Selective Vapor Condensation for the Synthesis and Assembly of Spherical Colloids with a Precise Rough Patch.

Patchy particles occupy an increasingly important space in soft matter research due to their ability to assemble into intricate phases and states. Being able to fine-tune the interactions among these particles is essential to understanding the principles governing the self-assembly processes. However, current fabrication techniques often yield patches that deviate chemically and physically from the native particles, impeding the identification of the driving forces behind self-assembly. To overcome this challenge, we propose a new approach to synthesizing spherical colloids with a well-defined rough patch on their surface. By treating polystyrene microspheres with vapors of a good solvent, here an acetone-water mixture, we achieve selective polymer corrugation on the particle surface resulting in a chemically similar yet rough surface patch. The key step is the selective condensation of the acetone-water vapors on the apex of the polystyrene microparticles immobilized on a substrate, which leads to rough patch formation. We leverage the ability to tune the vapor-liquid equilibrium of the volatile acetone-water mixture to precisely control the polymer corrugation on the particle surface. We demonstrate the dependence of patch formation on particle and substrate wettability, with the condensation occurring on the particle apex only when it is more wettable than the substrate, which is consistent with Volmer's classical nucleation theory. By combining experiments and molecular dynamics simulations, we identify the role of the rough patch in the depletion interaction-driven self-assembly of the microspheres, which is crucial for designing programmable supracolloidal structures.

Topologically Precise and Discrete Bottlebrush Polymers: Synthesis, Characterization, and Structure-Property Relationships.

As the complexity of polymer structure grows, so do the challenges for developing an accurate understanding of their structure-property relationships. Here, the synthesis of bottlebrush polymers with topologically precise and fully discrete structures is reported. A key feature of the strategy is the synthesis of discrete macromonomer libraries for their polymerization into topologically precise bottlebrushes that can be separated into discrete bottlebrushes (D = 1.0). As the system becomes more discrete, packing efficiency increases, distinct three-phase Langmuir-Blodgett isotherms are observed, and its glass transition temperature becomes responsive to side-chain sequence. Overall, this work presents a versatile strategy to access a range of precision bottlebrush polymers and unravels the impact of side-chain topology on their macroscopic properties. Precise control over side chains opens a pathway for tailoring polymer properties without changing their chemical makeup.

An Augmented Reality Device for Remote Supervision of Ultrasound Examinations in International Exercise Science Projects: Usability Study.

BACKGROUND: Support for long-distance research and clinical collaborations is in high demand and has increased owing to COVID-19-related restrictions on travel and social contact. New digital approaches are required for remote scientific exchange. OBJECTIVE: This study aims to analyze the options of using an augmented reality device for remote supervision of exercise science examinations. METHODS: A mobile ultrasound examination of the diameter and intima-media thickness of the femoral and carotid arteries was remotely supervised using a head-mounted augmented reality device. All participants were provided with a link to a YouTube video of the technique in advance. In part 1, 8 international experts from the fields of engineering and sports science were remotely connected to the study setting. Internet connection speed was noted, and a structured interview was conducted. In part 2, 2 remote supervisors evaluated 8 physicians performing an examination on a healthy human subject. The results were recorded, and an evaluation was conducted using a 25-item questionnaire. RESULTS: In part 1, the remote experts were connected over a mean distance of 1587 km to the examination site. Overall transmission quality was good (mean upload speed: 28.7 Mbps, mean download speed: 97.3 Mbps, mean ping: 21.6 milliseconds). In the interview, participants indicated that the main potential benefits would be to the fields of education, movement analysis, and supervision. Challenges regarding internet connection stability and previous training with the devices used were reported. In part 2, physicians' examinations showed good interrater correlation (interclass correlation coefficient: 0.84). Participants valued the experienced setting as highly positive. CONCLUSIONS: The study showed the good feasibility of the chosen design and a highly positive attitude of all participants toward this digital approach. Head-mounted augmented reality devices are generally recommended for collaborative research projects with physical examination-based research questions.

Catalytic Enhancement of Inductively Heated Fe3 O4 Nanoparticles by Removal of Surface Ligands.

Heat management in catalysis is limited by each material's heat transfer efficiencies, resulting in energy losses despite current thermal engineering strategies. In contrast, induction heating of magnetic nanoparticles (NPs) generates heat at the surface of the catalyst where the reaction occurs, reducing waste heat via dissipation. However, the synthesis of magnetic NPs with optimal heat generation requires interfacial ligands, such as oleic acid, which act as heat sinks. Surface treatments using tetramethylammonium hydroxide (TMAOH) or pyridine are used to remove these ligands before applications in hydrophilic media. In this study, Fe3 O4 NPs are surface treated to study the effect of induction heating on the catalytic oxidation of 1-octanol. Whereas TMAOH was unsuccessful in removing oleic acid, pyridine treatment resulted in a roughly 2.5-fold increase in heat generation and product yield. Therefore, efficient surfactant removal has profound implications in induction heating catalysis by increasing the heat transfer and available surface sites.

