Dielectric relaxation of some binary liquid mixtures containing polyethyleneglycol as one component

JournalofMokcularLiquida.4D (19Bl)lOs-118 El&&r SciencePublisheraB.V.,~terdam

DIELECTRIC

105

RELAXATION

MIXTURES

OF SOME

CONTAINING

Institut

22

M. Stockhausen

fifr Physikalische

January

The permittivity 30

MHz

and

(PEGDM); ethanol, from

an

mixture

GE2:

PEG

200

contributions

FZG

with

or water.

400

(Germany)

with

The

2

0)

toluene

description

or PEG

4CO dimethylether

to

ethyleneglycol,

of the dielectric

superposition

(PEG-PEGDM)

(PEG-H

has been measured at 20 OC between

ethyleneglycolmonomethylether,

unperturbed

components

MCmster,

1991)

72

apparently

and G_ SchiItz

Chemie der Universitat

of the following mixtures

methanol

AS

COJMPONIZNT

Miinster


LIQUID

POL YETEYLENEGLYCOL

ONE E. Wessling,

BINARY

of

spectra

contributions

the occurance

ranges

from

of strong

both

additional

which are ascribable to heteroassociation.

Introduction Chain molecules, dielectric moments (PEG),

even those with only terminal dipole moments,

relaxation are

behaviour

distributed

H(OCH2CH2)pOH.

temperature,

are widely

0167-7322/91/$03.50

8

exhibit

a non-Debye

in the liquid state [x]. All the more this is the case if

along

the

chain

backbone,

These substances, applied

not

least

as

with

which for p s

because

of their

1991 -ElfmvierSciencePubliehemB.V.

polyethyleneglycols

10 are liquids at room water

solubility.

Allrights~rved

The

dynamic

dielectric

aqueous

ones

information mixture

properties

systems

may

hydrogen

The absorption be described

by

of

segmental

continuous

relaxation

components. and

noticed

[lo])

motions

frequency

opposite

time

dietherated

concerning region

short)

from

of the

with increasing

This

properties

may

systems.

solute

and

meaningful those

information previous

studies of in

terminal

be

revealed

of PEGs

and

of

solvent

concerning

studies mostly

substances

and

hydroq

coils,

probably

groups.

A

relaxation

particularly

(e.g.

region is mainly

within the flexible

PEG

the

due to

while the

inter-

peculiarity

and

already

time (which anyway

as viscosity

is

varies in the

increasing

weight

interpretation

of the

itself but on the mutual

in the

dynamic

soIvents,

which

dielectric

in particular

cannot

assuming

that

such

therefore

in particular

worthwhile

to

the variation

laid stress on the variation

a

interaction

properties water,

unambiguously

at all. In order to attain a better understanding seems

of discrete

process.

contributions,

it

a sum

related

absorption

motion

chain length,

in polar

spectrum

It CZLIIeither

it has been inferred from comparative

PEGS

the

or by

is not aimed at a more thorough

of the polymer

absorption

systems

from

interactions,

but unstructured.

decrease is likely to result from the relatively

possibly

Solutions

unstructured

Apart

chain, dielectric

distributions

the ether oxygens

arises

present communication

which

of

is broadened

Qualitatively

of the chain ether group relaxation

dielectric

in particnlar

years

of intermolecular

that the higher frequency

association

sense.

solutions,

many

of the PEG

in early work is the decrease of the effective

surprisingly

The

for

to the knowledge

of pure PEGs

mono-

intramolecular

and dynamics

contribute

and of PEG

attention

spectrum

polypropyleneglycoi

lower

attracted

[2-5]

bonding effecta-

type spectral

studies

have

[3,5-Q],

on the conformation

particular

Debye

of pure PEGS

be

of

show

of the dielectric

of the

of the PEG

more

mixture

mixture again

resolved

subdivision

gather

effects

an into

might

be

behaviour

experimental partner,

chain length.

while

107

Here

we report

relative

molar

nonpolar with

on PEG

mixture

B~~IIM

using

mass of 400 or 200. They may be arranged

solvent and with a dietherated

a fkw protic liquids

covering

(a)

some results

including

the whole mixture

derivative

PEGB

in two groups:

as second mixture

water_ The following

400 -

toluene

PEG

400 -

polyethyleueglycol4OO-dimethylether

a mean

(a) with a

component,

(b)

systems have been studied

range (except for the first mentioned

PEG

with

example) :

