Summary: We demonstrate a novel approach for constructing photoactive multilayer films in which the aggregation of fluorescing molecules is effectively eliminated. In the films formed via a layer‐by‐layer electrostatic self‐assembly technique, the core‐shell amphiphilic copolymer, poly[(sodium 4‐styrenesulfonate)‐block‐vinylnaphthalene], was deposited. The isolated cores served as nanosized host sites for photoactive guest molecules (pyrene, perylene). The efficient energy transfer between polymeric chromophores and perylene molecules was observed.
AFM image of a nanostructured polymeric film prepared via a layer‐by‐layer technique and containing photoactive block copolymer poly[(sodium 4‐styrenesulfonate)‐block‐vinylnaphthalene]. Below is the representative height profile taken along the drawn line. 相似文献
It is shown that narrowband one‐dimensional photonic crystals can be fabricated from polymeric materials using laboratory scale layer‐multiplying coextrusion technology. The tuning of the photonic bandgap is demonstrated with films that selectively filter different regions of the visible electromagnetic spectrum. The layer uniformity of the photonic crystals is evaluated by comparing the measured UV‐vis transmission spectra with model simulations, and is independently confirmed with atomic force microscopy. Assemblies of alternating polystyrene and poly(methyl methacrylate) layers exhibit a narrow reflection band with close to 100% reflection in good agreement with the prediction for uniform layers. The flexibility of the process is demonstrated by the fabrication of elastomeric one‐dimensional photonic crystals. It is anticipated that this technology will enable the rapid and facile realization of new polymeric optical devices.
A poly(methyl methacrylate)‐block‐poly(acrylic acid)‐block‐poly(2‐vinyl pyridine)‐block‐poly(acrylic acid)‐block‐poly(methyl methacrylate) (PMMA‐PAA‐P2VP‐PAA‐PMMA), pentablock terpolymer has been synthesized by anionic polymerization with sequential addition of monomers and studied in aqueous media at low pH. The system exhibits combined properties and adopts the behavior of ‘telechelic’ polyelectrolytes and that of double hydrophilic polyampholytes. This complex behavior leads to the pentablock terpolymer forming a pH and temperature sensitive reversible hydrogel at very low polymer concentration.
A simple scheme to fabricate 2‐D arrays of Au/titania hybrid nanopatterns is presented, using polystyrene‐block‐poly(ethylene oxide) diblock copolymer (PS‐b‐PEO) as templates coupled with sol–gel chemistry. Both the functionalized Au nanoparticles (NPs) and titania precursors are selectively incorporated into the PEO domain. A series of morphologies ranging from nanodot to nanowire arrays is formed and the mechanism of morphological evolution is discussed. Such hybrid films exhibit characteristic localized surface plasmon resonance bands originating from the coupling between neighboring Au NPs spatially located in a controlled manner.
Two new “H” type of indole‐based chromophores were designed and successfully introduced to the polymeric system, the resultant polymers demonstrated enhanced NLO effects, good processability, thermal stability and nearly excellent transparency, indicating the advantages of “H” type chromophore moieties. And they could be promising candidates for the practical applications as new photonic materials.
Summary: Polyelectrolyte multilayer films of poly(acrylic acid) (PAA)/poly(allylamine hydrochloride) (PAH) and PAH/poly(sodium 4‐styrenesulfonate) (PSS) based on electrostatic interactions as a driving force are patterned by room‐temperature nanoimprint lithography (RT‐NIL). Under an imprinting pressure of 40 bar for 8 min, well‐defined pattern structures with a line width of ≈330 nm and a separation of ≈413 nm are achieved. Meanwhile, hydrogen‐bonding‐directed multilayer films of poly(vinyl pyrrolidone) (PVPON)/poly(methyl acrylic acid) (PMAA) and poly(4‐vinylpyridine)/PAA can also be patterned in a similar way by RT‐NIL. The successful imprinting of these films originates from the high compressibility and fluidity of the layered polymeric films under high pressure.
SEM image of an imprinted (PAH/PAA)*20 film on silicon wafer. 相似文献
While miniemulsion polymerization has proven to be well‐suited for conducting living/controlled radical polymerizations, emulsion polymerizations have proven to be far more challenging. Ab initio emulsion polymerizations, in which monomer droplets are present during polymerization, have thus far not been successful with TEMPO‐mediated polymerizations, as a result of colloidal instability and coagulum formation. By selectively inhibiting polymerization in the monomer droplets, it is demonstrated that droplet polymerization is responsible for the formation of large (>1 µm) particles that can lead to coagulum formation. Furthermore, we show that coagulum‐free latexes can be produced using a TEMPO‐mediated ab initio emulsion polymerization by suppressing droplet polymerization.
A reverse‐barrier technique is used to enable the treatment of electrospun poly(vinylidene fluoride) nanofibrous membranes with supercritical carbon dioxide. The treatment induces the formation of nanopores and extended‐chain β crystallites of small lateral dimensions in the nanofibers. It also creates interfiber junctions, resulting in a remarkable improvement in mechanical properties of the membranes. The treated membranes are able to retain their shape very well after loading with an ionic liquid (IL). The ionic conductivity of the IL‐loaded membrane is very close to that of the neat IL.
A dielectric elastomer derived from a polystyrene‐block‐poly(ethylene‐co‐butylene)‐block‐polystyrene triblock copolymer swollen with a midblock‐selective solvent is reported to show promise as a nanostructured organic actuator requiring no pre‐strain. This might provide an attractive alternative to conventional acrylic, siloxane, and polyurethane elastomers since the electromechanical properties are composition‐tunable.
