Effect of Plasma Treatment on Polymer Track Membranes

Full Paper

S796

Effect of Plasma Treatment on Polymer TrackMembranes

Lyubov Kravets,* Serguei Dmitriev, Gheorghe Dinescu, Andrada Lazea,Veronica Satulu

The effect of plasma treatment on the properties of poly(ethylene terephthalate) trackmembranes has been investigated. The influence of plasma treatment conditions and com-position of plasma-forming gas on basic membrane characteristics–pore size and shape,wettability, hydrodynamic, and electrochemical properties–were studied. It is shown thatthe plasma treatment of membranes can significantly improve their performance character-istics and give them a lot of useful properties.

Introduction

The membrane filtration is one of the most promising

technological separation processes for complex mix-

tures.[1] Of the materials used for this purpose, an

important part is played by track membranes (TM)

obtained by the irradiation of polymer filmswith energetic

heavy ions and subsequent etching of tracks of these

particles up to the through pores.[2,3] Owing to some

properties such as the small thickness and high uniformity

of pores, TM exhibit insignificant flow resistance to a feed

stream, high permselectivity, low adsorption of solutes,

and easy regeneration. All these properties are to the

advantage of TM as compared with other filtration

membranes and responsible for their wide use in

medicine, biotechnology, and other engineering areas.

The manufacturing technology of TM has recently

begun to develop a new line, the surface modification of

membranes, which is meant as a directed change in the

composition and structure of the surface layer aimed to

improve the membrane properties. There are various

methods formodification of polymermaterials by physical

and chemical means.[4] Plasma treatment is superior to

other methods, as it allows a wide variety of both non-

L. Kravets, S. DmitrievJoint Institute for Nuclear Research, Flerov Laboratory of NuclearReactions, Joliot-Curie Str. 6, 141980 Dubna, RussiaFax: (þ7)-49621-28933; E-mail: [email protected]. Dinescu, A. Lazea, V. SatuluNational Institute for Laser, Plasma and Radiation Physics, Ato-mistilor Str. 111, 77125 Magurele, Bucharest, Romania

Plasma Process. Polym. 2009, 6, S796–S802

� 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

polymerizing in plasma gas (inorganic compounds) and

plasma polymerizable compounds to be used–organic,

elementorganic, and some inorganic compounds (for

example, silane). New properties of the membranes

produced in this way mainly depend on a type of the

chemical compounds used for modification.

The main processes at the effect of non-polymerizing in

plasma gas (for example, air) on track membranes from

poly(ethylene terephthalate) (PET) are gas-discharge etch-

ing of a polymeric matrix and its hydrophilization.[5] It has

been shown that the gas-discharge etching of TM in the

plasma causes of both increase in the pore diameter[6] and

decrease in the a mass part of the low-molecular products

in the membrane.[7] The observed process of hydrophiliza-

tion of the TM surface on exposure to a gas-discharge is

related to the formation of functional, in particular

carboxylic, groups.[5] The appearance of COOH groups

can be explained by the oxidation of the end groups

formed at the break chemical bonds due to the active

plasma particles effect.

The main process at the treatment of materials by

plasma polymerizable compounds is a deposition of the

film onto their surface.[8] The plasma deposition of a thin

polymer layer onto the surface of microfiltration mem-

branes is of particular interest for improving their

performance characteristics. Depending on the duration

of the plasma treatment, one can obtain membranes for

microfiltration, ultrafiltration, and reverse osmosis.[5] In

the last case, a thin semipermeable layer that fully covers

the pores is deposited on the membrane surface. The

possibility of adjusting the thickness of the polymerized

DOI: 10.1002/ppap.200932002

Effect of Plasma Treatment on Polymer Track . . .

