Transparent film materials with excellent mechanical and thermal properties were elaborated by drying a latex suspension of armored polymer/Laponite composite particles. Low‐temperature TEM observation of ultrathin cross‐sections of the films indicated a unique network morphology characterized by a “honeycomb” distribution of the Laponite platelets remindful of the original particles morphology.
The catalytic properties of bis(phenoxy‐imine) Zr and Hf complexes incorporating perfluorophenyl groups with methylaluminoxane were investigated. The fluorinated complexes produced far higher‐molecular‐weight polyethylenes and ethylene/propylene copolymers with increased activities compared with the non‐fluorinated congeners. Moreover, the fluorinated complexes displayed a higher incorporation ability for propylene.
Rheology and tribology become more and more critical issues in order to satisfy the harsh requirements for ultra‐small head/media spacing HDDs. In this communication, MD simulations with a bead/spring model were employed to examine the nano‐rheological response of nonfunctional and functional PFPEs by analyzing the shear viscosity of nanoscale PFPE films and the relaxation processes as a function of wall interaction/separation and endgroup functionality. Our simulation results indicate that thin PFPE films show more solid‐like behavior, especially under high shear rate. The film deformation and shear viscosity change by tuning the film thickness and the endgroup functionality was discussed in conjunction with the relaxation processes.
Properties characteristic of the size, shape, and orientation as well as the rigidity of PMMA end‐grafted to an amorphous silica surface are calculated by use of fully atomistic molecular dynamics simulations with MMA as explicit solvent. Both the number of grafted chains and their tacticity is varied. Firstly, properties of one atactic end‐grafted chain are compared to those of the same chain without any surface being present. Secondly one, two, and four atactic grafted chains are evaluated to study the influence of grafting density (at low surface occupancy) and thirdly, results of single grafted iso‐, syndio‐, and atactic chains, respectively, are compared to elucidate the influence of tacticity. Additionally, the used force field is validated by calculation of the diffusion coefficient of solvent molecules.
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.
Summary: A new strategy was developed to prepare disorderly exfoliated nanocomposites, in which a soft siloxane surfactant with a weight‐average molecular weight ( ) of 1 900 was adopted to modify the clay. The modified clay slurry was then mixed with silicone rubber by hand, and exfoliation was achieved. The proposed mechanism thereof was verified by TEM and XRD. The physical entanglement of the soft siloxane surfactant plays a vital role in the diffusion and intercalation of the matrix molecules during the compounding of the slurry‐polymer mixture. This simple method is applicable to other silicone‐based materials reinforced by clay.
TEM micrograph of silicone rubber/clay‐sil nanocomposite. 相似文献
Furan ring‐functionalized solid surfaces are achieved by the initiated chemical vapor deposition (iCVD) method, a solvent‐free process to form films under mild conditions. The polymerization of furfuryl methacrylate monomer is initiated by a resistively heated filament wire. The functionality of the furan group in the iCVD film enabled Diels–Alder chemistry with 4‐phenyl‐1,2,3‐triazolin‐3,5‐dione (N‐PTD).
Summary: Self‐oscillating polymers and nano‐gel particles consisting of N‐isopropylacrylamide and the ruthenium catalyst of the Belousov‐Zhabotinsky reaction have been prepared. In order to clarify the crosslinking effect on the self‐oscillating behavior, the phase transition behaviors were investigated by measuring the transmittance and the fluorescence intensity of the polymer solution and the gel bead suspension. Cooperative effects due to crosslinking will play an important role for the design of nanoactuators.
Chemical structure of poly(NIPAAm‐co‐Ru(bpy)3). 相似文献
The free volume (voids) distribution in the lamellae of the conventional symmetric and amphiphilic diblock copolymers is studied via Monte–Carlo simulation based on the standard bond fluctuation model. Both in the conventional and amphiphilic block copolymers the voids are found to concentrate on the interfaces between the incompatible units, the magnitude of the effect being unexpectedly significant. A crystalline‐like ordering of voids with increase of the incompatibility between the different repeated units in amphiphilic copolymers is first reported and implications of this peculiarity for the morphology and mechanical properties of the amphiphilic copolymers are discussed.
The preparation of metal nanoparticles generally requires the use of mostly toxic reducing agents according to state‐of‐the‐art procedures. Here, we report that polysorbate 80, a polymeric nonionic surfactant, when reacted with a gold salt in water at room temperature, yields well‐dispersed gold nanoparticles. Furthermore, we could control the particle size by simply altering concentration or temperature. The synthetic procedure presented here is easy, inexpensive, straightforward, and user‐friendly.
