Pervaporation of ethanol-water mixture by plasma films prepared from hexamethyldisiloxane

Desalination, 70 (1988) 465-479 Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

PERVAPORATION

OF EX-HANOL-WATER

MIXTURE

465

BY PLASMA

FILMS PREPARED

FROM HEXAMETHnDISILOXANE N. INAGAKI,

S. TASAKA

and Y. KOBAYASHI

Laboratory of Polymer 3-5-l Johoku, Hamamatsu,

Chemistry, Faculty 432 (JAPAN)

of

Engineering,

Shizuoka

University

SUMMARY The plasma polymerization process was investigated to obtain plasma films like poly(dimethylsiloxane), and the formed films were applied as membranes for pervaporation of ethanol-water solution. A reaction chamber which had the triode electrode structure for initiation of a glow discharge was provided for preparation of films like poly(dimethylsiloxane) by plasma polymerization. Films plasma-polymerized from hexamethyldisiloxane (HMDSO) resembled poly(dimethylsiloxane) in spectroscopic view and were composed of dimethylsiloxane chains with branches of trimethylsilyl groups. The surface energy for the films was 19.6 mN/m. The films deposited from HMDSO on membrane showed good ethanol-selectivity in Nuclepore pervaporation of ethanol-water solution. The separation factor depended on the film thickness as well as the feed composition. The film-thickness effect was maximized at 34 nm thick, and the separation factor reached 4.5. A model for the separation process using our composite membrane was discussed.

INTRODUCTION Pervaporation is

interpreted

interested of

is a separation

by

separation ethanol

of

ethanol

include

membranes

(refs.

from

silicon

blems

including

poor

nol in practical

use

from

its

ments

recombine and

of

is an unique Molecules

electrons,

to form

different

for

e.g.,

azeotropic

for

separation Hydra

but have

and swelling

process.

pro-

by etha-

or copolymerization

from

This uniqueness

conventional

into plasma

and

and fit

11-13).

thin-film

deposits

toughness,

are

solution.

selectivity

by cross-linking

(refs.

molecule.

finally

ethanol

ethanol

poor

introduced radicals,

a large

recombination

OOll-9164/88/$03.50

films

suitable

fermented the

Modification

of these reactions

or ionic.

e.g., show

membranes

solution,

are

are

for pervaporation

membranes

aqueos

membranes

process

investigators

water-selective

ethanol

properties,

3-10).

polymer-forming by actions

mentation,

(refs.

polymerization

such as radical mented

film-forming

for improvement

Plasma

1,2).

films

Many

Water-selective

solution,

polymer

The separation

1).

Membranes

types,

concentrated

ethanol

and fluoro

solution. (ref.

solution.

two

ethanol-selective

dilute

phobic

is applied

from

while

from model

of ethanol-water

solution

water

solution,

process

sorption-diffusion

in the separation

ethanol-water

ethanol-selective

of

the

ions,

and

The repetition polymers

0 1966 Elsevier Science Publishers B.V.

polymerizations

are activated then

and frag-

activated

frag-

of the activation,

frag-

(ref.

two

results

14).

Therefore,

the

466 formed even

polymers when

crosslinked

are

the

different

same

monomers

and superior

The aim of this by plasma

conventional

are

in mechanical

study

polymerzation

in pervaporation

from

The

used.

to

polymer

evaluate

of ethanol-water

plasma

in chemical polymers,

structure

generally,

are

properties.

is to prepare and

polymers

the

films

like poly(dimethylsiloxane)

performance

of

the

formed

films

solution.

EXPERIMENTAL Plasma

polymerization

The system mm

reactor

system

operating diameter,

at 470

(150 x 150 mm, trode), electrode

mm

two

a thickness

The electrodes

for

with

a monomer

plate

electrodes

monitor,

a vacuum

an aluminum

and the lower

electrode

50 mm space

of The V

the

frequency

was

applied

electrode

was

grounded

the

and glass

plates)

Triode

middle

on which

were

plasma

These

between and

the the

polymers

upper

lower (porous

deposited

coupled

of a bell

parallel

a triode

electrode

Substrates

electrode.

inlet,

three steel

electrodes

enhancement structure:

Schema

of the reaction

chamber

system.

set-up.

steel

electrodes

horizontally

were

(approximately and

the

electrode

middle was

membranes, were

mounted

silicon

mesh,

400 volts) electrode.

biased

at

-50

wafers,

on the surface

Thickness Meter

1.

elec-

The upper

*Thickness Monitor

Fig.

