European Polymer Journal 47 (2011) 52–60

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European Polymer Journal

journal homepage: www.elsevier .com/locate /europol j

Structure of a spin-crossover Fe(II)–1,2,4-triazole polymer complexdispersed in an isotactic polystyrene matrix

Miguel Rubio a, Rebeca Hernández a, Aurora Nogales b, Anna Roig c, Daniel López a,⇑a Instituto de Ciencia y Tecnología de Polímeros, CSIC, Juan de la Cierva 3, 28006 Madrid, Spainb Instituto de Estructura de la Materia, CSIC, Serrano 119, 28006 Madrid, Spainc Institut de Ciència de Materials de Barcelona, CSIC, Campus de la UAB, 08193 Bellaterra, Spain

a r t i c l e i n f o a b s t r a c t

Article history:Received 28 July 2010Received in revised form 20 September2010Accepted 25 October 2010Available online 30 October 2010

Keywords:Metallo-organic polymerIsotactic polystyreneSpin-crossover transitionNucleation

0014-3057/$ - see front matter � 2010 Elsevier Ltddoi:10.1016/j.eurpolymj.2010.10.029

⇑ Corresponding author. Tel.: +34 91 569 29 00; faE-mail address: daniel@ictp.csic.es (D. López).

Isotactic polystyrene (i-PS) was employed as a matrix to disperse a metallo-organic poly-mer of [Fe(II) (4-octadecyl-1,2,4-triazole)3(ClO4)2] in order to obtain novel functional mate-rials exhibiting thermal spin-crossover transition. A detailed investigation of the structureof the metallo-organic polymer and metallo-organic polymer/iPS blends has been carriedout by DSC, WAXD and SAXS techniques as a function of temperature and metallo-organicpolymer/iPS proportion.

The results obtained confirm on the one hand that a structural transition associated witha change in the magnetic susceptibility of the metallo-organic polymer is preserved in thepresence of i-PS. This transition was found to be associated to both, an inter-conversion oflamellar structures into hexagonal structures and to an increase of inter-sheet distanceswithin the lamellar structures in metallo-organic polymer films prepared by casting fromtoluene solutions. On the other hand, an increase of the degree of crystallinity of the iPS isobserved in the presence of the metallo-organic polymer which suggests some nucleatingeffect of the metallo-organic polymer in the crystallization of isotactic polystyrene.

� 2010 Elsevier Ltd. All rights reserved.

1. Introduction

One-dimensional polymeric spin-transition (ST) com-pounds of d4–d7 transition metal ions are excellent candi-dates for advanced technological applications suchas sensors, displays and information storage [1–4]. Thesematerials can adopt two different magnetic states: ahigh-spin (HS) and a low-spin (LS) state, which can cross-over due to external stimuli such as temperature, pressure,electromagnetic radiation, etc., giving rise to variations inthe physical properties of the material like changes incolour, dielectric constant, intramolecular distances or spinstate [5–7].

In particular, linear polymeric chains of Fe(II) ionsbridged by triazole ligands extensively studied for the past20 years [8–11] continue to attract considerable attention.

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x: +34 91 564 48 53.

This metallo-organic polymer, with Fe(II) ions in an octa-hedral ligand field, exhibits a thermally induced transitionbetween two electronic states: a diamagnetic (S = 0) LSstate and a paramagnetic (S = 2) HS state. The spin transi-tion is accompanied by a strong thermochromism that pro-vides additional applications for these systems [12–15].

The main difficulty for the development of new func-tional materials is how to transfer the bulk properties ofthe metallo-organic polymer in the solid state to systemssuitable for technological applications. In some cases amicro- or nano-pattering of the switchable functional poly-mers is necessary for the application to be accomplished.In this sense, Langmuir–Blodgett techniques [16,17],layer-by-layer assembly [18], electron beam lithography[1] and self-organization of molecular ST units into hierar-chically organized domains across different length scaleshave been studied [4,19]. In other cases, the spatialarrangement of the ST polymers is not necessary to attainthe desired application and only a dispersion media

M. Rubio et al. / European Polymer Journal 47 (2011) 52–60 53

conferring mechanical and environmental stability [14] tothe metallo-organic polymer is required. In this context,the ability to isolate and preserve such linear metallo-or-ganic polymers in solution, gels and polymer films consti-tutes a route to obtain novel functional materials, althoughit has been little developed so far [20,21].

