Excited state chemistry of capsular assemblies in aqueous solution and on silica surfaces

Synthesis and encapsulation properties of two new water-soluble resorcinol-capped organic cavitands (tetra acid and octa acid; RTA and ROA) are reported in this Letter. Organic guest molecules template the formation of capsular assembly of the above cavitands in water. Depending upon the guest, either 1:2 (guest to host) or 2:2 capsular assemblies were formed. The excited state properties of guests such as anthracene, camphorthione, and 4,4'-dimethyl benzil were distinctly different within a capsular assembly from those when they were free in a solution. Importantly, the host-guest complexes of the above two hosts (RTA and ROA) as well as octa acid (OA) could be transferred to a silica surface. The excited state behavior of host-guest assemblies on silica surface resembled that in solution. The high cage effect in the decarbonylation products and high yield of rearrangement product obtained upon photolysis of 1-phenyl-3-tolyl-2-propanone included within RTA, ROA, and OA both in solution and on silica surface supported the conclusion that capsular assemblies of these hosts are stable on silica surface.     

Influence of natural organic matter on the deposition kinetics of extracellular polymeric substances (EPS) on silica

The influence of humic acid and alginate, two major components of natural organic matter (NOM), on deposition kinetics of extracellular polymeric substances (EPS) on silica was examined in both NaCl and CaCl(2) solutions over a wide range of environmentally relevant ionic strengths utilizing a quartz crystal microbalance with dissipation. Deposition kinetics of both soluble EPS and bound EPS extracted from four bacterial strains with different characteristics was investigated. EPS deposition on humic acid-coated silica surfaces was found to be much lower than that on bare silica surfaces under all examined conditions. In contrast, pre-coating the silica surfaces with alginate enhanced EPS deposition in both NaCl and CaCl(2) solutions. More repulsive electrostatic interaction between EPS and surface contributed to the reduced EPS deposition on humic acid-coated silica surface. The trapping effect induced by the rough alginate layer resulted in the greater EPS deposition on alginate-coated surfaces in NaCl solutions, whereas surface heterogeneities on alginate layer facilitated favorable interactions with EPS in CaCl(2) solutions. The presence of dissolved background humic acid and alginate in solutions both significantly retarded EPS deposition on silica surfaces due to the greater steric and electrostatics repulsion.     

Surface chemistry and annealing-driven interfacial changes in organic semiconducting thin films on silica surfaces

Vibrational sum frequency generation (VSFG) spectroscopy was used in conjunction with steady-state IR spectroscopy, atomic force microscopy (AFM), and spectroscopic ellipsometry to characterize organic semiconductor thin films that were vapor deposited on silica- and trimethoxy(octadecyl)silane (ODTMS)-functionalized silica surfaces. The growth of perylene derivative N,N'-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C(8)) was found to proceed differently on simple glass slides relative to that of native oxide on silicon and fused quartz slides. VSFG was applied to these samples to isolate structural changes that occurred specifically at the buried interface between the organic semiconductor and the silica dielectric upon thermal annealing. A model was introduced to globally fit the imide carbonyl symmetric and asymmetric interfacial spectra that included contributions from both inner and outer interfaces. The fits to the VSFG data and AFM topographic images revealed significant reordering at the outer interface on all substrates upon thermal annealing. Within the model, the spectroscopic data reported that the inner interfacial PTCDI-C(8) monolayer reoriented to a more reclined phase on bare substrates after annealing but remained essentially unchanged on ODTMS monolayers. Electrical characterization of PTCDI-C(8) field-effect transistors indicated that electron mobilities were higher on bare substrate devices but could be improved by a factor of 2 on both surface types by thermal annealing. The mobility effects were attributed to the annealing-driven coalescence of PTCDI-C(8) grain boundaries. Consistent with previous structural reports, the molecular rearrangements of the first monolayer of PTCDI-C(8) on bare substrates that were reported by VSFG spectroscopy had a noticeable impact on the device performance.     

Influence of polymeric additives on biomimetic silica deposition on patterned microstructures

Microstructured polymer films prepared by photochemical grafting of different polymers were used as restricted reaction areas in silica deposition experiments. Linear and branched poly(alkyleneimines) and poly(allylamine hydrochloride) in pure aqueous or phosphate-containing solutions were used as additives to silica precursor solutions. The silica deposits obtained by spin-coating these solutions onto microstructured polymer films were investigated by scanning electron microscopy and atomic force microscopy. Experiments with poly(alkylene imines) in the silica precursor solution show the deposition of smooth and granular silica structures that closely mimic the natural patterns. The structure formation can be explained by physicochemical processes. Hypotheses that have been made for the natural silification processes can be evaluated on this basis.     

Influence of surfactants on laser-induced copper deposition from solution

The influence of surfactants on the result of laser induced copper deposition from solution on the dielectric surface was studied. The dependences of the topology of the copper structures on the hydrophilic—lipophilic balance of non-ionogenic surfactants was found. The surface tension at the gas phase—solution interface was measured. The best results of laser deposition are obtained by the use of non-ionogenic surfactants with low values of hydrophilic—lipophilic balance.     

