The Fabrication Of Superhydrophobic,Superhydrophilic And PH Responsive Surfaces Based On Electrodeposited Surface

In this thesis we attempt to synthesis a kind of carboxyl-terminated dendronthiol, combining the electrodeposition on such molecular monolayer as thetemplate and the chemical modification together to fabricate the surfaces withdifferent wettabilities. Chapter one of this thesis is the introduction of some basic concepts ofself-assembled monolayer, dendrimer, surface wettablities (e.g.superhydrophobic and superhydrophilic surfaces), and some progress in the fieldof smart surface and pH responsive surface.In Chapter two, by using the convergent method introduced by C. J. Hawkerand J. M. J. Fréchet, we synthesized a kind of second generation ester-terminatedpoly (benzyl ether) dendron with benyl bromide at the focal point, which wasdonoted as (CH3OOC)4-[G-2]-Br. Such compound as the starting materials, firstreacted with thioacetic acid. After the hydrolysis of the terminal ester group andthe ester at the focal point, we get the target compound, (HOOC)4-[G-2]-SH.Such compound is confirmed with NMR, MS, IR. We also use XPS, STM, CA,IR to characterize the self-assembled monolayer of such molecule. To excludethe multilayer adsorption of (HOOC)4-[G-2]-SH by hydrogen bonding, werinsed the SAM sequently using a large amount of ethanol, 10% acetic acidethanolic solution, a large amount of ethanol, then dried in nitrogen. Rinsingwith only ethanol may cause the physical adsorption, or multilayer adsorption.The experimental results suggested that (HOOC)4-[G-2]-SH adsorbed on goldsurface through monolayer, but multilayer. XPS data suggested that(HOOC)4-[G-2]-SH chemisorbed on gold surface, forming Au-S bond. STM dataindicated that the SAM contain many defects, we speculate such defect should bethe defect of the monolayer by STM section analysis and Cerius2 simulation.Then using the dendron thiol self-assembled monolayer as the template, we usethe electrodeposition method to fabricate the gold rough surface with goldnanostructures. We use SEM, AFM, CV to characterize the gold rough surfacewith gold nanostructures. The result suggested that, surface roughness graduallyincreased with the increased electrodeposition time. The morphology of theelectrodeposited gold nanostructures can be adjusted by the electrodepositionpotential. We use different SAM as the template for electrodeposition. The datasuggested that (HOOC)4-[G-2]-SH SAM provided a good template to fabricategold rough surface with gold nanostructures, AFM data revealed that the surfaceroughness gradually increased with the increased electrodeposition time, whichis confirmed by the electrochemical results.In Chapter three, By the post chemical modification with different chemicalmaterials, we can fabricate the surfaces with different wettabilities, after themodification with C12-SH, the CA of such surface increased with the increasedelectrodeposition time,from less hydrophobic to superhydrophobic properties.To elucidate the origin of the above-mentioned superhydrophobicity, we useCassie equation to explain that. TA reflect the CA hysteresis, it decreased withthe increased electrodeposition time and surface roughness. It agrees well withthe Johnson and Dettre 's simulation work,they believed that CA hysteresisincreseded with the increased surface roughness in low roughness region;Whilerapidly decreased with the increased surface roughness when the roughness isquite large. We also investigate the relation of the CA on Cn-SH modifiedsurface and the values of chain length n. After the chemical modification withHO-C11-SH, the surface became superhydrophilic, and the water droplet spreadquickly on such surface. To elucidate the origin of the above-mentionedsuperhydrophilicity, we use Cassie hemiwicking model to explain that. Wedesigned a kind of pH responsive molecule, MUABA. The NMR,MS,IR dataconfirmed that target compound. We also use XPS, STM, CV, IR to characterizethe self-assembled monolayer of such molecule, MUABA on gold surface. Weuse the XPS to study the elemental composition and element binding energy ofMUABA SAM, which provide further evidences that the MUABA moleculesadsorbed on gold surface. STM images suggested SAM contain many defects,which is likely the Au vacancy island,as the average depth of such defects isabout 0.24 nm, according to the STM section analysis. CV data confimed thecompact MUABA monolayer with strong blocking effect for the electron transferis formed on gold surface. IR data suggested that, in MUABA SAM treated withpH = 1 solution, the hydrogen bonded and free carboxyl groups are coexisted.After the treatment of pH = 13 solution,there is no –COOH groups in MUABASAM any more,the –COOH group is deprotonized;from the surface energy dataand observed wettabilities, we speculate that under pH = 1 condition, thebenzene ring (nonpolar) group are likely to locate at the outermost surfacecontacted with the water in the MUABA SAM, in that case, under pH = 1condition, the dispersive component of surface energy predominated. Under pH= 13 condition, the carboxyl group ionized, may cause the induced alignment ofmonolayer,and let the carboxylate group contact with water, in that case, thepolar component of surface energy predominated. Further result of CA andsurface energy analysis suggested that MUABA monolayer on gold surface showpH responsiveness. By the chemical modification of such pH responsivemolecule onto the gold rough surface with gold nanostructures discussed in theChapter two, we fabricate the pH responsive surface, e.g. near superhydrophobicsurface under pH=1 condition, and superhydrophilic surface under pH=13condition. We also use the MUABA mixed monolayer to modify the gold roughsurface, to fabricate more large-scale pH responsive surface, superhydrophobicsurface under pH = 1 condition, superhydrophilic surface under pH = 13condition. We use XPS to study the different amount of MUABA adsorbed onrough and flat gold surface. According to the ratio of XPS atomic concentrationof C to N, i.e. using the C/N value, we can calculate the different MUABA in themixed monolayer on rough and flat gold surface (molar ratio) are 53.6% and18.7%, respectively. Comparing with the MUABA amount in the assemblysolution (MUABA 33%, polar ratio), the amount of MUABA on the roughsurface is increased,about 53.6%;while the amount of MUABA on the flatsurface is decreased,about 18.7%. That may be due to the fact that on roughgold surface MUABA are easier than C10-SH to adsorb on the substrate surface.And the concentration of MUABA in the mixed monolayer is diluted by C10-SH,which may benefit the conformation change of MUABA, as the pH responsivemolecule may need enough free room in the monolayer to change itsconformation under different pH conditions.We believe that such above-mentioned superhydrophobic, superhydrophilic,pH responsive surfaces can be used in many applications in the near future.