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The melt rheological properties of layered silicate nanocomposites with maleic anhydride (MA) functionalized polypropylene are contrasted to those based on ammonium-terminated polypropylene. While the MA functionalized PP based nanocomposites exhibit solid-like linear viscoelastic behavior, consistent with the formation of a long-lived percolated nanoparticle network, the single-end ammonium functionalized PP based nanocomposites demonstrated liquid-like behavior at comparable montmorillonite concentrations. The differences in the linear viscoelasticity are attributed to the presence of bridging interactions in MA functionalized nanocomposites. Further, the transient shear stress of the MA functionalized nanocomposites in start-up of steady shear is a function of the shear strain alone, and the steady shear response is consistent with that of non-Brownian systems. The weak dependence of the steady first normal stress difference on the steady shear stress suggests that the polymer chain mediated silicate network contributes to such unique flow behavior.
β-Cyclodextrin derivatives, MRCD and p-MRCD, which have a 4-(dimethylamino)azobenzene moiety with a carbonyl substituent at 2′ and 4′ positions, respectively, have been prepared as color change indicators for detecting organic compounds. In a 10% ethylene glycol solution, MRCD and p-MRCD form intramolecular self-complexes in which the pendant dye moiety is included in the cyclodextrin cavity with an orientation parallel and perpendicular to the cyclodextrin axisis, respectively. When guest molecules are added to the acidic solutions of MRCD (pH 1.60) and p-MRCD (pH 2.40), they exhibit color changes from yellow to red for MRCD and from orange to red for p-MRCD. These color changes, which arise from the structural change of the dye moieties from the azo form to the azonium one, are caused when MRCD and p-MRCD undergo a conformational change in which the dye moieties inserted in the cyclodextrin cavities are excluded to outside of the cavities upon guest accommodation. The extent of the guest-induced color changes of MRCD and p-MRCD depend on the shape, size, number, and position of the functional group of guest molecules. Selectivities between MRCD and p-MRCD in guest detection are roughly parallel and reflected in the host-guest binding constants. Among guest molecules examined, ursodeoxycholic acid and chenodeoxycholic acid were detected by MRCD and p-MRCD with high sensitivities. 1-Adamanetanecarboxylic acid and (-)borneol were also detected with high sensitivities. In neutral conditions, however, the selectivity in guest detection of p-MRCD is different from that in acidic conditions as shown by the fact that, for example, 1-adamantanol and 2-adamantanol were detected by p-MRCD with larger sensitivities than 1-adamanetanecarboxylic acid. The result indicates that the ionic nature of the guest molecules is an important factor for detection of the guest molecules. All these results demonstrate that MRCD and p-MRCD can be used as color change indicators for detecting various organic compounds in aqueous solution.
Poly(ethylene glycol) (PEG)-substituted cyclodextrins (CDs) with different chain lengths have been synthesized. PEG-substituted CDs formed self-threading complexes in aqueous solutions, and the conformational exchange dynamics between self-threading and dethreading could be regulated by its chain length.
