Characteristic Length of the Glass Transition in Isochorically Confined Polymer Glasses

We report the effect of isochoric confinement on the characteristic length of the glass transition (ξ_α) for polystyrene (PS) and poly­(4-methylstyrene) (P4MS). Utilizing silica-capped PS and P4MS nanoparticles as model systems, ξ_α values are determined from the thermal fluctuation model and calorimetric data. With decreasing nanoparticle diameter, ξ_α decreases, suggesting a reduction in the number of segmental units required for cooperative motion at the glass transition under confinement. Furthermore, a direct correlation is observed between ξ_α and the isochoric fragility (<i>m</i>_v) in confined polymers. Due to a nearly constant ratio of the isochoric to isobaric fragility in confined polymer nanoparticles, a correlation between ξ_α and <i>m</i>_v also implies a correlation between ξ_α and the volume contribution to the temperature dependence of structural relaxation. Lastly, we observe that when the fragility and characteristic length are varied in the same system the relationship between the two properties appears to be more correlated than that of across different bulk glass-formers

A One-Step and Scalable Continuous-Flow Nanoprecipitation for Catalytic Reduction of Organic Pollutants in Water

Efficient treatment of organic pollutants in water by a facile and green technique is a great challenge for environmental remediation. In this study, we report a simple and low-energy strategy for catalytic reduction of organic pollutants in water by continuous-flow flash nanoprecipitation. The one-step processing technique integrates rapid metal@polymer nanoparticle production and catalytic reaction in a continuous-flow fashion. Such a concept is successfully demonstrated for simultaneous formation of Au@polymer nanospheres and catalytic reduction of organic pollutants (e.g., methylene blue and 4-nitrophenol) in water. Furthermore, the catalytic reaction rate could be easily tuned by varying the processing parameters (e.g., feeding concentration). The activity of the nanocatalyst was demonstrated in five recycles without any detectable loss. The characteristics of continuous-flow mode make the one-step process scalable, promising processing methodology for wastewater treatment

Direct Measurement of the Local Glass Transition in Self-Assembled Copolymers with Nanometer Resolution

Nanoscale compositional heterogeneity in block copolymers can impart synergistic property combinations, such as stiffness and toughness. However, until now, there has been no experimental method to locally probe the dynamics at a specific location within these structured materials. Here, this was achieved by incorporating pyrene-bearing monomers at specific locations along the polymer chain, allowing the labeled monomers’ local environment to be interrogated via fluorescence. In lamellar-forming poly­(butyl methacrylate-<i>b</i>-methyl methacrylate) diblock copolymers, a strong gradient in glass transition temperature, <i>T</i>_g, of the higher-<i>T</i>_g block, 42 K over 4 nm, was mapped with nanometer resolution. These measurements also revealed a strongly asymmetric influence of the domain interface on <i>T</i>_g, with a much smaller dynamic gradient being observed for the lower-<i>T</i>_g block

A One-Step and Scalable Continuous-Flow Nanoprecipitation for Catalytic Reduction of Organic Pollutants in Water

Efficient treatment of organic pollutants in water by a facile and green technique is a great challenge for environmental remediation. In this study, we report a simple and low-energy strategy for catalytic reduction of organic pollutants in water by continuous-flow flash nanoprecipitation. The one-step processing technique integrates rapid metal@polymer nanoparticle production and catalytic reaction in a continuous-flow fashion. Such a concept is successfully demonstrated for simultaneous formation of Au@polymer nanospheres and catalytic reduction of organic pollutants (e.g., methylene blue and 4-nitrophenol) in water. Furthermore, the catalytic reaction rate could be easily tuned by varying the processing parameters (e.g., feeding concentration). The activity of the nanocatalyst was demonstrated in five recycles without any detectable loss. The characteristics of continuous-flow mode make the one-step process scalable, promising processing methodology for wastewater treatment

Transport and Stability of Laser-Deposited Amorphous Polymer Nanoglobules

We characterized the transport, i.e., time-of-flight, and nanoscale thermal properties of amorphous polymer nanoglobules fabricated via a laser-deposition technique, Matrix-Assisted Pulsed Laser Deposition (MAPLE). Here, we report the first experimental measurement of the velocity of polymer during MAPLE processing and its connection to nanostructured film formation. A nanoscale dilatometry technique using atomic force microscopy was employed to directly measure the thermal properties of MAPLE-deposited polymer nanoglobules. Similarly to bulk stable polymer glasses deposited by MAPLE, polymer nanoglobules were found to exhibit enhanced thermal stability and low density despite containing only thousands of molecules. By directly connecting the exceptional properties of the nanostructured building blocks to those of bulk stable glasses, we gain insight into the physics of glassy polymeric materials formed via vapor-assisted techniques

