Lyotropic Hexagonal Ordering in Aqueous Media by Conjugated Hairy-Rod Supramolecules

We report on a series of experiments on hydrogels formed by supramolecular hairy-rod conjugated polymers and their lyotropic liquid crystalline behavior. The system is an ionic complex between negatively charged poly[2-(3-thienyl)ethyloxy-4-butylsulfonate)] backbones and cationic cetrimonium side chains. These hairy-rod supramolecules form stable isotropic solutions under dilute conditions with enhanced photoluminescence relative to the neat polymer itself. The system displays an isotropic-liquid crystalline transition on increasing concentration, resulting in the formation of a hexagonally ordered lyotropic mesophase in which the polymer chains are packed into hexagonally ordered rod-like assemblies. The mesophase is thermosensitive and can be isotropized by moderate heating. Although theoretically predicted, the observation of such lyotropic mesophases in conjugated polymers has not been reported to date. The results here are rationalized in terms of the uncharacteristically long side chains and inherent polydispersity of the system which appear necessary for stabilization of this mesophase. These results may provide new routes for the fabrication of well ordered conjugated polymer films from such solution ordered precursors for high performance electro-optic devices

Facile Alignment of Amorphous Poly(ethylene oxide) Microdomains in a Liquid Crystalline Block Copolymer Using Magnetic Fields: Toward Ordered Electrolyte Membranes

Large area microdomain alignment in poly(ethylene oxide-b-6-(4′-cyanobiphenyl-4-yloxy) hexyl methacrylate) block copolymers was successfully accomplished by the application of a 6 T magnetic field while cooling from elevated temperatures in the melt state. Small-angle X-ray scattering demonstrated that lamellar and cylindrical PEO microdomains aligned with their interfaces along the applied field, whereas the smectic layers of the liquid crystalline mesophase are perpendicular to the field. This is in agreement with the positive diamagnetic anisotropy of the cyano-biphenyl mesogen and a homogeneous anchoring condition at the intermaterial dividing surface (IMDS) between the two blocks. The alignment of the system is driven by the diamagnetic anisotropy of the smectic mesophase and not by the crystallization of PEO at lower temperatures. The addition of poly(acrylic acid) and LiClO4 salt result in the suppression of PEO crystallinity and stronger segregation between the polymer blocks leading to improved order in the material. The resulting films are well aligned over millimeter length scales of area and thickness. We use a novel continuous rotational annealing approach to break the degeneracy of the lamellar alignment, permitting facile directed assembly of the system during a single cooling step. Our experiments demonstrate the creation of well-aligned arrays of amorphous PEO domains over large length scales and offer a route to functional materials, in particular, for selective transport applications such as solid ionic electrolytes

Programmable Thermo- and Light-Responsive Hydrogel Actuator Reinforced with Bacterial Cellulose

Hydrogels are a promising class of materials for soft actuators and soft robots due in part to their biocompatibility and the tunability of their mechanical properties. Poor mechanical durability and limited options for localized stimuli-responsive actuation control limit their actuation performance, however. Here, we report a strategy to realize a multistimuli responsive hydrogel actuator with enhanced mechanical properties by exploiting the structural advantages of bacterial cellulose (BC). A BC-incorporated thermoresponsive poly­(N-isopropylacrylamide) (PNIPAM) hydrogel forms a semi-interpenetrating network that exhibits a higher Young’s modulus compared to the pure hydrogel. We observe a distinct dependence of the hydrogel moduli and pore sizes on BC content. Simultaneously, the presence of BC enhances thermo-mechanical actuation, attributed to the pore-size-dependent deswelling kinetics of the hydrogel. Directly attaching gold nanoparticles (AuNPs) to the BC surface allows AuNPs to be uniformly dispersed throughout the hydrogel. This enables local stimulation and programming thermo-mechanical actuation of the hydrogel via photothermal effects upon visible light irradiation. The developed programmable hydrogel actuator is expected to be an attractive candidate for smart soft robots that must exhibit remotely controlled, on-demand actuation

