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Macromolecules 1993,26, 486-491

Morphology Transition from Cylindrical to Lamellar

Microdomains of Block Copolymers

Shini chi Sakurai,' Toshikazu Momii, Kazuh iro Taie,Mitsuhiro Shibayama, and S hunji Nomura

Depar tment of Polymer Science and Engineering, Kyoto Institute of Technology,Matsugasaki, Sakyo-ku , Kyoto 606, apan

Takeji Hashimoto

Depar tment of Polymer Chemis try , Kyot o Univers ity , Sakyo-ku, Kyoto 606-01, Japan

Received August 4,19 92; Reuised Manuscript Received October 6, 1992

ABSTRACT: Thermally induced morphology ransition from cylindrical olamellarmicrodomainswan foundfor a poly(styrenablock-butediene-block-s~ene)SBS)riblock copolymer havinga 0.66weight fractio n ofpolystyrene blocka by sm all-angle X-ray scattering (SAXS) nd transmission electron microscopy (TEM).Polybutadiene (PB) ylinders with hexagonal c l w packing were formed in a polystyrene (PS)matrix whenth e SBSwan cast from a methyl ethyl ketone solution. It wan found that the PB cylinders were transform edinto lamellae on annealing a t 160 OC. This is a transition from thermodynamically quasi-stable to stablemorphologies. On he baaisofSAXS nd TEM, the transition turned ou t tooccur via coalescence of cylinderswithout their translational movementa. It ia propoeed that an undulation of the interface induced by theinatabiIityof th e interface might play an mportant ole for the coalescence of the cylinders. It wan also foundby TEM hat the coherency of lamellar microdomains thus formed became higher with further annealing;

i.e., the persistence length of the undulating lamellaebecame longer.

I. Introduction

Inmultiphase polymeric systemsmorphology control isone of the most important research subjects, since their

mechanical properties depend stronglyon heir str uctu ral

In the case of block copolymers it is possible to design

multiphase domain structures of submicron (mesoscopic)

scale via microphase separation2so as to obtain desired

properties. A-B typeblock copolymers n melts may form

microdomains due to strong segregation between the AandB blockchains, and their morphologiesaredeterminedprimarily by composition of a block copolymer. M0lau3

has presented five fundamental morphologies, Le., A (B)spheres inaB (A)matrix, (B) cylinders in a B (A) matrix,

and albrnating lamellae. We have investigated system-

atically the microdomain structures of block copolymers

by small-angle X-rayscattering(SAXS)nd transmission

electron microscopy (TEM) and have obtained various

resultson he morphology, domainsize, heir dependencies

of molecular weight and compaaition, and so forth?'

Mei@ and Hdfand et al.O-14 have developed statisticalthermodynamical heories for microdomain structures of

block copolymers. Accordingtotheee heories,itispoeeibleto expect equilibrium domain sizes for respective mor-

phologies (e.g., spheres, cylinders, and lamellae) with a

given set of molecular weight and composition. These

theories allowus to predict also equilibrium morphologyina strong seigregationlimit. Hong,Noolandi,Whitmore,

andtheir co-workers have presented a functional integraltheory for copolymer/solventa blends1"17 and copolymer/

homopolymer"a The functional integral the-

ory which is a self-consistent theory makes no a-priori~ ~ ~ u m p t i o n sfweak orstrongsegregationlimits. Leibler19

has developed a Landau type mean-field theory on hemicrophamseparation transition (MST) in block copol-ymers and has presented the phase diagram for themicrodomainmorphologies n theweak-segregationlimitsasa function of " g a t io n power and composition of theblock copolymer. Recently Ohta and Kawasakim have

To whom cormpondonce &od d be a ddr e a d .

generalized Leibler's theory tothe strong-segregation imit

by taking into account a long-range interaction of the local

order parameter on the basis of the Ginzburg-Landau type

mean-field theory. More recently Fredrickson and Hel-fand2l have corrected Leibler's mean-field theory to take

into account the effect of composition fluctuationson he

MST. These theories expect that the morphologies are

changed with the segregation power. Since the segregation

power is a function of temperature, morphology may be

reversibly controlled and hence the transit ion between

the different kinds of morphologies mayoccurby changing

temperature. However,thiskind of thermally reversible

transition has not been experimentally conf i i ed up tothe present, except in our recent preliminary results.22

