Paul E. Schoen

Nanocrystalline metallic powders and films produced by the polyol method

Abstract The polyol method has been extended to synthesize metallic powders of Ru, Rh, Sn, Re, W, Pt, Au, Fe-Cu, Co-Cu, Ni-Cu, in addition to powders of Fe, Co, Ni, Cu, Pd and Ag which were previously prepared by others using this method. This method can also be used to deposit nanocrystalline metallic films on a variety of substrates, including PyrexTM, KaptonTM, TeflonTM, aluminum nitride, carbon fibers and alumina fibers. This can be a viable catalyst-free method for the deposition of conductive metallic films on non-conductive substrates.

Lipid-based tubule microstructures☆

Abstract Hollow tubule-shaped microstructures have been fabricated by self-organization of polymerizable diacetylenic phospholipid molecules. These microstructures have potential applications in a number of areas in materials science. A wide range of positional isomers of the diacetylenic lipids have been synthesized and all form tubules. A process for the deposition of thin metal coatings onto the exterior surfaces of the tubules has been developed. Results of spectroscopic and microscopic investigations of the lipids and microstructures are presented. Future issues important to the assessment of the ultimate utility of these materials are also presented.

Structure of Lipid Tubules Formed from a Polymerizable Lecithin

We have studied tubules formed from a polymerizable lipid in aqueous dispersion using freeze-fracture replication and transmission electron microscopy. The polymerizable diacetylenic lecithin 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine converts from liposomes to hollow cylinders, which we call tubules, on cooling through its chain melting phase transition temperature. These tubules differ substantially from cochleate cylinders formed by phosphatidylserines on binding of calcium. The tubules have diameters that range from 0.3 to 1 mum and lengths of up to hundreds of micrometers depending on conditions of formation. The thickness of the walls varies from as few as two bilayers to tens of bilayers in some longer tubules. Their surfaces may be either smooth, gently rippled, or with spiral steps depending on sample preparation conditions, including whether the lipids have been polymerized. The spiral steps may reflect the growth of the tubules by rolling up of flattened liposomes.

Structural, morphological, and magnetic study of nanocrystalline cobalt-copper powders synthesized by the polyol process

Nanocrystalline Co{sub {ital x}}Cu{sub 100{minus}{ital x}}(4{le}{ital x}{le}49 at.%) powders were prepared by the reduction of metal acetates in a polyol. The structure of powders was characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), extended x-ray absorption fine structure (EXAFS) spectroscopy, solid-state nuclear magnetic resonance (NMR) spectroscopy, and vibrating sample magnetometry (VSM). As-synthesized powders were composites consisting of nanoscale crystallites of face-centered-cubic (fcc) Cu and metastable face-centered cubic (fcc) Co. Complementary results of XRD, HRTEM, EXAFS, NMR, and VSM confirmed that there was no metastable alloying between Co and Cu. The NMR data also revealed that there was some hexagonal-closed-packed (hcp) Co in the samples. The powders were agglomerated, and consisted of aggregates of nanoscale crystallites of Co and Cu. Upon annealing, the powders with low Co contents showed an increase in both saturation magnetization and coercivity with increasing temperature. The results suggested that during preparation the nucleation of Cu occurred first, and the Cu crystallites served as nuclei for the formation of Co.

Pressure induced changes in liquid alkane chain conformation

Conformations of n‐alkane molecules in the liquid state have been studied as a function of temperature and pressure using Raman scattering. Observations of conformationally sensitive Raman bands in hexane, heptane, octane, and hexadecane reveal no sign of the pressure‐induced effects in polyethylene. Instead the Raman intensities indicate chain kinking as a function of pressure—a dramatic effect in the shorter chains, a slight effect for hexadecane. A theory based on considerations of conformational energy and translational entropy is presented which explains these effects qualitatively.

Color changes in chitosan and poly(allyl amine) films upon metal binding

The intense coloration of butterflies, snakes, hummingbirds and arthropods is due to reflective interference by stacked thin film layers of alternating high and low index of refraction materials. By controlling film thickness, it is also possible to create a single layer film of similar materials with well-defined color. Cross-linked chitosan and poly(allyl amine) hydrochloride thin films were assembled by dropping a dilute solution onto a spinning silicon substrate. Film quality and reproducibility were investigated, as well as the effects of cross-linking. Control of thickness could be used to determine film color. When dipped into a variety of metal ion solutions, the cross-linked films changed in thickness and color.

