KR100307806B1 - Surface-Modified Polymer Membrane Using Ion Beam and Method for Surface Modification - Google Patents

Abstract

The present invention relates to a polymer membrane surface-modified hydrophilically using an ion beam and a method for surface modification thereof, wherein the polymer membrane is irradiated with an ion beam having an energy of 2000 eV or less while introducing a reactive gas into the surface of the polymer membrane. The present invention provides a method of surface modification of a polymer membrane and a surface modified polymer membrane, wherein the surface of the activated polymer membrane and the reactive gas react with each other to activate a surface to form a hydrophilic group.

Description

Surface-Modified Polymer Membrane Using Ion Beam and Its Surface Modification Method

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to surface modification of polymer membranes, and more particularly, to a polymer membrane surface-modified hydrophilically using ion beams and a surface modification method thereof.

The demand for polymer membranes is increasing from chemical and environmental, medical, biotech and food industries to the premise of selective separation and efficient material permeation.In recent years, the development of new membrane materials has been developed due to the rapid development of high-tech industries. This is being done vigorously.

The material of the membrane is a material having excellent permeation amount and selectivity. The molecular cut-off, which is an index indicating the limit of the molecular weight that can be filtered, is stable, and the pores formed in the membrane are uniform and uniform in size. It should be well distributed, good chemical resistance, heat resistance and fouling resistance and good mechanical strength.

In the field of membrane manufacturing, the research on the development of new membrane material and the regulation of membrane structure has been mainly studied until now, but the development of new membrane material and manufacturing process has been limited to the limit in the 1990s. Therefore, rather than modifying the surface of the membrane rather than using the advantages of the existing material has been actively researched to solve the problem. In particular, many polymer materials, which could not be used as membrane materials due to the limitations of the material properties themselves, are used as membrane materials through surface modification, and the limitations of existing membranes such as heat resistance, chemical resistance, and contamination resistance are limited. I can solve it. In addition, by modifying the surface of the membrane, the permeation rate, selectivity, biocompatibility, and the like can be achieved. In addition, various surface modifications have been made according to the purpose of use. Membranes subject to surface modification are membranes in almost all fields, such as gas separation membranes, reverse osmosis membranes, ultrafiltration membranes and microfiltration membranes, and permeation membranes.

These membranes are divided into hydrophilic and hydrophobic polymer membranes according to their surface properties. This is to filter the sample through the membrane, depending on the type of sample, for example, in an aqueous solution or in an organic solvent. The hydrophilic and hydrophobic membranes are each classified according to the type. If you want to filter the solute dissolved in water, you need a hydrophilic membrane.

In this case, the hydrophilicity and hydrophobicity of the surface of the polymer membrane are confirmed by a wetting angle with water. The contact angle is defined as the angle between the tangent and the surface of the membrane when it is tangent from the contact point of the surface of the membrane to the surface of the droplet. According to the above definition, a small contact angle means that the water droplets spread widely and thinly on the surface of the membrane, and thus means that the membrane has high adsorption to water, that is, hydrophilicity. The contact angle is determined by dropping 0.025 ml of the third distilled water drop into four positions on the surface of the membrane using a contact angle measuring instrument, and measuring the contact angle through a microscope to determine the average value of the measured values at four positions.

Conventionally, the method mainly used for surface modification simply impregnates the membrane with a surfactant and impregnates the surface and internal pores of the membrane, and then dries it to improve the hydrophilicity of the membrane. And a grafting method in which a monomer solution is applied to the surface and then copolymerized by UV irradiation or the like.

Among them, there are two major problems in the method using the surfactant. First is the solubility of the surfactant in water. That is, since the surfactant is dissolved in water, there is a problem that the reliability and reproducibility of the stable permeability of the membrane are inferior. Second is non-uniformity that occurs upon application of the surfactant. That is, since the surfactant is unevenly applied to the membrane, in particular, in the medical industry, such as protein separation, fouling occurs easily due to intensive adsorption of the protein to the portion where the surfactant is not applied.

