GE-1030.001
`
`GE-1030.001
`
`

`
`Aims and Scope
`
`The Journal of Applied Polymer Science re(cid:173)
`ports progress and significant results in the sys(cid:173)
`tematic, practical application of polymer sci(cid:173)
`ence. Areas of focus include plastics and their
`composites, blends, elastomers, films and mem-
`
`branes, fibers , coatings and adhesives, studie
`of emulsions and lattices, aging of polymers,
`structural property-processing relationship,
`extrusion and molding, diffusion, and perme(cid:173)
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`
`GE-1030.002
`
`

`
`Novel Functional Polymers: Poly(dimethylsiloxane) (cid:173)
`Polyamide Multiblock Copolymer. VII.* Oxygen
`Permeability of Aramid-Silicone Membranes in a Gas(cid:173)
`Membrane-liquid System
`
`lAKED MATSUMOTO,I.2 TOSHIRO UCHIDA,1 AKIO KISHIDA,l TSUTOMU FURUZON O,1 IKURO MARUYAMA/
`MITSU RU AKASHl 1
`
`' Department of Applied Chemistry and Chemi cal Engineering , Faculty of Engineering , Kagoshim a University, 1-21-40
`Korimoto, Kagoshima 890 , Japan ;
`
`2l sukuba Resear ch Laboratory, NOF Corporation , 5-10 , Tokod ai, Tsukuba 300-2 6, Japan ;
`
`JOepartment of Clinical Laborator y Medi cin e, Facult y of Medi cin e, Kagoshim a University, 8-35-1 Sakur agaoka,
`Kagoshima 890, Japan
`
`Received 23 July 1996; accepted 24 October 1996
`
`(a r a mid )
`polyamide
`and aromatic
`( P DMS)
`ABSTRACT: Poly(dimethylsiloxane )
`multiblock copolymer ( PAS ) membranes containing ;?; 55 wt % ofPDMS were prepared.
`Their tensile strength, morphology, and oxygen permeation property were investigated.
`The observed high tensile strength of PAS with 55 wt % ofPDMS indicates the presence
`of PDMS-aramid co-continuous phases with lamellar st ruct u res ; furthermore, the mi(cid:173)
`crophase-separated structures of PAS membranes were observed by means of transmi s(cid:173)
`sion electron microscopy. The overall oxygen permeation resistance of a conventional
`silicone rubber showed typical dependence on stirrer speed, which was derived from
`the macroscopic relationship between the membrane-liquid interfacial resistance and
`the stirrer speed. However, the overall oxygen permeation resistances of the PAS mem(cid:173)
`branes were found not to simply depend on stirrer speed. Combining with the oxygen
`permeability of PAS in the case of a gas-membrane-gas system, the interface resistances
`of the membranes were evaluated. The interface resistances of the PAS membranes
`with the two-phase nature were more susceptible to the hydrodynamic parameter than
`that of the silicone rubber and became lower than that of the silicone rubber at higher
`stirr er speeds. The low interface resistance together with the high tensile strength of
`the PAS membranes enables us to provide highly oxygen permeable membranes in
`practical applications with a membrane-liquid interface. © 1997 J ohn Wiley & Sons, Inc.
`J Appl Polym Sci 64: 1153 -1159, 1997
`
`poly (dirnethylsiloxane ): silicone; polyamide; multiblock copolymer; oxy(cid:173)
`Key words:
`gen permeability; interface resistance
`
`* For Part I, cf. Ref. 13; for Part II, cf. Ref. 17; for Part III,
`ef. Ref. 14; for Part IV, cf. Ref. 18; for Part V, cf. Ref. 15; for
`Part VI, cf. Ref. 22.
`Correspondence to: M. Akashi.
`Contract grant sponsor: Ministry of Education , Science,
`Sports, and Culture, Japan.
`Contract grant number: 07558257.
`Contract grant sponsor: Ministry of Health and Welfare,
`Government of Japan.
`e 1997John Wiley & Sons, Inc. CCC 0021· 8995/97/06 1153-07
`
`INTRODUCTION
`
`Silicone polymers principally based on poly (di(cid:173)
`methylsiloxane ) (PDMS) have been widely used
`in medical fields because of their unique proper(cid:173)
`ties such as biocompatibility, chemical inertness,
`low surface energy, lubricity, flexibility, and gas
`
`1153
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`GE-1030.003
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`1154
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`MATSUMOTO ET AL.
