Novel morphology of polyethylene crystals created upon melt crystallization of spin-coated film

We demonstrate a strikingly novel morphology of high-density polyethylene (HDPE) crystal obtained upon melt crystallization of spin-coated thin film. This crystal gives windmill-like morphology which contains a number of petals. A detailed inspection on this morphology reveals that each petal is actually composed of terrace-stacked PE lamellae, in which the polymer chains within crystallographic a-c planes adopt similar to 45 degrees tilting around b-axis. The surrounding domains associated with a petal of the windmill composed of twisted lamellar overgrowths with an identical orientation of their long axis, which is the crystallographic b-axis shared by the petal and its corresponding twisted lamellar overgrowths.

Novel hydrophilic-hydrophobic multiblock copolyimides as proton exchange membranes: Enhancing the proton conductivity

A series of novel multiblock copolymers based on sulfonated copolyimides were developed and evaluated for use as proton exchange membranes (PEMs). In these multiblock copolyimides, the hydrophilic blocks were composed of the sulfonated dianhydride and the sulfonated diamine, with sulfonic acid groups on every aromatic ring (i.e., fully sulfonated). This molecular design was implemented to effectively enhance the proton conductivity. The properties of the multiblock copolyimides with varying IEC values or block lengths were investigated to obtain a better understanding of the relationship between molecular structure and properties of proton exchange membranes. The water uptake and proton conductivity were found to be highly dependent upon their structure. The block copolymers displayed significantly higher proton conductivities, especially at low relative humidity than the random copolymers with a similar IEC.

Conducting polyaniline film from aqueous dispersion: Crystallizable side chain forced lamellar structure for high conductivity

Aqueous conducting polyaniline dispersion was prepared employing acidic phosphate ester bearing hydrophilic ethylene glycol segment as dopant, and conducting film with electrical conductivity of 25 S/cm was obtained from the dispersion. Ordered self-assembly lamellar structure with interlamellar distance of 1.2 nm was observed in the film, which consisted of alternating layers of rigid polyaniline chain and flexible phosphate ester side chains, where the phosphate side chain layer was separated by two rigid polyaniline layers. The lamellar structure leading to high conducting film was formed due to the confinement of polyaniline chain by crystallizable phosphate side chain, since the electrical conductivity decreased by four orders of magnitude once the dopant side chain crystalline was destroyed. The crystallizable side chain forced lamellar structure is expected to be a new chance for highly conducting polyaniline.

Probing structural changes of spin-coated polystyrene film after swelling and precipitation by synchrotron GIUSAXS and AFM

Polystyrenc film of about 50 nm in thickness on silicon wafer was obtained by spin-coating in tetrahydrofuran solution.The film exhibits a rough surface as shown by atomic force microscopy images and ellipsometry data.

A monometallic tri-spin single-molecule magnet based on rare earth radicals

A mononuclear tri-spin single-molecule magnet based on the rare earth radical [Tb(hfac)(3)(NITPhOEt)(2)] (NITPhOEt = 4'-ethoxy-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) has been synthesized, structurally characterized and the alternating current signals show a slow relaxation of magnetization and frequency-dependent signals.

Two-Step Spin-Transition Iron(III) Compound with a Wide [High Spin-Low Spin] Plateau

A new iron(III) coordination compound exhibiting a two-step spin-transition behavior with a remarkably wide [HS-LS] plateau of about 45 K has been synthesized from a hydrazino Schiff-base ligand with an N,N,O donor set, namely 2-methoxy-6-(pyridine-2-ylhydrazonomethyl) phenol (Hmph). The single-crystal X-ray structure of the coordination compound {[Fe(mph)(2)](ClO4)(MeOH)(0.5)(H2O)(0.5)}(2) (1) determined at 150 K reveals the presence of two slightly different iron(III) centers in pseudo-octahedral environments generated by two deprotonated tridentate mph ligands. The presence of hydrogen bonding interactions, instigated by the well-designed ligand, may justify the occurrence of the abrupt transitions. 1 has been characterized by temperature-dependent magnetic susceptibility measurements, EPR spectroscopy, differential scanning calorimetry, and Fe-51 Mossbauer spectroscopy, which all confirm the occurrence of a two-step transition. In addition, the iron(III) species in the high-spin state has been trapped and characterized by rapid cooling EPR studies.

