Influence of charge distribution on the conformation of neutral polyampholytes

Summary Two polyampholyte copolymers based on sodium-2-acrylamido-2-methylsulfonate (NaAMPS) and methacryloyloxyethyltrimethylammonium chloride (MADQUAT) have been prepared either in homogeneous solution or by an inverse microemulsion polymerization technique. The copolymer microstructure was shown to depend on the method of preparation. The microemulsion polymerization yields copolymers with a monomer sequence distribution not far from random while those obtained by polymerization in solution have a strong tendency to alternation. The aqueous-solution properties of the two samples have been investigated by viscometry. The results show that the charge distribution along the copolymer chain affects considerably its conformation, in good agreement with recent theoretical studies. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994     

Cover Picture: Toward Large‐Scale Alignment of Electrohydrodynamic Patterning of Thin Polymer Films (Adv. Funct. Mater. 15/2006)

By integrating lithography and self‐assembly via electrohydrodynamic instabilities, Russel and co‐workers are able to guide initially flat polymer films to evolve into periodic arrays of pillars over regions much greater in extent than their natural domain sizes, as detailed on p. 1992. Novel structures that involve a combination of linear ridges and pillars are also produced, mainly as as result of the dynamic merging among preformed pillars. To pattern thin polymer films via electrohydrodynamic instabilities, we design and utilize two different kinds of mask patterns to guide pillars into alignment over regions much greater in extent than their natural domain sizes. First, narrow protruding ridges that intersect to form regular patterns on the mask trigger the growth of pillars beneath. Later, square and triangular packings of pillars develop in the regions enclosed by those ridges, preserving the registry from one domain to the next over a much larger area than within individual domains in unpatterned portions of the mask. Second, small square protrusions that are prealigned into a large regular array on the mask guide the formation of square packings of pillars in domains that conform to the mask, forming a large array of pillars. Novel structures involving a combination of linear ridges and pillars are also produced mainly due to the dynamic merging among preformed pillars. Finally, we find vertex symmetry of the mask pattern is necessary for generating and preserving ordered patterns on the polymer film.     

Design and fabrication of fluid controlled dynamic optical lens system

A novel small fluid controlled optical lens system that is capable of displaying dynamic variation of its focal length and field-of-view (FOV) is designed and fabricated. In this active lens system, appropriate volume of the optical fluid can be pumped into or out of the lens chamber to provide double-convex (DCX) or double-concave (DCV) lens effect. Simple optical imaging experiments were performed using different sets of glass lenses with fixed focal lengths to determine the optimum lens configuration required for designing a dynamic optical lens system. The experimental results obtained from the glass lenses demonstrate that a combination of a single DCX lens with three DCV lenses provides a wider FOV. The flexible membranes for fluid controlled lenses were fabricated using polydimethylsiloxane polymer material, which has good optical transparency and elasticity. A simple fluid injection system is used to vary the radius of curvature of the lenses, and thereby to change the focal length. A dynamic optical lens system with a combination of one DCX and multiple variable focal length DCV lenses as designed here can image an object with a wide range of focal length and FOV. With this fluid controlled optical system, the FOV and focal length could be continuously varied and a maximum FOV of 118.3° could be achieved. The smallest f-number (f_/#) for this fluid controlled single lens system was found to be 1.3, which corresponds to the numerical aperture value of 0.35.     

Structural and electrical properties of brush plated ZnTe films

Zinc telluride thin films were deposited by the brush plating technique at a potential of −0.90 V (SCE) on conducting glass and titanium substrates at different temperatures in the range 30–90 °C. The films were polycrystalline in nature with peaks corresponding to the cubic phase. Direct band gap of 2.30 eV was observed. XPS studiers indicated the formation of ZnTe. Depth profiling studies indicated a uniform distribution of Zn and Te throughout the entire thickness. EDAX measurements were made on the films and it was found that there was a slight excess of Te. The carrier concentration was found to vary from 10¹⁴–10¹⁵ cm⁻³ with increase of substrate temperature. The mobility was found to vary from 5 to 60 cm² V⁻¹ s⁻¹.     