`
`permeability.l" When it comes to applications
`such as artificial lungs " and contact lenses, 6.7 high
`gas permeability and good biocompatibility are
`among the most desired properties of silicone
`polymers. Such an application, however, is some(cid:173)
`times limited by the polymers' poor mechanical
`properties, especially low tensile strength due to
`the low level of intermolecular forces in the ab(cid:173)
`sence of reinforcing fillers. To improve the me(cid:173)
`chanical properties without sacrificing the desired
`properties of silicone polymers, many investiga(cid:173)
`tions have been reported on the synthesis and
`characterization of block or segmented siloxane
`the soft seg(cid:173)
`copolymers incl uding PDMS as
`ment.S- ll Consideration, however, also needs to
`be given to both the bu lk and the surface proper(cid:173)
`ties important to an application in biomedical de(cid:173)
`vices; detailed study on this point was not con(cid:173)
`ducted.
`Focusing on the high permeability to many
`gases and very good biocompatibility, we have
`been investigating PDMS and aromatic polyam(cid:173)
`ide (aramid ) multiblock copolymers, that is, ara(cid:173)
`mid-silicone resins (PAS), first synthesized by
`Kajiyama et a1. 12 In previous articles, we studied
`the synthesis and characteristics of PAS from a
`- ISIn that study,
`nove l biomaterial point ofview. 13
`PAS exhibited many of the desirable properties of
`aramid and PDMS for medical applications. The
`interaction between biomolecules (protein, cell,
`and tissue ) and PAS surfaces was found to be
`equal or relatively low compared with SILASTIC ®
`500_1. 15 We have reported that PAS can be molded
`into many forms, such as films and hollow fibers .16
`Their surface pro perties were also investigated in
`detail, 14.1 7 because the surface properties of copol(cid:173)
`ymers such as PAS, which seem to be strongly
`influenced by the molding method, play an im(cid:173)
`portant role in their functionality, especially in
`medical applications.
`The two-phase nature of PAS caused by the
`high degree of incompatibility of the PDMS seg(cid:173)
`ment with the aramid segment was clarified in
`part by evaluating the gas permeation and dy(cid:173)
`n amic thermomechanical properties. IS The gas
`permeation properties in a gas-membrane-gas
`system can be well predicted by the PDMS contri(cid:173)
`bution to the continuous phase. The presence of
`a liquid-membrane interface in most biomedical
`devices, however, urges us to understand the dif(cid:173)
`ference between the gas permeation in the solid
`phase and that in the liquid phase, together with
`the effect of boundary layer phenomena. In this
`study, for the purpose of clarifying the oxygen per(cid:173)
`meation behavior through PAS membranes to wa-
`
`ter, the oxygen permeability was investigated by
`means of a gas-membrane-liquid method. We dis(cid:173)
`cuss overall resistance to oxygen permeation be(cid:173)
`tween two phases, which consists of resistance
`in herent to the PAS membrane and the liquid(cid:173)
`membrane interfacial resistance, varying with hy(cid:173)
`drodynamic parameters.
`
`EXPERIMENTAL
`
`Preparation of PAS and M embran es
`
`PAS was prepared by low-temperature solution
`polycondensation through a two -step procedure
`according to the literature.P Briefly, a ,w-dichloro(cid:173)
`formyl-terminated aramid oligomers were pre(cid:173)
`pared by the reaction of 3,4'-diaminodiphenyl(cid:173)
`ether (Wakayama Seika Industry Co., Wakayama,
`Japan) with a calculated excess of isophthaloyl
`chloride (Wako Pure Chemical, Osaka, Japan ) in
`a chloroform-triethylamine-hydrochloride system
`at - 15°C for 5 min in the presence of triethyl(cid:173)
`amine as the hydrogen chloride acceptor under
`nitrogen. Next, the preformed aramid oligomers
`were reacted with PDMS-diamine (number-aver(cid:173)
`age molecular weight [Mnl of 1,680; Shin-Etsu
`Chemical Co., Tokyo, Japan) at -15°C for 1 h.
