Polyelectrolyte brushes (PEBs) are promising coatings for reducing ice adhesion and regulating water freezing at interfaces, yet direct measurements of nonfrozen water retention at subzero temperatures remain scarce. Here, we investigate the freezing behavior of water confined in poly([2-(methacryloyloxy)ethyl]trimethylammonium) (PMETA) brushes with chloride, iodide, and sulfate counterions using a custom-built low-temperature attenuated total reflectance infrared spectroscopy system. Furthermore, we quantify the fraction of water that was present within the brush that does not freeze as well as the changes in polymer volume fraction within the brush as a function of temperature. Spectroscopic analysis of water vibrational modes reveals that PMETA brushes retain 25-35 vol. % water even at -60 °C, providing direct evidence of substantial water confinement in charged polymer networks. These findings advance the fundamental understanding of interfacial water behavior in PEBs and suggest molecular design strategies for engineering anti-icing and cryo-lubricating surface coatings.

The deployment of novel sustainable plastics often encounters the problem of mechanical brittleness. This work demonstrates a supramolecular-additive strategy of imparting ductility to an otherwise brittle glassy polymer using poly(lactic acid) (PLA) as an example. In the presence of 5 wt % of a beta-alanine derivative, PLA displays ductile deformation with the uniaxial strain at break reaching similar to 50% and the modulus unaffected. The overall toughness is improved similar to 5.8 times, and embrittlement is absent over 50 days. The hierarchically self-assembled structure of the additive in the PLA phase is elucidated by a combination of X-ray scattering, spectroscopic, and microscopic methods. The mechanism of the ductile deformation is proposed to involve crazing initiated by the fracture of the supramolecular assemblies uniformly distributed in the PLA phase. The molecular structure of the additive is simple and thus practical, and the modular synthesis permits easy alterations for toughening different brittle plastics.

Allomelanin is a nitrogen-free class of melanin commonly found in plants and fungi. Although synthetic analogs have been developed from 1,8-dihydroxynaphthalene (1,8-DHN), detailed physicochemical comparisons with natural allomelanins remain limited. Herein, we extracted allomelanin from black knot fungus, chaga mushroom, and black oat using an acid-base extraction protocol, comparing them against a library of synthetic analogs derived from a range of putative, natural precursors. Spectroscopic analyses indicate that simple homopolymerization of 1,8-DHN does not adequately represent natural allomelanin structures. Instead, heterogeneous copolymerization of 1,8-DHN with catechol or tannic acid yields materials with physicochemical properties more consistent with natural extracts. This is also supported by their enhanced antioxidant and dye/metal adsorption properties. Like their synthetic counterparts, extracted natural allomelanins exhibit intrinsic porosity, reaching a Brunauer-Emmet-Teller area of 155 square meters per gram, potentially facilitating nutrient transport and toxin adsorption, although further studies will be required to probe this.

Improvement of underwater adhesion requires removal of interfacial water to enable intimate contact between surfaces. System parameters such as surface chemistry, elastic modulus, and surface roughness directly influence the nature of this contact. Although thermodynamic arguments suggest that hydrophobic surfaces should exhibit higher adhesion underwater than in dry conditions, nanoscale rigid roughness has been shown to trap water and significantly suppress underwater adhesion. In this work, we measure adhesion between rough-soft and smooth-hard hydrophobic surfaces and compare the results with predictions from the conformal contact mechanics model of Persson and Tosatti (P-T). We find that the conformal P-T model agrees well with dry experimental data and is insensitive to which surface is rough. In contrast, for underwater contacts, adhesion during approach is substantially lower for rough-soft elastomers than predicted by the conformal P-T model. Using infrared microscopy, optical modeling, and surfacesensitive spectroscopy, we demonstrate that these contacts are non-conformal and that a nanometer-thick layer of trapped water persists at the interface. A previously proposed modified P-T model accounting for non-conformal contact has successfully explained underwater adhesion for rough rigid surfaces with an average dry contact fraction of 0.44. However, the reduction in adhesion is significantly larger for the rough-soft surfaces studied here. Fitting our data with a non-conformal P-T model using the average dry fraction as a fitting parameter yields substantially lower values (approximately 0.24). Interestingly, during retraction, we observe the opposite trend, with pull-off adhesion exceeding theoretical predictions based on conformal contact. These results highlight the coupled roles of surface roughness and elastic modulus in regulating interfacial water removal and underwater adhesion, with potential implications for engineered and biomedical adhesive systems.

