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In this work, a novel PAA-[Fe.sup.3+]-[Al.sup.3+] hydrogel with triple network structure (TN) was synthesized via bimetallic ions synergistic cross-linking strategy. As-synthesized samples were characterized by scanning electron microscope, Fourier transform infrared analysis, and X-ray diffractometer. The relevant experiment results demonstrated that the hydrogel can rapidly self-heal in ambient temperature without any external stimulus with 95% healing efficiency in 60 s. Simultaneously, the relatively rapid self-healing of PAA-[Fe.sup.3+]-[Al.sup.3+] polymer can be obtained through the coordination of metal ions with the -CO[O.sup.-] in PAA and the oxygen of agar in the TN hydrogel system. And the prepared hydrogels demonstrate excellent mechanical properties--high tensile strength (the tensile strain [approximately equal to] 1.011 mm/mm, tensile stress [approximately equal to] 0.34 MPa) and large elasticity (the elongation at break [approximately equal to] 74%). Especially, the antimicrobial activity of the novel hydrogel against Staphylococcus aureus and Escherichia coli bacteria was investigated using the inhibition zone method, showing remarkable antibacterial activity., INTRODUCTION Nowadays, multi-functional hydrogels have been widely used in the adapters, human tissue and biomedicine industry due to their self-healing property, tunable pore structure, as well as great biocompatibility [1-6]. [...]

Supercritical carbon dioxide (scC[O.sub.2]) technology was used for preparation of functional pH sensitive chitosan-based aerogels characterized with micron size pores and their impregnation with thymol as a natural bioactive substance. Hydrogels based on chitosan, itaconic and methacrylic acids were transformed to alcogels and dried in the air or with scC[O.sub.2] to obtain xero- and aerogels, respectively. Applying 10 min of static and 120 min of dynamic scC[O.sub.2] drying at 11 MPa and 45[degrees]C followed with the decompression at a rate of 1 MPa/min yielded an advantageous aerogel with favorable swelling kinetics and elasticity, compared to the xerogel and aerogels obtained at other decompression rates and drying times. This aerogel was successfully loaded with thymol (up to 4.6 wt.%) using supercritical scC02 at 10 MPa and 35[degrees]C. In vitro studies of swelling in PBS at 37[degrees]C indicated a great potential of the obtained stimuli-responsive chitosan gels for topical administration of thymol known for antimicrobial, antioxidant and anti-inflammatory activities. POLYM. ENG SCI., 58:2192-2199, 2018., INTRODUCTIONChitosan (Ch) represents a vast resource produced at lowcost by deacetylation of chitin (poly-N-acetylglucosamine)--one of the most abundant natural polysaccharide isolated from exoskeletons of arthropods and mollusks, cell walls of [...]

Incomplete premelting at the edges of monolayer colloidal crystals is triggered by a bulk solid-solid phase transition and truncated by a mechanical instability that induces homogeneous bulk melting of the crystal; these observations challenge existing theories of two-dimensional melting. Surface melting in a model system When a crystal melts, it typically melts from the surfaces, starting with the formation of liquid-like 'premelt' surface layers at temperatures slightly below the melting point. In an effort to understand the mechanistic details of this process, Yilong Han and colleagues have investigated the melting behaviour of two-dimensional (monolayer, two-layer and three-layer) colloidal crystals -- model systems whose dynamics can be followed at the single particle level. They observe a variety of surface premelting, bulk-melting and solid-solid phase-transition phenomena, the interplay of which challenges current premelting and melting theories. Crystal surfaces typically melt into a thin liquid layer at temperatures slightly below the melting point of the crystal. Such surface premelting is prevalent in all classes of solids and is important in a variety of metallurgical, geological and meteorological phenomena.sup.1. Premelting has been studied using X-ray diffraction.sup.2 and differential scanning calorimetry.sup.3, but the lack of single-particle resolution makes it hard to elucidate the underlying mechanisms. Colloids are good model systems for studying phase transitions.sup.4 because the thermal motions of individual micrometre-sized particles can be tracked directly using optical microscopy.sup.5. Here we use colloidal spheres with tunable attractions to form equilibrium crystal-vapour interfaces, and study their surface premelting behaviour at the single-particle level. We find that monolayer colloidal crystals exhibit incomplete premelting at their perimeter, with a constant liquid-layer thickness. In contrast, two- and three-layer crystals exhibit conventional complete melting, with the thickness of the surface liquid diverging as the melting point is approached. The microstructures of the surface liquids differ in certain aspects from what would be predicted by conventional premelting theories. Incomplete premelting in the monolayer crystals is triggered by a bulk isostructural solid-solid transition and truncated by a mechanical instability that separately induces homogeneous melting within the bulk. This finding is in contrast to the conventional assumption that two-dimensional crystals melt heterogeneously from their free surfaces.sup.3,6 (that is, at the solid-vapour interface). The unexpected bulk melting that we observe for the monolayer crystals is accompanied by the formation of grain boundaries, which supports a previously proposed grain-boundary-mediated two-dimensional melting theory.sup.7. The observed interplay between surface premelting, bulk melting and solid-solid transitions challenges existing theories of surface premelting and two-dimensional melting., Author(s): Bo Li [sup.1] , Feng Wang [sup.1] , Di Zhou [sup.1] , Yi Peng [sup.1] , Ran Ni [sup.2] [sup.3] , Yilong Han [sup.1] Author Affiliations: (1) Department of [...]