We recently reported [22] on the gelation properties of[Fe(II) (4-octadecyl-1,2,4-triazole)3(ClO4)2] in three organicsolvents: toluene, cis- and trans-decalin as a way to obtaineasily manipulable and malleable materials for technologi-cal applications. The gathering of properties associated tothe metallo-organic polymer itself and the general proper-ties of gels (swelling, mechanical, responsive properties)was also sought. The results obtained in this study pointedto structural differences and different gelation mechanismsfor the metallo-organic polymer in different solvents andsuggested the need to deepen in the structural characteriza-tion of the metallo-organic polymer in both, the solid stateand the gel state and its dependence with temperature.

The aim of this study is twofold; on the one hand, as acontinuation of our previous work, the structure of theFe(II)-based metallo-organic polymer is analysed as a func-tion of temperature in the solid state. Besides, blends ofmetallo-organic polymer and isotactic polystyrene wereprepared as a route to obtain novel functional materialswith improved mechanical properties preserving the bulkproperties of the metallo-organic polymer. The resultingsystems have been subjected to detailed structural studiesby DSC and WAXD and SAXS techniques.

2. Experimental part

2.1. Materials

The metallo-organic polymer [Fe(II) (4-octadecyl-1,2,4-triazole)3(ClO4)2]n was obtained by a method reported pre-viously [22].

Isotactic polystyrene (90%) was purchased from Scien-tific Polymer Products, Inc. with a molecular weight of400,000 g/mol. To obtain amorphous samples, pure iPSwas melted at 270 �C for 10 min in a hydraulic press andsubsequently quenched to room temperature.

The solvent used for the preparation of solutions wastoluene supplied by Merck and used without furtherpurification.

2.2. Sample preparation

Film samples of pure metallo-organic polymer, pure iPSand their blends of different composition were prepared bycasting. Homogeneous solutions of both polymers wereobtained by mixing the appropriate amounts of polymerand solvent and heating at high temperature until com-plete dissolution (at 100 �C for the metallo-organic poly-mer and at 180 �C for the iPS). For the blends,homogeneous solutions of each polymer were mixed at100 �C and stirred until homogenization. Solutions werepoured out into Petri dishes and the solvent was allowedto evaporate in a dessicator at room temperature until con-stant weight.

Four iPS/metallo-organic polymer film samples wereprepared with different iPS/complex proportion (w/w):99.5/0.5, 99/1, 98/2 and 95/5.

2.3. Differential scanning calorimetry measurements

Thermal characterization of the films was conductedthrough Differential Scanning Calorimetry in a Perkin–El-mer DSC 7 Instrument. Cooling and heating sweeps wereperformed at a scanning rate of 10 �C/min. Films werecut into small pieces and put into 50 ll aluminium samplepans. Metallo-organic polymer film samples were sub-jected to the following thermal treatment: heated from 0to 80 �C, hold at 80 �C for 1 min and cooled down to 0 �Cin a subsequent cooling sweep. iPS film samples were sub-jected to a heating sweep between 0 and 240 �C, hold at240 �C for 1 min and a subsequent cooling down to 0 �C.iPS/complex films have been firstly subjected to a heatingsweep between 0 and 80 �C and quenched to 0 �C, holdfor 1 min and performed a second heating sweep to 80 �Cand quenched again to 0 �C, hold for 1 min and heating ina third sweep to 240 �C.

2.4. Magnetic measurements

The magnetic susceptibility with temperature measure-ments were carried out using a Quantum Design MPMS5XLSQUID magnetometer operating at 1000 Oe. Measure-ments were corrected from the diamagnetic contributionof the sample holder. Samples were subjected to coolingand heating cycles between �263 and 60 �C.

