Preparation Of Stimulus-responsive Nanofilms Based On Interface Assembly Of Nanoparticles

Recently stimulus-responsive films have aroused much interest because these materials not only possess structural advantages from their film-structure, but also endowed excellent performances from stimulus-responsive properties, such as intelligent, controllable, strong environmental adaptability etc. How to construct stimulus-responsive surfaces and expand the application fields of these materials have become a hotspot in the area of materials and chemistry. In this paper, we fabricated a series of stimulus-responsive films with peculiar responsibility based on the interface assembly of nanoparticles. The mechanism of stimulus-response and performances of these films on wettability or photoelectric properties were also investigated intensively. Based on these results we built up the relationships between the performances of the films and their compositions, structures and morphologies. Besides, we investigated a new method for the fabrication of TiO2 spheres (structure units of nanofilms) by modification of TiO2 precursor using chemical grafting strategy. The research details are listed below:(1) Fabrication of nanofilms with reversible, precisely controllable two-way responsive wettability based on layer-by-layer and chemical grafting strategy.Silica nanofilms with hierarchical micro/nano structure and enough roughness were fabricated using layer-by-layer method with silica nanoparticles as the assembly units. The acyl chloride groups were introduced on the films by sequence chemical modification method. On the other hand, ABC-type triblock copolymers of tert-butyl methacrylate (tBMA),2-hydroxyethyl methacrylate (HEMA), and 2-(diisopropylamino)ethyl methacrylate (DPAEMA) were synthesized through living radical polymerization mediated by a reversible addition-fragmentation chain transfer (RAFT) process and grafted onto these acyl chloride group functionalized silica films to form V-shaped polymer brush-grafted silica films. After hydrolysis, V-shaped polymer brushes with two arms of PDPAEMA and PMAA were produced. The as-obtained films not only exhibited reversible, one-to-one, precisely controllable wettability but also two-way response behavior as pH value increased. We further investigated the effect of the compositions and structures of copolymers on the wettablility of the films. Besides, surface elemental compositions, chemical states and distributions of polymer chains on the films were also studied using X-ray photoelectron spectroscopy and zeta-potential analyzer, indicating this special wettability was attributed to changes in the ionization state and free conformation of the highly independent V-shaped PMAA and PDPAEMA brushes in response to changes in pH.(2) Fabrication of nanofilms with unique reversible double-stimulus responsive wettability based on layer-by-layer and chemical grafting strategy.Silica nanofilms with hierarchical micro/nano structure and enough roughness were fabricated using layer-by-layer method with silica nanoparticles as the assembly units. The acyl chloride groups were introduced on the films by sequence modification method. On the other hand, ABC-type triblock copolymers synthesized through the sequential living radical polymerizations of DPAEMA, HEMA, and (4-(2-methylacryloyloxy) ethyloxy-40-trifluoromethoxy) azobenzene (MAAZO) mediated by RAFT polymerization, were grafted onto the surfaces of silica films through the reactions between the hydroxyl groups of the PHEMA middle segments and the acyl chloride groups of the silica film surfaces to form specific V-shaped polymer brushes with two arms of PDPAEMA and PMAAZO, respectively. The as-obtained V-shaped polymer-brush functionalized films exhibited a peculiar reversible double-stimulus responsive wettability, which was triggered only by the joint action of pH and UV light irradiation rather than either single stimulus. We further investigated the effect of the compositions and structures of copolymers on the wettablility of the film. The mechanisms of stimulus-response were studied using X-ray photoelectron spectroscopy and UV-vis spectrum, indicating this unique wettability was attributed to the special V-shaped grafting structure assisted switching of the chemical state of functional groups and the surface distribution of the special V-shaped polymer brushes under different stimuli.(3) Fabrication of superhydrophobic films with multiresponsive and reversibly tunable wettability based on evaporation induced self-assembly method.Poly(styrene-n-butyl acrylate-acrylic acid) synthesized by soap-free emulsion polymerization was mixed with TiO2 nanoparticles in tetrahydrofuran (THF). The mixture was then cast onto glass substrates, followed by drying at room temperature to form the intelligent films. The as prepared films not only exhibited initial superhydrophobic surface, but their wettability could reversibly switch between superhydrophobicity and superhydrophilicity under the stimulation of UV light irradiation, heat and pH switching. Various parameters such as concentration of TiO2 nanoparticles, glass-transition temperature of copolymers and drying temperature were studied in detail. The formation mechanisms of the superhydrophobic films and their multiresponse were investigated in detail using attenuated total reflection Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy, indicating that this special wettability was attributed to changes in the surface element compositions caused by treatment with acidic and alkaline solutions (deprotonation and reprotonation of COOH groups), and by UV light irradiation and thermal treatment (oxidation and transfer of polymer segments).(4) Fabrication of hierarchically ordered porous (HOP) TiO2 nanofilms with high photoelectric properties based on evaporation induced self-assembly method.Monodisperse Poly(styrene-co-acrylic acid) colloidal spheres which were synthesized from soap-free emulsion polymerization, and triblock copolymer P123 were served as macro-and mesoporous structure directing agents, respectively. Titanium chloride and titanium tetraisopropoxide were used as the titania precursors. When the mixture of polymer spheres, P123, and titania precursors were cast on substrates, and conducted for solvent evaporation, followed by 80℃ thermal treatment and 400℃ calcination, large-scale HOP TiO2 can be directly fabricated. Various parameters such as TiO2 precursors, copolymers, thermal treatment temperature and calcination temperature were studied in detail. The mechanisms of formation of HOP TiO2 were studied by FTIR, indicating that in situ chelation effect between the TiO2 precursors and the poly(styrene-co-acrylic acid) plays a key role in the fabrication of HOP TiO2. The as-obtained HOP TiO2 exhibits 50% and 70% larger the highest photocurrent under UV and visible lights, respectively, and far higher photoelectrocatalytic properties compared with commercial TiO2 (P-25).(5) A facile method for synthesis of TiO2 mesoporous spheres with tunable morphologies from an amphiphilic polymer/inorganic hybrid precursor.The novel amphiphilic polymer/inorganic hybrid TiO2 precursor was synthesized through the reaction of equimolar titanium tetraisopropoxide and amphiphilic block copolymer. By adjusting the conditions of hydrolysis and condensation reactions of the amphiphilic polymer-modified TiO2 hybrid precursors, mesoporous TiO2 spheres with various morphologies, including hierarchical porous, hollow, and raspberry-like structures, can be produced easily. The amphiphilic polymers and their concentrations on the surfaces and interiors of the TiO2 precursor beads play a vital role in the formation of the tunable morphologies. The final morphology of the TiO2 spheres was dependent upon the relative rate of aggregation, abruption, migration, and crystallization of certain TiO2 units during aging process.