Hongchen Dong

Recyclable Antibacterial Magnetic Nanoparticles Grafted with Quaternized Poly(2-(dimethylamino)ethyl methacrylate) Brushes

Highly efficient recyclable antibacterial magnetite nanoparticles consisting of a magnetic Fe(3)O(4) core with an antibacterial poly(quaternary ammonium) (PQA) coating were prepared in an efficient four-step process. The synthetic pathway included: (1) preparation of Fe(3)O(4) nanoparticles via coprecipitation of Fe(2+)/Fe(3+) in the presence of an alkaline solution; (2) attachment of an ATRP initiating functionality to the surface of the nanoparticles; (3) surface-initiated atom transfer radical polymerization (ATRP) of 2-(dimethylamino)ethyl methacrylate (DMAEMA); and (4) transformation of PDMAEMA brushes to PQA via quaternization with ethyl bromide. The success of the surface functionalization was confirmed by FT-IR, thermal gravimetric analysis (TGA), elemental analysis, and transmission electron microscopy (TEM). The PQA-modified magnetite nanoparticles were dispersed in water and exhibited a response to an external magnetic field, making the nanoparticles easy to remove from water after antibacterial tests. The PQA-modified magnetite nanoparticles retained 100% biocidal efficiency against E. coli (10(5) to 10(6)E. coli/mg nanoparticles) during eight exposure/collect/recycle procedures without washing with any solvents or water.

One-Pot Synthesis of Robust Core/Shell Gold Nanoparticles

A one-pot synthesis of thermally stable core/shell gold nanoparticles (Au-NPs) was developed via surface-initiated atom transfer radical polymerization (ATRP) of n-butyl acrylate (BA) and a dimethacrylate-based cross-linker. The higher reactivity of the cross-linker enabled the formation of a thin cross-linked polymer shell around the surface of the Au-NP before the growth of linear polymer chains from the shell. The cross-linked polymer shell served as a robust protective layer, prevented the dissociation of linear polymer brushes from the surfaces of Au-NPs, and provided the Au-NPs excellent thermal stability at elevated temperature (e.g., 110 degrees C for 24 h). This synthetic method could be easily expanded for preparation of other types of inorganic/polymer nanocomposites with significantly improved stability.

Flexible particle array structures by controlling polymer graft architecture.

Surface-initiated atom-transfer radical polymerization is used to synthesize particle brushes with controlled fraction of extended and relaxed conformations of surface-grafted chains. In the semidilute brush limit, the grafting of polymeric ligands is shown to facilitate the formation of ordered yet plastic-compliant particle array structures in which chain entanglements give rise to fracture through a polymer-like crazing process that dramatically increases the toughness and flexibility of the particle assembly.

Toughening fragile matter: mechanical properties of particle solids assembled from polymer-grafted hybrid particles synthesized by ATRP

The effect of polymer-graft modification on the structure formation and mechanical characteristics of inorganic (silica) nanoparticle solids is evaluated as a function of the degree of polymerization of surface-grafted chains. A transition from ‘hard-sphere-like’ to ‘polymer-like’ mechanical characteristics of particle solids is observed for increasing degree of polymerization of grafted chains. The elastic modulus of particle solids increases by about 200% and levels off at intermediate molecular weights of surface-grafted chains, a trend that is rationalized as a consequence of the elastic modulus being determined by dispersion interactions between the polymeric grafts. A pronounced increase (of about one order of magnitude) of the fracture toughness of particle solids is observed as the degree of polymerization of grafted chains exceeds a threshold value that is similar for both polystyrene and poly(methyl methacrylate) grafts. The increased resistance to fracture is interpreted as a consequence of the existence of entanglements between surface-grafted chains that give rise to energy dissipation during fracture through microscopic plastic deformation and craze formation. Within the experimental uncertainty the transition to polymer-like deformation characteristics is captured by a mean field scaling model that interprets the structure of the polymer shell of polymer-grafted particles as effective ‘two-phase’ systems consisting of a stretched inner region and a relaxed outer region. The model is applied to predict the minimum degree of polymerization needed to induce polymer-like mechanical characteristics and thus to establish ‘design criteria’ for the synthesis of polymer-modified particles that are capable of forming mechanically robust and formable particle solid structures.