Another possible way to control the morphology is an

application of thermally induced irreversible morpholog-

ical transition.B*N As for the irreversible transition, itwase.perimentallyconfiiedthatlamellarmicrodomainewhich were formed in the solution-cast films with a

selective solvent were transformed into cylindrical mi-

crodomains by annealing above the glass transition tem-

perature, TPB In t h i s case, it was considered that a

thermodynamically quasi-stable lamellar morphology,which was frozen due to vitrification during solvent

evaporation, was changed to a stable cylindrical mor-phology uponannealingaboveT,. Inthispaper we present

a similar irreversible but inverse morphology transitionfrom cylindricalto lamellar microdomainsasobserved by

S A X S and confirmed by TEM. Since the mechanism of

forming quasi-stable morphology with a selective cast-

solvent was a scope of the previous we exclusivelyfocus here on a mechanismof the morphology transitionfrom cylindricalto lamellar microdomains, elucidationofwhich may give a new aspect for morphology control.

11. Experimental Section

A poly(styrensblock-butadiene-block-s~ene)riblock co.polymer coded aa TR2400 the commercial sample of Jap anSynthetic R ubber Co., Ltd.)wan used. The number-averagemolecularweight, M., th e heterogeneity index, M,.IM., an d th eweight fraction of polystyrene (PS), H(, were determined to be

0024-9297/93/2226-0486$04.00/0 (8 1993 American Ch emical Society



486 Sakurai e t al. Macromolecules, Vol. 26, No. , 1993

1.0 - 0

0 0

0 0

0 0

0 0

0 0

0 0

0 0

0.5 -0 0

0 0

0 0

.8 o.o-s = -b h = 8mxto*(nm') sx1O'(nm")

28 (mln) ze (mln)- -

Figure 1. Slit-width (a) and slit-height (b) weighting functionsof the incident beam on the detector plane.

1 Dlmenrlonal

P- . .Scattered

PSPC ..... .......

cG=JX-rayr .........

//..... Stacked lllm ..... n: film normal

ifncldont

x / x'Through Vlew Edge Vlew

Figure 2. Schematic diagram showing the geometry of theexperimental setting of SAXS.

6.31 X lo', 1.15, and 0.56 by m emb rane osm ometry, GPC, andelemental analysis, respectively. Th e microstructure of poly-butadiene (PB) blocks was determined by infrared spectroscopy(Morero method%)to be 33,55, and 12 mol 9% for cis-1,4-, rans-1,4-, and l,& linkages, respectively. Th e film specimens were

obtained by evaporating the solvent methyl ethyl ketone (MEK)from ca.5 w t 9% polymer solution in MEK at room temperature.Since th e solubility param eter values" are 8.1-8.6,8.6-9.7, an d9.3 [ ~ a l / c m ~ ] ~ / ~or PB, PS, and MEK, respectively, MEK is aselectively good solven t for PS.SAXS measurements were performed with an apparatusn

consisting of a 12-kW rotating-anod e X-ray generator, a graph itecrystal for the incident beam monochromatization, a 1.5-mcamera, and a one-dimensional position-sensitive proportionalcounter (PSPC). Cu K a radiation with a wavelength,A, of 0.154nm was used. Th e incidentbeamwith aline-shaped crosssectionwas irradiated, and t he scatt ered X-rays were collected with th eone-dimensionalPSPC which was horizontally set. Th e incidentbeam attenuated by a nickel fib128 was directly measured bythe PSPC to determine th e weighting function of the opticalsystem used n thiswork, and th e result isshown in Figure 1.The

geometry of o ur experimental se tup of SAXS s schematicallyrepresented in Figure 2. The film normal is parallel to th epropagation direction of he incidentbeam or the through view

and p arallel to the scanningdirection of the PS PC for the edgeview. Themeasured scattered intensities were furth er correctedfor absorption due to the specimen, air scattering, thickness oftheepecimen,and therm al diffueescatteringarising from densityfluctuations. Th e absolute scattered intensity was obtained byth e nickel-foil method."

A Hitachi H-600S lectron microscop e waa used or the TEMof ultrathin sections of the specimens stained with osmiumtetraoxide (0804) .

