Formation and electrochemical desorption of self‐assembled monolayers as studied by ToF‐SIMS

Time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) was used to study a number of processes involving thiol‐based self‐assembled monolayers (SAMs) on nontextured (polycrystalline) gold (Au) films deposited on Si wafers. ToF‐SIMS turned out to be a convenient and versatile semiqualitative technique which readily verified electrochemical desorption of a SAM and formation of another SAM on the same sample via reincubation with another thiol. The technique, allowing one to follow simultaneously more than one species on the surface, showed that any formation of a mixed SAM on surfaces which did not undergo electrolysis was negligible with the applied time scale (minutes). Copyright © 2010 John Wiley & Sons, Ltd.     

Mechanisms of secondary ion emission from self‐assembled monolayers and multilayers

Alkanethiol self‐assembled monolayers/multilayers (SAMs) have been applied as model organic systems with which to investigate secondary ion formation and emission processes during kiloelectronvolt ion bombardment. Self‐assembled monolayer and multilayer films of 11‐mercaptoundecanoic acid capped with 1‐dodecanethiol were prepared on gold‐coated substrates. Samples with varying number of thiolate layers were studied using static secondary ion mass spectrometry to investigate the origin of molecular secondary ions and the influence of surface chemistry and structure. The nature of the thiolate bonding affects the type and abundance of the observed ions. The intensity of atomic and cluster ions derived from the substrate decreases exponentially with increasing number of thiolate overlayers because of losses in transmission through the organic overlayers. Intact molecular and cluster ions can escape from >100 Å below the surface of these structures. The variation of molecular‐ion yields with multilayer thickness suggests that a significant proportion of molecular ions originate from subsurface thiolate layers. The detection of ions comprised species from the substrate or bottom of the multilayer associated with species from the top layer supports the view that chemical association at or near the surface is a viable mechanism of formation for molecular secondary ions. Copyright © 2005 John Wiley & Sons, Ltd.     

Nonbiofouling surface based on amphiphilic alkanethiol self‐assembled monolayers

A series of novel amphiphilic alkanethiols used for preparation of nonbiofouling surfaces have been synthesized and characterized. Surface properties of the resultant self assembled layers have been studied by multiple characterization techniques, such as XPS, Grazing angle infrared spectroscopy (GA‐FTIR) and contact angle measurements. The antifouling performance of surfaces grafted with terminally fluorinated alkanethiols were assayed employing the fouling diatom Nitzschia and ubiquitous Staphylococcus aureus. The results indicated that amphiphilic alkanethiol‐grafted surfaces could effectively reduce the bacterial adhesion and settlement of the fouling diatom. Copyright © 2010 John Wiley & Sons, Ltd.     

Energy transfer from fluorene‐based conjugated polyelectrolytes to on‐chain and self‐assembled porphyrin units

A new water soluble fluorene‐based polyelectrolyte containing on‐chain porphyrin units has been synthesized via Suzuki coupling, for use in optoelectronic devices. The material consist of a random copolymer of poly{1,4‐phenylene‐[9,9‐bis(4‐phenoxy butylsulfonate)]fluorene‐2,7‐diyl} (PBS‐PFP) and a 5,15‐diphenylporphyrin (DPP). The energy transfer process between the PBS‐PFP units and the porphyrin has been investigated through steady state and time‐resolved measurements. The copolymer PBS‐PFP‐DPP displays two different emissions one located in the blue region of the spectra, corresponding to the fluorene part and another in the red due to fluorescent DPP units either formed directly or by exciton transfer. However, relatively inefficient energy transfer from the PFP to the on‐chain porphyrin units was observed. We compare this with a system involving an anionic blue light‐emitting donor PBS‐PFP and a anionic red light‐emitting energy acceptor meso‐tetrakisphenylporphyrinsulfonate (TPPS), self‐assembled by electrostatic attraction induced by Ca²⁺. Based on previous studies related to chain aggregation of the anionic copolymer PBS‐PFP, two different solvent media were chosen to further explore the possibilities of the self‐assembled system: dioxane–water and aqueous nonionic surfactant n‐dodecylpentaoxyethylene glycol ether (C₁₂E₅). In contrast, with the on‐chain PBS‐PFP‐DPP system the strong overlap of the 0‐0 emission peak of the PBS‐PFP and the Soret absorption band of the TPPS results in an efficient Förster transfer. This is strongly dependent on the solvent medium used. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Formation of alkane‐phosphonic acid self‐assembled monolayers on alumina: an in situ SPR study

