The design of responsive membranes whose interactions with inclusions can be controlled through the application of an external stimulus is reviewed with the aim to establish guidelines for introducing functionality into the materials. For a photo‐reactive AB membrane, we find that a gradient in light intensity can be harnessed to clean the system of any C “impurities”, or target the delivery of C to specific locations. By modeling the interactions between a lipid bilayer and Janus nanoparticles, we design a synthetic membrane with stable pores that can be controllably opened and closed. This leads to design rules for creating nanoparticle‐bilayer assemblies where the pores open and the cargo is released only when local environmental conditions reach a critical value.
New multifunctional copoly(2‐oxazoline) nanoparticles were prepared for cell studies. The polymer contains double‐bond side chains as potential reaction sites for “thio”‐click reactions as well as a fluorescein label covalently bound to the polymer backbone. Using the nanoprecipitation technique, spherical nanoparticles of 200–800 nm were obtained. Confocal laser scanning microscopy measurements revealed the cellular uptake of the nanoparticles.
The identification and control of a critical stage of polyaniline “nanotube” self‐assembly is presented, namely the granular agglomeration or growth onto nanorod templates. When the synthesis pH is held above 2.5, smooth insulating nanorods exhibiting hydrogen bonding and containing phenazine structures are produced, while below pH 2.5, small 15–30 nm granular polyaniline nanoparticles appear to agglomerate onto the available nanorod surface, apparently improving conductivity of the resulting structures by three orders of magnitude. This finding affects both fundamental theories of polyaniline nanostructure self‐assembly and their practical applications.
Summary: From kinetic theory we have rigorously derived singularity‐free Brownian dynamics analyses of nanoparticle rotational dynamics. The rigid non‐spherical nanoparticles incorporate all three rotational degrees of freedom. This was achieved by using the components of Cartesian rotation vectors as the generalized coordinates describing angular orientation. The new results constitute an important advance compared to the situation when Eulerian angles specify angular orientation. Our finding eliminates one of the main longstanding obstacles to detailed studies of nanoparticle rotational dynamics in the diffusion time domain. The described formalism is applicable to a wide range of nanoparticle systems including liquid crystals, biopolymers, and colloids.
Spherical nanoparticles with sizes from 80 to 200 nm are obtained by self‐assembly of highly functionalized 6‐deoxy‐6‐(ω‐aminoalkyl)aminocellulosecarbamates. The particles are very stable, nontoxic, and possess primary amino groups that are accessible to further modifications in aqueous suspension. The particles can be labeled with rhodamine B isothiocyanate without changing their size, stability, and shape. The nanoparticles obtained are investigated by means of photo correlation spectroscopy, zeta potential measurements, SEM and fluorescence spectroscopy. Incorporation of the nanoparticles in human foreskin fibroblasts BJ‐1‐htert and breast carcinoma MCF‐7 cells without any transfection reagent is proved by means of confocal laser scanning microscopy.
Nanomaterials have emerged as valuable tools in biomedical imaging techniques. Here, the synthesis and characterization of a novel fluorinated nanoparticle with potential applications as an MRI contrast agent is reported. Particles were synthesized using a free radical polymerization technique. Secondary ion mass spectrometry analysis showed that the particles' surface contained fluorinated groups and nitrogen‐containing groups. Solid‐state NMR spectroscopy suggested the presence of two distinct fluorine resonances, which conforms to the structure of the fluorinated monomer. Ongoing studies aim to evaluate the performance of the nanoparticles as MRI contrast agents both in vitro and in vivo.
Block copolymer nanopaticles were prepared from the mixture solutions containing good/poor solvents by a simple evaporation process. The block copolymers formed disorder, unidirectionally stacked lamellar, and onion‐like structures in nanoparticles depending on preparation temperatures. Thermal annealing induced the disorder‐order phase transition and order‐order phase transformation in the block copolymer nanoparticles, even though the annealing temperature is lower than the of one polymer segment. The unusual thermal behaviors suggest that the glass transition temperature of the block copolymer is decreased by the effect of nanoparticle, whose surface areas are larger than their volumes.
