm or less. It is well reported that many physical properties, such as the Young’s modulus, are thickness dependent when the film thickness is less than 100 nm. Here we utilize a cantilever bending methodology to quantify the swelling-induced stresses and relevant mechanical properties of Nafion films as a function of film thickness exposed to cyclic humidity. We observe a factor of 5 increase in the Young’s modulus in films thinner than 50 nm and show how this increased stiffness translates to reduced swelling or hydration. The swelling stress was found to increase by a factor of 2 for films approximately 40 nm thick. We demonstrate that thermal annealing enhances the modulus at all film thicknesses and correlate these mechanical changes to chemical changes in the infrared absorption spectra.

To the Editor: We recently evaluated a 48-year-old, nonsmoking Filipino female with a 3-week history of cough and hemoptysis. Physical examination was unremarkable. Chest radiography and computed tomography scan of [...]

Water transport and swelling properties of an ultrathin, selective polyamide layer with a hydrophilic polymer coating, i.e., a polymer bilayer, are studied using quartz crystal microbalance with dissipation (QCM-D). Specifically, QCM-D is used to measure the dynamic and equilibrium change in mass in a series of differential sorption experiments to determine the dependence of the apparent diffusion coefficient and equilibrium swelling of the bilayer as a function of the water vapor activity. To determine transport properties specific to the polyamide layer, sorption kinetics of the bilayer was modeled with a bilayer mass transport model. The swelling and water diffusion coefficients are interpreted according to the Painter–Shenoy polymer network swelling model and the solution-diffusion model, respectively.

Superamphiphobic surfaces, exhibiting high contact angles and low contact angle hysteresis to both water and low surface tension liquids, have attracted a great deal attention in recent years because of the potential of these materials in practical applications such as liquid-resistant textiles, self-cleaning surfaces, and antifouling/anticorrosion coatings. In this work, we present a simple strategy for fabricating of superamphiphobic coatings based on photopolymerization of hybrid thiol–ene resins. Spray-deposition and UV photopolymerization of thiol–ene resins containing hydrophobic silica nanoparticles and perfluorinated thiols provide a multiscale topography and low-energy surface that endows the surface with superamphiphobicity. The wettability and chemical composition of the surfaces were characterized by contact-angle goniometry and X-ray photoelectron spectroscopy, respectively. The hierarchical roughness features of the thiol–ene surfaces were investigated with field-emission scanning electron microscopy. Droplet impact and sandpaper abrasion tests indicate the coatings respectively possess a robust antiwetting behavior and good mechanical durability.

Cell sourcing continues to be a significant limitation to regenerative medicine especially in neural lineages where population heterogeneity during in vitroculture prevents definitive phenotype assessment. For nearly 40 years, the biological community has worked with amine-derivated surfaces and hydrogels, especially alginate, with little quantitative assessment of how local amine concentration influences the extent of neural differentiation and neurite extension. In this manuscript we show that the local concentration of amines distinctly influences mouse embryonic stem cell (ESC) lineage commitment and the length of neurite extensions both of which are early indicators of differentiation. The well-defined amine gradients are a highly relevant tool for identifying these critical concentrations and thresholds. We feel these results will be of critical importance to researchers developing new ex vivoculture materials for neural applications as well as the community exploring nerve regeneration in vivo.

Lung cancer remains a major medical impediment in which early diagnosis and timely treatment are key factors in its management. This study evaluated nonsmall cell lung cancer (NSCLC) patients in a large military medical center to determine the timeliness to diagnosis and curative surgery in comparison with published guidelines. A retrospective record review of tumor registry NSCLC surgery cases at Navy Medical Center San Diego (NMCSD) from 2004 to 2009 was conducted. Of the 84 patients, 49% were women, the median age was 63, 58% were Caucasian, and 71% represented ex- or active smokers. A significant number of women were Asian (30%) and nonsmokers (77%). The predominant histology was adenocarcinoma (86%) with positron emission tomography-computed tomography (PET-CT) nonavid (57%). Median time for pulmonologist evaluation was 8 days, median time for PET-CT was 13 days, median time for cardiothoracic surgery evaluation to thoracotomy was 25 days, and median time from pulmonologist evaluation to thoractomy was 59 days.

