We present for the first time an experimental study on the droplet deformation induced by an AC electric field in droplet-based microfluidics. It is found that the deformation of the droplets becomes stronger with increasing electric field intensity and frequency. The measured electric field intensity dependence of the droplet deformation is consistent with an early theoretical prediction for stationary droplets. We also proposed a simple equivalent circuit model to account for the frequency dependence of the droplet deformation. The model well explains our experimental observations. In addition, we found that the droplets can be deformed repeatedly by applying an amplitude modulation (AM) signal.

Here, we synthesize zwitterionic polymer brushes on polyester fabrics by atom transfer radical polymerization (ATRP) after a prefunctionalization step involving an aminolysis reaction with ethylenediamine. Aminolysis is an easy method to achieve homogeneous distributions of functional groups on polyester fibers (PET) fabrics. Varying the polymerization time and the prefunctionalization conditions of the reaction, it is possible to tune the amount of water retained over the surface and study its effect on protein adhesion. This study revealed that the polymerization time plays a major role in preventing protein adhesion on the PET surface.Polymers 2020, 12, 6 2 of 15 interactions between a surface and a bacteria cell envelope [12]. In addition, steric hindrance plays an important role in avoiding protein adhesion, which is a reason why not all hydrophilic surfaces are able to prevent fouling [13][14][15]. Functionalization by polymers implies either a surface grafting of the polymer on a surface (grafting to) or a polymerization using a "grafting from" approach. The latter is often preferred when a better control over grafting density is needed [16][17][18][19][20][21][22][23].Among all polymers, polyethylene glycol (PEGs) and zwitterionic polymers proved to be highly effective against the adhesion of foulants, since several coatings that prevent the attachment of proteins and bacteria have already been synthesized [24,25]. PEG and PEG derivatives were widely used in many applications, including implantable surfaces or the functionalization of nanoparticles (NPs) for drug delivery, where these systems could prolong the blood circulation time [26][27][28][29][30][31][32][33][34][35][36]. However, oxidative damage of PEGylated surfaces and PEG's non-biodegradability represents a major concern and limits its use to short-term applications [37].On the other hand, zwitterionic polymers proved to be very promising for such applications. Zwitterions are neutral but charged molecules containing both a positively and a negatively charged site [38,39]. This charge separation results in a pronounced hydration effect due to the strong interactions with water molecules [25,40].Among zwitterionic polymers, sulfobetaine methacrylate (SBMA) polymers showed low fouling properties and have attracted considerable attention also due to an upper critical solution temperature (UCST) behavior [41][42][43][44][45][46][47].The importance of realizing such antifouling surfaces extends to textile materials as well. For example, textiles used in filtration systems are extensively compromised by fouling, which lowers their durability and requires them to be replaced at short-term distances. Among all fibers, polyester fibers (PET) are broadly used because of their good workability and low price. In addition, it is possible to control filtrations properties by the fiber diameter, the mesh size, and the absolute material thickness [48]. The functionalization of polyester is very demanding due to its lack of functional groups within the polymer ...