Showing papers in "Langmuir in 2003"
TL;DR: In this paper, the Wenzel and Cassie−Baxter equations are put into proper mathematical-thermodynamic perspective and defined the conditions for determining the transition between the homogeneous and heterogeneous wetting regimes.
Abstract: Equilibrium wetting on rough surfaces is discussed in terms of the “competition” between complete liquid penetration into the roughness grooves and entrapment of air bubbles inside the grooves underneath the liquid. The former is the homogeneous wetting regime, usually described by the Wenzel equation. The latter is the heterogeneous wetting regime that is described by the Cassie−Baxter equation. Understanding this “competition” is essential for the design of ultrahydrophobic surfaces. The present discussion puts the Wenzel and Cassie−Baxter equations into proper mathematical−thermodynamic perspective and defines the conditions for determining the transition between the homogeneous and heterogeneous wetting regimes. In particular, a new condition that is necessary for the existence of the heterogeneous wetting regime is added. It is demonstrated that when this condition is violated, the homogeneous wetting regime is in effect, even though the Cassie−Baxter equation may be satisfied.
1,297 citations
TL;DR: In this paper, the chemical reduction of graphite oxide (GO) to graphite by either NaBH4 or hydroquinone and also its surface modification with neutral, primary aliphatic amines and amino acids are described.
Abstract: The chemical reduction of graphite oxide (GO) to graphite by either NaBH4 or hydroquinone and also its surface modification with neutral, primary aliphatic amines and amino acids are described. Treatment of GO with NaBH4 leads to turbostatic graphite that upon calcination under an inert atmosphere is transformed to highly ordered graphitic carbon, while the reduction with hydroquinone yields directly crystalline graphite under soft thermal conditions. On account of the surface-exposed epoxy groups present in the GO solid, its surface modification with neutral, primary aliphatic amines or amine-containing molecules (amino acids and aminosiloxanes) takes place easily through the corresponding nucleophilic substitution reactions. In this way, valuable GO derivatives can be obtained, like molecular pillared GO, organically modified GO affording in organic solvents stable organosols or hydrophilic GO affording in water stable hydrosols and possessing direct cation exchange sites. The potential combination of s...
1,168 citations
TL;DR: In this article, a general method to coat colloids with silica is described, which is especially useful for colloidal particles that cannot be covered directly with SiO2 by a Stober-like growth process.
Abstract: A general method to coat colloids with silica is described. The amphiphilic, nonionic polymer poly(vinylpyrrolidone) (PVP) was adsorbed to various colloidal particles such as small gold colloids, gold-shell silica-core particles, small and large silver colloids, boehmite rods, gibbsite platelets, and positively or negatively charged polystyrene. After this functionalization the stabilized particles could be transferred to a solution of ammonia in ethanol and directly coated with smooth and homogeneous silica shells of variable thickness by addition of tetraethoxysilane in a seeded growth process. The length of the polymer used strongly influences the stability of the colloids and the homogeneity and smoothness of the initial silica coating. This method is especially useful for colloidal particles that cannot be covered directly with SiO2 by a Stober-like growth process. Compared to methods known from the literature for the coating of such particles, this new method is faster and requires neither the use o...
1,009 citations
TL;DR: In this paper, X-ray absorption spectroscopy and transmission electron microscopy (TEM) studies corroborated silver metal uptake by alfalfa plants from a silver-rich solid medium and the subsequent formation of silver nanoparticles.
Abstract: The preparation and study of quantum dots and quantum wires play a very important role in nanotechnology. In this particular study, we report on the uptake of silver by living alfalfa plants. X-ray absorption spectroscopy and transmission electron microscopy (TEM) studies corroborated silver metal uptake by alfalfa plants from a silver-rich solid medium and the subsequent formation of silver nanoparticles. Silver nanoparticle alignment, structure, and coalescence were observed using TEM with an atomic resolution analysis. Dark field image TEM showed the connection of silver nanoparticles of different sizes by possibly noncrystalline silver atomic wires. To our knowledge, this is the first report on the formation of silver nanoparticles by a living plant system.
947 citations
TL;DR: In this article, the authors proposed a design procedure to develop a rough superhydrophobic substrate that accounts for the multiple equilibrium drop shapes, which is expected to work well to maximize the advancing contact angle of a drop.