111. Results and Discussion

(A ) Effects of Slit Smearing. Since the slit colli-mation with a finite slit height and a narrow slit breadth

was used, the scattered intensity thus obtained as a

TR 24 00 as-cam1

0.00 0.50 1.00 1.50 2.000 x 1 0 (nm")

0 30 BO 90 1202e(mln)

Figure 3. Semilogarithmic plots of the abeolute scatteredintensity Z b ) vs 8, measured at room temperature for as-castSBS specimens from a methyl ethyl ketone solution.

function of scattering angle, which iscalledhereafter SAXSprofile, is the smeared S A X S profile. Therefore, the

smeared profile should be desmeared. However, theconventional method for desmearing of the profilescanbe applied toan unoriented systembut not foran oriented

system.w Since the S A X S profiles for oriented syabmsare discussed in section III.B, we showfmt the effecta of

slit smearingon the S A X S profile.

It is known that the cylindrical microdomains in the

as-cast f h ave an orientation with their axes prefer-

entially oriented parallel to the film urface. Therefore,

the edge view gives the SAXS profile from oriented

microdomainswhile the through view does the profile from

unorientsd microdomains. Hence, the slit correction(desmearing%)can be done only for the through view. InFigure 3,the smeared and desmeared profiles for through

views of the as-cast specimen measured at room temper-

ature are shown in a semilogarithmicplot of the absolutescattered intensity vs the magnitude of the scatteringvector, s,which is given by

s = (2 sin B ) / A (1)

with B and A being half the scattering angle and the

wavelength of X-rays, respectively. Thefigure isutilieedto show effecta of the slit smearing on the profile. Thewidth and intensity of each individualecatteringpeak are

much affectad by the slit smearing. On the other hand,

the position of peak isnot affected very much. Althoughthe fmt-order peak shifta to a small s-region by thesmearing effect, theamount of the shift is1.6 X 10-8nm-'in s-value and is negligibly smaller than he differencebetween the position of the fwt-order peak for themastspecimen and that for the annealedspecimen,whichwill

be discussed later (see Figure 4 and section III.B).Therefore, in section III.B, we only focus on th e peakposition of the ameared S A X S profiles for edge view inthe oriented systems in order to discuss the morphologytransition.

(B) SAX8 Results. In Figure 3 the smeared SAXSprofile for edge view is also shown. Again the profile wasmeasured a t room temperature for the as-castspecimen.Several scattering peake or shoulders were observed a t

relative s-values of 1, 3'12, 41/2, 71/2, and (13)1/2 in the



Macmmokcuk8, VoL aS,No. ,1993

28 h,"J * a w n i

4. 8erdagarithmic plots of th e mead almoluteloatted intemity I ( # ) VII I for the apeeimem annealedat 158*C for edge view.measured at room temperature.

smeared profilea both for the through and edge views.Thesearedif€raction pealrs of hexagonally-packed cylin-

drical microdomains. Bragg spacing, d, was calculatedwith d = 1/81, where 81 is the e-value of the firs torder

peak. The spacingw88 estimated to be 30.7 and 23.2 nmfor through and edge views, respectively. This indicatesan anisotropic packing of the cylindrical microdomains inthe assast film. We will discuss this point later.

I t i sw o r t h y o f e ~ t h e SAXSpm fd e smo r e c l o e e l y .Thepeaksobserved at 8 labeled by (13)'/* re more likelythe scattering maxima arising from isolated cylindricalparticles rather than the lattice peaks because of theirspectral broadness. From the 8-value of the particle

seattaring peaks, he average radius of the cylinders. R,isroughly estimated using the following condition for theparticle scattering maxima of the isolated ~ylii nders:~~

fori = 1.2.3 , .. (2)

where 8r denotes the #-value of the ith-order particlaseatbringpeak. Iftheseatbringmaximaatthe pi t i o n slabeled by the numerical numbers, i, with black thickarrows are assigned to ith-order particle scatteringpeaks(i = 1.2). the calculated volume fractions, f, of the PBcylinders roughly egree with the molecular compositionof TR2400. In the calculation of f , we assumed theperfectly hexagonal packing of the cylinders and f is given

2 4 R = 4.98,8.364,11.46, ...

88

(3)

Th e 8F-valuea 0.0681 nn-l for both deameared and

smeared hrough views and 0.0903 nm-' for the smenrededge view give11.6and 8.78nm of the average radii of PBcylinders, respectively. The values of d were obtained tobe 30.9 and 23.2 nm. respectively, for the through and

edge views. Then f values were calculated to be 0.39 forboth eaaes. This in roughly consistent with the volumefraction of PB-block chaina 4 p ~=0.47) calculated fromthe molecular composition of r u p ~ 0.44.