Nanocomposites of Vertically Aligned Single-Walled Carbon Nanotubes by Magnetic Alignment and Polymerization of a Lyotropic Precursor

We demonstrate a novel path for the fabrication of thin-film polymer nanocomposites containing vertically aligned single-walled carbon nanotubes (SWNTs). Liquid crystal mesophases of hexagonally packed cylindrical micelles orient with their long axes parallel to an applied magnetic field and template the alignment of SWNTs sequestered in the micellar cores. The mesophase is a stable single-phase material containing monomers that can be polymerized after nanotube alignment to form the nanocomposite polymer. The space-pervasive nature of magnetic fields and the tunable physicochemical properties of multicomponent mesophases make this an attractive approach that can be leveraged for application in diverse nanocomposite systems

Programmable Thermo- and Light-Responsive Hydrogel Actuator Reinforced with Bacterial Cellulose

Hydrogels are a promising class of materials for soft actuators and soft robots due in part to their biocompatibility and the tunability of their mechanical properties. Poor mechanical durability and limited options for localized stimuli-responsive actuation control limit their actuation performance, however. Here, we report a strategy to realize a multistimuli responsive hydrogel actuator with enhanced mechanical properties by exploiting the structural advantages of bacterial cellulose (BC). A BC-incorporated thermoresponsive poly­(N-isopropylacrylamide) (PNIPAM) hydrogel forms a semi-interpenetrating network that exhibits a higher Young’s modulus compared to the pure hydrogel. We observe a distinct dependence of the hydrogel moduli and pore sizes on BC content. Simultaneously, the presence of BC enhances thermo-mechanical actuation, attributed to the pore-size-dependent deswelling kinetics of the hydrogel. Directly attaching gold nanoparticles (AuNPs) to the BC surface allows AuNPs to be uniformly dispersed throughout the hydrogel. This enables local stimulation and programming thermo-mechanical actuation of the hydrogel via photothermal effects upon visible light irradiation. The developed programmable hydrogel actuator is expected to be an attractive candidate for smart soft robots that must exhibit remotely controlled, on-demand actuation

Stable Sequestration of Single-Walled Carbon Nanotubes in Self-Assembled Aqueous Nanopores

We demonstrate the ability to stably sequester individual single-walled carbon nanotubes (SWNTs) within self-contained nanometer-scale aqueous volumes arrayed in an organic continuum. Large areal densities of 4 × 10⁹ cm^–2 are readily achieved. SWNTs are incorporated into a surfactant mesophase which forms 2.3 nm diameter water channels by lyotropic self-assembly. Near-infrared fluorescence spectroscopy demonstrates that the SWNTs exist as well-dispersed tubes that are stable over several months and through multiple cycles of heating and cooling. Absence of physical distortion of the mesophase suggests that the SWNTs are stabilized by adsorbed surfactants that do not extend considerably from the surface. Our findings have important implications for templated assembly of carbon nanotubes using soft mesophases and the development of functional nanocomposites

Morphology Development in Thin Films of a Lamellar Block Copolymer Deposited by Electrospray

Electrospray has been recently advanced as a novel approach for the continuous deposition of self-assembled block copolymer thin films. It represents an analogue of physical vapor deposition in which the development of well-ordered microstructures is predicated on relatively rapid relaxation of the polymer compared to its rate of deposition. Here we describe the morphology development of a lamellae-forming poly­(styrene-<i>b</i>-4-vinylpyridine) deposited by electrospray. Morphology was considered in the context of relative changes of the deposition and relaxation rates, with the latter significantly affected in some cases by the presence of residual solvent. We observe that the presence of residual solvent in deposited material accelerates the equilibration kinetics such that well-ordered alternating lamellar morphologies could be produced at deposition rates as high as 55 nm/min under “wet” spray conditions, whereas hexagonally packed micelles were produced when the polymer was deposited free of solvent, denoted as the “dry” spray limit. Molecular weight (MW) plays an important role in equilibration kinetics in the “dry” limit with a transition from poorly ordered to well-ordered lamellae produced by reducing MW. Film morphology was largely insensitive to temperature and flow rate over a broad range from 150 to 210 °C and from 3 to 18 μL/min respectively, although the orientation of the lamellae switched from parallel to perpendicular at elevated flow rates, potentially due to the influence of rapid solvent evaporation

