Air-side Surface Research Articles

Effects of Fluorine-Containing Graft and Block Copolymer Additives on Removal Characteristics of Dilute Benzene in Water by Microphase-Separated Membranes Modified with These Additives

This paper focuses on the effects of the addition of fluorine-containing graft or block copolymer additives composed of 1H,1H,2H,2H-heptadecafluorodecyl acylate (perfluoroalkyl acylate, PFA) and poly(dimethylsiloxane) macromonomer (PDMS) or PDMS macro-azo-initiator to a microphase-separated membrane consisting of PDMS and poly(methyl methacrylate) (PMMA) on the benzene/water selectivity for an aqueous dilute benzene solution during pervaporation and the surface characteristics and structures of the surface-modified PMMA/PDMS membranes. The addition of the fluorine-containing copolymer additives, PFA-g-PDMS and PFA-b-PDMS, to a PMMA-g-PDMS membrane yielded hydrophobic surfaces at the air side of surface-modified membranes due to the localization of their additives on the air-side surface of these membranes. The addition of a small amount of the PFA-g-PDMS and PFA-b-PDMS enhanced both the benzene/water selectivity and the permeability for an aqueous dilute benzene solution during pervaporation because of the formation of their hydrophobic surfaces and the existence of the microphase-separated structures with a continuous PDMS phase in the inner of these membranes. When larger amounts of the PFA-g-PDMS and PFA-b-PDMS were added to a PMMA/PDMS, the latter additive could keep the microphase-separated structures with a continuous PDMS phase, but the former did not. The relationship between the permeation and separation characteristics for the removal of benzene from an aqueous benzene solution and the structures the PMMA-g-PDMS membranes surface-modified with PFA-g-PDMS and PFA-b-PDMS as fluorine-containing polymer additives is discussed in detail.

Porous hydrophobic/hydrophilic composite membranes: Estimation of the hydrophobic-layer thickness

A porous hydrophobic/hydrophilic composite membrane can be prepared by the phase inversion method in one casting step from a polymer solution containing a hydrophilic polymer and a fluorinated surface modifying macromolecule (SMM). The surface analysis of these membranes indicate that there is a fluorine concentration gradient along the membrane thickness resulting from the migration of fluorinated blocks to the air side surface during membrane formation. In this paper, direct contact membrane distillation (DCMD) process has been applied, together with a new theoretical model, to estimate the hydrophobic-layer thickness of porous composite membranes. The theoretical model involves the structural characteristics of the membranes, the heat transfer mechanism and the physical nature of mass transport through porous composite membranes. The model was validated using two supported commercial poly-tetra-fluoro-ethylene membranes of different pore sizes and known thickness-layers. The effect of the hydrophilic polymer concentration in the casting solution on the formed hydrophobic-layer thickness of the composite membranes has been investigated. Also are studied the effects of stirring rate and temperature in the DCMD system on the determination of the hydrophobic-layer thickness. The results show that the hydrophobic-layer thickness increases with the concentration of the hydrophilic base polymer in the casting solution and is independent on the operational parameters selected to conduct the DCMD experiments. The proposed method can be used to measure the layer thickness of porous composite hydrophobic/hydrophilic membranes within random uncertainties less than 5%. The maximum deviation of each individual thickness from the corresponding average value is less than 9%. The estimated errors due to the different input membrane parameters associated in the mathematical model were discussed. The hydrophobic-layer thickness of the SMM blended membrane was found to be an order of magnitude lower than that of the commercial membranes frequently used in membrane distillation.

Air-side heat transfer enhancement of a refrigerator evaporator using vortex generation

In most domestic and commercial refrigeration systems, frost forms on the air-side surface of the air-to-refrigerant heat exchanger. Frost-tolerant designs typically employ a large fin spacing in order to delay the need for a defrost cycle. Unfortunately, this approach does not allow for a very high air-side heat transfer coefficient, and the performance of these heat exchangers is often air-side limited. Longitudinal vortex generation is a proven and effective technique for thinning the thermal boundary layer and enhancing heat transfer, but its efficacy in a frosting environment is essentially unknown. In this study, an array of delta-wing vortex generators is applied to a plain-fin-and-tube heat exchanger with a fin spacing of 8.5 mm. Heat transfer and pressure drop performance are measured to determine the effectiveness of the vortex generator under frosting conditions. For air-side Reynolds numbers between 500 and 1300, the air-side thermal resistance is reduced by 35–42% when vortex generation is used. Correspondingly, the heat transfer coefficient is observed to range from 33 to 53 W m −2 K −1 for the enhanced heat exchanger and from 18 to 26 W m −2 K −1 for the baseline heat exchanger.