Abstract: The apparent contact angle of a drop on a rough surface is often modeled using either Wenzel's or Cassie's formulas. Previous experiments are not conclusive regarding which formula to use and when. This information is critical in designing a superhydrophobic substrate for applications in microscale devices. A drop on a rough substrate can occupy multiple equilibrium states. These equilibrium states denote respective local minima in energy. The particular shape that a drop attains depends on how the drop is formed. We propose a design procedure to develop a rough superhydrophobic substrate that accounts for the multiple equilibrium drop shapes. The theory is expected to work well to maximize the advancing contact angle of a drop. It is noted in the end that appropriate models for the receding contact angles on rough substrate must be investigated further before appropriate design procedures, which will maximize the receding contact angle or minimize hysteresis (i.e., minimize the difference between the adv...
804 citations
TL;DR: In this article, an experimental characterization of a simple method for rapid formation of droplets, or plugs, of multiple aqueous reagents without bringing reagents into contact prior to mixing is presented.
Abstract: This paper reports an experimental characterization of a simple method for rapid formation of droplets, or plugs, of multiple aqueous reagents without bringing reagents into contact prior to mixing. Droplet-based microfluidics offers a simple method of achieving rapid mixing and transport with no dispersion. In addition, this paper shows that organic dyes at high concentrations should not be used for the visualization of flow patterns and mixing of aqueous plugs in multiphase flows in this system (fluorinated carrier fluid and PDMS microchannels). It reports an inorganic dye that can be used instead. This work focuses on mixing in plugs moving through straight channels. It demonstrates that, when traveling through straight microchannels, mixing within plugs by steady recirculating flow is highly sensitive to the initial distribution of the aqueous reagents established by the eddy flow at the tip of the forming plug (twirling). The results also show how plugs with proper distribution of the aqueous reagents could be formed in order to achieve optimal mixing of the reagents in this system.
765 citations
703 citations
TL;DR: In this paper, the nanoscale structure of composite polyamide reverse osmosis (RO) and nanofiltration (NF) membranes was investigated by transmission electron microscopy and atomic force microscopy.
Abstract: The nanoscale structure of composite polyamide reverse osmosis (RO) and nanofiltration (NF) membranes was investigated by transmission electron microscopy and atomic force microscopy. The study demonstrated that the polymer density and charge are distributed across the active polyamide layer in a highly nonuniform fashion. The polyamide films appear to be built of a negatively charged outer layer sitting on top of an inner layer possessing a small positive charge. This picture appears to be fairly general for all types of composite membranes and seems to reconcile previously reported contradictory experimental facts concerning measurements of charge for this type of membrane. The sharp boundary between the layers roughly corresponds to the region of the highest polymer density, that is, the actual selective barrier. The location of this barrier deep inside the RO films indicates that formation of the RO polyamide is not limited solely by monomer diffusion through the film, as was suggested previously, but...
647 citations
TL;DR: In this paper, the adsorption kinetics of small unilamellar egg-yolk phosphatidylcholine vesicles were investigated by the quartz crystal microbalance−dissipation (QCM−D) technique, as a function of surface chemistry (on SiO2, Si3N4, Au, TiO2 and Pt), temperature (273−303 K), vesicle size (25−200 nm), and osmotic pressure.
Abstract: The adsorption kinetics of small unilamellar egg-yolk phosphatidylcholine vesicles was investigated by the quartz crystal microbalance−dissipation (QCM−D) technique, as a function of surface chemistry (on SiO2, Si3N4, Au, TiO2, and Pt), temperature (273−303 K), vesicle size (25−200 nm), and osmotic pressure. On SiO2 and Si3N4, the vesicles adsorb intact at low coverage, followed by transformation to a bilayer at a critical coverage. On TiO2, oxidized Pt, and oxidized Au, the vesicles adsorb intact at all coverages and all studied temperatures. Variation of vesicle size does not change the qualitative behavior on any of the surfaces, but the quantitative differences provide important information about surface-induced vesicle deformation. In the low-coverage regime (where vesicles adsorb intact on all surfaces), the deformation is much larger on SiO2 than on the surfaces where bilayer formation does not occur. This is attributed to stronger vesicle−surface interaction on SiO2. The bilayer formation is therm...