We report on a novel fabrication approach to build multilayered optical tissue phantoms that serve as independently validated test targets for axial resolution and contrast in scattering measurements by depth-resolving optical coherent tomography (OCT) with general applicability to a variety of three-dimensional optical sectioning platforms. We implement a combinatorial bottom-up approach to prepare monolayers of light-scattering microspheres with interspersed layers of transparent polymer. A dense monolayer assembly of monodispersed microspheres is achieved via a combined methodology of polyelectrolyte multilayers (PEMs) for particle-substrate binding and convective particle flux for two-dimensional crystal array formation on a glass substrate. Modifications of key parameters in the layer-by-layer polyelectrolyte deposition approach are applied to optimize particle monolayer transfer from a glass substrate into an elastomer while preserving the relative axial positioning in the particle monolayer. Varying the dimensions of the scattering microspheres and the thickness of the intervening transparent polymer layers enables different spatial frequencies to be realized in the transverse dimension of the solid phantoms. Step-wise determination of the phantom dimensions is performed independently of the optical system under test to enable precise spatial calibration, independent validation, and quantitative dimensional measurements.

Single-wall carbon nanotube (SWCNT) films show significant promise for transparent electronics applications that demand mechanical flexibility, but durability remains an outstanding issue. In this work, thin membranes of length purified single-wall carbon nanotubes (SWCNTs) are uniaxially and isotropically compressed by depositing them on prestrained polymer substrates. Upon release of the strain, the topography, microstructure, and conductivity of the films are characterized using a combination of optical/fluorescence microscopy, light scattering, force microscopy, electron microscopy, and impedance spectroscopy. Above a critical surface mass density, films assembled from nanotubes of well-defined length exhibit a strongly nonlinear mechanical response. The measured strain dependence reveals a dramatic softening that occurs through an alignment of the SWCNTs normal to the direction of prestrain, which at small strains is also apparent as an anisotropic increase in sheet resistance along the same direction. At higher strains, the membrane conductivities increase due to a compression-induced restoration of conductive pathways. Our measurements reveal the fundamental mode of elasto-plastic deformation in these films and suggest how it might be suppressed.

The viscoelastic properties of polymer thin films can have a significant impact on the performance in many small-scale devices. In this work, we use a phenomenon based on a thermally induced instability, termed thermal wrinkling, to measure viscoelastic properties of polystyrene films as a function of geometric confinement via changes in film thickness. With application of the appropriate buckling mechanics model for incompressible and geometrically confined films, we estimate the stress-relaxation modulus of polystyrene films by measuring the time-evolved wrinkle wavelength at fixed annealing temperatures. Specifically, we use time−temperature superposition to shift the stress relaxation curves and generate a modulus master curve for polystyrene films investigated here. On the basis of this master curve, we are able to identify the rubbery plateau, terminal relaxation time, and viscous flow region as a function of annealing time and temperatures that are well-above its glass transition. Our measurement technique and analysis provide an alternative means to measure viscoelastic properties and relaxation behavior of geometrically confined polymer films.

We present a optical phantom approach for the characterization of OCT axial resolution and contrast via multilayered "bar charts." We explored two methods to fabricate these phantoms: the first is based on monolayers of light-scattering microspheres with an intervening layer of transparent silicone, and the second involves alternating layers of scatteringenhanced silicone and transparent silicone. Varying the diameter of the microspheres and the thickness of the silicone layers permits different spatial frequencies to be realized in the axial dimension of the phantoms. Because the phantom's dimensions are accurately known independent of the OCT system, no information about the system's spatial calibration is required. We quantified the degree to which the bars in each phantom could be resolved with OCT, which provides insights into the axial contrast transfer function. Initial testing of these phantoms on time-resolved and Fourier-domain OCT platforms indicated that our approach can provide accurate, system-independent estimates of resolution.

We report the use of a gradient library approach to characterize the structure and behavior of thin films of a thermally responsive block copolymer (BCP), poly(styrene-b-tert-butyl acrylate) (PS-b-PtBA), which exhibits chemical deprotection and morphological changes above a thermal threshold. Continuous gradients in temperature and film thickness, as well as discrete substrate chemistry conditions, were used to examine trends in deprotection, nanoscale morphology, and chemical structure. Thermal gradient annealing permitted the extraction of transformation rate constants (kt) for the completion of thermal deprotection and rearrangement of the film morphology from a single BCP library on hydroxyl and alkyl surfaces, respectively. The transformation rate constants ranged from 1.45 × 10−4s−1to 5.02 × 10−5s−1for temperatures between 185 and 140 °C for hydroxyl surfaces. For the same temperature range, the alkyl surfaces yielded ktvalues ranging from 4.76 × 10−5s−1to 5.73 × 10−6s−1, an order of magnitude slower compared to hydroxyl surfaces. Activation energies of the thermal deprotection and film transformation on these surfaces were also extrapolated from linear fits to Arrhenius behavior. Moreover, we noted a morphology shift and orientation transformation from parallel lamellae to perpendicular cylinders at the free surface because of changes in volume fraction and surface energetics of the initially symmetric BCP. Using gradient techniques, we are able to correlate morphological and chemical structure changes in a rapid fashion, determine kinetics of transitions, and demonstrate the effect of surface chemistry on the deprotection reaction in thermally responsive BCP thin films.

