This work reports results from the interactions of a series of monovalent and divalent cations with a triblock copolymer, poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO-PEO). Phase transition temperatures of the polymer in the presence of chloride salts with six monovalent and eight divalent cations were measured using an automated melting point apparatus. The polymer undergoes a two-step phase transition, consisting of micellization of the polymer followed by aggregation of the micelles, in the presence of all the salts studied herein. The results suggest that hydration of cations plays a key role in determining the interactions between the cations and the polymer. The modulation of the phase transition temperature of the polymer by cations can be explained as a balance between three interactions: direct binding of cations to the oxygen in the polymer chains, cations sharing one water molecule with the polymer in their hydration layer, and cations interacting with the polymer via two water molecules. Monovalent cations Na(+), K(+), Rb(+), and Cs(+) do not bind to the polymer, while Li(+) and NH4(+) and all the divalent cations investigated including Mg(2+), Ca(2+), Sr(2+), Ba(2+), Co(2+), Ni(2+), Cu(2+), and Cd(2+) bind to the polymer. The effects of the cations correlate well with their hydration thermodynamic properties. Mechanisms for cation-polymer interactions are discussed.
The best-known examples of smart, responsive hydrogels derive from poly( N-isopropylacrylamide) (PNIPAM) cross-linked polymer networks. These hydrogels undergo volume phase transitions (VPTs) triggered by temperature, chemical, and/or environmental changes. PNIPAM hydrogels can undergo more than 50-fold volume changes within ∼1 μs intervals. Studies have tried to elucidate the molecular mechanism of these extraordinarily large responses. Nevertheless, the molecular reaction coordinates that drive the VPT remain unclear. Using visible nonresonance Raman temperature-jump spectroscopy, we determined the molecular ordering of this VPT. The PNIPAM hydrophobic isopropyl and methylene groups dehydrate with time constants of 109 ± 64 and 104 ± 44 ns, initiating the volume collapse of PNIPAM. The subsequent dehydration of the PNIPAM amide groups is significantly slower, as our group previously discovered (360 ± 85 ns). This determination of the ordering of the molecular reaction coordinate of the PNIPAM VPT enables the development of the next generation of super-responsive materials.
The growth of highly crystalline rubrene thin films for organic field effect transistor (OFET) application remains a challenge. Here, we report on the vapor-deposited growth of rubrene films on the substrates made of cadmium arachidate (CdA) multilayers deposited onto SiO2/Si(100) via the Langmuir-Blodgett technique. The CdA films, containing 2n+1 layers, with integer n ranging from 0 to 4, are surface-terminated identically by the methyl group but exhibit the thickness-dependent morphology. The morphology and structure of both CdA and rubrene films are characterized by X-ray reflectivity (XRR), X-ray diffraction (XRD), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and atomic force microscopy (AFM). Crystalline rubrene films, evidenced by XRD and marked by platelet features in AFM images, become observable when grown onto the CdA layer thicker than 5L. XRD data show that vertical ordering, that is, ordering along surface normal, of CdA multilayer substrates exerts a strong influence in promoting the crystalline growth of rubrene films. This promoted growth is not due to the surface energy of CdA layer but derived from the additional interaction localized between rubrene and CdA island sidewall and presumably strengthened by a close dimensional match between the a-axis of rubrene lattice and the layer spacing of CdA multilayer. The best OFET mobility is recorded for 9L CdA substrate and reaches 6.7 × 10(-2) cm(2) V(-1) s(-1), presumably limited by the roughness of the interface between CdA and rubrene films.
Built-in self-test (BIST) is one of the most widely used design-for-testability (DFT) techniques, particularly for embedded random access memory (RAM). To ease the test and diagnosis flow, we have previously developed a synthesis compiler, called BRAINS which stands for BIST for RAM in Seconds. It possesses many nice features, such as accessibility, scalability, programmability, and flexibility, thereby improving the testability, yield, and reliability. However, for regular arrays, the conventional flow attaches a BIST circuit to each memory element, and scans in test patterns or performs sequential diagnosis, so is inefficient in terms of test time. In this work, we extend the BRAINS functions by taking advantage of the regular structure. With these extensions, the test and diagnosis flow becomes very simple. In the experiments on a 32-core array, the overall test time can be reduced by 6 to 23 times with only minor area overhead varying from 10% to 17%, as compared with the original BRAINS design.
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