The grafting method has the disadvantage of having to add polymer synthesis in a complicated process and expensive manufacturing cost.

Plasma is a method of forming a hydrophilic group by generating a plasma by low temperature glow discharge and then irradiating the plasma to the surface. At this time, it is difficult to control the energy of the plasma. Particles are irradiated onto the surface of the polymer to destroy the structure of the polymer membrane to change the molecular cutoff has a problem of lowering the characteristics of the membrane. In addition to plasma, there is also a method of using an energy ion beam of 1MeV or more or a medium energy ion beam of 5000 to 1MeV, which are generally considered to be high energy, and these devices need to accelerate the ion beam in order to obtain high energy. Area had a problem that is difficult to process.

Therefore, in the conventional method as described above, the molecular cutoff of the membrane is severely changed, and in particular, there is a problem of distorting the characteristic of the membrane by changing the size and distribution of the pores.

In order to solve the problems described above, the present invention provides a sulfon-based polymer compound, polystyrene, polyethylene, polyvinylidenfluoride, polyacryllonitride, cellulose acetate It is a polymer membrane made of one of acetate, polyimide, polyetherimide, aromatic polyamide, and polypropylene. The polymer membrane is irradiated with an ion beam having an energy of 2000 eV or less. It is an object of the present invention to provide a polymer membrane having a hydrophilic group that is not washed out by water by reacting the surface of the activated polymer membrane with a reactive gas while activating the surface.

In order to achieve the above object, the surface modification method of the polymer membrane according to the present invention activates the surface of the polymer membrane with the ion beam by irradiating an ion beam having an energy of 2000 eV or less while introducing a reactive gas into the polymer membrane surface. While reacting the surface of the activated polymer membrane with the reactive gas to form a hydrophilic group on the surface.

1 is a longitudinal sectional view showing a schematic configuration of a surface modification apparatus of a polymer membrane according to the present invention.

2 is a graph showing the change in contact angle of the polyethersulfone membrane surface with respect to the number of ions irradiated.

3 is a graph showing the change in contact angle of the polyethersulfone membrane surface with respect to the number of ions irradiated.

4a to 4d are photographs of the surface shape of the polyether sulfone membrane observed with a scanning electron microscope.

4A is a scanning electron micrograph showing the surface shape of a polyethersulfone membrane not surface treated with an ion beam.

4B is a scanning electron micrograph showing the surface shape of the polyethersulfone membrane after irradiation with an ion beam at an acceleration voltage of 300 V. FIG.

4C is a scanning electron micrograph showing the surface shape of a polyethersulfone membrane after irradiation with an ion beam at an accelerating voltage of 500 V.

4d is a scanning electron micrograph showing the surface shape of a polyethersulfone membrane after irradiation with an ion beam at an accelerating voltage of 1000 V.

5a to 5d are photographs of the surface shape of the polyether sulfone membrane observed with a scanning electron microscope.

5A is a scanning electron micrograph showing the surface shape of a polyethersulfone membrane not surface treated with an ion beam.

FIG. 5B is a scanning electron micrograph showing the surface shape of a polyethersulfone membrane after irradiation with 1 × 10 ¹⁵ particles / cm 2.

5C is a scanning electron micrograph showing the surface shape of a polyethersulfone membrane after irradiation with 1 × 10 ¹⁶ cells / cm 2.

5D is a scanning electron micrograph showing the surface shape of a polyethersulfone membrane after irradiation with 1 × 10 ¹⁷ particles / cm 2.

6a to 6c are graphs showing the results of XPS measurements on the surface of the polyethersulfone membrane, which are 1s of carbon, 1s of oxygen, and 2p of sulfur, respectively. × 10 ^15, the spectrum of the membrane after irradiated with an ion beam of 1 × 10 ¹⁷ gae / ㎠.

