Two types of oil modified tips as force sensors to detect adhesion forces between oil and membrane surfaces in fluid

- A direct method to transfer a dichloroethane (about 75 μm) droplet and a hexadecane droplet (around 40 μm) onto the end of a AFM cantilever was shown.
- An indirect method which can control the external diameter of an oil droplet with the help of a polystyrene (PS) microsphere (10 μm) was proposed.
- The adhesion forces between two types of oil modified tips and various ultrafiltration membranes were compared utilizing AFM force curves.

The surface resistance to oil is very important for filtration efficiency, film cleaning and life span of ultrafiltration membranes. The atomic force microscope (AFM) has provided unprecedented opportunities to study interface interactions. In this paper, the probe with an oil droplet modified was used as a force sensor for evaluating the oil resistance of membrane surfaces. The adhesion forces between two types of modified tips and a serial of membrane surfaces in fluid was detected via force curves. On the one hand, the AFM probe with an oil droplet immobilized directly was used to study the adhesion forces between a series of PVF/F127 membranes and a hexadecane droplet. On the other hand, a tip attached polystyrene (PS) microsphere covered with a layer of oil was employed. It was found that the oil antifouling performance of membranes was improved effectively through blending F127 with PVF. As the F127 additive varied from 0% to 60%, adhesion force detected by the AFM probe with an hexadecane droplet immobilized showed a decreasing tendency from 2.84 nN to 0.73 nN. Meanwhile, the average interaction force detected by the second modified tip decreased from 3.39 nN to 0.54 nN. The measured force behavior was in agreement with experimental observations of contact angle measurement, which indicated that the blend membranes had better antifouling.

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