The ability to design and assemble three-dimensional structures from colloidal particles is limited by the absence of specific directional bonds. As a result, complex or low-coordination structures, common in atomic and molecular systems, are rare in the colloidal domain. Here we demonstrate a general method for creating the colloidal analogues of atoms with valence: colloidal particles with chemically distinct surface patches that imitate hybridized atomic orbitals, including sp, [s.sup.p2], [s.sup.p3], [s.sup.p3]d, [s.sup.p3][d.sup.2] and [s.sup.p3][d.sup.3]. Functionalized with DNA with single-stranded sticky ends, patches on different particles can form highly directional bonds through programmable, specific and reversible DNA hybridization. These features allow the particles to self-assemble into 'colloidal molecules' with triangular, tetrahedral and other bonding symmetries, and should also give access to a rich variety of new microstructured colloidal materials., The past decade has seen an explosion in the kinds of colloidal particles that can be synthesized (1, 2), with many new shapes, such as cubes (3), clusters of spheres [...]

This paper reports a novel protocol consisting of the thermomodulated electrokinetic enrichment, elution, and separation of charged species based upon a thermoswitchable swelling-shrinking property of a poly(N-isopropylacrylamide), PNIPAAm, hydrogel. A 0.2-1 mm long PNIPAAm hydrogel plug was photopolymerized inside a glass microfluidic channel to produce a composite device consisting of the PNIPAAm hydrogel plug and the glass microchannel (abbreviated as plug-in-channel). After voltage was applied to the composite device, anions, such as FITC, could be enriched at the cathodic end of the PNIPAAm plug when the temperature of the plug was kept below its lower critical solution temperature (LCST, ~32[degrees]C). The concentrated analytes could then be eluted by electroosmotic flow when the temperature of the plug was heated above the LCST. The mechanism of the thermoswitchable ion enrichment/elution process was studied with the results presented. The analytical potential of the composite device was demonstrated for the temperature-modulated preconcentration, elution, and separation of FITC-labeled amino acids. 10.1021/ac101768j

We report on a novel binding gel for phosphate, based on ferrihydrite, and its use in diffusive gradients in thin films (DGT) for measuring labile phosphate species in waters, sediments, and soils. An existing method of binding layer preparation was modified to overcome potential problems with deterioration of ferrihydrite due to conversion to goethite. The gel was characterized regarding its suitability for conventional DGT measurements as well as for measuring two-dimensional distributions of P with high spatial resolution using laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS). The effects of pH, ionic strength and storage time of gels on phosphate binding were investigated and the kinetics of binding and the maximum binding capacity were determined. The gel is shown to have a considerably higher P capacity than the conventional ferrihydrite DGT binding layers. LA-ICPMS analysis of DGT standards with P concentrations ranging from 0.088 [+ or -] 0.005 to 4.47 [+ or -] 0.16 [micro]g [cm.sup.-2] resulted in reproducible calibration curves which could be described using a simple power function. We demonstrate that the new gel is well suited for analyzing small-scale changes of P concentrations in soils. Moreover, the gel can be used as an alternative to conventional DGT gels that incorporate powdered ferrihydrite, with improved characteristics for the determination of labile phosphate. 10.1021/ac101450j

In this technical note, we demonstrate a squeeze-film based spacer-free method for creating controllable submicrometer hydrogel films on planar substrates that can be used to photolithographically fabricate hydrogel microstructures. This new technique improves the photolithographic resolution and yield by providing a uniform and low-defect hydrogel film. The optimum polymerization initiation time for achieving such a layer was determined to be around 1 min. For patterning, the dried hydrogel film was coated with a parylene-C masking layer. Subsequent etching in oxygen plasma was used to transfer selected patterns of hydrogel to the substrate in a batch scale. 10.1021/ac100579v

