Phase Behavior of Charged Star Block Copolymers at Fluids Interface.

The phase behavior of block copolymers (BCPs) at the water-oil interface is influenced by the segmental interaction parameter ( χ ${\chi }$ ) and chain architecture. We synthesized a series of star block copolymers (s-BCPs) having polystyrene (PS) as core and poly(2-vinylpyridine) (P2VP) as corona. The interaction parameters of block-block ( χ ${\chi }$ PS-P2VP ) and block-solvent ( χ ${\chi }$ P2VP-solvent ) were varied by adjusting the pH of the aqueous solution. Lowering pH increased the fraction of quaternized-P2VP (Q-P2VP) with enhanced hydrophilicity. By transferring the equilibrated interfacial assemblies, morphologies ranging from bicontinuous films at pH of 7 and 3.1 to nanoporous and nanotubular structure at pH of 0.65 were observed. The nanoporous films formed hexagonally packed pores in s-BCP matrix, while nanotubes comprised Q-P2VP as corona and PS as core. Control over pore size, d-spacing between pores, and nanotube diameters was achieved by varying polymer concentration, molecular weight, volume fraction and arm number of s-BCPs. Large-scale nanoporous films were obtained by freeze-drying emulsions. Remarkably, the morphologies of linear BCPs were inverted, forming hexagonal-packed rigid spherical micelles with Q-P2VP as core and PS as corona in multilayer. This work provides insights of phase behaviors of BCP at fluids interface and offer a facile approach to prepare nanoporous film with well-controlled pore structure.

Janus bottlebrush compatibilizers.

Bottlebrush random copolymers (BRCPs), consisting of a random distribution of two homopolymer chains along a backbone, can segregate to the interface between two immiscible homopolymers. BRCPs undergo a reconfiguration, where each block segregates to one of the homopolymer phases, adopting a Janus-type structure, reducing the interfacial tension and promoting adhesion between the two homopolymers, thereby serving as a Janus bottlebrush copolymer (JBCP) compatibilizer. We synthesized a series of JBCPs by copolymerizing deuterated or hydrogenated polystyrene (DPS/PS) and poly(tert-butyl acrylate) (PtBA) macromonomers using ruthenium benzylidene-initiated ring-opening metathesis polymerization (ROMP). Subsequent acid-catalyzed hydrolysis converted the PtBA brushes to poly(acrylic acid) (PAA). The JBCPs were then placed at the interface between DPS/PS homopolymers and poly(2-vinyl pyridine) (P2VP) homopolymers, where the degree of polymerization of the backbone (NBB) and the grafting density (GD) of the JBCPs were varied. Neutron reflectivity (NR) was used to determine the interfacial width and segmental density distributions (including PS homopolymer, PS block, PAA block and P2VP homopolymer) across the polymer-polymer interface. Our findings indicate that the star-like JBCP with NBB = 6 produces the largest interfacial broadening. Increasing NBB to 100 (rod-like shape) and 250 (worm-like shape) reduced the interfacial broadening due to a decrease in the interactions between blocks and homopolymers by stretching of blocks. Decreasing the GD from 100% to 80% at NBB = 100 caused an increase the interfacial width, yet further decreasing the GD to 50% and 20% reduced the interfacial width, as 80% of GD may efficiently increase the flexibility of blocks and promote interactions between homopolymers, while maintaining relatively high number of blocks attached to one molecule. The interfacial conformation of JBCPs was further translated into compatibilization efficiency. Thin film morphology studies showed that only the lower NBB values (NBB = 6 and NBB = 24) and the 80% GD of NBB = 100 had bicontinuous morphologies, due to a sufficient binding energy that arrested phase separation, supported by mechanical testing using asymmetric double cantilever beam (ADCB) tests. These provide fundamental insights into the assembly behavior of JBCPs compatibilizers at homopolymer interfaces, opening strategies for the design of new BCP compatibilizers.

