Dynamic Contact Angle Measurements Research Articles

Wettability assisted selective deposition of polystyrene nanoparticles on glass fibers

This work presents a concept for creating different chemistries along thin, micrometer sized fibers to be used as substrates for selective localization of nanoparticles. Glass fibers have been surface modified to introduce hydrophilic and hydrophobic regions along their length. Dynamic contact angle measurements using the Wilhelmy technique shows a marked change in the wetting behavior, confirming the transition in chemical functionality along the fiber. These fibers were then used as substrates to localize polystyrene nanoparticles from an aqueous dispersion at the air-water interface via a dip-coating method. Low contact angles and faster de-wetting allowed the particles to predominantly confine onto the hydrophilic regions of the glass fibers, indicating that both the fiber surface properties as well as the curvature of the fiber influences the profile of the particle carrying fluid meniscus. Our results also indicate a velocity-dependent particle deposition morphology and image quantification analysis revealed a significantly higher density of nanoparticles to be deposited at higher withdrawal velocities.

Influence of Oxyfluorination on Geometrical Pull-Out Behavior of Carbon-Fiber-Reinforced Epoxy Matrix Composites

To improve the interfacial adhesion between carbon fibers and an epoxy matrix, carbon fibers were modified by oxyfluorination at different temperature conditions. Surface analyses of the oxyfluorinated carbon fibers were performed using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and dynamic contact angle measurements. The interfacial shear strength (IFSS) of a single carbon fiber/epoxy matrix was studied by employing single-fiber pull-out tests to confirm the interfacial adhesion. The pull-out behavior of the fiber from the matrix was discussed based on the Greszczuk’s geometrical model. Functional groups such as C-F, C-O, and COOH were present on the carbon fiber surfaces after oxyfluorination. Moreover, the presence of functional groups increased the surface polarity of the fibers, resulting in an increase in the IFSS owing to the improvement of the interfacial adhesive strength between the carbon fibers and the epoxy matrix.

Substrate-Independent Surface Energy Tuning via Siloxane Treatment for Printed Electronics.

Digital printing enables solution processing of functional materials and opens a new route to fabricate low-cost electronic devices. One crucial parameter that affects the wettability of inks for all printing techniques is the surface free energy (SFE) of the substrate. Siloxanes, with their huge variety of side chains and their ability to form self-assembled monolayers, offer exhaustive control of the substrate SFE from hydrophilic to hydrophobic. Thus, siloxane treatment is a suitable approach to adjust the substrate conditions to the desired ink, instead of optimizing the ink to an arbitrary substrate. In this work, the influence of different fluorinated and nonfluorinated siloxanes on the SFE of different substrates, such as polymers, glasses, and metals, are examined. By mixing several siloxanes, we demonstrate the fine tuning of the surface energy. The polar and dispersive components of the SFE are determined by the Owens-Wendt-Rabel-Kaelble (OWRK) method. Furthermore, the impact of the siloxanes and therefore the SFE on the pinning of droplets and wet films are assessed via dynamic contact angle measurements. SFE-optimized substrates enable tailoring the resolution of inkjet printed silver structures. A nanoparticulate silver ink was used for printing single drops, lines, and source-drain electrodes for transistors. These were examined in terms of diameter, edge quality, and functionality. We show that by adjusting the SFE of an arbitrary substrate, the printed resolution is substantially increased by minimizing the printed drop size by up to 70%.

Carbodiimide-mediated immobilization of acidic biomolecules on reversed-charge zwitterionic sensor chip surfaces.

The carbodiimide-mediated amine coupling of protein ligands to sensor chips coated with anionic polycarboxylate hydrogels, such as carboxymethyl dextran, is the predominant covalent immobilization procedure utilized in optical biosensors, namely surface plasmon resonance (SPR) biosensors. Usually, electrostatic interactions at a slightly acidic pH and low ionic strength are employed to efficiently accumulate neutral and basic ligands on the chip surface, which are then covalently coupled by surface-bound active N-hydroxysuccinimide (NHS) esters. Unfortunately, this approach is not suitable for acidic proteins or other ligands with low isoelectric points (IEPs), such as nucleic acids, because the charge density of the polycarboxylates is greatly reduced at acidic pH or because electrostatic attraction cannot be achieved. To overcome these drawbacks, we have established a charge-reversal approach that allows the preconcentration of acidic proteins above their IEPs. A precisely controlled amount of tertiary amines is applied to reverse the previous anionic surface charge while maintaining carbodiimide compatibility with future protein immobilization. The mechanism of this reversed-charge immobilization approach was demonstrated employing protein A as a model protein and using attenuated total reflectance Fourier transform infrared spectroscopy, dynamic contact angle measurements, colorimetric quantification, and SPR analysis to characterize surface derivatization. Furthermore, even though it had previously proven impossible to preconcentrate DNA electrostatically and to covalently couple it to polyanionic chip surfaces, we demonstrated that our approach allowed DNA to be preconcentrated and immobilized in good yields. Graphical abstract Principle of the covalent immobilization of acidic ligands on reversed-charge zwitterionic sensor chip surfaces.