By specifically binding derivatized colloidal particles and physisorbing nonderivatized particles to the surface of a quartz crystal microbalance (QCM), we have observed positive shifts of frequency, [DELTA]f, in contrast to the negative frequency shifts typically found in adsorption experiments. Evidently, the Sauerbrey relation does not apply to this situation. A comparison of frequencies shifts and bandwidths on different overtones reveals a coupled resonance: at low overtones, [DELTA]f is negative, whereas it is positive at high overtones, with maximal resonance bandwidth observed at the crossover point. As predicted by the Dybwad model, the spheres bound to the surface form resonating systems on their own. A composite resonator is formed, consisting of a large crystal with resonance frequency [omega] and the adsorbed spheres with resonance frequency [[omega].sub.S]. In the case in which the resonance frequency of the small spheres (firmly attached to crystal), [[omega].sub.S], is higher than the resonance frequency of the crystal, [omega], [DELTA]f of the composite system is negative (leading to the Sauerbrey limit). In the opposite limit (that is, in the case of 'large adsorbed particles hound to the sensor surface via a sufficiently weak bridge) [DELTA]f is positive. Such a behavior is known from sphere--plate contacts in the dry state. Finite element calculation demonstrates that this phenomena is also plausible in liquid phase media, with [DELTA]f critically dependent on the strength of the sphere--plate contact. Operated in this mode, the QCM most likely probes the contact strength, rather than the mass of the particle. 10.1021/ac902012e

This manuscript reports the use of near-infrared mullispectral imaging (NIR-MSI) microscopy to provide the first direct observation and spectral measurement of individual poly-(n-isopropylactylamide-co-acrylic acid) (NIPAM-co-AAc) hydrogel particles. The high sensitivity and high spatial resolution (~0.9 [micro]m/pixel) of the NIR-MSI microscope, coupled with its ability to measure images and spectra directly and simultaneously, allows the unprecedented in situ monitoring of the size, morphology, and spectroscopic properties of individual hydrogel particles, which respond strongly to external stimuli (e.g., changes in temperature and/or pH). Importantly, this novel technique allows, for the first time, the direct measurement of the lower critical solution temperature (LCST) phase transition of individual hydrogel particles rather than that of a collection of hydrogel particles. Furthermore, NIR-MSI measurements reveal that the LCST value is unique for each individual hydrogel particle, depending strongly on particle size, with larger particles exhibiting higher LCST values. 10.1021/ac902099d

Influence of the ionic compositions of bathing solution with multivalences is investigated on the responsive behavior of pH-sensitive hydrogel to environmental change in solution pH. It is based on a chemo-electro-mechanical formulation, previously termed the multief-fect-coupling pH-stimulus (MECpH) model, which is improved in this article by incorporating the finite deformation theory into the mechanical equilibrium. The improved MECpH model consists of the coupled nonlinear partial differential equations, which are solved via a meshless numerical technique called the Hermite-cloud method with the modified Newton iteration. After the MECpH model is examined by comparison between the computational results and experimental data available in literature, several case studies are numerically carried out to discuss the effects of the multivalent ionic compositions of surrounding solution on the variation of the deformation of the pH-stimulus-responsive hydrogel and the distributions of the diffusive ion concentrations and electric potential, when the hydrogel is placed in the buffered solutions. POLYM. ENG. SCI., 50:429-439, 2010.[C] 2009 Society of Plastics Engineers, INTRODUCTION Environmental-sensitive hydrogels are often called as smart biomaterials. One of them is pH-stimulus-responsive hydrogel. They are widely used in biomedical and biotechnology fields because of their excellent biocompalibility and [...]

