Collisions of Polar and Nonpolar Gases with Hydrogen Bonding and Hydrocarbon Self-Assembled Monolayers

Abstract

Molecular beam scattering experiments are used to explore collisions of 60 kJ/mol Ne, CD 4 , ND 3 , and D 2 O with long-chain CH 3 -, NH 2 -, and OH-terminated self-assembled monolayers (SAMs) created via the chemisorption of alkanethiols on gold. Time-of-flight measurements for the scattered gases reveal the extent of energy exchange and the propensity for a gas to thermally accommodate with the surface during a collision. Of the four gases studied, Ne transfers the least amount of translational energy into the monolayers and D 2 O the most. Neon atoms recoil from the OH-SAM with an average of 14.4 kJ/mol of energy, while D 2 O retains only 6.4 kJ/mol of its 60 kJ/mol incident energy when scattering from the same surface. Overall, the trend in final translational energies follows the order Ne > CD 4 > ND 3 > D 2 O for scattering from all three SAMs. The observed trend in the energy exchange is correlated with the gas-surface attractive forces, as determined by ab initio calculations. The thermal accommodation efficiencies of the four gases follow the opposite trend. Thermalization for the Ne atoms is nearly negligible for all three monolayers, whereas D 2 O and ND 3 approach near complete accommodation on all of the monolayers studied. The overall energy exchange and thermal accommodation efficiencies also depend markedly on the terminal group of the SAM. For Ne scattering, the trend for the overall energy transfer follows: CH 3 -> NH 2 -≈ OH-SAMs. In contrast, the overall D 2 O energy transfer is greater when colliding with the OH-SAM than the nonpolar CH 3 -SAM. Together, the results show that the extent of energy transfer depends on a balance between the rigidity of the surface, as affected by intrasurface hydrogen bonding, and the strength of the gas-surface attractive forces, as determined by intermolecular interactions.

Experimental and theoretical study of CO collisions with CH3- and CF3-terminated self-assembled monolayers

“…Of the gas/SAM scattering studies, those involving rare-gas collisions are the most mature. Various surface properties have been investigated, including the influence of alkane chain length, 13 odd-even chain length effects, 13 the presence of hydrogen-bonding terminal groups, 14,15 hydrogen bonding within the interior of the SAM, 16 the role of packing density, 17 and the effect of fluorination. 18,19 At the theoretical level, complementary molecular-dynamics simulations have unveiled a wealth of details concerning the mechanisms governing the scattering of rare gases from SAMs.…”

Carbon Nanotube/Hexa‐peri‐hexabenzocoronene Bilayers for Discrimination Between Nonpolar Volatile Organic Compounds of Cancer and Humid Atmospheres

“…The improved sensitivity of the 90% HBC‐C 12 ‐functionalized chemiresistors to nonpolar VOCs may be attributed to the preferred dissolution of nonpolar VOCs into the hydrophobic HBC‐C 12 layer ( cf. Ref 15…”

Dielectric behavior of thin films of unsaturated polyester‐resin/carbon nanotube semiconductor composites

“…7,[12][13][14][15][16] The polarity of an analyte molecule dominates the interaction with the sensors that are based on electronic transduction. 17 Polar compounds are usually detected directly through charge exchange between the analyte and the sensing unit. 9,[17][18][19][20] This charge transfer might also provide swelling of a polymer film due to electrostatic repulsion.…”

“…17 Polar compounds are usually detected directly through charge exchange between the analyte and the sensing unit. 9,[17][18][19][20] This charge transfer might also provide swelling of a polymer film due to electrostatic repulsion. Non-polar compounds can be detected through steric interaction, which might alter the charge carrier transference.…”

“…Non-polar compounds can be detected through steric interaction, which might alter the charge carrier transference. [17][18][19][20] In this paper we introduce a nano-composite capacity resistor gas sensor composed of unsaturated polyester resin (UPR)/carbon nanotubes (MWCNTs), where the polyester matrix is the acceptor, and its electronegative pull enables the CNTs to form p-type semiconductors, hence creating hole conductivity. 21,22 Additionally, oxygen absorption to the CNTs in ambient air also contributes to their p-type nature.…”