Poly(ethylene oxide)–polyelectrolyte blends:viscometric and thermal analysis behaviourValdir Soldi,1* Helena M Wilhelm,1 Marly da S Soldi,1 Jose RS Rodrigues,1

Alfredo TN Pires1 and Maria R Sierakowski21Laboratorio de Polımeros (Polimat), Departamento de Quımica, Universidade Federal de Santa Catarina, 88040-900, Florianopolis, SC,Brazil2Departamento de Bioquımica, Universidade Federal do Parana (UFPR), Brazil

Abstract: The miscibility of binary poly(ethylene oxide) (PEO) and sodium poly(4-styrene sulphonate)

(PSS) or [3,6]-ionene (ION) systems, was analysed in aqueous solutions and in the solid state by

viscometry and thermal analysis, respectively. Both techniques indicate partial miscibility of PEO±

PSS and immiscibility of PEO±ION blends. In water solution, the partial miscibility of the PEO±PSS

system is probably due to the counterion Na� which can partially provide the driving force association

in a similar manner to that observed for PEO±surfactant systems. In blend ®lms, the PEO±

polyelectrolyte interaction is also analysed in terms of the effect on the PEO crystallization observed

through optical microscopy, and the results indicate compatibility between the components in the

PEO±PSS system.

# 2000 Society of Chemical Industry

Keywords: blends; miscibility; poly(ethylene oxide); polyelectrolytes

INTRODUCTIONPhysical properties, such as miscibility of poly(ethy-

lene oxide) (PEO) solution and PEO in blends with

other polymers and/or surfactants, have received

considerable attention in recent decades. In general,

the miscibility is a result of intermolecular interactions

such as hydrogen bonds with the electron pair of the

oxygen, hydrophobic interactions between the methy-

lene units of the polymer and those of the surfactant

alkyl group, and ion±dipole interactions between the

sulphonate group and ether oxygens.1±7

In solution, viscometry is one of the simplest

methods for studying the interactions and properties

of polymer±polymer and polymer±surfactant systems.

Attractive interaction increases the viscosity of these

systems, although the effect on surfactants depends on

anionic,1 non-ionic2 or cationic3 characteristics. For

example, the reduced viscosity of mixtures formed by

PEO8±10 or polyvinyl pyrrolidone (PVP)1 with sodium

dodecyl sulphate (SDS) increases when aggregates of

surfactant are formed and are increasing in size in the

polymer chain, tending to behave in a manner similar

to a polyelectrolyte. The solution viscosity also

increases in PEO±non-ionic surfactant systems, and

in general a more hydrophobic surfactant is more

effective in forming large network structures.11

The cationic surfactant cetyl pyridinium chloride

only interacts with high molecular weight PVP or

poly(ethylene glycol) (PEG).12 The viscosity of poly-

styrene (PS)±PEO and PS±PEG blends was measured

in benzene as a function of the blend composition, and

the interaction parameter used was the difference

between the experimental and the theoretical values of

the two polymers.13 Through viscometry, Ylmaz etal14 showed that in dilute solutions, PS±PEO and

polybutadiene-graft-polystyrene (PBS)±PEO are im-

miscible systems, and the miscibility parameter de-

creases with the increase in temperature. Viscosity

studies of solutions of PS±poly(vinyl chloride) (PVC),

PS±poly(vinyl acetate) and PS±poly[(vinyl chloride-

co-vinyl acetate)] (VCVAc) in tetrahydrofuran showed

immiscibility in agreement with thermal analysis

studies of blend ®lms.15 In contrast, miscibility was

observed for PVC±poly(n-butyl methacrylate)

(PBMA) under the same conditions.15 Studies

through viscometry are also in agreement with the

solid-state analysis for PVC±poly [ethylene-co-(vinyl

acetate)] (EVA) compatibility and EVA±poly(styrene-

co-acrylonitrile) (SAN) imcompatibility.16

In this work, studies on the interaction of poly

(ethylene oxide) with [3,6]-ionene (cationic) and

sodium poly(4-styrene sulphonate) (anionic) polyelec-

trolytes are reported. The main purpose is to analyse

the viscometric behaviour of the blends in water

Polymer International Polym Int 49:81±87 (2000)

* Correspondence to: Valdir Soldi, Laboratorio de Polımeros (Polimat), Departamento de Quımica, Universidade Federal de Santa Catarina,88040-900, Florianopolis, SC, BrazilContract/grant sponsor: Conselho Nacional de Desenvolvimento Cientıficoe Tecnologico (CNPq)Contract/grant sponsor: Coordenacao de Aperfeicoamento de Pessoal de Nivel Superior (CAPES)(Received 14 October 1998; revised version received 22 June 1999; accepted 14 September 1999)

# 2000 Society of Chemical Industry. Polym Int 0959±8103/2000/$17.50 81

solution in comparison with solid ®lms analysed by

thermal analysis and optical microscopy techniques.

