플라즈마 처리된 폴리스티렌 막을 통한 순수한 CO₂와 N₂ 기체의 선택·투과 특성

Abstract

폴리스티렌 막(polystyrene membrane, PS)의 표면을 Ar, O2 플라즈마로 처리하고 처리 전후로 표면변화를 관찰하였으며, 막 표면을 FTIR-ATR, Contact angle, ESCA 와 AFM으로 분석하였다. CO₂, N₂의 투과도와 N₂에 대한 CO₂의 선택도는 연속흐름 기체 투과 분석장치(GPA)를 이용하여 측정하였다. 저온 플라즈마에 의해 처리된 폴리스티렌 막의 투과거동에 대한 처리시간, 출력세기, 가스주입 유량 및 반응기 내의 압력과 같은 플라즈마 처리 조건의 영향을 조사하였다. Ar플라즈마 처리의 경우 O/C비율이 0에서 0.179로 증가하고, 표면 거칠기가 15.86Å에서 71.64Å로 증가함으로써 접촉각은 처리전의 89.16°에서 18.1°로 감소하였다. 따라서 플라즈마 처리는 막 표면이 높은 친수성을 갖도록 만들었다. CO₂의 투과도와 선택도에 대한 Ar플라즈마 처리최적조건은 60W, 2min, 70℃이며, 투과도와 선택도는 각각 2.1×10^(-12)[m³(STP)·m/m²·sec·atm]와 4.51이었다. O₂플라즈마 처리의 경우에, 접촉각은 O/C비율(0.189)과 표면 거칠기(57.10Å)의 증가에 의해 13.56°로 감소하였다. 최적의 처리조건은 90W-2min-70℃이며, 값 7.1×10-12[m³(STP)·m/m²·sec·bar]와 값 11.5이었다. 플라즈마 처리 후 막 표면의 변화는 표면에서의 cross linking과 etching effect의 경쟁적인 관계에 의해 결정된다. 결국 플라즈마 처리된 막의 투과도와 선택도가, 플라즈마 기체, 처리시간, 출력세기등과 같은 플라즈마 상태를 제어함으로써 향상되었음을 확인할 수 있었다.; The surface of polystyrene membrane was treated by Ar, O₂ plasma. The surface changes was measured before and after the treatment, which was analyzed by means of FTIR-ATR, Contact Angle, ESCA and AFM. The permeability of CO₂, N₂ and selectivity of CO₂ relative to N₂ was measured using continuous flow gas permeation analyzer(GPA). The effect of plasma conditions such as treatment time, power input, gas flow rate and pressure in reactor on the transport properties of treated membrane was investigated. The mole ratio of O over C in the surface was increased from 0 to 0.179 with Ar plasma treatment and route mean square of surface was increased from 15.86Å to 71.64Å. Therefore the contact angle was decreased from 89.16° to 18.1°. Thus Plasma treatments made surface of membrane tend to be highly hydrophilic. The optimum condition for the CO₂ permeability and ideal selectivity of the plasma treated membrane was as follows: the measurement of Ar(60W, 2min, 70℃) plasma treatment was 1.14×10-12[m³(STP)·m/m²·sec·atm] and 4.22. In the case of O₂ plasma treatment, the contact angle was decreased at 13.56° with increase of O/C ratio(0.189Å) and route mean square of surface(57.10Å). The optimum condition for the CO₂ permeability and ideal selectivity of the plasma treated membrane was as follows: the measurement of O₂(90W, 2min, 70℃) plasma treatment was 7.1×10-12[m³(STP)·m/m²·sec·atm] and 11.5. After plasma treatment, the changes of membrane surface were all subtly linked with both cross-linking and etching effects. Finally, it was confirmed that the gas permeation capacity and selectivity of the modified membrane with plasma could be improved by an appropriate control of the plasma conditions such as treatment time, the power input and sort of plasma gas.