Evidence for Enhanced Tracer Diffusion in Densely Packed Interfacial Assemblies of Hairy Nanoparticles.

Nearly monodisperse nanoparticle (NP) spheres attached to a nonvolatile ionic liquid surface were tracked by in situ scanning electron microscopy to obtain the tracer diffusion coefficient Dtr as a function of the areal fraction ϕ. The in situ technique resolved both tracer (gold) and background (silica) particles for ∼1-2 min, highlighting their mechanisms of diffusion, which were strongly dependent on ϕ. Structure and dynamics at low and moderate ϕ paralleled those reported for larger colloidal spheres, showing an increase in order and a decrease in Dtr by over 4 orders of magnitude. However, ligand interactions were more important near jamming, leading to different caging and jamming dynamics for smaller NPs. The normalized Dtr at ultrahigh ϕ depended on particle diameter and ligand molecular weight. Increasing the PEG molecular weight by a factor of 4 increased Dtr by 2 orders of magnitude at ultrahigh ϕ, indicating stronger ligand lubrication for smaller particles.

Complete genome sequence of phi29-like Microbacterium foliorum podovirus phage PineapplePizza.

Bacteriophage PineapplePizza is a podovirus infecting Microbacterium foliorum NRRL B-24224. The genome is 16,662 bp long and contains 23 predicted protein-coding genes. Interestingly, PineapplePizza shows amino acid similarities to well-studied Bacillus subtilis phage phi29.

Conferring liver selectivity to a thyromimetic using a novel nanoparticle increases therapeutic efficacy in a diet-induced obesity animal model.

Optimization of metabolic regulation is a promising solution for many pathologies, including obesity, dyslipidemia, type 2 diabetes, and inflammatory liver disease. Synthetic thyroid hormone mimics-based regulation of metabolic balance in the liver showed promise but was hampered by the low biocompatibility and harmful effects on the extrahepatic axis. In this work, we show that specifically directing the thyromimetic to the liver utilizing a nanogel-based carrier substantially increased therapeutic efficacy in a diet-induced obesity mouse model, evidenced by the near-complete reversal of body weight gain, liver weight and inflammation, and cholesterol levels with no alteration in the thyroxine (T4) / thyroid stimulating hormone (TSH) axis. Mechanistically, the drug acts by binding to thyroid hormone receptor ß (TRß), a ligand-inducible transcription factor that interacts with thyroid hormone response elements and modulates target gene expression. The reverse cholesterol transport (RCT) pathway is specifically implicated in the observed therapeutic effect. Overall, the study demonstrates a unique approach to restoring metabolic regulation impacting obesity and related metabolic dysfunctions.

Nanoscale Porosity in Microellipsoids Cloaks Interparticle Capillary Attraction at Fluid Interfaces.

Anisotropic particles pinned at fluid interfaces tend toward disordered multiparticle configurations due to large, orientationally dependent, capillary forces, which is a significant barrier to exploiting these particles to create functional self-assembled materials. Therefore, current interfacial assembly methods typically focus on isotropic spheres, which have minimal capillary attraction and no dependence on orientation in the plane of the interface. In order to create long-range ordered structures with complex configurations via interfacially trapped anisotropic particles, control over the interparticle interaction energy via external fields and/or particle engineering is necessary. Here, we synthesize colloidal ellipsoids with nanoscale porosity and show that their interparticle capillary attraction at a water-air interface is reduced by an order of magnitude compared to their smooth counterparts. This is accomplished by comparing the behavior of smooth, rough, and porous ellipsoids at a water-air interface. By monitoring the dynamics of two particles approaching one another, we show that the porous particles exhibit a much shorter-range capillary interaction potential, with scaling intriguingly different than theory describing the behavior of smooth ellipsoids. Further, interferometry measurements of the fluid deformation surrounding a single particle shows that the interface around porous ellipsoids does not possess the characteristic quadrupolar symmetry of smooth ellipsoids, and quantitatively confirms the decrease in capillary interaction energy. By engineering nanostructured surface features in this fashion, the interfacial capillary interactions between particles may be controlled, informing an approach for the self-assembly of complex two-dimensional microstructures composed of anisotropic particles.

