Alan Hurd | Los Alamos National Laboratory (original) (raw)

Papers by Alan Hurd

Physical Review Letters, 2009

A hydrated, surface-tethered polymer network capable of fivefold change in thickness over a 25-37... more A hydrated, surface-tethered polymer network capable of fivefold change in thickness over a 25-37 degrees C temperature range has been demonstrated via neutron reflectivity and fluorescence microscopy to be a novel support for single lipid bilayers in a liquid environment. As the polymer swells from 170 to 900 A, it promotes both in- and out-of-plane fluctuations of the supported membrane. The cushioned bilayer proved to be very robust, remaining structurally intact for 16 days and many temperature cycles. The promotion of membrane fluctuations offers far-reaching applications for this system as a surrogate biomembrane.

Langmuir, 1991

In this paper we explore the idea that the variation of the surface area of an adsorbed film on a... more In this paper we explore the idea that the variation of the surface area of an adsorbed film on a porous solid, as a function of coverage (film volume), should yield structural information about the solid. We describe the formalizations for relating such film area measurements to surface roughness and micropore size distribution, showing that under weak thermodynamic and structural assumptions the two are uniquely related to each other. The surface roughness of four Cab-0-Si1 fumed silicas, two phase-separated glasses (CPG and Vycor), and two silica xerogels are obtained from combined water-nitrogen adsorption experiments (nitrogen adsorption on preadsorbed water films) and compared to results from scattering and molecular tiling. Also, the surface roughness of various silica gels is assessed from the change in surface area when the surface is coated with surfactant or is derivatized. The micropore size distributions from f i l m area measurements for Vycor and the xerogels are evaluated and compared to the resulta from micropore analysis, including Kelvin equation analysis, of nitrogen adsorption on the bare solids. The agreement between the film area results and the results from other methods, to the extent that they overlap, is excellent throughout. Specifically, we find that all of the Cab-0-Sils and the CPG glass are essentially smooth at length scales up to 1 nm. By contrast, Vycor and the base-catalyzed xerogel show an extended fractal behavior, with surface fractal dimension of 2.3 f 0.1 and 2.5 f 0.1, respectively, over a length range of about 0.2-10 nm (combination of all available data).

Journal of Non-crystalline Solids, 1995

Silica films with refractive indices in the range of 1.0061.036 (equivalent porosity 98.591%) h... more Silica films with refractive indices in the range of 1.0061.036 (equivalent porosity 98.591%) have been prepared at ambient pressure by a process wherein organo-siloxane polymers are deposited on a silicon substrate by conventional dip-coating at 25° C and ...

Langmuir, 1988

Fumed silica was studied by gas adsorption and small-angle scattering techniques to test whether ... more Fumed silica was studied by gas adsorption and small-angle scattering techniques to test whether the materials exhibit rough surfaces that would account for measurable differences in specific surface area. While the shapes of nitrogen and argon adsorption isotherms were identical for different grades of fumed silica, in disagreement with BET adsorption models of fractal surfaces, our other measurements support the notion that the roughness exists and differs from grade to grade. We attribute the failing of the BET fractal models to lateral interactions in the adsorbed layers. (4) Hall, P. J. Chem. Phys. Lett. 1986, 124, 467. (5) Rojanski, D.; Huppert, D.; Bale, H. D.; Dacai, X.; Schmidt, P. W.; Farin, D.; Seri-Levy, A.; Avnir, D.

Journal De Physique, 1988

2014 On présente une méthode permettant de visualiser par ellipsométrie une région d'un film en t... more 2014 On présente une méthode permettant de visualiser par ellipsométrie une région d'un film en train de sécher dans le procédé de dépôt par immersion ; cette méthode donne l'épaisseur du film et son indice de réfraction en fonction de la position. Les mesures préliminaires effectuées sur des sols alcooliques de TiO2 et de SiO2 indiquent que le film tend vers une fraction volumique d'environ 0,2 à l'état humide et suggèrent que le film résiste à une densification ultérieure pour des raisons cinétiques. Dans les films denses, le passage du front de séchage final produit un effondrement rapide du film sous l'effe des forces capillaires ; dans les films poreux formés de grands agrégats de SiO2, l'affaiblissement final du film est plus lent parce que les forces capillaires sont plus faibles. Les profils d'épaisseur indiquent que l'amincissement du film résulte d'une combinaison de l'évaporation et de l'écoulement gravitationnel.

