[show abstract][hide abstract] ABSTRACT: Cavitation is an intricate multiphase phenomenon that interplays with turbulence in fluid flows. It exhibits clear duality in characteristics, being both destructive and beneficial in our daily lives and industrial processes. Despite the multitude of occurrences of this phenomenon, highly dynamic and multiphase cavitating flows have not been fundamentally well understood in guiding the effort to harness the transient and localized power generated by this process. In a microscale, multiphase flow liquid injection system, we synergistically combined experiments using time-resolved x-radiography and a novel simulation method to reveal the relationship between the injector geometry and the in-nozzle cavitation quantitatively. We demonstrate that a slight alteration of the geometry on the micrometer scale can induce distinct laminar-like or cavitating flows, validating the multiphase computational fluid dynamics simulation. Furthermore, the simulation identifies a critical geometric parameter with which the high-speed flow undergoes an intriguing transition from non-cavitating to cavitating.
[show abstract][hide abstract] ABSTRACT: The pathway of interfacial self-assembly of large-scale, highly-ordered 2D nanoparticle/polymer monolayer or bilayer arrays from a toluene solution at an air/water interface was investigated using grazing-incidence small-angle scattering at a synchrotron source. Interfacial-assembly of the ordered nanoparticle/polymer array was found to occur through two stages: formation of an incipient randomly close-packed interfacial monolayer followed by compression of the monolayer to form a close-packed lattice driven by solvent evaporation from the polymer. Because the nanoparticles are hydrophobic, they localize exclusively to the polymer-air interface during self-assembly, creating a through thickness asymmetric film as confirmed by x-ray reflectivity. The interfacial self-assembly approach can be extended to form binary NP/polymer arrays. It is anticipated that by understanding the interfacial self-assembly pathway, this simple evaporative procedure could be conducted as a continuous process amenable to large area nanoparticle-based manufacturing needed for emerging energy technologies.
[show abstract][hide abstract] ABSTRACT: Lensless X-ray coherent diffraction imaging (CDI) has emerged as a
thriving field promising applications in materials and biological
sciences with a theoretical imaging resolution only limited by the X-ray
wavelength. Most CDI methods use transmission geometry, which is not
suitable for nanostructures grown on opaque substrates or for objects of
interest comprising only surfaces or interfaces. Attempts have been made
to perform CDI experiments in reflection geometry, both optically and
with X-rays, but the reconstruction resulted in mostly planar images,
with less success in the third dimension. Here, we discuss the
development of coherent surface scattering imaging in grazing-incidence
geometry that takes advantage of enhanced X-ray surface scattering and
interference near total external reflection. We demonstrate the
successful reconstruction of substrate-supported non-periodic surface
patterns in three dimensions with nanometre resolution in the direction
normal to the substrate, promising wide applications in elucidating
structures in substrate-supported and buried nanoelectronics and
[show abstract][hide abstract] ABSTRACT: As an increasingly important structural-characterization technique, grazing-incidence X-ray scattering (GIXS) has found wide applications for in situ and real-time studies of nanostructures and nanocomposites at surfaces and interfaces. A dedicated beamline has been designed, constructed and optimized at beamline 8-ID-E at the Advanced Photon Source for high-resolution and coherent GIXS experiments. The effectiveness and applicability of the beamline and the scattering techniques have been demonstrated by a host of experiments including reflectivity, grazing-incidence static and kinetic scattering, and coherent surface X-ray photon correlation spectroscopy. The applicable systems that can be studied at 8-ID-E include liquid surfaces and nanostructured thin films.
[show abstract][hide abstract] ABSTRACT: In recent years, X-ray radiography has been used to probe the internal structure of dense sprays with microsecond time resolution and a spatial resolution of 15 µm even in high-pressure environments. Recently, the 7BM beamline at the Advanced Photon Source (APS) has been commissioned to focus on the needs of X-ray spray radiography measurements. The spatial resolution and X-ray intensity at this beamline represent a significant improvement over previous time-resolved X-ray radiography measurements at the APS.
[show abstract][hide abstract] ABSTRACT: The development of the 3^rd and 4^th generation synchrotrons has
stimulated extensive research activities in x-ray imaging techniques.
