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The results of neutron-diffraction measurements are reported which confirm that superconducting TmRh4B4 orders magnetically at TM0.7 K. The modulated antiferromagnetic structure deduced from the data is of particular interest, considering the similarity of certain other physical properties of TmRh4B4 to those of the ferromagnetic, reentrant superconductor ErRh4B4. © 1983 The American Physical Society.

The study delves into the adsorption of sunflower proteins at the air/water interface using specular X-ray reflection. The research involved fitting models of the protein films to the reflectivity data, resulting in detailed images of the X-ray scattering length density profiles perpendicular to the air/water interface. The sunflower protein isolate that is examined consists of multiple components, and the study proposes a transition from a 1-slab model to a 4-slab model to represent the changing layer structure over time. This transition is significant as it reflects the increasing complexity of the protein film as more proteins adsorb at the interface. Initially, sunflower proteins form a monolayer at the air/water boundary, consisting of a protein-rich, hydrophobic portion closest to the interface and a more diffuse, hydrophilic portion extending into the bulk aqueous phase. The structural changes at the interface over time depend on the bulk protein concentration in the solution. For solutions at relatively low concentrations ( C ≤ 0.5 g/L), a lower amount of adsorption results in a larger, more extensive interface area for each species and a thinner protein adsorption layer. The overall thickness of a saturated monolayer is approximately 100 Å, which is close to the maximum dimension of sunflower globulins, with the thickness of the corresponding hydrophobic portion being about 20 Å. For solutions at relatively high concentrations ( C ≥ 1.0 g/L), even after forming a saturated monolayer, structural evolution continues within the experimental time frame, occurring on both hydrophilic and hydrophobic sides. Additional proteins from the bulk diffuse toward the interface, forming an extra layer in the water phase and causing an increase in the overall thickness. Furthermore, a distinct sublayer develops next to the air phase, indicating a further structuration of the hydrophobic portion.

A variety of structures encountered in nature only arise in materials under highly nonequilibrium conditions, suggesting to us that the scope for creating new functional block copolymer (BCP) structures might be significantly enlarged by embracing complex processing histories that allow for the fabrication of structures quite unlike those created under "near-equilibrium" conditions. The present work examines the creation of polymer film structures in which highly nonequilibrium processing conditions allow for the creation of entirely new types of transient BCP morphologies achieved by transitioning between different ordered states. Most previous studies of BCP materials have emphasized ordering them from their disordered state obtained from a solution film casting process, followed by a slow thermal annealing (TA) process at elevated temperatures normally well above room temperature. We have previously shown that achieving the equilibrium TA state can be accelerated by a direct solvent immersion annealing (DIA) preordering step that creates nascent ordered microstructures, followed by TA. In the present work, we examine the reverse nonequilibrium sequential processing in which we first thermally anneal the BCP film to different levels of partial (lamellar) order and then subject it to DIA to swell the lamellae. This sequential processing rapidly leads to a swelling-induced wrinkle pattern that initially grows with immersion time and can be quenched by solvent evaporation into its corresponding glassy state morphology. The article demonstrates the formation of wrinkling "defect" patterns in entangled BCP films by this sequential annealing that does not form under ordinary TA conditions. At long DIA times, these highly "defective" film structures evolve in favor of the equilibrium morphology of parallel lamellae observed with DIA alone. In conjunction with our previous study of sequential DIA + TA, the present TA + DIA study demonstrates that switching the order of these processing methods for block copolymer films gives the same final state morphology in the limit of long time as any one method alone, but with drastically different intermediate transient state morphologies. These transient morphologies could have many applications.

2-Dodecyldiethylenetriaminepentaacetic acid (C 12 -DTPA) is a chelating, amphoteric surfactant with a bulky headgroup containing eight pH-responsive groups. The hypothesis was that the amphoteric nature of the chelating surfactant would affect the interaction with another surfactant and, consequently, also the composition of mixed surface layers. Binary mixed monolayers of C 12 -DTPA and the anionic surfactant sodium dodecyl sulfate (SDS) were examined using neutron reflection and surface tension measurements. The experiments were conducted at pH 5, where the C 12 -DTPA monomers carried a net negative charge. Surface excess calculations at low total surfactant concentration revealed that the chelating surfactant dominated the surface composition. However, as the concentration was raised, the surface composition shifted toward an SDS-dominant state. This phenomenon was attributed to the increased ionic strength at increased concentrations, which altered the balance between competing entropic forces in the system. Interaction parameters for mixed monolayer formation were calculated, following a framework based on regular solution theory. In accordance with the hypothesis, the chelating surfactant's ability to modulate its charge and mitigate repulsive interactions in the surface layer resulted in favorable interactions between the anionic SDS and negatively charged C 12 -DTPA monomers. These interactions were found to be concentration-dependent, which was consistent with the observed shift in the surface layer composition., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

The kinetics and morphology of the ordering of block copolymer (BCP) films are highly dependent on the processing pathway, as the enthalpic and entropic forces driving the ordering processes can be quite different depending on process history. We may gain some understanding and control of this variability of BCP morphology with processing history through a consideration of the free energy landscape of the BCP material and a consideration of how the processing procedure moves the system through this energy landscape in a way that avoids having the system becoming trapped into well-defined metastable minima having a higher free energy than the target low free energy ordered structure. It is well known that standard thermal annealing (TA) of BCPs leads to structures corresponding to a well-defined stable free energy minimum; however, the BCP must be annealed for a very long time before the target low free energy structures can be achieved. Herein, we show that the same target low-energy structure can be achieved relatively quickly by subjecting as-cast films to an initial solvent annealing [direct immersion annealing (DIA) or solvent vapor annealing (SVA)] procedure, followed by a short period of TA. This process relies on lowering the activation energy barrier by reducing the glass-transition temperature through DIA (or SVA), followed by a multi-interface chain rearrangement through sequential TA. This energy landscape approach to ordering should be applicable to the process design for ordering many other complex materials.