<Description of the symbols for the main parts of the drawings>

10: vacuum chamber 20: gas inlet

30: ion source 40: substrate holder

50: vacuum pump

Hydrophilic polymer membranes are difficult to manufacture and unstable in organic solvents, so most polymer membranes are made of hydrophobic polymers, of which polysulfone and polyethersulfone are representative materials of sulfone-based polymer membranes. The material of the membrane used for ultra-fine filtration is polystyrene, polyethylene, polyvinylidenfluoride, polyacrylonitride, cellulose acetate, Polyimide, polyetherimide, aromatic polyamide, polypropylene, and the like. As described above, the aforementioned materials are hydrophobic materials. When the polymer membrane is manufactured using these materials, the materials are hydrophobic, which is a property of the material itself.

Accordingly, a polymer membrane made of hydrophobic polymers as described above hydrophilic surface modified according to the present invention and a surface modification method thereof will be described with reference to FIGS. 1 to 6.

First, Figure 1 is a longitudinal cross-sectional view showing a schematic configuration of the surface modification apparatus of the polymer membrane according to the present invention, the device is a gas inlet 20 for introducing a reactive gas into the interior of the vacuum chamber 10, It consists of an ion source 30 for generating an ion beam having a and a substrate holder 40 for mounting a sample opposite thereto, and a vacuum pump 50 is provided to maintain a constant degree of vacuum in the vacuum chamber. .

In this apparatus, ion assisted reaction (IAR: Ion Assist Reaction, hereinafter referred to as IAR) is used. That is, the ion beam is irradiated onto the surface of the membrane to activate the surface to facilitate the reaction with the reactive gas, thereby assisting the reaction of the surface of the polymer membrane with the reactive gas. Important experimental variables at this time are the ionization rate of the ion source 30, the control of the ion beam energy and the amount of reactive gas. In particular, the ion source 30, first, the ionization rate should be adjustable, second, because the bond in the polymer is a variety of types must be adjustable from a low acceleration voltage to a high acceleration voltage, and third, must operate in a stable state for a long time Fourth, in order to increase the reliability of the surface-modified polymer, the ion beam must be uniformly generated.

One example of the ion source 30 in the present invention that satisfies the above conditions is a cold hall cathode ion source, which independently and precisely controls the energy of the ion beam and the number of ions reaching the substrate, respectively. There are features that can be done. At this time, the energy of the ion beam is obtained by applying an acceleration voltage to the formed ion beam, and the number of irradiated ions can be adjusted by adjusting the current of the ion beam. In addition to the cold hollow cathode ion source, there is a Kaufman type ion source, a radio frequency (RF) ion source, or a high frequency (HF) ion source. The ion beam density can be obtained in a low energy region. It is done. The ion generating gas used in the ion source as described above is selected from an inert gas and oxygen, nitrogen, carbon dioxide, carbon monoxide and mixed gas thereof.

In addition, the reactive gas is selected from oxygen, carbon dioxide, carbon monoxide, ozone, and a mixture thereof.

According to one embodiment of the present invention, a method of surface modification of a polyethersulfone membrane using the apparatus as described above will be described in detail.

First, the commercially available polyethersulfone membrane is stored in midstream for 3 days to completely remove the surfactant, and then mounted on the substrate holder 40 in the vacuum chamber 10, and the vacuum degree in the vacuum chamber 10 is 1 ×. Keep at 10 ^-5 Torr.

Next, oxygen is injected into the reactor through the gas inlet 20 around the polyether sulfone membrane, argon is injected into the ion source 30 as an ion generating gas, and the discharge voltage is 400-500 V. After generating an ion beam, an energized ion beam is irradiated onto the polyethersulfone membrane with varying acceleration voltages in the range of 2000 V or less. At this time, the number of ions irradiated to the substrate by adjusting the current of the ion beam is set in the range of 1 × 10 ¹⁴ to 1 × 10 ¹⁷ pieces per 1 cm 2 area. The experimental variables, that is, the degree of vacuum, the discharge voltage, the acceleration voltage, and the number of irradiated ions are obtained through experiments as values that are surface modified with hydrophilicity.