Reimagining Hair Science: A New Approach to Classify Curly Hair Phenotypes via New Quantitative Geometric and Structural Mechanical Parameters.

Hair is a natural polymeric composite primarily composed of tight macrobundles of keratin proteins, which are highly responsive to external stimuli, similarly to the hydrogels and other natural fibrous gel systems like collagen and fibrin.Hair and its appearance play a significant role in human society. As a highly complex biocomposite system, it has been traditionally challenging to characterize and thus develop personal care products. Over the last few decades, a significant societal paradigm shift occurred among those with curly hair, accepting the natural morphological shape of their curls and styling their hair according to its innate, distinct, and unique material properties, which has given rise to the development of new hair classification systems, beyond the traditional and highly limited race-based distinction (Caucasian, Mongolian, and African). L'Oréal developed a hair typing taxonomy based on quantitative geometric parameters among the four key patterns─straight, wavy, curly, and kinky, but it fails to capture the complex diversity of curly and kinky hair. Acclaimed celebrity hair stylist Andre Walker developed a classification system that is the existing gold standard for classifying curly and kinky hair, but it relies upon qualitative classification measures, making the system vague and ambiguous of phenotypic differences. The goal of this research is to use quantitative methods to identify new geometric parameters more representative of curly and kinky hair curl patterns, therefore providing more information on the kinds of personal care products that will resonate best with them and thus maximize desired appearance and health, and to correlate these new parameters with its mechanical properties. This was accomplished by identifying new geometric and mechanical parameters from several types of human hair samples.Geometric properties were measured using scanning electron microscopy (SEM), photogrammetry, and optical microscopy. Mechanical properties were measured under tensile extension using a texture analyzer (TA) and a dynamic mechanical analyzer (DMA), which bears similarity to the common act of brushing or combing. Both instruments measure force as a function of applied displacement, thus allowing the relationship between stress and applied stretch ratio to be measured as a hair strand uncurls and stretches to the point of fracture. From the resulting data, correlations were made between fiber geometry and mechanical performance. This data will be used to draw more conclusions on the contribution that fiber morphology has on hair fiber mechanics and will promote cultural inclusion among researchers and consumers possessing curly and kinky hair.

Genome Sequences of Microbacterium foliorum Phages Anseraureola, Pondwater, and Yasuo.

Anseraureola, Pondwater, and Yasuo are bacteriophages with siphovirus morphology that infect Microbacterium foliorum NRRL B-24224. They were isolated from soil collected in Amherst, Massachusetts, and have genome lengths between 17,362 bp and 17,453 bp. These phages each contain 25 predicted protein-coding genes and are assigned to phage cluster EE.

Polystyrene-based Macromolecular Ammonium Halides for Tuning Color and Exchange Kinetics of Perovskite Nanocrystals.

Post-synthesis anion exchange of all-inorganic cesium lead halide perovskite nanocrystals (CsPbX3 NCs, where X=Cl, Br, and/or I) provides a rapid and simple means of tuning their band gap and photoluminescence emission wavelengths. Here we report color-shifting of CsPbX3 nanocrystals induced by a macromolecular source of halide ions, specifically using polystyrene with ammonium halides as pendent groups. This strategy for introducing new halides to the perovskite nanocrystals gave access to perovskite-polymer hybrid materials as solutions, thin films, or free-flowing powders. Spectroscopic measurements of the halide-exchanged nanocrystal products revealed high photoluminescence quantum yields across the visible spectrum, with exchange kinetics that were tunable based on the solution environment, suggesting an aggregation-inhibited exchange process that affords access to multi-colored solutions and films.

Dynamic Reconfiguration of Compressed 2D Nanoparticle Monolayers.

