Evolution of Porosity by Freeze Casting and Sintering of Sol-Gel Derived Ceramics

Freeze cast of aqueous ceramic powder slurries is described as a versatile process to fabricate complex-shaped ceramic parts. Since freezing of aqueous sols or powder suspensions include the nucleation and growth of ice crystals the evolving microstructure in particular the pore characteristics which are left behind after elimination of the solvent can be controlled by the freezing process. The freezing kinetics have then to be used to manifest the conditions for the formation of the intended porosity. The temperature profile in the freezing slurry was measured and calculated, in particular the movement of the freezing front through the slurry was determined. The results show that a homogeneous microstructure is reached in the surface region of the consolidated part. Individual ice crystals are detected within a distance of some hundred micrometers from the surface. The final pores are dendritic in shape with an elliptical cross section. The pores can grow up to several millimeters in length under the process conditions used in this study. The limits of freeze-sensitive slurry compositions should be investigated in further studies and the approach should be followed to increase the porosity by additional foaming steps.     

Influence of the Phase Morphology on the Viscoelastic Behaviour of Polymer Blends (PP-EPR)

Summary. Melts of polyethylene-propylene-rubber (EPR, blends of linear polyethylene, linear polypropylene, and PE-PP copolymer) show phase separation. The influence of the phase morphology on the viscoelastic behaviour is studied with the aid of the dynamical moduli. The measured moduli of the fraction of the linear homopolymer of an EPR agree with the moduli calculated from the molar mass distribution of this fraction. In contrast, the copolymer fraction shows a strong rubber-like behaviour (represented by a characteristic relaxation time spectrum). Mixtures of 80 wt% linear PP and of EPRs with low copolymer content are not rubber-like liquids. In addition, the moduli from them can be calculated from the moduli of the components with the aid of Palierne’s emulsion model. This clearly reveals that the linear PP forms the matrix in this case. Mixtures of 80 wt% linear PP and of EPRs with high copolymer content show rubber-like behaviour and Palierne’s emulsion model is not applicable on them. Obviously, the copolymer fraction forms a physical network.     

Low-temperature synthesis and growth mechanism of uniform nanorods of bismuth sulfide

A low-temperature solution-phase method has been demonstrated for the synthesis of uniform nanorods of Bi₂S₃ with diameter of 18 nm and length of below 200 nm. Transmission electron microscopy (TEM), selected-area electron diffraction (SAED), and X-ray diffraction (XRD) studies revealed that these nanorods were grown from a colloidal dispersion of amorphous Bi₂S₃ particles, which was first formed through a thermal reaction between Bi-thiol complexes Bi(SC₁₂)₃ and thioacetamide (TAA) in a pure dodecanethiol (C₁₂SH) solvent at a temperature of 95 °C. Based on these studies, the growth mechanism of Bi₂S₃ nanorods was properly proposed.     

CRYSTALLIZATION OF BLENDS OF AN ASYMMETRIC POLY（OXYETHYLENE）-b-POLY（OXYBUTYLENE） BLOCK COPOLYMER WITH POLY（OXYBUTYLENE）

An oxyethylene/oxybutylene block copolymer with asymmetric volume fraction (E115B103) was blended with oxybutylene homopolymer (Bh) at different volume fractions of the block (φE). Crystallization behavior of the blends was studied and was compared with that of the blends from a symmetric block copolymer (E114B56). It was found that the crystallization temperature of E115B103/B28 blend is lower than that of the blends from symmetric block copolymer. For the blend with φE= 0.30 breakout crystallization with an Avrami exponent n ≈ 3.0 is observed. At φE = 0.22 the blend exhibits a variable crystallization behavior: confined crystallization with n ≈ 1.0 at lower crystallization temperatures but breakout crystallization at high crystallization temperatures. For the blend with φE = 0.14 and sphere morphology confined crystallization occurs at all crystallization temperatures studied. When compared with the blends from symmetric block copolymer, confined crystallization occurs more easily in the E115B103/B28 blends. The SAXS results agree with the isothermal crystallization kinetics. Deformation of the confined crystalline block is observed in the blend with φE = 0.14 and mixed lamellar and cylinder morphologies in the blend with φE = 0.22.     

界面张力对高分子共混物梯度相形态形成的影响研究

研究了界面张力对ＰＰ／ＥＶＡ共混体系梯度相形态形成的影响。首先将ＥＶＡｃ进行皂化反应得到一系列－ＯＨ基含量不同即极性不同的ＥＶＡ，然后将这些ＥＶＡ分别与ＰＰ共混从而得到一系列相界面张力不同的共混物。说明通过对共混物相界面张力的调整，可以达到随意控制梯度相形态形成速度的目的。     

Calculation of the adsorption of rod-like molecules in narrow slit-shaped pores

The adsorption of rod-like molecules in slit-shaped pores was considered within the frame-work of the lattice-gas model. This model is applicable over a broad range of fluid concentrations (from the gaseous to the liquid state) and temperatures (including the critical region). In the calculation of the local distributions of mixture components in the equilibrium states, lateral interactions are taken into account. The equations of the model reflect the strong anisotropy of the distribution of mixture components along the normal to the pore wall surface and ordering of the rods along various directions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1476–1484, September, 2006.     