The term nanocomposite is widely employed to describe an extremely broad range of materials, where one of the components has a dimension on the submicron scale. A better and far more restrictive definition would require that a true nanocomposite be a fundamentally new material (hybrid) in which the nanometerscale component or structure gives rise to intrinsically new properties, which are not present in the respective macroscopic composites or the pure components. The latter definition necessitates that the nanostructure has dimensions smaller than a characteristic scale that underlies a physical property of the material. For example, for the electronic properties of a conductor or semiconductor, this scale would relate to the de Broglie wavelength of the electron (ranging from a few nanometers for a metal to hundreds of nanometers for a semiconductor), for the mechanical properties of a polymer it would relate to the size of the polymer coil or crystal (again ranging from a few nanometers to hundreds of nanometers), and for the thermodynamic properties of a polymer glass it would relate to the cooperativity length (a few nanometers).In this chapter we restrict our discussion even further, focusing on one subclass of polymer-inorganic nanocomposites, where the polymers are typically thermoplastics and the inorganic component is a high aspect ratio nanoscale filler. Particular emphasis will be given to principles that apply to pseudo-twodimensional layered inorganic fillers (such as 2:1 aluminosilicates, 1 -9 from where
A self-aligned process for InP/InGaAs HBTs using T-shaped emitter electrodes has been developed. Using this process, the difference in spacing bemeen the emitter mesa and the base electrode, due to the emitter orientations, can be minimized. The process also reduces differences in characteristics of the IiBTs. 0 1996 John Wiley & Sons, Inc. INTRODUCTIONThe InP-based heterojunction bipolar transistor (HBT) has great potential due to the high electron mobility of InGaAs in the base and the high electron velocity in the collector. These are caused by the large energy gap in the valley between I? and L [l]. The very high potential of the high cutoff frequency and high-speed circuit operation has already been demonstrated by many researchers [2-81. To obtain high performance, especially for low base resistance, a selfaligned process to bring the base electrode close to the emitter region is very important. In conventional self-aligned InP/InGaAs HBTs, the spacing between the emitter mesa and the base ohmic contact is formed by side etching of the emitter using a wet etch [6]. This wet etching process has good selectivity between InP and InGaAs. The shape of the emitter mesa, however, depends on the crystal plane orientations. The characteristics of HBTs are affected by whether the emitter electrode orientation is parallel or perpendicular to the orientation flat. The wet etching process has an another problem: It does not form an undercut in the (1171, (111) InP planes. So, in the conventional process, side etching has to be controlled by ctching of the InGaAs emitter cap.Recently, an article reporting that this process could be done by ECR dry etching was published [7]. All of these processes still have a limit though, in the minimum thickness of the emitter cap and emitter layers, because the total thickness must be thicker than the base metal to avoid shorting between the emitter and the base electrodes. The proposed process, using a T-shaped emitter electrode, offers better control when forming the desired spacing around the emitter mesa. This is because the undercut of the emitter electrode is not affected by isotropic side etching, unlike the conventional emitter etching process. It also avoids the minimum limit on the epitaxial layer thickness by optimizing the thickness of the lower emitter electrode metal. THE PROPOSED STRUCTURE AND THE PROCESS OF InP1InGaAs HBT A schematic of the InP/InGaAs HBT fabrication process is shown in Figure 1. Figure l(d) shows the proposed structure using a T-shaped emitter electrode. This electrode is made of two different metals that are selected because of their different etching rates. In our HBTs, the bottom metal is WSi, which was selected because of its high etching rate against RIE compared to W, the upper metal. These metals were also selected because they are not etched by the semiconductor etch and are very stable at high temperatures. The selectivity of W is more than 10 times that of WSi, so only WSi is etched toward the inside during overetching. The T shap...
Polypropylene (PP)/Ti‐MCM‐41 nanocomposites were prepared by isospecific propylene polymerization with Ti‐MCM‐41/Al(i‐C4H9)3 catalyst. The cross polarization/magic angle spinning (CP/MAS) 13C NMR spectrum of the composite was similar to that of the conventional isotactic PP, and the decrease in the pore volume of Ti‐MCM‐41 in the nanocomposites, as measured by N2 adsorption, was consistent with the value calculated from the weight loss in the thermogravimetric analysis (TGA) curve; both these facts attest to propylene polymerization within the mesopores of Ti‐MCM‐41. Alkali treatment followed by extraction with o‐dichlorobenzene allows us to extract the confined PP out of the Ti‐MCM‐41 mesopores. Although the PP/Ti‐MCM‐41 nanocomposites do not exhibit a crystalline melting point, the same PP when extracted from the mesopores showed a clear melting point at 154.7 °C; this indicates that the crystallization of PP confined in mesopores is strongly hindered. For the PP polymerized within the confinement, the molecular weight (Mw) and molecular weight distribution (Mw/Mn) were 84,000 and 4.3, respectively; these values were considerably smaller than those of the PP polymerized concurrently outside the Ti‐MCM‐41 mesopores (Mw = 200,000–450,000, Mw/Mn = 40–75). Therefore, the confinement also has a marked effect on the molecular weight of the PP. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3324–3332, 2003
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