In F w the smeared SAXS profdea for the edgeview are shown. These were measured at room temper-ature after annealingthe specimens a t 158OC for 3,5,10,20,30,60, and90min. For comparison, the profde of theas-cast fh as included in the f v e . A drastic change

of the SAXS profiles is neen between the 3- and 5-min

Morphology Ramition of BlockCopolymm 487nFig" . Schematicrepmantation of thehexagonally-packedcylinders with horimntally-ntretched ellipsoidal cylinder cm4od o n s ormedm th e an-castfh.

annealed specimens. The d m c t i o n peaks rom hexag-onally-packed cylinders were observed for the 3-minannealed specimen. On the other hand, the relativepositions of the scattering peaks for the specimensannealed for 5minor longercnnbe assigned by integers.Le.. 1, 2, 3, ...,relevant to the diffraction peaks of thealternating lamellar microdomains. Thus. it was found

thatthemorphologytransitionmmcylindricaltolamehmicrodomains occurred within 5 min upon a n n d i t158°C. Since thevolume raction ofPS s0.53, the lamellarmorphology is thermodynamically stable at room tam-perature an well an at 158"C. Therefore, this ransition

shouldbetdenasthatfromthethermodynamicallyquasi-stable cylindrical morphology, which was formed viacasting the block copolymer solutions with a selective

solvent, to the stahle lamellar morphology."Let un closely examine the change of the SAXS rofdea

with annealing time. The position of the fustorder peakshitted toward a smaller 8-region from 0.0431 to 0.0368nm-'within 3 min after annealing the as-castf h , ut no

more changed with further annealing. The Bragg spacingd-value for the 3-min annealed specimen is 27.2 nm. Thiipeak shift cnn be explained as follows. During solventevaporation, the cylindrical microdomains formed in theeastsolutionpreferentially orientwiththeiraxes naplanaparallel to the f h urface, an schematically shown inFigure 5a The domain structure maybe frozen-in whenthe PS-rich matrix phase is vitrified. Since the PS matrix

still contains a certain amount of the solvent, volumecontraction occurs during successive evaporation of thesolvent. In thisprocess the thickness of the castsolutiondecreases while keeping ita area constant, which may leadto the cylinders having elliptical c r w sections with theirlong axes oriented parallel to the f h urfaceas shown inF v e b in the as-castf h . This process may also end

to a compression of the hexagonal lattice in the direction

normal o thefh urface88 schematicallyshown in Figure5b(dn(1)<d,(10. Thisisconsistentwith theSAXSfortheas -e as t f i tha tis ,thespacingasobservedforthe~ugh

view (dl(l' = 30.9 nm) an larger than that for the edgeview (dl(l)= 23.4 nm). Asymmetric crw sections of the

cylinders were also found by SAXS with RI"' = 11.6 nmand Rl" ) =8.78 nm where RnC1) and RI") denote the radii

of the cylinders in the directions parallel and normal to



488 S h a i e t a l .

the freesurface of theas-castfilm, espectively. As i m i i

asymmetric c r w ection was previously reported for thespherical microdomains formed inthe solventcastfilm.32The asymmetric c r w sections of the cylinders tend tobecome circular, the compressed lattices tend to recovernormal hexagonal lattices, and hence ita residual strain isrelaxed when the as-cast film is annealed aboveTg f PS.Actually theSAXS rofiles of edge view showed the peakshifting towarda smaller s-regionasa consequence of theincrease of the spacing d in the direction normal to the

film rom dll(')(=23.4 nm) to d11(2)=27.2 nm). Here it wasquite reasonable to observe the following elations for theBragg spacings and the radii of the cylinders:

(2) = d , @ )= [d,")d, ( l ) ]1/2 andd ,R(2)= [R , ( l )R , ( l ) ] l / z4)

with R(2)= 10.3 nm. For this specimen, f = 0.39 wasobtained and again this is roughly consistent with themolecular composition.

It should be noted here that the positions of thescattering maxima locatedat the integer multiples ofthatof the f irs torder peak do not change upon annealing fortimes longer than 3 min and were therefore kept constantthroughout the transition. The average value of d was

27.2*0.5nm. Forthe5-,10-,20-,30-,and60-minannenledspecimens, the scattering peaks became sharper withannealing time, while there is no significant differencebetweentheprofdesof60-and9O-minannealedspecimens.These observations indicate that cylinders are rapidlytransformed intolamellae within5min,and then regularityof the alternating lamellae becomes higher upon furtherannealing in the time scale from 5 to 60 min.