(PEGDM),

H3C(OCH2CH2)pOCH3 (b)

PEG

200 -

ethyleneglycolmonomethylether

PEG

200 -

ethyleneglycol

PEG

200 -

ethanol (EtOH)

PEG

200 -

methanol

PEG

200 -

H20_

The complex range

between

experimental The

30 MHz uncertainty

chemicals

further

The

permittivity

were

(EG),

(EGM),

H3COCsCH2OH

HOCH2C%0H

(MeOH)

of the liquids and 72 GHz

was measured

employing

at 12 spot frequencies

different

experimental

in the

setups. The

is a few percent. All measure ments are at 20 OC. from

Aldrich,

Fluka

aud

Merck.

They

were

used

without

purification.

permittivity

the Cole-Cole

data

were tentatively

or Cole-Davidson

fitted

using relaxation

type. However,

time distributions

this was not found

possible

of in a

satisfactory

manner for all systems at any mixture composition.

description

of the results

which furthermore the dielectric

in terms of discrete

is advantageous

loss already

Debye

in comparing

Therefore

type spectral

components

different systems.

corrected for the conductivity

we prefer a

With

contribution,

Ci,

E”(W) being

a fit according

to

TiW

= !s si

d’(w)

i

was carried

1+T2w2 i

out and checked against the c’(w)

spectral components, It is difficult,

a formal analysis is obtained

however,

time ri and relaxation studied. certain

We

shall

composition_ systems

As

to interprete

on

with

the variation

described

will be considered

this leads

to some starting

the group

(b)

systems.

proceed

in detail

Using the minimnm

obtained

parameters

sense consistently

the aid of modified

of relaxation

parameters

in the following

sections,

first since they allow assumptions

results

for all the systems

analyses with the

parameters

in an analysis

which

chosen assumptions

are acceptable for the systems under consideration.

with the nonpolar

nearly

O-Xi), the total The

to decide simply

mixture

group

(a)

By analogy

requires

whether

more

or not the

400 with toluene or PEGDM

OKl dilution remains

the

used to analyze

number

PEG

by making

two

than the minimum

(4

of terms but allows

of

(relaxation

for a simple description.

on the mixture

Such a procedure

number

in that way.

the formally

strength Si) in a physical

therefore

assumptions

results

absorption

unchanged. relaxation is merely

liquid toluene, the shape of the PEG

At high enough strength, shifted

hi,

PEG

contents

is proportional

towards

higher

(mole

absorption fraction

to the PEG

curve

xPEG

2

concentration.

frequencies. However,

on further

lo9

loo

1

PEG

,

I

1

10

LOCI - ll33L3M

t

45% la

.I “PEO = 1

1

0.61 OAl

10

Fig_

I:

0

1WMHr

GHz

v-

Representative PEG400-PEGDM E ”

versus

only. rity).

absorption spectra of mixtures, dielectric LOSS frequency u.
dilution the total relaxation strength becomes less than the value ES: expected from cPEG proportionality; e.g. at xPEG = 0.4 there is ESi/ESf = 0.7. On the other hand, a remarkably simple mixture behaviour which appears to change almost linearly with mixture composition is exhibited by the polar-polar system PEG-FEGDM,

as may be seen from Fig. 1, where for clarity only fitting

curves are represented while the measured points are omitted. The results on this system suggest an analysis along the following lines. First, for the pure substances, a formal analysis is carried out which requires 4 terms for PEG 400 (where a minor low frequency term is nearly negligible) and 2 terma for PEGDM. Then

as

starting

assumption

for

the

mixtures the

Si

values

for

each

mixture

110

are

component Corresponding reduced

put

proportional

to

fits for PEG-toluene

as mentioned

posaible without

before,

the

respective

mixtures

cannot

substance

be achieved

concentration_ unless the Si are

while in the case of PEG-PEGDM

any additional

terms. They can be optimieed

fits

by variation

values and also by a slight variation of the Si values for some mixture This,

however,

still permits

to describe the PEG-PEGDM

with respect to the relaxation Generally, impairing

the

the

times

therefore tried to use constant mixture quality

range.

