The first direct characterization of structures of bi-molecular chain assemblies in a self-consistent series of pillared, layered organic-inorganic long-chain silver (n-alkane) thiolates, (AgS(CH 2 ) n CH 3 ; n ) 5, 6, 9, 11, 15, and 17), is reported using the combined application of infrared transmission spectroscopy and powder X-ray diffraction. The structural attributes elucidated include quantitative estimates of average chain orientation, chain conformation, chain-chain translational order, interpenetration of the contiguous layers, as well as void characteristics in the chain matrix. The evidence presented here establishes that the layered chain assemblies sandwiched between the inorganic Ag-S backbones in a double-layer arrangement are comprised of an ordered packing of all-trans-extended chains. The average chain in each assembly is oriented vertically away from the quasi-hexagonal Ag-S lattice, in a two-dimensional pseudo-monoclinic arrangement of domains of 60-70 translationally correlated chains. Small interpenetration between the contiguous layers leads to the formation of regularly spaced 1D channels or corridors. The three-dimensional network of 1D channels alternates between the chain layers. All the chain structural characteristics deduced here are in good conformity with those implied in the model proposed earlier by Dance and co-workers. The present results, together with the previous X-ray analysis for comparable short-chain AgSRs, are used to propose a two-step, hierarchical self-assembly mechanism for the formation of silver (n-alkyl) thiolates. It is proposed that the primary self-assembly process involves the organization of Ag + and RS -species into puckered sheets of quasi-hexagonally symmetric 2D lattices, with the chain substituents extending on each side. The subsequent self-assembly of these 2D building blocks in the third dimension via complementary stacking appears to complete the formation of sandwiched bimolecular chain assemblies.

Using temperature-dependent Fourier transform infrared (FTIR) spectroscopy, we probe the molecular level, chain-structural dynamics associated with solid−solid transitions between 25 and 250 °C in a layered inorganic−organic silver dodecanethiolate, AgS(CH2)11CH3. Spectroscopic evidence presented here establishes two major transitions:  the transition occurring at ∼130 °C is characterized by an abrupt, but fully reversible, change in the chain conformational order from an initial all-trans state to the one characterized by mixed or partial chain disorder. The observation of this phase transition is consistent with the previous predictions of a rapid and drastic change in the structural motif from an initial bilayer to the final micellar state. The second transition at about 190 °C, which is consistent with the previous assignment of micellar amorphous transition, is furthermore irreversible and represents thermal degradation of the material. Implications of these results for the general family of chain molecular assemblies in constrained molecular environments are discussed.

Successive depositions of precompressed Langmuir monolayers have been shown to allow reproducible formation of air-stable, lipid−alkylsiloxane hybrid bimolecular architectures at oxidic supports. Specifically, prepolymerized Langmuir−Blodgett films of n-octadecylsiloxane (OTS) monolayers on oxided silicon substrates were used as the hydrophobic templates, upon which compressed monolayers of dipalmitoyl-sn1-glycerophosphatidylcholine (DPPC) and monosialogangliosides (Gm1) were deposited from a low-temperature air−water interface by the horizontal deposition method. Structural features of each leaflet of the resultant bimolecular architectures, namely DPPC/OTS/SiO2/Si and Gm1/OTS/SiO2/Si, were characterized using a combined application of infrared spectroscopy, null-ellipsometry, and surface wetting measurements. In both cases, the outer lipid leaflet (DPPC or Gm1) was found to be structurally decoupled with respect to the inner OTS layer. The inner silane layer was composed of essentially untilted (cant angle, θ = 0−10°), all-trans chains at the dense packing of ∼19 Å2/molecule, consistent with the previously reported structure in solution-phase assembled OTS monolayers. The outer DPPC leaflet, however, was found to be composed of collectively tilted (θ = 36°), all-trans acyl chains at the lower chain-packing density (∼26−28 Å2/chain) whereas the outer Gm1 leaflet was concluded to have essentially untilted chains at similarly lower chain-packing densities (∼23−26 Å2/chain) but with the carbohydrate head-groups disposed in a topologically staggered conformation. The structural independence of the two leaflets in the two classes of bilayered architectures examined here confirms the possibility of independently manipulating the molecular structure in each leaflet of supported hybrid bilayers.

Prepolymerized n-octadecyltrichlorosilane (OTS) monolayers were deposited onto oxidized silicon substrates from precursor Langmuir monolayers (at an air−water interface) in two-dimensional liquid expanded (LE), liquid condensed (LC), or mixed (LE/LC coexistence phase) states at four different pulling rates. Morphologies of the transferred monolayers have been investigated using atomic force microscopy (AFM). The OTS monolayers formed from the LE phase precursor reveal an incipient condensation transition exhibiting a novel ring-in-a-ring morphology, wherein uniformly distributed circular domains consisting of two concentric walls of ordered OTS molecules in a high density phase both sandwich and encapsulate disordered OTS molecules in a reduced density phase. On the other hand, the monolayers formed from the LC/LE phase precursor implicate a complete condensation transition, evidenced in the AFM images showing a uniform tiling of near-circular domains composed of ordered OTS molecules in a dense monolayer phase. The monolayers derived from the 2D solid or LC precursor state reveal near-complete surface coverages and uniform film structures, comparable to those obtained by adsorption from a dilute organic solution of OTS molecules (conventional self-assembly process). These structural reconstructions at the substrate surface, namely lateral redistribution into 2D domains, condensation transitions and film coverages, are discussed in terms of the competition between short range and long range interactions. The most dominant effect of increasing pulling rates is the appearance of coalesced domain structures, presumably due to drainage of the water layer at the substrate surface as well as occasional substrate pinning. These results substantiate the idea that templating surface self-assembly of monolayers by using their Langmuir-phase precursors provides a useful alternative to classical solution-phase self-assembly approaches, and affords a wide range of control over film structures and surface morphologies.

When energy is deposited at the interface between two materials, then acoustic waves that are confined in the interface region and traveling in the plane of the interface may arise. In this article, we illustrate the feasibility and versatility of interface wave laser ultrasonics by presenting a selection of recently developed laser ultrasonic configurations for detecting acoustic waves at the free surface of a solid and at a liquid-solid interface in a variety of applications, such as nonlinear wave propagation, characterization of coatings, porous materials and substrates, and acoustic wave imaging.