The linear relationship between UV-absorbance of poly(styrene sulfonate)(PSS)／poly(diallyldimethyl ammonium choloride)(PDDA) and the number of MD films confirms that PSS／PDDA monolayers are alternately deposited. The contact angle of water on polyelectrolyte MD films indicates that the surface wettability varies with the number of deposited layers exhibiting a regular odd-even effect

when the number is low．This regularity becomes not obvious when more layers are deposited. This phenomenon shows that the structural defect of polyelectrolyte MD films aggravates with the increment of the number of layers．Through analyzing Atomic Force Microscopy (AFM) images of PSS／PDDA MD films

granular protrusion of about 1.5 nm height can be detected．It indicates that the surface of MD films is rough．This means that molecules of adjoining layers can penetrate into each other and form unclear interface. The results of AFM further verify the uneven surface properties and structural defect of the 20th layer of a PSS/PDDA MD film.