Programmable Thermo- and Light-Responsive Hydrogel Actuator Reinforced with Bacterial Cellulose

Hydrogels are a promising class of materials for soft actuators and soft robots due in part to their biocompatibility and the tunability of their mechanical properties. Poor mechanical durability and limited options for localized stimuli-responsive actuation control limit their actuation performance, however. Here, we report a strategy to realize a multistimuli responsive hydrogel actuator with enhanced mechanical properties by exploiting the structural advantages of bacterial cellulose (BC). A BC-incorporated thermoresponsive poly­(N-isopropylacrylamide) (PNIPAM) hydrogel forms a semi-interpenetrating network that exhibits a higher Young’s modulus compared to the pure hydrogel. We observe a distinct dependence of the hydrogel moduli and pore sizes on BC content. Simultaneously, the presence of BC enhances thermo-mechanical actuation, attributed to the pore-size-dependent deswelling kinetics of the hydrogel. Directly attaching gold nanoparticles (AuNPs) to the BC surface allows AuNPs to be uniformly dispersed throughout the hydrogel. This enables local stimulation and programming thermo-mechanical actuation of the hydrogel via photothermal effects upon visible light irradiation. The developed programmable hydrogel actuator is expected to be an attractive candidate for smart soft robots that must exhibit remotely controlled, on-demand actuation

Programmable Thermo- and Light-Responsive Hydrogel Actuator Reinforced with Bacterial Cellulose

Hydrogels are a promising class of materials for soft actuators and soft robots due in part to their biocompatibility and the tunability of their mechanical properties. Poor mechanical durability and limited options for localized stimuli-responsive actuation control limit their actuation performance, however. Here, we report a strategy to realize a multistimuli responsive hydrogel actuator with enhanced mechanical properties by exploiting the structural advantages of bacterial cellulose (BC). A BC-incorporated thermoresponsive poly­(N-isopropylacrylamide) (PNIPAM) hydrogel forms a semi-interpenetrating network that exhibits a higher Young’s modulus compared to the pure hydrogel. We observe a distinct dependence of the hydrogel moduli and pore sizes on BC content. Simultaneously, the presence of BC enhances thermo-mechanical actuation, attributed to the pore-size-dependent deswelling kinetics of the hydrogel. Directly attaching gold nanoparticles (AuNPs) to the BC surface allows AuNPs to be uniformly dispersed throughout the hydrogel. This enables local stimulation and programming thermo-mechanical actuation of the hydrogel via photothermal effects upon visible light irradiation. The developed programmable hydrogel actuator is expected to be an attractive candidate for smart soft robots that must exhibit remotely controlled, on-demand actuation

Dual-Functionality Fullerene and Silver Nanoparticle Antimicrobial Composites via Block Copolymer Templates

We present the facile prepartion of C₇₀ and Ag nanoparticle (NP) loaded block copolymer (BCP) thin films, with C₇₀ and Ag NPs working in tandem to provide virucidal and bactericidal activities, respectively. Polystyrene-<i>block</i>-poly-4-vinylpyridine (PS-P4VP) was used as a template, allowing C₇₀ integration into PS domains and in situ formation of Ag NPs in P4VP domains, while providing control of the nanoscale spatial distribution of functionality as a function of BCP molecular weight (MW). C₇₀ loaded PS-P4VP films were found to generate significant amounts of ¹O₂ under visible light illumination with no apparent dependence on BCP MW. An analogous C₇₀ loaded PS homopolymer film produced notably less ¹O₂, highlighting a possible critical role of morphology on C₇₀ photoactivity. The antimicrobial activity of Ag NP and C₇₀ loaded composites against the model PR772 bacteriophage and Escherichia coli was assessed, finding synergistic inactivation afforded by the dual functionality. BCPs were demonstrated as versatile platforms for the preparation of multifunctional antimicrobial coatings toward combating diverse microbial communities