While the phase separation of binary mixtures of chemically different polymer-grafted nanoparticles (PGNPs) is observed to superficially resemble conventional polymer blends, the presence of a "soft" polymer-grafted layer on the inorganic core of these nanoparticles qualitatively alters the phase separation kinetics of these "nanoblends" from the typical pattern of behavior seen in polymer blends and other simple fluids. We investigate this system using a direct immersion annealing method (DIA) that allows for a facile tuning of the PGNPs phase boundary, phase separation kinetics, and the ultimate scale of phase separation after a sufficient "aging" time. In particular, by switching the DIA solvent composition from a selective one (which increases the interaction parameter according to Timmerman's rule) to an overall good solvent for both PGNP components, we can achieve rapid switchability between phase-separated and homogeneous states. Despite a relatively low and non-classical power-law coarsening exponent, the overall phase separation process is completed on a time scale on the order of a few minutes. Moreover, the roughness of the PGNP blend film saturates at a scale that is proportional to the in-plane phase separation pattern scale, as observed in previous blend and block copolymer film studies. The relatively low magnitude of the coarsening exponent n is attributed to a suppression of hydrodynamic interactions between the PGNPs. The DIA method provides a significant opportunity to control the phase separation morphology of PGNP blends by solution processing, and this method is expected to be quite useful in creating advanced materials.

The surface adsorption of bovine serum albumin in pure water and salted aqueous solutions was studied by neutron reflection. With the contrast match technique, the surface excess in null reflecting water as a function of the protein concentration was revealed. It is found that, in a concentration range from 1 ppm (parts per million, mg/L) to 1000 ppm, without salts, the surface excess shows a profound peak at around 20 ppm; with salts, the surface excess increases steadily with the protein concentration. When the surface excess at a specific protein concentration is viewed, the introduction of sodium chloride causes either a salting down effect (surface adsorption decline) or a salting up effect (surface adsorption increase), depending upon the protein concentration. The salting up effect is observed at the low (∼1 ppm) and high (∼1000 ppm) concentrations, and the salting down effect dominates the intermediate concentration range. The change in solution pH relative to the isoelectric point (PI) can act as a simple indicator for the salting up or salting down behavior. When the solution pH is shifted toward the PI by adding salts, surface adsorption enhances; when the solution pH is shifted away from the PI by adding salts, surface adsorption declines.

The morphological structure and dynamics of confined polymers adjacent to the polymer-polymer interface have a profound effect on determining the overall physical properties of polymer blends. We measured the diffusion dynamics of poly(methyl methacrylate) (PMMA) melts confined between polystyrene (PS) layers using neutron reflectivity. Combinations of various thicknesses of PMMA and deuterated PMMA ( d PMMA) allowed us to experimentally reveal the nonmonotonic behavior of polymer mobility near the PS-PMMA interface. From the neutron reflectivity results, we found that the polymers adjacent to the immiscible polymer-polymer interface showed enhanced diffusion dynamics because of the repulsive interaction between PS and PMMA, whereas the polymer at local regions farther from the interface exhibited reduced dynamics. This is probably due to the nonspherical conformation of PMMA and spatial confinement near the PS-PMMA interface.

Collagen is a skeleton of native extracellular matrix (ECM) that is known to provide mechanical and structural stability. In an attempt to develop a new connective cellular model with the surrounding ECM without further experimental complications, such as the reconstitution of ECM receptors, we designed the experiments and discovered that the fibrillogenesis of membrane-bound collagen is not spontaneous as it is in the form of free collagen in bulk solution. The confocal microscopic results suggest that cholesterol is a crucial component that facilitates the fibril formation on the membrane surface. In situ X-ray and neutron reflectivity on Langmuir monolayer and solid-supported lipid bilayer models, respectively, reveal two features of cholesterol effects on the collagen fibril formation. Mainly, cholesterol increases the lateral lipid headgroup separation on the membrane surface, which promotes the association degree of collagen monomers. It also enhances the elastic modulus of the membrane to impede membrane filtration by the collagen assemblies.

Styrene-maleic acid (SMA) copolymers have recently gained attention for their ability to facilitate the detergent-free solubilization of membrane protein complexes and their native boundary lipids into polymer-encapsulated, nanosized lipid particles, referred to as SMALPs. However, the interfacial interactions between SMA and lipids, which dictate the mechanism, efficiency, and selectivity of lipid and membrane protein extraction, are barely understood. Our recent finding has shown that SMA 1440, a chemical derivative of the SMA family with a functionalized butoxyethanol group, was most active in galactolipid-rich membranes, as opposed to phospholipid membranes. In the present work, we have performed X-ray reflectometry (XRR) and neutron reflectometry (NR) on the lipid monolayers at the liquid-air interface followed by the SMA copolymer adsorption. XRR and Langmuir Π- A isotherms captured the fluidifying effect of galactolipids, which allowed SMA copolymers to infiltrate easily into the lipid membranes. NR results revealed the detailed structural arrangement of SMA 1440 copolymers within the membranes and highlighted the partition of butoxyethanol group into the lipid tail region. This work allows us to propose a possible mechanism for the membrane solubilization by SMA.