Superhydrophilic Surfaces via Polymer-SiO2 Nanocomposites

A novel procedure for the preparation of superhydrophilic surfaces is described. The method employs fabricating the surface from a mixture of silica nanoparticles (NPs) and polymers containing reactive trimethoxysilyl (TMOS) groups. Suitable polymers include quaternized poly(2-(dimethylamino)ethyl methacrylate) (PQDMAEMA) and poly(3-(trimethoxysilyl)propyl methacrylate) (PTMOSPMA). Condensation of the TMOS groups in a deposited film occurs under mild conditions and results in formation of a cross-linked polymer-SiO(2) nanocomposite coating covalently anchored onto a glass substrate. When silica nanoparticles, containing micrometer-sized agglomerates, are introduced into the film, a hierarchical micro/nanostructure within the coating is built up. Superhydrophilic behavior is achieved with a high weight ratio of fumed silica NPs or polymer/fumed silica NP bilayer coatings. The superhydrophilic surfaces have high stability and antifogging behavior and display easy cleaning characteristics. Furthermore, the superhydrophilic nanocomposite coatings containing PQDMAEMA exhibit antimicrobial properties against E. coli due to the presence of quaternary ammonium groups.

Hyperbranched Poly(ferrocenylene)s Containing Groups 14 and 15 Elements: Syntheses, Optical and Thermal Properties, and Pyrolytic Transformations into Nanostructured Magnetoceramics

A series of hyperbranched poly(ferrocenylene)s containing elements (E) of groups 14 [E=Si (hb-1), Ge (hb-2)] and 15 [E=P (hb-3), Sb (hb-4)] are prepared in good isolation yields (up to 82wt%) by the salt-eliminative polycoupling of dilithioferrocene with tri-(RECl3) or tetrachlorides of the elements (ECl4). While the polymers with no or small R groups are insoluble or partially soluble, those with long alkyl chains (R=CnH2n+1 with n ≥ 8) are completely soluble and film forming. The polymers exhibit solution properties characteristic of hyperbranched macromolecules: e.g. hb-1(18) shows a low intrinsic viscosity ([η]=0.02dL/g) despite its high absolute molecular weight (Mw=5 × 105). Spectroscopic analyses reveal that the polymers possess rigid skeleton structures with extended conjugations, with their absorption spectra tailing into the infrared region (>700nm). The polymers show good thermal stability with Td up to ~400°C and can be graphitized into iron-containing ceramics when pyrolyzed at high temperatures, with char yields up to ~60wt%. While calcinations of the Si-containing polymers (hb-1) at 1000°C under nitrogen give ceramics containing mostly α-Fe nanoparticles, those of Ge-(hb-2) and Sb-containing polymers (hb-4) are completely transformed into their iron-alloys. The ceramics from the P-containing polymers (hb-3) show diffraction patterns of iron phosphides. Iron silicide nanocrystals of “large” sizes are obtained when the pyrolysis of hb-1 is conducted at a high temperature of 1200°C under argon. This ceramic is highly magnetizable (Ms up to ~51emu/g) and shows near-zero remanence and coercivity; in other words, it is an outstanding soft ferromagnet with a high magnetic susceptibility and practically nil hysteresis loss.

Dangling Chain Elastomers as Repeatable Fibrillar Adhesives

This work reports on repeatable adhesive materials prepared by controlled grafting of dangling hetero chains from polymer elastomers. The dangling chain elastomer system was prepared by grafting poly(n-butyl acrylate) (PBA) chains from prefunctionalized polydimethylsiloxane (PDMS) elastomer networks using atom transfer radical polymerization. To study the effects of chain growth and network strain as they relate to network adhesion mechanics, various lengths of PBA chains with degree of polymerizations (DP) of 65, 281, 508, and 1200 were incorporated into the PDMS matrix. PBA chains with a DP value of 281 grafted from a flat PDMS substrate showed the highest (approximately 3.5-fold) enhancement of nano- and macroscale adhesion relative to a flat raw (ungrafted and not prefunctionalized) PDMS substrate. Moreover, to study the effect of PBA dangling chains on adhesion in fibrillar elastomer structures inspired by gecko foot hairs, a dip-transfer fabrication method was used to graft PBA chains with a DP value of 296 from the tip endings of mushroom-shaped PDMS micropillars. A PBA chain covered micropillar array showed macroscale adhesion enhancement up to approximately 7 times relative to the flat ungrafted prefunctionalized PDMS control substrate, showing additional nonoptimized approximately 2-fold adhesion enhancement due to fibrillar structuring and mushroom-shaped tip ending. These dangling hetero chains on elastomer micro-/nanofibrillar structures may provide a novel fabrication platform for multilength scale, repeatable, and high-strength fibrillar adhesives inspired by gecko foot hairs.

Impact of polymer graft characteristics and evaporation rate on the formation of 2-D nanoparticle assemblies.