layer and the wide range of organic compounds for

producing the membranes of this type make this method

very promising. So, using carbohydrates (cyclohexane, for

example) as a plasma-forming gas, a thin polymer

chemically stable film is formed on the surface exposed

to plasma of not possessing functional groups.[5] This

provides a way for producing hydrophobic composite

membranes possessing a chemical strength. While depos-

iting the polymer film from the discharge to hexamethyl-

disilazane, the membranes having bactericide properties

are formed.[5] A positive or negative charge appearing due

to the introduction of the functional groups is one more

thing allowing one to regulate the membrane character-

istics. For instance, the use of dimethylaniline[9] or acrylic

acid[10] as a plasma-forming gas serves as a basis for

creation of hydrophilic composite membranes. The use of

allyl alcohol as a plasma-forming gas allows one to

improve the hydrodynamic characteristics of the track

membranes.[11] Improvement of hydrodynamic properties

of the membranes formed at treatment of track mem-

branes in non-polymerizing gas plasma is observed, when

introducing cyclohexane in the composition of the plasma-

forming gas.[12]

In this paper, we investigated some new processes of

modification of the properties of track membranes from

poly(ethylene terephthalate) by RF-discharge in non-

polymerizing gases and plasma polymerizable com-

pounds.

Experimental Part

The object of the investigation was PET TMwith a thickness of 9.5

mm and an effective pore diameter of 215 nm (pore density was

2�108 cm–2). In order to produce themembrane, the PET filmwas

irradiated with krypton positive ions, accelerated at �3 MeV/

nucleon in the cyclotron U-400, and then subjected to the

physicochemical treatment on a standard procedure.[3] The pores

of this membrane are cylindrical channels, the cross-sections of

which are practically independent of the depth.

The treatment of the membrane samples and the deposition of

the polymer from organic compounds were performed in a

plasma-chemical setup realizing a RF discharge in parallel plate

configuration at the frequency of 13.56 MHz. Details on the

treatment procedure and the scheme of the plasma reactor set-up

are described previously.[10] The plasma treatment time and

discharge parameters were varied. Only one side of themembrane

was subjected to the plasma treatment.

The characteristics of the source and plasma modified

membranes were determined through a series of complementary

procedures. The amount of the polymer obtained by plasma and

graft polymerization on the membrane surface was defined by

relation [Equation (1)]:

Plasma

� 2009

Qg ¼ ðmg �moÞ � 100mo

(1)

Process. Polym. 2009, 6, S796–S802

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

where mo is the mass of source membrane and mg is the mass of

membrane with the polymer layer obtained by plasma poly-

merization or plasma-induced graft polymerization methods. The

study of the samplesmicrostructure aswell as the definition of the

pore diameter on the membrane surface was conducted by SEM

using the JSM-840 (JEOL) with the resolution of 10 nm. Before

scanning, a thin layer of gold was deposited by the thermal

evaporation of metal in vacuum. The change in the membrane

thickness was measured with an electronic counter of thickness

Tesa Unit (Austria), the precision of themeasuring being�0.1 mm.

The gas flow rate through the membranes–a flow of gas (air)

passing the membrane with a square 1 cm2–was defined at a

pressure drop of 104 Pa. Gas consumption was measured by a

float-type flow meter. On the basis of the values obtained

according to these experiments the gas-dynamical pore diameter

(an effective pore diameter) was determined. For calculation, we

used the Hagen–Poiseuille equation.[1] The error of measurements

at definition of the effective pore diameter was not more than 3%.

The water contact angle (as the sessile drop method) was

determined with a horizontal microscope equipped with a

goniometer. Six measurements were made at different places

on the membrane surface and averaged, the measurement

accuracy was �18. Permeability experiments for water solutions

with various pH values were carried out with the help of the

standard filtration installation FMO-2 (Russia) on membrane

samples with the area of 254 mm2. Before filtration, the

membranes were maintained in a relevant solution during

20 min. Then the prepared membranes were mounted on a cell

and placed below a water reservoir. Water was allowed to flow

through the membranes under the air atmosphere. The pH of the

permeating solutionswas adjusted by adding diluted hydrochloric

acid or sodium hydroxide. The water flow rate was determined by

measuring the volume of water solution that was able to pass

through the membrane per minute. Prior to each measurement,

the membranes were equilibrated with the test solution under

pressure until a stable flux was achieved with the difference

between two subsequent readings of less than 5%. Measurements

of the current–voltage characteristics of membranes were carried

out on a direct current in a two-chambered cell with Ag/AgCl

electrodes, containing awater solution of potassium chloride (KCl)

