HYDROGEN BOND DIRECTED SELF-ASSEMBLY OF π-SYSTEMS
Ronald K. Castellano
Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, FL 32611-7200, USA
Although "ordered" organic π-conjugated assemblies outperform "disordered" ones in many optoelectronic device applications, we are far from being able to port the well-understood supramolecular recipes of π-systems from solution to solid-state device environments. For the past several years we have been exploring hydrogen bond (H-bond) directed self-assembly of π-systems along these lines, for example, to enhance their absorption and charge transport properties for organic photovoltaic (OPV) applications. Various examples of oligothiophenes outfitted with heterocycles capable of forming H-bonded "rosettes" will be discussed in this context. The second part of the talk will introduce new monomers derived from [2.2]paracyclophane (pCp) that are capable of robust H-bond directed self-assembly into one-dimensional nanostructures in solution and the solid state. The design introduces transannular (intramolecular) H-bonds between pairs of pseudo-ortho-positioned amides as a way to preorganize the molecules for intermolecular H-bonding with two neighbors. The result is formation of homochiral, one-dimensional pCp stacks that show supramolecular polymer signatures in solution.
Functional Biomaterials via Modification of Kraft Lignin
Anthony N. Cauley, James N. Wilson
Department of Chemistry, University of Miami, 1301 Memorial Drive, Coral Gables, FL 33146, United States
Lignin, a cross-linked phenolic polymer found in plant cell walls, is the main contributor of strength and structure in wood. It is a byproduct of the paper and agricultural industry with several different isolation methods. Kraft lignin, with high phenolic hydroxyl content, can be readily modified via SN2 reaction to introduce numerous different functional groups. The modified lignins will self-assemble into nanostructures that can act as a “container” for organic dyes. The supramolecular assembly of lignin nanocontainer host and molecular guest lends itself to biologically relevant applications such as delivery and sequestration. Also, the substitution reactions can be used for introducing bio-orthogonal functional groups and subsequent conjugation chemistry to coat the surface in sensing molecules. This will open a new avenue towards novel polymer-bioconjugates that combine the utility of polymers with the functionality of biomolecules. Overall, lignin is a versatile material that has been underutilized as a renewable chemical resource and its amphiphilic nature can be easily modified for use in a variety of applications.
STABLE PICKERING EMULSIONS USING JANUS PARTICLES VIA MICROFLUIDICS
Bobby Haney1, Liheng Cai2, Dong Chen2, David A. Weitz2, Subramanian Ramakrishnan1
1Chemical and Biomedical Engineering - FAMU-FSU College of Engineering, Tallahassee FL 32310
2Department of Physics, Harvard University, Cambridge MA 02138
Stable Pickering emulsions are important to systems where controlled confinement of an oil or water phase is critical to its applications (enhanced oil recovery). The stability of the Pickering emulsions depends on the wetting properties of the particle and hence there is a need to control the chemistry of the particles and tune the surface tensions to enhance stability. In this regard, “Janus” particles with both hydrophobic (hb) and hydrophilic(hl) portions have recently been used to form stable emulsions. Stability can be enhanced and controlled by tuning the hb/hl ratios, concentration of particles, and size.
In this work we demonstrate a simple and reproducible method using glass capillary microfluidics to synthesize “Janus” particles with varying hb and hl domains. Flowrates of the chemical constituents were varied to control particle sizes (125- 400 microns) and hb/hl domain volume ratios (0.7 – 5.8). Using UV light, these droplets were cross-linked via photo-polymerization to form fairly monodispersed particles. These particles were used to make very stable water in oil and oil in water Pickering emulsions where the size of the emulsions were controlled by changing the size of the Janus particles. These large particle sizes permit un-aided visualization of particle stabilized emulsions.
Amphiphilic Homopolymers via Successive Post-Polymerization Modification Reactions
Tomohiro Kubo,a Maxym Tansky,a Kyle C. Bentz,a Kristin C. Powell,b C. Adrian Figg,a Jeremy L. Swartz,a Anuj Chauhan,b Daniel A. Savin,a Brent S. Sumerlin*a
a George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, PO Box 117200, Gainesville, Florida 32611, United States
b Department of Chemical Engineering, University of Florida, 1030 Center Drive, Gainesville, Florida 32611, United States
We demonstrated the systematic preparation of amphiphilic homopolymers, which exhibit greater tunability of their self-assembly behaviors, via post-polymerization modification. Successive nucleophilic aromatic substitution of 2,4,6-trichloro-1,3,5-triazine made a modular and facile synthesis possible, allowing for the systematic investigation of structure-property relationships. Light scattering measurements, dye encapsulation, and water-oil interfacial tension measurements indicated successful formation of amphiphilic homopolymers and provided greater insight into their solution properties.
