Christopher Y. Li

Morphology and Crystallization Behavior of HDPE/CNT Nanocomposite

Polymer carbon nanotube nanocomposites (PCNs) represent the first realized major commercial application of carbon nanotubes (CNTs). In this study, high density polyethylene (HDPE)/CNT PCNs have been prepared using a solution blending technique. Both pristine single‐walled nanotubes (SWNT) and polyethylene (PE) single crystal decorated CNTs (so called nano hybrid shish kebabs, NHSKs) have been used as the precursors for PCN preparation. Polarized light microscopy, transmission electron microscopy, scanning electron microscopy, differential scanning calorimetry, and thermogravimetry were used to study the morphology, crystallization behavior, and thermal stability of the resulting PCNs. The PCNs from pristine SWNTs possess a more dense morphology than do the PCNs prepared from NHSKs; PE single crystal lamellae are perpendicular or oblique to the CNT axis, leading to relatively “open‐structured” PCNs. Heterogeneous nucleation occurred in both nonisothermal and isothermal crystallization of PCNs and the crystallization kinetics are much faster than that of the pure HDPE. Thermal stability of PCNs showed dramatic enhancement (as high as 70°C/115°C improvement of T max in N2/air atmosphere, respectively), which is attributed to the formation of the free radical scavenging CNT network. Dedicated to Prof. Phillip H. Geils seventy-fifth birthday.

Alternating patterns on single-walled carbon nanotubes

Scientific and technological interest in one-dimensional nanomaterials, in particular carbon nanotubes, is a result of their fascinating properties and their ability to serve as templates for directed assembly. For applications in nanoelectronics it is necessary to create ordered arrays of nanotubes for large-scale integrated circuits, an area in which there has been significant progress, and to produce controllable patterns on individual nanotubes so that multiple transistors can be fabricated on them, an area where progress has been slower. Here, we show that judiciously selected crystalline block copolymers can be periodically decorated along carbon nanotubes, leading to amphiphilic, alternating patterns with a period of approximately 12 nm. In addition, end-functionalization of the block copolymers allowed gold nanoparticles to be periodically attached to the nanotubes. This approach provides a facile technique for the periodic patterning of one-dimensional nanomaterials.

Directed Self-Assembly of Nanoparticles for Nanomotors

We report, for the first time, the design and fabrication of a nanoparticle-based nanomotor system by directly self-assembling nanoparticles onto functional, nanometer-thin lamellae, such as polymer single crystals. Tens of thousands of judiciously selected nanoparticles (gold, iron oxide, and platinum nanoparticles) with sizes ranging from <5 to a few tens of nanometers have been introduced into a single nanomotor via directed self-assembly. The resulting nanomotor realizes functions such as autonomous movement, remote control, and cargo transportation by utilizing the advantages offered by nanoparticles, such as the small size, surface plasmon resonance, catalytic and magnetic properties. Because of the structural and functional versatility of nanoparticles, the facile fabricating procedure, and the potential for mass production, our strategy shows a key step toward the development of next generation multifunctional nanomotors.

Hybrid electrolytes with controlled network structures for lithium metal batteries.

Solid polymer electrolytes (SPEs) with tunable network structures are prepared by a facile one-pot reaction of polyhedral oligomeric silsesquioxane and poly(ethylene glycol). These SPEs, with high conductivity and high modulus, exhibit superior resistance to lithium dendrite growth even at high current densities. Measurements of lithium metal batteries with a LiFePO4 cathode show excellent cycling stability and rate capability.

Polymer Single Crystal As Magnetically Recoverable Support for Nanocatalysts.