The formation process of n‐alkane phosphonic acid CH₃ (CH₂)_n?1 PO(OH)₂ (n = 10,12,14,18) self‐assembled monolayers (SAMs), deposited from ethanol solutions on aluminum oxide, has been monitored in situ using surface plasmon resonance (SPR) spectroscopy. In addition, the two‐solvent approach is used to obtain both film thickness and refractive index of the fully formed adsorbed layers. A densely packed adsorbed layer is formed only for the longest molecules with n = 18. The chain length and solution concentration dependence of formation kinetics are studied, and the existence of two distinct kinetic steps is revealed. Fittings of the experimental results with various kinetic models are performed. Our analysis suggests that during the first kinetic step, a transition from a lying‐down to a standing‐up phase takes place, and the growth of this standing‐up phase is governed by second‐order kinetics. The second slow kinetic step is described by a modified first‐order Langmuir law. Copyright © 2009 John Wiley & Sons, Ltd.     

Preparation and functions of self‐assembled monolayers of helix peptides

Self‐assembled monolayers (SAMs) of helix peptides oriented vertically to a gold surface were prepared. Negative surface potentials of a few hundred millivolts were observed for the helix peptide SAMs when they were immobilized on gold through the N terminal of the peptides. However, positive surface potentials were generated in the helix peptide SAMs when the N terminal of the peptides was directed the opposite way. The large dipole moment of the helical peptide was thought to be the major factor for generation of the surface potential. The effect of the dipole moment on the electron transfer through the helix peptide SAMs was investigated. Photocurrent generation by photoexcitation of the N‐ethylcarbazolyl group of the peptide SAMs was accelerated by the dipole moment directed toward the gold substrate. Helical peptides were thus shown to be a suitable medium for electron transfer. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4826–4831, 2000     

Stabilization of self‐assembled microdroplets using short chain alcohols

The condensation of water vapor on a volatile polymeric solution leads to a porous surface after evaporation of both solvent and water. However, the stabilization of the water microdroplet is of great importance, which can be achieved using specific polymer or adding a third substance to the polymer solution. Short chain alcohols (methanol, ethanol, and n‐propanol) are utilized to fabricate a self‐assembled porous honeycomb film of linear, low molecular weight polystyrene using the breath figure technique. A combination of breath figure processing and the effect of alcohol on a water droplet can stabilize the pattern and make pores on the surface of the polymer film. The quality of the porous honeycomb film is strongly dependent on the type of alcohols and the concentration of polymer. In a specific range of polymer and alcohol concentration, pores cover all the surface of the polymer film. This method offers the possibility of producing a honeycomb structure with no trace of additive residual after the fabrication process and avoiding polymer modification. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 709–718     

Studies of protection of iron corrosion by rosin imidazoline self‐assembled monolayers

A type of rosin imidazoline (IM) has been synthesized using rosin acid and diethylenetriamine (DETA) as raw materials. The monolayers of IM were assembled on the surface of iron. The monolayers of the IM inhibitor were characterized by electrochemical impedance spectroscopy (EIS), electrochemical polarization curves and double‐layer capacitance. Surface analysis was carried out to establish the mechanism of corrosion inhibition of iron by X‐ray photoelectron spectroscopy (XPS) and scanning electron microscopy. The IM inhibitor showed good inhibition efficiency for iron in 0.1 M H₂SO₄. The inhibition mechanism of IM inhibitor was interpreted using molecular simulation. Copyright © 2006 John Wiley & Sons, Ltd.     

XPS and AFM characterization of the self‐assembled molecular monolayers of a 3‐aminopropyltrimethoxysilane on silicon surface,and effects of substrate pretreatment by UV‐irradiation

The self‐assembled (SA) molecular monolayers of a 3‐aminopropyltrimethoxysilane (3‐APTS) on a silicon (111) surface, and the effects of ultraviolet (UV) pre‐treatment for substrates on the assembling process have been studied using XPS and atomic force microscopy (AFM). The results show that the SA 3‐APTS molecules are bonded to the substrate surface in a nearly vertical orientation, with a thickness of the monolayer of about 0.8–1.5 nm. The SA molecular monolayers show a substantial degree of disorder in molecular packing, which are believed to result from the interactions of amine tails in the silane molecules used with surface functionalities of the substrates, and the oxygen‐containing species from the ambient. UV irradiation for silicon substrates prior to the self‐assembly reaction can enhance the assembly process and hence, significantly increase the coverage of the monolayer assembled for the substrates. Copyright © 2010 John Wiley & Sons, Ltd.     