of identical concentration on both sides of the membrane. The

volume of each chamber was 2.5 ml, the working area of the

membrane was 0.5 cm2. The concentration of the solution was

varied. Each point of the measurement corresponded to the

average value of the current during first 5–10 s. Before the

measurements, the membrane samples were maintained in a

corresponding solution of electrolyte during 1 h.

Results and Discussion

The performed research on the effect of the plasma

discharge on the track membranes allows one to establish

the following rules. One of the basic processes at the

treatment of membranes in the non-polymerizing gas

plasma is the gas-discharge etching of the polymer matrix

which is accompanied by the reduction of the membrane

thickness and increase of the pore size (Figure 1b). The

www.plasma-polymers.org S797

L. Kravets, S. Dmitriev, G. Dinescu, A. Lazea, V. Satulu

Figure 1. Electronic micrographs of the surface of the source PET TM (a) and membranetreated by air plasma for 600 s at a gas pressure of 0.26 Pa and discharge power of100 W (b).

S798

treatment of TM in the RF discharge plasma thus can be

used as amethod of pore etching. A detailed research of the

process of pore etching in the plasma shows that its rate

depends on the discharge parameters–increase in the gas

pressure and discharge power lead to increase in the etch

rate (Table 1). The etch rate also depends on the plasma-

forming gas composition. So, introducing oxygen into the

plasma-forming gas and increasing its concentration lead

to increase in the etch rate (Table 1). The use of pure oxygen

as a plasma-forming gas allows one to increase essentially

Figure 2. Electronicmicrographs of themetallic replicas from the pores of the source PETTM (a) and membrane treated by air plasma for 600 s at a gas pressure of 46.5 Pa anddischarge power of 300 W (b).

the etch rate and to intensify the process

of the gas-discharge etching. This makes

the process of gas discharge etching

more intensive.

The treatment by plasma of a non-

polymerizing gas (any from nitrogen, air,

or oxygen) causes change in the shape of

track membrane pores. As the results

show, the effect of the non-polymerizing

gas plasma on track membranes leads to

the formation of asymmetric track

membranes–the pore shape of the mem-

Table 1. Changing characteristics of the PET TM at the plasma treatment for 300 s.

Plasma-

forming

gas

Treatment regime Relative increase

in the effective

pore diameter

Poros

Gas pressure Discharge power

Pa W % %

– – – – 7.

Nitrogen 9.3 200 6.5 8.

Nitrogen 22.6 400 10.8 8.

Air 22.6 200 15.4 9.

Air 22.6 400 18.2 10.

Oxygen 22.6 400 22.7 10.

Oxygen 46.6 400 27.3 11.



branes formed during discharge etching

changes (Figure 2b). It is the basis for the

creation of asymmetric TM. Thus,

depending on the choice of discharge

parameters, it is possible to reach etching

conditions either in part of the channel

or along the whole length of the pore

channels. In both cases the track mem-

branes with a higher flow rate are

formed. The membranes in which only

a part of the pore channels was etched in

plasma are of special interest. As a result

of the gas-discharge etching in a layer of

such membranes, cone-shaped hollows

are formed thus increasing the volume porosity. The layer

not affected by plasma etching, whose structure remains

the same, will determine the separation properties of the

membranes. The use of such membranes allows one to

raise the effectiveness of the filtration processes. The

length of the conical parts of the pore channels and the

length of the unaffected layer can be checked by changing

the discharge parameters. This provides a way for

producing a wide variety of track membranes with

different characteristics.