A Gibbs monolayer of jammed, or nearly jammed, spherical nanoparticles was imaged at a liquid surface in real time by in-situ scanning electron microscopy performed at the single-particle level. At nanoparticle areal fractions above that for the onset of two-dimensional crystallization, structural reorganizations of the mobile polymer-coated particles were visualized after a stepwise areal compression. When the compression was small, slow shearing near dislocations and reconfigured nanoparticle bonding were observed at crystal grain boundaries. At larger scales, domains grew as they rotated into registry by correlated but highly intermittent motions. Simultaneously, the areal density in the middle of the monolayer increased. When the compression was large, the jammed monolayers exhibited out-of-plane deformations such as wrinkles and bumps. Due to their large interfacial binding energy, few (if any) of the two-dimensionally mobile nanoparticles returned to the liquid subphase. Compressed long enough (several hours or more), monolayers transformed into solid nanoparticle films, as evidenced by their cracking and localized rupturing upon subsequent areal expansion. These observations provide mechanistic insights into the dynamics of a simple model system that undergoes jamming/unjamming in response to mechanical stress.

Collective Nanoparticle Dynamics Associated with Bridging Network Formation in Model Polymer Nanocomposites.

The addition of nanoparticles (NPs) to polymers is a powerful method to improve the mechanical and other properties of macromolecular materials. Such hybrid polymer-particle systems are also rich in fundamental soft matter physics. Among several factors contributing to mechanical reinforcement, a polymer-mediated NP network is considered to be the most important in polymer nanocomposites (PNCs). Here, we present an integrated experimental-theoretical study of the collective NP dynamics in model PNCs using X-ray photon correlation spectroscopy and microscopic statistical mechanics theory. Silica NPs dispersed in unentangled or entangled poly(2-vinylpyridine) matrices over a range of NP loadings are used. Static collective structure factors of the NP subsystems at temperatures above the bulk glass transition temperature reveal the formation of a network-like microstructure via polymer-mediated bridges at high NP loadings above the percolation threshold. The NP collective relaxation times are up to 3 orders of magnitude longer than the self-diffusion limit of isolated NPs and display a rich dependence with observation wavevector and NP loading. A mode-coupling theory dynamical analysis that incorporates the static polymer-mediated bridging structure and collective motions of NPs is performed. It captures well both the observed scattering wavevector and NP loading dependences of the collective NP dynamics in the unentangled polymer matrix, with modest quantitative deviations emerging for the entangled PNC samples. Additionally, we identify an unusual and weak temperature dependence of collective NP dynamics, in qualitative contrast with the mechanical response. Hence, the present study has revealed key aspects of the collective motions of NPs connected by polymer bridges in contact with a viscous adsorbing polymer medium and identifies some outstanding remaining challenges for the theoretical understanding of these complex soft materials.

Membrane Remodeling by DNA Origami Nanorods: Experiments Exploring the Parameter Space for Vesicle Remodeling.

Inspired by the ability of cell membranes to alter their shape in response to bound particles, we report an experimental study of long, slender nanorods binding to lipid bilayer vesicles and altering the membrane shape. Our work illuminates the role of particle concentration, adhesion strength, and membrane tension in determining the membrane morphology. We combined giant unilamellar vesicles with oppositely charged nanorods, carefully tuning the adhesion strength, membrane tension, and particle concentration. With increasing adhesion strength, the primary behaviors observed were membrane deformation, vesicle-vesicle adhesion, and vesicle rupture. These behaviors were observed in well-defined regions in the parameter space with sharp transitions between them. We observed the deformation of the membrane resulting in tubulation, textured surfaces, and small and large lipid-particle aggregates. These responses are robust and repeatable and provide a new physical understanding of the dependence on the shape, binding affinity, and particle concentration in membrane remodeling. The design principles derived from these experiments may lead to new bioinspired membrane-based materials.

Solvent-Induced Assembly of Microbial Protein Nanowires into Superstructured Bundles.