(400

mesh

l-

Vacuum System

jar

was a stainless

A high voltage

middle

capacitively

and a stainless

plate.

apart.

a

and a magnetic

middle

was an aluminum

20 kHz against

system,

of glow discharge plate,

was

It consisted

(af).

height)

positioned

at

polymerization

of 20 kHz

aluminum

for initiation

was

plasma

a frequency

467 of

the

lower

action

chamber The

the

electrode

same

as reported 0.13

cm3(STP)/min

current

sided

adhesive

represented

in Fig.

procedures

for

plasma

elsewhere

(ref.

Pa,

at

was turned

af current

double

is schematically

experimental

to approximately 4.8

with

and

15 Pa

then

was

on and the

the 15).

the

polymerization reaction

monomer into

of the

re-

were

system

essentially

was

evacuated

gas

adjusted

to a flow rate

of

the

reaction

chamber.

af

polymerization

(HMDSO)

(purchased

Japan),

ethynyltrimethylsilane

(ETMS),

Petrach

System

tetramethylsilane

Co.,

from

detail

was conducted

The

at a constant

of 20 mA.

Hexamethyldisiloxane

Kogyo

The

1.

The

introduced

plasma

tape.

Inc.,

U.S.A.),

Japan),

Petrach

and

System

from

Tokyo

trimethylvinylsilane

U.S.A.)

were

used

Kogyo

Co.,

(TMVS) (purchased

(TMS) (purchased

bis(dimethylamino)methylvinylsilane

Inc.,

Kasei from

(BDMAMVS)

as monomers

without

from

Tokyo Kasei (purchased

further

purifi-

cation.

Elemental

analysis

The C, H, and N contents with

a Yanagimoto after

as Si02 tent

was

a difference

of the between

plasma

The Si content

TM-2 analyzer.

combustion

and Si contents

of the deposited

polymers the

polymers

was determined

in an oxygen

sample

were

weight

gravimetrically

atmosphere.

and

the

sum

determined

The 0 con-

of the

C, H, N,

determined.

IR and XPS spectra IR spectra Bunko fourier

of the plasma transform

XPS spectra on silicon ploying

of

wafers

Mg K o

the

FT/IR-3.

polymers

(approximately

plasma recorded

with

a Shimadzu

exciting

radiation

at 8 kV and 30 mA.

of the binding

energy

recorded

with a Nihon

100 nm thick)

electronspectrometer The Au core

deposited 750 em-

level

at 84.0

scale.

energy

Contact phosphate “C

as a KBr disk were

spectrometer

were

eV was used for calibration

Surface

polymers

infrared

with

data

were

(ref.

16).

angles

against an

of

the

Erma

water,

plasma

glycerol, films

contactanglemeter

analyzed

to estimate

formamide,

deposited G-I with

the

surface

diiodomethane,

on glass

plate

were

a goniometer.

energy

according

and

tricresyl

measured

at

The

contact

to Kaelble’s

20

angle method

Pervaporation Composite

membranes,

and 30 nm; 6 urn the

plasma

thick)

polymers

porous

(purchased

prepared

from

polycarbonate from the

films

Nuclepore silicon

Co.,

(Nuclepore; U.S.A.)

compounds,

and

pore

were

size,

coated

served

for

15 with per-

468 vaporation

experiments.

The

composite

membrane the

area

membranes

of 13.8 cm’.

ethanol-water

a flow rate was kept through

solution

rate

a measured

of

The

permeation

estimated

from

in traps

the

JGC-ZOFP)

rate

with

glycol

the following

liquid

of the

the

membrane

The vapor

in the

column

at

permeated

trap

over

liquid was determined

a separation

a

membrane

The vapor

collected

with

at 25 “C and

by liquid nitrogen.

of the

and

cell

of the side

gauge.

1000 supported

(R in kg/m2-h)

steel

was kept

side

downstream

cooled

by weighing

10 % polyethylene

upper

a Pirani

and the composition

(JEOL,

2 m long)

of the cell

at the with

was condensed

of time,

a gas chromatograph

in a stainless

on the

The pressure

was determined

period

vapor

circulated

100 Pa by monitoring

membrane

permeation

positioned

The temperature

was

of 5 ml/min.

below the

were

with

(3 mm diameter,

on Flusin

T (60/80

separation

factor

mesh).

