Confined crystallization of PVDF and a PVDF‐TFE copolymer in nanolayered films

Layer‐multiplying coextrusion was used in conjunction with isothermal recrystallization to study the confined crystallization of polyvinylidene fluoride (PVDF) and polyvinylidene fluoride‐tetrafluoroethylene (PVDF‐TFE) using polycarbonate (PC) and polysulfone (PSF) as confining materials. Three layered systems were produced (PC/PVDF, PSF/PVDF, and PC/PVDF‐TFE) with layer thicknesses ranging from 525 to 28 nm. The crystal morphology was affected by both layer thickness and recrystallization temperature. Specifically, increased recrystallization temperature and decreased layer thickness facilitated the formation of high aspect ratio in‐plane crystals in both PVDF based polymers. On the other side of the spectrum, thicker layers and lower recrystallization temperatures produced on‐edge PVDF crystals and isotropic PVDF‐TFE crystals. The morphology was correlated with oxygen permeability, which decreased by almost two orders of magnitude compared with the bulk. A variety of crystal structures were obtained and explained with nucleation and diffusion theory. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Physicochemical Studies of the Sea-Surface Microlayer

In physicochemical studies on the sea-surface microlayer (SML) in seawater, the main researches conducted were as follows: (1) It was found that there is an objective layer of sudden change in physical and chemical properties between the SML and the subsurface layer in seawater. (2) The SML thickness was determined and should be about 50±10 μm. (3) The Gibbs model of the SML was extended, and the multilayer model of the SML was advanced. (4) The original-location method, which corresponds with the traditional removal-location method, was founded and used to determine the SML thickness. The results obtained from the two methods were almost identical. (5) An abnormal phenomenon was found when the Gibbs solution adsorption was applied to the seawater system, the reason for which was discussed preliminarily.     

Enhanced electrical properties of highly oriented poly(vinylidene fluoride) films prepared by solid‐state coextrusion

Oriented poly(vinylidene fluoride) (PVDF) films with β‐form crystals have been commonly prepared by cold drawing of a melt‐quenched film consisting of α‐form crystals. In this study, we have successfully produced highly oriented PVDF thin films (20 µm thick) with β‐crystals and a high crystallinity (55–76%), by solid‐state coextrusion of a gel film to eight times the original length at an established optimum extrusion temperature of 160°C, some 10°C below the melting temperature. The resultant drawn films had a highly oriented (orientation function f_c = 0.993) fibrous structure, showing high mechanical properties of an extensional elastic modulus of 8.3 GPa and tensile strength of 0.84 GPa, along the draw direction. Such highly oriented and crystalline films exhibited excellent ferroelectric and piezoelectric properties. The square hysteresis loop was significantly sharper than that of a conventional sample. The sharp switching transient yielded the remnant polarization P_r of 90 mC/m², and the electromechanical coupling factor k_t was 0.24 at room temperature. These values are about 1.5 times greater than those of a conventional β‐PVDF film. Thus, solid‐state coextrusion near the melting point was found to be a useful technique for the preparation of highly oriented and highly crystalline β‐PVDF films with superior mechanical and electrical properties. The morphology of the extrudate relevant to such properties is discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2549–2556, 1999     

Oxygen barrier properties of crystallized and talc‐filled poly(ethylene terephthalate)

The improvement in oxygen barrier properties of poly(ethylene terephthalate) (PET) by incorporation of an impermeable phase such as crystallinity or talc platelets was examined. Crystallinity was induced by crystallization from the glassy state (cold crystallization). Microlayering was used to create talc‐filled structures with controlled layer architecture. The reduction of permeability in crystallized and talc‐filled PET was well described by Nielsen's model. Changes in permeability of crystalline PET could not be ascribed to the filler effect of crystallites only. Our data on solubility, obtained on the basis of measurements of the oxygen transport coefficients, confirmed a previous finding that the amorphous phase density of PET decreases upon crystallization. The data were amenable to interpretation by free volume theory. Talc‐filled materials processed by different methods showed the same permeability; however, much better mechanical properties were achieved by microlayering. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 847–857, 1999     

微层共挤出(PP+EVOH)/PP阻隔材料的结构与性能研究

利用微层共挤出技术制备了具有交替层状结构的(PP+EVOH)/PP复合材料,其中PP为聚丙烯,EVOH为乙烯-乙烯醇其聚物.通过扫描电子显微镜观察、气体渗透实验、差示扫描量热仪分析以及力学性能测试研究了微层共挤出复合材料的形态结构及其对复合材料气体阻隔性能、力学性能以及结晶性能的影响.研究结果表明,通过微层共挤出技术,PP层和(PP+EVOH)层沿挤出方向交替排列,EVOH在PP基体中的的分散形态由零维球形变为一维纤维状,进而演变为二维片状.这些形态导致微层共挤出材料的氮气渗透系数和断裂伸长率较普通共混物分别下降了两个数量级和提高了27倍,并且显著影响其结晶行为.当层数超过64层后,由于PP层减薄,界面增多,EVOH不仅对(PP+EVOH)层中PP相存在结晶成核作用,而且对PP层也有结晶成核作用.     

