1,720,985 research outputs found
Adsorption characteristics of p-xylene-alpha,alpha -dithol on gold and silver surfaces: Surface-enhanced Raman scattering and ellipsometry study
No full textThe adsorption behavior of p-xylene-alpha, alpha'-dithiol (p-XDT) on colloidal gold and silver surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). p-XDT chemisorbed dissociatively on both the gold and silver surfaces but as mono- and dithiolate, respectively. Regardless of the bulk concentration of p-XDT, only a monolayer was assembled on the silver surface with a flat orientation by forming two Ag-S bonds. On the gold surface, the monothiolate species, p-XDT1-, appeared to assume a rather flat orientation at a very low surface coverage, but as the surface coverage was increased, the adsorbate took a perpendicular orientation. Furthermore, when the bulk concentration of p-XDT was close to that required for a full-monolayer coverage limit, a band assignable to the S-S stretching vibration appeared at similar to 509 cm(-1) in the gold sol SER spectra. A separate ellipsometry measurement performed with vacuum-evaporated gold substrates revealed that up to trilayers could be assembled on gold in 1 mM n-hexane solution of p-XDT while only a monolayer formed in either methanol or ethanol solution. Although the exact causes were uncertain, such a difference in behavior seemed to have nothing to do with the oxygen species present in ethanol or methanol solution
Adsorption characteristics of 1,3-propanedithiol on gold: Surface-enhanced Raman scattering and ellipsometry study
No full textThe adsorption behavior of 1,3-propanedithiol (1,3-PDT) on a colloidal gold surface has been investigated by means of surface-enhanced Raman scattering (SERS). 1,3-PDT chemisorbed dissociatively on gold as a monothiolate. Moreover, we could clearly identify the S-S stretching band that reveals the formation of multilayers of 1,3-PDT on the colloidal gold surface. As for the case of 1,2-ethanedithiol. the intermolecular disulfide bond appeared to form even at a submonolayer coverage limit, implying that the adsorption of alpha,omega-alkanedithiol on gold does not take place homogeneously from the early stages of self-assembly. On the other hand, referring to the ab initio calculated vibrational frequencies of AuSCH2CH2CH2Cl, we could also analyze the concentration-dependent SER spectral features of 1,3-PDT in terms of the conformational isomerism around the two C-S bonds. Upon the increase of the bulk concentration of 1,3-PDT, a transition from a GG to GT conformation appeared to occur on the sol surface near the monolayer coverage limit; herein the first letter designates the conformation with respect to the C-C bond near the gold surface. On the basis of the concentration-dependent SER peak intensities, the 1,3-PDT-derivatized Au particles appeared to consist in nearly contact configurations. A separate ellipsometry measurement performed with vacuum-evaporated gold substrate revealed that at best one and one-half layered film could be assembled on gold in polar and protic solvents while up to three layers were assembled on gold in n-hexane solution of 1,3-PDT
Adsorption of 1,4-benzenedithiol on gold and silver surfaces: Surface-enhanced Raman scattering study
No full textThe adsorption behavior of 1,4-benzenedithiol (1,4-BDT) on colloidal gold and silver surfaces has been investigated by means of surface-enhanced Raman scattering (SERS). 1,4-BDT chemisorbed dissociatively on both gold and silver surfaces but as mono- and dithiolate, respectively. Regardless of the bulk concentration of 1,4-BDT, only a monolayer was assembled on the silver surface with a flat orientation by forming two Ag-S bonds. On the gold surface, the monothiolate species, 1,4-BDT-1, appeared to assume a rather flat orientation at a very low surface coverage, but as the surface coverage was increased, the adsorbate took a perpendicular orientation. Furthermore, when the bulk concentration of 1,4-BDT was close to that required for a full-monolayer coverage limit, a band assignable to the S-S stretching vibration appeared at similar to 536 cm(-1) in the gold sol SERS spectra. A separate ellipsometry measurement performed with vacuum-evaporated gold substrates revealed that up to tetralayers could be assembled on gold in 1 mM n-hexane solution of 1,4-BDT while at best a bilayer formed in either methanol or ethanol solution. The different adsorbate structure of 1,4-BDT on gold and silver was overall quite comparable to that of p-xylene-alpha,alpha ' -dithiol. (C) 2001 Academic Press
Promoting rebound of impinging viscoelastic droplets on heated superhydrophobic surfaces
No full textThe rebound of impinging droplets is a defining characteristic of superhydrophobic surfaces; yet, such an intriguing interfacial phenomenon can be effectively suppressed by adding a tiny amount of flexible polymers to induce non-Newtonian viscoelastic properties. In this work, however, we demonstrate the promoting effects of surface heating on the rebound of impinging viscoelastic droplets on superhydrophobic surfaces. The underlying mechanism for the promotion is that the local heat transfer at the liquid-solid interface causes the fast evaporation of the liquid and thus the breakup of the formed viscoelastic filaments, which hinder droplet recoiling. Therefore, the lower threshold velocity for rebound increases while the upper threshold velocity for rebound suppression decreases with increasing surface temperature, resulting in a wider regime for droplet rebound in the impact phase diagram. The surface heating effect on liquid-solid interactions also leads to a nontrivial dependence of the contact time on the impact velocity and a linear decrease of the restitution coefficient with the Weber number for diverse bouncing viscoelastic droplets, which can be rationalized by coupling the interfacial force and energy analyses. We envision that these findings would be useful in technological processes requiring control the retention of viscoelastic liquids on solid surfaces
