Assembled Monolayers Depends upon the Roughness of the Substrate and the Orientation of the Terminal Moiety

The origin of the odd even effect in properties of self-assembled monolayers (SAMs) and/or technologies derived from them is poorly understood. We report that hydrophobicity and, hence, surface wetting of SAMs are dominated by the nature of the substrate (surface roughness and identity) and SAM tilt angle, which influences surface dipoles/orientation of the terminal moiety. We measured static contact angles (theta(s)) made by water droplets on n-alkanethiolate SAMs with an odd (SAM(O)) or even (SAM(E)) number of carbons (average theta(s) range of 105.8-112.1 degrees). When SAMs were fabricated on smooth template-stripped metal (M-TS) surfaces [root-mean-square (rms) roughness = 0.36 +/- 0.01 nm for Au-TS and 0.60 +/- 0.04 nm for Ag-TS], the odd-even effect, characterized by a zigzag oscillation in values of theta(s), was observed. We, however, did not observe the same effect with rougher as-deposited (M-AD) surfaces (rms roughness = 2.27 +/- 0.16 nm for Au-AD and 5.13 +/- 0.22 nm for Ag-AD). The odd-even effect in hydrophobicity inverts when the substrate changes from Au-TS (higher theta(s) for SAM(E) than SAM(O), with average Delta theta(s) (vertical bar n - (n + 1)vertical bar) approximate to 3 degrees) to Ag-TS (higher theta(s) for SAM(O) than SAM(E), with average Delta theta(s) (vertical bar n - (n + 1)vertical bar) approximate to 2 degrees). A comparison of hydrophobicity across Ag-TS and Au-TS showed a statistically significant difference (Student\u27s t test) between SAM(E) (Delta theta(s) (vertical bar Ag evens - Au evens vertical bar) approximate to 5 degrees; P \u3c 0.01) but failed to show statistically significant differences on SAM(O) (Delta theta(s) (vertical bar Ag odds) (- Au odds vertical bar) approximate to 1 degrees; p \u3e 0.1). From these results, we deduce that the roughness of the metal substrate (from comparison of M-AD versus M-TS) and orientation of the terminal -CH2CH3 (by comparing SAM(E) and SAM(O) on Au-TS versus Ag-TS) play major roles in the hydrophobicity and, by extension, general wetting properties of n-alkanethiolate SAMs

Paramagnetic Ionic Liquids for Measurements of Density Using Magnetic Levitation

Paramagnetic ionic liquids (PILs) provide new capabilities to measurements of density using magnetic levitation (MagLev). In a typical measurement, a diamagnetic object of unknown density is placed in a container containing a PIL. The container is placed between two magnets (typically NdFeB, oriented with like poles facing). The density of the diamagnetic object can be determined by measuring its position in the magnetic field along the vertical axis (levitation height, h), either as an absolute value, or relative to internal standards of known density. For density measurements by MagLev, PILs have three advantages over solutions of paramagnetic salts in aqueous or organic solutions: (i) negligible vapor pressures; (ii) low melting points; (iii) high thermal stabilities. In addition, the densities, magnetic susceptibilities, glass transition temperatures, thermal decomposition temperatures, viscosities, and hydrophobicities of PILs can be tuned over broad ranges by choosing the cation–anion pair. The low melting points and high thermal stabilities of PILs provide large liquidus windows for density measurements. This paper demonstrates applications and advantages of PILs in density-based analyses using MagLev.Chemistry and Chemical Biolog

Using Magnetic Levitation to Separate Mixtures of Crystal Polymorphs

Magnetische Levitation (MagLev) ist eine einfache Trennmethode für Kristallpolymorphe mit Dichteunterschieden (Δρ) von nur 0.001 g cm−3. Für vier organische Verbindungen wurden dichtebasierte Trennungen verschiedener kristalliner Formen gezeigt: 5-Methyl-2-[(2-nitrophenyl)amino]-3-thiophencarbonitril, Sulfathiazol, Carbamazepin und trans-Zimtsäure.Chemistry and Chemical Biolog

Separation and enrichment of enantiopure from racemic compounds using magnetic levitation

Crystallization of a solution with high enantiomeric excess can generate a mixture of crystals of the desired enantiomer and the racemic compound. Using a mixture of S-/RS-ibuprofen crystals as a model, we demonstrated that magnetic levitation (MagLev) is a useful technique for analysis, separation and enantioenrichment of chiral/racemic products.Chemistry and Chemical Biolog