This

is just

is significantly

can

with

the

over

a

compositions.

as being “ideal”

(by

a factor

certain

PEG-PEGDM

range

two

it

was

over the whole

uncertainties,

of about

without

system

component

pussible within experimental

improved

parameters

varied

-ri values for each spectral

allowing the ri to be systematically The relaxation

be

In particular

quality.

mixtures

of the -ri

strengths of the mixture components.

relaxation

fit

are found

in the

but the fit variance)

by

varied-

obtained in that way for the two systems

are summarily

represented in Fig. 2.

(b) PEG The

200 with alcohols or water

absorption

monotonously

curves with

of

mixture

mixtures

of

composition

that as

group the

former

overview two examples

are given in Figs. 3,4 (omitting

1). While

with EGM

the mixtures

the gradual transition, case of PEG-water frequency absorption

do

not ones.

Fd

vary

(Fig. 3) resemble the PEGDM

,@

.a qualitatiye

the measured points ti.jn systems

(Fig.

Fig. 19 in

even a first glance at Fig. 4 shows a differing behaviour ip the

mixtures:

Here obviously

an add_itional contribution

to the low

appears at medium mixture ratios.

For the analysis of the group (b) data we adopt the tkk$ing the preceding

generally

PEG-PEGDM

taken from the pure mixture

system

proved to be ticeptabti,

components

assu,mption which for i&

fk&’ :Si values as

are put Illl(IroximateJy F).$$Q~$nal

to the

111 PEG 400 -Tot

0

1

2

0

1

=FEG

w

of

the

respective

component,

one

conceivable,

eince conformational

mixture

would

presupposes

probably

components,

self-association

fix mixtures

additional with EG

in

component that

a corresponding

five

manner

this

inkence

changee

Concerning

the

maximum

the

contribution

(as the PEG-toluene

strengths.

Concerning

can be drawn

PEG

system the second

on grounds

of their

view of Fige- 3,4 it is not unexpected constraint

spectral components_ and, in particular,

about

relaxation

comparative case8

concentration.

and related

lead to smaller

propertieSIn

in only some of the introducing

-

Relaxation parameters T. and S(log scales) versus PEG conc&ntrati;n for FEG400-toluene and -PEGDM mixtures. Full symbols stand for PEG, open symbols for PEGDM spectral components.

concentrafloti

shows)

2 mot/l

allows

for

an

Those complementary

with water.

ZLIGdyBiS

that

without

terms are required

The

a-

t

Figs_

100

Fl33200-EGM

I

already on

mentioned

The m3nuer

relaxation

ug

the

case

PEG

snmmtily

of

the

(b)

A

depicted

group

as

that

in

vary

Fig_

Generally.

with

to

as 6_

but

which

Among

obtained

for

of

the

for

the

the three

in

spectral

above-

effect

is

rich

This

the

absorption

alcohol

of

-ri

the PEG

as

hold

viscosity_

relaxation

pronounced

shift lees

initial

main

that

OHz

mixture

10

the

to

and

the

v-

~~chauget~

increasing data

the

with

1

impossible

PEGZOO-EGM

MHZ

peculiarity

Ioss

is

a

syateInf3

similar

an

dielectric ahow

of I>-

100

it is fouud ZOCr33G)_ noted

3

analyses

corresponding

be

PEG

content

of

time

Fig_

examples;

these

spectra

content,

(a)

frequencies.

PEG

inspection

parameters are

the

group

from

ccompnre

c3Har

therefore

for

the

relaxation

higher

from

Absorption -la*0

V

10

I

resulting

w-ithincreasi seen

towards

in

1

should

the

Xt

increasing

be

observedvzithMcOH-turea.

maximum

mixtures

can

dcoholdecrea.ses

systexns

viscosity-

ITLucture

PO@-EtOH


constant

as

times

3,4z

I

eventually

MHz

mostly

relaxation

composition

112

Fig.

‘i

I

7

t

5:

QJ

5

:

PEWO-EG

%EG-

PEG 200-EtOH

0

0

bV

l

5

0

mol/l

2II t

t.

I’

a’

5

A

I-

F 2;

4% I

A +t+ --l t++ a+* AAA

PEG200-H20

+. t__J t

A4

I -8 +a* l. AA

I ’ ’ ’ I ‘I

PEG MO- MeOH I , , , I

Relaxation parameters Ti and S. (log scales) vet8u8 PEG concentration for the group (b) mixtures given in thk captions. Full Bymbols concern spectral componenta ascribed to PEG, open eymbola thoec for the second mixture component, bar and cross symbols represent additional terms.