`The reaction was then continued at room temper(cid:173)
`ature for 48 h under nitrogen. The polymers were
`isolated by pouring the reaction mixture into
`methanol; a low-molecular-weight
`fraction en(cid:173)
`riched in PDMS was removed by washing the
`product three times with n -hexane; the residue
`was dried at 60°C for 48 h under vacuum. The
`observed PDMS contents of PAS in bu lk were cal(cid:173)
`culated from the SiCH3/aromatic H ratio in the
`IH nuclear magnetic resonance spectra, measured
`with a JEOL EX-90 (JEOL, Tokyo , Japan ). The
`inherent viscosity of PAS was measured with an
`Ostowald's viscometer at a concentration of 0.5 g/
`dL in N,N'-dimethylacetamide (DMAc) at 30°C.
`PAS membranes were cast from a 5 wt % DlVlAc
`solution on a TEFLON® sheet, and then the sol(cid:173)
`vent was evaporated at 50°C for 5 days. Finally,
`the membranes were dried at 60°C for 24 h in
`vacuo, and PAS memb ranes ranging in thickness
`from 30 to 100 11m were obtained. A SILASTIC®
`500-1 membrane with thickness of 125 11m was
`kindly donated by Dow Corning Japan Co. (Tokyo,
`Japan ).
`
`Tensile Strength M easurement
`
`Tensile strength was determined by the stress(cid:173)
`strain curves obtained with Autographs AGS-
`
`. j
`
`~ ..
`
`,.
`..
`
`I'
`>"
`'",
`"
`
`GE-1030.004
`
`

`
`Membrane
`
`Impeller
`
`Figure 1 Experimental apparatus for oxygen perme(cid:173)
`ability measurement.
`
`5kNB (Shimazu Co., Kyoto, Japan) at an elonga(cid:173)
`tion rate of 1.0 mm/min. Measurements were per(cid:173)
`room temperature with membrane
`formed at
`specimens (3 mm wide , 15 mm long, and 0.1 mm
`thick ), and three individual determinations were
`averaged.
`
`Tran sm ission Electron Microscopy
`
`The ultrathin PAS specimens were cast from a
`0.5 wt % DMAc solution on carbon-coated copper
`electron microscope grids of large mesh size (400
`mesh per inch ). The specimens were stained with
`a vapor of Ruo~9 for 15-20 min. Transmission
`electron microscopy (TEM) was done with a Hi(cid:173)
`tachi H-7000 transmission electron microscope
`(Hitachi Ltd., Tokyo, Japan) at 80 kV accelerat(cid:173)
`ing voltage.
`
`Oxygen Permeability Measurem en t
`
`The equipment used for the oxygen permeation
`experiment was fabricated by ourselves, referring
`to that of Okazaki and Yoshida." A picture of the
`equipment is shown in Figure 1. This apparatus
`is able to apply to the permeation experiment of
`liquid-to-gas, and gas-to-liquid
`liquid -to-liquid,
`system. Both of the asymmetric inner cylindrical
`tanks are made of poly (methyl methacrylate) of
`50 mm inner diameter and 60 mm length, and the
`other parts are made of polyvinyl chloride (PVC) .
`The sample membrane is placed between the two
`tanks with a PVC spacer of 5-mm thickness. The
`impeller installed in the tanks has six wings of
`10-mm width and 45-mm diameter. The rotation
`speed is altered by changing the applied voltage.
`
`PDMS-ARAMID MULTIBLOCK COPOLYMER. VII
`
`11 55
`
`For the gas permeation measurement, phosphate(cid:173)
`buffered saline (PBS) is filled in the right-hand
`tank under stirring and oxygen gas is purged into
`the empty left-hand tank without stirring. Thus,
`oxygen can permeate from left to right through
`the membrane. The oxygen dissolved in PBS
`through the membrane permeation is measured
`with an automatic blood gas analyzer, AVL-30
`(Radiometer Medical A/S, Copenhagen, Den(cid:173)
`mark ).
`
`RESULTS AND DISCUSSION
`
`Tensile Strength
`
`PAS and the PAS membranes prepared are sum(cid:173)
`marized in Table I. The stress-strain curves of
`the PAS membranes are shown in Figure 2. The
`tensile properties of the membranes are highly
`dependent on the PDMS content in the block co(cid:173)
`polymers, and the tensile strength of PAS was
`significantly higher than that of SILASTIC®500(cid:173)
`1. The higher tensile strength of the PAS mem(cid:173)
`branes compared with SILASTIC® 500-1 indi(cid:173)
`cates that PAS with 55 wt % of PDMS has as a
`high structural regularity as PDMS-aramid co(cid:173)
`continuous phases in lamella. The high ultimate
`elongation of PAS with 70 wt % of PDMS implies
`that the PDMS phase exists as the continuous
`phase with the aramid phase present as discrete
`domains" The elongation at break of PAS with
`55 wt % of PDMS was coincident with that of the
`aramid homopolymer.
