Home About us Contact
|
Home About us Contact | ||
|
|
||
Mica Surface (mica + surface)
Selected AbstractsDirect atomic force microscopy observations of monovalent ion induced binding of DNA to micaJOURNAL OF MICROSCOPY, Issue 3 2004J. S. ELLIS Summary Multivalent ions in solution are known to mediate attraction between two like-charged molecules. Such attraction has proved useful in atomic force microscopy (AFM) where DNA may be immobilized to a mica surface facilitating direct imaging in liquid. Theories of DNA immobilization suggest that either ,salt bridging' or fluctuation in the positions of counter ions about both the mica surface and DNA backbone secure DNA to the mica substrate. Whilst both theoretical and experimental evidence suggest that immobilization is possible in the presence of divalent ions, very few studies identify that such immobilization is possible with monovalent ions. Here we present direct AFM evidence of DNA immobilized to mica in the presence of only monovalent ions. Our data depict E. coli plasmid pBR322 adsorbed onto the negatively charged mica both after short (10 min) and long (24 h) incubation periods. These data suggest the need to re-explore current theories of like-charge attraction to include the possibility of monovalent interactions. We suggest that this DNA immobilization strategy may offer the potential to image natural processes with limited immobilization forces and hence enable maximum conformational freedom of the immobilized biomolecule. [source] Structures and Chiroptical Properties of Thermoresponsive Block Copolymers Containing L -Proline MoietiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 17 2007Hideharu Mori Abstract Amino acid-based block copolymers containing poly(A-Pro-OMe) have been synthesized by RAFT polymerization using the dithioester-terminated poly(DMA) as a macro-CTA. An amphiphilic block copolymer composed of polystyrene as a hydrophobic segment and poly(A-Pro-OMe) as a hydrophilic segment was also prepared using polystyrene as the macro-CTA. The chiroptical properties of the block copolymer, poly(DMA)- block -poly(A-Pro-OMe), was evaluated by specific rotation, CD, and UV-vis spectroscopy. The assembled structure of the block copolymer on a mica surface was characterized by SFM. Thermally induced phase separations of the random and block copolymers were also studied in aqueous solution. [source] New Polymeric Materials with Interferential Optical PropertiesMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 13 2007Leïla Ghannam Abstract Nature provides a wide pallet of colors but also a wide number of fascinating optical phenomena such as nacre or interferential effects, which can be observed in insect wings and shellfish. The origin of such effects is attributed to the presence of highly ordered arrangements in Nature's materials. The aim of this paper is to focus some new approaches and advances for creating interferential optical phenomena as observed in nature by tuning or modeling the polymer architectures or organization. A relatively simple method is described to prepare organic/inorganic hybrid pigments constituted of mica platelets and adsorbed polymer layers. It is shown that the color of mica is changed upon polymer adsorption, and when one of the copolymer sequences includes a dye, its color is influenced by the chemical properties of the mica surface. Moreover, a new facile route is presented to obtain highly ordered surfaces using ionomer macromolecular designs synthesized in one step by controlled radical polymerization. The preparation of films with very regular pore size and spatial organization is successfully realized by using ionomer solutions. An original property of these films with an iridescent color obtained by light diffraction as a result of the optical interferences of sunlight with the periodic honeycomb structures is presented. All these new materials based on polymeric controlled structures can reproduce nature by creating an optical interferential and iridescent material, which offers new fascinating applications as original bio-mimetic materials on inorganic surfaces. [source] Synthesis and SFM Study of Comb-Like Poly(4-vinylpyridinium) Salts and Their Complexes with SurfactantsMACROMOLECULAR RAPID COMMUNICATIONS, Issue 13 2006Marat O. Gallyamov Abstract Summary: Poly(4-vinylpyridinium) bromides containing octyl and dodecyl pendant groups were synthesized. Bromide anions in these polymer salts were substituted with dodecylsulfate and bis(2-ethylhexylsuccinate) anions using ion-exchange reactions. Initially, P4VP and its derivatives loaded with hydrophobic groups were deposited on a mica surface from diluted solutions in chloroform for visualization. Images of single adsorbed macromolecules were obtained using scanning force microscopy. Original P4VP chains form partially compacted self-intersecting coils. Loading the polymer chains with large hydrophobic groups and especially the increase in the number of alkyl tails (see Figure) per monomer unit of the polymer chain leads to the stretching of the coils, and the comb-like macromolecules adopt more and more extended self-avoiding 