In Situ Investigation Of The Formation Process And Mechanism Of Poly(Ethylene-co-vinyl Ethylene) Membranes Using An Ultrasonic Technique

Phase inversion is the main method of making polymer membranes. At present, most polymer membranes such as reverse osmosis, ultrafiltration and microfiltration were produced by phase inversion method. But there is lack of in situ real-time monitoring methods of the membrane process. In this work, in situ investigation of the formation process and mechanism of poly(ethylene-co-vinyl ethylene)(EVAL) membranes was studied using an ultrasonic technique.The effects of the EVAL concentration and the coagulation temperature on the phase inversion in the water/dimethyl sulfoxide(DMSO)/EVAL system were investigated. The membrane structures and performance were analyzed by SEM and purewater flux. The ultrasonic signals shifted ahead slower in the arrival time-domain as the EVAL concentration increased. It implies that the membrane inversion rate is slower. At the same time, the membranes obtained have a denser structure and lower purewater flux. Furthermore, the ultrasonic signals in the time-domain delayed a few seconds and then shifted ahead as the process of EVAL membrane formation. It suggests that the phase separation is delayed and the inversion rate becomes slow. The membranes obtained have a loose structure and high purewater flux.The effects of the 1-octanol concentration and the coagulation temperature on the phase inversion in the quaternary water/DMSO/1-octanol /EVAL system were also studied. The delay and shift ahead of ultrasonic signals in the time-domain are observed in the presence of 1-octanol and high coagulation temperature. It is related to the delay of the phase inversion of EVAL membranes. The ultrasonic signals in the time-domain delayed more obviously as an increase of 1-octanol concentration and coagulation temperature. It means the delay time of demixing is long, the phase inversion rate is slow. The asymmetric structure of the membrane disappears and symmetric EVAL membrane is formed. It is found that the purewater flux of the EVAL membrane increases and its rejection of the bovine serum albumin (BSA) rejection decreases as the 1-octanol concentration and coagulation temperature increase.Overall, the ultrasonic technique can detect the process of polymeric membrane formation and its phase inversion rate, it provides a new method on the study of themechanism of polymeric membrane formation.