poly(vinylidene fluoride ) ( pvdf ) is a partially crystalline linear hydrofluorocarbon polymer exhibiting extraordinary electrical properties , ranging from those of a typical dielectric polymer to those of a versatile ferroelectric material , as a consequence of its crystalline structure and the abundance of polymorphic phases .
four polymorphs ,  ,  ,  and  , have been documented so far [ 1 , 2 ] , and the fifth  form is strongly suggested to exist .
a rather strong electric moment in the pvdf monomer unit arises because of a strong electronegativity of fluorine atoms as compared to those of hydrogen and carbon atoms .
thus , each macromolecular chain possesses a dipole moment perpendicular to the polymer chain [ 4 , 5 ] .
if a polymer chain is packed in crystals to form parallel dipoles , the crystal possesses a net dipole moment as in polar  ,  , and  forms ; whereas , in antiparallel chain dipoles alignment , the net dipole moment vanishes as in nonpolar  and  phases .
the most common polymorph of pvdf is the  phase predominantly obtained during crystallization from the melt at moderate or high supercoolings [ 6 , 7 ] .
the  phase is formed also during polymerization , and it is characterized by a trans - gauche - trans - gauche ( tgtg ) conformation of macromolecular chains .
it is nonpolar and does not exhibit ferroelectricity ; however , when deformed , it displays a large flexoelectric effect , connected with the strain gradient .
the  phase can be transformed into three other polymorphic forms under an action of sufficient mechanical stress , heat , or electrical field .
the  phase , usually obtained during mechanical deformation of  spherulites [ 916 ] , is presently the most important polymorph of pvdf used extensively for piezoelectric and pyroelectric applications .
an all - trans ( tt ) molecular conformation of pvdf is responsible for the ferroelectric properties .
however , the fluorine atoms are too large to allow a simple all - trans conformation , and they are slightly offset to form a zigzag arrangement along the crystal c - axis .
the presence of  phase has been reported in pvdf films crystallized from the dimethyl sulfoxide , dimethyl acetamide , and dimethyl formamide solutions [ 18 , 19 ] as well as in the samples crystallized at high pressures [ 20 , 21 ] , at high temperatures [ 6 , 7 , 22 , 23 ] , and after annealing of the  phase crystals [ 7 , 24 ] .
the macromolecular chains of  phase are in the tttgtttg conformation and can be considered , regarding the ferroelectric effect , as an intermediate between the  and  phases . when formed during melt crystallization above 160  c , the  phase reaches the highest concentration close to 170  c .
the polar  phase can be formed by poling the antipolar  phase at high electric fields [ 26 , 27 ] .
this form has the same unit cell dimension along c - axis and macromolecular chain conformation as the  form , the difference lying in the interchain packing alone .
a fifth crystallographic form is the  phase containing the tttgtttg conformation of macromolecular chains similar to the  phase but in an antipolar arrangement .
mechanical deformation of the  phase at most temperatures leads to an almost complete transformation to  phase [ 13 , 14 ] , so for many years , oriented films containing  phase had not been available
. however , mackey et al .   showed that isothermal recrystallization of pvdf nanolayers in multilayered psf / pvdf films at high temperatures causes the phase transition from  to  phase crystals .
pvdf is used in a wide range of applications due to the ferroelectric properties of  ,  , and  crystals , which in turn is closely related to the alignment and orientation of those crystals .
there are many means of enforcing pvdf crystal alignment and orientation ; most of them adopted from known processes designed for commodity polymers .
the methods used to identify the polymorphic phases of pvdf and to determine the orientation of crystals in pure pvdf films or in blends with other polymers such as polyamide 11 ( pa 11 ) , poly(methyl methacrylate ) ( pmma ) , polyvinylpyrrolidone ( pvp ) , polycarbonate ( pc ) , and polysulfone ( psf )   include mainly x - ray diffraction [ 1 , 9 , 14 , 2934 ] , infrared spectroscopy ( ftir ) [ 6 , 11 , 12 , 29 , 31 , 33 , 3537 ] , raman scattering [ 38 , 39 ] , and nuclear magnetic resonance ( nmr ) . nevertheless , all methods mentioned above enabling identification of pvdf polymorphs , are insufficient to determine fully the preferred orientation of pvdf crystals and the texture of films . in the case of two - dimensional wide - angle x - ray diffraction ( waxs-2d )
, the information is incomplete because the alignment and orientation of pvdf crystals in the direction along the incident x - ray beam path can not be elucidated .