Physica D-nonlinear Phenomena, 2001

We report particle dynamics based studies of impulse propagation in a chain of elastic beads with... more We report particle dynamics based studies of impulse propagation in a chain of elastic beads with dissipative contacts and with randomly distributed masses. The interaction between the beads is characterized by the potential V (δ) ∼ δ n , δ ≥ 0 being grain overlap, n > 2 and at zero external loading, i.e., under conditions of "sonic vacuum" in which sound cannot propagate through the chain [J. Appl. Mech. Technol. Phys. 5 (1983) 733]. In the earlier work, we have confirmed the studies of Nesterenko and coworkers and have reported that impulses propagate as solitary waves in the system of interest in the absence of dissipation and disorder [Physica A 268 (1999) 644]. In the present study, we first discuss the effects of restitution and velocity dependent friction on the propagation of the impulse. We next report that the maximum energy E max of the solitary wave as it propagates from a chain of monodisperse grains of mass m to a chain with masses m(1 + r(z) ), where −1 ≤ r(z) ≤ 1 and = const. that measures the degree of randomness, decays with linear distance traveled z as exp(−α E z), α E ∼ 2+f (n) , f (n) being some n dependent constant for 2 < n < ∞. In monodisperse chains, the velocity of the solitary wave c ∼ E (n−2)/2n max . In polydisperse chains, we show that the propagation speed of a non-dispersive solitary wave decays with distance as exp(−α c z), where α c = α E (n − 2)/2n.

American Journal of Physics, 1989

Journal of The American Ceramic Society, 1990

This paper compares the structure ofA1203-Si02 xerogels prepared with A1203 contents ranging from... more This paper compares the structure ofA1203-Si02 xerogels prepared with A1203 contents ranging from 21 to 75 wt% (13 to 64 mol%). The 47 wt% AI2O3 xerogel (AI/Si = 1) exhibits anomalously low surface area (=1 m2/g) and skeletal density compared with other AI2O3-SiO2 compositions. Based on the results of nitrogen adsorptionlcondensation, helium displacement, high-resolution transmission electron microscopy (HRTEM), small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS), we attribute the low surface area and skeletal density (density of the solid phase which is inaccessable to helium) to the formation of closed micropores, whereas the higher surface area materials exhibit a slightly coarser texture comprising open pores with radii of =1 nm. X-ray diffraction (XRD) and 29Si and "A1 magic-angle spinning nuclear magnetic resonance (MASNMR) indicate no anomalous behavior in the 47% sample on molecular length scales. HRTEM indicates the presence of a small fraction of crystallites which is supported by the SAXS results, but it is unknown if this crystallinity is related to low surface area. Low-field 'H NMR spin-lattice relaxation measurements show that the physical structure of all of the "wet" gels is similar implying that pore closure occurs during drying. Consistent with this idea, gel surface area and density increased significantly when the pore fluid (water) was replaced with a lower surface tension fluid (formamide, dioxane, ethanol, water/surfactant). [