EXPERIMENTALMaterialsSodium polystyrene-4-sulphonate (PSS, Aldrich,

Mw=70000g molÿ1), [3,6]-ioneno (ION, Aldrich,

Mw�15000g molÿ1) and poly(ethylene oxide),

(PEO, Aldrich, Mw=300000g molÿ1) were used

without further puri®cation.

Sample preparationUndiluted PEO, ION and PSS were ®rst dissolved in

water under mechanical stirring. The PEO±polyelec-

trolyte solutions for the viscosity analysis were

prepared from the dilution of a stock solution

(concentration 1gdlÿ1 of PEO±PSS or PEO±ION).

Cast ®lms for thermal and microscopic analysis were

obtained by slow solvent evaporation of PEO±PSS or

PEO±ION solutions of different compositions at room

temperature and dried in a vacuum oven at 40°C for 3

days.

Viscosity measurementsThe apparatus used in this work was a Brook®eld

rotational viscometer (model LDV III) equipped with

1.1 RheoCalc software. `Coaxial-cone' (spindles ULA

and CS4-18) and `cone-and-plate' (spindles cp-40 and

cp-52) modes were used for low and high shear rates,

respectively. The measurements were carried out in a

concentration range of 0.2±1.0gdlÿ1, at 25.0�0.1°Cwith 0.1M NaCl. For pure PSS and ION, Newtonian

behaviour has been observed according to the litera-

ture.17,18 However, in our experiment, non-New-

tonian behaviour was observed at low shear rate (less

than about 180sÿ1) for PEO, and a Newtonian plateau

was observed at a higher shear rate. All the blends had

the same behaviour as pure PEO. The values of

apparent viscosity for pure components and mixtures

were taken in relation to the Newtonian plateau at a

shear rate of 180sÿ1 and were used to determine the

speci®c and intrinsic viscosities.

Thermal analysisThermal analyses were carried out on a Shimadzu

DSC-50. The samples were ®rst heated from room

temperature to 200°C and 300°C for PEO±ION and

PEO±PSS blends, respectively, at a heating rate of

10°Cminÿ1. The samples were then slowly cooled to

room temperature. The crystalline melting tempera-

ture (Tm) was measured in the second heating, at

10°Cminÿ1. For a PEO±PSS (70/30) blend, we also

analysed the in¯uence of the ®rst run over the second

run. The effect was noted after heating the sample

(®rst run) from room temperature to 100, 200, 250

and 300°C.

The thermal stability of the pure components and

blends was analysed by thermogravimetry (TGA)

using a Shimadu TGA-50 thermal analyser under

nitrogen atmosphere. The samples were heated from

room temperature to 800°C with a uniform heating

rate of 10°Cminÿ1. Pure ionene decomposition was

observed above 260°C, whereas PEO and PSS

remained stable up to approximately 360°C.

Morphology analysisThe morphology of PEO, PEO±ION and PEO±PSS

blends was analysed using hot-stage optical micro-

scopy (HSOM). Crystal structure was studied using

polarized light on an Olympus microscope. The

samples were heated between two cover glasses at

5°Cminÿ1 up to 200°C and 300°C for PEO±ION and

PEO±PSS blends, respectively, and the subsequent

cooling to room temperature was conducted at the

same rate.

RESULTS AND DISCUSSIONViscometric behaviourDifferent criteria have been used to predict the

miscibility of binary polymeric solution systems in

terms of viscosity,16,19±22 one of which considers the

comparison between the theoretical speci®c viscosity

determined by intrinsic viscosity additivity19 and the

experimental values determined using relative vis-

cosity. In eqn (1), Zspm is the speci®c viscosity of the

mixed polymer solution, [Z]A and [Z]B indicate the

intrinsic viscosities, and CA and CB denote the

concentrations of the components A and B.