(a ) were

equations.

W R=43.5x

-

where

W and

(1)

t are

the

weight

(in g) of the

permeant

and the

permeation

time

(in min), respectively.

o

%2JCw2

=

(2)

‘El”W where

1

and CE2 are

CEl

respectively.

cw1 respectively.

meant,

the

ethanol

concentration

are the

and cw2

water

of the

concentration

feed

and the

of the

feed

permeant,

and the per-

RESULTS Chemical silicon

composition

surface

property

of

plasma

polymers

prepared

from

compounds To

obtain

of silicon A triode in this

poly(dimethylsiloxane)-like

compounds structure

study

structure

for

with

construction study) initiation

a reaction

with

voltage

A glow

for

electrodes,

first

This

which

electrode

triggered

polymerization

in Fig.

reaction

is biased high

discussed.

1, was employed from as the

system

a diode electrode

with

400 V was used

electrode

by the

was

is different

of approximately second

plasma

is a familiar

In the

and the

The third

discharge

from

polymerization

as shown

discharge.

(A voltage

the

films

plasma

electrodes,

a glow

polymerization.

of a glow discharge. electrode.

parallel

of parallel

between

thin

system

of

for plasma

a high

is applied

three

initiation

a pair

used

ode structure,

second

and

(mesh

the

in this

electrode)

at -50 V against voltage

tri-

is confined

for the to

469

a space bias

surrounded

of the

plasma

polymers

deposit

on

polymers tion

between

third

formed

the

could

surface avoid

system

with

the

irradiation

under of the been

deposited

films

Colorless, the

silicon

polymer

irradiation

(ref.

deposition

Table

not?

transparent

compounds

1 shows

polymers

was

prepared

those

influence plasma

irradiation

from

has

with

CVD.

structure

the conventional

damage

investigated

of

the

silicon

influence

plasma

from

analysis

of

plasma the

which

polymerization

triode

was

l/3

structure. - l/4

of The

as slow

as

structure.

effects

the silicon

effect

by plasma

irradiation

from

chamber

of the diode

always

polymers.

deposited

reaction

reac-

are

of the triode

less

was

and plasma

and degradation

films

prepared of

plasma

1 - 2.5 ug/cm*-min,

chamber plasma

silicon chamber

the

polymers

This irradiation

reaction

Does

were

the

plasma

because

The

electrode,

deposited

polymerization,

somewhat.

with

mesh the

negative

space.

in the conventional

amorphous

the

The

films

using

rate

deposited

in the

the

While,

plasma

by the

occurs

through

the

structure 17).

electrode

Therefore,

the

of

with

for the formed

when used the reaction

plasma

or

down

irradiation.

compared

diode

composition

pass

will occur

preparation

second

electrode.

during

prepared

the

the

polymerization

structure

polymers

reactions

of chemical

and

plasma

properties of

by plasma

the

diode

films

chamber

polymerization

space third

in the

show good electrical reaction

in the of

of plasma

plasma

silicon

first

and plasma

possible

the

emphasized

Amorphous

the

electrode,

on

the

compounds.

elemental The plasma

composition

of

polymerizations

TABLE 1 Elemental under

composition

of

plasma

polymers

prepared

No plasma

TMS

W/FM (MJ/kg) 246

C2.4H6.701.3Si

217

TMVS

irradiation Atomic

K4H12SiJ* (C5H12Si)

ratio

C2.3H5.601.4Si

ETMS (C5H10Si)

101

C2.7H5.701.8Si

HMDSO (C3Hg00.5SiJ

170

C2.8H8.702.4Si

BDMAMVS K7H18N2SiJ

160

‘4 . 6H10 . 3’1 . gNt . tsi

:

plasma

irradiation

no irradiation.

Monomers

*

under

Atomic

ratio

of the monomers.

