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A methodology is introduced to synthesize main-chain liquid-crystalline elastomers (LCEs) using a thiol–acrylate-based reaction. This method can program an aligned LCE monodomain and offer spatio-temporal control over liquid-crystalline behavior.

We report the phase separation of a self-assembled monolayer formed from a binary mixture of adsorbates, n-decanethiol, and an amide-containing alkanethiol of similar length (3-mercapto-N-nonylpropionamide), as studied by scanning tunneling microscopy. While mixtures of n-alkanethiols of similar length (i.e., n-decanethiol and n-dodecanethiol) show no phase separation, the introduction of a hydrogen-bonding functionality buried deep within the film induces the formation of single-component domains on the nanometer scale. Phase separation occurs at all relative compositions studied, and for these molecules maintains the same exposed terminal functionality across the entire film. In nonequimolar concentrations of adsorbates, we observe that the solution component present in greater concentration will dominate the composition of the adsorbed monolayer in super proportion to that in solution, consistent with enthalpic contributions from both the solvent and intermolecular interactions of adsorbates.

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A general synthetic approach leading to well-defined, water-soluble gold nanoparticles is described that involves a simple, interfacial ligand exchange reaction between a 1.4 nm phosphine-passivated precursor and an anionic or cationic thiol-containing ligand. We demonstrate the utility of this route by synthesizing water-soluble gold nanoparticles that are stabilized by either an anionic ligand (2-mercaptoethanesulfonate), a cationic ligand (2-(dimethylamino)ethanethiol hydrochloride), or a mixture of both ionic and phosphine ligands. Although the course of the ligand exchange process depends on the nature of the incoming ligand, each of these nanoparticle products retain the small core size and narrow size distribution of the starting particle (1.4 ± 0.4 nm). The stabilities of these nanoparticles to elevated temperature, extremes of pH, and added salt are reported and found to depend on the nature of the exposed headgroups on the ligand shell. Salt-induced aggregation is not observed in any of the cases investigated. Resistance to aggregation is attributed to the protective nature of the ligand shell.

Hybrid self-assembled monolayers (SAMs) containing well-defined strata of different polarity enable insight into how fundamental interactions lead to higher order structure and may provide useful analogies for self-assembled multilayers, new hybrid materials, and functional biological interfaces. We report amide-containing alkanethiol SAMs with internal polar sublayers that are two amide groups thick and nonpolar overlayers comprising either dodecyl or hexadecyl chains. The assemblies have been characterized by X-ray photoelectron spectroscopy (XPS), contact angle goniometry, and external reflective infrared spectroscopy (FTIR-ERS). XPS demonstrates the SAMs are of monolayer thickness, chemisorbed to the gold substrate, and anisotropically oriented. Contact angle data show the methyl surface for n = 16 is highly ordered, but the surface for n = 12 is less well ordered. FTIR-ERS reveals that the alkyl chains for n = 16 are close packed, but that those for n = 12 are disordered. FTIR-ERS also shows that, although the two-amide sublayers are compositionally identical, they are well ordered and assume polyglycine-II-like conformations for n = 16, but they are poorly ordered for n = 12. Comparison of these two SAMs to each other in the context of previously reported one- and three-amide SAMs leads to two conclusions. (1) The threshold n for alkyl chain length ordering in two-amide SAMs is 12 ≤ n ≤ 16. Thus, in SAMs with internal amide sublayers both one and two amide groups thick, the threshold number of methylenes required to form ordered alkyl regions is significantly increased compared to alkanethiol SAMs, demonstrating destructive interference of the amide region with the hydrocarbon ordering process. (2) In two-amide SAMs the formation of a well-ordered amide region depends on the ordering of an overlying hydrocarbon region. This behavior differs with that previously demonstrated for one- and three-amide SAMs, in which the amide groups assume characteristic conformations regardless of hydrocarbon region thickness and order. For two-amide SAMs, the apparent dependence of amide ordering on complementary ordering in the alkyl region provides evidence of an energetic interplay between the two sublayers, manifested as a “reverse ordering” effect. The previously unobserved elastic−elastic character of the buried interface in two-amide SAMs is contrasted with the rigid−elastic interface found in the one-amide SAMs.

We have investigated the role of internal functionality in self-assembled monolayers of a family of amidecontaining alkanethiol molecules on Au{111} using scanning tunneling microscopy. In addition to van der Waals interactions that are present within n-alkanethiol self-assembled monolayers, hydrogen bonding between adjacent buried amide groups contributes to the stability of the amide-containing molecules on the surface and causes spontaneous phase separation upon coadsorption with an n-alkanethiol. A deposition solution concentration dependence study reveals that this is an observed trend across a range of examined solution compositions. Additionally, hydrogen bonding affects the packing structure of the amide-containing alkanethiol self-assembled monolayers. Although they adopt the same ( 3× 3)R30°base lattice as n-alkanethiolate self-assembled monolayers, the amide-containing molecules form superlattice structures that are more linear than n-alkanethiol monolayers due to the hydrogen bonds they form. The internal functionality of monolayers can be used to control their formation and stability.

Hybrid bilayers composed of the lipid phosphatidylcholine (PC) and a submonolayer of 1-decanethiol bound to gold nanoparticles are very stable to potassium cyanide.