Among all, coherent diffractive imaging (CDI) shows great promise, as
its resolution is only limited by the wavelength of the source. Most of
the CDI work reported thus far used transmission geometry, which however
is not suitable for samples on opaque substrates or in which only the
surfaces are the regions of interest. Even though two groups have
performed CDI experiments (using laser or x-ray) in reflection geometry
and succeeded in reconstructing the planar image of the surface, the
theoretical underpinnings and analysis approaches of their techniques
are essentially identical to transmission CDI. Most importantly, they
couldn't obtain the structural information along sample thickness
direction. Here, we introduce a reflection CDI technique that works at
grazing-incidence geometry. By visualizing Au nanostructures fabricated
on Si substrate, we demonstrate that this innovative imaging technique
is capable of obtaining both 2D and 3D information of surfaces or buried
structures in the samples. In the meanwhile, we will also explain the
grazing-incidence-scattering based-algorithm developed for 3D phase
[show abstract][hide abstract] ABSTRACT: A symmetric diblock copolymer, poly(pentafluorostyrene-b-styrene) (PPFS-b-PS), is synthesized by atom transfer radical polymerization (ATRP). The behavior of PPFS-b-PS thin films on silicon wafers is investigated. Lamellar microdomains oriented parallel to the film surface are formed when the thin films are heated to 220 °C for 24 h, due to preferential interfacial interactions and the low surface energy of the PPFS. An electric field is used to overcome the low surface energy of the fluorinated block and preferential interactions with the substrate so as to force the lamellar microdomains to orient normal to the surface.
Macromolecular Chemistry and Physics 11/2011; 212(22). · 2.39 Impact Factor
[show abstract][hide abstract] ABSTRACT: We monitor the structural evolution of a poly(tert-butyl methacrylate)-poly(methyl methacrylate) (PtBMA–PMMA) diblock copolymer thin film undergoing conversion via reactive annealing to yield poly(methacrylic acid)–poly(methyl methacrylate) (PMAA–PMMA). Using grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM), we confirm the generation of well-ordered cylindrical microdomains in the PtBMA–PMMA precursor film after solvent annealing. After initiating thermal deprotection, the high degree of ordering can be maintained up to 25% conversion of the diblock into PMAA–PMMA. Beyond this point, a significant decrease in the overall film thickness associated with the conversion process cannot accommodate the hexagonal lattice adopted by the cylindrical microdomains. At the same time, rearrangement of PMMA cores in a PtBMA matrix that is becoming progressively glassier presents further difficulties in maintaining a reasonable structure. The fully converted PMAA–PMMA film contains a system of cylindrical microdomains that lack good ordering.
[show abstract][hide abstract] ABSTRACT: The generation and presence of strain around nanostructures of oxides is a key to their growth, properties, and functions, but it has been a challenge to experimentally measure its sign, magnitude, and spatial distribution. Combining diffuse scattering with scanning x-ray nanodiffraction, we have mapped the strain distribution in an oxide-on-oxide nanopatterned structure with a high sensitivity (10−4) and a submicrometer spatial resolution. An edge-induced strain distribution is observed from a sample of CoFe2O4 nanolines epitaxially grown on MgO substrate, which agrees quantitatively with the numerical simulations.
[show abstract][hide abstract] ABSTRACT: The fabrication of nanostructured films possessing tricontinuous minimal surface mesophases with well-defined framework and pore connectivity remains a difficult task. As a new route to these structures, we introduce glycerol monooleate (GMO) as a template for evaporation-induced self-assembly. As deposited, a nanostructured double gyroid phase is formed, as indicated by analysis of grazing-incidence small-angle x-ray scattering data. Removal of GMO by UV/O(3) treatment or acid extraction induces a phase change to a nanoporous body-centered structure which we tentatively identify as based on the IW-P surface. To improve film quality, we add a co-surfactant to the GMO in a mass ratio of 1:10; when this co-surfactant is cetyltrimethylammonium bromide, we find an unusually large pore size (8-12 nm) in acid extracted films, while UV/O(3) treated films yield pores of only ca. 4 nm. Using this pore size dependence on film processing procedure, we create a simple method for patterning pore size in nanoporous films, demonstrating spatially-defined size-selective molecular adsorption.