Maintaining the integrity of cell membranes is indispensable for cellular viability. Poloxamer 188 (P188), a poly(ethylene oxide)- b -poly(propylene oxide)- b -poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer with a number-average molecular weight of 8700 g/mol and containing 80% by mass PEO, protects cell membranes from various external injuries and has the potential to be used as a therapeutic agent in diverse applications. The membrane protection mechanism associated with P188 is intimately connected with how this block copolymer interacts with the lipid bilayer, the main component of a cell membrane. Here, we report the distribution of P188 in a model lipid bilayer comprising 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) using neutron reflectivity (NR) and atomic force microscopy (AFM). We also investigated the association of a PEO homopolymer (PEO8.4K; M n = 8400 g/mol) that does not protect living cell membranes. These experiments were conducted following incubation of a 4.5 mmol/L polymer solution in a buffer that mimics physiological conditions with supported POPC bilayer membranes followed by washing with the aqueous medium. In contrast to previous reports, which dealt with P188 and PEO in salt-free solutions, both P188 and PEO8.4K penetrate into the inner portion of the lipid bilayer as revealed by NR, with approximately 30% by volume occupancy across the membrane without loss of bilayer structural integrity. These results indicate that PEO is the chemical moiety that principally drives P188 binding to bilayer membranes. No defects or phase-separated domains were observed in either P188- or PEO8.4K-incubated lipid bilayers when examined by AFM, indicating that polymer chains mingle homogeneously with lipid molecules in the bilayer. Remarkably, the breakthrough force required for penetration of the AFM tip through the bilayer membrane is unaffected by the presence of the large amount of P188 and PEO8.4K.

For polymer-blend films, local dynamics in confined polymer domains tend to differ from the bulk because of significant contributions from the polymer-polymer interface. Herein, we investigated the diffusion dynamics of entangled polymer thin films confined between different polymers in a direction perpendicular to the surface using neutron reflectivity. We found that a bilayer of poly(methyl methacrylate) (PMMA) and deuterated PMMA ( d PMMA) sandwiched between polystyrene (PS) layers exhibited significant increase in mobility near the polymer-polymer interface with decreasing PMMA thickness. This indicates that the contribution of repulsive interactions at the immiscible polymer-polymer interface becomes more significant as the film thickness decreases. We also found that the interfacial roughness between PMMA and PS (28 Å at equilibrium) and soft confinement of PS layers did not significantly affect the change in the diffusion dynamics of the adjacent PMMA. This was evidenced by comparison with the diffusion results of multilayers with a flat interface (8 Å at equilibrium) between PMMA and hard PS by UV cross-linking.

We investigated the effect of the morphological structure of a graphene oxide (GO) monolayer on the dewetting dynamics of the upper polymer thin films. The Langmuir-Schaefer (LS) technique was used to prepare a wrinkled GO ( wrGO) structure with a root mean square (rms) roughness of 22.7 Å. The dewetting behavior of poly(methyl methacrylate) (PMMA) thin films on the wrGO monolayers was perfectly prevented, whereas the PMMA thin films on a flat GO monolayer were dewetted at 203 °C. This wrinkle effect of the GO can be also obtained when the GOs monolayers are intercalated to the PMMA/polystyrene (PS) interface. In this multilayer, the flat GO monolayer at the interface between the PS and PMMA layers was spontaneously roughened with rms roughness of 46.9 Å after annealing and also prohibited the dewetting behavior. From the results, we found that to improve the compatibility of polymer blends by adding the two-dimensional nanosheets, it is important to control the morphological structure of the sheets at the interface, along with manipulation of the GO-polymer interactions.

In situ wide-angle X-ray scattering together with infrared imaging was performed during three-dimensional material extrusion printing and correlated with the development of the crystalline structure and subsequent thermomechanical properties. Identical samples were printed with nozzle motion either along the short axis or the long axis. The short axis mode had higher thermal retention, which resulted in later onset of crystal structure. The longer time spent at temperatures between the glass transition and the melting point produced samples with higher degree of crystallinity but also significantly increased brittleness. The tracer diffusion coefficient D ( T ) , together with its temperature dependence, was measured using neutron reflectivity, and the total interdiffusion length between filaments was then calculated using D ( T ) for each temperature point, as determined by the measured thermal profiles. This allowed us to define the time/temperature plane that yielded the minimum diffusion length Δ L that provides mechanical integrity of the printed features ( Δ L less than the radius of gyration of the poly(l-lactide)). The model was probed by printing structures at four nozzle temperatures and measuring the time dependence of the thermal profiles at filaments in the horizontal and vertical positions. The data indicated that the thermal retention was anisotropic, where higher values were obtained in the horizontal plane. Mechanical measurements indicated large differential increases in the torsional strength, corresponding to the direction with increased thermal retention.

We demonstrate that hybrid structures of graphene and single-walled carbon nanotubes (SWNTs) are precisely controlled at the liquid-gas interface. The functionalized SWNT Langmuir monolayers anchor single-layer graphene nanosheets (GNSs) suspended in water via Coulomb interaction at the interface. This GNS/SWNT hybrid multilayer electrode can be a promising anode material for Li-ion batteries, offering high specific capacity, outstanding power capability, and excellent cyclability.

Here we report a link between the interfacial structure and adhesive property of homopolymer chains physically adsorbed (i.e., via physisorption) onto solids. Polyethylene oxide (PEO) was used as a model and two different chain conformations of the adsorbed polymer were created on silicon substrates via the well-established Guiselin's approach: "flattened chains" which lie flat on the solid and are densely packed, and "loosely adsorbed polymer chains" which form bridges jointing up nearby empty sites on the solid surface and cover the flattened chains. We investigated the adhesion properties of the two different adsorbed chains using a custom-built adhesion testing device. Bilayers of a thick PEO overlayer on top of the flattened chains or loosely adsorbed chains were subjected to the adhesion test. The results revealed that the flattened chains do not show any adhesion even with the chemically identical free polymer on top, while the loosely adsorbed chains exhibit adhesion. Neutron reflectivity experiments corroborated that the difference in the interfacial adhesion is not attributed to the interfacial brodening at the free polymer-adsorbed polymer interface. Instead, coarse-grained molecular dynamics simulation results suggest that the tail parts of the loosely adsorbed chains act as "connector molecules", bridging the free chains and substrate surface and improving the interfacial adhesion. These findings not only shed light on the structure-property relationship at the interface, but also provide a novel approach for developing sticking/anti-sticking technologies through precise control of the interfacial polymer nanostructures.