621 citations
TL;DR: In this article, it was shown that there can be two contact angles on the same rough surface, depending on how a drop is formed, and that a transition can occur between the different states by an external disturbance.
Abstract: The apparent contact angle on a rough surface is usually modeled by either Cassie's or Wenzel's theory. We show, on the basis of experimental evidence, that there can be two contact angles on the same rough surface, depending on how a drop is formed. A transition can occur between the different states by an external disturbance. This paper compares the theoretical prediction with matching experiments. This leads to the establishment of a design criterion for a robust hydrophobic rough surface on which the apparent contact angle will not change as a result of an external disturbance.
611 citations
TL;DR: In this article, a three-step seed-mediated growth method was used to make gold nanoparticles, and different surfactants, alkyltrimethylammonium bromides (CnTAB, n = 10, 12, 14, 16, and 18) and cetylpyridinium chloride (C16PC), were chosen as stabilizers.
Abstract: A three-step seed-mediated growth method was used to make gold nanoparticles. Different surfactants, alkyltrimethylammonium bromides (CnTAB, n = 10, 12, 14, 16, and 18) and cetylpyridinium chloride (C16PC), were chosen as stabilizers. In general, it was found that as the length of the surfactant chain increased, the resulting gold nanoparticles' aspect ratio increased: the aspect ratio was 1 (for C10TAB), 5 ± 2 (C12TAB), 17 ± 3 (C14TAB), and 23 ± 4 (C16TAB). The plasmon absorption maxima for the gold nanoparticles varied as a function of the shape, from 520 nm (spheres) to beyond 2000 nm (high aspect ratio nanorods). We propose that the surfactant binds as a bilayer to the growing nanoparticle and assists in nanoparticle elongation via a “zipping” mechanism.
TL;DR: In this article, the authors studied oil-in-water emulsions stabilized by monodisperse, fluorescent silica colloids presenting either a smooth or a rough surface.
Abstract: We have studied oil-in-water emulsions stabilized by monodisperse, fluorescent silica colloids presenting either a smooth or a rough surface. The presence of the fluorescent core allows for direct visualization of the colloids on the surface of the emulsion droplets. Droplet interfacial tension, measured by micropipet tensiometry, is not modified by particle adsorption at the interface, suggesting a purely steric stabilization mechanism. Surface roughness is shown to considerably lessen the ability of particles to stabilize droplets. At variance with what is commonly assumed, no straightforward relation exists between the extent of particle interfacial adsorption and emulsion macroscopic stability; stable emulsions can be obtained even with very low droplet surface coverage. Finally, we directly monitor the Brownian motion of the adsorbed particles, showing that their surface diffusion coefficient is very close to the bulk value. Evidence of a possible role of particle surface dynamics on the stabilizatio...
TL;DR: In this article, a theoretical model is presented for the behavior of rod-like particles representing CNTs in electrospinning, and the degrees of orientation of polymer, surfactant, and MWCNT are studied using X-ray dif...
Abstract: The electrospinning process was used successfully to fabricate nanofibers of poly(ethylene oxide) (PEO) in which multiwalled carbon nanotubes (MWCNT) are embedded. Initial dispersion of MWCNTs in water was achieved using amphiphiles, either as small molecules (sodium dodecyl sulfate, SDS) or as a high molecular weight, highly branched polymer (Gum Arabic). These dispersions provided separation of the MWCNTs and their individual incorporation into the PEO nanofibers by subsequent electrospinning. The focus of this work is on the development of axial orientations in these multicomponent nanofibers. A theoretical model is presented for the behavior of rodlike particles representing CNTs in electrospinning. Initially the rods are randomly oriented, but due to the sinklike flow in a wedge they are gradually oriented mainly along the stream lines, so that straight CNTs are almost oriented upon entering the electrospun jet. The degrees of orientation of polymer, surfactant, and MWCNT were studied using X-ray dif...
TL;DR: In this article, a nanometer-scale Au or Ag core is functionalized with Raman active molecules and encapsulated in a glass shell, and the scattering from the Raman tag is amplified through surface enhanced Raman scattering.