�spm � ���ACA � ���BCB �1�Figure 1 shows the speci®c viscosities versus the

PEO weight fraction [WPEO=CPEO/(CPEO�CPSS(ION))] of PEO±PSS and PEO±ION (inset)

mixtures. In both systems the continuous line repre-

Figure 1. Specific viscosity of PEO–PSS blends in 0.1M NaCl at 25°C.Inset: PEO–ION blends under the same conditions. For both plots, the solidline represents the theoretical values determined considering the additivityas eqn (1), and the experimental values are shown by filled squares.

82 Polym Int 49:81±87 (2000)

V Soldi et al

sents the viscosity behaviour considering additivity

according to the above equation, using 1.72dlgÿ1,

0.20dlgÿ1 and 0.14dlgÿ1 as the intrinsic viscosities for

PEO, PSS and ION, respectively, in 0.1M of NaCl. In

the PEO±PSS system, the experimental data showed a

positive deviation in the PEO weight fraction above

0.5, indicating attractive interaction between the

components. However, a negative deviation was

observed below the PEO weight fraction of 0.5,

indicating immiscibility in this composition range.

For PEO±ION mixtures, a very clear negative devia-

tion was observed in all PEO composition ranges,

indicating a repulsive interaction which in turn caused

a shrinkage of the macromolecular coils. These results

show that PEO±ION is an immiscible system similar

to that reported in the literature for PEO±cationic

surfactant systems in which no interactions were

observed.23±26

To analyse the PEO±PSS system in greater detail,

another criterion was used to predict miscibility

between the components in water solution. In the

procedure developed by Sun et al,22 the Huggins

coef®cient Km can be de®ned by three types of

interactions: (i) a long-range hydrodynamic interac-

tion of pairs of single molecules (Km1) as in eqn (2),

Km1 �KA���2AW 2

A �KB���2BW 2B � 2�KAKB�0:5���A���BWAWB

����AWA � ���BWB�2�2�

where WA and WB correspond to a weight fraction of

the components A and B, respectively, and KA and KB

express the Huggins coef®cients for the pure compo-

nents; (ii) the formation of double molecules, which in

our case was neglected because of the absence of a

strong speci®c force of attraction between molecules

and suf®ciently low concentration, and (iii) the

intermolecular attraction or repulsion, represented

by Km3=a. In this condition, Km can be described

by

Km � Km1 �Km3 �

KA���2AW 2A�KB���2BW 2

B�2�KAKB�0:5���A���BWAWB

����AWA � ���BWB�2��

�3�and the value of a for the PEO±PSS system deter-

mined using

� � Km ÿKm1 �4�The Huggins coef®cients Km in the blend, and KA and

KB for pure components were determined by

�sp

C� ��� �K ���2C �5�

considering the slope of the plot of ZSP/C versus C.

According to the parameter a a miscible system is

related by a�0, and the system is immiscible when

a<0. In Table 1, we show the Huggins coef®cients

and a parameters for pure components and PEO±PSS

blends. Values of the Huggins coef®cients between 0.3

and 0.7 indicate weak association of the polymer26 and

are typical for a good solvent.27,28 Huggins coef®cients

higher than 0.7, as observed in PEO weight fractions of

0.85 and 0.70, indicates molecular entanglement

between chains, and in this case are probably due to

the interactions between the components. In this

composition, positive values of a were observed, and

according to this criterion, miscibility occurred above

the PEO weight fraction of 0.5, with immiscibility

occurring in blends of lower composition. Sun et al22

studied poly(vinyl chloride)±poly(methyl methacry-

late) blends using this method, and positive a values

were observed in all composition ranges. The depen-

dency on the concentration ratio of both polymers in

the mixture was also observed in PSS±PVP blends.29

The results indicate repulsive interactions between

the components in the PEO±ION mixtures. It is well

known30 that ionene properties in general are related to

Figure 2. DSC thermograms for pure components and PEO–ION blends ofdifferent compositions as indicated. Heating rate 10°Cminÿ1.