We have studied an orientation structure of self-assembled block copolymers (dPS-b-PMMA) of deuterated polystyrene (dPS) and poly(methyl methacrylate) (PMMA) confined between graphene oxide (GO) surfaces. The results of combination techniques, such as neutron reflectivity, time-of-flight secondary-ion mass spectrometry, grazing-incidence small-angle X-ray scattering, and scanning electron microscopy, show that self-assembled domains of the block copolymers in thin films near the GO sheets are oriented perpendicular to the surface of the GO monolayers, in contrast to the horizontal lamellar structure of the copolymer thin film in the absence of the GO monolayers. This is due to the amphiphilic nature of the GO, which leads to a nonpreferential interaction of both dPS and PMMA blocks. Double-sided confinement with the GO monolayers further extends the ordering behavior of the dPS-b-PMMA thin films. Continuous vertical orientation of the block copolymer thin films is also obtained in the presence of alternating GO layers within thick copolymer films.

We present a method for the direct measurement of the relative energy of interaction between a solvated polymer and a solid interface. By tethering linear chains covalently to the surface, we ensured the idealized and constant configuration of polymer molecules for measurement, modeling, and parameter estimation. For the case of amine-terminated polystyrene bound to a glycidoxypropyl silane film submerged in cyclohexane-d12, we estimated the χ parameter for the temperature range 10.7 °C to 52.0 °C, and found a downward sloping trend that crosses the χ = 0.5 threshold at 37 °C to 40 °C, in agreement with solution estimates for the same system. We simultaneously estimated the surface interaction parameter χ s at each temperature, finding a decreasing affinity of the chains for the surface with increasing temperature, consistent with empirical observations. The theoretical model shows some limitations in a stronger solvent (toluene-d8) that prevent rigorous parameter estimation, but we demonstrate a qualitative change in χ and χ s towards stronger solvency and weaker surface interaction with increasing temperature., Competing Interests: Notes The authors declare no competing financial interest. Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose. Official contribution of the National Institute of Standards and Technology; not subject to copyright in the United States.

We report that the addition of a non-photoactive tertiary polymer phase in the binary bulk heterojunction (BHJ) polymer solar cell leads to a self-assembled columnar nanostructure, enhancing the charge mobilities and photovoltaic efficiency with surprisingly increased optimal active blend thicknesses over 300 nm, 3-4 times larger than that of the binary counterpart. Using the prototypical poly(3-hexylthiophene) (P3HT):fullerene blend as a model BHJ system, we discover that the inert poly(methyl methacrylate) (PMMA) added in the binary BHJ blend self-assembles into vertical columns, which not only template the phase segregation of electron acceptor fullerenes but also induce the out-of-plane rotation of the edge-on-orientated crystalline P3HT phase. Using complementary interrogation methods including neutron reflectivity, X-ray scattering, atomic force microscopy, transmission electron microscopy, and molecular dynamics simulations, we show that the enhanced charge transport originates from the more randomized molecular stacking of the P3HT phase and the spontaneous segregation of fullerenes at the P3HT/PMMA interface, driven by the high surface tension between the two polymeric components. The results demonstrate a potential method for increasing the thicknesses of high-performance polymer BHJ solar cells with improved photovoltaic efficiency, alleviating the burden of stringently controlling the ultrathin blend thickness during the roll-to-roll-type large-area manufacturing environment.

Neutron and X-ray reflection measurements have been used to study the structure of the adsorbed layer of a chelating surfactant at the air/liquid interface. The chelating surfactant 2-dodecyldiethylenetriaminepentaacetic acid (C 12 -DTPA) has a large headgroup containing eight donor atoms that can participate in the coordination of metal ions. The donor atoms are also titrating, resulting in an amphoteric surfactant that can adopt a number of differently charged species depending on the pH. Very strong coordination complexes are formed with metal ions, where the metal ion can be considered as part of the surfactant structure, in contrast to monovalent cations that act as regular counterions to the negative net charge. Adsorption was investigated over a large concentration interval, from well below the critical micelle concentration (cmc) to five times the cmc. The most striking result is the maximum in the surface excess found around the cmc, which is consistent with previous indications from surface tension measurements. Adding divalent metal ions has a limited effect on the adsorption at the air/liquid interface. The reason is the coordination of the metal ion, resulting in compensating deprotonation of the complex. Small variations in the headgroup area of different metal complexes are found, correlating to the conditional stability constants. Adding sodium chloride has a significant effect on the adsorption behavior, and the results indicate that the protonation equilibrium is more important than the ionic strength effects. From combined fits of the neutron and X-ray data, a model that consists of a thick headgroup region and a relatively thin dehydrated tail region is found, and it indicates that the tails are not fully extended and that the limiting area per molecule is determined by the bulky headgroup.

We report the effects of compressed CO 2 molecules as a novel plasticization agent for poly(3-hexylthiophene) (P3HT)-conjugated polymer thin films. In situ neutron reflectivity experiments demonstrated the excess sorption of CO 2 molecules in the P3HT thin films (about 40 nm in thickness) at low pressure (P = 8.2 MPa) under the isothermal condition of T = 36 °C, which is far below the polymer bulk melting point. The results proved that these CO 2 molecules accelerated the crystallization process of the polymer on the basis of ex situ grazing incidence X-ray diffraction measurements after drying the films via rapid depressurization to atmospheric pressure: both the out-of-plane lamellar ordering of the backbone chains and the intraplane π-π stacking of the side chains were significantly improved, when compared with those in the control P3HT films subjected to conventional thermal annealing (at T = 170 °C). Electrical measurements elucidated that the CO 2 -annealed P3HT thin films exhibited enhanced charge carrier mobility along with decreased background charge carrier concentration and trap density compared with those in the thermally annealed counterpart. This is attributed to the CO 2 -induced increase in polymer chain mobility that can drive the detrapping of molecular oxygen and healing of conformational defects in the polymer thin film. Given the universality of the excess sorption of CO 2 regardless of the type of polymers, the present findings suggest that CO 2 annealing near the critical point can be useful as a robust processing strategy for improving the structural and electrical characteristics of other semiconducting conjugated polymers and related systems such as polymer:fullerene bulk heterojunction films.

