Annette M. Jacobson

Dry Spinning Based Spinneret Based Tunable Engineered Parameters (STEP) Technique for Controlled and Aligned Deposition of Polymeric Nanofibers

Polymeric nanofibers are finding increasing number of applications and hold the potential to revolutionize diverse fields such as tissue engineering, smart textiles, sensors, and actuators. Aligning and producing high aspect ratio fiber arrays (length/diameter > 2 000) in the sub-micron and nanoscale diameters has been challenging due to fragility of polymeric materials, thus making it difficult to deposit them as one dimensional structures functionally interfaced with other systems. Here, we present a pseudo dry spinning technique which allows precise control on fiber diameters and further allows deposition of fiber arrays in aligned configurations. Control on fiber diameters ranging from 50-500 nm and having lengths of several millimeters is achieved by altering the polymeric solution concentration. In the dilute and semi-dilute unentangled concentration domain droplets or beaded fibers are observed to form. Smooth uniform diameter fibers are observed to form at the onset of semi-dilute entangled concentration regime. For a given molecular weight, the increase in fiber diameter with increasing solution concentration is attributed to both the increase in the entanglement density and the decrease in the radius of gyration of solvated polymer molecules. Using this technique polymeric fiber arrays in single and multiple layers are demonstrated which can be used towards developing strong textiles, biological scaffolds, and sensor networks.

Effect of nonionic surfactant addition on bacterial metabolism of naphthalene: Assessment of toxicity and overflow metabolism potential

Abstract Two factors potentially accounting for the variability of bioremediation outcomes when surfactant micelles are used to increase polycyclic aromatic hydrocarbon (PAH) bioavailability were investigated: (1) surfactant toxicity and (2) the link between microbial metabolism and the intended effect of surfactant addition, enhanced solubilization and mass transfer from a solid phase. The nonionic surfactant, octaethyleneglycol mono n -dodecyl ether, did not alter the metabolism of succinate and glucose by an isolate from a creosote-contaminated soil indicating that the surfactant is nontoxic. When the culture was supplied with solid naphthalene, growth was limited by the dissolution of solid naphthalene after the aqueous-phase naphthalene was depleted. Moreover, increasing dissolution rate by increasing interfacial surface area increased the microbial growth rate. However, increasing bioavailability further by increasing interfacial surface area, introducing convective mass transfer, and adding surfactant were all found to reduce growth rate and prompt incomplete metabolism of naphthalene to a compound whose UV absorption corresponds to 1,2-naphthaquinone. Lowering the surfactant concentration diminished the metabolic overflow and permitted sustained growth. The results suggest that different mismatches between solubilization/mass transfer and metabolic capacity may be among the factors responsible for variable bioremediation outcomes.

Aqueous phase fluorescence quenching technique for measuring naphthalene partition coefficients in nonionic surfactant micelles.

A methodology is presented for determining the partition coefficients for polycyclic aromatic hydrocarbons (PAHs) distributed between the aqueous and the micellar pseudophases of nonionic surfactant solutions. The methodology entails measuring total PAH fluorescence and then using varying copper sulfate concentrations to quench the fluorescence contribution from aqueous pseudophase PAH. Additionally, front-surface sample analysis and absorption corrections to counteract inner-filter effects were used to extend the PAH concentration range over which quenching can be used. The methodology was tested by determining the partitioning of a model PAH (naphthalene) when the nonionic surfactant, octaethylene glycol mono-n-dodecyl ether (C 12 E 8 ), was present. Because the aqueous pseudophase is probed, both saturated and unsaturated systems were examined. Thus, the partition measurements are less restricted than those provided by frequently used analyses that must assume the aqueous pseudophase is saturated in order to close the solubilizate mass balance. The value obtained at saturation with naphthalene was in reasonable agreement with the partition coefficient (log K m ) for naphthalene in a similar nonionic surfactant. Moreover, log K m increased from 4.47 at saturation (0.64 mM naphthalene in 1.88 mM surfactant) to 5.03 at 0.057 mM naphthalene (also in 1.88 mM surfactant). In practice, the methodology may prove useful for characterizing partitioning behavior under the varied conditions found in the field, designing surfactant-enhanced biodegradation experiments, and ascertaining the effects of surfactant solubilization on PAH biodegradation rate