Polymeric One‐Dimensional Photonic Crystals by Continuous Coextrusion

It is shown that narrowband one‐dimensional photonic crystals can be fabricated from polymeric materials using laboratory scale layer‐multiplying coextrusion technology. The tuning of the photonic bandgap is demonstrated with films that selectively filter different regions of the visible electromagnetic spectrum. The layer uniformity of the photonic crystals is evaluated by comparing the measured UV‐vis transmission spectra with model simulations, and is independently confirmed with atomic force microscopy. Assemblies of alternating polystyrene and poly(methyl methacrylate) layers exhibit a narrow reflection band with close to 100% reflection in good agreement with the prediction for uniform layers. The flexibility of the process is demonstrated by the fabrication of elastomeric one‐dimensional photonic crystals. It is anticipated that this technology will enable the rapid and facile realization of new polymeric optical devices.

     

Direct determination of thickness of sea surface microlayer using a pH microelectrode at original location

The sea surface microlayer (SML) is the interface layer between seawater and atmosphere, which is a new study field developed from the intersecting and infiltration of ocean science and atmosphere science, including the SML physics, the SML chemistry, the SML biology etc. It in-volves the recip rocity of sea-air, the globe cycle and flux of substances, so it is a key item of the global cooperative research on ocean science[1,2]. It should also be an important research field of SOLAS (sur…     

The quantitation of butyltin and cyclohexyltin compounds in the marine environment of British Columbia

A HPLC/GF AA procedure based on the use of C-18 columns is described for the quantitation of butyltin species in marine samples. When a mass spectrometer was used as detector (HPLC MS), evidence was obtained for the presence of other tin compounds in the samples. Extracts of samples were treated with CH₃MgBr and examined by using GC MS; the presence of Bu_nSnMe_4?n (n = 3–1, Bu = butyl) and Cy_nSnMe_4?n (n = 3,2, Cy = cyclohexyl) was confirmed in the derivatized seawater, bivalve flesh, and bivalve shell samples. Quantitative data are given for butyl- and cyclohexyl-tin species in seawater and the surface microlayer, and oyster flesh.     

Use of electrochemical impedance spectroscopy to characterise the physical properties of ex situ reconstructed sea surface microlayer

The objective of this work was to develop electrochemical impedance spectroscopy (EIS) to characterise the physical properties of the sea surface microlayer ( ssm ). Samples from Lake Rogoznica in Croatia were extracted by n-hexane and dichloromethane (dcm) respectively and transferred to mercury electrodes. The EIS results were compared with those of a model phospholipid, dioleoyl phosphatidylcholine (DOPC) which forms near defect-free monolayers on a mercury surface. The ssm extracts formed inhomogeneous monolayers on the mercury surface and the dcm ssm extract monolayer showed greater surface roughness than the hexane ssm extract. The hexane ssm extract introduced defects and a greater surface roughness into mixed DOPC- ssm extract monolayers than the dcm ssm extract due to the lower compatibility of the non-polar hexane extract with the DOPC than that of the polar ssm extract. In addition, the dcm ssm component in the mixed DOPC- ssm monolayer showed an association with pyrene added to the solution.     

Multilayered polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) for high energy density capacitors with enhanced lifetime

The dielectric lifetime and corresponding damage morphology of polycarbonate/poly(vinylidene fluoride‐co‐hexafluoropropylene) (PC/P(VDF‐HFP)) layered systems are studied under constant direct current (DC) field. Melt blends of the two polymers are also considered for comparison. The dielectric lifetimes of the latter are systematically much shorter than the layered systems. The interfaces between the polymers act as flaws that induce up to two orders of magnitude difference between the layered and blend systems. The capacitance values versus time during breakdown progression exhibit an inversed S‐shape pattern. The three regimes in the S‐shape pattern are consecutively attributed to randomly isolated breakdowns, interconnecting breakdowns, and wearing‐out of the capacitor film. The film breakdown images during dielectric lifetime test confirmed the transition from randomly isolated breakdowns to interconnecting breakdowns. This transition was further evidenced by a bimodal distribution in the Weibull analysis. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012