RAFT inverse miniemulsion polymerization is demonstrated for the first time as an alternate way to synthesize hydrophilic polymer latexes. The kinetic behavior of inverse RAFT miniemulsion polymerization of acrylamide is similar to that observed in aqueous RAFT solution polymerization. A water‐soluble initiator provides better control than a lipophilic initiator in inverse RAFT miniemulsion polymerization under the conditions used here.
Polymer‐encapsulated silver nanoparticles were synthesized and sterically stabilized by a new core‐shell type system consisting of poly(S‐alt‐MA)‐graft‐PMMA copolymer that acts as a scaffold for the synthesis of size confined nanoparticles. The graft copolymer is synthesized via ambient temperature ATRP using the CuBr/PMDETA catalytic system at ambient temperature. The graft copolymer is hypothesized to function as a scaffold with the anhydride part interacting strongly with the silver ions, while the PMMA graft functions as a polymer brush that stabilizes the dispersion and prevents the particle aggregation due to a ‘polymer brush effect’. UV absorption and TEM studies confirm that the synthesized silver composite particles have a core‐shell structure.
A novel fluorescent nanoparticle with reversible on‐off switching properties has been synthesized. Three different wavelengths of light are used for switching‐on light, switching‐off light and excitation light, respectively. Thus, when this particle is used as a fluorescent probe by irradiation of the excitation light, the on‐off status can be maintained. We also showed that the on‐off status of the fluorescent particle even embedded in hydrogels can be remotely controlled by using two different wavelengths of light. These results promise that this kind of fluorescent particles will introduce a new concept and it will possibly be applied as a novel fluorescent probe, a photo memory, and a switching devise for photonics.
Highly dispersed ZnO nanoparticles with variable particle sizes were successfully prepared within an amphiphilic hyperbranched polyetherpolyol matrix via decomposition of an organometallic precursor in the presence of air leading to stable nanocomposites. The high degree of stabilization during and after the synthesis by the polymer permits control over the nanoparticle size and therefore, due to the quantum‐size‐effect, the particle properties. Furthermore, these polymer‐inorganic nanocomposites can easily be dispersed in apolar solvents to yield highly transparent, stable solutions.
A method to prepare shape‐changing nanospheres from liquid crystalline elastomers is reported. The nanosized colloids are prepared by a miniemulsion process. During this process, colloids are prepared from a liquid crystalline (LC) main‐chain polyester and subsequently crosslinked into a nanometer‐sized LC elastomer. The ability of these LC elastomers to change their shape at the phase transition temperature from the smectic A to the isotropic phase was detected by temperature‐dependent transmission electron microscopy. The phase transition‐induced shape change leads to strongly shape anisotropic nanosized elastomer particles.
This feature article reviews the authors' work combined with highlighted specific aspects of polyaniline (PANI) macro/nanostructures, focusing on such issues as the following. 1) The new development of a hard‐template method. 2) Evaluation of a template‐free method in universality, controllability, and simplicity as well as the self‐assembly mechanism. 3) Multi‐functionality based on a template‐free method associated with other approaches. 4) Cooperation effect of a micelle soft‐template and molecular interactions as a new tool to complex 3D microstructures assembled from 2D or 1D nanostructures. 5) Electrical and transport properties of a single PANI nanotube, as measured by a four‐probe method. 6) Sensors guided by reversible switching wettability through a doping/de‐doping process. An outlook is also briefly given.
The micellization of a polysiloxane‐ketimine has been studied in solvents of different polarity, i.e., dimethylformamide (DMF) and toluene. The critical micelle concentration was determined from surface tension measurements ‐in DMF‐, and from viscosity variation with concentration. Metal complex nanoparticles have been synthesized from this macromolecular ligand in DMF and in toluene, using the formed micelles as templates. Spectroscopic data (IR and UV‐vis) confirmed the metal complexation. TEM observations revealed the formation of nanoparticles with different morphologies, which were consistent with the assumed conformation of the ligand in solutions of the two selective solvents.