Fabrication of Low-Cost Paper-Based Microfluidic Devices by Embossing or Cut-and-Stack Methods

This communication describes the use of embossing, and “cut-and-stack” methods of assembly, to generate microfluidic devices from omniphobic paper, and demonstrates that fluid flowing through these devices behaves similarly to fluid in an open-channel microfluidic device. The porosity of the paper to gasses allows processes not possible in devices made using PDMS or other non-porous materials. Droplet generators and phase separators, for example, could be made by embossing “T”-shaped channels on paper. Vertical stacking of embossed or cut layers of omniphobic paper generated three-dimensional systems of microchannels. The gas permeability of the paper allowed fluid in the microchannel to contact and exchange with environmental or directed gases. An aqueous stream of water containing a pH-indicator, as one demonstration, changed color upon exposure to air containing HCl or NH3 gases.Chemistry and Chemical Biolog

Assembled Monolayers Depends upon the Roughness of the Substrate and the Orientation of the Terminal Moiety

The origin of the odd even effect in properties of self-assembled monolayers (SAMs) and/or technologies derived from them is poorly understood. We report that hydrophobicity and, hence, surface wetting of SAMs are dominated by the nature of the substrate (surface roughness and identity) and SAM tilt angle, which influences surface dipoles/orientation of the terminal moiety. We measured static contact angles (theta(s)) made by water droplets on n-alkanethiolate SAMs with an odd (SAM(O)) or even (SAM(E)) number of carbons (average theta(s) range of 105.8-112.1 degrees). When SAMs were fabricated on smooth "template-stripped" metal (M-TS) surfaces [root-mean-square (rms) roughness = 0.36 +/- 0.01 nm for Au-TS and 0.60 +/- 0.04 nm for Ag-TS], the odd-even effect, characterized by a zigzag oscillation in values of theta(s), was observed. We, however, did not observe the same effect with rougher "as-deposited" (M-AD) surfaces (rms roughness = 2.27 +/- 0.16 nm for Au-AD and 5.13 +/- 0.22 nm for Ag-AD). The odd-even effect in hydrophobicity inverts when the substrate changes from Au-TS (higher theta(s) for SAM(E) than SAM(O), with average Delta theta(s) (vertical bar n - (n + 1)vertical bar) approximate to 3 degrees) to Ag-TS (higher theta(s) for SAM(O) than SAM(E), with average Delta theta(s) (vertical bar n - (n + 1)vertical bar) approximate to 2 degrees). A comparison of hydrophobicity across Ag-TS and Au-TS showed a statistically significant difference (Student's t test) between SAM(E) (Delta theta(s) (vertical bar Ag evens - Au evens vertical bar) approximate to 5 degrees; P 0.1). From these results, we deduce that the roughness of the metal substrate (from comparison of M-AD versus M-TS) and orientation of the terminal -CH2CH3 (by comparing SAM(E) and SAM(O) on Au-TS versus Ag-TS) play major roles in the hydrophobicity and, by extension, general wetting properties of n-alkanethiolate SAMs.Reprinted with permission from Newcomb, Lucas B., Ian D. Tevis, Manza BJ Atkinson, Symon M. Gathiaka, Rafael E. Luna, and Martin Thuo. "Odd–even effect in the hydrophobicity of n-alkanethiolate self-assembled monolayers depends upon the roughness of the substrate and the orientation of the terminal moiety." Langmuir 30, no. 40 (2014): 11985-11992, doi:10.1021/la5032569. Copyright 2014 American Chemical Society.</p

1D and 2D metal–organic frameworks functionalized with free pyridyl groups

We show that a molecule constructed from an organic solid-state synthesis, namely, rctt-1,3-bis(2-pyridyl)-2,4-bis(4-pyridyl)cyclobutane (ht-2,4 ‘-tpcb) upon reaction with Cu(II) and Zn(II) ions gives one- (1D) and two-dimensional (2D) metal-organic frameworks (MOFs) of composition [Cu(hfac)(2)(2,4 ‘-tpcb-ht)](infinity) (where: hfac=hexafluoroacetylacetonate) (1) and [Zn(2,4 ‘-tpcb-ht)(2)(H2O)(2)](infinity)(2+), (2). Each MOF possesses uncoordinated, or free, 2-pyridyl groups that decorate the walls of each extended structure. (c) 2006 Elsevier B.V. All rights reserved