Journal of Fluid Mechanics, 1985

The resistance to oscillatory motions of arbitrary wavelengths in an infinitely dilute lattice of... more The resistance to oscillatory motions of arbitrary wavelengths in an infinitely dilute lattice of identical spheres, immersed in a viscous fluid, is calculated from the linearized Naviel-Stokes equation to lowest order in fluid inertia and sphere-volume fraction. The application we have in mind is to analyse the hydrodynamic modes in colloidal crystals (a lattice of Brownian particles repelling each other electrically), although other applications are possible. We find that'the friction per particle for both compressional and transverse shear modes is close to the Stokes value at short wavelengths, whereas at long wavelengths fluid backflow within the lattice is important and causes the friction to increase for compressional modes. For shear modes, in which backflow is not present, the friction decreases from the Stokes value at short wavelengths to zero at long wavelengths. At sufficiently long wavelengths, when the shear-mode friction becomes small enough, propagating viscoelastic modes are possible in a lattice with elastic forces between spheres. Fluid inertia is most important for long-wavelength transverse motions, since a significant amount of fluid mass gets carried along by each particle. Explicit results for a bcc lattice are presented along with interpolation formulas, and the pertinence of these results to colloidal crystals is discussed. Finally, the effects of constraining walls are explored by considering a one-dimensional lattice near a wall. Backflow imposed by the wall increases the friction factors for the lattice modes, showing that propagating modes are unlikely in colloidal crystals that are confined to a cell thinner than a critical length.

American Journal of Physics, 1988

This Resource Letter provides a guide to the literature on fractals. Although '&#x27... more This Resource Letter provides a guide to the literature on fractals. Although ''fractal'' is a relatively new term in science, unifying many new ideas with established ones, its wide application and general popularity have made it one of the fastest growing fields in statistical physics. The letter E after an item indicates elementary level or material of general interest to persons becoming informed in the field; the letter I, for intermediate level, indicates material of somewhat more specialized nature; and the letter A indicates rather specialized or advanced material. An asterisk (*) indicates those articles to be included in an accompanying Reprint Book.

Aerosol Science and Technology, 1990

... The strategy of this paper is to establish the essential factors which control structure in f... more ... The strategy of this paper is to establish the essential factors which control structure in flames by mapping growth processes (polymerization and aggregation) onto sim-ple computer-generated fractal models (Schaefer, 1988). ...

Physical Review E, 2001

We consider a chain of elastic beads subjected to vanishingly weak loading conditions, i.e., the ... more We consider a chain of elastic beads subjected to vanishingly weak loading conditions, i.e., the beads are barely in contact. The grains repel upon contact via the Hertz-type potential, Vinfinitydelta(n), n>2, where delta> or =0, delta being the grain-grain overlap. Our dynamical simulations build on several earlier studies by Nesterenko, Coste, and Sen and co-workers that have shown that an impulse propagates as a solitary wave of fixed spatial extent (dependent only upon n) through a chain of Hertzian beads and demonstrate, to our knowledge for the first time, that colliding solitary waves in the chain spawn a well-defined hierarchy of multiple secondary solitary waves, which is approximately 0.5% of the energy of the original solitary waves. Our findings have interesting parallels with earlier observations by Rosenau and colleagues [P. Rosenau and J. M. Hyman, Phys. Rev. Lett. 70, 564 (1993); P. Rosenau, ibid. 73, 1737 (1994); Phys. Lett. A 211, 265 (1996)] regarding colliding compactons. To the best of our knowledge, there is no formal theory that describes the dynamics associated with the formation of secondary solitary waves. Calculations suggest that the formation of secondary solitary waves may be a fundamental property of certain discrete systems.

Applied Optics, 1987

We have used dynamic light scattering to make in situ measurements of flame-synthesized silica pa... more We have used dynamic light scattering to make in situ measurements of flame-synthesized silica particles. Unlike many of the common Mie-scattering techniques, the technique used here does not rely on the absorption of light by the particles. This technique is, therefore, especially advantageous for the measurement of silica and other particles with real refractive indices. The dynamic-light-scattering technique has the additional advantage of being insensitive to particle optical properties.

