Fabrication Of Polymer Film By Dip-coating Method And Film-forming Mechanism Investigation

Recently, polymer thin film has becoming an idea material that could be widely used inbiomedicine, photoelectronics, sensor, energy, catalyst and other fields. Particularly, coating andfabrication of polymer nano film on top of solid has gained remark interest of researchers. In thisthesis, we took PVA water solution as example, we prepared PVA films on various substrates, andfinal we proposed the mechanism of film forming in microscopic. We systematically studied filmforming on solid surface with various surface morphology and chemical properties, includingsuperhydrophobic substrate, superhydrophilic substrate, super-lubricating substrate, hydrophobicand hydrophilic smooth substrate. We suggested the major advantage of dip-coating overcomingother methods, and relative mechanism. Our main results involves:(1) Due to the intrinsic anti-affinity properties of both superhydrophobic surface andsuper-lubricating surface, liquid is rather difficult to spread and form continuous film above them.In contrast, superhydrophilic surface exhibited excellent properties for assisting film formation,and on which we can obtain films through all kinds of film forming methods. Therefore,introducing roughness on top of hydrophilic solid will greatly enhance the possibility of filmformation.(2) On top of smooth solid, no matter hydrophilic or hydrophobic, we can force the wettingof liquid on it by dip-coating method, and eventually obtain uniform thin film. Comparing withthe well-known spin coating method, dip-coating method is suitable for preparing films in evenwider range, especially suitable for continuously preparing large-size films on top of solid surfacecontaining complex geometry and chemical properties.(3) We systematically investigated the film formation mechanism of PVA on top of PDMSand silicon. We found two regimes exist in correlating film thickness with dragging rate. At higher dragging rate, film thickness follow the relationship predicted by Landau-Levich theory, but withmuch higher coefficient. On the other hand, at lower dragging rate, film thickness is constant andindependent with the rate. Therefore, we revealed two mechanism that control the final filmthickness, i.e. film thickness of liquid dominant at high dragging rate regime, and evaporation ratedominant at low dragging rate regime.(4) We investigated the influence of concentration on the film thickness. We found that bychoosing proper concentration, we can prepare thin film within the rage of20-500nm, simply bydip-coating method. Combining the control of dragging rate and solution concentration, we canprecisely control the thickness of film. Based on the systematically study, we finally proposed themechanism of film formation on microscopic view.