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The wettabilities of the partially fluorinated polymers (ethylene-tetrafluoroethylene copolymer (ETFE), ethylene- chlorotrifluoroethylene copolymer (ECTFE), and poly(vinylidene fluoride) (PVDF)) were investigated by contact angle measurements. Zisman plots for ETFE and ECTFE exhibited linear relationships, while the Zisman plot for PVDF show- ed a slight curvature, which was interpreted to indicate strong non-dispersive interactions between the surface and the contacting liquids. The Lifshitz-van der Waals forces of the fluoropolymers were estimated to increase in the order of ETFE < PVDF << ECTFE. An evaluation of the polar or "acid-base" interaction energies showed that PVDF, which possesses the most acidic hydrogens among the examined fluoropolymers, has the strongest acid-base interactions.

We present the design of a micropillar array that leads to the formation of stable and uniform liquid crystal (LC) thin films for sensing applications. Photolithography and electroplating methods were employed to fabricate the micropillar array. By using this microfabricated structure, thin films of LC (5CB: 4'-pentyl-4-cyanobiphenyl) were formed and stabilized against gravitational forces and mechanical shock. The geometric profile of the supported LC thin film was simulated by using finite element methods. Orientational ordering transitions of nematic LCs in the supported thin films were used to detect liquid- and vapor-phase analytes via changes in the intensity of light transmitted through the LCs. The LC thin films supported by these microfabricated structures were tested and found to respond to dimethyl methylphosphonate gas.

A systematically varying series of monolayer-protected clusters (MPCs) was prepared by exposing small gold nanoparticles ( approximately 2 nm in diameter) to the following four adsorbates: n-octadecanethiol ( n - C18), 2-hexadecylpropane-1,3-dithiol ( C18C2), 2-hexadecyl-2-methylpropane-1,3-dithiol ( C18C3), and 1,1,1-tris(mercaptomethyl)heptadecane ( t - C18). The resultant MPCs were characterized by solubility studies, UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier-transform infrared spectroscopy (FT-IR). All of the MPCs were soluble in common organic solvents; moreover, analysis by TEM showed that the core dimensions were unaffected by exposure to any of the adsorbates. Separate studies by XPS revealed that the sulfur atoms in all MPCs were predominantly bound to the surface of gold (i.e., approximately 85% or better). Analysis by FT-IR showed that MPCs functionalized with n - C18 possessed alkyl chains having the greatest conformational order in both the solid-state and dispersed in solution; in contrast, those generated from the other three adsorbates were more liquid-like with reduced conformational order (or crystallinity). The rate of nanoparticle decomposition induced by cyanide ions was monitored by UV-vis spectroscopy. While MPCs functionalized with n - C18 showed the fastest rate of decomposition, those functionalized with C18C3 were the most resistant to decomposition. Overall, the following trend in chemical stability was observed, C18C3 >> C18C2 > t - C18 >> n - C18.

We report that surface-induced ordering of liquid crystals in the vicinity of chemically functionalized gold nanoparticles leads to changes in the localized surface plasmon resonance (LSPR) of the ...

We report two methods that involve tailoring of the chemical composition of the nematic liquid crystal 4-cyano-4′-pentylbiphenyl to achieve control over the orientational ordering of the liquid crystal on chemically functionalized surfaces. The first method involves the direct addition of 4-cyano-4′-biphenylcarboxylic acid to 4-cyano-4′-pentylbiphenyl. The second method involves exposure of 4-cyano-4′-pentylbiphenyl to ultraviolet light and photochemical generation of a range of products, including 4-cyano-4′-biphenylcarboxylic acid. The addition of the acid or exposure to ultraviolet light accelerated the rate at which the liquid crystal exhibited an orientational transition from planar to perpendicular (homeotropic) alignment on surfaces presenting ammonium groups. The appearance of the homeotropic orientation of the UV-treated 4-cyano-4′-pentylbiphenyl on ammonium-terminated surfaces was dependent on the thickness of the film of liquid crystal (13–50 μm), consistent with a dipolar coupling between the liquid crystal and the electric field associated with an electrical double layer generated at the ammonium surface. Although the addition of 4-cyano-4′-biphenylcarboxylic acid or UV treatment of the liquid crystal also promoted homeotropic orientations on surfaces presenting hydroxyl groups, the orientations of the UV-treated liquid crystal on the hydroxyl-terminated surface did not change with thickness of the film of liquid crystal in the manner observed on the ammonium-terminated surfaces. The latter result indicates that the mechanism leading to homeotropic anchoring on hydroxyl-terminated surfaces is distinct from that on ammonium-terminated surfaces. Measurements performed using polarization modulation infrared reflection–absorption spectroscopy suggest that hydrogen bonding between the 4-cyano-4′-biphenylcarboxylic acid and the hydroxyl-terminated surface is responsible for the homeotropic anchoring on the surface. Finally, the orientation of the liquid crystal on methyl-terminated surfaces was not influenced by the addition of 4-cyano-4′-biphenylcarboxylic acid nor UV treatment. These results illustrate how the chemical composition of liquid crystals can be manipulated to achieve control over their ordering on surfaces that possess chemical functionality relevant to the development of liquid crystal-based sensors and diagnostic tools. We illustrate the utility of this approach by using the tailored liquid crystal to amplify and optically transduce the presence of proteins arrayed on ammonium-terminated surfaces.