Abstract: Glass-coated, analyte-tagged nanoparticles (GANs) are core−shell particles where a nanometer-scale Au or Ag core is functionalized with Raman active molecules and encapsulated in a glass shell. The glass shell provides the particle with mechanical and chemical stability. Specifically, the glass coating renders the particle amenable to use in many solvents without altering the Raman spectral response and makes agglomeration a nonfactor. The density and thickness of the glass shell are controllable through synthetic conditions; thus, the rate of diffusion through the silica network can be tuned and the metal cores kept sequestered from any exterior reaction. This will allow for the attachment of biomolecules to the glass shell without altering the Raman response. GANs can be identified by the Raman spectrum of the attached Raman tag, and two differently labeled samples are unambiguously identified. The scattering from the Raman tag is amplified through surface-enhanced Raman scattering. The narrow bandwidth...
TL;DR: In this article, a method for the controlled assembly of unilamellar vesicles consisting of bilayers assembled one leaflet at a time was investigated, using water-in-oil emulsions stabilized by the material for the assembly.
Abstract: We investigate a method for the controlled assembly of unilamellar vesicles consisting of bilayers assembled one leaflet at a time. We use water-in-oil emulsions stabilized by the material for the ...
TL;DR: This paper presents results on the Fourier transform infrared spectroscopy, thermogravimetry, nuclear magnetic resonance, and X-ray photoemission characterization of gold nanoparticles capped with the alkylamines laurylamine and octadecylamine.
Abstract: In addition to alkanethiols and phosphine derivatives, alkylamines have been investigated as capping agents in the synthesis of organically dispersible gold nanoparticles. However, reports pertaining to gold nanoparticle derivatization with alkylamines are relatively scarce and their interaction with the underlying gold support is poorly understood. In this paper, we attempt a more detailed examination of this problem and present results on the Fourier transform infrared spectroscopy, thermogravimetry, nuclear magnetic resonance, and X-ray photoemission (XPS) characterization of gold nanoparticles capped with the alkylamines laurylamine (LAM) and octadecylamine (ODA). The capping of the gold nanoparticles with the alkylamines was accomplished during phase transfer of aqueous gold nanoparticles to chloroform containing fatty amine molecules. Thermogravimetry and XPS analysis of purified powders of the amine-capped gold nanoparticles indicated the presence of two different modes of binding of the alkylamine...
TL;DR: It is demonstrated that vascular smooth muscle cells undergo direct migration on radial-gradient-compliant substrata from soft to stiff regions of the substrate and that cells accumulate in the stiff regions after 24 h.
Abstract: Current solutions in the treatment of cardiovascular disease include angioplasty and the insertion of stents, but a large number of these cases result in restenosis. Biomaterial coatings that control vascular smooth muscle cell migration are therefore desirable. In this study, we describe a novel method to create substrata with defined gradients in mechanical compliance using photopolymerization and patterning. Cell speed was found to be 53 ± 2.6 μm/h on a substrate with a Young's modulus of 15 kPa compared to 40 ± 3.1 μm/h for a 28 kPa substratum (P < 0.005). We demonstrate that vascular smooth muscle cells undergo direct migration on radial-gradient-compliant substrata from soft to stiff regions of the substrate and that cells accumulate in the stiff regions after 24 h. Our results show that the pattern of the compliance gradient is important and that substrate compliance may be a key design parameter for modulation of cell migration for vascular tissue engineering applications.
TL;DR: This is the first report in which spatially resolved AFM force curves are used to distinguish regions of different elasticity at the surface of single microbial cells in relation with function (i.e., cell division), and this approach will provide fundamental insights into the spatial distribution of physical properties at heterogeneous microbial cell surfaces.
Abstract: Single microbial cells can show important local variations of elasticity due to the complex, anisotropic composition of their walls. An example of this is the yeast during cell division, where chitin is known to accumulate in the localized region of the cell wall involved in budding. We used atomic force microscopy (AFM) to measure quantitatively the local mechanical properties of hydrated yeast cells. Topographic images and spatially resolved force maps revealed significant lateral variations of elasticity across the cell surface, the bud scar region being significantly stiffer than the surrounding cell wall. To get quantitative information on sample elasticity, force curves were converted into force vs indentation curves. The curves were then fitted with the Hertz model, yielding Young's modulus values of 6.1 +/- 2.4 and 0.6 +/- 0.4 MPa for the bud scar and surrounding cell surface, respectively. These data lead us to conclude that in yeast, the bud scar is 10 times stiffer than the surrounding cell wall, a finding which is consistent with the accumulation of chitin in the bud scar region. This is the first report in which spatially resolved AFM force curves are used to distinguish regions of different elasticity at the surface of single microbial cells in relation with function (i.e., cell division). In future research, this approach will provide fundamental insights into the spatial distribution of physical properties at heterogeneous microbial cell surfaces.