0

*a a L-I 0.1

1

x$8 8

r--l

%A

102

, eEG200-EGM

114 components

for PEG 200 two lower frequency terms of equal relaxation

necessary

could be used (in Fig. 5, full triangles for 7i and full diamonds

strengths

for the equal

‘i)Discussion The

dielectric

molecular subject

relaxation

dipoles. to

The

components.

Moreover

group

moments

(conformation,

correlations

(heteroassociation)

reflects the stochastic

permanent

intramolecular

intermolecular

discussion

spectrum

correlations

and correlation

for example, hydrogen

of moments

of both

of

may

bonds)

as it is also for the second

should be taken into account.

will be restricted

of PEG,

intramolecular

(self--association),

mutual

motion

mixture

be aud

mixture partners

In view of that variety of effects the

to the qualitative

consideration

of some

conspicuous

featurea. used in the data analysis implies that the correlation

The model assumption of each mixture The

finding

component

that

this

effects

stay unaltered in the mixture as in the pure bulk liquids.

model

is appropriate

in the case of PEG-PEGDM

is not

unexpected in consideration of the f&t that these chain molecules are closely similar. The same holds for EGM with

a nonpolar

PEG

are feasible.

liquid,

which is similar to a terminal section of PEG. on the other

conformational

The results on toluene mixtures

are still more pronounced the introduction,

hand,

however,

with other solvents

For mixtures

and related

changes

indicate just those changes,

such a~ dioxane

we shall desist from discussing

which

(41. As mentioned

the conformation

of

in

point in

the present paper. The finding

that a simple “ideal”

regard in particular are (i) PEG-EG PEG-EtOH component

the systems

and PEG-H20,

and PEG-MeOH,

mixture

with obvious

behaviour deviations

where complementary

is possible

at all suggests

from that behaviour. terms are required,

where the relaxation times ascribable

to

These and (ii)

to the alcoholic

do not follow the otherwise observed dependency on mixture composition.

116

(i) With mixture

EG a weak additional

ratios

(bar symbols

term on the low frequency side is found at medium

in Fig.

5).

This

is aleo the case with

water.

feature with the latter is a stronger additional

term with an intermediate

time in the region of the PEG

(cross symbols

a small

diol molecule

components

PEG

offer two associogenous

with these substances

to heterointeractions;

are known

amounts

and H20

observed

ascribable

main relaxation

of PEG

from

other

occurance

of

molecules.

We

pyrrolidone

studies

complementary

somewhat

passes through observed water

relaxation

addition

term

though

a maximum

region

admixtures

the

is

however,

not

special

as with water also with

are unusual in character.

time

increases

with

to apply

to pure water,

at about cPEG

another

spectral

= 3.5 mol/l.

[7]

that to

the

protic

methyl-

of which

to that description resulting

[15,16],

We confine our

relaxation

content,

with

mode

which

approximately

change

As

from

strength

behavionr

is also

consequently [14,15].

represents

the water

constant

relaxation

more

drastically

on

We have reanalyzed

our

mode which is found to be possible, strengths

starting

and its relaxation A similar

terms.

to water. It is often possible for the

description

components

strengths

the PEG

of the solute than in the former description

compare

small

the effect is weaker in these cases and

of various other substances

relaxation

data according

of relatively

to the more intense of the two complementary

20 ps as extrapolated

by several

the

contributions

interactions

relaxation

on addition

rich

times,

its

above

being

water effect be considered in some detail. The question may be

for the moment

5 shows,

and the iufluence

[13]. It should be stressed,

an intermediate

raised as to whether PEG-H20

Fig.

with that fact,

term is missing.