ity Initial water

flow rate at

DP¼ 7T 104 Pa

Water contact

angle

ml/min cm2 Deg

2 4.25 65

2 5.50 50

5 6.10 45

7 8.43 35

1 9.15 30

9 11.25 25

8 13.10 20

DOI: 10.1002/ppap.200932002


Figure 3. pH dependence of flow rate for the: (a) source PET TM and the membranemodified in air plasma for 120 s at a gas pressure of 13.5 Pa and discharge power of300W; (b) composite membranes with the grafted layer of poly(acrylic acid) and poly(2-methyl-5-vinylpyridine).

The other processes proceeding at

treatment of TM by non-polymerizing,

in particular oxygen-containing, gas

plasma and caused by occurring destruc-

tion of polymer macromolecules are

hydrophilizationofmembrane superficial

layer and formation of radicals in it. The

surface hydrophilization is a result of

formation of the carboxylic groups. The

appearance of COOH groups is explained

by theoxidationof theend groups formed

at the break of chemical bonds. Besides,

theeffectofnon-polymerizinggasplasma

causes a morphological change in in the

surface relief (Figure 1b). Numerous craters appear the

initially smooth membrane surface and it gets rough. This

phenomenon is explained by different etch rates in plasma

for crystalline and amorphous regions. If varying the

treatment conditions and duration, the sizes of the crates

change too. The development of the erosion of the

membrane surface and their hydrophilization result in

increasingtheTMwettability.Thevalueofthewatercontact

angleessentiallydecreases, thussignificantly improvingthe

performance characteristics of the membranes. Change of

the discharge parameters influences the size of limiting

value of water contact angle (Table 1). So, the reduction of

plasma-forming gas pressure and increase in the discharge

power promote the achievement of a smaller value ofwater

contact angle. However, as the results of research show the

wettability of the membrane surface achieved by the gas-

discharge treatment decreases at storing the samples on air:

the value of the water contact angle for all modified

membrane growswith the course of time. This is stipulated

by the relaxation processes causing re-orientation of

functional surface groups in the volume of the polymer

matrix. Nevertheless, even three months after the plasma

treatment, the surface of the membranes remains hydro-

philic. For example, for the membranes modified by air

plasma after storing the samples the water contact angle is

less 458, i.e., 30% lower than that of the source membrane.

The increase in the membrane porosity causes increase

in its productivity: the initial water flow rate of the

asymmetric membrane is higher than the source one

(Table 1). The detailed research in the hydrodynamic

characteristics of themembranemodified by plasma of the

non-polymerizing gas shows that its permeability depends

in a greater degree upon the pH of the filtered solution in

comparison with the source membrane (Figure 3a). It is

explained by changing the properties of the membrane

surface layer. So, according to Figure 3a, thewater flow rate

G is equal to [Equation (2)]

Plasma

� 2009

G ¼ A� B � pH (2)

Process. Polym. 2009, 6, S796–S802

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

where A and B are constants defined by the nature and the

structure of the membrane surface layer. Parameter A

corresponds to the flow rate of the membrane for

[Hþ]¼ 1 mol � L�1, and B characterizes the conformation

mobility of the macromolecule chains of the surface layer

of the membrane.[13] The calculated values of parameter B

for the membranes under study are equal to 3.0� 10�2 for

the source membrane and 8.2� 10�2 for the modified one.