Putting Cocrystal Stoichiometry to Work: A Reactive Hydrogen-Bonded “Superassembly” Enables Nanoscale Enlargement of a Metal–Organic Rhomboid via a Solid-State Photocycloaddition

Enlargement of a self-assembled metal organic rhomboid is achieved via the organic solid state. The solid-state synthesis of an elongated organic ligand was achieved by a template directed [2 + 2] photodimerization in a cocrystal. Initial cocrystals obtained of resorcinol template and reactant alkene afforded a 1:2 cocrystal with the alkene in a stacked yet photostable geometry. Cocrystallization performed in the presence of excess template resulted in a 3:2 cocrystal composed of novel discrete 10-component hydrogen-bonded “superassemblies” wherein the alkenes undergo a head-to head [2 + 2] photodimerization. Isolation and reaction of elongated photoproduct with Cu(II) ions afforded a metal-organic rhomboid of nanoscale dimensions that hosts small molecules in the solid state as guests

Paramagnetic Ionic Liquids for Measurements of Density Using Magnetic Levitation

Paramagnetic ionic liquids (PILs) provide new capabilities to measurements of density using magnetic levitation (MagLev). In a typical measurement, a diamagnetic object of unknown density is placed in a container containing a PIL. The container is placed between two magnets (typically NdFeB, oriented with like poles facing). The density of the diamagnetic object can be determined by measuring its position in the magnetic field along the vertical axis (levitation height, <i>h</i>), either as an absolute value or relative to internal standards of known density. For density measurements by MagLev, PILs have three advantages over solutions of paramagnetic salts in aqueous or organic solutions: (i) negligible vapor pressures; (ii) low melting points; (iii) high thermal stabilities. In addition, the densities, magnetic susceptibilities, glass transition temperatures, thermal decomposition temperatures, viscosities, and hydrophobicities of PILs can be tuned over broad ranges by choosing the cation–anion pair. The low melting points and high thermal stabilities of PILs provide large liquidus windows for density measurements. This paper demonstrates applications and advantages of PILs in density-based analyses using MagLev

Odd–Even Effect in the Hydrophobicity of <i>n</i>‑Alkanethiolate Self-Assembled Monolayers Depends upon the Roughness of the Substrate and the Orientation of the Terminal Moiety

The origin of the odd–even effect in properties of self-assembled monolayers (SAMs) and/or technologies derived from them is poorly understood. We report that hydrophobicity and, hence, surface wetting of SAMs are dominated by the nature of the substrate (surface roughness and identity) and SAM tilt angle, which influences surface dipoles/orientation of the terminal moiety. We measured static contact angles (θ_s) made by water droplets on <i>n</i>-alkanethiolate SAMs with an odd (SAM^O) or even (SAM^E) number of carbons (average θ_s range of 105.8–112.1°). When SAMs were fabricated on smooth “template-stripped” metal (M^TS) surfaces [root-mean-square (rms) roughness = 0.36 ± 0.01 nm for Au^TS and 0.60 ± 0.04 nm for Ag^TS], the odd–even effect, characterized by a zigzag oscillation in values of θ_s, was observed. We, however, did not observe the same effect with rougher “as-deposited” (M^AD) surfaces (rms roughness = 2.27 ± 0.16 nm for Au^AD and 5.13 ± 0.22 nm for Ag^AD). The odd–even effect in hydrophobicity inverts when the substrate changes from Au^TS (higher θ_s for SAM^E than SAM^O, with average Δθ_{s |<i>n</i> – (<i>n</i> + 1)|} ≈ 3°) to Ag^TS (higher θ_s for SAM^O than SAM^E, with average Δθ_{s |<i>n</i> – (<i>n</i> + 1)|} ≈ 2°). A comparison of hydrophobicity across Ag^TS and Au^TS showed a statistically significant difference (Student’s <i>t</i> test) between SAM^E (Δθ_{s |Ag evens – Au evens|} ≈ 5°; <i>p</i> < 0.01) but failed to show statistically significant differences on SAM^O (Δθ_{s |Ag odds – Au odds|} ≈ 1°; <i>p</i> > 0.1). From these results, we deduce that the roughness of the metal substrate (from comparison of M^AD versus M^TS) and orientation of the terminal −CH₂CH₃ (by comparing SAM^E and SAM^O on Au^TS versus Ag^TS) play major roles in the hydrophobicity and, by extension, general wetting properties of <i>n</i>-alkanethiolate SAMs