The mechanical stability of polymeric nanostructures is critical to the processing, assembly, and performance of numerous existing and emerging technologies. A key predictor of mechanical stability is the elastic modulus. However, a significant reduction in modulus has been reported for thin films and nanostructures when the thickness or size of the polymer material decreases below a critical length scale. Routes to mitigate or even eliminate this reduction in modulus, and thus enhancing the mechanically stability of polymeric nanostructures, would be extremely valuable. Here, two routes to modulate the mechanical properties of polymers at the nanoscale are described. Exposure to ultraviolet light and ozone (UVO) cross-links the near surface region of high molecular mass PS films, rendering the elastic modulus independent of thickness. However, UVO cannot eliminate the decrease in modulus of low molecular mass PS or PMMA due to limited reaction depth and photodegradation, respectively. Alternatively, the thickness dependence of the elastic modulus of both PS and PMMA can be eliminated by addition of dioctyl phthalate (DOP) at 5% by mass. Furthermore, an increase in modulus is observed for films with thicknesses less than 30 nm with 5% DOP by mass in comparison to neat PS. Although DOP acts as a plasticizer for both PS and PMMA in the bulk, evidence indicates that DOP acts as an antiplasticizer at the nanoscale. By maintaining or even increasing the elastic modulus of polymers at the nanoscale, these methods could lead to improved stability of polymeric nanostructures and devices.

Polymer coatings are dependent on strongly bonded buried interfaces to maintain adhesion and protective properties over long application lifetimes. In this work, we detail the detection of buried interfaces with deviations from perfect bonded or perfect slip interfaces using surface indentation on thin films with large contact areas. The interfacial interactions between photopolymerized methacrylate films and a glass substrate were tailored using silane chemistry to create an interface that either easily releases from or cross-links with the polymer network. Creep compliance measurements on the polymethacrylate films were compared with predicted contact measurements for literature models of ideal interfaces. Nonideal contributions from interfacial effects were detected during experiments with high confinement. The extent of these effects varied with polymer network structure and polymer/substrate interface strength, with fluorinated interfaces exhibiting up to a 25% increase in indentation contact area as compared to an ideal bonded indentation due to the presence of a weak interface. The ability to probe the response of a buried interface under low indentation loads is attractive for testing and validating the interfacial properties and performance of coatings and films. This approach could be used to interrogate the fidelity of an interface in critical areas such as corrosion protection and encapsulation.

We utilize a vapor deposition setup and cross-diffusion of functionalized chlorosilanes under dynamic vacuum to generate a nearly linear gradient in surface energy and composition on a silicon substrate. The gradient can be tuned by manipulating chlorosilane reservoir sizes and positions, and the gradient profile is independent of time as long as maximum coverage of the substrate is achieved. Our method is readily amenable to the creation of gradients on other substrate surfaces, due to the use of vapor deposition, and with other functionalities, due to our use of functionalized chlorosilanes. Our gradients were characterized using contact angle measurements and X-ray photoelectron spectroscopy. From these measurements, we were able to correlate composition, contact angle, and surface energy. We generated a nearly linear gradient with a range in mole fraction of one component from 0.15 to 0.85 (34 to 40 mJ/m2in surface energy) to demonstrate its utility in a block copolymer thin film morphology study. Examination of the copolymer thin film surface morphology with optical and atomic force microscopy revealed the expected morphological transitions across the gradient.

Understanding the mechanical properties of polymers at the nanoscale is critical in numerous emerging applications. While it has been widely shown that the glass transition temperature (Tg) in thin polymer films generally decreases due to confinement effects in the absence of strong favorable interactions between the polymer and substrate, there is little known about the modulus of sub-100 nm polymer films and features. Thus, one might use this depressed Tgas a surrogate to estimate how the modulus of nanoconfined polymeric materials deviates from the bulk, based on constructs such as Williams−Landel−Ferry (WLF) time−temperature superposition principles. However, such relationships have not been thoroughly examined at the nanoscale where surface and interface effects can dramatically impact the physical properties of a material. Here, we measure the elastic modulus of a series of poly(methacrylate) films with widely varying bulk Tg’s as a function of thickness at ambient temperature, exploiting a wrinkling instability of a thin, stiff film on an thick, elastic substrate. A decrease in the modulus is found for all polymers in ultrathin films (<30 nm) with the onset of confinement effects shifting to larger film thicknesses as the quench depth (Tg,bulk− T) decreases. We show that the decrease in modulus of ultrathin films is not correlated with the observed Tgdecrease in films of the same thickness.