Protein-based electronic biomaterials represent an attractive alternative to traditional metallic and semiconductor materials due to their environmentally benign production and purification. However, major challenges hindering further development of these materials include (1) limitations associated with processing proteins in organic solvents and (2) difficulties in forming higher-order structures or scaffolds with multilength scale control. This paper addresses both challenges, resulting in the formation of one-dimensional bundles composed of electrically conductive protein nanowires harvested from the microbes Geobacter sulfurreducens and Escherichia coli. Processing these bionanowires from common organic solvents, such as hexane, cyclohexane, and DMF, enabled the production of multilength scale structures composed of distinctly visible pili. Transmission electron microscopy revealed striking images of bundled protein nanowires up to 10 µm in length and with widths ranging from 50-500 nm (representing assembly of tens to hundreds of nanowires). Conductive atomic force microscopy confirmed the presence of an appreciable nanowire conductivity in their bundled state. These results greatly expand the possibilities for fabricating a diverse array of protein nanowire-based electronic device architectures.

Bimodal Mesoporous Carbon Spheres with Small and Ultra-Large Pores Fabricated Using Amphiphilic Brush Block Copolymer Micelle Templates.

We report the self-assembly of amphiphilic polystyrene-block-poly(ethylene oxide) (PS-b-PEO) brush block copolymers (BBCPs) into spherical micelles in an ethanol/water mixture as an efficient templating approach to fabricate mesoporous carbon spheres using polydopamine as a carbon source. Mesopore sizes of up to 25 nm are well controlled and are dependent on the molecular weight (Mw) of the BBCP. Such large pores are difficult to obtain using traditional linear block copolymers templates. Furthermore, bimodal mesoporous carbon spheres with two populations of pore sizes (24.5 and 6.5 nm) are obtained using a BBCP coassembled with a small molecule surfactant (Pluronic F127). An oxygen reduction reaction is used to demonstrate that electrocatalytic performance can be tuned by controlling the carbon sphere morphologies. This work provides a novel and versatile method to fabricate carbon spheres with broadly tunable bimodal pore sizes for potential applications in catalysis, separations, and energy storage.

Construction from Destruction: Hydrogel Formation from Triggered Depolymerization-Based Release of an Enzymatic Catalyst.

Biomimetic systems that undergo macroscopic phase transformations by transducing and amplifying external cues are highly desirable for applications such as self-healing. Here, we report self-assembly of polyelectrolyte complexes into a vesicular structure that can accommodate hydrophilic guest molecules, including enzymes. Triggered depolymerization of one of the polyelectrolyte molecules in the complex causes the vesicle to disassemble and release its contents. Such a triggered release of enzymes causes molecular-scale events to be amplified due to the enzyme's catalytic properties. This feature has been utilized to demonstrate construction of hydrogels from the destruction of nanoscopic polymeric vesicles. The design principles developed here are broadly adaptable to other triggerable depolymerization motifs reported in the literature.

Ordered Nanoporous Carbons with Broadly Tunable Pore Size Using Bottlebrush Block Copolymer Templates.

We report the preparation of ordered porous carbon materials with tailored pore sizes selected between 16 and 108 nm using bottlebrush block copolymers (BBCPs) as templates. The nanoporous carbons are prepared via the cooperative assembly of polydimethylsiloxane-block-poly(ethylene oxide) (PDMS-b-PEO) BBCPs with phenol-formaldehyde resin yielding ordered precursor films, followed by carbonization. The assembly of PDMS-b-PEO BBCPs with the resin leads to films exhibiting a spherical morphology (PDMS as the minor domain) with uniform domain sizes between 18 and 150 nm in the bulk. The assembled PDMS sphere diameters scale linearly with BBCPs molecular weights, allowing precise control of domain size. Access to very large ordered domains is an enabling hallmark of BBCPs self-assembly, but reports of well-ordered spherical domains are not common. Carbonization of the ordered precursor films yields nanoporous carbon with uniform and tunable pore size. These nanoporous carbons are shown to exhibit excellent performance as supercapacitor electrodes with capacitance reaching up to 254 F g-1 at a current density of 2 A g-1.