Dynamic dip testing as a method to assess the condensate drainage behavior from the air-side surface of compact heat exchangers

A new method to assess the condensate drainage behavior of the air-side surface of compact heat exchangers—dynamic dip testing—is introduced. The new method is shown to provide highly repeatable data for real-time drainage. Results from experiments with more than 20 flat-tube and round-tube-and-fin heat exchangers are presented, and the data clearly show geometrical effects such as the impact of the tube type on condensate drainage. By comparing the results from dip testing to wind-tunnel experiments for the same heat exchangers, we find dip testing can serve as a powerful tool for assessing the condensate retention behavior. The coils retaining the most and the least condensate in a steady-state wind-tunnel test, likewise held the most and the least in a dip test. However, different amounts of water are retained on the air-side surface during dip tests and wind-tunnel tests. A model based on gravity, surface tension and drag effects is developed to help understand and predict the drainage behavior of heat exchangers. The new model and experimental approach are useful in screening heat exchangers for condensate retention and for assessing off-cycle drainage behavior.

Surface composition and property of film prepared with aqueous dispersion of polyurethaneurea-acrylate including fluorinated block copolymer

The aqueous dispersion of polyurethaneurea-acrylate (PUA) including small amount of fluorinated block copolymers containing carboxyl groups (PATF), which can be dissolved in water, was used to make films and the surface properties of these films were examined. The experimental data show that the modified PUA film exhibits a hydrophobic surface property, although the original surface of PUA film is hydrophilic. The surface composition of the modified PUA film was measured by ATR and XPS. The results indicate that there is a concentration gradient of the fluorine groups along the lines of thickness of the modified film and towards the outmost surface layer, resulting from the migration of fluorinated blocks to the air side surface of the modified PUA film during the film formation process. However, the PUA film can not be modified effectively by adding the sodium salt of PATF, since the urethane groups in the system are easy to occupy on the surface of the film.

複合型インピンジ冷却構造の研究(ガスタービン技術の最先端 : 伝熱・燃焼,ガスタービン技術の最先端)

For a turbine cooling air reduction, an integrated impingement and pin fin cooling configuration was developed. This configuration integrated impingement cooling and pin fin cooling devices into one body, aiming at an enhancement of the effective heat transfer area. Not only a cooling performance improvement but also an establishment of manufacturing process and keeping sufficient strength and life are the subjects of this research. A staggered type cooling configuration was designed to get better cooling performance in manufacturing limitations. A cooling performance test was conducted, and it was confirmed that a heat conductance enhancement factor for a cooling air side surface of a staggered type specimen was 1.2-1.3. And the staggered type gave superior cooling performance over the conventional type that had no pin, for given pressure drop. An actual size staggered type specimen was successfully manufactured. A fatigue test was also conducted, and it was confirmed that there was no higher stress concentration in a staggered type specimen than that in a conventional type specimen.

Grafting of lactose-carrying styrene onto polystrene dishes using plasma glow discharge and their interaction with hepatocytes.

Lactose-carrying styrene (VLA)-grafted polystyrene (PS) dish (PS-VLA) was prepared by treatment of PS dish with oxygen plasma glow discharge followed by the graft polymerization of VLA. The surface topology and hepatocytes behavior on PS-VLA were examined by comparison with those on a PVLA-coated PS dish (PS-PVLA). According to the results of surface topologies obtained by a phase mode of atomic force microscope (AFM), it was found that PS-VLA exhibits a pointed texture image similar to forest while PS-PVLA exhibits a phase-separated, cloud-like image. In an experiment involving hepatocytes adhesion, the cells more slowly adhered to PS-VLA than to PS-PVLA during the first 2 h incubation. According to topological data, it may be suggested that lactose density on the air side surface of PS-VLA is lower than that of PS-PVLA, thus leading to the slow adhesion of hepatocytes to PS-VLA.