Lateral phase separation based on chirality in a polymerizable lipid and its influence on formation of tubular microstructures

Abstract No difference is believed to exist between the physical properties of racemic and enantiomeric phospholipids. We report here the first observation of lateral phase separation of phospholipids on the basis of the chirality of the glycerol backbone. The chiral polymerizable diacetylenic lecithin 1,2-bis-(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine, or l -DC8,9PC, spontaneously forms hollow cylindrical structures, or tubules, and similar right-handed helices. To determine the influence of chirality of the lipid on the morphology of the resultant microstructures, d -DC8,9 and rac-DC8,9PC were synthesized. The T vs. XL phase diagram for the lipids in excess water indicates formation of a racemic mixture, with no appreciable co-crystallization of the enantiomers in the bilayer plane. When exposed to tubule-forming conditions, rac-DC8,9PC produced tubules, right- and left-handed helices, and a small proportion of anomalous microstructures such as flat and loosely-wound sheets, and pairs of tubules linked by sheets. The formation of chiral structures is consistent with the thermodynamic data, suggesting that lateral phase separation on the basis of chirality is responsible for formation of tubules from rac-DC8,9PC liposomes, and that when monomer is precipitated from alcoholic solution the resultant microstructures are of predominantly one handedness or the other. The unusually poor miscibility of the enantiomers is the low temperature phase can be explained by hydrocarbon chain packing constraints imposed by the diacetylene moiety.

Interaction of metallized tubules with electromagnetic radiation

Several diacetylenic lecithins form tubular microstructures (tubules) when their liposomes are cooled through the chain‐melting transition. Recently, the tubules have been metal plated by an electroless technique. This paper reports on the interaction of permalloy coated tubules with electromagnetic radiation. At 10 vol % loading of tubules in an epoxy matrix has a real dielectric constant e’≊50 at a frequency of 9.5 GHz. Simple electrodynamics accounts well for the observed results. Far higher values of e’ may be achievable with longer tubules and with improved metal coatings.

Differential scanning calorimetric study of the thermotropic phase behavior of a polymerizable, tubule-forming lipid

A comparative study of the polymorphism exhibited by the polymerizable, tubule-forming phospholipid 1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3- phosphocholine (DC23PC) and its saturated analog 1,2-ditricosanoyl-sn-glycero-3-phosphocholine (DTPC) in aqueous suspension is reported. Differential scanning calorimetry (DSC), as well as freeze-fracture electron microscopy and Raman spectroscopy, have been used to study the influence on phase behavior of rigid diacetylene groups in the fatty acyl chains of a phosphatidylcholine. DTPC large multilamellar vesicle (MLV) and small unilamellar vesicle (SUV) suspensions were found to retain liposome morphology after chain crystallization had occurred. In marked contrast, diacetylenic DC23PC suspensions do not maintain liposomal morphology in converting to the low temperature phase. Large MLVs of DC23PC with outer diameters in excess of 1 micron convert to a gel phase with cylindrical or tubular morphology at 38 degrees C, just a few degrees below the lipids chain melting temperature (TM(H), i.e. temperature of an endothermic event observed during a heating scan) of 43.1 degrees C. Unlike the large MLVs, small MLVs or SUVs of DC23PC, with diameters of 0.4 +/- 0.3 micron and 0.04 +/- 0.02 micron, respectively, exhibit metastability in the liquid-crystalline state for several tens of degrees below the chain melting temperature prior to converting to a gel phase which, by electron microscopy, manifests itself as extended multilamellar sheets. Raman data collected at TM(H) -40 degrees C demonstrate that the gel state formed by DC23PC is very highly ordered relative to that of DTPC, suggesting that special chain packing requirements are responsible for the novel phase behavior of DC23PC.

Pressure measurement at high temperatures in the diamond anvil cell

The frequency shift of the R1 ruby fluorescence peak has been measured in the diamond anvil cell along the ice/water melting curve in the temperature interval 25–200 °C and pressure interval 0–40 kbars. The temperature and pressure coefficients of the frequency shift were found to be independent in this region. Using a least‐squares‐fitting program to find the fluorescence peak positions, we could reproducibly measure pressures to ±0.2 kbar at 25 °C and to ±0.5 kbar at 300 °C. The temperature coefficient of the frequency shift of R1 in the interval 25–300 °C was determined to be −0.149 cm−1/°K. Large systematic errors in the pressure determination were found to arise when nonuniformity of temperature in the diamond anvil cell caused uncertainty in the ruby temperature.