TL;DR: In this article, a model for predicting the Derjaguin−Landau−Verwey−Overbeek (DLVO) interaction energy between colloidal particles and rough membrane surfaces is developed.
Abstract: Recent experimental investigations suggest that interaction of colloidal particles with polymeric membrane surfaces is influenced by membrane surface morphology (roughness). To better understand the consequences of surface roughness on colloid deposition and fouling, it is imperative that models for predicting the Derjaguin−Landau−Verwey−Overbeek (DLVO) interaction energy between colloidal particles and rough membrane surfaces be developed. We present a technique of reconstructing the mathematical topology of polymeric membrane surfaces using statistical parameters derived from atomic force microscopy roughness analyses. The surface element integration technique is used to calculate the DLVO interactions between spherical colloidal particles and the simulated (reconstructed) membrane surfaces. Predictions show that the repulsive interaction energy barrier between a colloidal particle and a rough membrane is lower than the corresponding barrier for a smooth membrane. The reduction in the energy barrier is ...
TL;DR: In this article, the authors used thermogravimetric analysis (TGA) for determination of the surface density (OH/nm2) and carbon content of silica and titania powders made by flame aerosol and sol−gel processes.
Abstract: Thermogravimetric analysis (TGA) is investigated for determination of the OH surface density (OH/nm2) and carbon content of silica and titania powders made by flame aerosol and sol−gel processes. It is shown that it is possible to distinguish between physically adsorbed and chemically bound water and to rapidly determine the OH surface density even of small powder samples (<0.2 g) by TGA calibrated with LiAlH4 titration data. The high accuracy of the OH surface density determination by TGA is confirmed further with additional LiAlH4 titration data of silica powders and by comparison with the specifications of commercially available silica Aerosil and titania P25 powders. Furthermore, by connecting a CO2 sensor or a mass spectrometer to the TGA balance, it is possible to verify the carbon content and determine other components (organic residues) of the powders. Thereby, it is shown that flame-made powders have high purity while the preparation conditions of sol−gel powders greatly affect their purity. At a...
TL;DR: In this article, gold nanoparticles were prepared in the presence of poly(amidoamine) (PAMAM) dendrimers (generations 3.0 and 5.0) with surface amino groups by laser irradiation.
Abstract: Gold nanoparticles were prepared in the presence of poly(amidoamine) (PAMAM) dendrimers (generations 3.0 and 5.0) or poly(propyleneimine) (PPI) dendrimers (generations 3.0 and 4.0) with surface amino groups by laser irradiation. UV−visible absorption, dynamic light scattering, and transmission electron microscopy have been used to study the formation and structure of the nanocomposites. The reduction of Au3+ ions proceeded with an increase of the irradiation time, and the average diameters of the gold nanoparticles obtained tended to decrease with an increase of the dendrimer concentration. It is suggested that the dendrimers are adsorbed on the nanoparticles as a monolayer. Studies of the reduction reaction of 4-nitrophenol by the gold nanoparticles with NaBH4 reveal that the rate constants for PPI dendrimers are higher than those for PAMAM dendrimers, whereas the size of the PPI dendrimer of the same generation is considerably smaller than that of the PAMAM dendrimer.
TL;DR: In this article, a set of poly(l-lysine) grafted with poly(ethylene glycol) (PLL-g-PEG), a polycationic copolymer that is positively charged at neutral pH, spontaneously adsorbs from aqueous solution onto negatively charged surfaces.