Table 1. Huggins constant values and a parameter for pure components andPEO–PSS blends in 0.1M NaCl at 25°C

System WAa Km Km1 a

PEO±PSS 1 0.368 ± ±

0.80 0.875 0.367 0.508

0.70 0.815 0.366 0.449

0.50 0.336 0.365 ÿ0.029

0.30 0.253 0.361 ÿ0.108

0 0.338 ± ±

a Weight fraction of PEO in the blend.

Polym Int 49:81±87 (2000) 83

Viscometry and thermal analysis of PEO/polyelectrolyte blends

the high linear charge density in the main chain, and the

conformation of [3,6]-ionene, for example, is extended

duetotheelectrostaticrepulsive interactionbetweenthe

ionizable groups. Interactions between ionenes and

non-ionic polymers are reported in a few papers,31±33

and in general are associated with the complexation

between the ionene quaternary ammonium group and

high molecular weight polymers.

Partial miscibility, therefore, hasbeen observed in the

PEO±PSS system. As has already been discussed,8,9

charge repulsion between the aggregates expands the

polymer coil dimensions, increasing the reduced vis-

cosity. The effect of the counterion on the PEO±anionic

surfactant interaction has also been reported,34,35 and

the results show that sodium dodecyl sulphate interacts

more strongly with PEO than with lithium or cupric

dodecyl sulphate. This effect is attributed to the af®nity

ofthecounterionforthecomplexationwiththepolymer,

and in the case of the divalent cupric counterion it is

attributed to the larger degree of hydration compared

with that of the monovalent Na�. In the PEO±PSS

system, the counterion Na� can partially provide the

driving force association, because in water it is simulta-

neously electrostatically bound to PSS and is coorde-

nated with PEO. Similar behaviour was observed in

complexes of PEO with salts of alkali metals.36 In the

interaction between the ether oxygens of PEO and the

alkali-metal cation, three ethylene oxide repeat units are

coordinated with one Na� ion in this case, as con®rmed

Figure 3. DSC thermograms for pure components and PEO–PSS blendsof different compositions as indicated. Heating rate 10°Cminÿ1.

Figure 4. Ratio of enthalpic heat variation of pure PEO and the calculatedvalue corresponding to PEO in the blend versus polyelectrolytepercentage: &, PEO–PSS; ~, PEO–ION.

Figure 5. DSC thermograms for pure PEO and PEO–PSS blend (70/30) asa second run with the first scan up to: (A) 300°C, (B) 100°C, (C) 200°C, (D)250°C and (E) 300°C. Heating rate 10°C minÿ1.

84 Polym Int 49:81±87 (2000)

V Soldi et al

by wide-angle X-ray scattering. For the PEO±PSS

system studied in this work, the counterion Na� is

probably responsible for the coordination of both

polymer and polyelectrolyte in a similar manner to that

reported for the PEO±SDS system by Dubin et al.37

Thermal analysis of blend filmsThe DSC thermograms of PEO±ION blends are

shown in Fig 2. The curves at the top and the bottom

are for undiluted PEO and ION, respectively. The

intermediate curves are for blends containing 25wt%,

Figure 6. Optically polarizedphotomicrographs of pure PEO (A) andblends with PEO–ION (w/w) of 55/45 (B)and 25/75 (C). For blends 85/15 (w/w) thePEO crystallization temperatures were:46°C (D), 41°C (E) and 39°C (F). The baris 100mm long. [ ]

Figure 7. Optically polarizedphotomicrographs of pure PEO (A) andblends with PEO–PSS (w/w) with 85/15 (B),40/60 (C) and (D) 10/90. The bar is 100mmlong. [ ]

Polym Int 49:81±87 (2000) 85

Viscometry and thermal analysis of PEO/polyelectrolyte blends

55wt%, and 70wt% PEO. The melting temperature

Tm of PEO at 62°C did not change with the presence

of ION as may be observed in intermediate curves.

The endothermic peak simply indicates that the

absorbed heat decreases proportionally with the

percentage decrease of PEO in the blend. This

indicates that ION acts merely as a diluent and does

not affect PEO crystallization.