Role of solution chemistry and ion valence on the adhesion kinetics of groundwater and marine bacteria

The role of solution chemistry on bacterial adhesion has been investigated using a radial stagnation point flow (RSPF) system. This experimental system utilized an optical microscope and an image-capturing device to directly observe the deposition kinetics of a groundwater bacterium, Burkholderia cepacia G4g, and a marine bacterium, Halomonas pacifica g. Experiments were carried out under well-controlled hydrodynamic and solution chemistry conditions, allowing for the sensitivity of bacterial adhesion behavior to be examined under a range of ionic strength and valence (KCl vs CaCl2) simulating groundwater and marine environments. Complimentary cell characterization techniques were conducted to evaluate the electrophoretic mobility, hydrophobicity, surface charge density, and viability of the bacteria under the same range of conditions. Solution chemistry was found to have a marked effect on the electrokinetic and surface properties of bacteria and the quartz collector, as well as on the resulting rate of bacterial deposition. Comparable adhesion trends were observed for B. cepacia G4g and H. pacifica g. Specifically, the deposition rates of the two bacteria species in both KCl and CaCl2 solutions increased with ionic strength, a trend consistent with traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, which considers the combination of van der Waals and electrostatic double-layer interaction forces. However, in some cases, experimental results showed bacterial deposition behavior to deviate from DLVO predictions. On the basis of the systematic investigation of bacterial cell characteristics, it was found that Ca2+ ions play a distinct role on bacterial surface charge, hydrophobicity, and deposition behaviors. It is further suggested that bacterial adhesion is determined by the combined influence of DLVO interactions, electrosteric interactions associated with solution chemistry, and the hydrodynamics of the deposition system.     

Nonlinear friction characteristics between silica surfaces in high pH solution

Molecular-scale characteristics of friction forces between silica particles and silica wafers in aqueous solutions of the normal (pH 5.6) and high pH (pH 10.6) are investigated, using the lateral force measuring procedure of the atomic force microscope (AFM). Various significant differences of friction characteristics between solutions of normal and high pH's are found. In the case of solutions of normal pH, the friction force increases linearly with increasing loading force, as the Amonton's law for solid bodies indicates. However, in the case of high pH solutions, the increasing rate with the loading force is considerably reduced in the low loading region, but the value increases abruptly above a critical loading force to overcome the magnitude of friction force of normal pH above the region of very high loading. It is very interesting to know that this nonlinear force curve at high pH is independent of the atomic-scale roughness of surfaces, although the magnitude of friction is greatly influenced by the roughness in the case of normal pH. The reason why the friction at high pH is independent of the surface roughness is postulated to be due to the hairy-like layer formed on the silica surface. The existence of hairy-like layers at high pH is proven directly by the dynamic method of normal force measurements with AFM and the thickness is estimated to be at least ca. 1.3 nm.     

Influence of shape and surface properties of microstructured reaction areas on the deposition of silica

Differently shaped reaction areas for silica deposition were created by photochemical grafting of hydrophobic poly(acrylic acid 2-ethyl-hexylester) as barrier and a hydrophilic polymer employing a mask having hexagons, pentagons, squares and stripes. Poly(ethylene glycol), poly(acrylic acid), branched and linear poly(ethylene imine) and linear poly(methylpropylene imine) have been applied as hydrophilic polymer in the reaction area. These patterned films have been used in silica mineralization experiments by dipping them into a silica precursor solution. Investigations of the polymer films and silica depositions have been done by contact angle measurements, ellipsometry and scanning electron microscopy (SEM). Silica deposition occurs only in the hydrophilically coated areas, resulting in regular arrays of lens-like silica particles. There are only minor differences due to the shape of the reaction area. The influence of the different hydrophilic polymers can be explained by their wetting behaviour.     

Influence of the deposition method, temperature and deposition time on the corrosion inhibition of lead dodecanoate coatings deposited on lead surfaces

Electrochemical impedance measurements have been used to investigate the influence of the deposition method, including time and temperature, upon the corrosion inhibition characteristics of lead dodecanoate coatings on lead electrodes. The results were analysed using multivariate statistics and show that, in general, these easily prepared coatings are very protective against corrosion. The temperature proves to be an important parameter for the quality and the corrosion inhibition efficiency of the coating. A comparison between two different electrochemically assisted deposition methods, immersion using a reduction pretreatment and cyclic voltammetry, does not show significant differences. Using the immersion technique at room temperature, the deposition time was tested as the third influencing parameter for the corrosion inhibition efficiency of the deposited lead dodecanoate coatings. A longer deposition time of the lead into the sodium dodecanoate solution provides a layer with a somewhat higher corrosion resistance.     

Influence of the specific surface area on crystallization process kinetics of some silica gels

The influence of the specific surface area on the crystallization processes of two silica gels with different specific surface areas has been investigated in non-isothermal conditions using DTA technique. The activation energies of the crystallization processes were calculated using four isoconversional methods: Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink and Tang. It has been established that, the decrease of the surface area from S=252.62 m² g⁻¹, in the case of sample GS2, to S=2.52 m² g⁻¹, in the case of sample GS1, has determined a slight increase of the activation energy of the crystallization process of the gels. Regardless of the isoconversional method used, the activation energy (E _α) decreases monotonously with the crystallized fraction (α), which confirms the complex mechanism of gels crystallization. It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the crystallization processes of the studied silica gels.     