Chemistry of Materials 04/2011; 23(8):2107-2112. · 8.24 Impact Factor
[show abstract][hide abstract] ABSTRACT: The rapid assembly of icosohedral virus-like particles (VLPs) into highly ordered (domain size > 600 nm), oriented 2D superlattices directly onto a solid substrate using convective coating is demonstrated. In-situ grazing-incidence small-angle X-ray scattering (GISAXS) is used to follow the self-assembly process in real time to characterize the mechanism of superlattice formation, with the ultimate goal of tailoring film deposition conditions to optimize long-range order. From water, GISAXS data are consistent with a transport-limited assembly process where convective flow directs assembly of VLPs into a lattice oriented with respect to the water drying line. Addition of a nonvolatile solvent (glycerol) modified this assembly pathway, resulting in non-oriented superlattices with improved long-range order. Modification of electrostatic conditions (solution ionic strength, substrate charge) also alters assembly behavior; however, a comparison of in-situ assembly data between VLPs derived from the bacteriophages MS2 and Qβ show that this assembly process is not fully described by a simple Derjaguin-Landau-Verwey-Overbeek model alone.
[show abstract][hide abstract] ABSTRACT: The microphase separation of block copolymers in thin films continues to be of great value for the fabrication of nanostructured materials. While highly ordered arrays of microdomains can be easily achieved in some block copolymers, proper processing of others are more challenging. Obtaining ordered morphologies in poly(methacrylic acid)-poly(methyl methacrylate) (PMAA-PMMA), a diblock possessing polyelectrolyte functionality, offers unique associative properties and aqueous reaction chemistries otherwise inaccessible by most other block copolymer films. Due to the limited choices of suitable solvents with sufficiently high vapor pressure and the thermal degradation temperature of PMAA being lower than its glass transition temperature, direct solvent and thermal annealing of PMAA-PMMA are not ideal for generating ordered nanostructures. Here, we begin by solvent annealing poly(tert-butyl methacrylate)-poly(methyl methacrylate) (PtBMA-PMMA) films at room temperature. We then thermally anneal the films to convert the PtBMA block to PMAA. We present results from atomic force microscopy (AFM) and grazing-incidence small-angle x-ray scattering (GISAXS) studies.
[show abstract][hide abstract] ABSTRACT: A bile salt (sodium taurodeoxycholate, NaTDC) was used to prevent phase separation between silica and lipid in self-assembled long-chain diacyl phosphatidylcholine/SiO(2) films. Phase diagrams for NaTDC/didecanoyl phosphatidylcholine/SiO(2) and NaTDC/egg phosphatidylcholine/SiO(2) films were investigated through grazing-incidence small-angle X-ray scattering at a synchrotron source.
Chemical Communications 02/2011; 47(6):1806-8. · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ability of the Small Angle X-ray Scattering (SAXS) technique to measure small droplets generated by the nucleation process within a highly dynamic supercritical ethylene jet both inside and outside an injector was successfully demonstrated. Droplet nucleation, droplet size distribution, droplet growth, and the dependence of droplet nucleation/condensation on flow properties can be explored with the SAXS technique.
Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 01/2011; 649(1):219-221. · 1.14 Impact Factor
[show abstract][hide abstract] ABSTRACT: The packing of electronic molecules into planar structures and an ensured pi-pi interaction within the plane are preferred for efficient organic transistors. Thin films of organic electronics are exemplar, but the widely adopted molecular design and associated fabrication lead to limited ordering in multistack construction motifs. Here we demonstrate self-assembled nanolayers of organic molecules having potential electronic utility using an amphiphilic silane as a building block. Unlike a cross-linked (tetrahedral) configuration found in conventional siloxane networks, a linear polymer chain is produced following silane polycondensation. As a result, hydrophobic branches plus a noncovalent pi-pi interlocking between the molecules promote planar packing and continuous stacking along the surface normal. In contrast to conventional pi-pi stacking or hydrogen bonding pathways in a fibrous construct, multistacked nanolayers with coexisting pi-pi and herringbone interlocking can provide unmatched properties and processing convenience in molecular electronics.