Emerging needs for fast charge/discharge yet high-power, lightweight, and flexible electronics requires the use of polymer-film-based solid-state capacitors with high energy densities. Fast charge/discharge rates of film capacitors on the order of microseconds are not achievable with slower charging conventional batteries, supercapacitors and related hybrid technologies. However, the current energy densities of polymer film capacitors fall short of rising demand, and could be significantly enhanced by increasing the breakdown strength (EBD) and dielectric permittivity (εr) of the polymer films. Co-extruded two-homopolymer component multilayered films have demonstrated much promise in this regard showing higher EBD over that of component polymers. Multilayered films can also help incorporate functional features besides energy storage, such as enhanced optical, mechanical, thermal and barrier properties. In this work, we report accomplishing multilayer, multicomponent block copolymer dielectric films (BCDF) with soft-shear driven highly oriented self-assembled lamellar diblock copolymers (BCP) as a novel application of this important class of self-assembling materials. Results of a model PS-b-PMMA system show ∼50% enhancement in EBD of self-assembled multilayer lamellar BCP films compared to unordered as-cast films, indicating that the breakdown is highly sensitive to the nanostructure of the BCP. The enhancement in EBD is attributed to the "barrier effect", where the multiple interfaces between the lamellae block components act as barriers to the dielectric breakdown through the film. The increase in EBD corresponds to more than doubling the energy storage capacity using a straightforward directed self-assembly strategy. This approach opens a new nanomaterial paradigm for designing high energy density dielectric materials.

The stability or wettability of thin polymer films on solids is of vital interest in traditional technologies as well as in new emerging nanotechnologies. We report here that nanoscale structures of polymer chains adsorbed onto a solid surface play a crucial role in the thermal stability of the film. In this study, polystyrene (PS) spin-cast films (20 nm in thickness) with eight different molecular weights prepared on silicon (Si) substrates were used as a model. When low molecular weight (Mw≤ 50 kDa) PS films were subjected to thermal annealing at temperatures far above the bulk glass transition temperature, dewetting occurred promptly, while high molecular weight (Mw≥ 123 kDa) PS films were stable for at least 6 weeks at 150 °C. We reveal a strong correlation between the film stability and the two different interfacial structures of the adsorbed polymer chains: their opposing wettability against chemically identical free polymer chains results in a wetting-dewetting transition at the adsorbed polymer-free polymer interface. This is a unique aspect of the stability of polymer thin films and may be generalizable to other polymer systems regardless of the magnitude of solid-polymer attractive interactions.

We report in situ nanostructures and dynamics of polybutadiene (PB) chains bound to carbon black (CB) fillers (the so-called "bound polymer layer (BPL)") in a good solvent. The BPL on the CB fillers was extracted by solvent leaching of a CB-filled PB compound and subsequently dispersed in deuterated toluene to label the BPL for small-angle neutron scattering and neutron spin echo techniques. The results demonstrate that the BPL is composed of two regions regardless of molecular weights of PB: the inner unswollen region of ≈ 0.5 nm thick and outer swollen region where the polymer chains display a parabolic profile with a diffuse tail. In addition, the results show that the dynamics of the swollen bound chains can be explained by the so-called "breathing mode" and is generalized with the thickness of the swollen BPL.

Block-copolymer orientation in thin films is controlled by the complex balance between interfacial free energies, including the inter-block segregation strength, the surface tensions of the blocks, and the relative substrate interactions. While block-copolymer lamellae orient horizontally when there is any preferential affinity of one block for the substrate, we recently described how nanoparticle-roughened substrates can be used to modify substrate interactions. We demonstrate how such 'neutral' substrates can be combined with control of annealing temperature to generate vertical lamellae orientations throughout a sample, at all thicknesses. We observe an orientational transition from vertical to horizontal lamellae upon heating, as confirmed using a combination of atomic force microscopy (AFM), neutron reflectometry (NR) and rotational small-angle neutron scattering (RSANS). Using molecular dynamics (MD) simulations, we identify substrate-localized distortions to the lamellar morphology as the physical basis of the novel behavior. In particular, under strong segregation conditions, bending of horizontal lamellae induce a large energetic cost. At higher temperatures, the energetic cost of conformal deformations of lamellae over the rough substrate is reduced, returning lamellae to the typical horizontal orientation. Thus, we find that both surface interactions and temperature play a crucial role in dictating block-copolymer lamellae orientation. Our combined experimental and simulation findings suggest that controlling substrate roughness should provide a useful and robust platform for controlling block-copolymer orientation in applications of these materials.

Moisture attack on adhesive joints is a long-standing scientific and engineering problem. A particularly interesting observation is that when the moisture level in certain systems exceeds a critical concentration, the bonded joint shows a dramatic loss of strength. The joint interface plays a dominant role in this phenomenon; however, why a critical concentration of moisture exists and what role is played by the properties of the bulk adhesive have not been adequately addressed. Moreover if the interface is crucial, the local water content near the interface will help elucidate the mechanisms of criticality more than the more commonly examined bulk water concentration in the adhesive. To gain a detailed picture of this criticality, we have combined a fracture mechanics approach to determine joint strength with neutron reflectivity, which provides the moisture distribution near the interface. A well-defined model system, silica glass substrates bonded to a series of polymers based on poly(n-alkyl methacrylate), was utilized to probe the role of the adhesive in a systematic manner. By altering the alkyl chain length, the molecular structure of the polymer can be systematically changed to vary the chemical and physical properties of the adhesive over a relatively wide range. Our findings suggest that the loss of adhesion is dependent on a combination of the build-up of the local water concentration near the interface, interfacial swelling stresses resulting from water absorption, and water-induced weakening of the interfacial bonds. This complexity explains the source of criticality in environmental adhesion failure and could enable design of adhesives to minimize environmental failure.