Polymer Stereocomplexation as a Scalable Platform for Nanoparticle Assembly.

DNA-mediated assembly of inorganic particles has demonstrated to be a powerful approach for preparing nanomaterials with a range of interesting optical and electrical properties. Building on this inspiration, we describe a generalizable gram-scale method to assemble nanoparticles through the formation of poly(methyl methacrylate) (PMMA) triple-helices. In this work, alkene-terminated syndiotactic (st-) and isotactic (it-) PMMA polymers were prepared and subsequently functionalized to afford nanoparticle ligands. Nanoparticles with complementary st- and it-PMMA ligands could then be spontaneously assembled upon mixing at room temperature. This process was robust and fully reversible through multiple heating and cooling cycles. The versatility of PMMA stereocomplexation was highlighted by assembling hybrid structures composed of nanoparticles of different compositions (e.g., Au and quantum dots) and shapes (e.g., spheres and rods). These initial demonstrations of nanoparticle self-assembly from inexpensive PMMA-based materials present an attractive alternative to DNA-based nanomaterials.

Effects of exercise on depression and anxiety in persons living with HIV: A meta-analysis.

OBJECTIVE: The purpose of this systematic review and meta-analysis was to examine the effects of exercise on depression and anxiety in people living with HIV (PLWH), and to evaluate, through subgroup analysis, the effects of exercise type, frequency, supervision by exercise professionals, study quality, and control group conditions on these outcomes. METHOD: A literature search was conducted through four electronic databases from inception to February 2019. Considered for inclusion were randomized controlled trials (RCTs) investigating exercise interventions and depression or anxiety as outcomes in people living with HIV (≥ 18 years of age). Ten studies were included (n = 479 participants, 49.67% females at baseline), and the standardized mean difference (SMD) and heterogeneity were calculated using random-effect models. An additional pre-post meta-analysis was also conducted. RESULTS: A large effect in favor of exercise when compared to controls was found for depression (SMD = -0.84, 95%CI = [-1.57, -0.11], p = 0.02) and anxiety (SMD = -1.23, 95%CI = [-2.42, -0.04], p = 0.04). Subgroup analyses for depression revealed large effects on depression for aerobic exercise only (SMD = -0.96, 95%CI = [-1.63, -0.30], p = 0.004), a frequency of ≥3 exercise sessions per week (SMD = -1.39, 95%CI = [-2.24, -0.54], p < 0.001), professionally supervised exercise (SMD = -1.40, 95%CI = [-2.46, -0.17], p = 0.03]), and high-quality studies (SMD = -1.31, 95%CI = [-2.46, -0.17], p = 0.02). CONCLUSION: Exercise seems to decrease depressive symptoms and anxiety in PLWH, but other larger and high-quality studies are needed to verify these effects.

Impairments of postural control, functional performance and strength in morbidly obese patients awaiting bariatric surgery in comparison to healthy individuals.

[Purpose] There is a lack of information evaluating specific markers of performance in patients awaiting bariatric surgery. We aimed to assess the postural control, functional performance, strength and endurance performance for morbidly obese patients awaiting bariatric surgery compared to lean controls. [Subjects and Methods] All parameters were assessed by modified Y-balance test, timed-up-and-go-test, maximum strength testing on resistance exercise equipment and cardio-pulmonary exercise testing on a cycle ergometer in 10 morbidly obese patients awaiting bariatric surgery and 10 age- and sex-matched lean controls. [Results] It was found that significant differences existed for overall modified Y-balance test in morbidly obese patients awaiting bariatric surgery versus lean controls (0.37 ± 0.03 vs. 0.47 ± 0.02 cm.cm-1), timed-up-and-go-test (9.33 ± 1.23 vs. 7.85 ± 1.73 sec) and several variables of cardio-pulmonary exercise testing. Overall absolute strength expressed in kilogram was similar, yet when relativized to body weight strength differences were notable (0.4 ± 0.17 vs. 0.83 ± 0.32 kg.kg-1). [Conclusion] The results of this study demonstrate the need for comprehensive functional assessment prior to surgery with an identified demand for subsequent tailored physical training prescription that should begin before surgery.

Controlled Formation and Binding Selectivity of Discrete Oligo(methyl methacrylate) Stereocomplexes.