2.5. Wide angle X-ray diffraction

Wide Angle X-ray diffraction (WAXD) experiments werecarried out in a Bruker D8 Advance diffractometer equippedwith nickel-filtered CuKa radiation operated at 40 kV and40 mA (k = 1.54 A). X-ray diffraction data between 1 and35� 2h, at room temperature, and between 3 and 35� 2h,for measurements with the temperature sample cell, werecollected at scanning rate of 0.2 s and increment of 0.024.The profiles were collected using a Gobel mirror equippedwith a position-sensitive detector (Vantec 1).

Diffractograms were obtained at different temperatureson heating metallo-organic polymer film samples from 0 to80 �C. Then, samples were hold at 80 �C for 1 min andcooled down to 0 �C in a subsequent cooling sweep.

iPS/metallo-organic polymer films were subjected tothe same thermal protocol followed for DSC experiments:A heating sweep between 0 to 80 �C, obtaining diffracto-grams at different temperatures; quench to 0 �C; hold at0 �C for 1 min and a second heating sweep within the sameinterval of temperature; finally, the sample was quenchedagain to 0 �C, hold at 0 �C for 1 min and a third heatingsweep was performed between 0 and 240 �C, obtainingspectra at different temperatures.

2.6. Small-angle X-ray scattering

Small-Angle X-ray Scattering (SAXS) experiments werecarried out on a Bruker AXS Nanostar small-angle X-ray

54 M. Rubio et al. / European Polymer Journal 47 (2011) 52–60

scattering instrument. The instrument uses CuKa radiation(1.54 Å) produced in a sealed tube. The scattered X-rays aredetected on a two dimensional multiwire area detectorand can be converted to one-dimensional scattering by ra-dial averaging and represented as a function of momentumtransfer vector q (q = 4psin h/k) in which h is half the scat-tering angle and k is the wavelength of the incident X-raybeam.

The raw intensity data [I(q)] were corrected for detectorlinearity, sample absorption, background scattering, andchanges in incident beam intensity. The Bragg long period(LB) was determined from the position of the peak in theLorentz-corrected SAXS intensity, I(q)q2.

3. Results and discussion

3.1. Metallo-organic polymer films

In the DSC profile shown in Fig. 1, the metallo-organiccomplex exhibited an endothermic peak at T = 51 �C uponheating. This endothermic peak could be assigned to thespin transition as reported for similar iron(II) complexes[6,23]. The DH of the endotherm was evaluated to 52 J/gin concordance with the enthalpy found for similar sys-tems [23]. Nevertheless, the magnetic characterization ofthe complex suggests that the main spin-crossover processtakes place at lower temperatures.

The magnetic properties of the metallo-organic polymerwere measured on cooling and heating over the tempera-ture range of �260 and 60 �C and the results are depictedin Fig. 2. The observation of this figure reveals a low-spinto a high-spin transition occurring in two different steps:a low temperature step, very smooth that occurs withoutthermal hysteresis at around �60 �C. This step involvesmost of Fe(II) ions, provokes a significant change in themagnetic susceptibility and the transition of colour frompink to yellow. The other step takes place more abruptlyat around 52 �C, involves only a slight change of the mag-netic susceptibility, shows some hysteresis and does notentail any colour change.

Fig. 1. DSC curves on heating at 10 �C/min for the metallo-organicpolymer.

The occurrence of two-step SC transitions has been pre-viously reported for different spin crossover systems andhas been accounted for by different theories [24,25]. How-ever, these two-step SC transitions usually involve 50% ofFe(II) ions each. In our case only a small change of the mag-netic suspectibility is observed at 52 �C. This suggests thatthe structural transition at around 52 �C only provokes arearrangement of the spatial distribution of spins ratherthan a spin-crossover transition. Therefore, the genuinespin-crossover transition takes place at lower tempera-tures, around �60 �C.