This paper shows that an introduction of thiosulfate anions in place of bromide anions greatly improves both chemical and thermal stability of tetraoctylammonium-protected gold nanoparticles. Tetraoctylammonium thiosulfate [(Oct)4N+-O3SS]-protected gold nanoparticles are synthesized by the reduction of (Oct)4N+-AuCl4 to Au(I)-SSO3-, followed by the addition of sodium borohydride. The presence of thiosulfate anions instead of bromide anions on the surface of gold nanoparticles results in a significant dampening of the surface plasmon band of gold at 526 nm due to the strong interaction between thiosulfate and the gold nanoparticle surface. Cyanide decomposition and heating treatment studies suggest that (Oct)4N+-O3SS-protected nanoparticles have much higher overall stability compared to (Oct)4N+-Br-protected gold nanoparticles.

The unsaturated aryl-substituted ferrocenophanes 1,1‘-(1-phenylbuta-1,3-diene-1,4-diyl)ferrocene and 1,1‘-(1-mesitylbuta-1,3-diene-1,4-diyl)ferrocene were synthesized and used to prepare high molecular weight conjugated polymers by ring-opening metathesis polymerization. X-ray crystal structures of the phenyl- and mesityl-substituted monomers showed substantial bond angle strain in the butadiene bridge. The monomers were readily polymerized upon exposure to a tungsten-based initiator to give high molecular weight polymers that were soluble in common organic solvents. UV/vis spectral analysis indicated that the aryl moieties gave rise to enhanced conjugation when compared to related alkyl-substituted ferrocene-containing polymers. The enhanced conjugation was further supported by electrochemical analysis. The thermal stability of the new ferrocene-containing polymers was similar to that of oligomeric poly(ferrocenylene), and the conductivities upon doping were on the order of 10-5 S cm-1.

The structural and interfacial properties of self-assembled monolayers (SAMs) on gold derived from the adsorption of a series of 1,1,1-tris(mercaptomethyl)alkanes (i.e., CH3(CH2)mC[CH2SH]3, where m = 9, 11, 13, 15) were investigated. The new SAMs, which possess uniformly low densities of alkyl chains, were characterized by ellipsometry, contact angle goniometry, and polarization modulation infrared reflection absorption spectroscopy. Additional analysis of the SAMs by X-ray photoelectron spectroscopy permitted a direct calculation of the packing densities of the SAMs on gold. The results as a whole, when compared to those obtained on SAMs generated from normal alkanethiols (CH3(CH2)m+2SH), 2-alkylpropane-1,3-dithiols (CH3(CH2)mCH[CH2SH]2), and 2-alkyl-2-methylpropane-1,3-dithiols (CH3(CH2)mC(CH3)[CH2SH]2) having analogous chain lengths, demonstrate that the 1,1,1-tris(mercaptomethyl)alkanes afford SAMs with alkyl chains having the lowest packing density and least conformational order.

A substituted ferrocenophane, 1,1′-((1-tert-butyl)-1,3-butadienylene)ferrocene, was synthesized and polymerized via ring-opening metathesis polymerization (ROMP) to give soluble high molecular weight polymers with ferrocenylene units in the backbone. The monomer readily underwent polymerization upon exposure to a tungsten-based metathesis initiator, W(CHC6H4-o-OMe)(NPh)[OCMe(CF3)2]2 (THF), to give high molecular weight polymers (Mw=ca. 300,000). The molecular weights could be varied systematically by adjusting the monomer-to-catalyst ratio. UV/vis spectra revealed a bathochromic shift for the polymer, consistent with enhanced conjugation compared to the monomer. The polymer exhibited thermal properties similar to oligomeric poly(ferrocenylene). Cyclic voltammetry of the polymer suggested that the iron centers are coupled electronically. Upon doping with I2 vapor, the polymers displayed semiconducting properties (σ=10−5 S cm−1). Theoretical calculations were used to evaluate the nature of the bonding in these and related polymers.