Dialdehyde starch‐crosslinked chitosan films and their antimicrobial effects

For improved mechanical and water‐swelling properties of chitosan films, a series of transparent films were prepared with dialdehyde starch as a crosslinking agent. Fourier transform infrared and X‐ray analysis results demonstrated that the formation of Schiff's base disturbed the crystallization of chitosan. The mechanical properties and water‐swelling properties of the films were significantly improved. The best values of the tensile strength and breaking elongation were 113.1 MPa and 27.0%, respectively, when the dialdehyde starch content was 5%. All the crosslinked films still retained obvious antimicrobial effects toward S. aureus and E. coli, and they showed potential for biomedical applications. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 993–997, 2003     

Coupled lubrication and Stokes flow finite elements

A method is developed for performing a local reduction of the governing physics for fluid problems with domains that contain a combination of narrow and non‐narrow regions, and the computational accuracy and performance of the method are measured. In the narrow regions of the domain, where the fluid is assumed to have no inertia and the domain height and curvature are assumed small, lubrication, or Reynolds, theory is used locally to reduce the two‐dimensional Navier–Stokes equations to the one‐dimensional Reynolds equation while retaining a high degree of accuracy in the overall solution. The Reynolds equation is coupled to the governing momentum and mass equations of the non‐narrow region with boundary conditions on the mass and momentum flux. The localized reduction technique, termed ‘stitching,’ is demonstrated on Stokes flow for various geometries of the hydrodynamic journal bearing—a non‐trivial test problem for which a known analytical solution is available. The computational advantage of the coupled Stokes–Reynolds method is illustrated on an industrially applicable fully‐flooded deformable‐roll coating example. The examples in this paper are limited to two‐dimensional Stokes flow, but extension to three‐dimensional and Navier–Stokes flow is possible. Copyright © 2003 John Wiley & Sons, Ltd.     

Thickness dependence of free‐standing thin films

Below a critical thickness, of about 60 nm, the glass transition temperature of polystyrene (PS) films decreases with film thickness, as demonstrated using free‐standing films. A geometrical model is developed here describing this phenomenon in the case of ideal (Gaussian) chains. This model, which can be considered as an application of the free volume model, assumes that the decrease of the glass transition temperature from thick to ultrathin films is due to the modification of the interpenetration between neighboring chains. The theoretical curve deduced from the model is in excellent agreement with the PS experimental results, without using any adjustable parameters. From these results, it can be concluded that new chain motions, usually buried in bulk samples, are expressed by the presence of the surface. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 10–17, 2007     

用电泳技术制备YBCO高温超导厚膜

介绍了电泳技术制备YBCO高温超导厚膜的实验方法和YBCO高温超导厚膜的电学性质测量 ,讨论了在学生小型科研实验或设计实验中开展此实验的学时安排、注意事项和实验内容的扩展 .     

Structure and optical properties of lead iodide based two-dimensional perovskite compounds containing fluorophenethylamines

Phenethylammonium-based perovskites, which can be regarded as a semiconductor/insulator multiple quantum well consisting of lead halide semiconductor layers sandwiched between phenethylammonium insulator layers were prepared. To investigate the effects of the electronic state and the orientation of organic insulator layers on the optical properties of layered perovskites, fluorine substituted analogues were also prepared. The structure and optical properties were investigated by the XRD, UV–Vis absorption, and fluorescence measurements. The exciton absorption peak was shifted by the substitution of fluorine atoms in organic ammonium compounds. It became clear that the optical properties of two-dimensional perovskite compounds were controlled by the substitution of fluorine atoms.     

Electrical characterization of low temperature deposited TiO2 films on strained-SiGe layers

Thin films of titanium dioxide have been deposited on strained Si_0.82Ge_0.18 epitaxial layers using titanium tetrakis-isopropoxide [TTIP, Ti(O-i-C₃H₇)₄] and oxygen by microwave plasma enhanced chemical vapor deposition (PECVD). The films have been characterized by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Dielectric constant, equivalent oxide thickness (EOT), interface state density (D_it), fixed oxide charge density (Q_f/q) and flat-band voltage (V_FB) of as-deposited films were found to be 13.2, 40.6 Å, 6×10¹¹ eV⁻¹ cm⁻², 3.1×10¹¹ cm⁻² and −1.4 V, respectively. The capacitance–voltage (C–V), current–voltage (I–V) characteristics and charge trapping behavior of the films under constant current stressing exhibit an excellent interface quality and high dielectric reliability making the films suitable for microelectronic applications.