FIG. 2 shows the number of ions irradiated to the surface of the polyether sulfone membrane within the above range, the amount of oxygen is 6 ml / min, and the ions irradiated when the acceleration voltage is 300, 500, or 1000 V, respectively. Change in contact angle with respect to the number of.

As shown in FIG. 2, the contact angle of the polyethersulfone after surface modification with an ion beam in an oxygen atmosphere is decreased at 75 °, which is a contact angle before surface modification, and in particular, when irradiated with an ion beam of 300 V, an ion beam of 500 V or 1000 V is used. The decrease in contact angle is greater than in the case of irradiation. In addition, when the number of ions irradiated is 1 × 10 ¹⁵ / cm 2 or more, the contact angle increases, but is lower than the contact angle before surface modification, so that the surface-modified surface is hydrophilic in the range of 1 × 10 ¹⁴ to 1 × 10 ¹⁷ particles / cm 2. The effect can be obtained. The minimum contact angle was measured at 12 ° when irradiated with an ion beam of 300 V at an ion irradiation amount of 1 × 10 ¹⁵ ions / cm 2.

As described above, at 300 V, which is the acceleration voltage showing the minimum contact angle, the contact angle with respect to the number of ions irradiated on the surface of the polyethersulfone membrane when oxygen inflow is changed to 0, 4, 6, 8 ml / min. Is shown in FIG. 3.

As shown in FIG. 3, the decrease in contact angle is greater when oxygen is introduced, and the minimum contact angle is 12 ° at an ion irradiation dose of 1 × 10 ¹⁵ ion counts / cm 2 when the inflow of oxygen is 6 ml / min. Was measured. In addition, FIG. 3 illustrates the case of oxygen inflows of 0, 4, 6, and 8 ml / min, but the contact angle decreases at an oxygen inflow amount of 10 ml / min or less through the experiment. At this time, the oxygen inflow amount of 10 ml / min or less is a value determined by the size of the vacuum chamber and the size of the specimen used in the experiment. For example, larger specimens and larger vacuum chambers will require greater oxygen inflow.

Next, FIGS. 4A to 4D show the surface of the polyethersulfone membrane which has not been surface treated with an ion beam and the polyethersulfone membrane after irradiating 1 × 10 ¹⁵ pieces / cm 2 argon ion beams at acceleration voltages of 300, 500 and 1000 V, respectively. The image was observed by scanning electron microscope. 4B, which is the surface shape of the polyethersulfone surface-modified with a 300 V ion beam, is not different from that of FIG. 4A without surface treatment with an ion beam, indicating that the surface structure of the membrane was not damaged. On the other hand, in the case of surface treatment with ion beams of 500 and 1000 V, a partially aggregated shape is observed in FIG. 4C and 4D, in which a high energy ion beam irradiated to the surface collapses the structure of the membrane. The more severe the collapse of the membrane structure, the more deformed the molecular cut off of the membrane and the uneven pore size and distribution.

Next, FIGS. 5A to 5D show polyethersulfone membranes not surface-treated with ion beams, the energy of the ion beams is fixed at 300 V, and the number of irradiated ions is 1 × 10 ¹⁵ , 1 × 10 ¹⁶ , and 1 × 10 ^{17, respectively.} It is the photograph which observed the surface shape of the polyether sulfone membrane after surface-treatment with the number / cm <2> by the scanning electron microscope. 4B, which is the surface shape of the polyether sulfone surface-modified with an ion beam of 1 × 10 ¹⁵ ions / cm 2, is not different from that of FIG. On the other hand, agglomerated shapes are observed in FIGS. 4C and 4D, which are surface treated with ion beams of 1 × 10 ¹⁶ and 1 × 10 ¹⁷ ions / cm 2, and particularly, in FIG. 4D, excessively aggregated shapes are shown.