Abstract: Poly(l-lysine) grafted with poly(ethylene glycol) (PLL-g-PEG), a polycationic copolymer that is positively charged at neutral pH, spontaneously adsorbs from aqueous solution onto negatively charged surfaces, resulting in the formation of stable polymeric monolayers and rendering the surfaces protein-resistant to a degree related to the PEG surface density. A set of PLL-g-PEG polymers with different architectures was synthesized. The grafting ratio, g, of the polymer, defined as the ratio of the number of lysine monomers to the number of PEG side chains, was systematically varied between 2 and 23, and PEG molecular weights of 1, 2, and 5 kDa were used. The polymers were adsorbed onto niobium oxide-coated substrates, leading to highly different but well-controlled PEG surface densities with maximal values of 0.9, 0.5, and 0.3 chains/nm2 for the three PEG molecular weights, respectively. Time-of-flight secondary-ion mass spectrometry (ToF-SIMS) was used in conjunction with the in situ optical waveguide light...
TL;DR: In this paper, superhydrophobicity was built in by using organofunctionalized inorganic monomers and setting the conditions so that they were retained in the product.
Abstract: Intrinsically superhydrophobic foams with contact angles greater than 150° were prepared using a sol−gel phase-separation process. Hydrophobicity was built in by using organofunctionalized inorganic monomers and setting the conditions so that they were retained in the product. The materials were characterized by advancing and receding water contact angle measurements, scanning electron microscopy, and infrared spectroscopy. The sol−gel phase-separation preparation method used was simple and produced roughness and hydrophobicity in the same material, thus obviating the need for a hydrophobic coating to achieve superhydrophobicity. Superhydrophobicity was retained when the materials were cut or abraded. On heating, a rapid hydrophobic to hydrophilic transition was present at around 400 °C, generating a material that absorbed water rapidly. “Flat” sol−gel materials prepared without phase separation treated in the same manner showed a more gradual contact angle change, but the switch from hydrophobicity to hy...
TL;DR: In the quantitative studies presented in this article, dispersions of oil droplets in water are formed by the addition of water to a solution of the oil dissolved in a solvent, which causes the oil to supersaturate and then nucleate into small droplets.
Abstract: The “ouzo effect” enables one to create a dispersion of small droplets in a surrounding liquid phase without the use of surfactants, dispersing agents, or mechanical agitation: a phenomenon which can be of value in many disciplines. In the quantitative studies presented here, dispersions of oil droplets in water are formed by the addition of water to a solution of the oil dissolved in a solvent. This causes the oil to supersaturate and then nucleate into small droplets. The mean droplet diameter is a function only of the oil-to-solvent ratio at a given temperature. The number density of droplets formed can be controlled independently from the droplet diameter by changing the amount of water added. Smaller droplets are formed by using more hydrophilic cosolvents. The droplet size distribution is typically log−normal. The width of the distribution can be narrowed by mixing the components at an elevated temperature and then allowing the dispersion to cool.
TL;DR: A convenient method for immobilizing biologically active ligands to self-assembled monolayer of alkanethiolates on gold (SAMs) based on monolayers that present maleimide and penta(ethylene glycol) groups is reported.
Abstract: This paper reports a convenient method for immobilizing biologically active ligands to self-assembled monolayers of alkanethiolates on gold (SAMs). This methodology is based on monolayers that present maleimide and penta(ethylene glycol) groups. The maleimide groups react efficiently with thiol-terminated ligands, whereas the penta(ethylene glycol) groups prevent the nonspecific adsorption of protein to the substrate. The rate and selectivity of the immobilization of a ferrocene-thiol conjugate were characterized using cyclic voltammetry. This paper presents three examples of biochips prepared using this methodology. In the first example, four carbohydrate-thiol conjugates were immobilized to monolayers and the lectin-binding properties of the substrates were examined using fluorescence and surface plasmon resonance spectroscopy. The second biochip was used to study the enzymatic phosphorylation of the immobilized peptide IYGEFKKKC by the tyrosine kinase c-src. Monolayers presenting this peptide were then...
TL;DR: In this article, a real-time analytical procedure is developed to study geopolymerization of amorphous aluminosilicates in real time using Fourier transform infrared (FTIR) spectroscopy.