`
`Morphology
`
`The transmission electron micrographs of ultra(cid:173)
`thin membranes (ca. 50 - 80 nm thickness ) of
`PAS are shown in Figure 3. We confirmed that the
`PDMS component was more easily stained with
`RuO, than was the aramid component." Thus,
`the black area indicates a PDMS phase, and the
`white area corresponds to an aramid phase. Two(cid:173)
`phase morphology was clearly observed for the
`PAS membranes with 55 and 70 wt % of PDMS,
`despite enrichment of the PDMS segment on the
`outermost surface of the PAS membranes, re(cid:173)
`vealed by the X-ray photoelectron spectroscopy
`and dynamic contact angle measurements.lv' ?
`
`O xygen Permeability
`
`A schematic view of a cross-section of the mem(cid:173)
`brane is shown in Figure 4. The buildup of oxygen
`
`GE-1030.005
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`

`
`1156
`
`MATSUMOTO ET AL.
`
`Table I Preparation of PAS and PAS Membranes
`
`PAS
`
`PDMS
`
`Ararnid"
`
`PAS-55
`PAS-55-90
`PAS-70
`PAS-70-30
`PAS-70-60
`
`1,680
`1,680
`1,680
`1,680
`1,680
`
`1,375
`1,375
`720
`720
`720
`
`PDMS Conte nt"
`(w t %)
`
`55
`55
`70
`70
`70
`
`b
`T/inh
`(dU g)
`
`0.51
`
`0.27
`
`Thickn ess
`( p m)
`
`90
`
`30
`60
`
`• Ca lculated from Si-CH 3/aromatic-H rat io in th e IH nu clear magn et ic resonance spectrum.
`b Measured at a concentration of 0.5 g/dL in DMAc at 30°C.
`
`from the slope of semilogarithmic plots of eq. (2),
`assuming the existence of a quasi-steady-state re(cid:173)
`gime-neglecting the rate of oxygen accumula(cid:173)
`tion in the membrane phase."
`Figure 5 shows the overall oxygen permeation
`resistances ( 11K) of the membranes at the various
`stirrer speeds ranging from 80 to 580 rpm. 1/K
`
`partial pressure, r in mmHg, was recorded as a
`function of time. From the material balance,
`Vdr/dt = KA (r* - n
`
`(1)
`
`where V is the buffer solution volume ( em"), A is
`the membrane surface area (cm''), r is the partial
`pressure of oxygen in buffer solution, r * is the
`equilibrated partial pressure of oxygen in the gas
`phase, and K is the overall oxygen permeation
`coefficient (cm/sec Lf' Integrating eq. (1) from
`time (sec) t = 0 to t = T, one obtains
`
`log f l T" -
`
`r o]l[r* -
`
`r )) = (K A / 2.303V) t
`
`(2)
`
`The overall oxygen permeation re sistance, 11K,
`of the PAS membranes can be easily calculated
`
`100
`
`Do
`
`-CIS
`:E-m 40e
`
`en
`
`V
`
`PAS-55
`
`PAS-55
`
`20
`
`o
`
`400
`Straln(%)
`
`800
`
`PAS-70
`
`lOOnm
`
`Figure 2 Stress -strain curves for PAS and SILAS(cid:173)
`TIC® 500 -1.
`
`Figure 3 Transmission electron micrographs of th e
`membrane.
`
`r. j
`
`'.
`.,
`
`'I
`
`GE-1030.006
`
`

`
`Gas Phase
`
`Boundary Layer
`
`Liquid Phase
`
`r
`
`PDMS-ARAMID MULTIBLOCK COPOLYMER. VII
`
`1157
`
`150r.p.rn.
`
`450
`400
`350
`
`300
`250
`200
`150
`100
`SO
`
`Membrane
`Figure 4 A schematic view of a cross-section of the
`membrane.
`
`Figure 6 Overall oxygen permeation resistances of
`the membranes as a function of n - 0. 7 . n is the stirrer
`speed expressed in rpm. ( 0) PAS-55-90, ( .6) PAS-70(cid:173)
`30, ( 0) PAS-70-60, (X) SILASITC®500-1.