(C) EM Results. In order to confirm the morpho-logical transition discussed in section IILB, the TEMinvestigation was conducted on ultrathin sectionsof thespecimens stained with 0 8 0 4 . Theobserved microdomainstructures for the as-caat and annealed specimens (an-

nealed a t 150 'C for 30,60, and 120 min) are shown inFigures 6 9 , where PB microdomains are selectively

stained with 0 8 0 4 . The hexagonally-packed PBcylindersare dominantly seen for the as-castspecimen in Figure 6.Contrary to this, highly ordered alternating lamellae with

uniform lamellar thickness are observed for the 120-minannealed specimen in Figure 9. Hence, the TEM obser-vation definitely revealed the morphology transition.

Here let ueclosely examine the electron micrographs toelucidate the mechanism of the transition from cylindersto lamellae. In the 30-min annealed specimen (Figure7)alternating lamellar microdomains are dominant. How-ever, this morphology is much different from tha t of the120-minannealed specimen (Figure9). The characteristicfeatures of the morphology for the 30-min annealedspecimen are as ollows: (1)Coherency of lamellar s tackis considerably low; i.e., their persistence lengths alongtheir interfaces are considerably short or the interface isundulating, and the size of the stacks normal to theinterfaces is also small. (2) There are still many regionsin which cylinders exist, causing defects for the lamellarmorphology. (3) There are regions showing probably the

mesh morphology33 in which the mesh layer composed ofPB are stacked in the matrix of PS. In Figure 7 thehexagmdy-packed cylinders are manifested in the circledregion A, while the region in the circle B is seeminglyshowing the mesh morphology. The characteristic shapeof the P B amella with undulating interfacesor PB meshis considered asa transient structure which may appearjust after coalescence of cylinders. The cylinders whichareasyetnottransformedandthemeshmorphology,hoth

Macromolecules, Vol.ZS,No. , 1999

Figure 6. Electron micrograph of the as-cast specimen.

ofwhichare he defecta forthe lamellarmorphology, werestill observed in the 60-minannenled specimen in Figure8,theformerdefectbeinghighlighted hythecircledregionA.(D)echanism ofMorphologyTraniition. On the

hasis of the SAXS andTEM observations, we present a

schematic diagram in Figure 10in which the morphologytransition isviewed along the axis of the cylinders initially

existing n theas-castfh. Partsa-d represent cylindricalmorphology,a transient state from cylinders to lamellae,

andlamellarmorphologywithlowcoherenceandthatwithhigh coherence, respectively. The model view alongthedirection normal to the cylinder axis will be presented

later in Figure 11. Parts a 4 manifest the characteristicfeatures of the morphology observed for the as-cast (morarigorously for the 3-min annealed specimen), 30-, 60-, and

120-min annealed specimens, respectively. In part h thecrw section of each as-transformed cylinder sellipsoidlikeand neighboring cylinders tend to he interconnected as

highlighted in regionA in Figure 8,for example, where the

original cylinder positions are indicated with thin circles.Such deformation of the cylinders results in decreasing

mean curvature of the interface and hence in the relaxationof an excessbending free energy. The cylindersasyet nottransformed in the original hexagonal lattice are high-lighted in part c.

Since no peak shift was observed in the SAXSprofdesthroughout the morphology transition, it is not possible

to consider that the transition is induced by collisions ofthe cylinders with their translational movements. The nopeak shift also implies that the spacing d of (100)planein the cylinders turns into the interlamellar spacingD ,while conserving the condition of d = D. Aa revealed bySAXS nd TEM, the transition froma to c iscomparablyfast. On the other hand, the protea from c to d is slow.This is because a global change of the lamellar micro-

domains to increase coherence of lamellae should involve



Macromolecules, Vol.26, o. 3, 1593 Morphology Transition of Block Copolymers 489

Figure 7. Electron micrograph of the 30-min annealed specimen (annealed at 150"0.

a long-range cooperative ordering of lamellae or partialdestruction-and-reformation of the undulating lamellae.Further investigationonthesloworderingprocessdeservesfuture work.