The evaporating sessile droplet of a mono/didisperse colloid on a plate is a very useful and handy technique in micro/nano/bioapplications to separate, pattern, and control the particles. Although the fundamental nature of the evaporation phenomena and its applications have been extensively proposed, the crucial forces affecting a single particle motion in an evaporating droplet are not reported yet. To elucidate the impact of various forces including the drag, electrostatic, van der Waals, and surface tension forces on the particle motion in suspension, the magnitudes of them are compared using the scale analysis. In the early stage of the evaporation, in which the contact line is fixed, the motion of a single particle suspended in liquid are mostly affected by drag force. Later, with the incidence of the contact line recession, the surface tension force takes over the control of the single particle motion. 10.1021/ac902288z

A method for the affinity capture of specific proteins from a complex mixture using a polyacrylamide gel technique is described. The approach is based on the orthogonal electro-transfer of proteins separated by ordinary polyacrylamide gel electrophoresis (PAGE) to a ligand-coupled polyacrylamide gel (Li-PAG), which is placed under the PAGE gel. Upon electro-transfer, the proteins orthogonany migrate from the PAGE into the Li-PAG, based on the net charge. During migration to the Li-PAG, proteins that specifically interact with a ligand can be transiently trapped in the Li-PAG, while those that do not interact with a ligand pass through it. This method permits the separation of the proteins that can specifically interact with a ligand, even when present in a complex mixture. The method is demonstrated by applying it to the onestep isolation of a trypsin inhibitor from a crude extract of soybean flour. 10.1021/ac902290q

Optical fluorescence sol gel sensors have been developed for the detection of carbon dioxide gas in the 0.03-30% range with a detection limit of 0.008% (or 80 ppm) and a quantitation limit of 0.02% (or 200 ppm) C[O.sub.2]. Sol-gels were spin-coated on glass slides to create an organically modified silica-doped matrix with the 1-hydroxypyrene-3,6,8--trisulfonate (HPTS) fluorescent indicator. The luminescence intensity of the HPTS indicator (513 nm) is quenched by C[O.sub.2], which protonates the anionic form of HPTS. An ion pair technique was used to incorporate the lipophilic dye into the hydrophllic sol-gel matrix. Ti[O.sub.2] particles ( 10.1021/ac901890r

We describe the synthesis and characterization of degradable nanogels that display bulk erosion under physiologic conditions (pH = 7.4, 37[degrees]C). Erodible poly(N-isopropyl-methacrylamide) nanogels were synthesized by copolymerization with N,O-(dimethacryloyl) hydroxylamine, a cross-linker previously used in the preparation of nontoxic and biodegradable bulk hydrogels. To monitor particle degradation, we employed multiangle light scattering and differential refractometry detection following asymmetrical flow field-flow fractionation. This approach allowed the detection of changes in nanogel molar mass and topology as a function of both temperature and pH. Particle erosion was evident from both an increase in nanogel swelling and a decrease in scattering intensity as a function of time. Following these analyses, the samples were recovered for subsequent characterization by direct particle tracking, which yields hydrodynamic size measurements and enables number density determination. Additionally, we confirmed the conservation of nanogel stimuli-responsivity through turbidity measurements. Thus, we have demonstrated the synthesis of degradable nanogels that erode under conditions and on time scales that are relevant for many drug delivery applications. The combined separation and light scattering detection method is demonstrated to be a versatile means to monitor erosion and should also find applicability in the characterization of other degradable particle constructs. 10.1021/ac901725m

We report simulations of glassy arrest in hard-core particles with short-range interparticle attraction. Previous experiments, theory, and simulations suggest that in this kind of system, two qualitatively distinct kinds of glasses exist, dominated respectively by repulsion and attraction. It is thought that in the former, particles are trapped 'topologically,' by nearest-neighbor cages, whereas in the latter, nonergodicity is due to interparticle 'bonds.' Subsequent experiments and simulations have suggested that bond breaking destabilizes attractive glasses, but the long-term fate of these arrested states remains unknown. By running simulations to times a few orders of magnitude longer than those reached by previous experiments or simulations, we show that arrest in an attractive glass is, in the long run, also topological. Nevertheless, it is still possible to distinguish between 'nonbonded' and 'bonded' repulsive glassy states. We study the melting of bonded repulsive glasses into a hitherto unknown 'dense gel' state, which is distinct from dense, ergodic fluids. We propose a 'modified state diagram' for concentrated attractive particles, and discuss the relevance of our results in the light of recent rheological measurements in colloid--polymer mixtures. colloids | glass transition | nonergodicity

During the weathering of gold deposits, exceptionally pure, Keywords: gold, weathering, nanoparticles, critical zone, nanoplates, colloid.

The stability of colloidal-surfactant mixture in terms of Fuchs stability ratio, W and surfactant adsorption is studied using small-angle light scattering technique. The adsorption of surfactant influences the stability of the dispersion at a lower surfactant concentration than saturation point and at higher concentrations, the formation of surfactant micelles results in depletion-induced destabilization effects.