Therefore, from the above experiments, in the case of polyethersulfone membrane, it is necessary to adjust the acceleration voltage and the amount of irradiated ions to reduce the contact angle without changing the size and distribution of the molecular cutoff and pores which are inherent to the membrane. There is. At this time, the acceleration voltage and the amount of irradiated ions influence each other. That is, generally, when the acceleration voltage decreases, the structure of the membrane tends not to collapse even when the amount of irradiated ions is large compared to when the acceleration voltage decreases.

In addition, the acceleration voltage at which the structure of the membrane collapses and the amount of irradiated ions vary depending on the type of reactive gas.

As mentioned earlier, the decrease in contact angle is closely related to the formation of hydrophilic groups on the polymer surface, which was determined by performing XPS (X-ray Photoelectron Spectroscopy, XPS) measurement.

FIG. 6 is a XPS measurement result of the polyethersulfone surface. FIG. 6A is a 1s spectrum of carbon, FIG. 6B is a 1s spectrum of oxygen, and FIG. 6C is a 2p spectrum of sulfur. 6A to 6C show spectra for membranes before irradiation with ion beams in order from the peaks below and after irradiation with ion beams of 1 × 10 ¹⁵ and 1 × 10 ¹⁷ pieces / cm 2. As another experimental variable of surface modification, the acceleration voltage is 300 V and the inflow of oxygen is 6 ml / min.

In the 1s spectrum of carbon shown in Fig. 6a, a double bond of carbon and oxygen as a hydrophilic group in the membrane after surface modification with an ion beam of 1x10 ¹⁵ particles / cm 2 compared to the result of the membrane before irradiation with the ion beam , C = O bond) and the above-mentioned C = O bond and oxygen bond (hereinafter referred to as 0-C = O bond). When the ion beam of 1 × 10 ¹⁷ atoms / cm 2 is irradiated, the peak due to oxygen, that is, the peak due to the C═O bond and the OC═O bond, decreases and the carbon-to-carbon single bond (hereinafter referred to as CC bond) The main peak by is widened because of the overlapping peaks of amorphous carbon that adversely affect hydrophilicity. As a result, the amount of oxygen constituting the hydrophilic group was increased in the membrane after surface modification with an ion beam of 1 × 10 ¹⁵ cells / cm 2 compared with before the irradiation with the ion beam, and the membrane after surface modification with an ion beam of 1 × 10 ¹⁷ cells / cm 2. Decreased again.

In the 1s spectrum of oxygen shown in Fig. 6b, after surface modification with an ion beam of 1 × 10 ¹⁵ cells / cm 2, the spectrum was generated by the hydrophilic group C = O bond compared to before irradiation with ion beams, and 1 × 10 ¹⁷ cells / When the ion beam of 2 cm 2 was irradiated, the height of the peak was considerably reduced, indicating that the amount of oxygen was reduced. In addition, it can be seen that the peak due to the double bond with sulfur (hereinafter referred to as S = O bond) disappeared when 1 × 10 ¹⁷ particles / cm 2 of the ion beam was irradiated. At this time, since C = O binding energy and S = O binding energy are similar, it is difficult to distinguish between these two peaks. Therefore, the peak disappeared when 1 × 10 ¹⁷ / cm 2 ion beam is irradiated. The peak due to the O bond can be seen from the 2p spectrum of sulfur.

In the 2p spectrum of sulfur shown in Fig. 2c, the peak due to the bonding with oxygen, i.e., -SO ₂ -peak, almost disappeared when the ion beam of 1x10 ¹⁷ atoms / cm 2 was irradiated.

The amount of oxygen can be seen from the area of the spectra shown in FIG. Table 1 shows the amount of oxygen as the atomic ratio to carbon. The atomic ratio O / C represents the amount of oxygen obtained by dividing the area of the oxygen 1s spectrum shown in FIG. 6B by the sensitivity factor of oxygen based on the value before the ion beam irradiation, that is, the value before the ion beam irradiation. Value. S / C which is an atomic ratio of sulfur is also the value calculated | required by the same method.