Swelling behavior of polyelectrolyte and polyzwitterion brushes derived from poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) in water vapor is investigated using a combination of neutron and X-ray reflectivity and spectroscopic ellipsometry over a wide range of relative humidity (RH) levels. The extent of swelling depends strongly on the nature of the side-chain chemistry. For parent PDMAEMA, there is an apparent enrichment of water vapor at the polymer/air interface. Despite extensive swelling at high humidity level, no evidence of charge repulsion is found in weak or strong polyelectrolyte brushes. Polyzwitterionic brushes swell to a greater extent than the quaternized brushes studied. However, for RH levels beyond 70%, the polyzwitterionic brushes take up less water molecules, leading to a decline in water volume fraction from the maximum of ~0.30 down to ~0.10. Using a gradient in polymer chain grafting density (σ), we provide evidence that this behavior stems from the formation of inter- and intramolecular zwitterionic complexes.

We report the chain conformations of polymer molecules accommodated at the solid-polymer melt interfaces in equilibrium. Polystyrene "Guiselin" brushes (adsorbed layers) with different molecular weights were prepared on Si substrates and characterized by using x-ray and neutron reflectivity. The results are intriguing to show that the adsorbed layers are composed of the two different nanoarchitectures: flattened chains that constitute the inner higher density region of the adsorbed layers and loosely adsorbed polymer chains that form the outer bulklike density region. In addition, we found that the lone flattened chains, which are uncovered by the additional prolonged solvent leaching (∼120 days), are reversibly densified with increasing temperature up to 150 °C. By generalizing the chain conformations of bulks, we postulate that the change in probabilities of the local chain conformations (i.e., trans and gauche states) of polymer molecules is the origin of this densification process.

In situ neutron reflectivity was used to study thermally induced structural changes of the lamellae-forming polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP) block copolymer thin films floating on the surface of an ionic liquid (IL). The IL, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, is a nonsolvent for PS and a temperature-tunable solvent for P2VP, and, as such, micellization can be induced at the air-IL interface by changing the temperature. Transmission electron microscopy and scanning force microscopy were used to investigate the resultant morphologies of the micellar films. It was found that highly ordered nanostructures consisting of spherical micelles with a PS core surrounded by a P2VP corona were produced. In addition, bilayer films of PS homopolymer on top of a PS-b-P2VP layer also underwent micellization with increasing temperature but the micellization was strongly dependent on the thickness of the PS and PS-b-P2VP layers., (© 2011 American Chemical Society)

Tailoring the structure of films deposited by plasma-enhanced chemical vapor deposition (PECVD) to specific applications requires a depth-resolved understanding of how the interface structures in such films are impacted by variations in deposition parameters such as feed position and plasma power. Analysis of complementary X-ray and neutron reflectivity (XR, NR) data provide a rich picture of changes in structure with feed position and plasma power, with those changes resolved on the nanoscale. For plasma-polymerized octafluorocyclobutane (PP-OFCB) films, a region of distinct chemical composition and lower cross-link density is found at the substrate interface for the range of processing conditions studied and a surface layer of lower cross-link density also appears when plasma power exceeds 40 W. Varying the distance of the feed from the plasma impacts the degree of cross-linking in the film center, thickness of the surface layer, and thickness of the transition region at the substrate. Deposition at the highest power, 65 W, both enhances cross-linking and creates loose fragments with fluorine content higher than the average. The thickness of the low cross-link density region at the air interface plays an important role in determining the width of the interface built with a layer subsequently deposited atop the first.

The blend films of small-molecule semiconductors with insulating polymers exhibit not only excellent solution processability but also superior performance characteristics in organic thin-film transistors (OTFTs) over those of neat small-molecule semiconductors. To understand the underlying mechanism, we studied triethylsilylethynyl anthradithiophene (TESADT) with small amounts of impurity formed by weak UV exposure. OTFTs with neat impure TESADT had drastically reduced field-effect mobility (<10(-5) cm(2)/(V s)), and a disappearance of the high-temperature crystal phase was observed for neat impure TESADT. However, the mobility of the blend films of the UV-exposed TESADT with poly(α-methylstyrene) (PαMS) is recovered to that of a fresh TESADT-PαMS blend (0.040 cm(2)/(V s)), and the phase transition characteristics partly return to those of fresh TESADT films. These results are corroborated by OTFT results on "aged" TIPS-pentacene. These observations, coupled with the results of neutron reflectivity study, indicate that the formation of a vertically phase-separated layer of crystalline small-molecule semiconductors allows the impurity species to remain preferentially in the adjacent polymer-rich layer. Such a "zone-refinement effect" in blend semiconductors effectively removes the impurity species that are detrimental to organic electronic devices from the critical charge-transporting interface region.

Photoresist materials enable the fabrication of advanced integrated circuits with ever-decreasing feature sizes. As next-generation light sources are developed, using extreme ultraviolet light of wavelength 13.5 nm, these highly tuned formulations must meet strict image-fidelity criteria to maintain the expected performance gains from decreases in feature size. However, polymer photoresists appear to be reaching resolution limits and advancements in measurements of the in situ formed solid/solid and solid/liquid interface is necessary. This Review focuses on the chemical and physical structure of chemically amplified photoresists at the lithographic feature edge at length scales between 1 nm and 100 nm. Neutron reflectivity measurements provide insight into the nanometer-scale composition profiling of the chemical latent image at an ideal lithographic line-edge that separates optical resolution effects from materials processing effects. Four generations of advanced photoresist formulations were examined over the course of seven years to quantify photoresist/photoacid and photoresist/developer interactions on the fidelity of lithographic features. The outcome of these measurements complement traditional resist design criteria by providing the effects of the impacts of the photoresist and processing on the feature fidelity. These physical relations are also described in the context of novel resist architectures under consideration for next-generation photolithography with extreme-ultraviolet radiation., (Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We report the nucleation process of methane hydrate on the molecular scale. A stationary planar interface separating methane gas and liquid water was studied by using in situ neutron reflectivity. We found that the angstrom-scale surface roughening is triggered as soon as the water phase contacts methane gas under the hydrate forming conditions. In addition, it was found that the microscopic surface structure remains unchanged until a macroscopic hydrate film is developed at the interface. We therefore postulate that the angstrom-scale surface roughening is attributed to the formation of microscopic hydrate "embryos" in a "dynamic equilibrium" manner.