Optical measurements of dynamic wetting and dynamic contact angle.

We present a method of optical measurement of the dynamic wetting, the dynamic contact angles, and the changes of the dynamic curved liquid surface corresponding to dynamic wetting, which uses the critical light reflection from dynamic curved liquid surfaces due to the dynamic wetting. When an expanded and collimated laser beam impinges on the dynamic curved liquid surfaces at glancing incidence, the special reflection patterns, which correspond to the different states of the dynamic wetting, are observed. Based on an analytic relation between the bright/dark region width and the height of down-/up-curved liquid surfaces, we proposed a method of optical measurement. In the experiment, a rod such as iron, copper, or aluminum is immersed at constant speed (u=0.2 mm/s) into a liquid bath and withdrawn out gradually. We measured the changing curve of the dynamic contact angle of the iron rod and the characterization of the dynamic curved liquid surface of the iron rod.

Effect of viscous force on dynamic contact angle measurement using Wilhelmy plate method

Wilhelmy plate method does not consider viscous force in the force balance equation to measure the dynamic contact angle and this results in a significant error in the measurement. Differences between the results obtained by optical method and Wilhelmy plate method indicate the importance of viscous force in the force balance equation. A theoretical viscous model is proposed, which must be considered in the force balance equation in Wilhelmy plate method to increase the accuracy of the dynamic contact angle measurement, especially for the case of highly viscous liquids and for experiments at large speeds of the plate, which can lead to large shear rate along the surface of the plate.

Strategies to hydrophilize silicones via spontaneous adsorption of poly(vinyl alcohol) from aqueous solution

It is challenging to achieve long-lasting hydrophilicity by surface modification of polydimethylsiloxane (PDMS), principally due to the hydrophobic recovery that occurs. This involves the migration of low molecular weight species from the bulk to the surface and is driven by the reduction of interfacial free energy. In this study, spontaneous adsorption of poly(vinyl alcohol) was carried out on Sylgard PDMS films and their modified derivatives. PDMSox1s, PDMSox60s, and PDMSox60s+2k were prepared by 1-s oxygen plasma, 60-s oxygen plasma, and 60-s oxygen plasma followed by covalent attachment of linear PDMS of 2 kDa molecular weight on PDMS films, respectively. Surface morphology was characterized by optical and atomic force microscopy and hydrophilicity was monitored by dynamic water contact angle measurements. It was found that negligible PVOH adsorption takes place on PDMSox60s due to the lack of hydrophobic driving force and that extensive PVOH thin film dewetting on PDMS and PDMSox1s results in insignificant improvement in hydrophilicity. However, a continuous PVOH thin film albeit with some small holes was obtained on PDMSox60s+2k. PDMSox60s+2k-PVOH exhibits advancing and receding contact angles of 80–90°/16 ± 2°, which are significantly lower than 123 ± 5°/97 ± 2° on unmodified PDMS. A range of static contact angles were also measured, some of which are lower than those reported in the literature. The PDMSox60s+2k-PVOH system demonstrates superior long-term and hydrolytic stability, which are attributed to the removal of the driving force for hydrophobic recovery by inserting a hydrophobic PDMS layer between a hydrophilic, plasma-oxidized, PDMS bulk and a hydrophilic PVOH exterior. This is a new concept in addressing hydrophobic recovery of hydrophilized silicones. The spontaneous nature of the adsorption process and the crystallinity of the PVOH barrier layer are the other advantages demonstrated in this study.