Confinement-Induced Change in Chain Topology of Ultrathin Polymer Fibers

Despite the several decades study of the confinement effect of the polymeric nanomaterials, how the confinement influences 1D polymeric fiber nanomaterials is little understood. Here, we report that confinement can render ultrathin polymeric fibers rigid. By observing the changes in the crystalline and amorphous morphologies of electrospun nylon-6 nanofibers with variations in diameter and shape, we reveal that their crystalline phase changes into highly packed, stable α phase when the diameter is smaller than 120 nm. In addition, the molecular motion of the amorphous chains is severely suppressed with decrease in nanofiber diameter, indicating that the amorphous chains are also closely packed, forming a rigid structure. Indeed, the change in chain topology by confinement suppressed the release of rhodamine B from the ultrathin nanofibers. These findings allow us new insights for the design and development of advanced 1D polymer nanomaterials

Core–Shell Fe₃O₄ Polydopamine Nanoparticles Serve Multipurpose as Drug Carrier, Catalyst Support and Carbon Adsorbent

We present the synthesis and multifunctional utilization of core–shell Fe₃O₄ polydopamine nanoparticles (Fe₃O₄@PDA NPs) to serve as the enabling platform for a range of applications including responsive drug delivery, recyclable catalyst support, and adsorbent. Magnetite Fe₃O₄ NPs formed in a one-pot process by the hydrothermal approach were coated with a polydopamine shell layer of ∼20 nm in thickness. The as prepared Fe₃O₄@PDA NPs were used for the controlled drug release in a pH-sensitive manner via reversible bonding between catechol and boronic acid groups of PDA and the anticancer drug bortezomib (BTZ), respectively. The facile deposition of Au NPs atop Fe₃O₄@PDA NPs was achieved by utilizing PDA as both the reducing agent and the coupling agent. The nanocatalysts exhibited high catalytic performance for the reduction of <i>o</i>-nitrophenol. Furthermore, the recovery and reuse of the catalyst was demonstrated 10 times without any detectible loss in activity. Finally, the PDA layers were converted into carbon to obtain Fe₃O₄@C and used as an adsorbent for the removal of Rhodamine B from an aqueous solution. The synergistic combination of unique features of PDA and magnetic nanoparticles establishes these core–shell NPs as a versatile platform for multiple applications

Spatially Distributed Rheological Properties in Confined Polymers by Noncontact Shear

When geometrically confined to the nanometer length scale, a condition in which a large portion of the material is in the nanoscale vicinity of interfaces, polymers can show astonishing changes in physical properties. In this investigation, we employ a unique noncontact capillary nanoshearing method to directly probe nanoresolved gradients in the rheological response of ultrathin polymer films as a function of temperature and stress. Results show that ultrathin polymer films, in response to an applied shear stress, exhibit a gradient in molecular mobility and viscosity that originates at the interfaces. We demonstrate, via molecular dynamics simulations, that these gradients in molecular mobility reflect gradients in the average segmental relaxation time and the glass-transition temperature

Additive Growth and Crystallization of Polymer Films

We demonstrated a polymeric thin film fabrication process in which molecular-scale crystallization proceeds with additive film growth, by employing an innovative vapor-assisted deposition process termed matrix-assisted pulsed laser evaporation (MAPLE). In comparison to solution-casting commonly adopted for the deposition of polymer thin films, this physical vapor deposition (PVD) methodology can prolong the time scale of film formation and allow for the manipulation of temperature during deposition. For the deposition of molecular and atomic systems, such a PVD manner has been demonstrated to facilitate molecular ordering and delicately manipulate crystalline morphology during film growth. Here, using MAPLE, we deposited thin films of a model polymer, poly­(ethylene oxide) (PEO), atop a temperature-controlled substrate with an average growth rate of less than 10 nm/h. The mechanism of deposition is sequential addition of nanoscale liquid droplets. We discovered that the deposition process leads to the formation of two-dimensional (2D) PEO crystals, composed of monolamellar crystals laterally grown from larger nucleus droplets. The 2D crystalline coverage and crystal thickness of the films can be manipulated with two processing parameters, deposition time, and temperature