The phase behavior of a molecular brush-C(18) grafted to the surface of both a silicon wafer and SiO(2) nanoparticles was investigated as a function of temperature using neutron reflectometry (NR) and small-angle neutron scattering (SANS), respectively. The experiments demonstrate a phase change in the brush layer characterized by a straightening of the molecular configuration, increase in shell thickness, and increase in solvent concentration with decreasing temperature that corresponds to gelation in the nanoparticle dispersion.

The depth profile of swelling polyelectrolyte layers is characterized by a static bulk layer and an asymmetric profile with position and shape parameters that describe the intermediate and solution side of the interfacial region. The characteristic width in the solution-side region exceeds the dimensions of the individual chains and therefore is comprised of weakly associated polymers. Contrary to that observed for polyelectrolyte gels and brushes stabilized by cross-links or by covalent bonds to the substrate, respectively, these swelling layers exhibit a more complex response to monovalent and divalent salts. Salt causes an initial contraction of the solution-side interface; layer expansion and polymer dissolution follow at higher salt concentration. The swelling layers measured by neutron reflectivity with mass change verified by quartz crystal microbalance exhibit nonequilibrium responses to the salt concentration, as observed through this interplay between swelling and dissolution. Further, the asymmetric profiles approach, but do not reach, symmetric shapes as expected by mean field equilibrium interfaces. These measurements, motivated by technological needs of photoresist materials, highlight the significance of hydrophobic interactions in determining the structure of associating polymer molecules at the lithographic feature edge.

The origins for abrupt adhesion loss at a critical relative humidity (RH) for polymeric adhesives bonded to inorganic surfaces have been explored using a model poly(methyl methacrylate) (PMMA) film on glass. The interfacial and bulk water concentrations within the polymer film as a function of D 2O partial pressure were quantified using neutron reflectivity. Adhesion strength of these PMMA/SiO 2 interfaces under the same conditions was quantified using a shaft loaded blister test. A drop in adhesion strength was observed at a critical RH, and at this same RH, a discontinuity in the bulk moisture concentration occurred. The moisture concentration near the interface was higher than that in the bulk PMMA, and at the critical RH, the breadth of the interfacial water concentration distribution as a function of distance from the SiO 2/PMMA interface increased dramatically. We propose a mechanism for loss of adhesion at a critical RH based upon the interplay between bulk swelling induced stress and weakening of the interfacial bond by moisture accumulation at the PMMA/SiO 2 interface.

We have demonstrated that monolayer films of randomly charged polystyrene sulfonated acid (PSSA) can be produced by the Langmuir technique, and observed the micro-domain structures, produced by the phase separation of electrostatically charged moieties and the hydrophobic moieties. Using atomic force microscopy and Langmuir isotherm, we found three specific regimes for the polyelectrolytes with various degrees of sulfonation (4-35%); very low charged PSSA (4-5%) in the hydrophobic regime, moderately charged PSSA (6-16%) which possessed a well-balanced nature between electrostatic and the hydrophobic interactions, and strongly amphiphilic nature of PSSA (6-16%) in the ionomer regime. Finally, we could categorize PSSA 35% in the polyelectrolyte regime, due to the dominance of the electrostatic interactions over the hydrophobic interactions.

The penetration of a transcription-activating factor (TAT)-derived, cell-penetration peptide onto 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or 1,2-dipalmitoyl-sn-glycero-3-[phospho-L-serine] (DPPS) monolayer on phosphate-buffered saline subphase was characterized. The surface area at the target pressure increased noticeably by the peptide penetration from the subphase to the phospholipid monolayer, which might suggest a direct penetration of the peptide across the pure phospholipid bilayer membrane. Interestingly, the more significant area increase at 35 mN/m was monitored from DPPC monolayer, contrary to the simple charge interaction: the net neutral DPPC, the net-negative DPPS, and the positive TAT-derived peptides (TDP). X-ray reflectivity measurements as well as the molecular area from pi (surface pressure)-A (area) isotherms suggest that the packing density of DPPS at the target pressure is too high to allow the effective penetration of the peptide into the monolayer and the positively charged peptides can be entrapped at the negative electrostatic well of DPPS headgroup layer, leading to the simple adsorption on the DPPS monolayer instead of penetration into it. Thus, more penetration with less adsorption of the peptide is induced by DPPC monolayer than DPPS monolayer.

We present a study on the initial wetting behaviors of two low molecular weight alkanes, heptane and octane, at the vapor/water interface using both neutron and X-ray reflectometry. Combined X-ray and neutron reflectivity studies data showed that a uniform film, which has never been reported, was formed continuously at 25 degrees C. As the adsorptive deposition continued, each adsorbed film was saturated at a specific equilibrium thickness: 48 and 36 A for deuterated heptane and octane, respectively, and 21 A for hydrogenated octane. The thickness of the adsorbed layer measured by neutron reflectivity is in agreement with that measured using X-ray reflectivity. Our observations of continuous and saturated adsorption behaviors are analyzed qualitatively using a kinetic adsorption model.

