Chuanjun Xia

Intercalation of polymerization initiators into montmorillonite nanoparticle platelets: free radical vs. anionic initiator clays

We have investigated the properties of clay surface bound initiators for the preparation of polymer-layered silicate nanocomposite materials: one for anionic and two for free radical polymerization. These organic cations were intercalated into the galleries of montmorillonite clay by cation exchange. The structural, thermal, and compositional properties of the three types of initiator clays were studied and compared. X-ray diffraction studies showed that all three systems were swelled after initiator intercalation and the increase of interlayer d-spacing was dependent on the structure and molecular chain length of the initiators. Thermal gravimetric analysis, differential scanning calorimetry, and X-ray photoelectron spectroscopy traces indicated the presence of the initiator on clay and a complete cation exchange process was achieved only by adding excessive amounts of initiator. Infrared spectra compositionally confirmed the successful initiator intercalation into the clay platelets. Important differences were found between surface bound mono and dicationic free radical initiators.

Surface structural characterization and mechanical testing by nanoindentation measurements of hybrid polymer/clay nanostructured multilayer films

Nanostructured montmorillonite/poly(diallyldimethylammonium chloride) multilayer thin films were fabricated up to 100 layers thick by stepwise alternating polyelectrolyte and clay deposition from solution. The structure and morphology of the films were characterized by x-ray diffraction, ellipsometry, atomic force microscopy, and quartz crystal microbalance ex situ and in situ measurements. The mechanical properties were tested by nanoindentation. The hardness of the multilayer thin film was 0.46 GPa. The thin films modulus was correlated to its ordering and anisotropic structure. Both hardness and modulus of this composite film were higher than those of several other types of polymer thin films.

Ultrathin Film Electrodeposition of Conjugated Polymers on Conducting Surfaces

The class of π-conjugated polymers as solid state materials has been investigated ranging from its use as electrically conducting polymers to electroluminescent (EL) and laser-active materials.1 Synthesis using mainly aromatic and heteroaromatic polymer structures has been investigated.2 In particular, the study of polyfluorenes and its derivatives are of recent interest as photoactive fluorescent and laser-generating materials.3, 18 The systematic synthesis of microstructured polyfluorene materials with fluoren-2,7-diyl units either by Pd4 or Ni-catalyzed 5 coupling of 2,7-dibromofluorenes has found applications in the fabrication of blue polymer light emitting diode (PLED) devices. The chemical oxidation of fluorenes with FeCl3 6 or electrochemical oxidation of fluorenes has also been reported.7 Substitution on the 9-fluorenyl position enhances the solubility and processability of the resulting polyfluorene polymers.8

Conjugated Polymer Network Ultrathin Films on Metal Interfaces using the Precursor Polymer Approach: Design, Synthesis and In-situ Characterization

We have reported recently a novel method for cross-linking conjugated polymers involving a “precursor polymer” route, where the electrochemical method can be used to prepare ultrathin films on conducting metal and metal oxide surfaces. In this paper, we present the design, synthesis, protocol, and recent results in the application of these thin film materials. An emphasis will be given on how these films are characterized in-situ by a combined surface plasmon spectroscopy (SPS) and electrochemical approach. As a methodology, the concept can be extended to new methods of electrodeposition, patterning, and grafting of conjugated polymers on electrochemically addressable metal surfaces. Compared to spin-cast or electropolymerized monomer films, they are very robust both thermally and mechanically. Other applications of these films to sensors, dielectric materials, non-lithographic patterning, etc. are currently being investigated.

The Precursor Polymer Approach to Electrodeposition and Patterning of Conjugated Polymer Ultrathin Films

In this paper, we report strategies for electrodepositing and patterning ultrathin films of conjugated polymers on flat electrode surfaces using the precursor polymer approach. This involves a rational synthesis design of the precursor polymer followed by careful electrodeposition and characterization of ultrathin films on conducting substrates. This has resulted in the preparation of smooth, high optical quality films, which should be important for applications involving flat electrode surfaces in devices. Characterization was made using surface sensitive spectroscopic and microscopic techniques. Copolymerization with monomers, polymer backbone design, and grafting on modified surfaces are key points in this strategy. Novel methods of in-situ characterization techniques have also been developed combing electrochemistry and surface plasmon resonance techniques.