Metallic nanostructures in a polymer matrix and substrate fabrication and structural characterization

Metal nanostructures are of considerable interest in the field of plasmonics and metamaterials and could have a wider impact if they are successfully embedded in a stable, inert and flexible polymer matrix. Fabrication of such structures is challenging for a variety of reasons including thermal stability, material compatibility with processing steps and general handling of material. In this work we have demonstrated the fabrication of metal nanostructures and embedded them in a polymer. Furthermore, these structures were fabricated on a flexible polymer membrane and detached from a carrier substrate. Characterization of these structures was performed with SEM, TEM and EDS.     

Nano-enabled microtechnology: polysulfone nanocomposites incorporating cellulose nanocrystals

Microchannel devices hold the potential to transform many separation processes. This preliminary study investigated the feasibility of incorporating cellulose nanocrystals (CNXLs) into polysulfone, a commonly used ultrafiltration membrane polymer. Incorporating CNXLs into non-water soluble polymers without aggregation has been problematic. A solvent exchange process was developed that successfully transferred an aqueous CNXL dispersion into the organic solvent N-methylpyrrolidone (NMP), which is a solvent for polysulfone (PSf). Films were prepared from the solution of PSf in NMP with dispersed CNXLs by a phase inversion process. Films were then examined by scanning electron microscopy and tested for their transport and mechanical properties. The interaction between the polymer matrix and the CNXL filler was studied by means of thermogravimetric analysis (TGA), which suggested a close interaction between the polymer and filler at the 2% filler loading. The tensile modulus showed a large increase beyond 1% filler loading, which could be due to a percolation effect. The water vapor transport rate increased with increase in filler loading. Agglomeration of the CNXLs seemed to be taking place at filler loadings >7%.     

Synthesis and post-processing of nanomaterials using microreaction technology

A critical barrier to the routine use of nanomaterials is the tedious, expensive means of their synthesis. Microreaction technology takes advantage of the large surface area-to-volume ratios within microchannel structures to accelerate heat and mass transport. This accelerated transport allows for rapid changes in reaction temperatures and concentrations leading to more uniform heating and mixing which can have dramatic impacts on macromolecular yields and nanoparticle size distributions. Benefits of microreaction technology include higher yield and reactant conversion, better energy efficiency and less by-product generation. Microreactors can help minimize the environmental impact of nanoproduction by enabling solvent free mixing, integrated separation techniques and reagent recycling. The possibility of synthesizing nanomaterials in the required volumes at the point-of-use eliminates the need to store and transport potentially hazardous materials and provides the flexibility for tailoring complex functional nanomaterials. Recognizing these benefits for nanosynthesis, continuous flow microreactors have been used by several research groups to synthesize and characterize nanomaterials. An overview of these efforts and issues related to scale up and other post synthesis processes such as separation and deposition are presented in this paper.     

Robust, functionalizable, nanometer-thick poly(acrylic acid) films spontaneously assembled on oxidized aluminum substrates: structures and chemical properties

Immersion of oxidized aluminum substrates in ethanol solutions of poly(acrylic acid) (PAA), followed by extensive solvent immersion, results in tenaciously chemisorbed, nanometer scale, controllable thickness films for a wide range of solution concentrations and molecular weights. Atomic force microscope images reveal isolated polymer globules from adsorption in low-concentration solutions with crossover to conformal, highly uniform, nanometer-thickness films at higher concentrations, an indication that the chemisorbing chains start to overlap and trap underlying segments to form planar chemisorbed films only two or three chains in thickness. Quantitative IR reflection spectroscopy in combination with chemical derivitization on a standard set of 1.0(±0.2) nm thick films reveals a film structure with 5.5(±1) chemisorbed -CO(-)(2) groups/nm(2) and 6.3 unattached -CO(2)H groups/nm(2), with up to ～3.6/nm(2) available for chemical derivitization, a comparable number to typical self-assembled monolayer coverages of ～4-5 molecules/nm(2). Thermal treatment of the ～1 nm chemisorbed films, at even extreme temperatures of ～150 °C, results in almost no anhydride formation via adjacent -CO(2)H condensation, in strong contrast to bulk PAA, a clear indication that the films have a frozen glass structure with effectively no segment and side group mobility. Overall, these results demonstrate that these limiting thickness nanometer films provide a model surface for understanding the behavior of strongly bound polymer chains at substrates and show potential as a path to creating highly stable, chemically functionalized inorganic substrates with highly variable surface properties.