full texture determination can be achieved using x - ray pole figures technique . in the literature
, there is practically no information about this technique used to examine the texture of pvdf . only wang and cakmak   applied waxs pole figures of ( 020 ) plane to examine the orientation of pvdf  phase crystals in injection - molded pvdf and pvdf / pmma blends . in this article , we concentrate on the full texture determination of pvdf nanolayers in multilayered psf / pvdf film systems utilizing x - ray pole figures of reflections from selected crystallographic planes .
semicrystalline poly(vinylidene fluoride ) ( pvdf ) homopolymer solef 6010 from solvay solexis crystallizing from the melt in the  phase   and amorphous polysulfone ( psf ) , udel p-3703 obtained from solvay advanced polymers , were chosen as raw materials to produce 12-m thick psf / pvdf film systems by layer - multiplying coextrusion at conditions described in details by mackey et al . .
the compositions of all film systems studied in the paper are collected in table  1 . in each layered system , the pvdf nominal layer thickness was varied from 28 to 225  nm .
the multilayered psf / pvdf films were isothermally recrystallized using two oil baths containing silicon oil at recrystallization temperatures of 145  c and 170  c , respectively .table 1the as - extruded and recrystallized multilayered psf / pvdf film systemssample codenumber of layerscomposition ( v / v ) psf / pvdfpvdf nominal layer thickness ( nm)recrystallization temperature / time ( c / h)#110/100#1a10/100145/5#1b10/100170/96#23270/30225#33270/30225145/5#425650/5047#525650/5047170/96#625670/3028#725670/3028170/96 the as - extruded and recrystallized multilayered psf / pvdf film systems the overall orientation of crystallographic planes of the samples was determined by means of computer - controlled waxs system equipped with a pole figure attachment associated with a wide - angle goniometer ( dron 2.0 ) coupled to a sealed tube source of filtered cu k radiation ( phillips ) , operating at 50  kv and 30  ma .
the specimens in the form of sandwiched films ( at least 1    1  cm ) and approximately 0.15  mm thick were assembled with extrusion direction vertical .
the waxs reflection scans of the samples were collected with the step of 0.05. the x - ray data for pole figure construction were collected for selected reflections .
experimental x - ray diffraction data were corrected for background scattering , sample absorption , and defocusing of the beam .
all pole figures were plotted with the pod program ( los alamos national lab , nm ) .
semicrystalline poly(vinylidene fluoride ) ( pvdf ) homopolymer solef 6010 from solvay solexis crystallizing from the melt in the  phase   and amorphous polysulfone ( psf ) , udel p-3703 obtained from solvay advanced polymers , were chosen as raw materials to produce 12-m thick psf / pvdf film systems by layer - multiplying coextrusion at conditions described in details by mackey et al . .
the compositions of all film systems studied in the paper are collected in table  1 . in each layered system , the pvdf nominal layer thickness was varied from 28 to 225  nm .
the multilayered psf / pvdf films were isothermally recrystallized using two oil baths containing silicon oil at recrystallization temperatures of 145  c and 170  c , respectively .table 1the as - extruded and recrystallized multilayered psf / pvdf film systemssample codenumber of layerscomposition ( v / v ) psf / pvdfpvdf nominal layer thickness ( nm)recrystallization temperature / time ( c / h)#110/100#1a10/100145/5#1b10/100170/96#23270/30225#33270/30225145/5#425650/5047#525650/5047170/96#625670/3028#725670/3028170/96 the as - extruded and recrystallized multilayered psf / pvdf film systems
the overall orientation of crystallographic planes of the samples was determined by means of computer - controlled waxs system equipped with a pole figure attachment associated with a wide - angle goniometer ( dron 2.0 ) coupled to a sealed tube source of filtered cu k radiation ( phillips ) , operating at 50  kv and 30  ma .
the specimens in the form of sandwiched films ( at least 1    1  cm ) and approximately 0.15  mm thick were assembled with extrusion direction vertical .
the waxs reflection scans of the samples were collected with the step of 0.05. the x - ray data for pole figure construction were collected for selected reflections .
experimental x - ray diffraction data were corrected for background scattering , sample absorption , and defocusing of the beam .
all pole figures were plotted with the pod program ( los alamos national lab , nm ) .