The WAXD diffractogram corresponding to the metal-lo-organic polymer recorded at room temperature shownin Fig. 3 presents four diffraction peaks at 2h values of2.7�, 5.4�, 8.1�and 21.5�. The first three peaks with Braggspacings in the ratio 1:2:3 arise from the lamellar struc-ture of the metallo-organic complex. From the first Braggpeak (2h = 2.7�) an inter-sheet spacing of 32 Å can be de-duced. Taken into account that the length of the 4-octa-decyl-1,2,4-triazole (ODT) is 23 Å, the system can bedescribed as layers of transition metal (II) ions interca-lated between two layers of ODT. It is important to notethat the aliphatic chains in this structure might be inter-digitated since the distance between layers of Fe(II)(d = 32 Å) is significantly lower than the distance thatwould correspond to the aliphatic chains without beingoverlapped (d = 46 Å) [26]. The broad peak located at2h = 21.5� that corresponds to a distance d = 4.1 Å hasbeen previously attributed to a two dimensional hexago-nal alkyl chain lattice [27,28].

According to these results, a schematic representation(Fig. 4a) of the metallo-organic polymer can be proposedin which sheets of rodlike backbones of iron(II) ions areseparated by interdigitated alkyl chains. This lamellarorganization gives rise to a fibrilar morphology that canbe observed by AFM (see Supplementary material).

In order to monitor the structural organization of themetallo-organic complex with the temperature, tempera-ture WAXD experiments were carried out. Fig. 5a showsthe WAXD profiles of the metallo-organic complex uponheating. It is important to remark that for these experi-ments, the design of the temperature cell is such that itprevents the observation of the first Bragg peak at2h = 2.7� assigned to the inter-sheet spacing (d = 32 Å).The behaviour of this peak with temperature will be fol-lowed with small-angle X-ray scattering as reported inthe next section. Taking into account this, the first observa-ble peak in the temperature diffraction patterns is the onelocated at 2h = 5.4� with the Miller index (2 0 0). The thor-oughly observation of this peak allows one to infer thepresence of a shoulder at 2h = 6.5�. This shoulder can be ac-counted for as the second Bragg reflexion of an hexagonalstructure with an interlayer spacing of d = 24 Å (consider-ing that for an hexagonal structure the Bragg reflexionspeaks fulfil the relation 1:(3)1/2:. . .) [29]. See Fig. 4b for aschematic representation of the hexagonal structure.Therefore, the metallo-organic polymer films consist of atwo-population system of lamellar and hexagonal struc-tures with a higher proportion of lamellar structures.

At temperatures above 50 �C, associated with a changein the magnetic susceptibility of the metallo-organic

Fig. 2. vT�T vs. T on cooling and heating modes for the metallo-organic polymer. The inset emphasises the thermal hysteresis of the transition at hightemperatures: (s) 1st cooling; (h) 1st heating and (}) 2nd cooling. Pictures show the colour change of the polymer with temperature. (For interpretation ofthe references in colour in this figure legend, the reader is referred to the web version of this article.)

Fig. 3. WAXD profile of the metallo-organic polymer at roomtemperature.

M. Rubio et al. / European Polymer Journal 47 (2011) 52–60 55

polymer, the peak at 2h = 5.4� shifts to 2h = 4.7� and the(3 0 0) diffraction peak at 2h = 8.1� shifts to 2h = 7.2�. Theposition of the diffraction peak corresponding to the hex-

Fig. 4. Schematic illustration of the supramolecular unit st

agonal structure at 2h = 6.5� does not shift. On the otherhand, the intensity of the diffraction peaks associated tothe lamellar structure decreases whereas the intensity ofthe reflections linked to the hexagonal structure increasesat temperatures above 50 �C.

According to this, the increase of temperature above50 �C provokes both, a change in the lamellar structure ofthe metallo-organic polymer whose inter-sheet spacing in-creases from 32 to 40 Å and the transformation of part ofthe lamellar structures to hexagonal structures (seeFig. 4). On the other hand, the position and intensity ofthe broad peak between 2h = 17.5� and 21.5� does also varywith temperature: a shoulder can be observed at tempera-tures below 30 �C. This is in agreement with a two-popula-tion system and indicates that the alkyl hexagonal chainpacking is also affected. Therefore, the changes in the mag-netic susceptibility found at around 52 �C (see Fig. 2)would be associated to the changes of the lamellar struc-ture of the iron(II) chains and not to the breaking up ofpacking of the alkyl side chains of the triazole ligand.