The effect of polymer functionalization on the two-dimensional (2-D) assembly of uniform as well as highly asymmetric binary colloidal mixtures with both neutral and incompatible polymer grafts is presented. In ordered assemblies of uniform particle brush systems, the observed size-segregation is analogous to that of hard sphere colloidal systems, suggesting that lateral capillary interactions are responsible for the crystal nucleation in the early stages of assembly formation. Structure formation in binary blends of asymmetric particle brush systems is found to be strongly influenced by three major energetic contributions, that is, the interfacial energies associated with the particle brush/air boundaries, the interfacial energies between the distinct brush components, as well as the elastic energy associated with the stretching of the polymer-brush to fill the interstitial regions within locally ordered particle arrays. Our results demonstrate the relevance of capillary interactions in soft particle brush systems but also highlight distinctive differences in the order formation as compared to hard sphere colloidal systems. In particular, the compliant response of grafted polymer chains is shown to promote phase separation in binary blends of incompatible and asymmetric colloidal systems.

Nanoanesthesia: a novel, intravenous approach to ankle block in the rat by magnet-directed concentration of ropivacaine-associated nanoparticles.

BACKGROUND:As an alternative to current methods of local nerve block, we studied the feasibility of producing ankle block in the rat with IV injection of magnetic nanoparticles (MNPs) associated with ropivacaine and application of a magnet at the ankle. METHODS:The anesthetic effect of magnet-directed ropivacaine-associated MNPs (MNP/Ropiv) was tested in the rat using paw withdrawal latencies from thermal stimuli applied to the hindpaw. The MNP/Ropiv complexes consisted of 0.7% w/v ropivacaine and 0.8% w/v MNPs containing 12% w/w magnetite (Fe3O4). The effect of IV injection of MNP/Ropiv with 15, 30, and 60-minute magnet application to the right ankle was compared with the effect without magnet application on the left hindpaw, to conventional ankle block with 0.1% or 0.2% ropivacaine, and to IV injection of MNPs alone with 30-minute magnet application to the right ankle. In addition, the pharmacokinetics of the MNP/Ropiv complexes were determined. RESULTS:IV injection of MNP/Ropiv with magnet application at the ankle significantly increased paw withdrawal latencies from thermal stimuli compared with pretreatment baselines in the same paw (P < 0.0001) and compared with the contralateral paw without magnet application (P < 0.0001). IV injection of MNPs alone had no significant effect on paw withdrawal latency. Absolute ropivacaine concentrations in ankle tissue, and ankle tissue-to-plasma concentration ratios were higher in the MNP/Ropiv group with 30-minute magnet application compared with MNP/Ropiv group without magnet application (mean ± SEM, 150 ± 10 ng/g vs 105 ± 15 ng/g, respectively, and 6.1 ± 0.8 vs 4.2 ± 0.7, respectively). CONCLUSIONS:The current study establishes proof of principle that it is possible to produce ankle block in the rat by IV injection of MNP/Ropiv complexes and magnet application at the ankle. The results indicate that further study of this approach is warranted.

Hyperbranched Polymers Containing Transition Metals: Synthetic Pathways and Potential Applications

Incorporation of transition metals into organic monomers and polymers has been thoroughly examined over the past five decades in light of the promising electrical, magnetic, optical, sensing and catalytic properties that these organometallic materials possess [1–4]. Thanks to their intriguing properties, which are often inaccessible by their pure organic parents, these organometallic polymers have found applications in the coating, pharmaceutical, and aerospace industries. Whereas many of these studies focused on the synthesis of linear polymers with either transition metals integrated into the main chain or attached as pendant groups at the side chains, the preparation and study of highly branched three dimensional (3-D) macromolecular architectures—such as dendrimers and hyperbranched polymers containing organometallic complexes—has only recently received greater attention. Depending on their position, metal centers have been shown to act as cores, simulating artificial models of biological systems such as metalloenzymes, as well as connectors, branching points, and terminal (surface) units distributed throughout the whole structure with potential applications in the field of sensors, catalysts, and as light-harvesting antennas [5,6]. Despite their structural beauty, dendrimer synthesis needs to be carried out in a thoughtful manner involving multistep reaction and purification protocols in order to construct the various tree-like generations, which will in many cases restrict their potential applications to academic interests only [7]. Moreover, recent advances in mass spectrometric techniques have revealed depictions of dentrimers showing them to be highly idealized and that the real samples indeed exhibit imperfections and structural defects [8]. 1 Background 21 2 Research and Discussion 22 2.1 Theoretical Background 22 2.2 Synthetic Pathways 23 3 Conclusion and Future Considerations 33 References 33