Synthesis of neamine libraries for RNA recognition using solution phase chemistry

Selective protection of the 6′-amino group of neamine allows the preparation of aminoglycoside libraries by reductive amination and Ugi multicomponent coupling.     

Confinement and deposition of solution droplets on solvophilic surfaces using a flat high surface energy guide

A method of depositing small amounts of solution on flat micron scale surface areas on a hydrophilic substrate or die was developed. This method utilizes the capillarity of a flat, high surface free energy guide. Interfacial forces confine the solution between the guide and the substrate surface. The liquid follows the movement of the guide along the surface and can be moved to the desired area. The thermodynamic background of the method is given and its application to coat one arm of a gold plasmonic Mach-Zehnder interferometer with bovine serum albumin is described. This method, which is related to but different from microcontact printing and dip-pen microlithography, can be utilized in the manufacturing of biosensors and other lab-on-a-chip structures, and is particularly suitable to development stage devices.     

Effect of solution chemistry and speciation on shelf-life of silica sols and characteristics of deposited mesoporous thin films

The effects of storage temperature and time on deposition characteristics of molecularly templated silica sols, used in synthesis of mesoporous silica films, were investigated by preparing acid catalysed water-ethanol-TEOS sols with surfactant and analysing by silicon-29 NMR spectroscopy over a period of multiple days, and by producing films after specific storage times corresponding to collection of NMR spectral data, and analysed for thickness and porosity.     

Induced detachment of coalescing droplets on superhydrophobic surfaces

Coalescence of a falling droplet with a stationary sessile droplet on a superhydrophobic surface is investigated by a combined experimental and numerical study. In the experiments, the droplet diameter, the impact velocity, and the distance between the impacting droplets were controlled. The evolution of surface shape during the coalescence of two droplets on the superhydrophobic surface is captured using high speed imaging and compared with numerical results. A two-phase volume of fluid (VOF) method is used to determine the dynamics of droplet coalescence, shape evaluation, and contact line movement. The spread length of two coalesced droplets along their original center is also predicted by the model and compared well with the experimental results. The effect of different parameters such as impact velocity, center to center distance, and droplet size on contact time and restitution coefficient are studied and compared to the experimental results. Finally, the wetting and the self-cleaning properties of superhydrophobic surfaces have been investigated. It has been found that impinging water drops with very small amount of kinetic impact energy were able to thoroughly clean these surfaces.     

Influence of molecular organization of an azido alcohol solution on the urethane formation kinetics

The quantitative data on the influence of molecular organization of CH₂Cl₂ solutions of diazidopropanol and its non-azide analog (isopropanol) and the concentrations of the alcohols and catalyst (dibutyltin dilaurinate) on the kinetics of urethane formation via the reaction with 1,6-hexamethylene diisocyanate were obtained. The series of reactivity were composed for various associates of hydroxyl groups of these alcohols in solutions in the catalytic and non-catalytic reactions.     

Changes of methylated silica surfaces on ageing

Silica rendered hydrophobic by organosilanes is a widely used model material in colloid chemistry, biological research, catalysis, etc. However, it is often overlooked that the surface properties of silica, and silica made hydrophobic be reacting with silane, change with time when the substrate is immersed in aqueous solution. Therefore the experimental conditions when such model systems are employed have to be carefully assessed. This paper summarizes the findings of the force measurement tests between air bubbles and silica particles hydrophobized with organosilanes such as trimethylchlorosilane and 1,1,1,3,3,3-hexamethyl-disilazane. The results showed that the attractive forces as well as the adhesion between the air bubbles and silica particles decrease with the time of aging in aqueous solution. The silica surfaces rendered hydrophobic with organosilanes become hydrophilic with time due to hydration. The hydrophobicity could be restored by heating the samples at 190?^○C. The atomic force microscopy imaging on silica plates revealed that in addition to hydration, decomposition of the organosilane layer also takes place.     

Functionalization of colloidal silica and silica surfaces via silylation reactions

A series of trialkoxysilane compounds tipped with primary amine groups were used to functionalize the surfaces of glass and colloidal silica. Streaming potential and microelectrophoretic mobility measurements were used to monitor the stability of the functionalized surfaces.Hydrolytic breakdown of the surface-to-silane coupling was induced by either successively increasing and decreasing the pH of the solution in contact with the surface, or by aging the derivatised surfaces in aqueous solution over prolonged periods of time. The chemistry of the spacer units between the trialkoxysilane group and the primary amine tip had a major influence on the subsequent hydrolytic stability. Large hydrophobic spacer groups showed small changes in the electrokinetic properties on storage, but large changes when successively titrated with acid and base through the pH range. The behavior observed with small hydrophobic spacer groups was that large changes in electrokinetic properties were obtained on storage and with pH titration.