The diffraction patterns of the metallo-organic complextaken upon cooling to room temperature (Fig. 5b)demonstrates that the structural transition is reversible

ructures in the film of the metallo-organic complex.

Fig. 5. WAXD profiles of the metallo-organic polymer obtained onheating (a) and on cooling (b) at different temperatures.

Fig. 6. SAXS patterns of the metallo-organic polymer obtained on heatingat different temperatures. For an easier visualization, the q-region 0.12–0.22 is shown in the inset.

Fig. 7. DSC curves obtained on heating at 10 �C/min for a film of themixture metallo-organic polymer/iPS in proportion 1/99 (w/w).

56 M. Rubio et al. / European Polymer Journal 47 (2011) 52–60

as denoted by the fact that the two peaks located at2h = 4.7� and 7.2� transform into the peak at 2h = 5.4�(2 0 0) and the (3 0 0) diffraction peak at 2h = 8.1� at tem-peratures below T = 35 �C.

Fig. 6 shows the SAXS scattering patterns correspondingto the metallo-organic complex upon heating. At tempera-tures above 50 �C, the peak at q = 0.2 Å�1, characteristic ofthe distance between layers shifts to q = 0.16 Å�1 indicat-ing that the distance between layers increases in agree-ment to similar systems based on Fe(II)–1,2,4-triazolecomplexes [14]. Interestingly, the scattering peak atT = 50 �C presents a broad shoulder at low q-valueswhereas the scattering peak at T = 55 �C exhibit a shoulderat high q-values. This result might indicate that in thistemperature range (T = 50–55 �C) the system is a mixtureof low-spacing lamellar structures and high-spacinglamellar structures, plus the corresponding hexagonalstructures. It is important to note that the first Braggreflexion associated to the hexagonal structure (secondBragg reflexion at 6.5� observed by WAXD) that should ap-pear at q = 0.26 A�1 cannot be observed as it is out of theexperimental limits of the SAXS instrument.

3.2. iPS/metallo-organic polymer films

DSC experiments carried out on a 1/99 (g metallo-organic polymer/g iPS) highlight that the presence of iPSdoes not prevent the structural transition of the metallo-organic complex (Fig. 7). However the transition shifts tohigher temperatures (at around 60 �C) with respect to thetransition exhibited by the pristine metallo-organic com-plex and the associated enthalpy is significantly lower, asexpected due to dilution effects. After quenching to 0 �C,the DSC thermogram did not show any transition suggest-ing that the presence of iPS avoid the structural transitionof the complex to be reversible with temperature, probablydue to a solubilisation of the complex inside the iPS matrix.A third heating scan performed on the same samplequenched to 0 �C showed a melting endotherm corre-sponding to the iPS, which demonstrates that the iPS crys-tallizes in the presence of the metallo-organic complex.

M. Rubio et al. / European Polymer Journal 47 (2011) 52–60 57

Moreover, the peak position (Tm = 223 �C) and the enthalpyassociated to the melting of iPS (DH = 24 J/g) do not changedue to the presence of the metallo-organic polymer, asdemonstrated by the comparison of the DSC thermogramsof the mixture and the pure iPS, respectively (results notshown here).

The WAXD diffractograms taken at T = 20 �C and atT = 60 �C for a mixture in proportion 5/95 (g metallo-or-ganic polymer/g iPS) are shown in Fig. 8a. As can be ob-served, the diffraction peak located at 2h = 5.4� in thediffractogram at T = 20 �C disappears at T = 60 �C, hence,this peak can be assigned to the second order Bragg peak(2 0 0) of the lamellar morphology of the metallo-organicpolymer in the mixture.

Fig. 8b shows the WAXD diffractograms as a function oftemperature upon quenching the 5/95 film to 0 �C. No peakcorresponding to the metallo-organic complex is observedin the diffractogram at T = 20 �C but six diffraction peakscorresponding to the iPS crystalline structure [30] at2h = 8�, 14�, 16�, 18�, 22� and 24� were identified with Mill-er indices (1 1 0), (3 0 0), (2 2 0), (2 1 1), (4 1 1) and (3 2 1),

Fig. 8. WAXD profiles of a 5/95 (w/w) film obtained on heating atdifferent temperatures: (a) First heating sweep at 30 and 60 �C and (b)Third heating sweep at various temperatures as indicated in the figure.

respectively. These results are in agreement with the DSCthermograms and they indicate on the one hand that thelamellar morphology of the metallo-organic complex doesnot reform in the presence of iPS and on the other handthat the iPS crystallinity is preserved. At temperaturesabove 220 �C, the iPS melting temperature, two broadhalos are observed at 2h � 18.9� that arises from phenyl–phenyl correlations and at 2h � 9.5� due to intermolecularcorrelations of backbone atoms [31].