Plasma

irradiation

W/FM (MJkg)

Atomic

290

C3,7H8.201.1N0.2Si

290

‘5

170

‘6 . 6H12 . 9’1 . BNO. lsi

120

C2.6H5.601.3Si

ratio

. BHll . 3’1 . gsi

and

470 were

performed

MJkg). tative

The W/FM expression

apparent

input

electrical and

under

observe

some

formed

under

differences

yielded

in silicon

content.

mass

of

of the

polymers

poor

C/S1 and H/Si

atomic

TMS, TMVS, and ETMS, shown

irradiation), atron),

2.4 and 6.7 (under

2.3 and

2.7

and

the

plasma

tinctive (Si2p core

5.7

5.6 (under

(under polymers

differences level)

monomer,

where

was could

of typical

Binding

1.3 -

(in J/set),

no irradiation);

1.8 independently

plasma

polymers

the

plasma 3.7 and

However, of the

prepared

We could

content

and rich

polymers

prepared

8.2 (under

plasma

plasma

plasma

O/Si plasma

polymers No plasma

irradi-

irradiation),

atomic

ratio

irradiation.

Fig. 2 shows from

an

(in mol/sec),

plasma

11.3 (under

12.9 (under

in XPS spectra.

means

W, F, and M are the flow rate

and hydrogen

5.8 and

respectively.

for quanti-

no irradiation:

for the

6.6 and

100 - 300

parameter

between

1, were

of

respectively.

under

in carbon

in Table

be observed

the

(in kg/mol),

ratios

values

14) was used

W/FM

formed

no irradiation);

no irradiation),

(ref.

composition

and those

W/FM

The

monomer

in elemental

irradiation

plasma

the

(at

by Yasuda

conditions.

for a glow discharge

weight

plasma

conditions

proposed

operating

per unit

energy

irradiation

from

the

energy

molecular

operating

parameter

of

input

the

similar

for Dis-

XPS spectra

TMVS and ETMS.

The

Energy (eV)

for plasma polymers prepared from TMVS (A, A’) and ETMS Fig. 2. XPS spectra (B, B’) under plasma irradiation (A’, B’) and under no irradiation (A, B).

471 plasma with

polymers peaks

mers

not

different mers

be

completely

oxidation

formed

peak

Sizp geneous the

near

levels

sense

preparation

irradiation

but

103 eV with that states may

reaction

of plasma

with

surely

of

with

the

from

Wave Fig. 3. IR spectra methylsiloxane) (B).

resembled

Number of

plasma

100.9,

These

peaks

silicon

atoms

poly-

Si spectrum

silicon

Conclusively, structure

having

plasma

moieties

whose of the hetero-

the

restriction

of silicon

moieties.

may be adequate

for

like poly(dimethylsiloxane).

spectroscopic

HMDSO

100.2,

The comparison

makes

homogeneity

triode

99.6,

Si spectra 2P plasma poly-

ETMS.

While the

of 3 eV.

view

among

the

HMDSO, TMS, TMVS, ETMS, and BDMAMVS showed

prepared

to

a symmetric

atoms). for

at

from

18-21).

irradiation

silicon

peaks

related

showed

be favorable

complex

103.7 eV for the

prepared

a FWHM value

chamber

polymers

from

are

the plasma

oxidation

showed

102.6, and

irradiation

irradiation the

Comparison from

plasma 102.2,

@iOx, x = 1 - 4) (refs.

no plasma

indicates

(many plasma

In this

the

101.8,

assigned

number

under

appeared core

under

100.2,

from TMVS, and Si spectra 2P 103.6 eV for the plasma polymers

102.2,

could

of

99.6,

prepared

101.8,

formed

at

mostly

plasma that

polymers the

prepared

plasma

poly(dimethylsiloxane).

Fig.

prepared

(A) and

polymers

3 shows

IR

x 10-Z(cm-l) polymers

from

HMDSO

polyfdi-

472 spectra

for

(PS048,

purchased

absorption

plasma

CH3

streching

and 617 cm -’ ported

that

the

dimethylsilyl ((CH3)3Si-), for both

C-H

and

HMDSO

methylsilyl

the

may

be

in CH3

(ref.

2967

(C-H

22).

vibration

deformation we assume

composed

dimethylsiloxane

streching

860,

Smith

(ref.

