Esteban E. Ureña-Benavides

Solvents for sustainable chemical processes

The properties and some key applications of solvents such as (1) supercritical fluids (SCFs), (2) gas-expanded liquids (GXLs) and organic-aqueous tunable solvents (OATS), (3) water at elevated temperature (WET), and (4) switchable solvents like reversible ionic liquids (RevILs) are discussed in this review. Each system offers a unique set of properties to enable alternative strategies for varied applications. These applications range from chemical transformations, product separation, catalyst recycling, nanomaterial processing, and CO2 capture. For each application, however, the common thrust is to enable greener and sustainable solutions for chemical processes.

Effect of jet stretch and particle load on cellulose nanocrystal-alginate nanocomposite fibers.

Alginate fibers have found many applications such as the preparation of dressings to treat exuding wounds, drug delivery, enzyme immobilization, etc.; however, their use is limited due to poor mechanical properties. Cellulose nanocrystals (CNCs) were isolated from cotton and introduced into calcium alginate fibers with the goal of improving their strength and modulus. The isolated CNCs are elongated nanoparticles of crystalline cellulose with an average length of 130 nm with a standard deviation (s) of 63 nm, an average width of 20.4 nm (s = 7.8 nm), and an average height of 6.8 nm (s = 3.3 nm). The CNCs were mixed with an aqueous sodium alginate dope solution and wet spun into a CaCl(2) bath to form fibers. It was found that if the apparent jet stretch (ratio of the fiber draw velocity to extrusion velocity) is kept constant, addition of the nanocrystals reduces the tensile strength and modulus of the material; however, a small concentration of CNCs in the dope solution increases the tensile energy to break and enables an increase in the fiber spinning apparent jet stretch ratio by nearly 2-fold at up to 25% CNCs load; the maximum ratio of 4.6 is observed at 25 wt % CNC loading as compared to a maximum of 2.4 for the native alginate. Mechanical testing showed a 38% increase in tenacity and a 123% increase in tensile modulus with 10 wt % CNCs loading and an apparent jet stretch of 4.2. The data suggest that alignment of the nanocrystals in the composites is a key factor influencing the mechanical properties. CNCs have potential to become a biocompatible, renewable, and cost-effective solution to reinforce alginate fibers.

Quantitative detection of single walled carbon nanotube in water using DNA and magnetic fluorescent spheres.

Carbon nanotubes (CNTs) possess unique properties that have led to an increase in their research and usage for a wide variety of fields. This growing demand of CNTs poses a major public health risk given its unregulated release into the environment. Unfortunately there is a significant information gap on the actual quantity of CNTs in the environment due to limitation of existing detection methods. This is mainly owing to the ubiquitous carbon chemistry of CNT. In response we developed a method (CNT-capture method) that is able to structurally differentiate CNT from other interference carbon materials in an aqueous medium. The affinity between single walled nanotubes (SWNTs) and specific single stranded DNA (ssDNA) was employed to capture SWNTs in water. SWNT-specific separation was obtained via magnetic separation. Dual fluorescent labels attached to sandwich ssDNA probes were used for quantification. The specific affinity between DNA and SWNTs was verified and no significant side-interactions were observed. With optimized incubation duration (30 min) and buffer composition (10(-7) % sodium dodecyl sulfate and pH 7.9), a calibration curve of quantification (R(2) = 0.90) was obtained with a range of SWNT concentration (0.05-10 μg/mL) against graphene as a planar analog. Comparison to other spectroscopy based methods was carried out to highlight the specificity and sensitivity of the presented method for CNT detection in aquatic sample.

Cellulose Nanocrystal Reinforced Alginate Fibers—Biomimicry Meets Polymer Processing

This research takes a biomimetic approach to the design of polymer nanocomposites and demonstrates structure-property relationships that are controllable via processing conditions. Cellulose nanocrystals (CNCs) measuring 130 nm (length) × 20.4 nm (width) × 6.8 nm (height) were isolated from cotton by sulfuric acid hydrolysis and were incorporated in an alginate fiber wet spinning dope solution. Incorporating CNCs within the alginate fiber enables a nearly two-fold increase in the apparent jet stretch (JA ), ratio of the linear draw speed to extrusion velocity. Fiber spinning at a constant JA resulted in an unexpected decrease in fiber modulus and increase in toughness. Alternatively, fiber spinning at the maximum JA resulted in modulus increases that are predicted by the Halpin-Tsai model and the Hui-Shia model. Wide-angle X-ray diffraction (WAXD) was used to elucidate the structure and orientation of cellulose nanocrystals (CNC) within the alginate nanocomposite fibers and provide correlations with mechanical property enhancements. The spread of the azimuthal intensity distribution of the CNC (2,0,0) reflection increased with higher CNC loads until the nanoparticles within the matrix spiraled around the longitudinal axis. The appearance of a spiral angle with increasing CNC load resulted in a step reduction in modulus and increase in toughness. Increased fiber stretching during spinning retarded the appearance of the spiral assembly and increased CNC alignment. This spiral orientation is also observed in native cellulose fibers as a microfibril angle and is deterministic of their mechanical properties.

Static light scattering of triaxial nanoparticle suspensions in the Rayleigh-Gans-Debye regime: application to cellulose nanocrystals

A simple method has been developed to measure the dimensions of triaxial nanoparticles through light scattering data. The application of Debyes expansion of the form factor has been extended beyond the second moment of the difference of distances (radius of gyration). Analytical expressions have been derived for the fourth and sixth moments that are valid for all nanoparticle shapes. The moments provide information about the aspect ratio of the nanoparticles regardless of the geometry. If a shape is assumed, simple algebraic expressions for the moments can be obtained for monodisperse and polydisperse samples, which can be used to solve for specific nanoparticle dimensions. The methods described here have been applied to static light scattering measurements of dilute aqueous suspension of triaxial cellulose nanocrystals isolated from cotton. When the polydispersity is included, the dimensions determined from light scattering data (6.4 × 28 × 152 nm) are in close agreement with atomic force microscopy measurements. This methodology can be easily applied to nanoparticles of complex shapes and extended to other scattering techniques; it would be especially useful for polymer based nanoparticles and biological macromolecules.