2D conformations when deposited on the substrate. Polymer chains with large hydrophobic groups and increasing number of alkyl tails per monomer unit of the polymer chain. [source] Effect of maleated polypropylene and impact modifiers on the morphology and mechanical properties of PP/Mica compositesPOLYMER COMPOSITES, Issue 6 2006H. Yazdani Composites of polypropylene (PP) with mica powder and impact modifiers were produced by internal mixer. A major drawback in the use of mica-filled PP is its low impact resistance. In the present study, the effect of the maleated PP (MAPP) and impact modifiers was evaluated on the composite properties separately and together. Thus, two different styrene-ethylene/butylene-styrene triblock copolymers (SEBS) and one ethylene-propylene-diene terpolymer (EPDM) have been used as impact modifiers in the PP-mica composites. Addition of MAPP had a negative effect on the composite notched impact strength and elongation at break but had a positive effect on tensile strength when used together with impact modifiers. All three elastomers increased the impact strength of the PP-mica composites but the addition of maleated SEBS (SEBS-MA) granted the greatest improvement in impact strength. It was inferred from the scanning electron microscopy that SEBS-MA had a stronger interaction with mica surface than the other impact modifiers. POLYM. COMPOS., 27:614,620, 2006. © 2006 Society of Plastics Engineers [source] Molecular-scale investigation of polymerization, nucleation, and growth of polystyrene particle by atomic force microscopyASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008Tetsuya Yamamoto Abstract To clarify the mechanism of the nucleation and growth processes in the soap-free polymerization of polystyrene latex particles in water, the polymerization process was investigated on a molecular scale, by using an atomic force microscope (AFM), as well as a scanning electron microscope (SEM) and a dynamic light scattering apparatus (DLS). A ,cationic' initiator was employed to make all the polymeric materials produced, such as oligomers, embryos, nuclei, and grown particles, adsorb electrostatically on the negatively charged mica plate of molecular-scale smoothness. This in situ transfer of polymeric materials in the bulk onto the mica surface enables us to observe the images of polymeric materials during the reaction process and to estimate what is happening in the nucleation and growth processes of particles, at least qualitatively. The most important findings of the present study are that1 these molecular-scale polymeric materials, to which much attention has not been paid probably because of the difficulty of detection, are continuously born in the bulk throughout the reaction process of particle formation, and2 they play an important role in the growth of particles. Copyright © 2008 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Photoinduced Luminescence Blinking and Bleaching in Individual Single-Walled Carbon NanotubesCHEMPHYSCHEM, Issue 10 2008Carsten Georgi Abstract The temporal evolution of photoluminescence in individual single-walled carbon nanotubes (SWNT) under strong laser irradiation is studied and pronounced blinking and bleaching is observed, caused by photoinduced oxidation that subsequently quenches mobile excitons. The nanotubes are isolated with sodium cholate and spun onto either a glass or mica surface. Their bleaching behavior is investigated for variable laser intensities in air and argon atmosphere. The decay rate for luminescence bleaching generally increases with higher laser intensity, however saturating on mica substrates, which is attributed to limited availability of oxygen in the vicinity of the nanotubes. Step-like events in the luminescence time traces corresponding to single oxidation events are analyzed regarding relative step height and suggest an exciton diffusion range of about 105 nm. [source] Forces between Surfactant-Coated ZnS Nanoparticles in Dodecane: Effect of Water,ADVANCED FUNCTIONAL MATERIALS, Issue 16 2006Alig, R. Godfrey Abstract The forces between mica surfaces confining solutions of spherical and rod-shaped ZnS nanoparticles (diameter ca. 5,nm) coated with hexadecylamine or octadecylamine surfactant in dodecane have been measured in the absence and after the introduction of trace amounts of water. Initially, or at very low water content, the water molecules cause the nanoparticles to aggregate and adsorb on the hydrophilic mica surfaces, resulting in a long-range exponentially decaying repulsive force between the surfaces. After longer times (>,20,h), water bridges nucleate and grow between the nanoparticles and mica surfaces, and attractive capillary forces then cause a long-range attraction and a strong (short-range) adhesion. It is found, as has previously been observed in nonaqueous bulk colloidal systems, that even trace amounts of water have a profound effect on the interactions and structure of nanoparticle assemblies in thin films, which in turn affect their physical properties. These effects should be considered in the design of thin-film processing methodologies. [source] | |||||||||||||