796,

in sym700,

23) has re-

appears at 1412 cm-l in -1 . in trimethylsilyl groups

vibration that

groups),

1260 (C-H

streching),

1454 and 1415 cm

symmetric

shows

in CH3 groups).

in CH3 groups),

the reference of

at

1020 (Si-0

deformation and at

appears

the plasma chains

at

1260 cm-l

polymers

with

prepared

branches

of tri-

moieties.

Table

2 shows

the

critical

surface

from

TMS, TMVS, ETMS, HMDSO,

from

HMDSO

possessed

methylsiloxane) which

1087,

in CH3 groups)

asymmetric

From

polymers

1454, 1408 (C-H asymmetric

peaks

deformation

groups),

((CH3)2Si-)

that

groups.

poly(dimethylsiloxane) plasma

symmetric deformation -1 (C-H deformation

absorption

asymmetric

deformation

groups

and The

799, and 686 cm

in CH3

(C-H

HMDSO U.S.A.).

in CH3 groups),

shows

1410 (C-H

deformation

Inc.

1257 (C-H

841,

poly(dimethylsiloxane)

metric

from

System

groups),

streching),

CH3 groups),

from

prepared

Petrach

at 2960(C-H

of

1044 (Si-0 While,

from

peaks

deformation

polymers

This table

a surface

(22.1

contained

mN/m).

nitrogen

indicates

energy

The

moieties,

that

these

energy

of the

and BDMAMVS. of

plasma

polymers polymers

19.6

mN/m

polymers

possessed

plasma

plasma

The plasma

higher

polymers

comparable

prepared

surface

possess

from

energy

hydrophobic

prepared prepared to

poly(di-

BDMAMVS,

of 34.1 mN/m. surfaces.

TABLE 2 Surface

energy

of plasma Surface

Monomers

energy

Surface

energy

Pervaporation The

24.2 29.6 29.3 19.6 34.1

Y,

23.6 29.2 21.3 17.3 22.0

0.6 0.4 8.0 2.4 12.1

of Nuclepore

polymers

membrane

experiments. on

( Y,) = Y sd

with plasma

plasma

pervaporation

Nuclepore of

(mN/m)

Y,d

YS

TMS TMVS ETMS HMDSO BDMAMVS

polymers.

+ Y sp

polymer prepared

(pore

size

membrane ethanol-water

membranes from

HMDSO

were

deposited

15 nm) and used as membranes itself,

as shown

solution.

The

in Fig. permeants

on the

surface

for pervaporation

4, had through

no influence Nuclepore

473

0

10

20

Ethanol Concentration

30

in Feed (wt%)

Fig. 4. Permeant composition through as a function of feed composition.

membrane

had

concentration

the of the

the azeotropic Fig. the

5 shows

feed

solution

typical

(a)

factor

varied

results of

was

indicating

plasma

films

increasing

the

near

20 wt%

ethanol.

including

silicon

plasma

films

lost

ration

of 4 wt%

as a function out

at

ethanol

and fluorine that

the

34, and 41 nm thick of the

thin

ethanol possessed

ethanol

even

size,

when

15 nm)

the

ethanol

This indicates

that

ethanol

film

prepared the

that

solution

from

composite

depended

using

HMDSO.

The

membrane

strongly

composition.

concentration

A similar

feed

of the

in pervaporation

an

The separation

of the

dependence

is

on the thicksolution, separation

using other

memb-

polymers. plasma

films

showed

selectivity:

For

a separation

factor

solution,

concentrations

of ethanol-water

factor

feed composition has been observed

It is of interest

(pore

0 to 100 wt%.

as well as the feed

with

ranes

solution

polymers

The separation

decreased

on the

from

plasma

and became unity factor

feed

in pervaporation

the 4.5,

membrane.

ness of the deposited

as the

membrane

occurred.

membranes

ethanol-selective factor

composition

pervaporation

composite

separation

same

Nuclepore

respectively.

thickness.

The

ethanol

example,

the

plasma

but films

thick of 27,

of 4.5, 3.1, and 1.0 in pervapo-

Fig. 6 shows pervaporation

of 4 and 8 wt%.

selectivity

The

the

separation

experiments separation

were factor

factor carried increased

474

4

0

5

10

15 20

25 30

Ethanol Concentration in Feed

(wt%)

Fig. 5. Separation factor Ca, (),a ) and flux (A, 0, n ) as a function of ethanol concentration in feed; plasma film thickness de osited on Nuclepore, 27 nm thick, A , A ; 34 nm thick,0 , l ; 41 nm thick, 0 , 4.