A two-angle model of dynamic wetting in microscale capillaries under low capillary numbers with experiments

ObjectivesAn accurate model of the dynamic contact angle θd is critical for the calculation of capillary force in applications like enhanced oil recovery, where the capillary number Ca ranges from 10−10 to 10−5 and the Bond number Bo is less than 10−4. The rate-dependence of the dynamic contact angle under such conditions remains blurred, and is the main target of this study. ExperimentsFeaturing with pressure control and interface tracking, the innovative experimental system presented in this work achieves the desired ranges of Ca and Bo, and enables the direct optical measurement of dynamic contact angles in capillaries as tiny as 40 × 20 (width × height) μm and 80 × 20 μm. The advancing and receding processes of wetting and nonwetting liquids were tested. FindingsThe dynamic contact angle was confirmed velocity-independent with 10−9 < Ca < 10−5 (contact line velocity V = 0.135–490 μm/s) and it can be described by a two-angle model with desirable accuracy. A modified two-angle model was developed and an empirical form was obtained from experiments. For different liquids contacting the same surface, the advancing angle θadv approximately equals the static contact angle θo. The receding angle θrec was found to be a linear function of θadv, in good agreement with our and other experiments from the literature.

The effect of high voltage electrostatic field (HVEF) treatment on bonding interphase characteristics among different wood sections of Masson pine (Pinus massoniana Lamb.)

Abstract High voltage electrostatic field (HVEF) treatment has been investigated as an optimization method for enhancing the bonding performance of wood via increasing its polarization degree and improvement of the penetration of phenol formaldehyde (PF) adhesive. As the wood surfaces from cross cut (C), radial cut (R) and tangential cut (T) behave differently, five cut combinations formed the samples to be tested, namely C-C, R-R, R-T, T-T (always parallel to grain) and T-T⊥, where the grains were perpendicular to each other. The gluing and HVEF treatments were performed simultaneously. The sample surfaces were characterized by electron spin resonance (ESR) spectroscopy, dynamic contact angle (CAdyn) measurements, X-ray densitometry, fluorescence microscopy, Fourier-transform infrared (FTIR) spectroscopy and measurements of compression shear bonding strength (CSBS). An increased surface energy led to decreased CAdynS in the following order: cross section&lt;tangential section&lt;radial section. Obviously, the triggered free electrons of the HVEF treatments changed the wood surfaces. The penetration depth of PF into wood cell decreased significantly and the maximal density increased after the HVEF treatment. The lower CAdyns also contributed to the better reaction of the wood surface with the PF resin. The CSBS of the five sample combinations was enhanced owing to a better performance of adhesive aggregation, which was increased by 18% (C-C), 24% (T-T), 26% (T-T⊥), 31% (R-T) and 42% (R-R), respectively. Pore size and pore size distribution contributed a lot to the bonding properties of HVEF-treated wood sections.

Dipole model of vorticity at the moving contact line

In theoretical analyses of the moving contact line, an infinite force along the solid wall has been reported based off the non-integrable stress along a single interface. In this investigation we demonstrate that the stress singularity is integrable and results in a finite force at the moving contact line if the contact line is treated as a one-dimensional manifold and all three interfaces that make up the moving contact line are taken into consideration. This is due to the dipole nature of the vorticity and pressure distribution around the moving contact line. Mathematically, this finite force is determined by summing all the forces that act over an infinitesimally small cylindrical control volume that encloses the entire moving contact line. With this finite force, we propose a new dynamic Young’s equation for microscopic dynamic contact angle that is a function of known parameters only, specifically the interface velocity, surface tension, and fluid viscosity. We combine our model with Cox’s model for apparent dynamic contact angle and find good agreement with published dynamic contact angle measurements.

Enhancing interfacial strength and hydrothermal aging resistance of silicone resin composites by different modification of carbon fibers with silica nanoparticles

Besides the well‐designed combination of the fibers and matrix resin, the fiber‐matrix interface plays a key role in bulk properties of composites. Here, the chemical grafting of silica nanoparticle (SiO2) onto fiber surface (CF‐g‐SiO2) using the bridging toluene‐2,4‐diisocyanate has been achieved and compared with the physical adsorption one (CF‐ad‐SiO2). Fourier transform infrared spectroscopy and X‐ray photoelectron spectroscopy confirmed the covalent bonding nature between SiO2 and CF. By atomic force microscopy observation, coating or grafting SiO2 on the surface of CFs also enhanced fiber surface polarity and roughness. However, CF‐g‐SiO2 showed a better uniform distribution of SiO2 on the fiber surface compared with CF‐ad‐SiO2 with the serious agglomeration of SiO2. These results of dynamic contact angle measurements indicated that CF‐ad‐SiO2 and CF‐g‐SiO2 had the similar increase degree of surface free energy, which contributed to improve the wettability between CFs and matrix resin. Interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) showed great enhancements, especially for CF‐g‐SiO2 composites, which increased 10.92% in ILSS and 10.71% in IFSS compared with those of CF‐ad‐SiO2 composites. Moreover, the interfacial reinforcing mechanisms have also been studied. Additionally, the introduced Si‐O‐Si bonds at the interface by SiO2 coating or grafting resulted in the different improved degree of the hydrothermal aging resistance. The results showed that the quality of fiber‐matrix interface could be tuned by varying the bonding natures between CFs and the modifiers, and chemically grafting SiO2 onto the fiber surface is the promising multifunctional reinforcement. POLYM. COMPOS., 40:E975–E982, 2019. © 2018 Society of Plastics Engineers

