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Nuclear reaction analysis: A study on the interface formation in polymer mixtures below the critical point. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/masy.19910450128] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Abstract
We present a complete analysis of the structure of polyethylene (PE) nanoparticles synthesized and stabilized in water under very mild conditions (15 degrees C, 40 atm) by a nickel-catalyzed polymerization in aqueous solution. Combining cryogenic transmission electron microscopy (cryo-TEM) with X-ray scattering, we demonstrate that this new synthetic route leads to a stable dispersion of individual PE nanoparticles with a narrow size distribution. Most of the semicrystalline particles have a hexagonal shape (lateral size 25 nm, thickness 9 nm) and exhibit the habit of a truncated lozenge. The combination of cryo-TEM and small-angle X-ray scattering demonstrates that the particles consist of a single crystalline lamella sandwiched between two thin amorphous polymer layers ("nanohamburgers"). Hence, these nanocrystals that comprise only ca. 14 chains present the smallest single crystals of PE ever reported. The very small thickness of the crystalline lamella (6.3 nm) is related to the extreme undercooling (more than 100 degrees C) that is due to the low temperature at which the polymerization takes place. This strong undercooling cannot be achieved by any other method so far. Dispersions of polyethylene nanocrystals may have a high potential for a further understanding of polymer crystallization as well as for materials science as, e.g., for the fabrication of extremely thin crystalline layers.
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Switching layer stability in a polymer bilayer by thickness variation. PHYSICAL REVIEW LETTERS 2007; 98:267802. [PMID: 17678129 DOI: 10.1103/physrevlett.98.267802] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2007] [Indexed: 05/16/2023]
Abstract
We use optical and scanning force microscopy to explore the possibility of switching the stability of a bilayer of poly(methyl methacrylate) (PMMA) on polystyrene by simply changing the film thickness. We show that for thin PMMA layers on thicker polystyrene films the PMMA layer is unstable to thickness fluctuations. However, polystyrene layers are unstable when they are substantially thinner than the now stable PMMA film. Dewetting morphologies are cataloged as a function of the thickness of individual polymer layers by identifying which layer is unstable by which mechanism, be it spinodal dewetting or heterogeneous thermal nucleation. Our results are in good agreement with a linear stability analysis of the influence of long-range dispersion forces, but also indicate the influence of film preparation and small variations of material properties.
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Scaling behavior of the reorientation kinetics of block copolymers exposed to electric fields. SOFT MATTER 2007; 3:448-453. [PMID: 32900064 DOI: 10.1039/b614143a] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We have followed the reorientation kinetics of various block copolymer solutions exposed to an external electric DC field. The characteristic time constants follow a power law indicating that the reorientation is driven by a decrease in electrostatic energy. Moreover, the observed exponent suggests an activated process in line with the expectations for a nucleation and growth process. When properly scaled, the data collapse onto a single master curve spanning several orders of magnitude both in reduced time and in reduced energy. The power law dependence of the rate of reorientation derived from computer simulations based on dynamic density functional theory agrees well with the experimental observations. First experiments in AC electric fields at sufficiently high frequencies confirm the notion that the reorientation process is dominated by differences in the dielectric constants rather than by mobile ions.
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Interactions between Methyl Cellulose and Sodium Dodecyl Sulfate in Aqueous Solution Studied by Single Molecule Fluorescence Correlation Spectroscopy. Macromolecules 2006. [DOI: 10.1021/ma0616920] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Site-Specific Binding of the 9.5 Kilodalton DNA-Binding Protein ORF80 Visualized by Atomic Force Microscopy. Biomacromolecules 2005; 6:1252-7. [PMID: 15877339 DOI: 10.1021/bm0494489] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Atomic force microscopy (AFM) has been used to examine the binding properties of the DNA-binding protein ORF80 to DNA. ORF80 is a 9.5 kDa protein that binds site-specifically to double-stranded DNA of the sequence TTAA-N(7)-TTAA. Direct sizing of the protein complexes on DNA fragments from the plasmid pRN1 with AFM shows that the protein ORF80 binds preferentially to two positions. These positions agree well with the ORF80 binding sites determined by footprinting analysis. The measurements allow an estimate of the stoichiometry of the DNA-protein complexes. In contrast to previous results, the single-molecule experiments suggest that only a low number of ORF80 molecules bind to a DNA-binding site.