Syntheses of polyolefin‐based stereoregular diblock copolymers for self‐assembled nanostructures

The preparation of polyolefin‐based stereoregular diblock copolymers by postpolymerization of ethenyl‐capped syndiotactic polypropylene‐based propylene/norbornene copolymer (sPP‐based P‐N copolymer) led to the successful generation of a structurally uniform stereoregular diblock copolymer for self‐assembly studies. The ethenyl‐capped prepolymer was prepared by conducting propylene/norbornene copolymerization in the presence of Me₂C(Cp)(Flu)ZrCl₂/MAO. Ozonolysis of ethenyl‐capped sPP‐based P‐N copolymer provided the formyl group end‐capped, end‐functionalized prepolymer with a quantitative functional group conversion ratio. Subsequently, connecting the formyl end‐group of the stereoregular prepolymer by coupling with living anionic polystyrene resulted in the high yield production of stereoregular diblock copolymer (sPP‐based P‐N‐block‐polystyrene), which is difficult to prepare by other methods. The resulting stereoregular diblock copolymer possesses precise chemical architecture to self‐organize into consistent nanostructures as evidenced by transmission electron microscopy and small angle X‐ray scattering. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4843–4856, 2008     

Adsorption and orientation kinetics of self‐assembled films of octadecyltrimethoxysilane on aluminium oxide surfaces

X‐ray photoelectron spectroscopy (XPS) and near‐edge x‐ray absorption fine structure (NEXAFS) spectroscopy have been used to study the time‐dependent adsorption and molecular orientation behaviour of octadecyltrimethoxysilane (ODTMS) on native aluminium oxide surfaces. By measuring the adsorption isotherm using XPS, we show that ODTMS molecules exhibit oscillatory adsorption. The oscillatory adsorption behaviour for ODTMS is analogous to that observed for its simpler short‐chain ‘cousin’—propyltrimethoxysilane (PTMS)—and suggests that the length of the functional alkyl chain on an organosilane does not have a significant influence upon the oscillatory adsorption mechanism. The oscillation in the ODTMS adsorption isotherm shows a maximum and a minimum in coverage at an adsorption time of ～30 and ～65 s, respectively, for a 0.75% ODTMS solution in a 90% ethanol–10% water mixture at pH 4. The time‐dependent orientation behaviour of the ODTMS molecules during adsorption was examined using angular‐dependent carbon K‐edge NEXAFS spectroscopy. We show that the alignment of the ODTMS film changes systematically with deposition time and appears to be correlated with coverage measurements obtained using XPS. In particular, by combining the XPS and NEXAFS results we demonstrate that the minimum ODTMS coverage corresponds to a film whose alignment appears to be predominantly randomized. Copyright © 2005 John Wiley & Sons, Ltd.     

Photoinitiated polymerization of styrene from self‐assembled monolayers on gold. II. Grafting rates and extraction

Ultrathin films of polystyrene (PS) were grown from self‐assembled monolayers by the “grafting‐from” technique. The initiating system consisted of a dithiol azobisisobutyronitrile‐type free‐radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform‐reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 °C, and a water‐jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 °C during extraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3284–3291, 2002     

Dendronized supramolecular polymers self‐assembled from dendritic ionic liquids

The synthesis, structural, and retrostructural analysis of a library of self‐assembling dendrons containing triethyl and tripropyl ammonium, pyridinium and 3‐methylimidazolium chloride, tetrafluoroborate, and hexafluorophosphate at their apex are reported. These dendritic ionic liquids self‐assemble into supramolecular columns or spheres which self‐organize into 2D hexagonal or rectangular and 3D cubic or tetragonal liquid crystalline and crystalline lattices. Structural analysis by X‐ray diffraction experiments demonstrated the self‐assembly of supramolecular dendrimers containing columnar and spherical nanoscale ionic liquid reactors segregated in their core. Both in the supramolecular columns and spheres the noncovalent interactions mediated by the ionic liquid provide a supramolecular polymer and therefore, these assemblies represent a new class of dendronized supramolecular polymers. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4165–4193, 2009     

Ion condensation onto self‐assembled nanofibers

Self‐assembled peptide amphiphile (PA) nanofibers are a class of supramolecular materials with promising applications in nanotechnology. Alignment of nanofibers, which is essential for biomaterials applications, is achieved at low salt concentrations in the PA nanofiber suspensions. Regardless of its importance, the effect of ion concentration on the properties of these nanostructures remains unexplored. Using atomistic molecular dynamics simulations, canonical PA nanostructures are investigated to elucidate the relationship between counterion condensation and morphological changes. Simulations reveal that nanofibers with the highest cross‐section density have expanded radii. This expansion decreases the accessible volume for sodium counterions and diminishes the counterion translational entropy, while also reducing the total electrostatic potential. Interestingly, we show that the competition between these effects leads to a fraction of condensed counterions independent of the fiber radius. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 901–906     

X‐ray‐induced degradation of OEG‐terminated SAMs on silica surfaces during XPS characterization

Oligo ethylene glycol layers are widely used in biosensor applications, mainly for their anti‐fouling abilities. Such surfaces are often characterized by X‐ray photoelectron spectroscopy (XPS) as this method allows a precise determination of the surface chemical composition. We show herein that X‐rays used during XPS characterization quickly and significantly degrade oligo ethylene glycol immobilized onto silica substrates. It is therefore necessary to introduce a correcting factor to assess the true (i.e. without degradation) corresponding ether contribution in the XPS spectrum of such organic layers. Eventually, fluorescence scans show the loss of anti‐fouling properties of the degraded surface, leading to greater amounts of adsorbed (fluorescently labeled) protein. Copyright © 2015 John Wiley & Sons, Ltd.     

