Hybrid nanostructures for energy transfer and harvesting
Silca or Siloxane based nanoparticles; Synthesis and surface functionalization
Hybrid nanostructures derived from silica, or siloxanes have been the focus of intense research due to the unique possibilities to combine the properties of the organic moieties with those of the siloxane or silica matrix. Reliable synthesis of 2 to <100 nm sizes of these hybrid particles with a narrow average size distribution would provide opportunities to tailor organic moieties and polymer ligands (ranging from small molecules to functionalized molecules/dyes) in manners to depend upon the applications
Difficulties in functionalization of nanoparticle surface with various types of ligands and difficulties in dispersion in specific polymer matrices are the key factors slowing down the use of ligand functionalized nanoparticles into applications.
Recent research on organosilica hybrids, ormosils or silsesquioxanes and bridged silsesquioxanes has provided examples of tailoring various types of organic moieties onto particles for wide variety of applications.Such organosilica particles and/or bulk materials have potential applications as nano-fillers in polymer systems for use in adhesives, coatings, composites and dental fillings. Significant advances have been made towards their use in fuel cells, optic devices and sensors, much of which is carried out with bulk materials.
Recently, methods to take advantage of such hybrid nanoparticles have been much advanced by pioneering work from a few research groups. However, application of these hybrids towards solar cells remains unrevealed. It is highly desirable to tailor photoactive organic functionalities in such hybrids in terms of their potential applicability towards optoelectronic devices including photovoltaic. This will involve developing better synthetic methodologies, designing novel optical active hybrid nanostructures and assembling them in organic polymer matrices including compatible, newly designed block copolymer matrices.
Design and synthesis of functionalized siloxane nanoparticles for energy transfer and harvesting
Syntheses of organosilica nanoparticles are attracting, increasing attention due to the well known potential applications described in the introduction. The usual method used to prepare such hybrid ormosils is the well-known hydrolytic sol-gel route, which involves base or acid catalyzed hydrolysis and condensation reactions of monomeric alkoxy silane precursors in aqueous solvent systems. In addition to the hydrolytic sol-gel route, some other approaches have been developed in recent years by few other research groups to produce organosilicas, including a modified Stöber sol-gel route, a non-hydrolytic sol-gel route, miniemulsion polymerization and biomimetric approaches. Recently, Noda et al introduced miniemulsion polymerization in the presence of a non-ionic emulsifier to synthesize spherical methylsilsesquioxane particles with an average diameter of 0.2-2.0 μm. Later, this method was modified to yield a spherical organosilica network with controlled particle size from 3nm-15nm, using benzethonium chloride emulsifier in aqueous sodium hydroxide solution. To date, a range of organosilicas with the general formula [R2SiO3]n, (R is methyl, phenyl, ethyl, octyl, mercaptopropyl, vinyl, acrylic, aminopropyl, and isocyanate) has been synthesized using size controlled emulsion polymerization method and/or modified Stöber sol-gel routes.
Since the organic functional groups of these hybrid particles can fulfill two functions, including modification of the inorganic core and resulting in improved compatibility with a host matrix, it is desirable to improve these methodologies to obtain variety of organosilicas having reactive functional groups as well as fluorescence moieties including donor and acceptors. Indeed, there is less effort devoted to the synthesis of such silsesquioxane nanoparticles and there is no literature records describing optically active nanohybrids. Nonetheless, it is desirable tailoring organic functionalities to these particles in terms of their potential applications. Moreover, the capability of chemically tailoring the surface of silica nanoparticles made from Stöber method is limited due to their less surface coverage of ligands (less residual silanol groups) as well as the difficulties having functionalization with specific ligands.
Conjugated organic molecules have been the subjects of continuous interest for possible applications in electronic and optoelectronic devices or as photoactive materials. Synthetic efforts aimed at -conjugated systems having well-defined architectures are driven by the desire to impart specific optical and elesdctrical properties to materials by control of their molecular structure. Helicity is often an essential factor that can modulate the electronic properties of conjugated molecules and influence their solid-state self-organization.