A water‐soluble, sulfur‐containing fluorescent conjugated polymer exhibits a visible fluorescence color change for detection of mercury in the presence of thymine. A new concept provides the design of a sensor ensemble using a simple combination method. This strategy avoids the need for complicated design and synthesis of a recognition group, eliminating the tedious synthetic efforts for the preparation of a sensor material.
High molecular weight poly(9,10‐bis(p‐(2‐ethylhexyloxy)phenyl)‐2,6‐anthracenevinylene) (2,6‐PAV) was synthesized with 2,6‐dimethylanthraquinone as a key intermediate. The as‐synthesized polymer is readily soluble in common organic solvents and can be used for spin‐coating. The as‐synthesized polymer exhibits a broad absorption band ranging from 280 to 520 nm and a bluish green emission band with a peak at 500 nm. The polymer shows good thermal stability, and no distinct glass transition is observed. A simple device with the configuration ITO/PEDOT:PSS/2,6‐PAV/Ba/Al showed a turn‐on voltage of 4.8 V and a maximal brightness of 340 cd · m−2.
pH‐responsive PHEMA‐based polymeric nanostructures were grown in a controlled manner by ATRP‐based surface‐initiated polymerization. Initiator nanopatterns were obtained on silicon wafers covered with OTS resists made by AFM scanning probe oxidation lithography. AFM images confirmed isolated grafting of stimuli‐responsive hedge and dot brush structures exhibiting dimensions corresponding to a few tens of chains.
A novel top‐surface imaging process was successfully established using selective chemisorption of amine‐functionalized poly(dimethyl siloxane) onto the carboxylic groups formed on the surface of diazoketo‐functionalized polymer film by UV light irradiation. The chemisorbed poly(dimethyl siloxane) worked as an efficient etch mask for the subsequent oxygen plasma etching process for pattern generation. High‐resolution patterns were resolved with the new imaging process.
It is demonstrated that polymeric materials can be directly converted into molecular (chiral) recognition nanofiber membranes by simultaneously applying an electrospray deposition and an alternative molecular imprinting during the membrane preparation process. Polysulfone with a degree of substitution of 0.88 was adopted as the candidate polymeric material for molecularly imprinted nanofiber membranes. Molecularly imprinted nanofiber membranes imprinted by Z‐D ‐Glu recognize the D ‐isomer in preference to the corresponding L ‐isomer and vice versa. The amino acid preferentially incorporated into the membrane is selectively permeated through the membrane by using a concentration gradient as a driving force for membrane transport.
Summary: Supramolecular interaction of fully methylated hyperbranched polyethylenimines (PEI) with a mesogen‐based carboxylic acid, 5‐(p‐cyanobiphenoxy)pentanoic acid, results in the formation of supramolecular complexes exhibiting thermotropic liquid crystalline (LC) mesophases. In contrast to the common smectic mesophases of most dendritic LC polymers, nematic LC phases were observed. The complexation of PEI and the mesogen units is due to electrostatic interaction between the carboxylate groups and the ammonium end groups of PEI. LC properties were investigated by a combination of differential scanning calorimetry, polarizing light optical microscopy, and X‐ray diffractometry.
Schematic illustration of the supramolecular assembly of CBPA with PEIMe backbone. 相似文献
We report that the nanostructures of poly(styrene‐block‐4‐vinylpyridine) block copolymer (PS‐b‐P4VP) thin film on a wafer substrate can be re‐assembled by sequential vapor treatment using selected solvents. Metal or other inorganic nanoparticles that were randomly pre‐loaded inside or on the surface of PS‐b‐P4VP thin film could be pulled to the rim of PS and P4VP along with the movements of PS and P4VP blocks during the treatment. As a result, the patterned polymeric or inorganic/polymer composite nanoisland and nanoring arrays were fabricated.
Strong electrolyte temperature‐sensitive hydrogels were synthesized by radiation polymerization using N‐isopropylacrylamide and sodium 2‐acrylamido‐2‐methylpropanesulfonate. The influence of irradiation dose and mole ratio of the monomers was examined by swelling measurements in aqueous solution and organic solvents. The hydrogels without any pollution were applied in concentrating protein.
Effect of irradiation dose on swelling ratios of P(NIPA‐co‐NaAMPS) hydrogels. 相似文献
A novel pH‐responsive polymer vesicle obtained by the aqueous self‐assembly of carboxy‐terminated hyperbranched polyesters is reported. The synthesis is very simple, just a one‐step esterification of the commercially available hydroxy‐terminated hyperbranched polyester of Boltorn Hx (x = 20, 30, 40) with succinic anhydride. The vesicle size can be controlled from 200 nm to 10 µm by simply adjusting the solution pH as well as the degrees of branching (or generation).
The free radical grafting of polyethylene with vinyl monomers by reactive extrusion was studied numerically. Numerical computation expressions of key variables, such as the concentrations of the initiator and polymer, grafting degree, average molecular weight and apparent viscosity, were deduced. The evolutions of the above variables were predicted by means of an uncoupled semi‐implicit iterative algorithm. The monomer conversion monotonically increases with decreasing throughput or increasing initial initiator concentration; with increasing barrel temperature, the monomer conversion first increases then decreases. The simulated results are nearly in good agreement with the experimental results.