The greater significance of B for the membrane treated by

plasma specifies a larger conformation mobility of the

macromolecule segments of the polymer. This stipulates

an easier re-orientation of the surface carboxylic groups in

a water solution. The conformation stability of polymer

macromolecules of the membrane surface layer is

determined by the pH value of the solution. It is connected

to a degree of ionization of the carboxylic groups. For

example, in the acidic medium the dissociation of surface

COOH groups is suppressed and the membrane goes to a

neutral stable form. As a consequence, the permeability of

the membrane remains at a high level. On increasing the

solution pH, there is a dissociation of COOH groups. The

dissociation grows with increase in the pH value. As a

result, on the membrane surface a negative charge

appears. The presence of the charge on the membrane

surface stimulates decreasing the initial water flow rate. A

similar dependence is also observed for the source

membrane, but it is expressed in a smaller degree. The

more significant changing of the flow rate for the

membrane modified by plasma is explained by a greater

concentration of surface functional COOH groups which

are formed during the plasma treatment.[8]

The radicals formed in the surface of the membranes at

plasma treatment allow one to perform the process of

polymer grafting. In this case, the composite membranes

so-called ‘‘smart’’ or ‘‘intelligent’’ with unique properties

can be prepared. That is, suchmembranes whose transport

properties can be regulated by changing environmental

conditions such as temperature, electrical, or magnetic

fields, solvent composition, solution pH, pressure.[14,15] As

our research shows, the graft polymerization of 2-methyl-



S800

5-vinylpyridine (MVP) or acrylic acid (AA) induced by the

air plasma on the PET track membrane surface leads to the

formation of the composite membranes, the water

permeability of which can be controlled by changing

the solution pH. These results can be explained by the

conformation transition of macromolecules of the grafted

polymer layer from an expanded state ‘‘coil’’ into a

compact state ‘‘globule’’, and vice versa. So, the research on

water permeability dependence on the solution pH of the

membrane with a grafted layer of poly(2-methyl-5-

vinylpyridine) with a grafting yield of 7.2% demonstrates

its abnormal behavior (Figure 3b). Note, in this case the

effective pore diameter decreases down to 160 nm. This

membrane is not penetrative in the region from 1 to 3 pH

at pressure drop up to 7� 104 Pa. If increasing pH, one can

observe a linear increase of the water flow rate. Such a

behavior of the membrane is explained by various

conformational states of grafted poly(2-methyl-5-vinyl-

pyridine) macromolecules which causes changing the pore

diameter. At low pH values of the solution due to

protonating the nitrogen atoms of pyridine groups, the

segments of the macromolecules of the grafted polymer

acquire a positive charge that results in its swelling –

formation of gel,[15] causing a membrane pore contraction.

The membrane pores are ‘‘closed’’ in this state (Figure 4a).

The macromolecules of poly(2-methyl-5-vinylpyridine)

have an extended conformation state ‘‘coil’’. Such a

conformational state of macromolecules resulting from

the electrostatic interaction of charged segments with

water molecules is permanent. It leads to the complete

contraction of pores in the acidic medium (pH from 1 up

to 3).

Increase of filtrate pH (the drop of ion concentration Hþ

in the solution) leads to the loss of the charge on the

nitrogen atoms, i.e. transition of segments of the poly(2-

methyl-5-vinylpyridine) macromolecules to a neutral

state. Therefore, the electrostatic interaction gets weaker.

With decrease in the Coulomb interaction, the non-

Figure 4. Schematic illustration of changing the conformational stamacromolecules on the track membrane surface. For the grafted layer5-vinylpyridine): (a) mediumwith low pH; (b) mediumwith high pH; fpoly(acrylic acid): (a) medium with high pH; (b) medium with low p



electrostatic interaction of hydrophobic groups, in this

case, of non-polar CH3– and CH2– groups increases.[16] That

results in a collapse of gel–transition of macromolecules in

a compact conformational state ‘‘globule’’. The membrane

pores are ‘‘open’’ in this state (Figure 4b) that leads to

increase in the membrane pore diameter; thus, its water

permeability increases. The grafting of poly(2-methyl-5-

vinylpyridine) on the PET TM surface induced by plasma

thus results in forming a composite mechanochemical

membrane, the permeability of which is controlled by

changing pH of the solution. For the membrane with a

grafting yield of 7.2% at pH¼ 3 one can observe change-

over to an operation mode of a ‘‘chemical valve’’ i.e. at

smaller pH values of the filtrate the membrane gets

impermeable for water molecules. At higher pH values of

the filtrate the membrane gets permeable for water

molecules. Clearly, the boundary value of pH solution

where the membrane changes for this mode will be

determined by the properties of substrate and the grafted

polymer layer.