Hawaiian stream gobies exhibit diverse adhesive abilities that can be used by these fishes to help climb waterfalls. Mucus is recognized as contributing to successful performance in many adhesive systems, but potential specializations of mucus production and composition have not been tested in these fishes. This study examines how anatomical (sucker size and goblet cell density) and biochemical (mucus composition) traits may contribute to adhesive success in climbing gobies. Using histological and spectroscopic analyses, we quantified the density of mucus-producing goblet cells in adhesive structures (lips and pelvic suckers) and assessed differences in mucus chemistry between the pelvic suckers and the body. Goblet cell density in lips and suckers increased with climbing ability, aligning with species distribution across stream elevations. The non-climbing Stenogobius hawaiiensis exhibited the lowest goblet cell densities, while the best climbers (Sicyopterus stimpsoni and Lentipes concolor) showed the highest densities. Among inching climbing gobies that use the mouth to climb especially as juveniles, goblet cell density in the lips was, instead, greater in adult individuals. This suggests that mucus production of the lips may have a broader protective role during interactions with rough substrates, rather than a strict relationship with adhesive performance. Infrared spectroscopy of mucus revealed similar chemical signatures in both sucker and caudal peduncle mucus, suggesting that mucus composition does not change across the body to enhance adhesion. These findings indicate that goblet cell density and, thus, enhanced mucus production (rather than compositional changes) may aid the adhesive performance of climbing gobies, contributing to their ecological success. Understanding these adhesive mechanisms from tissue to whole-animal levels of organization clarifies the specific factors that were specialized during the evolution of the distinctive locomotor behavior of these amphidromous fishes.

Orb spiders use glue-coated viscid silk in their webs that maximizes adhesive forces by optimizing spreading across insect surfaces while maintaining strong bulk cohesion. While glue adhesion on smooth hydrophilic glass is well understood, insect cuticles vary in wettability and wax coatings that resist glue spreading, potentially allowing insects to escape webs. Here, we tested the adhesiveness of viscid silk on the superhydrophobic lotus leaf, an extreme case of a hydrophobic surface, to explore whether hydrophobic cuticles can help insects evade webs. We compared adhesion of viscid silk on three substrates: natural lotus leaves (superhydrophobic due to waxes and microtopography), lotus leaves treated with oxygen plasma (hydrophilic but maintaining microtopography), and smooth hydrophilic glass. We found that viscid silk adheres better to the superhydrophobic lotus leaves than to other surfaces, but that adhesion was always higher on the lotus leaves, regardless of surface energy. These findings demonstrate that viscid silk is resilient to a wide range of surface hydrophobicity and leverages microtopography to increase adhesion, both of which are vital for generalist predators like orb-weaving spiders and may inspire the development of tunable adhesives with multifunctional applications in biomedical, industrial, and robotic fields.

We compare the pH-triggered nucleation of the pharmaceutical diclofenac in bulk solution and at the air-water interface, using a combination of cryo-transmission electron microscopy, surface-specific spectroscopy and microscopy, and molecular dynamics simulations. In solution, simulation data reveal diclofenac forms dynamically ordered, liquid-like pre-nucleation clusters (PNCs), following a nonclassical nucleation pathway. At the air-water interface, nucleation occurs earlier during the titration process. The promoted nucleation is attributed to the interfacial enrichment of protons at this hydrophobic interface, elevated interfacial apparent pK a for diclofenac, as well as the interface-induced ordered diclofenac-water structures. While hydrophobic interactions drive the first air-diclofenac-water layer, further diclofenac molecules tend to separate from water by forming hydrogen-bonded dimers, characteristic of the crystal structure. These findings provide molecular-level insights into organic nucleation, highlighting the importance of hydrophobic interfaces in controlling the process, with potential implications for various applications in pharmaceutical and materials science.

Strong interactions of polyelectrolytes (PEs) with water have been used to control many technological applications of PEs in cryopreservation as well as in anti-icing or lubricating coatings. In all of these cases, knowledge of the phase diagrams of PE with water is important, particularly at low temperatures, where the ice phase is more stable. In this work, we study the phase diagrams of negatively and positively-charged PEs by using infrared spectroscopy (IR) and differential scanning calorimetry (DSC). The results show a coexistence curve of the ice phase in equilibrium with the PE-rich phase in water. The phase diagrams for positively- and negatively-charged PEs were similar, and a nearly 40% volume fraction of water to polymer remains unfrozen. Comparison of the collected data with the predictions from a theoretical model based on the Gibbs-Thomson and Flory-Huggins models reveals that the concentrated PE-water phase has closely associated counterions, and the entropy of the counterions does not play a dominant role. This finding is surprising since PEs are expected to have strongly dissociated charges under these conditions. Interestingly, we also found evidence of a stable unfrozen water PE phase that does not change upon further cooling to -100 °C. These observations are important for applications where controlling the formation of ice is critical.