Langmuir, 2001

Silica/diblock films with various mesostructures of large characteristic length scales were synth... more Silica/diblock films with various mesostructures of large characteristic length scales were synthesized through evaporation-induced self-assembly (EISA). The structure-directing agents used were amphiphilic polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymers of high molecular weights. The synthesis process began with a dilute homogeneous solution of a silica precursor and the diblock copolymer in a mixture of tetrahydrofuran (THF) and water. After this dilute solution was cast, THF preferentially evaporated; accordingly, the species in the depositing film increasingly concentrated and the solvent quality for the diblock progressively decreased. At some critical point, cooperative self-assembly of both the PSb-PEO diblock and the silicate started. Subsequently, liquid-crystalline mesophases were obtained. The present study indicates that silica/diblock films with different mesostructures can be synthesized by using one identical diblock; as the volume ratio of the diblock to silica increases, mesostructures change progressively from regular to inverted (reverse) via lamellar. For the silica/diblock films with regular mesophases, copolymer removal produces mesopores; highly ordered mesoporous silica films with different pore sizes result from using diblocks with different molecular weights. Particularly noteworthy is the ready formation of the silica/diblock multi-bilayer vesicular mesostructures. The present system is believed to be the first to use high glass transition temperature (Tg ≈ 373 K), PS-based amphiphilic diblock copolymers to prepare silica/diblock films with regular and reverse mesophases, as well as multi-bilayer vesicular mesostructures, through solvent evaporation-induced self-assembly. (1) Kresge, C.; Leonowicz, M.; Roth, W.; Vartuli, C.; Beck, J. Nature 1992, 359, 710. (2) Huo, Q.; Margolese, D. I.; Clesla, U.; Feng, P.; Gler, T. E.; Sleger, P.; Leon, R.; Petroff, P. M.; Schuth, F.; Stucky, G. D. Nature 1994, 368, 317. (3) (a) Tanev, P. T.; Pinnavaia, T. J. Science 1995, 267, 865. (b) Markus, T.; Franck, A.; Chesne, A. D.; Leist, H.; Zhang, Y.; Ulrich, R.; Schadler, V.; Wiesner, U.

Physical Review Letters, 1989

Quasielastic light scattering from Brownian particles in the rarefied environment of a glow disch... more Quasielastic light scattering from Brownian particles in the rarefied environment of a glow discharge exhibits Gaussianlike intensity correlation functions owing to the long mean free paths of the particles. The shape of the correlation function depends on the particles&amp;amp;amp;amp;amp;#39; average thermal velocity and friction coefficient, which can be related to aggregate mass and structure, and indicates a crossover from kinetic

Journal of The American Ceramic Society, 1995

Pyranine (8-hydroxy-l,3,6-trisulfonated pyrene) was used as an in situ fluorescence probe to moni... more Pyranine (8-hydroxy-l,3,6-trisulfonated pyrene) was used as an in situ fluorescence probe to monitor the chemical evolution during sol-gel thin film deposition of silica by the dip-coating process. The sensitivity of pyranine luminescence to protonation/deprotonation effects was used to quantify changes in the water/alcohol ratio in real time as the substrate was withdrawn from the sol reservoir. The spatially resolved spectral results showed that preferential evaporation of alcohol occurred, and that the solvent composition in the vicinity of the drying line reached values in excess of 80 vol% water. Correlation of the luminescence results with the interference pattern of the depositing film allowed the solvent composition to be mapped as a function of film thickness.

Journal of Physical Chemistry B, 2003

Inorganic mesoporous thin-films are important for applications such as membranes, sensors, low-di... more Inorganic mesoporous thin-films are important for applications such as membranes, sensors, low-dielectricconstant insulators (so-called low κ dielectrics), and fluidic devices. Over the past five years, several research groups have demonstrated the efficacy of using evaporation accompanying conventional coating operations such as spin-and dip-coating as an efficient means of driving the self-assembly of homogeneous solutions into highly ordered, oriented, mesostructured films. Understanding such evaporation-induced self-assembly (EISA) processes is of interest for both fundamental and technological reasons. Here, we use spatially resolved 2D grazing incidence X-ray scattering in combination with optical interferometry during steady-state dipcoating of surfactant-templated silica thin-films to structurally and compositionally characterize the EISA process. We report the evolution of a hexagonal (p6 mm) thin-film mesophase from a homogeneous precursor solution and its further structural development during drying and calcination. Monte Carlo simulations of water/ethanol/surfactant bulk phase behavior are used to investigate the role of ethanol in the self-assembly process, and we propose a mechanism to explain the observed dilation in unit cell dimensions during solvent evaporation.