The grafting of poly(acrylic acid) from a gas phase at

elevated temperature on the membrane modified by

plasma results in formation of a mechanochemical

membrane with ‘‘chemical valve’’ too. For the membrane

that has a grafting yield of Qg¼ 7.4% and effective pore

diameter of 190 nm at pH values more than 8 the full pore

contraction is observed due to negative charge on the

segments of the macromolecules of the grafted polymer

macromolecules resulted from the dissociation of car-

boxylic groups. This leads to swelling the polymer layer

and formation of gel. Such a conformational state of the

macromolecules leads to the contraction of pores. The

membrane pores are ‘‘closed’’ under this condition

(Figure 4a). Decrease in the filtrate pH leads to loss of

the charge on the segments of the grafted polymer

macromolecules. That results in a collapse of gel –

transition ofmacromolecules in a compact conformational

state. The membrane pores are ‘‘open’’ in this condition

te of the graftedof poly(2-methyl-or grafted layer ofH.

(Figure 4b) that leads to increasing the

membrane pore diameter; thus, its water

permeability increases. Thus, for the

membrane with a grafted poly(acrylic

acid) layer change-over to an operation

mode of a ‘‘chemical valve’’ one can

observe at pH¼ 8, i.e., at higher pH values

of the filtrate themembrane gets imperme-

able for water molecules. At smaller pH

values of the filtrate, the membrane gets

permeable for water molecules.

Deposition of the thiophene (Th)

plasma polymer layer on the PET TM

surface leads to the formation of com-

posite membranes that possess asym-

metry of conductivity in electrolyte

DOI: 10.1002/ppap.200932002


Figure 5. Current–voltage characteristics of source PET TM and the composite membranes with the PPTh layer in KCl solution withconcentration of 10�4 (a) and 10�3 mol�L�1 (b).

solutions–the effect of the current rectification. This effect

is similar to p–n transition in semiconductors. The ‘‘diode-

like’’ behavior of the modified membranes allows one to

use it as an electrical valve. Such a property can be

explained first of all that the formedmembranes have two

layers with an antipolar conductivity. Indeed, if the

polymer matrix of the source membrane is characterized

by the presence on the surface of cation-exchange

carboxylic groups. The surface of this layer has an average

hydrophilization level: the water contact angle of PET TM

is 658. In KCl (pH of which is 6.0) solutions there is a

dissociation of surface COOH groups. It leads to the

formation of anion segments on macromolecules of the

polymer. The presence of a negative charge on the

macromolecules segments causes swelling of a surface

layer of the membrane and formation of polyelectrolyte

gel.[15] The layer formed by the plasma polymerization of

thiophene (PPTh), as the research shows, contains an

anion-exchange sulfuric groups. However, the concentra-

tion of the anion-exchange sulfuric groups is very small. As

a result, this layer has a hydrophobic character. For the

membranes with a PPTh layer, the value of the water

contact angle is 888. Therefore, swelling this layer is

practically absent. The contact of those layers causes

asymmetry of conductivity for the composite membrane

in the electrolyte solution under the electric field (Figure 5).

Figure 6. Electronic micrographs of the surface of the PET track membranes treated bythiophene plasma for 60 (a) and 300 s (b).