Gold Nanoparticle-Based, Paper Devices for Rapid and Sensitive Colorimetric and Electrochemical Biosensing
Pingping Liang, Bhargav Guntupalli, Haixiang Yu and Yi Xiao*
Department of Chemistry and Biochemistry, Florida International University, 11200 SW 8th Street, Miami, FL, 33199. *Corresponding author: email@example.com
Paper-based devices are an attractive option for colorimetric and electrochemical detection of small-molecule targets onsite for a number of reasons: (1) they are low-cost, lightweight, portable, disposable and user-friendly; (2) they can be manufactured with excellent reproducibility; (3) they require smaller volumes of sample and reagents. We have developed a paper-based device that consists of mixed cellulose ester paper supporting a wax-encircled, gold nanoparticle (AuNP)-coated film atop a cotton absorbent layer, sandwiched between two plastic cover layers. This paper-based device makes it possible to monitor NAD+-driven biochemical processes in the presence or absence of selective dehydrogenase inhibitors, with a readout that can be interpreted by naked-eye observation within 4 min in a 25 µL sample volume. In parallel, we have established an ambient filtration method that provides a simple and novel way to rapidly generate porous thin gold films (thickness ~40 nm) atop a layer of carbon nanotubes (CNTs) on paper for use as disposable electrodes, without the need for sophisticated instruments, clean-room environments, or any post-growth process. We have used these paper-based electrodes to achieve specific and simultaneous detection of dopamine and serotonin. Clearly, these hybrid films exhibit fast electron transfer and excellent electrocatalytic properties that are similar to purchased gold films, but with a larger electroactive surface that lends itself to more sensitive analyte detection.
Reversible-covalent hydrogels linked by photosensitive coumarin dimers
Christopher P. Kabb1, Christopher S. O'Bryan2, W. Gregory Sawyer2, Thomas E. Angelini2, Brent S. Sumerlin1
1. George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida
2. Department of Mechanical and Aerospace Engineering, University of Florida
Coumarin derivatives undergo a [2+2] cyclization upon exposure to long-wave UV irradiation (365 nm). This process can be reversed using short-wave UV light (254 nm) to revert the dimers to their monomeric form. Therefore, networks crosslinked by coumarin groups are an ideal candidate as reversible-covalent gels. In this work, copolymerization of coumarin-containing monomers with a hydrophilic comonomer resulted in water soluble, linear polymers. These “prepolymers” were irradiated with long-wave UV in the absence of a photoinitiator to yield free-standing hydrogels. Importantly, the gels were reverted back to soluble copolymers upon short-wave UV irradiation. This material provides an opportunity for preparing patterned hydrogels through a post-gelation photoetching method. Traditional limitations of this technique, such as the requirement for uniform etching in one direction, have been overcome by combining these materials with a 3D soft matter printing methodology. We have printed cylinders in which the interior coumarin gel is surrounded by a nondegradable gel, and upon exposure of these cylinders to short-wave UV irradiation, the coumarin gel is reverted to soluble prepolymers and washed away to yield a thin, hollow hydrogel tube.
Next-Generation Oil Dispersants from Hollow Amphiphilic Nanocapsules
a) George & Josephine Butler Polymer Research Laboratory, Center for Macromolecular Science & Engineering, Department of Chemistry, University of Florida, Gainesville, FL, USA
b) Tulane University, Chemistry Department, New Orleans, LA, USA. E
Hollow amphiphilic crosslinked nanocapsules were synthesized by sequential grafting-from of crosslinked hydrophobic polycaprolactone (PCL) via ring-opening polymerization and grafting-to of hydrophilic poly(ethylene glycol) (PEG) onto 70 nm silica nanoparticles, followed by removal of the silica core. To accomplish the crosslinking of the PCL layer a bis-caprolactone monomer was used. The effects on the brush properties of PCL grafted silica nanoparticles with crosslinker were investigated. Incorporation of only 0.25 mol% crosslinker in the bulk grafting reaction resulted in dramatic effects, such as significantly enhanced brush length and high chain molecular weight dispersities. Hollow PCL nanocapsules were synthesized by performing the grafting reaciton of PCL with 2.5 mol% crosslinker under dilute conditions. Upon removal of the silica core, a significant increase in hydrodynamic radius was observed due to the relief of constrain of surface tethered chain ends and swelling in a good solvent. PEG was then coupled to particles grafted with crosslinked PCL to yield amphiphilic block polymer grafted silica nanoparticles, which displayed excellent dispersibility in water, and resulted in a contraction of the PCL layer, as determined by dynamic light scattering. Core removal of the amphiphilic block polymer grafted silica nanoparticles gave hollow amphiphilic crosslinked nanocapsules which displayed significant swelling in good, non-selective solvent conditions, and a collapsed hydrophobic core block in aqueous conditions. Finally, the amphiphilic materials, both before and after core removal, were determined to be effective at stabilizing hydrocarbons in water, with the hollow nanocapsules having ca. 15 times greater uptake capacity.
Design principles for crystalline polymers: packing, polymerization mechanism and applications to energy conversion
Jose L. Mendoza-Cortes
†Department of Chemical & Biomedical Engineering, FAMU-FSU College of Engineering and
‡Scientific Computing Department, Materials Science and Engineering Program, High Performance Material Institute, Condensed Matter Theory-National High Magnetic Field Laboratory, Florida State University, Tallahassee Florida 32310, United States
Computational chemistry and materials science algorithms are now powerful enough that they can predict many properties of materials and molecules before they are synthesized. This new tool has allow us to start designing crystalline polymers. In the first part of the talk, I will discuss some principles we have been using to design the packing of crystalline polymers, then we will discuss the polymerization mechanism of a classic polymeric reaction and finally, we will discuss the application of several of these new materials to energy storage (hydrogen storage) and energy conversion (thermoelectrics).