Luis B. Modesto-Lopez

Electrospray-assisted characterization and deposition of chlorosomes to fabricate a biomimetic light-harvesting device

Photosynthesis is an efficient process by which solar energy is converted into chemical energy. Green photosynthetic bacteria such as Chloroflexus aurantiacus have supramolecular antenna complexes called chlorosomes attached to their cytoplasmic membrane that increase the cross section for light absorption even in low-light conditions. Self-assembled bacteriochlorophyll pigments in the chlorosome interior play a key role in the efficient transfer and funneling of the harvested energy. In this work it was demonstrated that chlorosomes can be rapidly and precisely size-characterized online in real time using an electrospray-assisted mobility-based technique. Chlorosomes were electrospray-deposited onto TiO2 nanostructured films with columnar morphology to fabricate a novel biomimetic device to overcome the solvent compatibility issues associated with biological particles and synthetic dyes. The assembled unit retained the viability of the chlorosomes, and the harvesting of sunlight over a broader range of wavelengths was demonstrated. It was shown that the presence of chlorosomes in the biomimetic device had a 30-fold increase in photocurrent.

Size Distribution and Morphology of Liposome Aerosols Generated By Two Methodologies

Pulmonary delivery of sustained release formulations needs drug encapsulation in a suitable matrix, as well as the generation of aerosols with high lung penetration and suitable release characteristics. Nanometer sized liposomes offer the potential for biocompatibility, controlled release and easy internalization in the lung. For uniform dose delivery and drug release kinetics, it is of interest to understand generation techniques to obtain aerosols containing nearly monodispered nanometer sized dry particles. Two aerosolization techniques, air-jet atomization and electrohydrodynamic atomization (EHDA) were studied to identify conditions under which the inclusion of one-liposome-per-drop could be achieved. In air-jet atomization, low lipid concentrations resulted in a unimodal aerosol with a median mobility diameter of 94 (± 3.5) nm, while higher concentrations led to larger median diameters, implying possible inclusion of multiple liposomes per drop. In EHDA, tuning drop sizes in the range of 130 to 200 nm, as well as the use of high lipid concentrations, resulted in a bimodal aerosol distribution, with peaks at 35 and 100 nm mobility diameters. TEM images of the liposome aerosol from EDHA showed fused liposomes, resulting in cylindrical structures with different physical diameters. It was hypothesized that deformation of liposomes to cylindrical structures in the micro-capillary liquid tip of the electrospray, and interactions along the axial or cross sectional surfaces led to dry particles with different mobility sizes.

Films of Graphene Nanomaterials Formed by Ultrasonic Spraying of Their Stable Suspensions

Graphene, a two-dimensional carbon allotrope, exhibits excellent optoelectronic properties. The assembly of graphene into films provides a platform to deepen the study of its interaction with varying surfaces, to engineer devices, and to develop functional materials. A general approach to produce graphene films consists of preparing a dispersion and laying it on a substrate of choice, followed by solvent evaporation. Here, we report the preparation of stable suspensions of new types of graphene nanomaterials namely, graphene nanoflowers (GNFs) and multi-layer graphene (MLG) flakes, in ethanol, N,N-dimethylformamide (DMF), and N-methyl-2-pyrrolidone (NMP). Sprayable suspensions of both GNFs and MLG were prepared in DMF/ethanol, which showed high stability, without addition of any surfactant. The stable suspensions were used to deposit micrometer-thick MLG/GNF films on glass substrates. Calculations of initial droplet size and of timescale of droplet evaporation are performed and possible thermophoretic effects on droplet deposition discussed as well. Coating glass substrates with a methacrylic acid–methyl methacrylate (MA) copolymer prior to the deposition significantly improved the adhesion of the nanomaterials to the substrate. With the MA coating, a substrate coverage of nearly 100% was achieved at 14-min spraying time for 0.05 wt% GNF and 0.1 wt% MLG suspensions. Raman spectra of the GNF and MLG films reveal that the films were made of MLG in which the individual graphene layers rotated from each other as in turbostratic graphene. This work provides a general approach to prepare graphene nanomaterial suspensions and to create films for a variety of applications. The spraying process applied in the current work is highly scalable and allows control of film characteristics through process parameters. Copyright 2015 American Association for Aerosol Research

Visualization and Size-Measurement of Droplets Generated by Flow Blurring® in a High-Pressure Environment

ABSTRACT Flow Blurring® (FB) atomization is a highly efficient method to produce aerosols. It originates from an unexpected turbulent back flow motion in the interior of the atomizer. The onset for the appearance of such pattern is dictated by a geometrical parameter, ϕ, that is, the ratio of the distance from the tip of the liquid feeding tube to the discharge orifice (H), and the diameter of the discharge orifice (D). In this work, a FB atomizer with a nominal ϕ = 1/6 was used to produce water and ethanol droplets into pressurized environments (>1 MPa). The droplet size distributions and mean droplet speeds were investigated using (1) direct visualization with an ultra-high-speed video camera coupled with an automated droplet measurement (ADM) program and (2) using a light scattering instrument. Light scattering measurements, with water and ethanol, varying the driving pressure to produce the aerosol (ΔP), indicate a power dependence of ∼2/5 of the dimensionless mean droplet diameter (/Do) on the dimensionless liquid flow rate (Q/Qo). At higher liquid flow rate, the optical resolution of the droplets is improved compared to lower volumetric flow rates, thus facilitating analyses with the ADM program. The approach outlined herein provides a guideline for characterization and implementation of the FB technology in high-pressure applications. Copyright

Oriented Single-Walled Carbon Nanotubes as Saturable Absorber for Passive Q-Switching of a Tm:KLuW Microchip Laser

A Tm:KLuW laser is Q-switched with a saturable absorber based on aligned SWCNTs, generating a maximum average output power of 260 mW with a slope efficiency of 12%. The shortest pulse duration is 97 ns.