`
`o
`
`0.01
`
`0.02
`
`0.03
`
`0.04
`
`0.05
`
`0-4·7
`
`decreased exponentially with increasing the stir(cid:173)
`rer speeds. The overall oxygen permeation resis(cid:173)
`tance in terms of permeation coefficients is broken
`down into two resistances inherent to its compo(cid:173)
`nent membrane and liquid-membrane interface
`in series: 25
`
`(3)
`
`where K; is the membrane permeation coefficient
`(em/ sec), and K L is the liquid-membrane interfa(cid:173)
`cial permeation coefficient (em/ sec) . The liquid(cid:173)
`membrane interface resistance (l/KL ) was as(cid:173)
`sumed to be inversely proportional to the stirrer
`speed, n (rpm), raised to some exponent, c, esti-
`
`mating the macroscopic relationship between in(cid:173)
`terfacial resistance and Reynolds number (Re;
`wr 2u , where w is the angular velocity [rad/sec},
`r is the membrane radius [em], and u is the kine(cid:173)
`matic viscosity [cm'i/secl ).
`the stirrer speed."
`Therefore, the membrane resistance may be de(cid:173)
`termined if the overall resistances, plotted as a
`function of (l/n Y, are extrapolated with a best
`statistical fit straight line to infinite stirrer speed.
`In Figure 6, the overall oxygen permeation re(cid:173)
`sistances of the membranes are plotted by setting
`C equal to 0.7, which was reported to yield the
`best statistical fit
`in many types of interfacial
`transport data.26
`28 The plot for the silicone mem(cid:173)
`-
`brane, SILASTIC®500-1, gave a straight line over
`the wide range of speeds used, and its membrane
`resistance obtained by extrapolation was almost
`the same as reported in the literature.r" On the
`other hand, data obtained for the PAS membranes
`did not show excellent agreement with theoretical
`predictions based on a stagnant boundary layer
`formation; there seem to be critical stirrer speeds
`around 150 rpm separating two regimens of the
`stirrer speed. The overall oxygen permeation re(cid:173)
`sistances of the PAS membranes containing 70 wt
`% of PDMS were equal to or less than that of
`the conventional silicone rubber at stirrer speeds
`~ 1 5 0 rpm.
`The modified Wilson plot described above im(cid:173)
`plicitly assumes that a unique exponent yielding
`a straight line does exist over the entire range of
`speeds or, in effect, that the flow regimen of the
`boundary layer formed on the membrane is the
`same for all speeds. The plots obtained for the
`PAS membranes, however, showed two distinct
`
`450 - ~
`400 -
`350 - ~
`300 -
`A •
`250 -
`200 -
`X ~~ 1c ~
`150 -
`A-
`-
`SO -
`
`j
`~
`
`100
`
`C
`
`A
`
`X
`
`,
`
`,
`200
`
`C
`
`A
`
`,
`
`C
`
`~ ~X
`
`,
`
`A
`
`,
`
`,
`600
`
`0
`
`100
`
`300
`
`400
`
`500
`
`stirrer speed, r.p.m,
`
`Figure 5 Overall oxygen permeati on resistances of
`the membranes at the various stirrer speeds. ( 0) PAS-
`55-90, ( .6) PAS-70-30 , ( 0) PAS-70-60, (X) SILASITC®
`500-1.
`
`GE-1030.007
`
`

`
`1158
`
`MATSUMOTO ET AL.
`
`regions; therefore, the true membrane resistance
`may not be determined by extrapolating 11K to
`infinite stirrer speed.