Three-dimensional printing of alginate-gelatin-agar scaffolds using free-form motor assisted microsyringe extrusion system

In current study, three-dimensional scaffolds of alginate-gelatin-agar were fabricated using free-form motor assisted microsyringe (MAM) extrusion system. Briefly, a hydrogel solution comprised of 18 wt% sodium alginate, 4 wt% gelatin, and 12 wt% agar was prepared by dissolving all components in sterile deionized water. Cubic scaffold with dimensions 9 × 9 × 9 mm3 were printed in a layer-by-layer fashion and sintered. Fourier transform infrared (FTIR) spectroscopy confirmed the chemical structure of scaffold. Field emission scanning electron microscopy (FE-SEM) analysis showed the fabrication of highly porous scaffolds with patterned structure and uniformly distributed holes at the surface. The dynamic contact angle measurement of alginate-gelatin-agar scaffold demonstrated its hydrophilic nature. The maximum tensile strength at breaking point, Young’s modulus, and elongation strain of scaffold were found to be 31.21 MPa, 0.83 GPa, and 2.51%, respectively. The scaffold supported the adhesion and growth of Hela cells. The interaction of scaffold with Escherichia coli and Saccharomyces cerevisiae as determined by the cell viability analysis through Alamar Blue assay demonstrated improved growth of microbial cells. This study can provide new dimension to the current bioprinting technology to develop patterned structure and microbes based micro/nano robots and devices.

Changes in surface characteristics of titanium and zirconia after surface treatment with ultraviolet light or non-thermal plasma.

Positive effects of irradiation with ultraviolet (UV) light or treatment with non-thermal plasma on titanium and zirconia surfaces have been described in various studies. The aim of this study was to assess and compare the changes in the physicochemical surface conditions of titanium and zirconia surfaces after a short treatment with UV light or with non-thermal plasmas of argon or oxygen. Titanium and zirconia samples with moderately rough surfaces were treated for 12 min either in a UV-light oven or in a non-thermal plasma reactor that generates non-thermal plasmas of oxygen or argon. Changes in surface conditions were assessed by confocal microscopy, dynamic contact angle measurement, and X-ray photoelectron spectroscopy (XPS). No changes in roughness occurred. Ultraviolet irradiation and non-thermal plasma significantly increased the wettability of the titanium and zirconia surfaces. X-ray photoelectron spectroscopy showed an increase of oxygen and a significant decrease of carbon after treatment with either method. Thus, ultraviolet light and non-thermal plasma were found to be able to improve the chemical surface conditions of titanium and zirconia following a short exposure time. However, further in vitro and in vivo studies are needed to determine the relevance of the results.

Facile fabrication of uniform hierarchical structured (UHS) nanocomposite surface with high water repellency and self-cleaning properties

In the present study, two-stage process for the fabrication of superhydrophobic Ni-Cu-TiO2 nanocomposite coatings on the copper substrate has been introduced. Surface modification was performed on the electrodeposited coatings by myristic acid-ethanol solution to achieve superhydrophobicity. Additionally, in order to further study the roughness effect, instead of addition of copper ions in electrodeposition bath, three substrates were roughened by electrochemical etching method. Water repellency properties were studied through measurement of static and dynamic contact angles, and performing bouncing test, self-cleaning and water-jet evaluation. The samples were electrodeposited in various current densities, and the highest corrosion resistance and water repellency properties were obtained for the sample which was electrodeposited in two consecutive steps and modified by a fatty acid called myristic acid (which significantly reduces surface energy of the coating). The highest water contact angle (161°) and the lowest contact angle hysteresis (3°) were obtained for the sample which was coated by 10 mA/cm2 (144 min) and 20 mA/cm2 (18 min), respectively. Since this approach does not require any sophisticated equipment and materials, it shows promising future in the fabrication of superhydrophobic coatings.