Finally let us consider a poasible scheme for thetransition pr- without the translational movement ofthe cylinders. The scheme should involvecoalescence ofcylinders, as shown in Figure 11. The precursory step tothe cylinder coalescence s the development of undulationsalong the length of the cylinders. For purely viscoussystems this undulation is known as Tomotika's insta-bility.% However, in our systemtheundulation s primarilydriven by a change in the interface curvature, i.e., thecurvature in the as-cast film becomes unstable at theannealing temperature, and the systems tend to achievethe new curvature equilibrium at this annealing temper-

ature. Thus a primarily physical fador associated withthis processmay beelasticdeformationofthe blockchainsand interfaces, which is triggered by the relaxation of theunfavorable chain conformations for both PS and PBblocks in the quasi-stable morphology frozen in the as-

cast film. When the SBS with .$ps equal to 0.53forms thecylindrical microdomains of the PB chains in the matrixof the PS chains under the condition of both chains

satisfying he requirement or incompressibility,PSchainsin the matrix are forced to expand and PB chains in thecylinders are forced to contract, causing convex curvaturetoward the center of the PB cylinders (see par t1of Figure11). This unfavorable conformationcan be relaxed whenthe specimen is annealed aboveTg f the glassy PS phase,which brings a change in the interface curvature and inthe cross-sectional shape (part b of Figure 10)and henceinstability and undulation of the interface in the as-cast

f h see part 2 of Figure 11). The s i m i i undulatinginterfacea were previously reported by Cohen et al." forthe morphology transition of cylinders pinching off into

spheres. When the undulating interfaces accidentally

approach each other and coalesce, channelscan be formedbetween the adjacent cylinders (see part 3 of Figure 11).

Duringstages2 nd 3 he average interface curvaturestartato decrease. This reduction of the curvature continuesthrough the transition process, decreasing the excessbending free energy encountered n the as-castfilms.Thechannel grows in the direction along the axes of cylinders(see part 4 of Figure 11) n such a way that the cylindersare eventually transformed to lamellae, asshown by part

5 of Figure 11. The growth of the channel is similar tozippering. Duringstages 3 and 4, the PB meshes throughwhich the PS channels traverse are formed as an inter-mediate structure. In this transition scheme presented inFigure 11 he translational movement of the cylinders isnot necessarily considered. The interfacial thicknessshould be roughly kept constant throughout coalescenceof cylinders because interfacial thickness is govemed onlyby segmental interaction between PS and PB chains.As revealed by SAXSand T E M observations, cylinders

coalesced and were transformed into lamellae, whiledissolution of the cylindrical microdomains was notobserved prior to formation of the lamellar microdomains.This indicates that morphology transition does not nec-essarily require the entire dissolution of the domain

structure. Let us consider this reason. Figure 12 scbamatically shows the change of the free energy involved inthe morphology transition. Along with the transition pathvia the disordered state, the free energy barrier isconsiderably large due to the mixing of strongly repulsive



49 0 Sakuraietal.

Figure 8. Electronmicmgraphofthe60-minannealedspecimen(annealed at 150"0 .

Figure9. Electron micrographofthe 120-min mea led spen(annealed at 150 OC).

PS and PB block chains. On the other hand, the energy

barrier for the coalescencescheme is expected toberathersmall because it involves only the local disruption of the

Macromolecules, Vol.26,No. , 1993

D,, intercylinder distance

-1 d 1 (a) (b)

d: Bra& spacing D.( D interlamellar distance

(C ) (d )

Figure 10. Two-dimensional projection for the change ofstructure. a 4 epresent cylindricalmorpho1ogy.a tranaientstatafrom cylinders to lamellae, and lamellar morphology with lowcoherence and that with high coherence, respectively, andcorrespond to the morphologiesobse~edor the =-east (morerigorously for the 3-min annealed specimen),30-, & and 120-min annealed specimens presented in Figures 7, 8 and 9,respectively.

1 - m... ........ ....15) (4 )

Figure 11. Scheme for morphological transition includingeoalearanceof cylinders.

interfaceandlocalmixingofunlikesegmentaas presentedin Figure 11. Therefore, the transition scheme involvingthe coalegcence of the cylinders maybe more reasonablefrom the viewpoint of the lower energy barrier for thetransition than the transition scheme involving the dis-

ordering.

IV. Concluding Remarks

In thin study the morphology transition from cylindernto lamellae was studied complementarily by S A X S andTEM. It was found that the PB cylinders existingmetastably in the solution-castfilmsweretranformed intothermodynamically stable lamellae on annealing at 150

shinichi sakurai et al- morphology transition from cylindrical to lamellar microdomains of block...

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