The functionalization of magnetite (Fe3O4) nanoparticles with dopamine‐derived clickable biomimetic anchors is reported. Herein, an alkyne‐modified catechol‐derivative is employed as the anchor, as i) the catechol‐functional anchor groups possess irreversible covalent binding affinity to Fe3O4 nanoparticles, and ii) the alkyne terminus enables further functionalization of the nanoparticles by the grafting‐onto approach with various possibilities offered by ‘click’ chemistry. In the present work, azido‐end group functionalized Rhodamine and poly(ethylene glycol) (PEG) are utilized to coat the iron oxide nanoparticles to make them fluorescent and water soluble.
Summary: A well‐dispersed gold nanoparticle/poly(N‐isopropylacrylamide) (PNIPAm) hydrogel nanocomposite with thermoswitchable electrical properties is prepared by the copolymerization of functional Au nanoparticles with N‐isopropylacrylamide. It is found that the electrical conductivity of the nanocomposite changes by two orders of magnitude at moderate temperature (Ttran) upon temperature stimuli. The change of electrical properties is reversible during a heating and cooling cycle.
Schematic illustration of the mechanism of the thermo‐switchable electronic properties of the Au nanoparticle/PNIPAm composite. 相似文献
PS grafted silica nanoparticles have been prepared by a tandem process that simultaneously employs RAFT polymerization and click chemistry. In a single pot procedure, azide‐modified silica, an alkyne functionalized RAFT agent and styrene are combined to produce the desired product. As deduced by thermal gravimetric and elemental analysis, the grafting density of PS on the silica in the tandem process is intermediate between analogous “grafting to” and “grafting from” techniques for preparing PS brushes on silica. Relative rates of RAFT polymerization and click reaction can be altered to control grafting density.
A novel and versatile approach for the mixing of ZnO nanofillers into a host polymer matrix, poly(ethyl methacrylate) (PEMA), is reported. Firstly, ZnO nanoparticles are deposited onto the surface of polystyrene (PS) colloidal particles in a “raspberry‐like” fashion and subsequently obtained PS/ZnO composite particles are mixed into the PEMA matrix in the range of 0.5 to 5 wt.‐%. Microscopic analyses reveal a homogenous distribution of PS/ZnO domains into the PEMA matrix even at 5 wt.‐% loading level. Thermogravimetric analysis and differential scanning calorimetry results indicate an improvement in thermal stability of PEMA matrix after mixing with PS/ZnO filler particles. A significant enhancement in mechanical properties of PEMA matrix in the presence of PS/ZnO particles has been evidenced by dynamic mechanical analysis and three point bending measurements.
We report the simple one‐pot synthesis of size tunable zinc oxide nanoparticles (ZnO NPs) out of an organometallic ZnO precursor using the self‐assembly of solution phase polystyrene‐block‐poly(2‐vinylpyridine) micelles. The resulting hybrid material could be deposited on various substrates in a straightforward manner with the NPs showing size‐dependent absorption and photoluminescence due to the quantum‐size effect. We compare the results to the assembly of preformed NPs which are selectively incorporated in the poly(2‐vinylpyridine) core of the micelles due to the high affinity of ZnO to vinylpyridine.
A TEMPO bromide salt is used to functionalize a silica surface with nitroxyl moieties. The functionalization reaction takes place in 48 h under mild conditions. In a second step, grafts of styrene‐maleic anhydride copolymer are grown from the functionalized silica surface by heating it in the presence of the monomers. FT‐IR and TGA analysis show that the silica was first functionalized with nitroxide moieties, and then that grafts of styrene‐maleic anhydride grew from the functionalized silica surface. A reaction mechanism is proposed in order to explain the findings. The results suggest that the oxoaminium salts are good candidates for the functionalization and grafting of surfaces that contain hydroxy groups and for the generation of hybrid materials with improved properties.
