Yongli Mi

Bamboo fiber‐reinforced polypropylene composites: A study of the mechanical properties

A new type of bamboo fiber-reinforced polypropylene (PP) composite was prepared and its mechanical properties were tested. To enhance the adhesion between the bamboo fiber and the polypropylene matrix, maleic anhydride-grafted polypropylene (MAPP) was prepared and used as a compatibilizer for the composite. The maleic anhydride content of the MAPP was 0.5 wt %. It was found that with 24 wt % of such MAPP being used in the composite formulation, the mechanical properties of the composite such as the tensile modulus, the tensile strength, and the impact strength all increased significantly. The new composite has a tensile strength of 32–36 MPa and a tensile modulus of 5–6 GPa. Compared to the commercially available wood pulp board, the new material is lighter, water-resistant, cheaper, and more importantly has a tensile strength that is more than three times higher than that of the commercial product.

A replicable tetrahedral nanostructure self-assembled from a single DNA strand.

We report the design and construction of a nanometer-sized tetrahedron from a single strand of DNA that is 286 nucleotides long. The formation of the tetrahedron was verified by restriction enzyme digestion, Ferguson analysis, and atomic force microscopy (AFM) imaging. We further demonstrate that synthesis of the tetrahedron can be easily scaled up through in vivo replication using standard molecular cloning techniques. We found that the in vivo replication efficiency of the tetrahedron is significantly higher in comparison to in vitro replication using rolling-circle amplification (RCA). Our results suggest that it is now possible to design and replicate increasingly complex, single-stranded DNA nanostructures in vivo.

DNA Computing and Molecular Programming

This book constitutes the thoroughly refereed post-conference proceedings of the 16th International Conference on DNA Computing and Molecular Programming, DNA16, held in Hong Kong, China, in June 2010. The 16 revised full papers presented were carefully selected during two rounds of reviewing and improvement from 59 submissions. The papers are well balanced between theoretical and experimental work and address all areas that relate to biomolecular computing, including demonstrations of biomolecular computing, theoretical models of biomolecular computing, biomolecular algorithms, computational processes in vitro and in vivo, analysis and theoretical models of laboratory techniques, biotechnological and other applications of DNA computing, DNA nanostructures, DNA devices such as DNA motors, DNA error evaluation and correction, in vitro evolution, molecular design, self-assembled systems, nucleic acid chemistry, and simulation tools.

Miscibility in blends of poly (4-vinylpyridine)/poly (4-vinylphenol) as studied by 13C solid-state NMR

Abstract The miscibility of poly (4-vinylpyridine) (P4VP) with poly (4-vinylphenol) (PVPh) blends was investigated over a wide range of compositions by differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance (NMR) spectroscopy. DSC results show that the T g s of the P4VP/PVPh blends are much higher than those of the calculated weight-average values. The proton spin–lattice relaxation times in the laboratory frame, T 1 ( H ), and the rotating frame, T 1 ρ ( H ), were studied as a function of blend composition. T 1 ( H ) and T 1 ρ ( H ) results demonstrate that the spin diffusion can completely average out the entire relaxation process. It was also found that the intimate mixing of the polymer blends restricts the local chain mobility.

High-pressure DSC study of thermal transitions of a poly(ethylene terephthalate) carbon dioxide system

Abstract The thermal transitions of a poly(ethylene terephthalate)/carbon dioxide (PET/CO2) system were investigated by using a differential scanning calorimeter accessorized with a high-pressure DSC cell. It was found that the glass transition temperature of PET decreases with an increase in the CO2 pressure due to the plasticization effect, which is quite noticeable even at rather low CO2 pressures. The sorbed CO2 enhances the mobility of the chain segments and depresses the crystallization temperature of the PET. The CO2-induced crystallization of PET at high pressure is attributed mainly to the plasticization effect, which causes a lower Tg than room temperature for PET, and hence crystallization of PET can occur at room temperature. The sorbed CO2 was also found to be able to induce the crystallization of PET at temperatures lower than the glass transition temperature of PET. The results of high-pressure DSC were supported by measurements of wide-angle X-ray diffraction (WAXD).

Examination of miscibility at molecular level of poly(hydroxyether of bisphenol A)/poly(N-vinyl pyrrolidone) blends by cross-polarization/magic angle spinning 13C nuclear magnetic resonance spectroscopy