As mentioned earlier, the atomic ratios O / C and S / C in Table 1 are the atomic ratios of oxygen and sulfur to carbon, respectively, from which the relative amounts of oxygen and sulfur contained in the membrane can be seen. The atomic ratio of oxygen, ie O / C, increased from 1.1 to 1 × 10 ¹⁵ / cm 2 ion beams before irradiation with ion beams, and then increased to 1.21 and surface modified with 1 × 10 ¹⁷ ion / cm 2 ion beams. Afterwards it can be seen that the decrease to 0.65.

Therefore, when the energy of the ion beam is 300 eV from FIG. 6 and Table 1, the hydrophilicity is improved after surface modification with an ion beam of 1 × 10 ¹⁵ pieces / cm 2, and surface modified with an ion beam of 1 × 10 ¹⁷ pieces / cm 2. Later it was found that the improved hydrophilicity worsened again. However, in finding suitable conditions for surface modification, the number of ions depends on the energy of the ion beam. For example, lowering the energy of the ion beam may improve the hydrophilicity of the surface even with a larger number of ions.

In the above, an example of surface modification of a polyethersulfone membrane generally used among polymer membranes by an ion assist reaction is disclosed, but the present invention is not limited thereto, in addition to a sulfone-based polymer including polyethersulfone, polystyrene, Polyethylene, polyvinylidenfluoride, polyacrylonitride, cellulose acetate, polyimide, polyetherimide, aromatic polyamide It is also applicable to the surface modification of membranes made of polymers such as polypropylene.

As described above, the polymer membrane surface-modified by the ion assist reaction has an effect of providing an excellent hydrophilic polymer membrane having a much lower contact angle than commercial polymer membranes.

In addition, by irradiating ions with an energy of 2000 eV or less, the surface structure of the membrane is not disrupted, thereby reducing the molecular cutoff and uniform pore size and distribution, which are inherent to the membrane.

In addition, when the experiment under the same experimental variable in the same experimental device, there is an effect excellent in reproducibility showing the same result.

Claims (7)

By irradiating an ion beam having an energy of 2000 eV or less while introducing a reactive gas to the surface of the polymer membrane, the surface of the activated polymer membrane reacts with the reactive gas to form a hydrophilic group by activating the surface of the polymer membrane with the ion beam. Surface modification method of the polymer membrane, characterized in that consisting of. The method of claim 1, wherein the reactive gas is one of oxygen, nitrogen, carbon dioxide, carbon monoxide, ozone, and a mixture thereof. The method of claim 1, wherein the ion source is one of a cold hallow cathode ion source, a Kaufman type ion source, a radio frequency (RF) ion source, and a high frequency (HF) ion source. A method for surface modification of a polymer membrane, characterized in that a high ion beam density can be obtained in a low energy region. The method of claim 1, wherein the number of ions reaching the surface of the polymer membrane is 1 × 10 ¹⁴ to 1 × 10 ¹⁷ per 1 cm 2 area. The surface modification of the polymer membrane of claim 1, wherein the hydrophilic group comprises at least one of a CO bond, a C═O bond, a (C═O) —O bond, a CN bond, and a C═N bond. Way. The method of claim 1, wherein the polymer membrane is a sulfone-based polymer compound, polystyrene, polyethylene, polyethylene, polyvinylidenfluoride, polyacryllonitride, cellulose acetate, Method of modifying the surface of a polymer membrane, characterized in that made of one of polyimide, polyetherimide, aromatic polyamide, polypropylene. Sulfonated polymer compounds, polystyrene, polyethylene, polyvinylidenfluoride, polyacrylonitride, cellulose acetate, polyimide, polyetherimide ( A polymer membrane made of one of polyetherimide, aromatic polyamide, and polypropylene. The polymer membrane is activated by irradiating an ion beam having an energy of 2000 eV or less to activate the surface of the polymer membrane and a reactive gas. A polymer membrane, characterized in that a hydrophilic group which is not washed out by water is formed on the surface by reacting.