Papers by Elizabeth K. Mann
Journal of Low Temperature Physics, 1979
Neutral excitations generated in a discharge near a sharp tungsten tip operated in either the fie... more Neutral excitations generated in a discharge near a sharp tungsten tip operated in either the field emission or field ionization mode in liquid helium were detected with a surface ionization detector submerged in the liquid. The measured times of flight of the neutral excitations from the tip to the detector are in excellent agreement with a model in which the neutral entities drift with the fluid which is set in motion by the force of the ion current extracted from the discharge. Times of flight as long as 30 sec were measured. These data, along with measurements reported by other workers, clearly identify the neutral 3 + excitation as an a Eu metastable helium molecule. We report a lower limit of 10 sec on the lifetime of this state. 3 + were long-lived metastable atomic 2~$1 or diatomic a Eu states. Rayfield z measured the time of flight of these entities between the source and an ion detector in the vapor by modulating the neutral excitation current with an electric field in the region immediately in front of the alpha source. The flight time of 1.4 msec at temperatures-<0.7 K was independent
Journal of the Optical Society of America A, 1996
Scanning angle reflectometry around the Brewster angle has been used to investigate the optical p... more Scanning angle reflectometry around the Brewster angle has been used to investigate the optical properties of an assembly of polystyrene latex particles deposited on a silica-water interface. The surfaces are partially covered with particles of radius 120 nm, yielding stable films. A second particle sample, with a radius ranging between 50 and 300 nm, is then introduced. A simple model based on the Mie theory of particle light scattering describes the data well, both for the monomodal and bimodal particle size distributions, with only two parameters in the analysis: one particle size and one particle coverage (the other being known and fixed). The determined particle size is in good agreement with values determined by electron microscopy. The polydispersity within each particle size distribution may easily be taken into account within this model: polydispersity in the range of several tens of nanometers has no significant effect on the particle size determined from the analysis but leads to an underestimation of the particle density by a quantity that depends only on the mean size and the size distribution for the particles.
MRS Proceedings, 1996
Scanning Angle Reflectometry (SAR) is used to investigate the structure of protein layers deposit... more Scanning Angle Reflectometry (SAR) is used to investigate the structure of protein layers deposited sequentially, first the antigen and then the antibody, on a silica surface. The reflectivity curves are analyzed by means of the optical invariants, a general description valid in the thin film limit which permits the determination of three and only three structural parameters for a dielectric layer, independent of any model of the layer. The three parameters can be related to the first two moments of the mass density in the layer, or to an average film thickness and density. In addition, a new invariant is constructed which directly yields information about the distribution of mass in the layer, and thus goes beyond the usual uniform layer model.
The Journal of Chemical Physics, 1995
The statistical properties of surfaces covered by irreversibly adsorbed colloidal particles are s... more The statistical properties of surfaces covered by irreversibly adsorbed colloidal particles are studied as a function of the Péclet number (or equivalently as a function of their rescaled radius R*). More precisely, the radial distribution function g(r) is determined as a function of the coverage θ for five systems corresponding to different values of R*. Also measured is the reduced variance σ2/〈n〉 of the number n of adsorbed particles on surfaces of given area out of the adsorption plane. Finally, the evolution of 〈n〉 with the concentration of particles in solution during the deposition process is determined for the different systems. This allows us to obtain information on the available surface function Φ. All these parameters are compared to their expected behavior according to the random sequential adsorption (RSA) model and to the ballistic model (BM). It is found that the radial distribution function of the system of particles characterized by R*<1 is well predicted by the...
The Journal of Chemical Physics, 1996
We investigated the suitability of reflectometry as a sizing method for polystyrene latex particl... more We investigated the suitability of reflectometry as a sizing method for polystyrene latex particles. This technique, where the particles are adsorbed at a quartz/water interface, involves the analysis of the reflection around the Brewster angle of light polarized in the plane of incidence. A computation of a full reflectivity curve containing about 20 datapoints, taking into account all electromagnetic interactions, is extremely complex and may take up to 100 h on an Indy R4600 computer (Silicon Graphics, Mountain View, CA). To use the complete electromagnetic theory for analysis of experiments therefore is impractical. We analyzed the experimental reflectivity curves using an approximate theory (free-sphere model), which neglects all electromagnetic interactions between different particles and their images in the substrate. To assess the errors introduced by neglecting these interactions, we have calculated reflectivity curves using the full electromagnetic theory for this system, ...
The Journal of Chemical Physics, 1995
The irreversible random adsorption of particles on a surface is guided by the available surface f... more The irreversible random adsorption of particles on a surface is guided by the available surface function φ. The relative fluctuation σ2/〈n〉 in the number of particles n in a finite region provides one characterization of the distribution of these particles on the surface. We show rigorously that the two quantities are given by the same expression to first order in the surface coverage, for any irreversible adsorption process. This is confirmed in two particular cases: for random sequential adsorption, where values for σ2/〈n〉 from numerical simulations can be compared to an analytic expression for φ, and for Ballistic deposition, where experimental values for deposition under a strong gravitational influence can also be compared to an existing analytical expression for φ.
