Carl C. Gryte

Water sorption and diffusion behaviours in thin films of photosensitive polyimides

Abstract Several photosensitive polyimide (PSPI) precursors were synthesised by the acid/base complexations of conventional poly(amic acid) precursors with photochemically cross-linkable 2-(dimethylamino)ethyl methacrylate. PSPIs in films were prepared from the photosensitive precursors by thermal imidisation, whereas the corresponding PIs in films were prepared from the conventional poly(amic acid)s: rod-like poly(p-phenylene pyromellitimide) (PMDA-PDA), rigid (poly(p-phenylene biphenyltetracarboximide) (BPDA-PDA), semi-flexible poly(4,4′-oxydiphenylene biphenyltetracarboximide) (BPDA-ODA), semi-flexible poly(4,4′-oxydiphenylene pyromellit-imide) (PMDA-ODA), and flexible poly(4,4′-oxydiphenylene benzophenonetetracarboximide) (BTDA-ODA). Water sorption and diffusion behaviours in the PSPIs were gravimetrically measured at 25°C in 100% relative humidity and compared with those of the corresponding PIs. For the PSPIs as well as the PIs, the water sorption and diffusion behaviours were nearly Fickian, regardless of the backbone chemistry. However, those were strongly dependent upon the polyimide backbone chemistry and precursor origin. In addition, those in polyimides were affected by the bulky photosenistive groups, even though they were temporarily linked to the precursor polymers and then debonded from the backbones and ultimately outgassed during the thermal imidisation process. For PMDA-PDA, BPDA-PDA and BPDA-ODA, the PSPIs absorbed water more quickly than the corresponding PIs, whereas for PMDA-ODA and BTDA-ODA, the PSPIs absorbed water less quickly than the corresponding PIs. In contrast to the water diffusion, all the PSPIs absorbed slightly more or a great deal more water than the corresponding PIs, depending on the backbone chemistry. All the measured water sorption and diffusion behaviours in the PSPIs were understood by considering changes in the morphological structure (namely, chain order and orientation), voids, and residues possibly induced by the bulky photosensitive groups, in addition to the Tg as well as the chemical affinity to water.

Water diffusion and sorption in films of high-performance poly(4,4′-oxydiphenylene pyromellitimide): effects of humidity, imidization history and film thickness

Abstract Poly(4,4′-oxydiphenylene pyromellitimide) (PMDA—ODA) films of 10–109 μm thickness were prepared from its poly(amic acid) precursor by thermal imide-ring-closure formation at various temperatures. Water sorption in the films was measured at 25°C over 22–100% relative humidity using an electromicrobalance. Water diffusion in all the films was a nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. Depending upon humidity, film thickness and imidization history, the diffusion coefficient and water uptake varied in the ranges of 1 × 10 −9 to 3 × 10 −9 cm 2 s −1 and 0.4 to 4.5 wt%, respectively. Overall, both the diffusion coefficient and the water uptake increased with increasing humidity and film thickness, but decreased as the imidization temperature and time increased. The water sorption results were interpreted by consideration of morphological variations (molecular order, chain orientation and microvoids) due to film thickness and imidization history.

Dielectric relaxation and deuteron NMR of water in polyimide films

Polyimide films containing up to 3.2 wt. % water (H2 O or D2 O) have been studied by dielectric relaxation (DR) and 2H nuclear magnetic resonance (NMR) spectroscopies. Dielectric loss measurements show the presence of a double peak near 200 K due to water, with two components designated as γ1 and γ2 . The γ2 peak, which appears at the lower temperature, is only present for the interior portion of thick (>25 μm) films and rapidly decreases as the moisture content decreases. Correspondingly, deuteron NMR measurements show the presence of narrow and broad lines, which are correlated, respectively, with the γ1 and γ2 DR peaks. The spin‐spin relaxation time T2, is much longer for the narrow line than for the broad line. The γ1 DR peak and the narrow NMR line are attributed to sites where isolated water molecules are only loosely coupled to the polymer chains. The γ2 and broad NMR lines involve small clusters of water molecules with associated nuclear magnetic dipole‐dipole coupling. Additional measurements on ...