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Combinatorial Mapping of the Phase Behavior of ABC Triblock Terpolymers in Thin Films: Experiments. Macromolecules 2005. [DOI: 10.1021/ma049048d] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Direct imaging and mesoscale modelling of phase transitions in a nanostructured fluid. NATURE MATERIALS 2004; 3:886-891. [PMID: 15568030 DOI: 10.1038/nmat1258] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/02/2004] [Accepted: 09/15/2004] [Indexed: 05/24/2023]
Abstract
The kinetics of phase transitions is essential for understanding pattern formation in structured fluids. These fluids play a key role in the morphogenesis of biological cells, and they are very common in pharmaceutical products and plastic materials. Until now, it has not been possible to follow phase transitions in structured fluids experimentally in real time and with high spatial resolution. Previous work has relied on static images and indirect experimental evidence from spatially averaging scattering experiments. Simulating the processes with computer models is a further challenge because of the multiple time and length scales involved. Our movies based on in situ scanning force microscopy show the time sequence of the elementary steps of a phase transition in a fluid film of block copolymer from the cylinder to the perforated lamella phase. The movies validate a versatile simulation model that gives physical insight into the nature of the process. Our approach provides a means of improving the study and understanding of pattern formation processes in nanostructured fluids. We expect a significant impact on nanotechnology where block copolymers serve as self-organized templates for the synthesis of inorganic nanostructured materials.
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Microscopic mechanisms of electric-field-induced alignment of block copolymer microdomains. PHYSICAL REVIEW LETTERS 2002; 89:135502. [PMID: 12225034 DOI: 10.1103/physrevlett.89.135502] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2002] [Indexed: 05/23/2023]
Abstract
We investigate the microscopic mechanisms responsible for microdomain alignment in block copolymer solutions exposed to an electric field. Using time-resolved synchrotron small-angle x-ray scattering, we reveal two distinct processes, i.e., grain boundary migration and rotation of entire grains, as the two dominant microscopic mechanisms. The former dominates in weakly segregating systems, while the latter is predominant in strongly segregated systems. The kinetics of the processes are followed as a function of polymer concentration and temperature and are correlated to the solution viscosity.
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Phase behavior in thin films of cylinder-forming block copolymers. PHYSICAL REVIEW LETTERS 2002; 89:035501. [PMID: 12144400 DOI: 10.1103/physrevlett.89.035501] [Citation(s) in RCA: 350] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2001] [Indexed: 05/23/2023]
Abstract
We have experimentally determined a phase diagram for cylinder-forming polystyrene-block-polybutadien-block-polystyrene triblock copolymer in thin films. The phase behavior can be modeled in great detail by dynamic density functional theory. Deviations from the bulk structure, such as wetting layer, perforated lamella, and lamella, are identified as surface reconstructions. Their stability regions are determined by an interplay between surface fields and confinement effects.
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UV light-damaged DNA and its interaction with human replication protein A: an atomic force microscopy study. Nucleic Acids Res 2002; 30:2686-91. [PMID: 12060686 PMCID: PMC117290 DOI: 10.1093/nar/gkf378] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
We have imaged a non-damaged and UV-damaged DNA fragment and its complexes with human replication protein A (RPA) using tapping mode atomic force microscopy (AFM). For imaging, molecules were immobilized under nearly physiological conditions on mica surfaces. Quantitative sizing of the 538 bp DNA before and after UV light treatment shows a reduction in the contour and persistence lengths and mean square end-to-end distance as a consequence of UV irradiation. Complexes of the UV-damaged DNA with RPA, an essential component of the initial steps of nucleotide excision repair, can be detected at high resolution with AFM and reveal conformational changes of the DNA related to complex formation. By phase image analysis we are able to discriminate between protein and DNA in the complexes. The DNA molecules are found to 'wrap' around the RPA, which in turn results in a considerable reduction in its apparent contour length.