Effects of microcrystalline phases and quenched in defects on corrosion of rapidly solidified Ti47Cu53and Ti50Cu50alloys

In order to evaluate the effects of microcrystalline phases and quenched in defects on the corrosion of rapidly solidified Ti47Cu53 and Ti50Cu50 alloys, electrochemical studies have been performed on each side of alloy ribbons separately in acidic chloride environments at room temperature. In the as solidified condition, air pockets were found to be the more detrimental defects from the view point of corrosion when compared with the microcrystalline phases that initially lie beneath a thick air formed oxide film on the air side surface. Compositional differences between the two sides of the alloy ribbons were found to play an insignificant role in influencing the corrosion of the alloys.

Hydrophilic (Hydrogen-Bonding) Polystyrene Surface by Substrate-Induced Surface Segregation of Benzene Groups

The measurement of contact angle on polystyrene (PS) films solvent cast on acid-cleaned glass substrates was used in conjunction with the Lifshitz−van der Waals/acid−base approach in order to investigate the surface functional-group compositions as well as the physical nature and the strength of intermolecular interactions between the film surfaces and various testing liquids. The static contact angle for water observed on the air-side surface of the films (80°) was consistent with the literature. However, the glass-side surface of the films was found to be hydrophilic with a water contact angle of 62°. This hydrophilic character was shown to arise from (i) the substrate-induced surface segregation of benzene groups in the film casting process with consequent formation of benzene-rich PS surface and (ii) the relatively strong hydrogen-bond-accepting (electron-donating) character of the aromatic rings of polymer. The strength of hydrogen bond between the water molecule and the aromatic moiety was estimated...

Acrylic polyester resins containing perfluoropolyethers structures: Synthesis, characterization, and photopolymerization

Poly(ε-caprolactone-b-perfluoropolyether-b-εcaprolactone) (PCL–PFPE–PCL) block copolymers having different PCL block lengths and end-capped with methacrylate groups were prepared and characterized. Spectroscopic analyses confirmed the expected molecular structure of the products. After UV curing, the films revealed the presence of two amorphous phases, corresponding to fluorinated and hydrogenated moieties, respectively. The material containing long PCL blocks showed also a crystalline phase. Surface properties of the UV-cured films were evaluated: The surfaces have a very high hydrophobic character in spite of the presence of many polar OH groups present in the polymeric network and a high hysteresis in wetting. An enrichment of fluorine at the air-side surface was shown by contact-angle measurements, except when long PCL sequences are present. The θadv angles decreased by increasing the content of PCL, that is, by decreasing the content of fluorine. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 651–659, 2000

Acrylic polyester resins containing perfluoropolyethers structures: Synthesis, characterization, and photopolymerization

Poly(ε-caprolactone-b-perfluoropolyether-b-εcaprolactone) (PCL–PFPE–PCL) block copolymers having different PCL block lengths and end-capped with methacrylate groups were prepared and characterized. Spectroscopic analyses confirmed the expected molecular structure of the products. After UV curing, the films revealed the presence of two amorphous phases, corresponding to fluorinated and hydrogenated moieties, respectively. The material containing long PCL blocks showed also a crystalline phase. Surface properties of the UV-cured films were evaluated: The surfaces have a very high hydrophobic character in spite of the presence of many polar OH groups present in the polymeric network and a high hysteresis in wetting. An enrichment of fluorine at the air-side surface was shown by contact-angle measurements, except when long PCL sequences are present. The θadv angles decreased by increasing the content of PCL, that is, by decreasing the content of fluorine. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 651–659, 2000