Residual stress, a pervasive consequence of solid materials processing, is stress that remains in a material after external forces have been removed. In polymeric materials, residual stress results from processes, such as film formation, that force and then trap polymer chains into nonequilibrium stressed conformations. In solvent-cast films, which are central to a wide range of technologies, residual stress can cause detrimental effects, including microscopic defect formation and macroscopic dimensional changes. Since residual stress is difficult to measure accurately, particularly in nanoscale thin polymer films, it remains a challenge to understand and control. We present here a quantitative method of assessing residual stress in polymer thin films by monitoring the onset of strain-induced wrinkling instabilities. Using this approach, we show that thin (>100 nm) polystyrene films prepared viaspin-coating possess residual stresses of ≈30 MPa, close to the crazing and yield stress. In contrast to conventional stress measurement techniques such as wafer curvature, our technique has the resolution to measure residual stress in films as thin as 25 nm. Furthermore, we measure the dissipation of residual stress through two relaxation mechanisms: thermal annealing and plasticizer addition. In quantifying the amount of residual stress in these films, we find that the residual stress gradually decreases with increasing annealing time and plasticizer amounts. Our robust and simple route to measure residual stress adds a key component to the understanding of polymer thin film behavior and will enable identification of more effective processing routes that mitigate the detrimental effects of residual stress.

The adhesion between poly(dimethylsiloxane) (PDMS) hemispheres coated with layer-by-layer (LbL) assemblies of polyelectrolytes and rigid, planar substrates was investigated using Johnson, Kendall, and Roberts (JKR) contact mechanics. Measurements were performed against amine-functionalized glass slides both in air and in aqueous solutions of controlled pH. Despite the increased density of negatively charged carboxylate groups, LbL-functionalized PDMS exhibited lower adhesion because of the combined effects of increased surface roughness and the high Young’s modulus of the coating. Measurements of coated PDMS in aqueous solutions revealed tunable adhesion behavior dominated by pH-mediated changes in the mechanical properties of the coating. Smoothing the surface of the LbL coatings by aqueous salt annealing led to a significant increase in adhesion. Our results suggest that LbL assembly can be an effective means of surface functionalization for in situ adhesion measurements, but understanding and predicting the adhesion behavior requires comprehensive knowledge of the chemical, mechanical, and topological properties of the coating and how such properties change in response to the ambient environment.

Muscarinic receptor agonists increase water secretion from the acinar cells of respiratory, sweat, salivary, and lacrimal glands. Mice lacking the gene for aqueous water channel aquaporin (Aqp) 5 exhibit methacholine-induced bronchiolar hyperreactivity when compared to normal mice. Individuals with asthma also have enhanced airway responsiveness to methacholine and diminished airway hydration. Because Aqp5 in humans is also expressed in respiratory, sweat, salivary, and lacrimal glands, we hypothesized that those individuals with exercise-induced asthma and excessive bronchiolar reactivity should also have decreased muscarinic receptor-dependent sweat, salivary, and tear gland secretions.

The article features an in-town house that uses sustainable materials, water conservation and solar energy to improve the homeowners' quality of life. Several materials used include reclaimed lumber for the hardwood floors on the first level, fiber-cement siding and a metal roof made of 26 percent recycled material. Fly ash, a waste product of coal-fired generators, was used as a replacement for half of the cement in all the concrete footings and foundations.

The elastic moduli of ultrathin poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrology. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the observed decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The observed decrease in the apparent modulus highlights issues in mechanical stability and robustness of sub-40 nm polymer films and features.

As technology continues towards smaller, thinner and lighter devices, more stringent demands are placed on thin polymer films as diffusion barriers, dielectric coatings, electronic packaging and so on. Therefore, there is a growing need for testing platforms to rapidly determine the mechanical properties of thin polymer films and coatings. We introduce here an elegant, efficient measurement method that yields the elastic moduli of nanoscale polymer films in a rapid and quantitative manner without the need for expensive equipment or material-specific modelling. The technique exploits a buckling instability that occurs in bilayers consisting of a stiff, thin film coated onto a relatively soft, thick substrate. Using the spacing of these highly periodic wrinkles, we calculate the film's elastic modulus by applying well-established buckling mechanics. We successfully apply this new measurement platform to several systems displaying a wide range of thicknessess (nanometre to micrometre) and moduli (MPa to GPa).