Macroporous cross‐linked organic polymer based on N‐acryloxysuccinimide (NAS) and ethylene dimethacrylate (EDMA) was prepared inside 75 µm id fused silica capillary as a functionalizable monolithic stationary phase for chromatographic applications. Succinimide groups on the monolith surface provide reactive sites able to react readily through standard electrophile–nucleophile chemistry. Propargylamine was used to prepare alkyne functionalized poly(NAS‐co‐EDMA). Onto this azido‐reactive polymer surface was grafted β‐cyclodextrin (CD) via a triazole ring utilizing the copper(I)‐catalyzed 1,3‐dipolar cyclo‐addition reaction. Chemical characterization was performed in situ after each synthetic step by means of Raman spectroscopy. Good enantioseparations of flavanone enantiomers, chosen as test chiral compound, were achieved under reversed phase conditions by both capillary electrochromatography and nano‐liquid chromatography (nano‐LC) techniques. These results demonstrate the potentiality and usefulness of click chemistry in the preparation of β‐CD containing chiral organic polymer monolith.
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.
A close correllation between molecular‐level interactions and macroscopic characteristics of polymer networks exists. The characteristics of the polymeric hydrogels assembled from β‐cyclodextrin (β‐CD) and adamantyl (AD) substituted poly(acrylate)s can be tailored through selective host–guest complexation between β‐CD and AD substituents and their tethers. Dominantly, steric effects and competitive intra‐ and intermolecular host–guest complexation are found to control poly(acrylate) isomeric inter‐strand linkage in polymer network formation. This understanding of the factors involved in polymeric hydrogel formation points the way towards the construction of increasingly sophisticated biocompatible materials.
We present a computer study of the association behavior of copolymer chains with a gradient part and soluble tail of variable length. As a simulation method we use dynamic Monte Carlo simulation on a simple cubic lattice with pair interaction parameters. The solvent quality and selectivity is modeled by the variation of pair interaction parameters between nearest neighbors on the lattice. The role of the length of soluble part in the self‐assembly and its effect on the structure of aggregates was the main goal of this work. The size and structure of aggregates were analyzed using an improved topological classification method which has been developed and tested in the present study. The structure and association numbers of aggregates were compared with those of linear diblock copolymers.
In this communication, β‐cyclodextrin modified quantum dots were used as a water‐soluble “supramolecular” cross‐linker (SCL) because of its surface's supramolecular activity. The guest monomer‐loaded SCL (mSCL) can be used to copolymerize with water‐soluble monomers leading to transparent hybrid supramolecular hydrogels. This simple and versatile method opens new venues for the preparation of hybrid supramolecular hydrogels and the host–guest chemistry of cyclodextrins.
A dextran‐based dual‐sensitive polymer is employed to endow gold nanoparticles with stability and pH‐ and temperature‐sensitivity. The dual‐sensitive polymer is prepared by RAFT polymerization of N‐isopropylacrylamide from trithiocarbonate groups linked to dextran and succinoylation of dextran after polymerization. The functionalized nanoparticles show excellent stability under various conditions and can be stored in powder‐form. UV and DLS measurements confirm that the temperature‐induced optical changes and aggregation behaviors of the particles are strongly dependent on pH.
Summary: A chitin‐xylan hybrid polysaccharide having β(1 → 4)‐linked alternating structure of N‐acetyl‐D ‐glucosamine and D ‐xylose was synthesized via chitinase‐catalyzed polymerization. An oxazoline derivative of D ‐xylosyl‐β(1 → 4)‐N‐acetyl‐D ‐glucosamine ( 1 ) was effectively polymerized by the catalysis of chitinase from Bacillus sp., giving rise to a water‐soluble chitin‐xylan hybrid polysaccharide ( 2 ) in good yields. Molecular weights ( ) of 2 reached 1 500, which corresponds to 8–10 saccharide units.
A chitin‐xylan hybrid polysaccharide ( 2 ) synthesized via chitinase‐catalyzed polymerization. 相似文献
The shielding effect of nano TiO2 on collagen under UV radiation was investigated using UV spectrophotometry. The results indicate that the shielding of collagen under UV radiation in the presence of nano TiO2 is significant. For 2.5 wt.‐% of TiO2, there is a greater shielding effect of UV radiation than that for 0.5 wt.‐% of TiO2. In addition, this study gives hints that a novel tanning agent with a UV shielding function can be formulated by using nano TiO2.
UV absorption of collagen under UV radiation after adding 2.5 wt.‐% TiO2. 相似文献
Disulfide‐functionalized hyperbranched poly(amido amine)s (HPAMAMs) were synthesized by Michael addition polymerization of N,N'‐cystaminebisacrylamide and 1‐(2‐aminoethyl)piperazine. The novel HPAMAMs displayed bright fluorescence, and the emissions bands cover nearly the whole visible wavelength range. When polymer solutions were excited at 330–385, 460–490, and 510–550 nm, blue, green, and red solutions were observed, respectively. The HPAMAMs are biodegradable and they can be easily cleaved by 2‐mercaptoethanol or glutathione, leading to a decrease in the fluorescence intensity. Studies of applications of the biocompatible and biodegradable HPAMAMs in fluorescence imaging technology and biological science are in progress.
Summary: A superhydrophobic coating was facilely fabricated in one step by casting bisphenol A polycarbonate (PC) solution under moisture. Vapor‐induced phase separation occurred during the solidifying process and a rough surface with a micro‐nano‐binary structure (MNBS) similar to the microstructure shown on lotus leaf was formed.