The relative crystallinity Xc,WAXS, was obtained from theintegrated intensity over the observed Bragg reflections(after subtraction of the amorphous background), normal-ized by the intensity integrated over the full WAXS profile.

Results corresponding to the film compositions (5/95and 1/99) were compared to the crystallinity of pristineiPS film in Fig. 9. At temperatures below the iPS glass tran-sition (Tg = 81 �C, as determined by DSC) the relative crys-tallinity does not change with temperature for any of thesamples and the presence of the metallo-organic complexinduces an increase of the relative crystallinity with re-spect to pristine iPS. At temperatures above the glass tran-sition temperature (around 81 �C for the pure iPS andaround 90 �C for the 5/95 sample), the relative crystallinitydecreases sharply for pure iPS and 5/95 samples. After-wards, an increase of the relative crystallinity with tem-perature is obtained for both samples till the meltingtemperature at around 220 �C. There is no change is therelative crystallinity in the whole temperature range forthe sample with a composition 1/99.

The decrease of crystallinity with temperature can beaccounted for by the melting of the lowest stability portionof the polystyrene lamella [31]. Then, the melting fractionof polystyrene can recrystallised in a more stable form, giv-ing rise to an increase in the relative crystallinity. Both, theincrease in the relative crystallinity in relation to pure iPSand its invariance with temperature for the sample 1/99suggest the occurrence of a heterogeneous nucleation pro-cess induced by the metallo-organic polymer. These resultscould be interpreted as follows: At low concentration ofthe metallo-organic polymer, the dilution effect provokesmost of the complex being present as individual fibrils thatcan act as nucleating agents for the crystallisation of iPS. Athigher polymer complex concentrations phase separationoccurs: 3D crystallites of polymer complex are obtainedthat cannot nucleate the crystallisation of iPS. As the tem-perature increases above the structural transition of thecomplex, individual fibrils could be obtained that might in-duce the crystallisation of iPS.

In order to study in more detail the influence of temper-ature on the structure of the metallo-organic complexmixed with iPS, SAXS experiments were carried out onfilms with different metallo-organic polymer/iPS contents(1/99; 2/98 and 5/95).

For SAXS conducted on iPS at 30 �C and 80 �C, no dis-cernible SAXS intensity maximum but a monotonouslydecreasing profile is observed (Fig. 10a). The absence of ascattering maximum is attributed on the one hand, to thenegligible electron contrast between the lamellar andamorphous layers and on the other hand to the fact thatSAXS measurements are carried out at temperaturesbelow Tg.

Fig. 9. Crystallinity as a function of temperature obtained from WAXD experiments for (j) iPS; (d) 5/95 metallo-organic polymer/iPS mixture (w/w) and(N) 1/99 metallo-organic polymer/iPS mixture (w/w).

Fig. 10. SAXS profiles of (a) iPS film; (b) 5/95 metallo-organic polymer/iPS mixture (w/w); (c) 2/98 metallo-organic polymer/iPS mixture (w/w) and (d) 1/99metallo-organic polymer/iPS mixture (w/w), obtained at (d) 30 �C and (s) 80 �C. Lorentz representation in the insets.