Let the pronounced

attention

protic sites. The additional

not only been inferred from dielectric

relaxation

[4] and tetramethylurea,

the low frequency

in Fig. 5). Both EG as

may be connected

[11,12],

measurements

have found

relaxation

hydrogen bonds between small donor molecules and

on water has previously

but also from ultrasonic

Another

with

some

previous

too, in order to

results

see Fig. 6_ It turns out that on the water concentration

on

other

scale the

116

80

I

I

60-

t

si

c

v:

VV do 0

v

20w

e

30

6:

to just the same extent

intensity

[14,15])_ This “bulk” is relatively

mixtures depicted

6)_ A

process ie gradually

still

slower

the diehxtric

the relaxation in bulk

water

substituted

third

term

position

of the aqueous

of the relaxation

(see cross symbols

(for f&her

by a (ca)

a loss in

shows

examples

component

INX

20 pa process, which

compare e-g. diethyleneglycol

spectral

of the PEG-H20 component:

while

generally artsignedto affected (“hydration”) The

water,

(about

aqueous

70 ps)

is not

to water is quationable.

behavioux

vanishes

of pure

as with other admixtures

in Fig_ 6 since its assignment

On the whole

operative

ie characteristic

weak Ear the present case of PEG,

(Fig.

concerning

Qlv ,o 50 mol/l

Relaxation strengths S. of some water rkch mixtures accordin; to a modified description mode, where relaxation Full symbols: times are nearly constant. RI20 ps. O IO ps. open symbols: ~~ TAtueous mixtures with the following substanceste PEG200 (this work); m poly1200 and 40000 [16];

procest3, which

10 ps relaxation

-

Oo

I 40

0

-

V

*v

FiR.

I’ v

strength

a slower

system is not exceptional

The relaxation one is built

process which is

up,

which

may

be

water. maximum

in Fig. 5) corresponds

of the intermediate

to a ratio of about

additional

6.8 mol H20

per

117 mol PEG,

equivalently

measurements seems

about 3 H20

indicative

enable

characteristic

due

fast

motion

This

should,

of the involved

water

For PEG-

proportion

only.

component

heteroassociation,

EtOH

(about

involving

and PEG-MeOH

thus the mean alcohol of the main

2000

water

model

time

EtOH

the relaxation state,

residence within

which

decrease time

(open upright such

MeOH,

that

molecules

to

20 ps

is

triangles

is shortened of EtOH

of heteroassociation

just

caused

by

molecule

network.

However,

since

In that

has

molecules

of PEG.

containing

a more

of a lifetime

heteroassociation,

in

Additional systems,

provided

so that the

state

is shorter

than

of the alcohol

relaxation

time

main relaxation

the influence

time (full triangles)

of PEG

on the alcohols

manner from that on water

Support of this work by the Fonds der Chemischen acknowledged.

in

by PEG,

from that. It might be, however,

The convergence

are

it is the decrease

[18]. In terms

in a heteroassociated

respect

thns

correlation,

former

on addition

increasing

it is

strengths

is affected

the

and MeOH

in Fig. 5) with the PEG

an inference.

gratefully

which

moment

the alcohol

possibly

(apart

Possibly

relaxation

the alcohol

as often supposed

obviously

of an alcohol

differs in a qualitative

than

in the analysis

the selfasoclated

supports

about

time is a measure of the residence time of alcohol

are not required

lifetime

(i.e.

ps) is here observed

yield

is only little influenced.

than the latter,

there is no direct indication a

infer that

which indicates

rather

structure

the associated terms

molecules

enough

water.

the analyses

One might

structure,

relaxation

with

complicated

be loose

It appears to be special for protic liquids.

to concentration.

markedly

IR and NMR

[17]. Such a number

however,

affected in another manner than the normal “hydration” (ii)

From

per repeat unit have been estimated

additional

with EG

“bridging”

to

unit of PEG.

time)_

low frequency

from water)

per ether repeat

of a direct interaction.

a relatively

The

2 H20

Indnstrie

is

118

PI

G. Klages

and M. Strasemann,

PI PI

N_ Koizumi,

J- Chem.

M- Davies,

G. Williams

141

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and G.D.

V. L6nnecke-Gabel,

WI

U. Kaatze,

0.

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and M. Stockhausen,

PhD thesis Ghttingen

Gattmann,

82 (1978),

R

Podbieleki,

64 (1960), Colloid

575

P&m.

Sci.

U_ Kaatze,

Ber. Bunsenges.

U. Kaatze,

Progr. Colloid Polym.

PI

G-

Masszi,

1990 R

Pottel

and U. Terveer,

J. Phys-

112

PI PI

(1986),

1403

625

Loveluck,

E. Dachwitz

30a (1975),

330

151

Chem.

Phys. 27 (1957).

E. Wessling,

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Phys.

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Lakatos,

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Acta

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Stockmayer,

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21