The crystallization through an amorphous precursor is analyzed in a colloidal model system. The overall nucleation rate of the crystalline phase is determined by the nucleation rate of crystals in the dense droplets and the multistep crystallization (MSC) has promoted the production of defect-free crystals.

Transmission microscopy with soft X-rays (TXM) is used for imaging in-situ polyelectrolyte assemblies in aqueous environment. The method is found to be element specific, exhibiting a lateral resolution of 20 nm, and is coming up as a highly promising approach in colloid and polyelectrolyte science.

The size-tunable synthesis and three-dimensional self-organization of the nearly monodispersed perylene nanoparticles is described. The method contains a homogeneous solution phase, which makes it extremely useful for facile separation of nucleation and the growth stages.

The computer simulations and a theoretical model were used to examine the link between the kinetics of clustering and the phase behavior of dilute colloids with short range attractions of moderate strength. The weak attractions are found to be associated with a gas phase of small clusters, intermediate with liquid-gas separation and strong attractions with fractal unbreakable clusters.

Silica colloidal crystals were investigated for their potential as high surface area materials to enhance sensitivity over planar surfaces for microarrays using fluorescence detection. A relation was derived showing how crystal thickness and transmission, as well as colloid size, combine to determine the optically accessible surface area for enhancing sensitivity. Experimentally, crystals of 250-nm colloids were prepared with thicknesses determined by SEM to be 1.6, 4.2, and 11.0 [micro]m. The material was sintered at 1000 [degrees]C to make it durable without affecting the crystalline structure, as confirmed by SEM. UV/visible spectrometry showed the depth of penetration (1/e) to be 8.4 [micro]m at 488 nm for these materials. Fluorescein-labeled streptavidin and biotin were used as a model ligand-receptor pair. For the fluorescence measurements, biotin was covalently bonded to the silica surfaces, and the fluorescence was detected from the captured streptavidin-fluorescein. The observed fluorescence enhancement agreed well with the theory developed here. Compared to a planar surface, the colloidal crystal of 11.0 [micro]m in thickness enhanced the fluorescence by nearly a factor of 80, with only a 0.3% increase in fluorescence background.

The nature and role of potential active species in C-C coupling reactions of the Heck type were investigated by using catalyst systems with ligand-free inorganic salts, simple inorganic complexes, and supported and nonsupported (colloidal) Pd particles. From the experimental reports it is concluded that the active species is generated in situ in catalytic systems at higher temperature conditions of more than 100 degree Celsius.

The distribution of diffusional fluxes is measured by using a microfluidics device filled with a colloidal suspension of a small number of microspheres. A new fluctuation theorem is introduced for the fluxes, which is confirmed quantitatively by the experiments.

Several parameters like the substrate withdrawing speed and the colloidal suspension temperature are measured and examined to study the effects of liquid bridge and the evaporation temperatures on the manufacture of colloidal multilayers. The results of the study show that the water between the colloidal spheres that is formed by the capillary force highly affects and influences the number of formed colloidal crystal layers.

Monte Carlo computer simulations in the isothermic-isobaric ensemble were used to determine the phase diagram of a two-dimensional model system for colloidal particle at the air-water interface. The analysis of isotherms, translational and orientational correlation functions as well as structure factor provide evidence of the existence of a melting first-order transition.

The demonstration conducted shows that mondisperse colloidal particles in emulsion droplets can be organized into colloidal crystals by microwave irradiation. The result revealed that packing quality of colloidal crystals obtained by microwave-assisted self-organization was good enough to show photonic band gap characteristics.

This paper reports the first application of a combined approach utilizing split-flow thin-cell (SPLIT) separation to size fractionate natural aquatic colloids and particles collected from freshwater samples. No sample preconcentration was performed although some samples were investigated after alteration of the ambient pH. The unfractionated and fractionated samples were analyzed by scanning electron microscopy (SEM), environmental SEM, and 3D excitation emission matrix fluorescence. Qualitative and quantitative results by microscopy indicated that SPLITT produces well-resolved fracfionations at appropriate sizes but with some perturbation of the sample. In addition, tryptophan-like fluorescence was shown to be caused by different organic moieties compared with humic-like and fulvic-like fluorescence. Tryptophan-like fluorescence intensity is found mainly in the particulate material but is not pH dependent, while humic-and fulviclike fluorescence intensities are dependent on pH but not on size. Fulvic-like fluorescence intensity normalized to absorbance, related to fluorescence efficiency and molar mass, varies with size.