Direct Measurement of Static and Dynamic Contact Angles Using a Random Micromodel Considering Geological CO2 Sequestration

The pore-level two-phase fluids flow mechanism needs to be understood for geological CO2 sequestration as a solution to mitigate anthropogenic emission of carbon dioxide. Capillary pressure at the interface of water–CO2 influences CO2 injectability, capacity, and safety of the storage system. Wettability usually measured by contact angle is always a major uncertainty source among important parameters affecting capillary pressure. The contact angle is mostly determined on a flat surface as a representative of the rock surface. However, a simple and precise method for determining in situ contact angle at pore-scale is needed to simulate fluids flow in porous media. Recent progresses in X-ray tomography technique has provided a robust way to measure in situ contact angle of rocks. However, slow imaging and complicated image processing make it impossible to measure dynamic contact angle. In the present paper, a series of static and dynamic contact angles as well as contact angles on flat surface were measured inside a micromodel with random pattern of channels under high pressure condition. Our results showed a wide range of pore-scale contact angles, implying complexity of the pore-scale contact angle even in a highly smooth and chemically homogenous glass micromodel. Receding contact angle (RCA) showed more reproducibility compared to advancing contact angle (ACA) and static contact angle (SCA) for repeating tests and during both drainage and imbibition. With decreasing pore size, RCA was increased. The hysteresis of the dynamic contact angle (ACA–RCA) was higher at pressure of one megapascal in comparison with that at eight megapascals. The CO2 bubble had higher mobility at higher depths due to lower hysteresis which is unfavorable. CO2 bubbles resting on the flat surface of the micromodel channel showed a wide range of contact angles. They were much higher than reported contact angle values observed with sessile drop or captive bubble tests on a flat plate of glass in previous reports. This implies that more precaution is required when estimating capillary pressure and leakage risk.

Poly(lactic acid)/Organo-Montmorillonite Nanocomposites: Synthesis, Structures, Permeation Properties and Applications

Polylactic acid (PLA)/organo-montmorillonite nanocomposites were prepared by the solution casting method using chloroform as solvent. The clays were organically modified by four different modifiers, ternary amine with two alkyl (tallow) tails, primary amine containing silane with a single tail, ammonium salt with a single alkyl (tallow) tail, and ammonium salts with two alkyl (tallow) tails. The structural characterization of the nanocomposite films was performed using Raman spectroscopy and the internal structure of the nanocomposites in the nanometer range was studied using wide-angle X-ray diffraction analysis. All the nanocomposites exhibited superior improvement when compared to neat PLA. Differential scanning calorimetry (DSC) was performed to study the thermal behavior of the prepared composites. Among the used clay types, M24 was the most effective in improving the water vapor and oxygen barrier properties. Water vapor and oxygen permeability of the nanocomposite films were decreased up to 80 and 49% when using M24 clay, respectively. Surface properties of the films were investigated with dynamic contact angle measurements. The migration studies of neat PLA and nanocomposites were performed for three types of food simulants.

Wettability alteration of reservoir rocks to gas wetting condition: A comparative study

AbstractProductivity of gas condensate reservoirs reduces significantly due to the near wellbore condensate/water blockage phenomenon. A novel, permanent solution to alleviate this problem is near wellbore wettability alteration of reservoir rocks to preferentially gas wetting conditions; industrial chemical materials are good candidates for this purpose, because of their eco‐friendly characteristics, economical price, and mass production. In this paper, a comparative study is conducted on two industrial fluorinated chemicals, MariSeal 800 and SurfaPore M. Static and dynamic contact angle measurements, spontaneous imbibition, and core flooding tests were conducted to investigate the effect of utilized chemical agents on surface wetting behaviour and fluid flow characteristics of rock samples. Contact angle measurements demonstrate that the liquid phase is changed to a non‐wetting phase after chemical treatment and MariSeal 800 has a greater potential to decrease the surface free energy of the calcite surface. Although both chemicals reveal great potential in static contact angle measurements, further experiments were conducted to distinguish between their abilities. Spontaneous air liquid imbibition tests and endpoint relative permeability measurements approved the potential of utilized chemicals to improve liquid phase mobility and decrease critical condensate saturation, which improve production parameters and reservoir productivity. Liquid phase endpoint relative permeabilities of sandstone core samples were improved by factors of 1.74 and 2.62; furthermore, irreducible liquid phase saturations were decreased by factors of 0.68 and 0.5 using MariSeal 800 and SurfaPore M chemicals. The results of this research help efficient selection of chemical agents for further field applications.