in order to identify and select the x - ray diffraction peaks for further detailed analysis of crystalline structure and texture of our multilayered psf / pvdf films , we summarized the current knowledge about predicted and observed x - ray reflections from the pvdf crystals . in tables  2 , 3 , 4 , and 5 ,
the most important known diffraction peaks are collected for the  ,  ,  , and  crystallographic forms of pvdf.table 2the data for crystallographic planes of  form of pvdf and the observed wide - angle diffraction peaks 
 d 
 calc 
interplanar distance calculated from the unit cell of  form pvdf crystals ( orthorhombic , a  =  0.496  nm , b  =  0.964  nm , c  =  0.462  nm ) ; 2calc  wide angle of diffraction maximum calculated from the bragg s law ( n  =  2dsin ) , where  , wavelength of the incident x - ray beam has been assumed to 0.15418  nm ; d 
 obs and 2obs  interplanar distance and wide angle of diffraction maximum observed in the references [ 1 , 33 , 4350]table 3the data for crystallographic planes of  form of pvdf and the observed wide - angle diffraction peaks 
 d 
 calc  interplanar distance calculated from the unit cell of  form pvdf crystals ( orthorhombic , a  =  0.858  nm , b  =  0.491  nm , c  =  0.256  nm ) ; 2calc  wide angle of diffraction maximum calculated from the bragg s law ( n  =  2dsin ) , where  , wavelength of the incident x - ray beam , has been assumed to 0.15418  nm ; d 
 obs and 2obs  interplanar distance and wide angle of diffraction maximum observed in the references [ 43 , 4547 , 50 , 51]table 4the data for crystallographic planes of  form of pvdf and the observed wide - angle diffraction peaks 
 d 
 calc  interplanar distance calculated from the unit cell of  form pvdf crystals ( monoclinic , a  =  0.497  nm , b  =  0.966  nm , c  =  0.918  nm , -angle  =  92.9 ) ; 2calc  wide angle of diffraction maximum calculated from the bragg s law ( n  =  2dsin ) , where  , wavelength of the incident x - ray beam , has been assumed to 0.15418  nm ; d 
 obs and 2obs  interplanar distance and wide angle of diffraction maximum observed in the references [ 1 , 7 , 33 , 34 , 43 , 45 , 51]table 5the data for crystallographic planes of  form of pvdf and the observed wide - angle diffraction peaks 
 d 
 calc  interplanar distance calculated from the unit cell of  form pvdf crystals ( orthorhombic , a  =  0.496  nm , b  =  0.964  nm , c  =  0.462  nm ) ; 2calc  wide angle of diffraction maximum calculated from the bragg s law ( n  =  2dsin ) , where  , wavelength of the incident x - ray beam , has been assumed to 0.15418  nm ; d 
 obs and 2obs  interplanar distance and wide angle of diffraction maximum observed in the reference   the data for crystallographic planes of  form of pvdf and the observed wide - angle diffraction peaks 
 d 
 calc  interplanar distance calculated from the unit cell of  form pvdf crystals ( orthorhombic , a  =  0.496  nm , b  =  0.964  nm , c  =  0.462  nm ) ; 2calc  wide angle of diffraction maximum calculated from the bragg s law ( n  =  2dsin ) , where  , wavelength of the incident x - ray beam has been assumed to 0.15418  nm ; d 
 obs and 2obs  interplanar distance and wide angle of diffraction maximum observed in the references [ 1 , 33 , 4350 ] the data for crystallographic planes of  form of pvdf and the observed wide - angle diffraction peaks 
 d 
 calc  interplanar distance calculated from the unit cell of  form pvdf crystals ( orthorhombic , a  =  0.858  nm , b  =  0.491  nm , c  =  0.256  nm ) ; 2calc  wide angle of diffraction maximum calculated from the bragg s law ( n  =  2dsin ) , where  , wavelength of the incident x - ray beam , has been assumed to 0.15418  nm ; d 
 obs and 2obs  interplanar distance and wide angle of diffraction maximum observed in the references [ 43 , 4547 , 50 , 51 ] the data for crystallographic planes of  form of pvdf and the observed wide - angle diffraction peaks 
 d 
 calc  interplanar distance calculated from the unit cell of  form pvdf crystals ( monoclinic , a  =  0.497  nm , b  =  0.966  nm , c  =  0.918  nm , -angle  =  92.9 ) ; 2calc  wide angle of diffraction maximum calculated from the bragg s law ( n  =  2dsin ) , where  , wavelength of the incident x - ray beam , has been assumed to 0.15418  nm ; d 
 obs and 2obs  interplanar distance and wide angle of diffraction maximum observed in the references [ 1 , 7 , 33 , 34 , 43 , 45 , 51 ] the data for crystallographic planes of  form of pvdf and the observed wide - angle diffraction peaks 
 d 
 calc  interplanar distance calculated from the unit cell of  form pvdf crystals ( orthorhombic , a  =  0.496  nm , b  =  0.964  nm , c  =  0.462  nm ) ; 2calc  wide angle of diffraction maximum calculated from the bragg s law ( n  =  2dsin ) , where  , wavelength of the incident x - ray beam , has been assumed to 0.15418  nm ; d 
 obs and 2obs  interplanar distance and wide angle of diffraction maximum observed in the reference   figure  1 presents the waxs diffractograms of as - extruded pvdf control film , pvdf control film annealed at 145  c for 5  h , pvdf control film annealed at 170  c for 96  h , and psf / pvdf film systems.fig .