Abstract: Geopolymerization is a general term to describe all the chemical processes that are involved in reacting aluminosilicates with aqueous alkaline solutions to produce a new class of inorganic binders called geopolymers. In the present work, a novel analytical procedure is developed to study geopolymerization of amorphous aluminosilicates in real time. This procedure involves first conducting a series of well-designed leaching experiments, within which an aluminosilicate is alkali-activated with aqueous alkaline solutions of varying alkalinities and soluble silicate dosages. The leached solutions are diluted and analyzed using inductively coupled plasma equipped with optical emission spectroscopy (ICP−OES), and the activated solid particles are separated, washed, desiccated, and analyzed by Fourier transform infrared (FTIR) spectroscopy. By comparing the results obtained from the ICP−OES and the FTIR analyses, a linear calibration curve can be constructed to correlate the extent of the alkali-activation of t...
TL;DR: In this paper, the experimental equilibrium data for the single component dye−chitosan systems have been analyzed using the linearized forms of Langmuir, Freundlich, and Redlich−Peterson isotherms.
Abstract: The ability of chitosan as an adsorbent for the removal of acid dyestuff, namely, acid green 25, acid orange 10, acid orange 12, acid red 18, and acid red 73, from aqueous solution has been studied. The experimental equilibrium data for the single component dye−chitosan systems have been analyzed using the linearized forms of Langmuir, Freundlich, and Redlich−Peterson isotherms. The Langmuir isotherm was found to provide the best theoretical correlation of the experimental data for the adsorption of all five acid dyes. On the basis of the Langmuir analysis, the monolayer adsorption (saturation) capacities were determined to be 645.1, 922.9, 973.3, 693.2, and 728.2 mg of dye per gram of chitosan for acid green 25, acid orange 10, acid orange 12, acid red 18, and acid red 73, respectively. The differences in adsorption capacities may be due to the effect of molecular size and the number of sulfonate groups of each dye. The results demonstrated that monovalent and/or smaller dye molecules have superior adsor...
TL;DR: In this paper, the wetting behavior on surfaces with a single, circular heterogeneous island was studied, where small sessile drops were deposited on the center of an island and liquid was sequentially added, eventually forcing the contact line to advance beyond the island perimeter onto the surrounding area.
Abstract: Wetting behavior was studied on surfaces with a single, circular heterogeneous island. Lyophobic islands were created on lyophilic Si wafers using polystyrene. Alternately, lyophobic perfluoroalkoxy fluoropolymer film was etched to make lyophilic domains. Contact angles and hysteresis were measured with water and hexadecane. Small sessile drops were deposited on the center of an island and liquid was sequentially added, eventually forcing the contact line to advance beyond the island perimeter onto the surrounding area. Even though the underlying contact area contained a mixture of lyophilic and lyophobic domains, the contact angles, both advancing and receding, were equal to the angles exhibited by the homogeneous periphery. Or in other words, if the heterogeneity was completely contained with the contact area and did not intersect the contact line, then no area averaging of the contact angles occurred. These findings suggest that interactions at the contact line, not the contact area, control wetting of...
TL;DR: The effects of different poly(ethylene glycol) (PEG) attachment strategies upon the adhesion of a Gram-negative bacteria (Pseudomonas sp.) was tested and showed that both substrates were chemically uniform after each surface modification step.
Abstract: The effects of different poly(ethylene glycol) (PEG) attachment strategies upon the adhesion of a Gram-negative bacteria (Pseudomonas sp) was tested PEG was covalently immobilized, at the lower critical solution temperature of PEG, to a layer of branched poly(ethylenimine) (PEI) PEI was both physically adsorbed to a stainless-steel (SS) substrate and covalently immobilized to a carboxylated poly(ethylene terephthalate) (PET−COOH) surface On both substrates, the PEI and PEG grafting conditions were optimized so that the levels of surface coverage after each step were maximized and were the same on both substrates, as judged by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry (ToF-SIMS) Also, ToF-SIMS imaging showed that both substrates were chemically uniform after each surface modification step Thus, the two surfaces differ only in the mode of attachment of PEI to the substrate In bacterial adhesion experiments, the optimal SS−PEG surface was not capable of reduci
TL;DR: In this paper, ordered mesoporous silica adsorbents were prepared by grafting amino- and carboxylic-containing functional groups onto MCM-41 for the removal of Acid blue 25 and Methylene blue dyes from wastewater.
Abstract: Ordered mesoporous silica adsorbents were prepared by grafting amino- and carboxylic-containing functional groups onto MCM-41 for the removal of Acid blue 25 and Methylene blue dyes from wastewater...