Tridentate benzylthiols on Au(111): control of self-assembly geometry.

A set of hexasubstituted benzene derivatives with three thiol groups in the 1, 3, 5 positions and varied aliphatic substituents in the 2, 4, 6 positions (Me3-BTMT, Et3-BTMT, ODe3-BTMT) has been synthesized and self-assembled on Au(111). The resulting self-assembled monolayers (SAMs) are characterized by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and electrochemistry. The molecular orientation and long-range order are affected by the “gear effect” of the hexasubstituted benzene ring and van der Waals interactions between the physisorbed alkyl chains drive.

Double-striped metallic patterns from PS-b-P4VP nanostrand templates.

A new nanometallic pattern, characterized by randomly disposed double or twin one-dimensional stripes and that adds to the nanotechnology toolbox, has been obtained from a unique template possessing the nanostrand morphology. This morphology had previously been shown to form in Langmuir-Blodgett films made from a polystyrene-poly(4-vinylpyridine) (PS-P4VP) diblock copolymer blended with 3-n-pentadecylphenol (PDP). The nanostrand backbone is composed of PS, and it is bordered along both sides by a P4VP monolayer, visualized for the first time by high resolution atomic force microscopy.

High thermal stability of block copolymer-capped Au and Cu nanoparticles.

Producing solution-based metal nanoparticles that do not agglomerate at elevated temperatures remains challenging. We show that thermally stable Au and Cu nanoparticles can be prepared using polystyrene-poly(4-vinylpyridine) diblock copolymers as capping agents. These materials remain stable when their solutions are subjected to prolonged heating up to 160 °C for more than 48 h.

Directing the assembly of gold nanoparticles with two-dimensional molecular networks.

Lamellar patterns resulting from the adsorption of p-dialkoxybenzene derivatives on HOPG have been investigated as molecular templates for directing the assembly of thiol-capped gold nanoparticles (AuNP). STM characterization at the liquid-solid interface reveals the periodic arrangement of AuNP on top of the self-assembled molecular network (SAMN), spanning hundreds of nanometers. The resulting superlattices are notably different from the close-packed structures formed by spherical nanoparticles during evaporative drying.

Understanding and controlling morphology formation in Langmuir-Blodgett block copolymer films using PS-P4VP and PS-P4VP/PDP.

This contribution offers a comprehensive understanding of the factors that govern the morphologies of Langmuir-Blodgett (LB) monolayers of amphiphilic diblock copolymers (BCs). This is achieved by a detailed investigation of a wide range of polystyrene-poly(4-vinyl pyridine) (PS-P4VP) block copolymers, in contrast to much more limited ranges in previous studies. Parameters that are varied include the block ratios (mainly for similar total molecular weights, occasionally other total molecular weights), the presence or not of 3-n-pentadecylphenol (PDP, usually equimolar with VP, with which it hydrogen bonds), the spreading solution concentration ("low" and "high"), and the LB technique (standard vs "solvent-assisted").

Pressure-induced order transition in nanodot-forming diblock copolymers at the air/water interface.

Understanding and controlling the processes in block copolymer (BC) monolayers at the air/water interface during surface area compression is a key issue for producing ultrathin films of predetermined morphology with well-defined order and known dimensions. Langmuir isotherms of nanodot-forming BC monolayers generally display a plateau indicative of a 2D phase transition, which has been the subject of various interpretations in the literature. Here, based on investigations of Langmuir-Blodgett and Langmuir-Schaefer nanodot films of PS-P4VP mixed with 3-n-pentadecylphenol (PDP), we show by atomic force microscopy (AFM) that it involves a change in nanodot packing order (from quasi-hexagonal to quasi-square), argued to be a general phenomenon for nanodot BC monolayers.

π-conjugation and charge polarization in fluorene-dibenzothiophene-S,S-dioxide co-oligomers by Raman spectroscopy and quantum chemistry.

The Raman spectra of a series of fluorine (F)∕dibenzothiophene-S,S-dioxide co-oligomers (S) of different length and alternation sequences in their backbones (FSF, FFSFF, FSFSF, and FASAF; A is the -C≡C- bridge) have been recorded and simulated theoretically. It is shown that Raman spectroscopy is useful to probe π conjugation and ground state electron polarization in these molecules, phenomena directly related with the existence of intramolecular charge-transfer processes owing to the combination of electron donor (fluorene) and acceptor (dibenzothiophene-S,S-dioxide) groups. Their geometric, electronic, and vibrational properties have been studied by density functional theory B3LYP∕6-311G(2d,p) quantum chemical calculations and compared with those for fluorene homo-oligomers.

Nanostrand formation of block copolymers at the air/water interface.

Langmuir-Blodgett monolayers consisting of a network of nanostrands have occasionally been reported in the literature, but are often coexistent with other morphologies, which is not useful for potential applications. With the use of PS-P4VP/PDP, a polystyrene-poly(4-vinyl pyridine) diblock copolymer of 12 mol % VP content mixed with 3-pentadecylphenol, it is shown that the disordered nanostrand network morphology can be obtained reproducibly and uniformly over large surface areas by spreading chloroform solutions of relatively high copolymer concentration. Use of a more slowly evaporating spreading solvent, 1,1,2,2-tetrachloroethane, and a low subphase temperature, 8-9 °C, results in much more densely aligned nanostrands.