58 M. Rubio et al. / European Polymer Journal 47 (2011) 52–60

Fig. 10b shows the SAXS patterns of the 5/95 (g metallo-organic polymer/g iPS) at T = 30 �C and at T = 80 �C. At

T = 30 �C, the scattering peak at q = 0.19 Å correspondingto the inter-sheet spacing of the metallo-organic complex

M. Rubio et al. / European Polymer Journal 47 (2011) 52–60 59

is observed which indicates that its lamellar morphology ismaintained upon mixing with iPS. A broad shoulder is lo-cated at q = 0.06 Å which could be attributed to a long per-iod of iPS even if pristine iPS does not present a scatteringpeak at this temperature (see Fig. 10a). This would indicatethe formation of iPS crystals with long-range order in thepresence of the metallo-organic complex and therefore itsuggests a nucleating effect. The intensity I(q) correctedwith the Lorentz factor q2 is shown in the inset. The max-imum corresponding to the first Bragg reflexion associatedto the lamellar structure of the complex shifts fromq = 0.19 Å�1 to q = 0.17 Å�1 indicating an increase of theinter-sheet distance from d = 32 Å to d = 37 Å. Further-more, the scattering intensity of the first Bragg reflexionat T = 80 �C is increased relative to the scattering intensityat T = 30 �C indicating that the magnitude of the electrondensity fluctuation is significantly increased as a conse-quence of the increase in the crystalline fraction.

Similar results are obtained for the 2/98 (g metallo-organic polymer/g iPS) film (Fig. 10c).

The results obtained are significantly different when themetallo-organic polymer concentration is further de-creased as can be observed in Fig. 10d for the 1/99(g metallo-organic polymer/g iPS). At T = 30 �C, no peakcorresponding to the metallo-organic complex is observedand in addition, a broad peak at q = 0.09 A�1 is readilyvisible which could be attributed to the iPS. The fact thatthis diffraction peak is shifted towards higher q-valuesand that the scattering intensity greatly increases withrespect to the SAXS patterns exhibited by the films witha higher metallo-organic complex shown in Fig. 10b andc indicates, on the one hand, that the iPS crystalline sizeis smaller and, on the other hand, an increase of crystallin-ity with the addition of the metallo-organic complex.Results suggests that the lower the metallo-organic com-plex concentration in the iPS, the higher the nucleatingeffect and this is possibly due to the absence of self-organi-zation of the metallo-organic polymer into 3D structures atthese concentrations, and supports the explanation givenabove for the nucleation process to some extent.

6. Conclusions

The structure of films of [Fe(II) (4-octadecyl-1,2,4-tria-zole)3(ClO4)2]n polymer obtained by casting from toluenesolutions consists of a two-population mixture of lamellarand hexagonal structures in which lamellar structures arethe major component. The heating of the polymer filmsabove 51 �C entails a thermal transition whose effect istwofold: some lamellar structures transform into hexago-nal structures and other lamellar structures undergo anincrease of their inter-sheet distances. The transition isthermally reversible and the cooling down of the filmsmakes the system to recover the original state.

Metallo-organic polymer/iPS blend films can beobtained by casting from mixtures of solutions of bothpolymers in toluene. The presence of iPS in the systemdoes not prevent the metallo-organic polymer from crys-tallising but shifts the thermal transition associated witha change of the magnetic susceptibility to higher tempera-

tures. Nevertheless, the presence of iPS impedes this ther-mal transition to be reversible as in the case of pristinemetallo-organic polymer film.

The effect of the metallo-organic polymer in the crystal-lisation properties of iPS is more conspicuous: the degreeof crystallinity of the iPS increases due to the presence ofthe metallo-organic polymer. The effect is more pro-nounced at low metallo-organic polymer concentrations.SAXS experiments also reveal the formation of iPS crystalsof smaller size and with long-rage order in the presence ofthe metallo-organic polymer. Both results suggest a nucle-ating effect of the metallo-organic polymer in the crystalli-sation of iPS.

Acknowledgments

Financial support from CICYT (MAT2008-01073 andMAT2008-03232) and Fundación Domingo Martínez isgratefully acknowledged. M.R. thanks the Ministerio deCiencia e Innovación (Spain) for his FPI fellowship. R.Hthanks CSIC for a JAE postdoctoral contract. Authorsacknowledge E. Verde and M. Hernández for WAXD exper-iments and AFM images, respectively.

Appendix A. Supplementary data

Supplementary data associated with this article can befound, in the online version, at doi:10.1016/j.eurpolymj.2010.10.029.

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