It should be noted that the asymmetry of

conductivity for composite membranes

with a PPTh layer is observed only in the

case when a semipermeable layer of

polymer is formed that practically blocks

the pores on the surface of the source PET

TM. So, at plasma treatment of the

membrane for 60 s the thickness of the

deposited PPTh layer is quite small

(around 100 nm), and the pores are not

blocked (Figure 6a) and, as a conse-

quence, the asymmetry of conductivity

in the electrolyte solution does not arise

(Figure 5). On the contrary, at the plasma



treatment of the membrane for 300 s, on its surface a

semipermeable polymer layer with the thickness of

400 nm is obtained that almost completely blocks the

pores (Figure 6b). The pores of this layer have a pore

diameter at a level of 10–30 nm. Formembrane of this type

the asymmetry of conductivity is observed (Figure 5). The

size of this effect can be characterized by rectification

coefficient (kr) which is calculated as a ratio of values of the

current in two mutually opposite directions at a potential

of 1 V. The conducted research shows that the rectification

coefficient for themembrane treated by plasma for 300 s in

KCl solution with concentration 10�3 mol�L�1 is equal to

1.8, and in the solution with concentration 10�4 mol�L�1

is 1.5.

The appearance of the asymmetry of conductivity for

the membrane with semipermeable PPTh layer on the

surface can be resulted from the distinction of the

resistance of the system at changing the current direction.

So, under direct current reverse bias condition when the

PPTh layer of the membrane is inverted to the anode,

significant decrease in its resistance is observed. This effect

is connected with the reduction of pH solution at the

surface of this layer due to occurrence of a gradient of

concentration of ions Hþ and protonating of sulfur atoms.

The formation of the positive charge on the segments of

PPThmacromolecules leads to the essential swelling of this



S802

layer that promotes carrying the current. Under direct

current forward bias condition, at the surface of the PPTh

layer of the composite membrane which is inverted to

the cathode, the concentration of hydroxyl ions grows. The

protonating of sulfur atoms in this case does not take

place, and the absence of the charge on the segments of

the polymer macromolecules leads to the dehydration of

the layer and, as a consequence, to its collapse.[16] It causes

increase in the resistance of the system and, accordingly,

decreasing the current. One cannot exclude the fact that

during the plasma treatment of the source PET TM, having

cylindrical pores, in the process of deposition of the PPTh

layer, on its surface the pore geometry changes. The

membrane pores, as the research shows, get an asym-

metric (conical) form. The pore diameter on the untreated

side of the membrane does not change, and it essentially

decreases on the side subjected to plasma treatment. For

PET TM with the conical form of pores the effect of

asymmetry of conductivity is known and described in

detail by Siwy.[17] According to those results, the

asymmetry of conductivity is caused not only by the pore

geometry, but also by the presence of the gel phase in a

narrow part of the pore produced due to swelling of the

surface layer of the membrane. In our case, we cannot

exclude the influence of changing the pore geometry of the

membrane on their electrochemical properties. In other

words, the appearance of the effect of conductivity

asymmetry for PET TM with a semipermeable PPTh layer

on the surface can be caused both by the contact of two

layers having chemically different functional groups and

by changing the pore geometry.

Conclusion

Thus, the presented examples of research in the process of

the track membranes treatment by non-polymerizing

gases show that the plasma modification method can be

successfully applied to alter their properties, such as

wettability, hydrodynamic characteristics, and increase in

its productivity. The plasma-induced graft polymerization

of 2-methyl-5-vinylpyridine and acrylic acid can be used to

obtaining pH-responsive membranes. Besides, the deposi-

tion of polymer on its surface by the plasma polymeriza-

tion of thiophene can be applied for the formation of

composite membranes possessing the asymmetry of

conductivity in the electrolyte solution–a rectification



effect. The membranes with such properties can be used in

biotechnology and medicine. They can also be used for

controllable drug delivery, in biosensor control, for

modeling processes of regulation in the cell.

Acknowledgements: This work was supported by grants (No 06-02-90878 and No 08-08-12207) from the Russian Foundation forBasic Research.

Received: July 25, 2008; Revised: February 10, 2009; DOI: 10.1002/ppap.200932002

Keywords: non-polymerizing gas plasma; plasma polymerizablecompounds; plasma treatment; track membranes

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DOI: 10.1002/ppap.200932002

Effect of Plasma Treatment on Polymer Track Membranes

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