重力对异向聚集过程影响的探讨

自９０年代初,分散体系聚集过程的微重力研究开始受到重视,并有一系列论文发表［１ -４］．Ｆｏｌｋｅｒｓｍａ［３,４］ 等人在最近发表的文章中,公布了他们的最新研究结果．在探空火箭实现的微重力条件下,他们发现聚集速率要比地面实验快１１倍多．为了解释这一现象,他们把重力的影响分为两部分,即沉降和自然对流．用密度匹配法,检验了在无沉降时的聚集过程．得到的结果是,聚集速率在无重力沉降影响时会比有沉降时快２．７倍．即便如此,微重力实验的聚集速率仍高出４．２倍．他们推断,这一巨大差异是由在地面上无法避免的自然…     

Fluorinated siloxane-containing waterborne polyurethaneureas with excellent hemocompatibility, waterproof and mechanical properties

Two series of polyurethaneurea (PUU) aqueous dispersions consisting of fluorinated siloxane segments were prepared from a high-molecular-weight (M_n = 8361) α,ω-dihydroxypoly[(3,3,3-trifluoropropyl)methylsiloxane] (PTFPMS), dimethylolpropionic acid, isophorone diisocyanate and ethylenediamine, with poly (tetramethylene oxide) and polycarbonate polyols as soft segments, respectively. These anionic aqueous dispersions were stable at the ambient temperature for more than 6 months, with particle sizes ranging from 45 to 98 nm. Both series of PUU films showed the excellent waterproof properties, i.e. the decrease in water absorption and surface energy upon the incorporation of PTFPMS segments. The phase mixing increased in the fluorinated siloxane-containing polyether-based PUUs and the phase separation increased first then decreased in the fluorinated siloxane-containing polycarbonate-based PUUs, with increasing PTFPMS content. All the PTFPMS-modified PUU films showed excellent mechanical properties. The polycarbonate-based PUU film consisting of 5 wt.% PTFPMS had a tensile strength of 60.7 MPa and a breaking elongation of 632%, owing to the increase in the ordered hydrogen bonding degree and the microphase-separation degree between the hard and soft segments in the system. In vitro hemolysis and dynamic clotting time measurements indicated that the thromboresistance was enhanced markedly with increasing PTFPMS content for both series of PUUs, which could be ascribed to the synergistic effect between the carboxylate groups and the PTFPMS segments migrating onto the surfaces of the films.     

Refractive index and material dispersions of multi-component oxide glasses

Refractive index dispersion curves in the wavelength region of 0.40 to 5.03 μm are presented for multi-component oxide glass systems: borate, silicate, aluminate, germanate, tellurite, antimonate and heavy metal gallate. The material dispersion was determined using the refractive index data. Reflection spectra in the ultraviolet and infrared regions were measured to investigate the effects of electronic transitions and lattice vibrations on the material dispersion. Thallium tellurite, thallium antimonate and lead gallate glasses exhibit zero material dispersion wavelengths (ZMDWs) over 2.4 μm. The factors affecting the ZMDW are discussed.     

Synthesis and characterization of zinc oxide nanoparticles: application to textiles as UV-absorbers

We report the synthesis and characterization of nanosized zinc oxide particles and their application on cotton and wool fabrics for UV shielding. The nanoparticles were produced in different conditions of temperature (90 or 150 °C) and reacting medium (water or 1,2-ethanediol). A high temperature was necessary to obtain small monodispersed particles. Fourier transformed infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray powder diffractometry (XRD) were used to characterize the nanoparticles composition, their shape, size and crystallinity. The specific surface area of the dry powders was also determined. ZnO nanoparticles were then applied to cotton and wool samples to impart sunscreen activity to the treated textiles. The effectiveness of the treatment was assessed through UV–Vis spectrophotometry and the calculation of the ultraviolet protection factor (UPF). Physical tests (tensile strength and elongation) were performed on the fabrics before and after the treatment with ZnO nanoparticles.     

Simultaneous entrainment of oil and water droplets in high Reynolds number gas turbulence in horizontal pipe flow

We develop a 1D cross sectional concentration profile model for oil and water droplets that coexist in the turbulent gas phase (of Re ∼ 10⁶) in near horizontal stratified pipe flows. Entrainment of the oil and water mixture from a liquid film near the bottom of the pipe into the gas is modeled based on earlier single-fluid entrainment correlations. A Gamma distribution for the droplet sizes based on the breakup of liquid filaments, is adopted. An explicit algebraic–exponential formula for the total concentration profile for either phase can then be derived.