Effect of flow maldistribution on hollow fiber dialysis — experimental studies

Abstract Counter-current hollow fiber dialyzers were studied. Performance of loosely packed hollow fiber dialyzers deviated from the prediction based on ideal flow distribution while well packed dialyzers did not deviate. The flow maldistributions were characterized by tracer analysis. The behavior of dialyzers was simulated with a model based on bypass now.

CPS 768 Formation of anisotropic ice-agar composites by directional freezing

Aqueous agar gels were directionally frozen in a temperature gradient of 10 °C/ cm at rates between 8.8×10−5 cm/sec and 8.8×10−4 cm/sec to form highly anisotropic ice-agar composites. Observations of the vitrified agar domains which were localized at the ice grain boundaries were made and the ice domain size was measured as a function of the solidifying conditions. The segregation of the noncrystalline agar was dominated by the vitrification character of the agar gel. Thermal analysis indicated that ice crystallization rate decreased to a negligible level as the water content of the gel decreased to approximately 50 percent by weight agar.

Application of computed tomography to oil recovery from porous media.

Local oil saturation (fluid composition within the void spaces of sandstone) is computed from pixel image data. Limitations of CT observation of fluid displacement are discussed. Images of viscous fingering, time derivatives of local composition, and residual oil distribution are given for the case of water displacing oil from porous media.

Computer-assisted tomography for the observation of oil displacement in porous media

Computer assisted tomography (CAT) uses computerized mathematical algorithms to reconstruct tomographic images of an object. The image reconstruction is based on multiple X-ray measurements made around the objects periphery. This technique has been used to obtain oil saturation distribution information during immiscible oil displacement in Berea Sandstone cores. This technique is directed toward investigating the various problems involved in oil recovery processes: (1) heterogeneity of the porous structure; (2) surface interactions between oil, the displacing fluid, and the reservoir rock formation; and (3) the viscosity ratio between the 2 fluids. The flow phenomenon is complex. Previous experimental methods have offered insufficient information for the understanding of oil recovery processes. The CAT scan image acquisition is rapid, thus it yields directly the local oil compositions over a cross section as a function of spatial position and time. Dynamic fluid distribution profiles then can be used to analyze the effectiveness of various oil recovery strategies. 10 references.

The effect of anionic polyelectrolytes on the crystallization of calcium oxalate hydrates

Abstract Calcium oxalate was precipitated from supersaturated calcium oxalate solutions in the presence of different water soluble polymers: poly(acrylic acid), poly(methacrylic acid), poly(styrene sulfonate-alt-maleic anhydride), poly(maleic anhydride), and poly(vinyl sulfonate). The supersaturated solutions were made with initial calcium and oxalate concentrations of 4×10 -3 M and 1.5×10 -3 M respectively. In the presence of anionic polyelectrolytes there was a change in the hydrate from of calcium oxalate which precipitated. With low concentrations of polyelectrolyte (up to 1 ppm) only the monohydrate was formed, at intermediate concentration (1–50 ppm) trihydrate was the predominant product, and at high concentrations (above 50 ppm) the dihydrate form was the dominant product. Nonpolyelectrolytes had no effect on the crystallization and thus only calcium oxalate monohydrate was formed. This effect was found to occur with all polyelectrolytes used regardless of molecular weight or charge. The change from one hydrate from to another occured at a lower polymer concentration with the low molecular weight polymers.

On the mechanism of dewatering colloidal aqueous solutions by freeze-thaw processes

Abstract Domestic sewage sludge of different solids content has been solidified by crystallization in a temperature gradient. From thermal analysis, it was determined that the segregated solute matrix contained approx. 50% water after freezing. The morphology of the segregated iceŗystals was reported, and the domain size of the ice crystals was correlated with the crystallization rate. It was found that the extent of sludge dewatering after directional solidification was independent of the size of the ice domains but dependent on the strength and integrity of the solute matrix during the draining step.

Model for the shape of polymer spherulites formed in a temperature gradient

A model is presented to account for the spherulitic morphology obtained during the oriented crystallization of a polymer in a moving temperature gradient. The model considers the sample to be divided into a series of narrow isothermal regions and, using an analogy to Snell’s law, correctly predicts the observed fibrillar curvature. Computer simulation of the proposed model yields spherulitic shapes that are consistent with the experimental results. A mechanism is proposed to account for the shapes observed, and the factors which affect them are discussed.