Self-assembled monolayers (SAMs) were prepared by the adsorption of aliphatic dithiocarboxylic acids (ADTCAs) onto the surface of gold. The films were characterized using a variety of analytical te...

The complexes cis- and trans-ReOMe2(bipy)Cl, where cis or trans refers to the Me–Re–Me regiochemistry, were observed to react as follows: (1) with the alkylating agents RMgCl (R=CH2SiMe3 and CH2Ph) and RLi (R=Me) to give ReOMe2(bipy)R, and (2) with the alkoxides NaOR′ (R′=Me and Et) to give trans-ReOMe2(bipy)(OR′). The complex ReOMe2(bipy)CH2SiMe3 was observed by 1H NMR spectroscopy to undergo trans to cis isomerization, which proceeded via reversible first-order kinetics, with ΔH°=1.60(4) kcal mol−1 and ΔS°=3.7(1) eu. At room temperature, ΔG°=0.5(1) kcal mol−1 and Keq=0.42(2), indicating a weak thermodynamic preference for the trans isomer. The activation parameters for the trans to cis isomerization were ΔH‡1=26(2) kcal mol−1 and ΔS‡ 1=10(7) eu, and those for the reverse cis to trans isomerization were ΔH‡ −1=27(2) kcal mol−1 and ΔS‡ −1=14(7) eu. Treatment of a mixture of cis- and trans-ReOMe2(bipy)CH2SiMe3 with anhydrous HCl gave ReOMe(bipy)(CH2SiMe3)Cl; similar treatment of ReOMe3(bipy) and ReOMe2(bipy)CH2Ph gave cis-ReOMe2(bipy)Cl. Exposure of ReOMe(bipy)(CH2SiMe3)Cl to AgPF6 in acetonitrile-d3 gave the cationic nitrile adduct [ReOMe(bipy)(CH2SiMe3)(CD3CN)][PF6].

The wettabilities of fluorinated polymers were evaluated using a series of contacting probe liquids ranging in nature from nonpolar aprotic to polar aprotic to polar protic. Fully fluorinated polymers were wet less than partially fluorinated polymers, highlighting the weak dispersive interactions of fluorocarbons. For partially fluorinated polymers, the interactions between the distributed dipoles along the polymer backbone and the dipoles of the contacting liquids were evaluated using both polar and nonpolar probe liquids. The results demonstrate that the surface dipoles of the fluoropolymers generated by substituting fluorine atoms with hydrogen or chlorine atoms can strongly interact with polar contacting liquids. The wettabilities of the partially fluorinated polymers were enhanced by increasing the density of dipoles across the surfaces and by introducing differentially distributed dipoles.

A series of 2-alkyl-2-methylpropane-1,3-dithiol derivatives with increasing alkyl chain lengths (i.e., CH3(CH2)mC(CH3)[CH2SH]2, where m = 7, 9, 11, 13, 15) were synthesized and used to generate self-assembled monolayers (SAMs) on gold. The resulting monolayers were analyzed by ellipsometry, contact angle goniometry, polarization modulation infrared reflection-absorption spectroscopy, and X-ray photoelectron spectroscopy. These data were compared with those obtained on SAMs on gold derived from normal alkanethiols (CH3(CH2)(m+2)SH) and 2-monoalkylpropane-1,3-dithiols (CH3(CH2)(m)CH[CH2SH]2) having the same number of carbon atoms in the primary chain. The results demonstrate that the 2-alkyl-2-methylpropane-1,3-dithiols generate conformationally disordered monolayer films in which the density of alkyl chains is less than those generated from normal alkanethiols and the 2-monoalkylpropane-1,3-dithiols.

This report describes the preparation and characterization of palladium nanoshells protected with alkanethiol self-assembled monolayers (SAMs) and their application as efficient catalysts. Monodispersed silica core particles (∼100 nm in diameter) were prepared and coated with a thin layer of palladium (∼20 nm in thickness). Subsequently, the palladium nanoshells were treated with two separate alkanethiol adsorbates having different alkyl chain lengths: dodecanethiol (C12SH) and hexadecanethiol (C16SH). The optical properties, morphology, and chemical structure/composition of these nanoshells were thoroughly examined by ultraviolet-visible spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. Additional studies revealed that these SAM-coated palladium nanoshells possessed enhanced colloidal stability in nonpolar solvents and in the solid state. Further, palladium nanoshells modified with C16SH SAM coatings were employed in the Suzuki coupling of phenylboronic acid with iodobenzene in organic solvents. Notably, these SAM-coated nanoshells afforded a greater conversion yield than that of related bare palladium nanoshells.