Substantial improvement of nanotube processability by freeze-drying

Effects of Non-covalent Functionalization and Initial Mixing Methods on SWNT/PP and SWNT/EVOH Composites

We report that a simple, low-cost type of spray-freeze drying (SFD) significantly improves the dispersion of single-walled carbon nanotubes (SWNTs) in thermoplastic polymers. Conventional SFD requires costly specialized equipment and large amounts of material, both of which are impediments to laboratory research on nanomaterial composites. Our method uses more readily available equipment and can be adapted to use milligrams to grams of material. A household spray bottle containing an aqueous nanomaterial dispersion is used to spray the dispersion into a dish of liquid nitrogen. The resulting material is then lyophilized in a standard laboratory freeze dryer. The usefulness of this simplified method was explored by comparing the properties of polypropylene (PP) composites produced by this method to those produced by a previously reported rotary evaporation method in which the dispersion is vacuum-dried onto the polymer. The role of the initial dispersion state was explored by using pristine SWNTs as well as SWNTs stabilized by two common SWNT stabilizers: polyvinylpyrrolidone (PVP) and sodium dodecyl sulfate. Based on rheological, thermal, and morphological characterization, the porous friable structures produced by SFD resulted in better SWNT dispersion compared to composites produced by a previously reported rotary evaporation method. However, the PP/PVP-SWNT nanocomposites produced by both methods contained large aggregates. To verify that this aggregation behavior was the result of thermodynamic incompatibility between PP and PVP, ethylene vinyl alcohol (EVOH) nanocomposites containing PVP-SWNT were also produced using the SFD method. The results of this research show how a low-cost alternative to SFD along with careful consideration of compatibility is a promising approach to produce nanocomposites.

Loading, release profile and accelerated stability assessment of monoterpenes-loaded solid lipid nanoparticles (SLN)

Glycerol monostearate solid lipid nanoparticles (SLN) were produced by hot high-pressure homogenization technique to load alpha-pinene, citral, geraniol or limonene. SLN were composed of 1 wt.% monoterpene, 4 wt.% of Imwitor^® 900K as a solid lipid and 2.5 wt.% of Poloxamer188 as a surfactant. Empty SLN consisted of 5 wt.% of Imwitor^® 900K and 2.5 wt.% of Poloxamer188. The mean particles size (Z-Ave) and polydispersity index (PDI) of SLN were analyzed by dynamic light scattering (DLS), while the zeta potential (ZP) of each formulation were measured by electrophoretic light scattering. LUMiSizer^® was applied to calculate the velocity distribution in the centrifugal field and instability index. Drug release profile from SLN was analyzed using Franz cell diffusion cells assayed by UV-Vis spectrophotometry, whereas the gas chromatography technique was applied to determine the encapsulation parameters of volatile monoterpenes. The matrix state, polymorphism and phase behavior of SLN were studied by X-ray diffraction (XRD, low and wide angles) and differential scanning calorimetry (DSC). Selected monoterpenes were successfully loaded in glycerol monostearate SLN. A burst release profile within the first 15 min was observed for all formulations, being the modified release profile dependent on the type of monoterpene and on the encapsulation efficiency.

Production of ready-to-use few-layer graphene in aqueous suspensions

Graphene has promising physical and chemical properties such as high strength and flexibility, coupled with high electrical and thermal conductivities. It is therefore being incorporated into polymer-based composites for use in electronics and photonics applications. A main constraint related to the graphene development is that, being of a strongly hydrophobic nature, almost all dispersions (usually required for its handling and processing toward the desired application) are prepared in poisonous organic solvents such as N-methyl pyrrolidone or N,N-dimethyl formamide. Here, we describe how to prepare exfoliated graphite using a ball mill. The graphene produced is three to four layers thick and ∼500 nm in diameter on average, as measured by electron microscopy and Raman spectroscopy; can be stored in the form of light solid; and is easily dispersed in aqueous media. Our methodology consists of four main steps: (i) the mechanochemical intercalation of organic molecules (melamine) into graphite, followed by suspension in water; (ii) the washing of suspended graphene to eliminate most of the melamine; (iii) the isolation of stable graphene sheets; and (iv) freeze-drying to obtain graphene powder. This process takes 6-7 or 9-10 d for aqueous suspensions and dry powders, respectively. The product has well-defined properties and can be used for many science and technology applications, including toxicology impact assessment and the production of innovative medical devices.

Giant Permittivity Polymer Nanocomposites Obtained by Curing a Direct Emulsion

Near-percolated CNT-polymer composites are promising high-permittivity materials. The main challenge in the field consists of finding compromises that allow high permittivity and low losses in frequency ranges of interest. Using an emulsion approach and optimizing the size of the droplets and the curing procedure, we obtain unprecedented performances and measure giant permittivity larger than 20,000 at 100 Hz along with a conductivity below 10(-4) S/m.