Symbiotic Self-Assembly Strategy toward Lipid-Encased Cross-Linked Polymer Nanoparticles for Efficient Gene Silencing.

A novel "symbiotic self-assembly" strategy that integrates the advantages of biocompatible lipids with a structurally robust polymer to efficiently encapsulate and deliver siRNAs is reported. The assembly process is considered to be symbiotic because none of the assembling components are capable of self-assembly but can form well-defined nanostructures in the presence of others. The conditions of the self-assembly process are simple but have been chosen such that it offers the ability to arrive at a system that is noncationic for mitigating carrier-based cytotoxicity, efficiently encapsulate siRNA to minimize cargo loss, be effectively camouflaged to protect the siRNA from nuclease degradation, and efficiently escape the endosome to cause gene knockdown. The lipid-siRNA-polymer (L-siP) nanoassembly formation and its disassembly in the presence of an intracellular trigger have been extensively characterized experimentally and through computational modeling. The complexes have been evaluated for the delivery of four different siRNA molecules in six different cell lines, where an efficient gene knockdown is demonstrated. The reported generalized strategy has the potential to make an impact on the development of a safe and effective delivery agent for RNAi-mediated gene therapy that holds the promise of targeting several hard-to-cure diseases.

Role of Oligoethylene Glycol Side Chain Length in Responsive Polymeric Nanoassemblies.

An oft-desired feature of a responsive nanomaterial is that it should undergo disassembly or morphological change upon application of a specific stimulus. The extent of response has been found to depend on factors such as the nature and the number of responsive functionalities incorporated into these particles. In this work, the length of oligoethylene glycol (OEG) side chains associated with the polymers has been shown to greatly influence the responsive behavior of polymeric nanoparticles. The integrity of these OEG-based polymeric assemblies was found to depend not only on the chemical cross-links but also on the physical cross-links in these aggregates in cases where the polymer chains bear long OEG side chains. The physical cross-linking in longer OEG side chain containing polymeric nanogels is present in the form of crystalline domains. Our results here highlight that these ethylene glycol-based hydrophilic units are not to be ignored as spectator units with water-solubilization characteristics but must be analyzed in the context of assembly stabilization and triggerability with the targeted stimulus.

Assessing Pair Interaction Potentials of Nanoparticles on Liquid Interfaces.

The pair interaction potentials of polymer-grafted silica nanoparticles (NPs) at liquid surfaces were determined by scanning electron microscopy, exploiting the nonvolatility of ionic liquids to stabilize the specimens against microscope vacuum. Even at near contact, individual, two-dimensionally well-dispersed NPs were resolved. The potential of mean force, reduced to the pair interaction potential for dilute NPs, was extracted with good accuracy from the radial distribution function, as both NP diameter and grafted polymer chain length were varied. While NP polydispersity somewhat broadened the core repulsion, the pair potential well-approximated a hard sphere interaction, making these systems suitable for model studies of interfacially bound NPs. For short (5 kDa) poly(ethylene glycol) ligands, a weak (< kB T) long-range attraction was discerned, and for ligands of identical length, pair potentials overlapped for NPs of different diameter; the attraction is suggested to arise from ligand-induced menisci. To understand better the interactions underlying the pair potential, NP surface-binding energies were measured by interfacial tensiometry, and NP contact angles were assessed by atomic force microscopy and transmission electron microscopy.

Functional polymers for growth and stabilization of CsPbBr3 perovskite nanoparticles.

We introduce an approach to synthesize polymer-stabilized CsPbBr3 perovskite nanoparticles (NPs) using ammonium bromide-functionalized polymers as both bromide precursors and stabilizing ligands. The polymer-passivated NPs exhibit significant advantages over conventional perovskite NPs owing to their facile dispersion in polymer matrices and enhanced optoelectronic stability.