Helicenes deserve interest both as polyconjugated systems and as chiral materials. Indeed they have been investigated as conjugated polymers, as macroscopic liquid crystalline fibers, as chiral aggregates with very high specific optical rotation, and also as chiral ligands in asymmetric catalysis. Moreover, these compounds have potential applications in asymmetric molecular recognition, nonlinear optics, liquid crystals, and circularly polarized luminescence (CPL) for back-lighting in LCD displays. Despite the popularity of helicenes and their potential applications, there is limited effort devoted to the design of highly functionalized photoactive helicenenes.
Recent advances have provided helicenes/chiral conjugated macromolecules being applied towards the fabrication of light-emitting diodes, field effect transistors, photodiodes, photovoltaic cells, fluorescent sensors and other devices.
One challenge in this area is to obtain materials with inherent chirality at the molecular level rather than from an aggregate or supramolecular structure. Recent research on these systems revealed that chirality or preferred helical confirmations can be achieved by introducing angular connectors (e.g. 1,3-phenylenes, 2,7-naphthylenes) to π-conjugated backbone. Also prior research on helical aromatic molecules evidenced that; these molecules can undergo spontaneous organization into macroscopic fibrous structures comprised of hexagonally arrayed columns of helicenes with aligned helix axes. The extraordinary strong chiral properties of such helicenes are now recognized as a key enabling factor for the development of synthetic approaches to nonracemic helicenes as organic materials. Our focus is to synthesize novel nonracemic helicenes and fine tune their optical properties as active layer for organic photovoltaics. The sub-tropics of this study include: 1) design and synthesis of novel helicenes/heterohelicenes and chiral π-conjugated macromolecules, and 2) assembly of functionalized helicenes on semiconducting nanaorods.
Facilities and Resources
Laboratory space designated to my research group includes four labs each approximately 400 square feet and each one includes a ventilation hood that is designed to carry out all the syntheses. All the labs are fully equipped for materials synthesis and post purifications. Undergraduate and graduate students have access to desk space in the laboratories.
Department of Chemistry
The department typically provides a reduced teaching load (usually a three-credit course per semester) for junior faculty with significant research activity and also supports the research by providing lab space and access to department capital equipments (NMR spectrometer (JEOL, 500 MHz), ATIR spectrometer (Spectrum One), Fluorescence spectrometer, UV-visible spectrometer, AFM, and GC/MS.
The department also provides access to basic laboratory supplies (routine glassware, for example) and pays for tanks of specialty gases. The department, in conjunction with the dean’s office and the Office of Sponsored Programs, provides travel support for the faculty member to attend meetings. The department also provides financial support for some student travel, especially when the students are presenting at national meetings.
Materials Characterization Center (MCC)
The MCC, which is closely affiliated with the department, has provided sample analyses at nominal cost and has also provided financial support for students and research supplies via several modest grants.
MCC is equipped with necessary equipments for elemental analysis, TGA, DCS and XRD analysis.
Ogden College Central Facility
Ogden college central facility is equipped with capital equipment such as, TEM, SEM, and fluorescence optical microscopes with three different filters. All faculties have access to all the central facilities including Biotechnology center and Material characterization center, which is available at no cost to the principal investigator.
- TEM (JEOL, 100CX): has options allowing it to be used at 120kV accelerating potential and as an STEM and SEM. It is equipped with an IXRF energy dispersive X-ray analysis system.
- SEM (JEOL 5400LV): This microscope has secondary electron and backscattered electron detectors. The secondary electron detector is used in high vacuum mode with conductive (e.g. gold coated) samples and has a resolution of around 25 nm. The backscattered electron detector can be used in high vacuum mode with conductive samples, or in low vacuum mode ("LV") with non-conductive samples. The resolution of the backscattered electron detector is roughly 250 nm. This instrument is also equipped with an IXRF energy dispersive X-ray analysis and digital imaging system. For most elements it has a sensitivity of 1 part per 200 but can analyze samples as small as 1 cubic micrometer.