Surface characterization of polyimide films

Various kinds of poly(amide acid)s were prepared by the reaction of four kinds of acid dianhydride and three kinds of diamine in N,N-dimethylacetamide (DMAc). Polyimide films were prepared by casting the poly(amide acid) solution on soda glass substrates, followed by thermal imidization at various temperatures. Contact angles of polyimide films for the sides in contact both with air and with glass substrate (air side and glass side, respectively) were measured to evaluate the dispersive component (γDS) and the nondispersive component (γPS) of surface free energy (γS) of polyimide films. It was shown that, for the air side, γPS value decreased greatly and γDS values increased slightly with the development of imidization. Values of γPS for the glass side were much higher than those for the air side. Poly(amide acid) solution was also cast on quartz glass and silicone rubber, and was thermally imidized. The γPS for the quartz glass side was almost the same as that for the soda glass side. But the γPS for the silicone rubber side was as low as the γPS for the air side. Attenuated total reflection infrared spectroscopy of polyimide films showed that the degree of imidization for the glass side surface was not as high as that for the air side surface, and that the amount of polar groups for the glass side surface was higher than that for the air side surface. Among the various kinds of polyimides, there is a slight but clear difference in the values of γS and its components, which can be rationalized from the difference in the chemical structure. It was also found that thermal degradation and oxidation can be easily detected from the change of surface free energy and its components for the polyimide films after being treated at high temperatures in both air and vacuo.

Determination of Orientational Distribution of Side Chains of Polyimide Layer for Liquid Crystal Alignment by Surface Second-Harmonic Generation

We have determined the orientational distribution function (ODF) of the side chain polyimide (PI) films used for liquid crystal alignment. The second-harmonic generation (SHG) in four sample geometries were measured as a function of polarizer rotation angle. To determine ODF, we developed a new fitting method of the five layer model using the maximum entropy method. We found that the ODF of the side chains of PI film of the air-side surface is quite different from that of the substrate side.

Effects of Zr on microstructure and mechanical properties of Al-Cu base ribbons spun by planar flow casting

The effects of the Zr addition on the solidification behavior and mechanical properties of the AI-Cu alloy ribbon have been investigated. Zr addition reduced the average grain size of the ribbon at the wheel-side surface, and promoted the microstructural transition into cellular/dendritic structure. Another noteworthy effect of Zr was the homogenization of the microstructure. The addition of Zr up to 0.5 wt.% in the /U-4.3 wt.% Cu ribbon resulted in a considerable increase in hardness at both the wheel-side and the air-side surfaces. The yield strength increased with the addition of Zr due to the grain refincment and more homogeneous distribution of ZrAI, particles. despite no noticeable improvement of the ductility.

Selective Accumulation of Functional Groups at the Film Surfaces of Stereoregular Poly(methyl methacrylate)s

Contact angles of water on stereoregular poly(methyl methacrylate)s (PMMA) solvent-cast in the form of films against a glass substrate were measured by using the sessile drop method. The syndiotactic films exhibited contact angle values indicative of relative dominance of the nonpolar α-methyl and methylene groups of polymer chains at the air-side surface and the polar ester groups at the glass-side surface of the films. The selectivity in the surface exposure of functional groups increased rapidly with syndiotacticity. On the contrary, the wetting results for the isotactic films showed no effect of the polarity of contacting medium on the surface chemical composition and the wettability of the films represented an average for α-methyl, methylene, and ester groups both at the air-side and at the glass-side surface. The observed influence of tacticity on the surface activity of stereoregular PMMAs was interpreted in terms of the surface conformational structure of these materials.

Magnetic properties of Fe73.5Cu1Nb3−xUxSi13.5B9 (x = 1, 2, 3) nanocrystalline alloys

The influence of uranium content and annealing on the magnetic properties and Hall effect of Fe73.5Cu1Nb3−xUxSi13.5B9 (x = 1, 2, 3) nanocrystalline alloys prepared by melt spinning were investigated. Measurements of magnetic properties of surface layers confirmed higher concentration of uranium in the air-side surface layers than in the wheel-side layers.