:,A, :;,

’

57

0

0

10

20

30

40

50

100

200

300

400

Plasma Film Thickness (nm> Fig. 6. Separation factor in pervaporation nol, 0, 0 and 8 wt%, A 1 as a function size 15 nm; 0, 30 nm. with

increasing

4 wt% at

ethanol

used

film

thickness,

reached

and 3.8 at 8 wt% ethanol),

41 nm thick.

another was

the

of ethanol-water of plasma film

Nuclepore

A similar having

as a substrate

effect

a larger (Fig.

6).

of the pore The

a maximum and afterward

size

film

thickness

solution thickness;

at

34 nm thick

decreased could

of 30 nm instead

separation

factor

(4 wt% etha0, A, pore

was

rapidly

(4.5

at

to unity

be observed

when

of 15 nm pore

size

maximized

at

200

475 nm thick

and was

producible

evidence

from

HMDSO

maximum could

the

independent

of

thickness

also

showed

separation

the

factor

and

effect

substrates.

other

ETMS (a = 4.5),

ethanol the

The

is not

selectivity.

surface

haphazard

plasma

and

films

of

the

prepared

BDMAMVS

A relationship

energy

but re-

(a = 2.1)

between

deposited

the

plasma

films

were

com-

not be observed. The performance

pared

with

rate

for

sited for

Therefore,

(a = 1.5), TMVS (~1 = 3.4),

TMS

besides

3.1.

those

our

on

composite

Nuclepore,

pervaporation The

polymers

tributes

from

10 to

and

hydrophobic

plasma 0.46

solution,

in this

The table

and permeation

HMDSO and depo-

been

in the

separation and the

permeation

3 summarizes

have

listed

The

study

and the

from

Table

which

properties,

factor

prepared

membranes

10-2 kg/m’-h. ability

films

kg/m’-h.

surface.

on polymer

formed

The separation

ethanol-selective

of 3.0 to 25 depending

yet good in separation

4.5

ethanol-water

with

membrane

membranes.

membrane, was

of

investigators. fluoro

of the composite

of other

table

factor

are

that

by many silicon

is in the

permeation

indicates

membranes

prepared

rate

widely

our membrane

or

range dis-

is not

rate.

TABLE 3 Performance

of membranes

Membranes

Ethanol cont. in feed(wt%)

Plasma films from HMDSO Styrene-dimethylsiloxane copolymer Styrene-fluoroalkyl acrylate graft copolymer Polydimethylsiloxane block copolymer Poly[l-(trimethylsilyl)1-propyne] Zeolite-filled silicon rubber Gore-Tex *:

in pervaporation

of ethanol-water

Separation factor

solution.

Flux (kg-m/m*-h)

Reference

0.46*

ours 12

4

4.5

7

3.1-25

l.l-2.7~10-~

8

16.3-45

0.6-l.l~lO-~

24 -6

10

5.7-9.4

1.1-5.6x10

10

11.2

1.15x1o-3

25

5-5.5

14.9-16.5

3.6-5.1~10-~

26

a

3-5.5

3.3-6.1

27

13

in kg/m’-h.

DISCUSSION

The separation interpreted

in understanding rate,

but

especially

process

by the does the

in pervaporation

sorption-diffusion membrane

not

completely

film-thickness

model.

behaviors

such

explain effect

of ethanol-water The concept as

ethanol

characteristics

as illustrated

solution of the

is frequently

model

selectivity

and

of our composite Fig.

6.

Why does

the

is helpful permeation membrane, separation

476 factor

reach

the maximum

Firstly, banes

we discuss

porous

complete

at 34 nm thick?

or

plugging

films

about

result

into

the

non-porous of pores

five

times

pores

ments

showed

which

was

the

about

lo3

times

of membrane

as thick

consideration

to plug the

membrane

membranes?

of Nuclepore

that

the

same

when

the

composite

membranes

nm may be not non-porous

The surface concentration, 69.56

mN/m

and 28.93 tension

by

tension

especially (water),

mN/m the

at

Preferential Sorption

Fig. 7.

48.25

A tentative

less

model

(ref.

ethanol

Capillary Streaming

size.