Toward a hydrocarbon-based chemical for wettability alteration of reservoir rocks to gas wetting condition: Implications to gas condensate reservoirs

Recently, wettability alteration has been much attended by researchers for studying well productivity improvement in gas condensate reservoirs. Previous studies in this area only utilized water/alcohol based chemicals for this purpose. While, hydrocarbon nature of the blocked condensate in retrograde gas reservoirs, may motivate application of hydrocarbon based chemical agents. In this study, a new hydrocarbon based wettability modifier is introduced to alter wettability of carbonate and sandstone rocks to preferentially gas wetting condition. Static and dynamic contact angle measurements, spontaneous imbibition and core flooding tests were conducted to investigate the effect of proposed chemical on surface wetting behavior, and fluid flow characteristics at core scale. SEM, EDX, EDX map and FTIR tests are used to characterize the adsorbed chemical layer and also to endorse the adsorption of fluorinated chemicals on both sandstone and carbonate rock surfaces. It is inferred from the results of contact angle hysteresis at different levels of tilt angle that the surface roughness increased as a result of treatment with the new chemical. Measurements of surface free energy of calcite thin section at different tilt angles, by means of dynamic contact angle method, showed a significance decrease due to treatment with the new chemical, the factor of reduction ranges from 0.24 to 0.03. The results of air-water and air-n-decane spontaneous imbibition tests showed remarkable decrease in the ultimate imbibed liquids by a factor of 0.14 and 0.34, respectively. Also, core flooding experiment results demonstrated improvement of liquid phase endpoint relative permeability by a factor of 1.73 as a result of treatment with the proposed chemical fluid. The proposed chemical is miscible with dropped out condensate and does not suffer from instability due to reservoir brine salinity. Effectiveness, as well as hydrocarbon base of the proposed chemical makes it an attractive candidate for possible applications to enhance condensate recovery due to both condensate and water blockage in gas reservoirs by wettability alteration technique.

Effects of surface treatments and bonding types on the interfacial behavior of fiber metal laminate based on magnesium alloy

Fiber metal laminates based on magnesium alloys (MgFML) with different surface treatments and different bonding types were tested and analyzed. By using dynamic contact angle measurement and scanning electron microscopy (SEM), it was found that phosphating treatment can significantly improve the surface energy and wettability of magnesium alloy, and the surface energy of phosphated magnesium alloy was approximately 50% higher than that of abraded-only magnesium alloy. The single cantilever beam (SCB) test showed that the interfacial fracture energies of directly bonded MgFMLs based on abraded-only magnesium and abraded + phosphated magnesium were 650 J/m2 and 1030 J/m2, respectively, whereas the interfacial fracture energies of indirectly bonded MgFMLs were 1650 J/m2 and 2260 J/m2, respectively. Phosphating treatment and modified polypropylene interleaf were observed to improve the tensile strength and interfacial fracture toughness of MgFML. In addition, the rougher surface was more conducive to enhance the bonding strength and interfacial fracture toughness of MgFML.

Organosilane Chemical Gradients: Progress, Properties, and Promise.

Chemical gradients play an important role in nature, driving many different phenomena critical to life, including the transport of chemical species across membranes and the transport, attachment, and assembly of cells. Taking a cue from these natural processes, scientists and engineers are now working to develop synthetic chemical gradients for use in a broad range of applications, such as in high-throughput investigations of surface properties, as means to guide the motions and/or assembly of liquid droplets, vesicles, nanoparticles, and cells and as new media for stationary-phase-gradient chemical separations. Our groups have been working to develop new methods for preparing chemical gradients from organoalkoxysilane and organochlorosilane precursors and to obtain a better understanding of their properties on macroscopic to microscopic length scales. This review highlights our recent work on the development of controlled-rate infusion and infusion-withdrawal dip-coating methods for the preparation of gradients on planar glass and silicon substrates, on thin-layer chromatography plates, and in capillaries and monoliths for liquid chromatography. We also cover the new knowledge gained from the characterization of our gradients using sessile drop and Wilhelmy plate dynamic water contact angle measurements, X-ray photoelectron spectroscopy mapping, and single-molecule tracking and spectroscopy. Our studies reveal important evidence of phase separation and cooperative interactions occurring along multicomponent gradients. Emerging concepts and new directions in the preparation and characterization of organosilane-based chemical gradients are also discussed.