The triple-helix stereocomplex of poly(methyl methacrylate) (PMMA) is a unique example of a multistranded synthetic helix that has significant utility and promise in materials science and nanotechnology. To gain a fundamental understanding of the underlying assembly process, discrete stereoregular oligomer libraries were prepared by combining stereospecific polymerization techniques with automated flash chromatography purification. Stereocomplex assembly of these discrete building blocks enabled the identification of (1) the minimum degree of polymerization required for the stereocomplex formation and (2) the dependence of the helix crystallization mode on the length of assembling precursors. More significantly, our experiments resolved binding selectivity between helical strands with similar molecular weights. This presents new opportunities for the development of next-generation polymeric materials based on a triple-helix motif.

Elucidating the Impact of Molecular Structure on the 19F NMR Dynamics and MRI Performance of Fluorinated Oligomers.

To understand molecular factors that impact the performance of polymeric 19F magnetic resonance imaging (MRI) agents, a series of discrete fluorinated oligoacrylates with precisely defined structure were prepared through the combination of controlled polymerization and chromatographic separation techniques. These discrete oligomers enabled thorough elucidation of the dependence of 19F NMR and MRI properties on molecular structure, for example, the chain length. Importantly, the oligomer size and dispersity strongly influence NMR dynamics (T1 and T2 relaxation times) and MR imaging properties with higher signal-to-noise ratio (SNR) observed for oligomers with longer chain length and shorter T1. Our approach enables an effective pathway and thus opportunities to rationally design effective polymeric 19F MR imaging agents with optimized molecular structure and NMR relaxivity.

A Versatile and Efficient Strategy to Discrete Conjugated Oligomers.

An efficient and scalable strategy to prepare libraries of discrete conjugated oligomers (D = 1.0) using the combination of controlled polymerization and automated flash chromatography is reported. From this two-step process, a series of discrete conjugated materials from dimers to tetradecamers could be isolated in high yield with excellent structural control. Facile and scalable access to monodisperse libraries of different conjugated oligomers opens pathways to designer mixtures with precise composition and monomer sequence, allowing exquisite control over their physical, optical, and electronic properties.

Effects of Tailored Dispersity on the Self-Assembly of Dimethylsiloxane-Methyl Methacrylate Block Co-Oligomers.

The effect of dispersity on block polymer self-assembly was studied in the monodisperse limit using a combination of synthetic chemistry, matrix-assisted laser desorption ionization spectroscopy, and small-angle X-ray scattering. Oligo(methyl methacrylate) (oligoMMA) and oligo(dimethylsiloxane) (oligoDMS) homopolymers were synthesized by conventional polymerization techniques and purified to generate an array of discrete, semidiscrete, and disperse building blocks. Coupling reactions afforded oligo(DMS-MMA) block polymers with precisely tailored molar mass distributions spanning single molecular systems (D = 1.0) to low-dispersity mixtures (D ≈ 1.05). Discrete materials exhibit a pronounced decrease in domain spacing and sharper scattering reflections relative to disperse analogues. The order-disorder transition temperature (TODT) also decreases with increasing dispersity, suggesting stabilization of the disordered phase, presumably due to the strengthening of composition fluctuations at the low molar masses investigated.

A Versatile and Scalable Strategy to Discrete Oligomers.

A versatile strategy is reported for the multigram synthesis of discrete oligomers from commercially available monomer families, e.g., acrylates, styrenics, and siloxanes. Central to this strategy is the identification of reproducible procedures for the separation of oligomer mixtures using automated flash chromatography systems with the effectiveness of this approach demonstrated through the multigram preparation of discrete oligomer libraries (D = 1.0). Synthetic availability, coupled with accurate structural control, allows these functional building blocks to be harnessed for both fundamental studies as well as targeted technological applications.

Pentafluorophenyl Ester-Functionalized Nanoparticles as a Versatile Platform for Selective and Covalent Inter-nanoparticle Coupling.

Preparing chemically selective nanoparticle (NP) building blocks to make robust structures from different NP compositions often requires complex hetero-bifunctional ligand pairs that have limited scalability and versatility. Here we describe pentafluorophenyl ester-functionalized nanoparticles (PFP-NPs) as versatile building blocks for covalent inter-NP coupling. This approach allows for a rapid and dense grafting of PFP-functionalized Au NPs onto several types of amine-functionalized NPs (metals, semiconductors, and insulators) and selective identification of amine-functionalized quantum dots (QDs) in solution. Such simple yet efficient inter-NP reactions suggest the suitability of PFP-NPs as a versatile functional platform for numerous NP-based applications.

Simple Benchtop Approach to Polymer Brush Nanostructures Using Visible-Light-Mediated Metal-Free Atom Transfer Radical Polymerization.

The development of an operationally simple, metal-free surface-initiated atom transfer radical polymerization (SI-ATRP) based on visible-light mediation is reported. The facile nature of this process enables the fabrication of well-defined polymer brushes from flat and curved surfaces using a "benchtop" setup that can be easily scaled to four-inch wafers. This circumvents the requirement of stringent air-free environments (i.e., glovebox), and mediation by visible light allows for spatial control on the micron scale, with complex three-dimensional patterns achieved in a single step. This robust approach leads to unprecedented access to brush architectures for nonexperts.