We carried out in-situ X-ray reflectivity study of nine n-alkane chains (CnH2n+2) on Si substrate, n in the range of 17-30. These films formed under vacuum at equilibrium vapor pressure of the respective alkane molecule. For all the alkanes studied we found a bilayer structure on the substrate, a higher density vertical layer at the air-film interface with the layer thickness equal to the all-trans length of the respective molecule, and a lower density layer below it with the molecules lying horizontal on the substrate. This model was earlier proposed for C32 films on Si by Volkmann et al.11 We observe that this model can fit the entire range of data from C17 to C30 in our experiments.

Neutron and synchrotron X-ray studies of arachidic-acid monolayers compressed to the collapse region, beyond their densely packed molecular area, reveal that the resulting structures exhibit a surprising degree of reproducibility and of order. The structure of the collapsed monolayers differs for films that are spread on pure water or on CaCl2 solutions. On pure water, the collapsed monolayer forms a stable crystalline trilayer structure, with acyl-chain in-plane packing practically identical to the three-dimensional (3D) crystal structure of fatty acids. For monolayers spread on Ca2+ solutions, the collapsed film consists of a bi- and trilayer mixture with a ratio that changes by the collapse protocol. Our analysis suggests that the bilayer structure is inverted, i.e., with the hydrophobic tails in contact with the water surface and the calcium ions bridging the polar heads. The inverted bilayer structure possesses a well-ordered crystalline slab of calcium oxalate monohydrate intercalated between two acyl chains. We provide theoretical arguments rationalizing that the observed structures have lower free energies compared with other possible structures and contend that the collapsed structures may, under certain circumstances, form spontaneously.

Atomic force microscopy, reflection absorption infrared spectroscopy, and X-ray reflectivity studies reveal that poly(L-lactic acid) molecules in Langmuir-Blodgett (LB) films exist as 10(3) helices over nearly the entire length of the polymer chain. This feature gives rise to LB films with highly ordered nanoscale smectic liquid crystalline-like surface patterns with low surface roughness and lamellar spacings that scale with molar mass. These studies provide a new approach for controlling surface morphology with a biodegradable polymer commonly used for drug delivery and tissue engineering.

The depth profile of the counterion concentration within thin polyelectrolyte films was measured in situ using contrast variant specular neutron reflectivity to characterize the initial swelling stage of the film dissolution. We find substantial counterion depletion near the substrate and enrichment near the periphery of the film extending into the solution. These observations challenge our understanding of the charge distribution in polyelectrolyte films and are important for understanding film dissolution in medical and technological applications.

We investigated an effect of CO2 sorption on the compatibility of immiscible polystyrene (PS) and polybutadiene (PB) bilayers by using in situ neutron reflectivity. By labeling either polymer with deuterium, we found that the excess CO2 molecules were adsorbed to both top PS and bottom PB layers when the bilayers were exposed to CO2 at the narrow T and P regime near the critical point of pure CO2. Furthermore, we clarified that this excess sorption of CO2 molecules increased the interfacial width between the layers up to 100 angstroms even near room temperature, while the interfacial width without CO2 exposure has been reported to be at most 40 A even at the highest temperature (T congruent with 175 degrees C).

Monolayers of 2-(3,4,5-(trisdodecyloxyl)phenyl)[1,3,4]oxadiazole based "tripod" dye, P2G, has been studied at the air/water interface with in situ X-ray reflectivity. Compression of the disordered Langmuir-Blodgett monolayer film induces a transition to a unique ordered phase, representing a supramolecular assembly with a unique spatial distribution and orientation of the molecules. At low pressure, the molecules having face-on orientation are interdigitated by the three arms. After first transition in the pi-A isotherm, the molecular conformation is turned into an edge-on orientation, where the molecules are self-assembled into supramolecular structures.

Moisture absorption in poly(4-tert-butoxycarbonyloxystyrene) (PBOCSt) films supported on Al(2)O(3) sputter coated silicon wafers is measured using neutron and X-ray reflectivity. Accumulation of water at the interface during moisture exposure results in an apparent film-thickness-dependent swelling for ultrathin PBOCSt films. The swelling of a film on Al(2)O(3) is less than the swelling of a film of the same thickness on SiO(x) for films thinner than 20 nm. This is due to comparatively less moisture accumulation at the Al(2)O(3)/PBOCSt interface. A simple, zero adjustable parameter model consisting of a fixed water-rich layer at the interface and bulk swelling through the remainder of the film describes the thickness-dependent swelling quantitatively. The influence of four different Al(2)O(3) surface treatments on the moisture distribution within PBOCSt films was examined: bare Al(2)O(3), tert-butylphosphonic acid, phenylphosphonic acid, and n-octyltrichlorosilane. Both the phenyl and the octyl surface treatments reduce the accumulation of water at the polymer/substrate interface. The tert-butyl treatment does not reduce the interfacial water concentration, presumably due to insufficient surface coverage.

Moisture absorption in model photoresist films of poly(4-hydroxystryene) (PHOSt) and poly(tert-butoxycarboxystyrene) (PBOCSt) supported on silicon wafers was measured by X-ray and neutron reflectivity. The overall thickness change in the films upon moisture exposure was found to be dependent upon the initial film thickness. As the film becomes thinner, the swelling is enhanced. The enhanced swelling in the thin films is due to the attractive nature of the hydrophilic substrate, leading to an accumulation of water at the silicon/polymer interface and subsequently a gradient in concentration from the enhancement at the interface to the bulk concentration. As films become thinner, this interfacial excess dominates the swelling response of the film. This accumulation was confirmed experimentally using neutron reflectivity. The water rich layer extends 25 +/- 10 A into the film with a maximum water concentration of approximately 30 vol %. The excess layer was found to be polymer independent despite the order of magnitude difference in the water solubility in the bulk of the film. To test if the source of the thickness dependent behavior was the enhanced swelling at the interface, a simple, zero adjustable parameter model consisting of a fixed water rich layer at the interface and bulk swelling through the remainder of the film was developed and found to reasonably correspond to the measured thickness dependent swelling.