Le Journal de Physique Colloques, 1978
Berichte der Bunsengesellschaft für physikalische Chemie, 1994
ABSTRACT We have studied mixed molecular layers of polydimethylsiloxane (PDMS) and surfactants, u... more ABSTRACT We have studied mixed molecular layers of polydimethylsiloxane (PDMS) and surfactants, using different techniques: surface tension, ellipsometry, neutron reflectivity and Brewster angle microscopy. On pure water, the polymer layer is generally inhomogeneous, showing surface domains of different discrete thicknesses. The penetration of the polymer into the surfactant monolayer found on the surface of aqueous surfactant solutions depends on the surfactant. On a surfactant layer with little penetration by the polymer, the polymer layer remained inhomogeneous. With other surfactants, the polymer penetrated appreciably into the surfactant layer, and the polymer layer was homogeneous. These differences between surfactants correlate with the wetting behavior of PDMS on the aqueous surfactant solutions.
Europhysics Letters (EPL), 1995
ABSTRACT
Biophysical Journal, 2018
Organic fluorophores, such as Cy3 and Cy5, have been widely used as chemical labels to probe dyna... more Organic fluorophores, such as Cy3 and Cy5, have been widely used as chemical labels to probe dynamics and functions of membrane proteins. While several water-soluble fluorophores have been reported interacting strongly with membrane lipid, detailed fluorophore-lipid interactions and the effect of fluorescent labeling on the natural dynamics of target proteins has not been revealed by experiment. We employed the highly mobile membrane mimetic (HMMM) model in a large set of all-atom molecular dynamics simulations to unravel the spontaneous partitioning of sulfo-Cy3/Cy5 fluorophores into lipid bilayers with different lipid compositions. Spontaneous membrane partitioning of Cy3/ Cy5 captured in these simulations reveals two steps. Electrostatic interaction between Cy3/Cy5's sulfo-group and lipid headgroups facilitates the fast membrane association of fluorophores, followed by slow insertion into the lipid bilayer core. Using biased-exchange umbrella sampling, free energy calculations with full-tailed lipids revealed a higher energy barrier for partitioning into negatively charged (PS) membrane than uncharged (PC/PE) membrane. Furthermore, the effect of fluorophore-lipid interactions on membrane protein has been examined by covalently linking Cy5 to the transmembrane helices of glycophorin A. Equilibrium simulations show non-trivial effect of Cy5-tagging on the helix-tilting angle and lateral diffusion inside a membrane, depending on the position of tagging site relative to the membrane. Our results suggest that fluorophore-lipid interactions can affect the structure and natural dynamics of membrane proteins.
Bulletin of the American Physical Society, 2015
Langmuir, 2004
A systematic study of five different, symmetric bent-core liquid crystals in Langmuir thin films ... more A systematic study of five different, symmetric bent-core liquid crystals in Langmuir thin films at the air/water interface is presented. Both the end chains (siloxane vs hydrocarbon) and the core (more or less amphiphilic) are varied, to allow an exploration of different possible layer structures at the interface. The characterization includes systematic surface pressure isotherms, Brewster angle microscopy, and surface potential measurements. The properties of these layers are strongly dependent on the individual type of molecule: the molecules with amphiphilic end chains lie quite flat on the surface, while the molecules with hydrophobic end chains construct multilayer structures. In both cases, the three-dimensional collapse structure is reversible.
Biophysical Journal, 2012
Biophysical Journal, 2011
APS Ohio Sections Fall Meeting Abstracts, Oct 1, 2003
Experimental studies of Langmuir monolayers of bent-core molecules demonstrate that the propertie... more Experimental studies of Langmuir monolayers of bent-core molecules demonstrate that the properties of these layers are strongly dependent on the individual type of molecule. Measurements of surface pressure and potential, and Brewster angle microscopy (BAM) have been combined and analyzed in order to study molecular configurations. A better understanding of packing and orientation of the molecules can be made by considering their 3D spacefilling models. Spacefilling 2D projections onto the surface and their comparison ...
Biochimica et Biophysica Acta (BBA) - Biomembranes, 2014
Bulletin of the American Physical Society, 2010
Langmuir Films have been source of high expectations not just because of the opportunity that the... more Langmuir Films have been source of high expectations not just because of the opportunity that they provide to study low-dimensional fluids, but also because of the practical and potential applications that comes from the possibility to transfer these thin films into another surface, through Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) techniques. We use these transference techniques to deposit a monolayer of a bent-core liquid crystal molecule (Z2B) into different substrates, to use later as alignment layer in a liquid crystal cell, where the direction and degree of the alignment is changed by increasing and decreasing the packing of the molecules in the monolayer (dipping the substrate on a Langmuir Trough with different surface pressures).
Bulletin of the American Physical Society, 2011
Using one of the most commonly studied synthetic molecule, 4-Cyano-4&amp;amp;amp;amp;amp;amp;... more Using one of the most commonly studied synthetic molecule, 4-Cyano-4&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;-pentylbiphenyl (5CB), we were able to pull freely suspended membranes of different thicknesses into circular frames of up to 20mm diameter. Films pulled this way were distorted using a speaker, while a laser light was shone onto them for studying the far field reflection and learn about resonant frequency modes and
Uploads
Papers by Elizabeth K. Mann