`Eq. (3) can be rewritten as follows :23.24
`
`11K = SLIP + 1IKL
`
`(4)
`
`where P is the oxygen permeability of the mem(cid:173)
`brane (em" standard temperature and pressure
`[STP] ern/em" sec cmHg ) S is the solubility of
`oxygen in water (em [STP]/cm 3 cmHg ), and Lis
`the thickness of the membrane (em) . Because the
`transport mechanism of oxygen through the mem(cid:173)
`brane in liquid-membrane-gas permeation is as(cid:173)
`sumed to be about the same as in the case of gas(cid:173)
`membrane-gas permeation.i" P can be deter(cid:173)
`mined by a routine high-vacuum method.f" The
`two-phase nature ofthe PAS membranes, similar
`to that obtained in the previous study, 18 on which
`the gas permeability of the membrane mainly de(cid:173)
`pended, was confirmed in part by both the tensile
`strength properties and TEM. Therefore, the oxy(cid:173)
`gen permeability of PAS membranes with 55 and
`70 wt % ofPDMS may be determined as 1.8 X 10 - 8
`and 2.1 X 10 - 8 (em" [STP] ern/em" sec cmHg ),
`respectively, from the previous prediction; " The
`oxygen permeability of SILASTIC® 500-1 is re(cid:173)
`ported as 6 X 10 - 8
`(em" [STP] cm/cm'' sec
`cmHg).23 The membrane resistance, SLIP, was
`calculated by an S of 3.7 X 10 - 4 (em" [STP]/cm 3
`cmHg ) at 25°C. Subtraction of the calculated
`membrane resistance from the measured overall
`oxygen permeation resistance yields the interface
`resistance.
`The liquid-membrane interface resistances are
`plotted as a function ofn - 0.7 in Figure 7. The inter(cid:173)
`face resistances of the PAS membranes decreased
`with increasing stirrer speeds having two distinct
`regions, but were not dependent on the membrane
`thickness. All of the interface resistances of the
`PAS membranes had almost the same dependence
`on the stirrer speed; at a stirrer speed < 150 rpm,
`the interface resistances of the PAS membranes
`were higher than that of the silicone rubber, and
`at stirrer speeds ~ 150 rpm, they were lower than
`that of the silicone rubber, while the interface re(cid:173)
`sistance of the silicone rubber showed a linear
`relationship with n - 0.7 . It was indicated by mea(cid:173)
`surement of the torque on a cellophane membrane
`with R e characterizing the turbulence in the bulk
`of the liquid that: above Re """ 30 ,000, correspond(cid:173)
`ing to a stirrer speed of about 320 rpm, the mem(cid:173)
`brane boundary layer is
`turbulent; below Re
`""" 20,000, a stirrer speed of about 210 rpm, the
`boundary layer is laminar. A transition region,
`
`ISOr.p.m,
`
`e
`
`~c
`
`A
`
`~
`.,
`~
`
`350
`
`300
`
`250
`
`200
`
`150
`
`100
`
`SO
`
`o
`
`0.01
`
`0.02
`
`0.03
`
`0.04
`
`0.05
`
`0.0·7
`
`Figure 7 Liquid-membrane resistances as a function
`of n - 0. 7 . n is the stirrer speed expressed in rpm. (0)
`PAS-55-90, (.6. ) PAS-70-30, ( 0 ) PAS-70-60, ( X ) SILAS(cid:173)
`ITC®500-1.
`
`where the flow changes from laminar to turbulent,
`may exist beginning at Re """ 20,000-25,000.26 It
`is assumed that the dependence of the flow regi(cid:173)
`men in the proximity of the PAS membranes on
`the stirrer speed is similar to that of the cello(cid:173)
`phane membrane rather than the silicone rubber;
`in other words, the interface resistances of the
`PAS membranes with the two-phase nature are
`more susceptible to the hydrodynamic parameter
`relevant to the stirrer speed than that of the sili(cid:173)
`cone rubber.
`
`CONCLUSIONS
`
`The oxygen permeation properties of PAS mem(cid:173)
`branes in the gas-membrane-liquid system were
`clarified in part by evaluating the interface resis(cid:173)
`tances of the membranes. The interface resis(cid:173)
`tances of the PAS membranes with the two-phase
`nature were more susceptible to the hydrody(cid:173)
`namic parameter than that of the silicone rubber
`and became lower than that of the silicone rubber
`at higher stirrer speeds. The low interface resis(cid:173)
`tance together with the high tensile strength of
`the PAS membranes enables us to provide highly
`oxygen permeable membranes in practical appli(cid:173)
`cations with a membrane-liquid interface.
`
`The authors express their thanks to Kozo Shiraishi, the
`president ofShiraishi Hospital and Prof. YoshitoIkada,
`Research Center for Biomedical Engineering , Kyoto
`University, for his assistance in the measuring of oxy(cid:173)
`gen permeability.
`
`, ,
`, .
`~ .
`
`0' J
`
`~ ,
`
`.....,
`
`..,
`
`.,
`o,·r
`
`"
`
`GE-1030.008
`
`

`
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`GE-1030.009