1the waxs diffractograms of as - extruded pvdf control film , pvdf control film annealed at 145  c for 5  h , pvdf control film annealed at 170  c for 96  h , and psf / pvdf multilayered films , obtained in the reflection mode .
the curves have been shifted for better visualization the waxs diffractograms of as - extruded pvdf control film , pvdf control film annealed at 145  c for 5  h , pvdf control film annealed at 170  c for 96  h , and psf / pvdf multilayered films , obtained in the reflection mode .
the curves have been shifted for better visualization for as - extruded 0.15-mm thick pvdf control film ( sample # 1 ) , five diffraction peaks with maxima at 17.75 , 18.30 , 19.85 , 26.50 , and 35.90 are observed in fig . 
1 . their positions imply that they are reflected from ( 100 ) , ( 020 ) , ( 110 ) , ( 021 ) , and ( 200 ) crystallographic planes of pvdf  phase crystals .
annealing of pvdf control film at 145  c for 5  h ( sample # 1a ) causes refining of  crystals , note the intensification of ( 021 ) reflection at 26.50 and the appearance of ( 120 ) , ( 111 ) , and ( 002 ) reflections at 25.55 , 27.80 , and 35.80 , respectively .
annealing of the pvdf control film at 170  c for 96  h ( sample # 1b ) drastically changes the crystalline content .
the reflections of ( 020 ) , ( 110)/(101 ) , and ( 004 ) crystallographic planes of pvdf  phase crystals are observed at 18.55 , 20.20 , and 39.20 , respectively .
the film # 2 contains only 30  vol.% of pvdf in the form of 255-nm thick layers between 70  vol.% of psf layers . from the x - ray diffraction peaks
, it is evident that the pvdf crystals are also of the  phase although the diffraction is of rather low intensity due to lower concentration of pvdf in the film and probably due to a spatial orientation of  crystals .
after isothermal recrystallization at 145  c of the 225-nm thick pvdf layers in the psf / pvdf film ( sample # 3 ) , two diffraction peaks appeared , at 35.85 for ( 200 ) plane of  phase and at 39.10. this last diffraction peak was identified as pvdf  phase crystal ( 004 ) reflex [ 1 , 34 , 52 ] .
other diffraction peaks with ( hk0 ) indices are not well seen in reflection ; hence , the crystalline fraction of the sample # 3 consists of a combination of  and  phases , however , oriented .
the film # 4 contains 50  vol.% of pvdf in the form of 47-nm layers between 50  vol.% of psf layers . from the x - ray diffraction peaks in the reflection mode , it is evident that the pvdf crystals are of the  and  phases , although the diffraction is again of rather low intensity due to a spatial orientation of  and  crystals .
other diffraction peaks with ( hk0 ) indices are not well seen in the reflection mode due to spatial orientation .
after isothermal recrystallization at 170  c of the 47-nm thick pvdf layers in the psf / pvdf film ( # 5 ) , only one diffraction peak at 39.10 of ( 004 ) reflection of  phase is seen .
no sign of  form can be noticed . in the film # 6 with 28-nm thick pvdf layers the diffraction peaks from the  form with diffraction maxima from planes ( 020 ) , ( 100 ) , ( 110 ) , and ( 200 ) are observed .
no diffraction from ( 021 ) of  form and no  form reflections are noticed .
after isothermal recrystallization at 170  c of the 28-nm thick pvdf layers in the psf / pvdf film ( sample # 7 ) , the diffraction peaks at 17.65 , 35.95 , and 39.10 are seen which are identified as the ( 100 ) of  form overlapped with the ( 020 ) of  form , the ( 200 ) of  form , and the ( 004 ) of  phase , respectively .