15 nm). the

that

of plasma

Taking

Sakata’s

may be a critical

thickness

Permeation composite

pervaporation

with

with

solution 20 wt%.

at

8 wt%

30).

experimembrane

experiment

Therefore

became

polymers

than

34

35.50

adsorption

on the

ethanol

at

40 “C is

tension mN/m

with composite

at

decrease of

ethanol

Evaporation

for pervaporation

conclude

thinner

strongly

surface

an exponential

the

we

micropores.

depends The

ethanol,

Such

suggests

thick.

plasma

membranes

than

mN/m

of

pore

mem-

reported

the deposition

across

the

41 nm

deposited

of ethanol-water

41.6 wt%

addition

at

but porous

at

rate

for

permeation rate was 1 x -5 3 x 10 cms(STP)/cm’-see-cmHg

that

size,

our composite

deposition was over 34 nm thick. Actually, the -2 10 cm’(STP)/cm*-set-cmHg at 27 nm thick

nitrogen and

(pore

as used

the

requires

membrane

permeation

specimen

less

28,291 has

(refs.

of 34 nm thick

membrane

nitrogen

Are

Sakata surfaces

as the

the deposition

construction.

membranes.

19.6 wt%, in surface molecules

477 at

the

31)

interface

have

ethanol-water of

at the

On the

membranes

have

are

then

basis

separation

at the

above

using our composite

stage

(ref.

at

flow)

for

the

would

preferetial it

be

is

assumed

and ethanol-water

propose

out.

model

The composite

in size.

Ethanol

of the

micropores,

wall

The separation

micropore.

reverse

a tentative

(Fig. 7).

molecules

hydrophobic

The concept

size.

and

Consequently,

membrane

membranes

the wall of the

(ref.

materials

with the solution.

to two the

co-workers

assumed

molecules

we could

evaporated

micropore

ferential-sorption-capillary Sourirajan

consideration

comparable

onto

to the

ethanol

contacted

of the

are

and

surface.

of our composite

process

molecules

adsorption

may be related

of

and

membrane

hydrophobic

adsorption

adsorbed

Morimoto

between

calorimetry,

membrane

micropores

adsorbed

solution.

the

the surface

predominantly

the

at

similar

between

the

interaction

immersion

when the composite

for the

and

molecules

that

interface

cules

from

ethanol

unreasonable

solution

air the

solution

adsorption not

between

discussed

mole-

operates

and mainly

The film-thickness is similar

osmosis

to the

membranes

effect

model

(pre-

proposed

by

32).

CONCLUSION The like

plasma

pervaporation process

restriction

is favorable

reaction

the plasma

process

and

of ethanol-water

The

1. The

polymerization

poly(dimethylsiloxane),

chamber

the

the

to

were

obtain

applied

of silicon

during

moieties

electrode

films for

as follows.

plasma

of the

structure

for preparation

plasma

as membranes

are summarized

irradiation

triode

and is available

investigated films

Results

plasma

homogeneity with

irradiation

was

formed

solution.

of

for

the

polymerization

formed

restricts

of plasma

polymers.

influences

films

of

like poly(di-

methylsiloxane). Films

2.

plasma-polymerized

from

poly(dimethylsiloxane)

in spectroscopic

chains

of

with

branches

trimethylsilyl

hexamethyldisiloxane

view

and

are

(HMDSO)

composed

groups.

The

surface

from

HMDSO

and

resemble

of dimethylsiloxane energy

for

the

films

is 19.6 mN/m. The

3. membrane

show

The separation tion.

The

factor

reaches 4.

ranes wall

films

good ethanol-selectivity factor

molecules

depends

film-thickness

A tentative micropores are

on the

effect

in pervaporation film

thickness

deposited

on Nuclepore

of ethanol-water

as well

as the

is maximized

at 34 nm thick,

the

separation

process

adsorption

of ethanol

solution.

feed

and the

composiseparation

4.5.

is proposed. of

plasma-polymerized

model

for

The preferential of

evaporated.

the

composite

membranes,

The separation

onto the wall of the micropores.

operates

and

using

our composite

molecules then

mainly

the at the

occurs

adsorbed adsorption

membat

the

ethanol stage

478 REFERENCES

4

5

6

7

8 9 10 11

12

13 14 15 16 17 18 19 20 21 22 23 24

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