In this Letter, we report, for the first time, using polymer single crystal as magnetically recoverable support for nanoparticle catalysts. This catalyst system is composed of polymer single crystal, platinum nanoparticles, and iron oxide nanoparticles, which act as support, catalysts, and magnetic responsive materials, respectively. Platinum nanoparticles and iron oxide nanoparticles were bonded onto thiol groups and hydroxyl groups on a tailor-designed polymer single-crystal surface. Because of its quasi 2D nature, polymer single crystal possesses high surface area to volume ratio (2.5 × 10(8) m(-1)), which is ∼40 times higher than its nanosphere counterpart of the same volume. This high surface to volume ratio facilitates the high loading of both nanoparticles, which ensures efficient catalytic reaction and reliable nanoparticle recycling. Synergetic interactions between platinum and iron oxide nanoparticles also led to further improvement in catalytic activity.

Mimicking bone nanostructure by combining block copolymer self-assembly and 1D crystal nucleation.

The orientation and spatial distribution of nanocrystals in the organic matrix are two distinctive structural characteristics associated with natural bone. Synthetic soft materials have been used to successfully control the orientation of mineral crystals. The spatial distribution of minerals in a synthetic scaffold, however, has yet to be reproduced in a biomimetic manner. Herein, we report using block copolymer-decorated polymer nanofibers to achieve biomineralized fibrils with precise control of both mineral crystal orientation and spatial distribution. Exquisite nanoscale structural control in biomimetic hybrid materials has been demonstrated.

Polymer single crystal templated janus nanoparticles.

Top-selective surface modification has been widely used for the synthesis of Janus nanoparticles (NPs). Herein we demonstrate that polymer single crystals can serve as generic substrates to immobilize NPs and the resultant NPs are Janus in nature. This technique is generic because various NPs as well as polymer single crystal substrates can be used. Single crystals of poly(ethylene oxide), polycaprolactone, and polyethylene-block-poly(ethylene oxide) have been successfully used to immobilize gold, magnetic, and semiconducting NPs. Subsequent dissolution of the single crystals led to various types of Janus NPs and NP clusters with different polymer brushes.

Polymer single crystal-decorated superhydrophobic buckypaper with controlled wetting and conductivity.

Herein we report fabrication of uniform, free-standing nanohybrid buckypaper with high carbon nanotube (CNT) contents (13-70%) using polymer single crystal-decorated CNTs as the precursor. Polyethylene single crystals were periodically grown on CNT surfaces, forming a nanohybrid shish kebab (NHSK) structure. Vacuum filtering a NHSK suspension led to polymer single crystal-decorated buckypaper (named as NHSK paper) with a wide range of CNT contents and uniform CNT dispersion. Porosity, surface roughness, and conductivity of NHSK paper can be controlled by tuning the polymer single crystal size. Because of the hierarchical roughness created by intra- and inter-NHSK nanostructure, NHSK paper with controlled kebab size exhibits both superhydrophobicity and high surface water adhesion, which mimics the rose petal effect. We anticipate that this unique NHSK paper can find applications in sensors, electrochemical devices, and coatings.

Tuning Ion Conducting Pathways Using Holographic Polymerization

Polymer electrolyte membranes (PEMs) with high and controlled ionic conductivity are important for energy-related applications, such as solid-state batteries and fuel cells. Herein we disclose a new strategy to fabricate long-range ordered PEMs with tunable ion conducting pathways using a holographic polymerization (HP) method. By incorporating polymer electrolyte into the carefully selected HP system, electrolyte layers/channels with length scales of a few tens of nanometers to micrometers can be formed with controlled orientation and anisotropy; ionic conductivity anisotropy as high as 37 has been achieved.

A study of polyimide thermoplastics used as tougheners in epoxy resins — structure, property and solubility relationships

A series of organo-soluble aromatic polyimides have been synthesized from four different dianhydrides and two different diamines. The main purpose of this research was to develop new toughening agents from thermoplastic polyimides for epoxy resins. Thus, the solubility of these polyimides in epoxy resins is crucial to obtain a homogeneous mixture before curing. The structure dependence of these polyimides on solubility, thermal and mechanical properties was investigated in this study. The subglass relaxation processes in polyimides were also discussed based on the non-cooperative and cooperative motion proposed by Starkweather. A suitable polyimide has been found for toughening epoxy resins.