hence , the coexistence of  and  forms can be noticed . in thinner pvdf layers ,
the  phase crystals grow with structural defects and with orientation controlled by the psf / pvdf interface . in the cases of films # 2 ,
# 4 , and # 6 with pvdf nanolayers , the peak from ( 004 ) plane of  phase becomes narrower and more intense when the samples were isothermally recrystallized at 145 or 170  c .
this ( 004 ) peak is isolated from other diffraction peaks and we postulate that it can be used for clear and precise determination of c - axis orientation of  crystals .
similar role for the orientation of  crystals can be served by ( 021 ) reflection which is also isolated from other diffraction peaks .
this crystallographic plane is tilted by 46.22 with respect to c - axis of  crystals .
it is then postulated that the orientation of  and  crystals can be precisely determined from pole figures of ( 021 ) and ( 004 ) planes , respectively .
the orientation of pvdf chains in the crystals was examined using x - ray pole figures .
the pole figures of normals to the ( 004 ) plane for all multilayered psf / pvdf film systems are collected in fig . 
2the pole figures of normals to the ( 004 ) planes of pvdf  crystals : a as - extruded pvdf control film , b psf / pvdf film with nominal pvdf layer thickness of 225  nm , c psf / pvdf film with nominal pvdf layer thickness of 255  nm isothermally recrystallized at 145  c , d psf / pvdf film with nominal pvdf layer thickness of 47  nm , e psf / pvdf film with nominal pvdf layer thickness of 47  nm isothermally recrystallized at 170  c , f psf / pvdf film with nominal pvdf layer thickness of 28  nm , and g psf / pvdf film with nominal pvdf layer thickness of 28  nm isothermally recrystallized at 170  c .
the normal direction is the center of pole figures 
  the pole figures of normals to the ( 004 ) planes of pvdf  crystals : a as - extruded pvdf control film , b psf / pvdf film with nominal pvdf layer thickness of 225  nm , c psf / pvdf film with nominal pvdf layer thickness of 255  nm isothermally recrystallized at 145  c , d psf / pvdf film with nominal pvdf layer thickness of 47  nm , e psf / pvdf film with nominal pvdf layer thickness of 47  nm isothermally recrystallized at 170  c , f psf / pvdf film with nominal pvdf layer thickness of 28  nm , and g psf / pvdf film with nominal pvdf layer thickness of 28  nm isothermally recrystallized at 170  c .
the normal direction is the center of pole figures 
  from the pole figure in fig . 
2a , it is seen that there is no preferred orientation of that small amount of  phase crystals present in the pvdf control film ( sample # 1 ) , except for a slight orientation due to the extrusion process .
the non - annealed film # 2 with 255-nm thick pvdf layers also does not show any orientation of  crystals ( fig . 
a brief estimation on the basis of waxs 2 diffractogram indicated that the content of  crystals is low in that sample ( see fig .  1 ) .
annealing at 145  c of that film produced some small amount of  crystals ( sample # 3 ) ; however , they are only little oriented with c - axis ( normal to ( 004 ) planes ) perpendicular to the film surface , as it can be judged from fig .  2c .
non - annealed film # 4 with 47-nm thick pvdf layers also contain only small amount of  crystals , and they are unoriented as it can be deduced from the ( 004 ) pole figure in fig . 
in contrast , a strong texture of ( 004 ) planes is detected in fig . 
2e for film # 5 with 47-nm thick pvdf layers after annealing at 170  c for 96  h. non - annealed film # 6 with 28-nm thick pvdf layers also contained very little amount of  crystals ( fig . 
after isothermal recrystallization of that film at 170  c for 96  h ( sample # 7 ) , most of  crystals were transformed to  crystals showing very strong texture with most of normals to the ( 004 ) planes being perpendicular to the film surface ( fig . 
pvdf crystals are laying flat to the film plane exactly indicating the suggested alignment of  phase crystals as showed by mackey et al . .
at higher recrystallization temperature , i.e. , at 170  c pvdf nanolayers recrystallized as in - plane  phase crystals .
the above data on the orientation of pvdf  crystals in nanolayers , especially that crystals in thinner layers are more perfectly oriented with c - axes perpendicular to the film surface , led to the conclusion that the interface between psf and pvdf plays an important role in the orientation of  crystals .
however , it is not clear whether the martensitic transformation of  to  crystals occurs via macromolecular chains reorientation or the chains were already oriented perpendicular to the interfaces in  crystals while the transformation relies on a conformation change from tgtgtgtg to tttgtttg. the answer can be found by investigating the  crystal texture of non - annealed samples .
the pole figures of normals to the ( 021 ) planes of  crystals for non - annealed multilayered psf / pvdf films ( samples # 2 , # 4 and # 6 ) are presented in fig . 