Adsorption of 4,4 -biphenyl diisocyanide on gold nanoparticle surfaces investigated by surface-enhanced Raman scattering
No full textWe investigated the spectral features of the nu(NC) bands when 4,4'-biphenyl diisocyanide (BPDNC) is adsorbed on gold nanoparticle surfaces by surface-enhanced Raman scattering (SERS). The mode of adsorption of BPDNC on gold nanoparticles was found to change with the bulk concentration. At low concentrations of BPDNC, only the nu(NC)(bound) band was conspicuous at 2185 cm(-1) and the free NC stretching band was barely detected in,the SERS spectra. When the bulk concentration was increased, the nu(NC)(free) band became prominent at similar to2123 cm(-1). BPDNC was assumed to bridge two different gold particles at low concentrations, but as the concentration was increased, the bridge appeared to be broken and bonded to the gold particle only via one of the two isocyanide groups. On the basis of the electromagnetic surface selection rule, we attempted to explain the orientation of the adsorbate on Au surfaces by determining the relative enhancement factor of each vibrational band. Copyright (C) 2003 John Wiley Sons, Ltd
Binding of aromatic isocyanides on gold nanoparticle surfaces investigated by surface-enhanced Raman scattering
No full textThe adsorption structure and binding of phenyl isocyanide (PNC), 2,6-dimethyl phenyl isocyanide (DMPNC), and benzyl isocyanide (BZI) on gold nanoparticle surfaces have been studied by means of surface-enhanced Raman scattering (SERS). PNC, DMPNC, and BZI have been found to adsorb on gold assuming a standing geometry with respect to the surfaces. The presence of the v(CH) band in the SERS spectra denotes a vertical orientation of the phenyl ring of PNC, DMPNC, and BZI on An. The lack of a substantial red shift and significant band broadening of the ring breathing modes implied that a direct ring pi orbital interaction with metal substrates should be quite low. For PNC, the band ascribed to the C-NC stretching vibration was found to almost disappear after adsorption on An. On the other hand, the C-NC band remained quite strong for DMPNC after adsorption. This result suggests a rather bent angle of C-NdropC: for the nitrogen atom of the NC binding group on the surfaces, whereas a linear angle of C-NdropC: should be more favorable on gold surfaces due to an intramolecular steric hindrance of its two methyl groups. SERS of BZI on gold nano-paticles also supports a bent angle of :CdropN-CH2 for its nitrogen atom, suggesting a preference of sp(3) (or sp(2)) hybridization for the nitrogen atom
Adsorption and stability of phthalic acid on a colloidal silver surface: surface-enhanced Raman scattering study
No full textThe adsorption characteristics of phthalic acid on a silver surface were investigated by means of surface-enhanced Raman scattering (SERS). For a reliable analysis of the SER spectrum, we also performed an ab initio vibrational wavenumber calculation, The SER spectral features dictated that the phthalic acid molecules should be bound to silver as dicarboxylate, but in contrast with earlier reports, with a strongly tilted orientation with respect to the surface normal. The degree of tilt appeared to increase with increase in the bulk pH, Such a tilted orientation was presumed to occur by the simultaneous sigma- and pi-type coordination of carboxylate groups to silver caused by the steric hindrance and electrostatic repulsion between the two carboxylate groups. Probably owing to the latter effects, phthalic acid on silver was easily displaced with aromatic mono-acids that could be bound to silver by forming only sigma-type coordination. A sigma-type coordination therefore seemed to be more important than a pi-type coordination for an aromatic carboxylic acid derivative to assemble a robust monolayer on a silver surface. Copyright (C) 2000 John Whey & Sons, Ltd.This work was supported by the Korea Science and Engineering Foundation(KOSEF) through the Center for Molecular Catalysis at Seoul
National University (SNU) and by the Korea Research Foundation through the Research Institute for Basic Sciences at SNU. S.W.J. thanks the KOSEF for an Intern Research Fellowship
Surface-induced photoreaction of benzyl phenyl sulfide monolayers on silver and its application to preparing patterned binary monolayers
No full textBenzyl phenyl sulfide (BPS, C6H5CH2-S-C6H5) is readily converted on silver to benzenethiolate by irradiation with visible light. By using this knowledge and invoking the fact that BPS is easily replaced by carboxylic acids, we have demonstrated by surface-enhanced Raman scattering that patterned binary monolayers can be prepared on silver using the self-assembled monolayers of BPS as a lithographic template. Although the example shown in this work, that is, binary monolayers composed of benzenethiolate and 4-cyanobenzoate, is rather preliminary and quite limited in scope, its application prospects are thought to be very good. Because surface-induced photoreaction of aromatic sulfides including BPS can occur even on gold induced by UV radiation, the present method is expected to be applicable to forming patterns and structures with a wide variety of materials on silver and gold with features that range from nanometers to micrometers in size
Surface-initiated, enzymatic polymerization of biodegradable polyesters
No full textEnzyme-catalyzed, ring-opening polymerization of biodegradable aliphatic polyesters has successfully been applied to surface-initiated polymerization (see Figure). Using lipase B as a catalyst, a thin film of poly (epsilon-caprolactone) (PCL) and poly(p-dioxanone) (PPDX) on a gold substrate (after a formation of self-assembled monolayers terminating in hydroxyl groups) is formed
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