[show abstract][hide abstract] ABSTRACT: Critical photonic, electronic, and magnetic applications of two-dimensional nanocrystal superlattices often require nanostructures in perfect single-crystal phases with long-range order and limited defects. Here we discovered a crystalline phase with quasi-long-range positional order for two-dimensional nanocrystal superlattice domains self-assembled at the liquid-air interface during droplet evaporation, using in situ time-resolved X-ray scattering along with rigorous theories on two dimensional crystal structures. Surprisingly, it was observed that drying these superlattice domains preserved only an orientational order but not a long-range positional order, also supported by quantitative analysis of transmission electron microscopy images.
[show abstract][hide abstract] ABSTRACT: The morphology of poly(styrene-b-ethylene-r-butylene) (SEB) and poly(styrene-b-ethylene-r-butylene-b-styrene) (SEBS) thin films annealed both above (165 °C) and below (125 °C) the bulk order−order transition temperatures (OOT) (140 °C) was characterized with grazing incidence small-angle X-ray scattering (GISAXS), dynamic secondary ion mass spectrometry (d-SIMS), and atomic force microscopy (AFM). The SEBS thin film morphology is always spherical, regardless of film thickness or annealing temperature, leading us to conclude that the OOT for films up to five layers of spheres is depressed by at least 10 °C relative to the bulk. In contrast, the SEB film morphology at both 125 and 165 °C is always cylindrical, except when the film thickness is less than tcyl, a monolayer of cylinders. For SEB film thicknesses, t, less than tcyl at 165 °C either a partial or full monolayer of spheres forms (thickness tsph) with coexistence of patches of spheres and cylinders when tsph < t < tcyl. Thus, we conclude that the OOT for SEB film thickness between tcyl and 5tcyl is increased by at least 20 °C over that of the bulk. This complex phase behavior can be understood qualitatively by considering two small contributions to the free energy f per block copolymer chain in the films: (1) an increase in f due to packing frustration and (2) a decrease in f due to the entropy of chain ends near the block copolymer film surfaces. The SEBS has no chain ends near the surface, and we propose that the larger packing frustration of SEBS chains in the square Wigner−Seitz cells of the cylinder monolayer, and the surface half-layers in thicker films, leads to the stabilization of the spherical morphology, which has a smaller packing frustration in the monolayer and surface half-layers. The SEB cylinders and sphere monolayers have the same packing frustration as those of the SEBS, but the contribution of the added entropy of chain ends near the surface is larger for the cylinders than for the spheres, more than offsetting the effect of packing frustration and thus stabilizing the cylindrical morphology at temperatures above the OOT.
[show abstract][hide abstract] ABSTRACT: The ability for thin liquid films to wet and remain thermodynamically stable on top of one another is a fundamental challenge in developing high quality paints, coatings, adhesives, and other industrial products. Since intermolecular interactions and interfacial energies dominate in the film thickness regime from tens to hundreds of nanometers, it is desirable to tune these long-range and short-range forces in a simple, controllable manner. Starting from an unstable model homopolymer bilayer (poly(styrene)/poly(4-vinylpyridine)), we demonstrate that sandwiching an additional homopolymer layer (poly(4-bromostyrene)) between the two layers can provide needed surfactancy. As the thickness of this center layer is increased, the full trilayer transitions from unstable (thin) to stable (moderate) to unstable (thick). We experimentally show using x-ray standing waves generated via total external reflection (TER-XSW), atomic force microscopy (AFM), and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) that this behavior can be directly attributed to the autophobic dewetting phenomenon, in which the surfactant layer is thin enough to remain stable but thick enough to shield the neighboring layers, highlighting a general approach to stabilizing multilayer systems.
[show abstract][hide abstract] ABSTRACT: Block copolymer self-assembly is a burgeoning subject in polymer and materials science driven by both fundamental and applied inspirations. Whereas the vast majority of block copolymer studies have focused on highly symmetric morphologies, here we report the first observation of an unusual asymmetric cylindrical phase in thick films of an organic/organometallic block copolymer, poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS). Microscopy and X-ray scattering data establish the lack of symmetry in this structure and reveal an unusual 3-D network organization. Following selective removal of the PS matrix, the remaining nanoporous film has characteristics of potential value in separation applications such as substantial interconnection (mechanical strength), uniform pore size, and chemical and physical stability.