Corrosion behaviour of rapidly solidified Zr 76Ni 16Fe 8 alloy in chloride environments

Amorphous alloys possess better corrosion resistance than crystalline alloys because these are devoid of defects present in a crystalline lattice and are compositionally more homogeneous. The conclusions drawn by the authors are as follows: (1) Corrosion behavior of rapidly solidified Zr[sub 76]Ni[sub 16]Fe[sub 8] alloy ribbon varies across its thickness in chloride environments. (2) Wheel side surface of the ribbon (fully amorphous structure) possesses better corrosion resistance than the air side surface of the ribbon (partial crystallinity) in the chloride environments. (3) Among the three factors, namely, partial crystallinity, air pockets and compositional difference induced in rapidly solidified Zr[sub 76]Ni[sub 16]Fe[sub 8] alloy ribbon, partial crystallinity appears to be the most harmful as far its corrosion resistance in chloride environments is concerned.

Surface properties of films containing poly(vinyl alcohol) having an n-alkylthio group at one end

Abstract Surface properties of the poly(vinyl alcohol) (PVA) blend films composed of conventional PVA and PVA having an n-alkylthio end group of 4–18 carbon atoms (Rn-PVA; n = 4–18) were studied by contact angle measurements and XPS analysis. In the blend films, Rn-PVA distributed preferentially on the air side surface (but not on the opposite side) depending on the chain length of n-alkylthio end groups. The critical surface tensions, γc, and surface-free energies, γs, of the R 12- PVA PVA-HCA blend were the lowest of all R n- PVA PVA-HCA blends. The polar component of the surface free energy, γps, of the blends with Rn-PVA of n = 8–16 was substantially zero, from which these film surfaces were deduced to be predominantly covered with n-alkyl chains. The C/O ratio, the ratio of the carbon atoms to the oxygen atoms in the surface layer estimated by XPS analysis, had some correlation with γc and γs. However, it was suggested that the surface properties were affected not only by the composition of the surface but also by the arrangement of the n-alkyl chains on the surface.

Surface studies on the ultrathin membrane prepared by spreading the polymer solution on a water surface

Ethylene-vinyl alcohol copolymer (EVA) and ethylene-vinyl alcohol-acrylic acid terpolymer (EVA-AA) ultrathin membranes were prepared by spreading the polymer solutions on a water surface. The surfaces of the polymers were characterized by ζ-potential and ESCA measurements. The EVA membrane has nearly the same ζ-potential at both surfaces, that is, the air side and the water side surface. The results of the ESCA measurements demonstrated that the EVA membrane had more OH groups at the water side surface than at the air side surface. The EVA-AA membrane from DMSO solution had a higher ζ-potential on the water side surface than on the air side surface. However, the EVA-AA membrane from DMAc solution had the same ζ-potential on both surfaces. The ESCA measurement showed that EVA-AA membrane from DMSO solution had more than twice the amount of −COOH groups on the water side surface compared with the air side surface. On the other hand, in the membrane from DMAc solution the amount of COOH groups was observed to be the same at both sides.

Surface properties of poly(vinyl alcohol) films with a fluoroalkyl group at one end

Surface properties of poly(vinyl alcohol) (PVA) films with a fluoroalkyl group at one end, H(CF 2)− n CH 2O(CH 2)− 3SPVA and F(CF 2)− 7CONHCH 2CH 2SPVA, were studied by contact angle measurements and X.p.s. analysis. H(CF 2)− n CH 2O(CH 2)− 3SPVA and F(CF 2)− 7CONHCH 2CH 2SPVA distributed preferentially on the air-side surface, and the surface showed properties corresponding to the characteristics of the fluoroalkyl end groups. Surface free energy, γ s, was in good agreement with critical surface tension, γ c, for F(CF 2)− 7CONHCH 2CH 2SPVA and n-C 12H 25SPVA, which had no polar component of γ s, and with γ c (max) for a series of H(CF 2)− n CH 2O(CH 2)− 3SPVAs which had a polar component. The γ s of F(CF 2)− 7CONHCH 2CH 2SPVA films altered by heat treatment, gave a minimum value at 80°C and increased with a rise in heat treatment temperature above 120°C, which was thought to be caused by distribution changes of the end groups. γ s was closely related to the distributions of CF 3 and CF 2 groups in the surface layer estimated by X.p.s. analysis.