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Surface reconstruction of an ordered fluid: an analogy with crystal surfaces. PHYSICAL REVIEW LETTERS 2001; 87:035505. [PMID: 11461568 DOI: 10.1103/physrevlett.87.035505] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2001] [Indexed: 05/23/2023]
Abstract
The surface structure of a lamellar polystyrene-block-polybutadiene-block-polymethylmethacrylate (SBM) triblock copolymer forms a complex reconstruction, which breaks the two-dimensional continuous translational symmetry of an ideal (homogeneous) SBM surface. Despite the very different types of matter and order, our findings reveal a remarkable analogy with the well-known phenomenon of surface reconstruction of single crystals, in particular, with the (2x1) "buckling row" reconstruction of the Si(100) surface. Similarities and differences between both classes of materials are discussed on the basis of symmetry considerations.
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Tapping Mode Atomic Force Microscopy on Polymers: Where Is the True Sample Surface? Macromolecules 2001. [DOI: 10.1021/ma001311x] [Citation(s) in RCA: 195] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Wetting in a phase separating polymer blend film: quench depth dependence. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 2000; 62:940-50. [PMID: 11088551 DOI: 10.1103/physreve.62.940] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/19/1999] [Revised: 04/10/2000] [Indexed: 04/15/2023]
Abstract
We have used 3He nuclear reaction analysis to measure the growth of the wetting layer as a function of immiscibility (quench depth) in blends of deuterated polystyrene and poly(alpha-methylstyrene) undergoing surface-directed spinodal decomposition. We are able to identify three different laws for the surface layer growth with time t. For the deepest quenches, the forces driving phase separation dominate (high thermal noise) and the surface layer grows with a t(1/3) coarsening behavior. For shallower quenches, a logarithmic behavior is observed, indicative of a low noise system. The crossover from logarithmic growth to t(1/3) behavior is close to where a wetting transition should occur. We also discuss the possibility of a "plating transition" extending complete wetting to deeper quenches by comparing the surface field with thermal noise. For the shallowest quench, a critical blend exhibits a t(1/2) behavior. We believe this surface layer growth is driven by the curvature of domains at the surface and shows how the wetting layer forms in the absence of thermal noise. This suggestion is reinforced by a slower growth at later times, indicating that the surface domains have coalesced. Atomic force microscopy measurements in each of the different regimes further support the above. The surface in the region of t(1/3) growth is initially somewhat rougher than that in the regime of logarithmic growth, indicating the existence of droplets at the surface.
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Real space observation of dynamic scaling in a critical polymer mixture. PHYSICAL REVIEW LETTERS 1993; 71:3669-3672. [PMID: 10055042 DOI: 10.1103/physrevlett.71.3669] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Microscopic observation of atomic disorder near the roughening transition at vicinal copper surfaces. PHYSICAL REVIEW LETTERS 1993; 70:2455-2458. [PMID: 10053566 DOI: 10.1103/physrevlett.70.2455] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Formation of an ultrathin amorphous layer at In/Pd interfaces observed by local and nonlocal techniques. PHYSICAL REVIEW. B, CONDENSED MATTER 1993; 47:10048-10051. [PMID: 10005107 DOI: 10.1103/physrevb.47.10048] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Binding and mobility of isolated indium atoms on Si(111)7 x 7. PHYSICAL REVIEW LETTERS 1992; 68:377-380. [PMID: 10045876 DOI: 10.1103/physrevlett.68.377] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Monolayer-resolved detection of magnetic hyperfine fields at Cu/Ni(111) interfaces. PHYSICAL REVIEW LETTERS 1991; 66:3199-3202. [PMID: 10043724 DOI: 10.1103/physrevlett.66.3199] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Magnetic hyperfine field at 111In probes in the topmost atomic layer of Ni(111) surfaces. PHYSICAL REVIEW LETTERS 1990; 64:2202-2205. [PMID: 10041610 DOI: 10.1103/physrevlett.64.2202] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Dynamics of mixing between partially miscible polymers. PHYSICAL REVIEW LETTERS 1990; 64:1119-1121. [PMID: 10041304 DOI: 10.1103/physrevlett.64.1119] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Interfacial structure in polymer mixtures below the critical point. PHYSICAL REVIEW LETTERS 1989; 63:616-619. [PMID: 10041128 DOI: 10.1103/physrevlett.63.616] [Citation(s) in RCA: 30] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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