The alternating current (ac) response is investigated theoretically in colloidal suspensions consisting of suspended radially inhomogeneous graded particles having complex permittivity profiles under an external ac electric field. The existence of exact analytical solutions of the local potentials in the graded particles in terms of the hypergeometric functions is demonstrated.

The change in the optical properties of the guest--host colloidal solution was assessed by using optical transmission spectroscopy while the variation in crystal structure was examined using scanning electron micro microscopy (SEM). The disruption in the crystalline lattices depends on the relative deviation in sizes of the guest and host particles and the concentration of the guest colloid.

A simple chemical method is introduced to produce copper particles, which has the ability to shape the particle without using any capping agent or template. The reactant concentration and temperature exerted a strong influence on the shape of the copper particles.

A model based on PBE in dimensionless form is developed for the aggregation of colloidal dispersion in nonsheared conditions. A demonstration that the measured aggregation kinetics could be accurately described by population balance equations, which is the Smoluchowski aggregation equation, at all solid volume fractions investigated is presented.

Rheological investigations are presented to determine the influence of hydrophobicity interactions in concentrated colloidal suspensions. The resulting viscoelasticity of the suspensions is also examined.

Self-consistent field theory for adsorption and association is utilized to calculate the adsorption of the ionic surfactant (C16P3(super +)) on two neutral, slightly hydrophobic solids separated by a thin aqueous film and immersed in an infinite reservoir of aqueous 1:1 electrolyte. The change in surfactant adsorption as a function of the separation between the solids is discussed in relation to the forces between the solids as well as the shape of the adsorption.

Photoenhancement effect in colloidal CdSe and (CdSe)ZnS core-shell quantum dots attached to a variety of surfactant molecules in aqueous and nonaqueous environment is observed. Results show that the effect occurs in dots suspended in a variety of organic or aqueous situations.

Hard spherocylinders (cylinders of length L and diameter D capped at both ends with two hemispheres) provide a suitable model for investigating entropy-driven mesophase formations in real colloidal fluids that are composed of rigid rodlike molecules. Results of extensive Monte Carlo simultions of this model is presented.

The investigations made on the particle properties, which show variations within the ensembles of colloidal II-VI and III-V semiconductor nanocrystals, are reported. A theoretical model is explained, which describes the evolution of an ensemble of nanocrystals in a colloidal solution.

The study presents a report on gold colloids, which are covalently derivatized with hydrophilic polymer brushes. A description on the preparation and properties of gold colloids is provided.

Synthetic procedure for preparation of monodisperse thiol-stabilized gold colloids is described. This colloidal solution organizes in two-and-three dimensional structures.

Gold nanorods is found to change their shape after excitation with intense pulsed laser irradiation. The result indicate that the influence of the laser pulse width on the photothermal treatment of gold nanorods are in very good agreement with the laser ablation studies on bulk metal films.

The normal modes and the density of states (DOS) of any material provide a basis for understanding its thermal and mechanical transport properties. In perfect crystals, normal modes are plane waves, but they can be complex in disordered systems. We have experimentally measured normal modes and the DOS in a disordered colloidal crystal The DOS shows Debye-like behavior at low energies and an excess of modes, or Boson peak, at higher energies. The normal modes take the form of plane waves hybridized with localized short wavelength features in the Debye regime but lose both longitudinal and transverse plane-wave character at a common energy near the Boson peak. 10.1126/science.1187988

Extremely uniform packing of colloidal silica in capillaries is shown. Reversed-phase electrochromatograms of DiI-[C.sub.12] exhibit plate heights as low as 0.23 [micro]m and a reduced plate height as low as 0.7, using 75 [micro]m i.d. capillaries packed with 330 nm silica particles. The contribution from the A term is 0 [+ or -] 20 nm in electrochromatography. The particles are shown to form colloidal crystals inside the capillaries. Optical images show Bragg diffraction, indicative of crystallinity. Scanning electron microscopy (SEM) images show face-centered cubic crystallinity, and the porosity is 0.25 [+ or -] 0.01, which is in agreement with that for face-centered cubic crystals. The capillaries are fritless, and 100 [micro]m i.d. capillaries packed with silica colloidal crystals withstand pressures of at least 12 400 psi. 10.1021/ac100062t

The nonlinear Rayleigh-Gans-Debye theory is described and used to probe molecules adsorbed on nanometer size colloidal particles. It is observed that optical second-harmonic generation from molecules adsorbed occurs at angles as large as 90 degree away from the fundamental beam direction.