3the pole figures of normals to the ( 021 ) planes of  crystals in non - annealed multilayered psf / pvdf films with pvdf nominal layer thickness of a 255  nm , b 47  nm , and c 28  nm .
the normal direction is the center of the pole figure 
  the pole figures of normals to the ( 021 ) planes of  crystals in non - annealed multilayered psf / pvdf films with pvdf nominal layer thickness of a 255  nm , b 47  nm , and c 28  nm .
the normal direction is the center of the pole figure 
  it is evident that the ( 021 ) planes of  crystals are preferentially oriented at 4045 with respect to the normal to psf / pvdf interfaces in all three multilayered psf / pvdf films .
stronger clustering of the ( 021 ) normals is observed for thinner 28-nm pvdf layers .
apparently , further refinement of chains orientation perpendicular to film surface occurs during isothermal recrystallization at 145 or 170  c facilitated by interaction of pvdf macromolecules with psf / pvdf interface .
the pvdf nanolayers in all as - extruded psf / pvdf films crystallized into the  phase structure .
after isothermal recrystallization at 170  c ,  phase crystals in pvdf layers transformed into  phase crystals .
the x - ray diffraction in conjunction with pole figures was used to examine the texture of pvdf in multilayered psf / pvdf films .
the ( 021 ) planes of  crystals are well suited to use them for the determination of the pvdf crystal texture .
there is some orientation of the ( 021 ) planes at 4045 to the psf / pvdf interface in all as - extruded multilayered films . for  crystals ,
the ( 004 ) planes may be used for the determination of  crystal orientation . since the normals to ( 004 )
planes are parallel to macromolecular chains , the pole figures enabled the determination of the overall orientation of pvdf  crystals for thermally treated multilayered psf / pvdf film systems .
most of those  crystalline lamellae are in - plane position which resulted from initial similar orientation of  crystals in as - extruded  psf / pvdf  films .
further refinement of the texture occurs during isothermal recrystallization in conjunction with transformation of  to  crystals and due to the interaction of pvdf with  psf / pvdf  interface .
the initial orientation of  crystals and resulted  crystal orientation after  to  transition are illustrated in fig . 
4schematics of the orientation types of pvdf crystals : a mixed orientation of  crystals in as - extruded multilayered psf / pvdf films and b in - plane orientation of  crystals in recrystallized multilayered psf / pvdf films schematics of the orientation types of pvdf crystals : a mixed orientation of  crystals in as - extruded multilayered psf / pvdf films and b in - plane orientation of  crystals in recrystallized multilayered psf / pvdf films such in - plane orientation of polymer crystals with macromolecular chains perpendicular to the interface was reported previously by us for the system of nearly amorphous poly(ethylene - co - acrylic acid ) ( eaa ) and crystalline polyethylene oxide ( peo ) . such a possibility was also postulated by ma , hu , and reiter defining such system as crystals on sticky walls .
 wide - angle x - ray scattering in conjunction with pole figure technique was used to study the texture of poly(vinylidene fluoride ) ( pvdf )  and  phase crystals in nanolayered polysulfone / poly(vinylidene fluoride ) films ( psf / pvdf ) produced by layer - multiplying coextrusion . in all as - extruded psf / pvdf films 
 , the pvdf nanolayers crystallized into the  phase crystals . 
 a large fraction of those crystals was oriented with macromolecular chains perpendicular to the psf / pvdf interface as evidenced from the ( 021 ) pole figures . 
 further refinement of the texture occurs during isothermal recrystallization at 170  c in conjunction with transformation of  to  crystals . 
 the  crystals orientation was probed with the ( 004 ) pole figures showing the c - axis of pvdf  crystals perpendicular to the psf / pvdf interface . 
 the thinner the pvdf layers the stronger the orientation of  crystals . 
 it was proven that the x - ray reflections from the ( 021 ) planes of  crystals and from the ( 004 ) planes of  crystals are not overlapped with other reflections and can be effectively used for the texture determination of pvdf nanolayers in multilayered psf / pvdf films . 
Introduction
Experimental
Materials
X-ray measurements
Results and discussion
Conclusions