Study of bulk morphology of polymer latex films using laser confocal fluorescence microscopy

Ｐｏｌｙｍｅｒｆｉｌｍｆｏｒｍａｔｉｏｎｆｒｏｍｅｉｔｈｅｒｌａｔｅｘｏｒｓｏｌｕｔｉｏｎｉｓｑｕｉｔｅａｎｉｎｔｅｒｅｓｔｉｎｇｂｕｔｃｏｍｐｌｉｃａｔｅｄｓｕｂｊｅｃｔｄｅａｌｉｎｇｗｉｔｈｄｉｆｆｕｓｉｏｎ,ｉｎｔｅｒｐｅｎｅｔｒａｔｉｏｎａｎｄｃｏａｇｕｌａｔｉｏｎｏｆｐｏｌｙｍｅｒｃｈａｉｎｓ,ａｎｄｅｓｐｅｃｉａｌｌｙｃｏｒｒｅｌａｔｅｄｔｏｔｈｅｐｒｏｐｅｒｔｉｅｓｏｆｔｈｅｆｉｎａｌｌｙｆｏｒｍｅｄｆｉｌｍ.Ｍａｎｙｓｔｕｄｉｅｓ[1—3]ｈａｖｅｂｅｅｎｃａｒｒｉｅｄｏｕｔｏｎｌａｔ…     

Au nanolayers deposited on polyethyleneterephtalate and polytetrafluorethylene degraded by plasma discharge

Polyethyleneterephtalate (PET) and polytetrafluorethylene (PTFE) foils were modified by plasma discharge. The effect of plasma modification on polymer surface wettability and on properties of gold coatings were studied as a function of time from plasma exposure (aging time) and polymer substrate temperature. Thickness, sheet resistance, and surface topology of gold layers were studied. Aging of the plasma‐exposed samples is accompanied by increase in contact angle, which is explained by rearrangement of the polymer segments in the polymer surface monolayer, and a decrease in the concentration of polar groups. The aging also leads to a decline in surface roughness R_a measured by atomic force microscopy (AFM). Under deposition conditions, comparable thicknesses of deposited Au layers were prepared on pristine PET and plasma‐treated PET and PTFE samples. The thinnest Au layers were evaporated onto pristine PTFE. The sheet resistance decreases with increasing thickness of Au layer. Plasma treatment leads to an increase of PTFE surface roughness, which becomes even more pronounced after Au deposition. A higher roughness shows that the PET samples are deposited with the Au layer at temperatures above the glassy transition temperature T_g. Copyright © 2006 John Wiley & Sons, Ltd.     

Single crystals of regio-selectively substituted cellulose hetero-esters

Lamellar single crystals of some regio-selectively substituted cellulose hetero-esters: cellulose propionate diacetate (CPDA, 2,3-di-O-acetyl-6-O-propionyl cellulose), cellulose acetate dipropionate (CADP, 6-O-acetyl-2,3-di-O-propionyl cellulose), cellulose butyrate diacetate (CBDA, 2,3-di-O-acetyl-6-O-butyryl cellulose) and cellulose acetate dibutyrate (CADB, 6-O-acetyl-2,3-di-O-butyryl cellulose), have been prepared at high temperature in a mixture of dibenzyl ether andn-tetradecane. The CPDA crystals were lozenge-shaped whereas those of CADP, CBDA and CADB had a ribbon morphology. CPDA crystals gave well-resolved electron diffractograms from which the reciprocal lattice parameters a^*=0.807 nm^–1,b ^*=0.400 nm^–1 and ^*=90° could be determined. Systematic absences occurred at every odd reflection along the two orthogonal axesa ^*andb ^*. Thus, the CPDA diffraction pattern is consistent with a p_gg symmetry. For CADP, the electron diffraction pattern is consistent with a p_mg two-dimensional space group withb the unique axis along the ribbon direction. The diagram yields the reciprocal lattice parameters a^* = 0.902 nm^–1,b ^*=0.651 nm^–1 and ^*=90°. The CBDA electron diffractogram yields the following cell parameters and two-dimensional space group:a ^*=0.482 nm^–1,b ^*=0.659 nm^–1 and ^*=90°, and a p_gg symmetry; and that of CADB:a ^*=0.834 nm^–1,b ^*=0.645 nm^–1 and ^*=90°, and a p_mg symmetry.     

Morphology and mechanical properties of ultra-high molecular weight polyethylene-poly(tetrafluoroethylene) blend films

This paper deals with the morphology and mechanical properties of blend films for polytetrafluoroethylene (PTFE) and ultra-high molecular weight polyethylene (UHMWPE) prepared by kneading techniques. This experiment was carried out for blend films, prepared with different compositions of PTFE and UHMWPE to improve thermal properties of PE. In spite of the incompatibility of the two polymers, the blend film with the PTFE/UHMWPE composition =75/25 was maintained under the measurement of complex modulus at temperature higher than 300°C. This indicates that the UHMWPE chains dispersed in PTFE fibrous texture were not separated by the melting flow of UHMWPE at 300°C. To check the origin of this interesting phenomenon, the morphology of the blend films was investigated by using scanning electron microscopy, X-ray diffraction, and¹³C nuclear magnetic resonance.