Materials in low Earth orbit (LEO) face radiation, atomic oxygen erosion, and extreme temperature fluctuations, which can severely compromise their structural and functional integrity. Developing lightweight, multifunctional materials capable of withstanding these harsh conditions is critical for long-term space exploration and sustainable extraterrestrial settlements. This study evaluates the structural stability and radiation shielding efficacy of polylactic acid (PLA) and biocomposites, including PLA infused with fungal melanin, synthetic melanin, or animal melanin, and a compressed mycelium (CMy) coated with PLA (PLA-CMy), after exposure to the LEO environment. Samples were deployed on the Materials International Space Station Experiment-Flight Facility platform for approximately 6 mo in zenith- and wake-facing orientations. Postflight analyses comparing flight-exposed samples to Earth controls revealed composition- and orientation-dependent differences in mass loss, optical properties, and surface morphology. Notably, fungal melanin reduced mass loss and surface wrinkle formation, indicating a protective effect against PLA degradation in LEO. Biocomposites also demonstrated shielding effects by protecting an underlying polyvinyl chloride backing layer from damage. These findings demonstrate PLA's performance in space and highlight fungal melanin as a bioderived additive to enhance PLA resilience under LEO conditions, advancing the development of sustainable materials for future space missions.

The contact between two rough surfaces has been a topic of significant interest since early studies on Coulombic friction and remains crucial for numerous technological applications. However, theoretical progress has outpaced experiments due to the challenges in measuring contact areas across scales ranging from subnanometers to macroscopic dimensions. Here, we demonstrate the use of commonly available infrared-based (IR) spectroscopy in combination with finite-difference time-domain (FDTD) optical simulations to measure separation gaps and contact areas for glassy polymers ranging in roughness over two orders in magnitude. With the combined IR and FDTD simulations, we can overcome the optical diffraction limits and take advantage of the chemical specificity of IR spectroscopy to overcome limitations due to scattering. The scaling of the contact area ratio as a function of pressure illustrated the limitations of using pure elastic or plastic deformation in explaining the results. At both low and high pressures, the contact area ratios scale linearly with pressure as expected for purely elastic deformations at low pressures or plastic deformations at high pressures. However, if analyzed over a broad range of pressure, the power laws we observe are much larger than 1, exemplifying the need to consider elastoplastic models in explaining results for softer polymer contacts compared to other brittle, glassy materials. In comparison, the separation gaps scale exponentially with pressure, as expected. These results have important implications for the interpretation of properties such as friction, adhesion, and conductivity for softer, glassy contact interfaces.

Melanin is ubiquitous in nature, and how the arrangement and concentration of melanin affect its optical and thermal properties aids in understanding the role of melanin in natural systems and technological applications. In this study, a model system consisting of silica and melanin particles with different compositions and degrees of mixing is designed to study the impact on light absorption. The structures are generated using coarse‐grained molecular dynamics simulations, and their optical properties were calculated using finite‐difference time‐domain simulations. The results show that the supraballs with uneven distribution of melanin particles (strongly demixed) exhibit higher absorption (in the range of 360–1000 nm) at melanin concentrations of 40%–80%. Even for a simulation box with a thickness of 16 μm, the strongly demixed samples with melanin concentrations of 50%–100% absorb almost 80% of the total input light at 360–1000 nm. Since light absorption also correlates with thermal heat, thermal heat maps are presented for these systems as a function of melanin concentration and particle distribution. The fundamental knowledge of how melanin distribution alters power absorption will inform the development of photothermally responsive materials for medical applications (photothermal agents), sensors/communication devices, and coatings.

Melanin is a biological nanomaterial with a variety of functions, for example, its ability to quench free radicals. Even though the surface chemistry of melanin is important for these properties, this area has remained relatively unexplored. Here, we compare differences in surface properties of polydopamine (PDA, synthetic mimic of natural melanin) nanoparticles synthesized using three different bases commonly reported in the literature. We use a fluorescence assay and X-ray photoelectron spectroscopy (XPS) to characterize the surface functionalities of nanoparticles synthesized using these three bases. Fluorescence measurements reveal that the PDA synthesized using tris and bicine bases had higher concentrations of amine and carbonyl groups compared to PDA synthesized using ammonium hydroxide. XPS measurements confirmed the presence of carbonyl and amine groups. However, this technique was not able to distinguish the differences in surface chemistry that we observed using fluorescence spectroscopy. Using a 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical trap assay, we demonstrated that the PDA nanoparticles synthesized using tris and bicine were more effective in quenching free radicals compared to PDA synthesized using ammonium hydroxide, correlating with a higher fraction of carbonyl groups on the surface of the PDA nanoparticles.