Figure 3 shows DSC results in the melting region for

PEO±PSS blends. The curve at the top represents pure

PSS, the intermediate curves are for blends with 25,

40, 55, 70 and 85wt% PEO, and undiluted PEO is

given by the bottom curve. In relation to the

endothermic peaks in the PEO±PSS blends with

compositions between 40 and 70% of PEO, changes

to values lower than those of the undiluted semicrys-

talline component, indicate partial miscibility between

the components in this composition range. The

broadening of the endothermic peaks is probably

related to changes in the PEO crystallization. The

effect of both polyelectrolytes on the PEO melting

temperature was analysed in terms of the melting

enthalpies of PEO in the blend in comparison with the

value for undiluted PEO. The ratios of the melting

enthalpy of PEO in the blend and in undiluted form

are shown in Fig 4 for both systems studied. In the

PEO±ION system, the ratio is unity, indicating the

absence of effect due to ION in the blend. This

behaviour is in agreement with the viscometric and

DSC data, and is indicative of immiscibility between

the components. In contrast, in the PEO±PSS system

the ratio of enthalpies deviates signi®cantly from unity,

indicating that the PSS disturbs the PEO crystallinity,

in agreement with the partial miscibility discussed

above.

Figure 5 shows the PEO melting curves of PEO±

PSS (70/30) blends, obtained as a second run, after

running samples at different annealing temperatures in

the ®rst run. Thermograms A and E represent a

second run of pure PEO and blend, respectively,

which were ®rst scanned up to 300°C and than cooled

to room temperature. In the same manner, samples B,

C and D were ®rst run up to 100°C, 200°C and

250°C, respectively. The presence of a shoulder in B

and a double melting peak in C indicates two crystal

populations give rise to the melting behaviour. We also

observed that with the temperature increase in the ®rst

run, the endothermic peaks broadened and shifted to a

lower melting temperature. The above behaviour is

related to changes of crystallization during quenching.

Morphology and PEO crystallizationFigure 6 shows the photomicrograph of pure PEO and

PEO±ION blends. Pure PEO crystallization (Fig 6A)

shows a typical spherulitic structure with ®brous

subunits extended radially outwards from the central

nucleus, as has been previously discussed.38 Blends

with 85% PEO (Fig 6D±F) at different crystallization

temperatures showed the same spherulitic morphology

in the PEO domains. Similar behaviour was observed

in blends with 55% of PEO (Fig 6B). The amount of

ION in the mixture remains in speci®c domains

without perturbing the PEO crystallization. With

25% PEO (Fig 6C), crystal formation is not very

clear, probably because of the presence of large

domains of ION. Apparently, some crystals must be

present in the clear part of the photomicrograph. The

immiscibility of the PEO±ION system is once again in

agreement with the DSC results.

In Fig 7, we show the PEO crystallization in the

presence of 15, 60 and 90% of PSS in the blend (Fig

7B±D). The decrease in spherulite size and change in

morphology when the PSS content in the blend

increases is clear. In compositions with 15 and 60%

of PSS the crystal distribution is very homogeneous,

indicating the in¯uence of one component over

Figure 8. Optically polarizedphotomicrographs of blends PEO–PSS85/15 (w/w) at different crystallizationtemperatures: (A) 49°C, (B) 47°C, (C)45°C and (D) 41°C. The bar is 100mm long.[ ]

86 Polym Int 49:81±87 (2000)

V Soldi et al

another. In blends with a large amount of PSS (90%),

the PEO crystal grows inspeci®c domains but with the

same characteristics in size and morphology. Micro-

graphs kept at different crystallization temperatures

are shown in Fig 8 for blends with 85% PEO. As may

be observed, PEO crystallization is very fast and the

PEO crystal size is smaller, achieving a homogeneous

distribution in the matrix.

In conclusion, it is clear that the solution viscosity

data are in agreement with the behaviour observed by

thermal analysis studies of blend ®lms. Partial mis-

cibility is observed for PEO±PSS systems with PEO

concentration higher than 50wt%. In terms of vis-

cosity, the results show behaviour similar to the data

reported for PEO±surfactant interactions, and the

counterion Na�must be responsible for the miscibility

of PEO with the anionic polyelectrolyte. These

conclusions are supported by the effect of PSS on

PEO crystallization as observed by optical microscopy.

ACKNOWLEDGEMENTSThis research was supported by Conselho Nacional de

Desenvolvimento Cientõ®co e TecnoloÂgico (CNPq)

and CoordenacËaÄo de AperfeicËoamento de Pessoal de

NõÂvel Superior (CAPES).

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Polym Int 49:81±87 (2000) 87

Viscometry and thermal analysis of PEO/polyelectrolyte blends