Coccidioidomycosis is a fungal disease with protean manifestations endemic to the Lower Sonoran Life Zone, which includes the hot deserts of the southwestern United States and areas of Mexico. Two hundred and twenty-three patients were found to have coccidioidomycosis at our institution from 1994-2002, the largest reported cohort of coccidioidomycosis patients since the 1950s. Of these patients, 58% presented with isolated pulmonary disease, 14% had high (>116) complement fixation titers without clear evidence of dissemination, 22% had definite disseminated disease, and 5% had unclassified disease. Enzyme immunoassay was a reliable diagnostic tool in those with symptomatic disease, but had a low specificity in those who were asymptomatic. Complement fixation titers of ≥116 were associated with dissemination to bone or skin but were not helpful in evaluating central nervous system disease. Thirteen percent of patients with high complement fixation titers (>116) without clear evidence of dissemination on presentation and 7% of those with isolated pulmonary disease eventually progressed to disseminated disease; 30% of Filipino patients with pulmonary disease progressed to disseminated disease. Nonwhite race was a predictor for dissemination; African American patients more often developed disseminated bony disease while Filipinos were more likely to develop cutaneous or central nervous system disease. Relapse of disseminated coccidioidomycosis occurred in 24% of patients; the risk was highest (71%) among those with central nervous system disease. Azole therapy was generally inferior to amphotericin B in disseminated disease. Predictors of permanent disability included African American or Filipino race, central nervous system disease, and bony disease.

Semi-interpenetrating networks (SIPNs) of N,N-dimethylacrylamide (DMAm)–N,N-dimethylamino-ethylacrylamide (DMAEAm), or N,N-dimethylacrylamide (DMAm)–2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) containing cellulose or chitin were synthesized in 9% LiCl–N,N-dimethylacetamide (DMAc). The SIPNs were formulated to contain (1, 2, or 5% w/w) cellulose or 0.8% w/w chitin. Control systems (without polysaccharide) were also synthesized in 9% LiCl–DMAc. An acrylamide (Am)–AMPS hydrogel was synthesized for comparison with the SIPN composites. The swelling behavior of these materials was investigated as a function of pH (DMAEAm-containing networks) or electrolyte concentration (AMPS-containing networks). The DMAm–AMPS materials were found to have higher equilibrium water content (EWC) values in deionized water than the DMAm–DMAEAm materials. The EWC of the DMAm–DMAEAm materials was largest between pH 4 and 5 due to the protonation of the tertiary amine, with the chitin-containing material exhibiting the largest EWC. The DMAm–AMPS materials exhibited a decrease in EWC values with an increase in electrolyte concentration. Polymer–surfactant interactions were shown to exist for surfactants of opposite charge of the ionic mer units incorporated into the polymeric network. Surfactant sequestration by the polysaccharide-containing materials was greater than that of the control gels; however, the rates of surfactant binding were lower. Release of the bound surfactant was achieved by the disruption of the charge–charge interactions by changing the pH of the medium (DMAEAm-containing networks) or by the addition of electrolyte (AMPS-containing networks). The DMAm–DMAEAm SIPNs released only 4% of the surfactant originally sequestered. By contrast, the DMAm–AMPS SIPNs released approximately 80%. The control Am–AMPS hydrogel–surfactant complex collapsed in the presence of electrolyte, and no surfactant was released from the complex. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 989–998, 1999

Surface-textured polymer nanocomposite (PNC) films are utilized in many device applications, and therefore understanding the relaxation behavior of such films is important. By extending an in situ wrinkle relaxation method, we observed that the thermal stability of wrinkled PNC films, both above and below the glass transition temperature (Tg), is proportional to a film’s nanoparticle (polymer grafted and bare) concentration, with a slope that changes sign at a compensation temperature (Tcomp) that is determined to be in the vicinity of the film’s Tg. This provides unambiguous confirmation of entropy–enthalpy compensation (EEC) as a general feature of PNC films, implying that the stability of PNC films changes from being enhanced to becoming diminished by simply passing through this characteristic temperature, a phenomenon having evident practical ramifications. We suggest EEC will also arise in films where residual stresses are associated with the film fabrication process, which is relevant to nanotech device applications.