Soft solids are sticky. They attract each other and spontaneously form a large area of contact. Their force of attraction is higher when separating than when forming contact, a phenomenon known as adhesion hysteresis. The common explanation for this hysteresis is viscoelastic energy dissipation or contact aging. Here, we use experiments and simulations to show that it emerges even for perfectly elastic solids. Pinning by surface roughness triggers the stick-slip motion of the contact line, dissipating energy. We derive a simple and general parameter-free equation that quantitatively describes contact formation in the presence of roughness. Our results highlight the crucial role of surface roughness and present a fundamental shift in our understanding of soft adhesion.

Characterization of synthetic and natural melanin nanoparticles (MNPs) has been challenging due to the variability of properties and chemical bonding. Although eumelanin was the first to be discovered, four additional subcategories of melanin now exist including pheomelanin, neuromelanin, allomelanin and pyomelanin. Mass spectrometry (MS) methods have provided crucial insights into the bonding, structure, and mechanism regarding MNP formation, but inconsistent findings in the literature have caused further confusion in the analysis and structure of MNPs. This mini-review will focus on the types of MS experiments that have been used to analyze MNPs and what kind of information can be gained from different ionization sources, collisional activation experiments, and reaction monitoring quantitative methods when analyzing different subcategories of MNPs. Additionally, future directions regarding alternative applications of MNPs in MS experiments, mass defect analyses of complex mixtures, and a standardized nomenclature for isomeric redox states will all be addressed. (c) 2023 The Authors. Polymer International published by John Wiley & Sons Ltd on behalf of Society of Industrial Chemistry. Examples of different ionization sources commonly used for synthetic/natural melanin nanoparticles (MNPs) and different structural information that has been reported from each technique are shown. The yellow boxes represents sources that are under vacuum while the green box represents sources that are at or near atmospheric pressure. image

AbstractPolymer brushes have found extensive applications as nano‐scale surface coatings with responsive properties, particularly in achieving tunable friction in solvent environments. Here, a special property of hygroscopic polyelectrolyte‐grafted brushes, where the friction forces change by over two orders of magnitude within a narrow range in humidity is reported. Using mechanical measurements of nano‐scale modulus and water absorption coupled with friction and surface‐sensitive spectroscopy, this sharp change in friction is controlled by a humidity‐induced glass transition that abruptly shifts the mode of sliding is demonstrated. Contrary to expectations based on conventional thinking regarding brush lubrication, friction remains large and humidity‐independent below the glass transition even for systems that absorb as much as 30–40% water by volume. This results in an abrupt change in friction past the glass transition humidity. Tuning the chemistry of brushes and their humidity‐induced glass transition offers the tunability to control the on/off friction (or slipperiness) for nanoactuators, ratchets, and catheters, without the need for externally applied lubricating liquids.

Introduction The design of biological structures and the materials composing those structures are intimately connected to performance in biological systems. Spider webs present an excellent example of how design and materials interact during their function in capturing prey. Major shifts in how spider webs capture prey have occurred due to evolutionary changes in both web architecture and silk properties. However, these shifts are mostly described for long timescales deep within the spider’s tree of life. Hawaiian Tetragnatha presents an opportunity to ask if such shifts can occur at much shorter timescales because web design diverges significantly among closely related species on the same island while also converging with more distant relatives on other islands. Here, we provide an initial test of whether or not silk properties diversified during the recent adaptive radiation of Hawaiian Tetragnatha . Methods We obtained radial and capture spiral silk from orb webs for spiders on two islands and tested their tensile and adhesive properties. We also used solution-state NMR to compare the composition of low molecular weight compounds in the glue because of their influence on capture spiral stickiness. Results Results showed differences in the stiffness of radial silk among four populations of Hawaiian Tetragnatha , while extensibility remained unchanged. Although not statistically different, radial strength and toughness varied twofold among species. Stickiness varied threefold among the four populations of orb weavers. No conspicuous qualitative differences in the low molecular weight compound composition of aggregate glue were found, suggesting that differences in capture spiral stickiness were due to the amount or arrangement of glue droplets on threads. Discussion While our sampling is modest, our data provide the first evidence that silk properties can evolve measurably over the relatively short timescales of the adaptive radiation of Hawaiian Tetragnatha spiders.

This proposal was for carrying out research on creating novel hybrid nanostructures with novel and interesting functional properties with the help of advanced structural on adding 0.001, 0.01 and 0.02 mg of Au nanoparticles . From the reflectivity measurements, and the intensities of the various order diffraction peaks from the multilayers, we were able to reconstruct the electron density profiles of the films normal to their surfaces. characterization techniques . There were 3 components to the research: (1) seeing if new hybrid nanostructures could be synthesized from Au nanoparticles and lipid multilayers (2) making artificial cells from Galactopyranose-Derived Single-Chain Amphiphiles and sponge phases of lipid/amphiphile mixtures , and (3) characterizing the pair distribution function for complex nanoparticles of melanin to understand/predict the structural colors seen in aggregates of such nanoparticles.