Christina M. Othon

Ferroelectric polymer Langmuir-Blodgett films for nonvolatile memory applications

We review the potential for integrating ferroelectric polymer Langmuir-Blodgett (LB) films with semiconductor technology to produce nonvolatile ferroelectric random-access memory (NV-FRAM or NV-FeRAM) and data-storage devices. The prototype material is a copolymer consisting of 70% vinylidene fluoride (VDF) and 30% trifluoroethylene (TrFE), or P(VDF-TrFE 70:30). Recent work with LB films and more conventional solvent-formed films shows that the VDF copolymers are promising materials for nonvolatile memory applications. The prototype device is the metal-ferroelectric-insulator-semiconductor (MFIS) capacitance memory. Field-effect transistor (FET)-based devices are also discussed. The LB films afford devices with low-voltage operation, but there are two important technical hurdles that must be surmounted. First, an appropriate method must be found to control switching dynamics in the LB copolymer films. Second, the LB technology must be scaled up and incorporated into the semiconductor-manufacturing process, but since there is no precedent for mass production of LB films, it is difficult to project how long this will take.

Single-cell printing to form three-dimensional lines of olfactory ensheathing cells

Biological laser printing (BioLP) is a unique tool capable of printing high resolution two- and three-dimensional patterns of living mammalian cells, with greater than 95% viability. These results have been extended to primary cultured olfactory ensheathing cells (OECs), harvested from adult Sprague-Dawley rats. OECs have been found to provide stimulating environments for neurite outgrowth in spinal cord injury models. BioLP is unique in that small load volumes ( approximately microLs) are required to achieve printing, enabling low numbers of OECs to be harvested, concentrated and printed. BioLP was used to form several 8 mm lines of OECs throughout a multilayer hydrogel scaffold. The line width was as low as 20 microm, with most lines comprising aligned single cells. Fluorescent confocal microscopy was used to determine the functionality of the printed OECs, to monitor interactions between printed OECs, and to determine the extent of cell migration throughout the 3D scaffold. High-resolution printing of low cell count, harvested OECs is an important advancement for in vitro study of cell interactions and functionality. In addition, these cell-printed scaffolds may provide an alternative for spinal cord repair studies, as the single-cell patterns formed here are on relevant size scales for neurite outgrowth.

Hydration dynamics at fluorinated protein surfaces

Water-protein interactions dictate many processes crucial to protein function including folding, dynamics, interactions with other biomolecules, and enzymatic catalysis. Here we examine the effect of surface fluorination on water-protein interactions. Modification of designed coiled-coil proteins by incorporation of 5,5,5-trifluoroleucine or (4S)-2-amino-4-methylhexanoic acid enables systematic examination of the effects of side-chain volume and fluorination on solvation dynamics. Using ultrafast fluorescence spectroscopy, we find that fluorinated side chains exert electrostatic drag on neighboring water molecules, slowing water motion at the protein surface.

Charge Transfer Assisted by Collective Hydrogen‐Bonding Dynamics

Bipolar disorder: Femtosecond spectroscopy of samples in protic and aprotic solvents of similar polarities reveals that charge-transfer processes are substantially facilitated by the formation of solute-solvent hydrogen-bond networks (see picture). This notion of molecular-specific interactions is not part of the continuum dielectric models of solvation and should be of significance to biological processes such as those of enzymes.

Water absorption and dielectric changes in crystalline poly(vinylidene fluoride-trifluoroethylene) copolymer films

Crystalline Langmuir–Blodgett copolymer films of vinylidene fluoride with trifluoroethylene (70%:30% and 80%:20%) absorb water. Water absorption is accompanied by film swelling, as indicated by an increase in lattice spacing, sometimes by as much as 5%. This water absorption, between 0 and 40 °C, is a result of intercalation or occupation of interstitial sites between the layers of the film, not just water molecules filling voids and defect sites alone. An increase in the film capacitance is observed, although the polymer chains retain all trans configuration of the ferroelectric phase.

Solvation in protein (un)folding of melittin tetramer-monomer transition.

Protein structural integrity and flexibility are intimately tied to solvation. Here, we examine the effect that changes in bulk and local solvent properties have on protein structure and stability. We observe the change in solvation of an unfolding of the protein model, melittin, in the presence of a denaturant, trifluoroethanol. The peptide system displays a well defined transition in that the tetramer unfolds without disrupting the secondary or tertiary structure. In the absence of local structural perturbation, we are able to reveal exclusively the role of solvation dynamics in protein structure stabilization and the (un)folding pathway. A sudden retardation in solvent dynamics, which is coupled to the change in protein structure, is observed at a critical trifluoroethanol concentration. The large amplitude conformational changes are regulated by the local solvent hydrophobicity and bulk solvent viscosity.

Effects of electron irradiation on the ferroelectric properties of Langmuir-Blodgett copolymer films

The effect of irradiation on the ferroelectric properties of Langmuir-Blodgett films of the copolymer poly(vinylidene fluoride-trifluoroethylene) was investigated using 1‐MeV electrons for doses from 0.16to1.10MGy, where 1Gray(Gy)=100rad. Irradiation causes a systematic decrease in the phase-transition temperature, crystallinity, and spontaneous polarization of the films. The crystallinity and spontaneous polarization of the films decreased by amounts proportional to the dose, both tending toward zero near a dose of 1.30MGy. The ferroelectric-paraelectric phase-transition temperature, however, was only reduced by about 12%, indicating that the primary effect of irradiation was to convert a crystalline ferroelectric material to a noncrystalline dielectric.

Switching kinetics of ferroelectric polymer nanomesas

The switching dynamics and switching time of ferroelectric nanomesas grown from the paraelectric phase of ultrathin Langmuir–Blodgett vinylidene fluoride and trifluoroethylene copolymer films are investigated. Ferroelectric nanomesas are created through heat treatment and self-organization and have an average height of 10 nm and an average diameter of 100 nm. Ferroelectric nanomesas are highly crystalline and are in the ferroelectric phase and switch faster than 50 μs. The dependence of switching time on applied voltage implies an extrinsic switching nature.

Electron Irradiation Effects on Ferroelectric Copolymer Langmuir-Blodgett Films

The effect of irradiation on the ferroelectric properties of Langmuir-Blodgett films of the copolymer poly(vinylidene fluoride-trifluoroethelene) is investigated using 1.26 MeV electrons with dosages from 16 to 110 Mrad. Irradiation causes a systematic decrease in the phase transition temperature, coercive field and polarization of these thin films.

Retardation of Bulk Water Dynamics by Disaccharide Osmolytes.

The bioprotective nature of disaccharides is hypothesized to derive from the modification of the hydrogen bonding network of water which protects biomolecules through lowered water activity at the protein interface. Using ultrafast fluorescence spectroscopy, we measured the relaxation of bulk water dynamics around the induced dipole moment of two fluorescent probes (Lucifer Yellow Ethylenediamine and Tryptophan). Our results indicate a reduction in bulk water reorganization rate of approximately 30%. We observe this retardation in the low concentration regime measured at 0.1 and 0.25 M, far below the onset of glassy dynamics. This reduction in water activity could be significant in crowded biological systems, contributing to global change in protein energy landscape, resulting in a significant enhancement of protein stability under environmental stress. We observed similar dynamic reduction for two disaccharide osmolytes, sucrose and trehalose, with trehalose being the more effective in reducing solvation dynamics.