The miscibility of poly(hydroxyether of bisphenol A) (phenoxy) and poly(N-vinyl pyrrolidone) (PVP) was investigated by differential scanning calorimetry (DSC) and high-resolution solid-state nuclear magnetic resonance (NMR) techniques. The DSC studies showed that the phenoxy/PVP blends have a single, composition-dependent glass transition temperature (T g ). The S-shaped T g -composition curve of the phenoxy/PVP blends was reported, which is indicative of the strong intermolecular hydrogen-bonding interactions. To examine the miscibility of the system at molecular level, high-resolution solid-state 13 C nuclear magnetic resonance (NMR) technique was employed. Upon adding phenoxy to system, the chemical shift of carbonyl carbon resonance of PVP was observed to shift downfield by 1.6 ppm in the 13 C cross-polarization (CP)/magic angle spinning (MAS) together with the high-power dipolar decoupling (DD) spectra when the concentration of phenoxy is 90 wt %. The observation was responsible for the formation of intermolecular hydrogen bonding. The proton spin-lattice relaxation time T 1 (H) and the proton spin-lattice relaxation time in the rotating frame T 1p (H) were measured as a function of the blend composition. The T 1 (H) result was in good agreement with the thermal analysis, i.e., the blends are completely homogeneous on the scale of 20 ∼ 30 nm. The six results of T 1p (H) further indicated that the blends were homogeneous on the scale of 40 ∼ 50A.

UNIQUIMER 3D, a software system for structural DNA nanotechnology design, analysis and evaluation

A user-friendly software system, UNIQUIMER 3D, was developed to design DNA structures for nanotechnology applications. It consists of 3D visualization, internal energy minimization, sequence generation and construction of motif array simulations (2D tiles and 3D lattices) functionalities. The system can be used to check structural deformation and design errors under scaled-up conditions. UNIQUIMER 3D has been tested on the design of both existing motifs (holiday junction, 4 × 4 tile, double crossover, DNA tetrahedron, DNA cube, etc.) and nonexisting motifs (soccer ball). The results demonstrated UNIQUIMER 3Ds capability in designing large complex structures. We also designed a de novo sequence generation algorithm. UNIQUIMER 3D was developed for the Windows environment and is provided free of charge to the nonprofit research institutions.

Solid-state n.m.r. investigation of crosslinkable blends of novolac and poly(ϵ-caprolactone)

Abstract The miscibility, phase behavior, and intermolecular interaction of novolac/poly(ϵ-caprolactone) (PCL) blends, before and after curing, were investigated by the high resolution solid-state nuclear magnetic resonance (n.m.r.) technique. It was found that there exists hydrogen-bonding interaction between the carbonyl groups of PCL and the hydroxyl groups of novolac, which results in the downfield shift of carbonyl carbon resonance of PCL and the upfield shift of hydroxyl-substituted carbon resonance of novolac. The interaction also broadens the line width of carbonyl carbon resonance. After curing with 15 wt% hexamine (relative to novolac content), hydrogen-bonding interaction still exists between the components in the crosslinked blends. However, the relative amount of hydrogen bonds decreases significantly. Both the uncured and the cured novolac/PCL blends exhibit composition-dependent miscibility. The curing causes an increase of the domain size in the amorphous phase and a reaction of miscibility between the two components.

Characterization of blends of poly(vinyl chloride) and poly(N‐vinyl pyrrolidone) by FTIR and 13C CP/MAS NMR spectroscopy

Blends of poly(vinyl chloride) (PVC) with Poly(N-vinyl pyrrolidone) (PVP) were investigated by Fourier infrared spectroscopy (FTIR) and high-resolution solid-state 13 C cross-polarization/magic angle spinning (CP/MAS) nuclear magnetic resonance (NMR) spectroscopy. The intermolecular interactions between PVP and PVC are weaker than the self-association of PVP and the inclusion of the miscible PVC results in the decreased self-association of PVP chains, which was evidenced by the observation of high-frequency shift of amide stretching vibration bands of PVP with inclusion of PVC. This result was further substantiated by the study of 13 C CP/MAS spectra, in which the chemical shift of carbonyl resonance of PVP was observed to shift to a high field with inclusion of PVC, indicating that the magnetic shielding of the carbonyl carbon nucleus is increased. The proton spin-lattice relaxation time in the laboratory frame (T 1 (H)) and the proton spin-lattice relaxation time in the rotating frame (T 1ρ (H)) were measured as a function of the blend composition to give the information about phase structure. It is concluded that the PVC and PVP chains are intimately mixed on the scale of 20-30A.

Dynamics of a Stick-Jump Contact Line of Water Drops on a Strip Surface

In this study, we prepared microscale periodic rough structures consisting of parallel strips on a silicon surface. The width of each strip was equal to the gap between the strips, and the silicon surface was silanized with perfluorooctyltrichlorosilane. We studied the wetting characteristics of water drops as they advanced and receded on patterned surfaces in a direction perpendicular to the strip. Water drops were observed to advance or recede in a smooth manner when the strip width was smaller than 32 microm but in a stick-jump manner when the strip width was larger than 50 microm. The regular strip-patterned substrates enabled us to deduce the relationship between the stick-jump behavior and the feature size of the substrate. For surfaces on which water drops showed stick-jump behavior, the oscillation amplitude of the contact angle decreased with decreasing strip width. In addition, the jumping distances of the contact lines, for both advancing and receding water drops, were nearly equal to the strip period. A 2D model was applied to analyze the contact line motion on the patterned surfaces, which showed reasonable agreement with the experimental results.