Asymmetric 1,4‐conjugation addition of diethylzinc to cyclic enones catalyzed by a self‐assembled copper complex

A new self‐assembled catalyst system based on copper complex was developed for the 1,4‐conjugation addition of diethyl zinc to cyclic enones. The self‐assembled catalyst was readily prepared from (R)‐[1,1′]binaphthalenyl‐2,2′‐diamine (1a), (L )‐tryptophan (3f) and copper(I) chloride (CuCl). Several enones were found to be suitable substrates in the presence of the self‐assembled copper catalyst [10 mol% (R)‐1a, 10 mol% (L )‐3f and 10 mol% CuCl] under optimized conditions. The desired products were afforded with high isolated yields (up to 98%) and moderate to good enantioselectivities (up to 80% ee) in mild conditions (at 0 °C). Copyright © 2009 John Wiley & Sons, Ltd.     

Correlation of architecture with excimer emission in 100% pyrene‐labeled self‐assembled polymers

Pyrene was incorporated as pendant unit to side‐chain urethane methacrylate polymers having a short ethyleneoxy or a long polyethyleneoxy spacer segment. The short‐spacer pyrene urethane methacrylate was also incorporated either as block or random copolymer (1:9) along with polystyrene. The excimer emission was observed to be different for different polymers with the random copolymer exhibiting the lowest efficiency. But, the total quantum yield was highest (? = 0.58) for random copolymer due to the high emission coefficient of monomer compared to that of excimer. The polymer dynamics were compared by steady state emission and fluorescence decay in THF or THF/water (9:1) solvent mixture and films. The solid state decay profile showed decay without a rise time indicating presence of ground state aggregates. In THF/water (9:1), the decay profile at the excimer emission (500 nm) showed a rise time indicating dynamic excimers. The evolution of excimeric emission centred ～430 or ～480 nm as a function of temperature was also studied in THF/water (9:1). The I_E/I_M ratio for the λ_{343 nm} excitation exhibited steady increase with temperature with the block copolymer PS‐b‐PIHP exhibiting the highest ratio and highest rate of increase; whereas, the random copolymer PS‐r‐PIHP had the lowest I_E/I_M ratios. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Lotus bioinspired superhydrophobic,self‐cleaning surfaces from hierarchically assembled templates

The super hydrophobic, self‐cleaning properties of natural species derive from the fine hierarchical topography evolved on their surfaces. Hierarchical architectures which are function‐mimetic of the lotus leaf are here described and created from multi‐scale hierarchical assembled templates. The first level of hierarchy was a micromachined dome structure template and the second level of hierarchy was added by layering a thin nanoporous membrane such as porous anodized alumina or an ion track etch membrane. The assembled templates were nanoimprinted by a single step process on thermoplastic films. The wetting angle of the surfaces reached a value of 160° and the self‐cleaning behavior was observed. The superhydrophobic behavior remained over 1 year after fabrication, which demonstrates the stability of these polymeric self‐cleaning topographies. © 2014 Wiley Periodicals, Inc. J. Polym. Sci. Part B. Polym. Phys. 2014 , 52, 603–609     

Formation of long‐range stripe patterns with sub‐10‐nm half‐pitch from directed self‐assembly of block copolymer

We have demonstrated directed self‐assembly of poly(styrene‐b‐dimethylsiloxiane) (PS‐b‐PDMS) down to sub‐10‐nm half‐pitch by using grating Si substrate coated with PDMS. The strong segregation between PS and PDMS enables us to direct the self‐assembly in wide grooves of the grating substrate up to 500 nm in width. This process can be applied to form various type of sub‐10‐nm stripe pattern along variety of grating shape. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Triethanolamine‐catalyzed expeditious and greener synthesis of 2‐amino‐4H‐chromenes

Triethanolamine (TEOA), an inexpensive and eco‐friendly base, was used to efficiently catalyze the three‐component condensation reaction of heterocyclic/aromatic aldehyde, (α/β)‐naphthol, and malononitrile in water to give the corresponding substituted 2‐amino‐4H‐chromene derivatives with excellent yields.