Relaxation time and conductivity of comb-like gel polymer electrolytes

Using the copolymer of acrylonitrile (AN), methyl methacrylate (MMA), and poly(ethylene glycol) methyl ether methacrylate as a backbone and poly(ethylene glycol) methyl ether (PEGME) with 1100 molecular weight as side chains, comb-like gel polymers and their Li salt complexes were synthesized. The dynamic mechanical properties and conductivities were investigated. Results showed that the gel copolymer electrolytes possess two glass transitions: alpha-transition and beta-transition. Based on the time-temperature equivalence principle, a master curve was constructed by selecting T. as reference temperature. By reference to T-0 = 50 degrees C, the relation between log c, and c was found to be linear. The master curves are displaced progressively to higher frequencies as the content of plasticizer is increased. The relation between log tau(p) and the content of plasticizer is also linear.

Enhanced electrical conductivity of highly crystalline polythiophene/insulating-polymer composite

Poly(3-butylthiophene) (P3BT)/insulating-polymer composites with high electrical conductivity have been prepared directly from the solution. These composites exhibit much higher conductivity compared to pure P3BT with the same preparation method provided that P3BT content is higher than 10 wt %. Morphological studies on both the pure P3BT and the composites with insulating polymer show that P3BT highly crystallizes and develops into whisker-like crystals. These nanowires are homogeneously distributed within the insulating polymer matrix and form conductive networks, which provide both extremely large interface area between conjugated polymer and insulating polymer matrix and highly efficient conductive channels through out the whole composite. In contrast, the conductivity enhancement of P3HT/PS composite is not so obvious and drops down immediately with increased PS content due mainly to the absence of highly crystalline whisker-like crystals and much larger scale phase separation between the components. The results presented here could further illuminate the origin of conductivity formation in organic semiconducting composites and promote applications of these polymer semiconductor/insulator composites in the fields of organic (opto-)electronics, electromagnetic shielding, and antistatic materials.

Preparation and transport properties of a bulk icosahedral quasicrystalline Ti45Zr35Ni17Cu3 alloy

A bulk alloy which consists of the single icosahedral quasicrystalline phase (I-phase) in Ti45Zr35Ni17CU3 alloy has been fabricated by mechanical alloying and subsequent pulse discharge sintering technique. Crystallographic structure analyses show that the bulk alloy is an I-phase. The transport properties of the bulk alloy are examined, and the results show that the room-temperature thermal conductivity is 5.347 W K-(1) m(-1), and the electrical conductivity decreases with increasing the temperature from 300 to 450K. The Seebeck coefficient is negative at the temperature range from 300 to 360K, and changes to positive from 370 to 450K. Hall effect measurements indicate the bulk I-phase alloy has a high carrier concentration. The specific heat capacity increases when the temperature increases from 280 to 324 K.

Fast densification and electrical conductivity of yttria-stabilized zirconia nanoceramics

Nanocrystalline 8YSZ (8 mol% yttria stabilized zirconia) bulk samples with grain sizes of 20-30 nm were synthesized by Sol-Gel method and then densified under a high pressure of 4.5 GPa at 1273 K for 10 min. The method led to the densification of 8YSZ to a relative density higher than 92% without grain growth. Fourier transmission Raman spectroscopy suggested that 8YSZ underwent a phase transition from the cubic phase to a phase mixture (tetragonal plus a trace of monoclinic) after the densification, which decreased the electrical conductivity to a certain degree as concluded from the impedance spectroscopy.

Formation of ordered microphase-separated pattern during spin coating of ABC triblock copolymer

In this paper, the authors have systematically studied the microphase separation and crystallization during spin coating of an ABC triblock copolymer, polystyrene-b-poly(2-vinylpyridine)-b-poly(ethylene oxide) (PS-b-P2VP-b-PEO). The microphase separation of PS-b-P2VP-b-PEO and the crystallization of PEO blocks can be modulated by the types of the solvent and the substrate, the spinning speed, and the copolymer concentration. Ordered microphase-separated pattern, where PEO and P2VP blocks adsorbed to the substrate and PS blocks protrusions formed hexagonal dots above the P2VP domains, can only be obtained when PS-b-P2VP-b-PEO is dissolved in N,N-dimethylformamide and the films are spin coated onto the polar substrate, silicon wafers or mica. The mechanism of the formation of regular pattern by microphase separation is found to be mainly related to the inducement of the substrate (middle block P2VP wetting the polar substrate), the quick vanishment of the solvent during the early stage of the spin coating, and the slow evaporation of the remaining solvent during the subsequent stage. On the other hand, the probability of the crystallization of PEO blocks during spin coating decreases with the reduced film thickness. When the film thickness reaches a certain value (3.0 nm), the extensive crystallization of PEO is effectively prohibited and ordered microphase-separated pattern over large areas can be routinely prepared.