Azulene methacrylate polymers: synthesis, electronic properties, and solar cell fabrication.

We report the synthesis of novel azulene-substituted methacrylate polymers by free radical polymerization, in which the azulene moieties represent hydrophobic dipoles strung pendant to the polymer backbone and impart unique electronic properties to the polymers. Tunable optoelectronic properties were realized by adjusting the azulene density, ranging from homopolymers (having one azulene group per repeat unit) to copolymers in which the azulene density was diluted with other pendant groups. Treating these polymers with organic acids revealed optical and excitonic behavior that depended critically on the azulene density along the polymer chain. Copolymers of azulene with zwitterionic methacrylates proved useful as cathode modification layers in bulk-heterojunction solar cells, where the relative azulene content affected the device metrics and the power conversion efficiency reached 7.9%.

Stretching of assembled nanoparticle helical springs.

Hybrid materials that possess high inorganic fractions of nanoscale particles can be advantageous for a wide range of functions, from optoelectronic or electronic devices to drug delivery. However, many current nanoparticle (NP) based materials lack the necessary combination of simple fabrication and robust mechanical properties that span across length scales greater than tens of microns. We have developed a facile, evaporative assembly method called flow coating to create NP based ribbons that can subsequently form helical structures. Here we analytically examine the stretching properties of these helical ribbons which are nanometers thick, microns wide, and arbitrarily long. We find that the force-extension behavior is well described by the elastic and surface energies, which can be used as a guideline for their design. In addition, we show that the properties may be tuned by changing the ribbon dimensions or material composition to yield a different stiffness. These macroscale mechanical properties, along with properties inherent to the nanometer length scale of the particles can provide tunable multifunctionality for a number of applications.

Highly conductive ribbons prepared by stick-slip assembly of organosoluble gold nanoparticles.

Precisely positioning and assembling nanoparticles (NPs) into hierarchical nanostructures is opening opportunities in a wide variety of applications. Many techniques employed to produce hierarchical micrometer and nanoscale structures are limited by complex fabrication of templates and difficulties with scalability. Here we describe the fabrication and characterization of conductive nanoparticle ribbons prepared from surfactant-free organosoluble gold nanoparticles (Au NPs). We used a flow-coating technique in a controlled, stick-slip assembly to regulate the deposition of Au NPs into densely packed, multilayered structures. This affords centimeter-scale long, high-resolution Au NP ribbons with precise periodic spacing in a rapid manner, up to 2 orders-of-magnitude finer and faster than previously reported methods. These Au NP ribbons exhibit linear ohmic response, with conductivity that varies by changing the binding headgroup of the ligands. Controlling NP percolation during sintering (e.g., by adding polymer to retard rapid NP coalescence) enables the formation of highly conductive ribbons, similar to thermally sintered conductive adhesives. Hierarchical, conductive Au NP ribbons represent a promising platform to enable opportunities in sensing, optoelectronics, and electromechanical devices.

Highly stretchable nanoparticle helices through geometric asymmetry and surface forces.

Geometric asymmetry and surface forces are used directly the shape transformation of two-dimensional nanoparticle (NP)-based ribbons into three-dimensional helices. The balance between elasticity and surface tension dictates the helical radius dimension. NP helical ribbons have exceptional mechanical properties, displaying high stretchability, helical shape recovery after extension, and low-strain stiffness values similar to biological helices.

Large deformation and adhesive contact studies of axisymmetric membranes.

A model membrane contact system consisting of an acrylic copolymer membrane and a PDMS substrate was utilized to evaluate a recently developed nonlinear large-deformation adhesive contact analysis. Direct measurements of the local membrane apex strain during noncontact inflation indicated that the neo-Hookean model provides an accurate measure of membrane strain and supports its use as the strain energy function for the analysis. Two membrane contact geometries, exhibiting significantly different strain distributions during withdrawal, were investigated. The first examines the wet contact of an air pressurized membrane. The second looks at the dry contact of a fluid deformed membrane in which a stepper motor controls membrane-substrate separation. A time-dependent modulus emerges from the analysis, with principal tensions obtained from a comparison of predicted and experimental membrane profiles. The applicability of this numerical analysis for determining membrane tension, however, is limited by wrinkling instabilities and viscoelasticity. For this reason, a conceptually simpler method, based on the direct measurement of the membrane tension and contact angle, was also utilized. The traditional peel energy defined with this direct measurement accurately described the membrane/substrate adhesive interactions, giving well-defined peel energies that were independent of the detailed strain state of the membrane.