Free release static coating of glass capillary columns; rapid coating at lower temperatures and elevated pressures

The coating speed upon static coating of glass capillary columans was evaluated in terms of inner diameter and length of the column, viscosity and pressure of solvent vapor, etc. From the equation obtained it can be shown that a smaller diameter of a microbore column restricts solvent vapor transfer to the orifice of the column drastically. To compensate for this restriction, a higher pressure at the meniscus is needed. As an alternative to using a higher coating temperature, application of more volatile solvents such as n-butane and isobutane is proposed. Several glass capillary columns (130 μm i.d.) were coated with SE-54 dissolved inpentane-acetone mixed with n-butane or isobutane and the column performances were evaluated. Selection of these solvents permitted free release static coating of ca. 100 μm columns at lower or even ambient temperatures and they were equally suitable as commonly applied solvents (e.g. pentane) to coat highly efficient columns.     

Effect of solvent composition on free release static coating of capillary columns

Summary Three aspects with respect to the selection of solvents for static coating of capillary columns, i.e. coating speed, occurrence of bumping and solubility of stationary phases are discussed. Hypotheses are proposed in an attempt to explain the observed facts that mixed solvents result in much higher coating speeds than those obtained from pure solvents, that a proper choice of solvents together with a good and uniform deactivitation of the column inner wall is needed to prevent bumping. Stationary phase solubility vs. solvent composition is also briefly discussed.     

Free release static coating of glass capillary columns; Static coating at elevated pressure — Theoretical considerations and practice

Summary Static coating of glass capillary columns has hitherto solely been carried out by evaporation of the stationary phase solvents under vacuum conditions. However, since a solvent vapour pressure higher than the external pressure is the only requirement for the vapour to flow out of the column, evacuation should not be necessary. Several important factors in the static coating procedure, such as mass (solvent vapour) — and heat transfer, heat of vaporisation of the solvent and viscosity of the stationary phase solution at elevated temperature and outlet pressure are discussed, principally to rationalise an improved static coating procedure. The alternative, so-called free-release static coating procedure, was evaluated practically by coating several columns with OV-101 and SE-30. Coating speed was found to be rapid and relatively constant whereas coating efficiency was between 80 and 100%.     

Static coating of capillary columns by means of liquefied gases

The technique of spontaneous coating of capillary columns employing liquefied butane and ethylene chloride as solvents of the stationary phase is described. These solvents and their mixtures are suitable for apolar and medium-polar stationary phases. The dependence of coating time on coating temperature and on the composition of the mixture of solvents was observed. It was found that the coating efficiency decreases with increasing coating speed.     

A novel sealing method in static coating fused-silica capillary column

Summary In this paper a new sealing method for the static coating of capillary columns is described. When one end of the fully filled capillary was immersed into liquid nitrogen in a Dewar flask, the coating solution at this end would be frozen and became a temporary seal, and an air-free solvent/seal interface was obtained. No bumping has ever been found at the interface, even when butane was used as solvent. By applying this sealing method, several capillary columns, including some narrow bore capillary, had been successfully coated.     

Free-release static coating of glass capillary columns: Coating with medium polar and polar stationary phases

Summary Principles are proposed to select solvents for the coating of glass capillary columns with medium-polar and polar stationary phases applying the free-release static-coating technique, practical examples are given, demonstrating that this technique is suitable to coat stationary phases like OV-1701 and Carbowaxes.     

Three minimum wet thickness regions of slot die coating

An experimental study was carried out to determine the minimum wet thickness of slot die coating for low-viscosity solutions. There exist three distinct coating regions (I, II, and III), depending on the physical properties of the coating fluid, die geometry, and flow conditions. A critical Reynolds number was found, below which viscous and surface tension effects are important. In Region I, the minimum wet thickness increases with increasing capillary number and becomes independent of capillary number in Region II. Region III exists above the critical Reynolds number where fluid inertia is dominant. In this region, the minimum wet thickness decreases as Reynolds number increases. Flow visualization on the coating bead reveals that the position of the downstream meniscus of the coating bead determines the types of coating region, whereas the shape and position of the upstream meniscus determine the type of coating defects. It was also observed that the downstream meniscus was not located at the die lip corner and both the static and dynamic contact angles varied under different conditions. These findings are critical for realistic theoretical study of slot die coating.     

Sol-gel immobilized short-chain poly(ethylene glycol) coating for capillary microextraction of underivatized polar analytes

Sol-gel coating with covalently bonded low-molecular-weight (MW<300 Da) poly(ethylene glycol) (PEG) chains was developed for capillary microextraction (CME). The sol-gel chemistry proved effective in the immobilization of low-molecular-weight PEGs thanks to the formation of chemical bonds between the organic-inorganic hybrid sol-gel PEG coating and the fused silica capillary inner surface. This chemical anchorage provided excellent thermal and solvent stability to the created sol-gel PEG coating as is evidenced by its high upper limit of allowable conditioning temperature (340 degrees C) and its practically identical performance before and after rinsing with various solvents. The prepared sol-gel PEG coating provided simultaneous extraction of moderately polar and highly polar analytes from aqueous samples without requiring derivatization, pH adjustment or salting-out procedures. Detection limits on the order of nanogram per liter (ng/L) were achieved in CME-GC-flame ionization detection experiments designed for the preconcentration and trace analysis of both highly polar and moderately polar compounds extracted directly from aqueous media using sol-gel short-chain PEG coated microextraction capillaries.     

Sol-gel immobilized cyano-polydimethylsiloxane coating for capillary microextraction of aqueous trace analytes ranging from polycyclic aromatic hydrocarbons to free fatty acids

Sol-gel coating containing highly polar cyanopropyl and nonpolar poly(dimethylsiloxane) components (sol-gel CN-PDMS coating) was developed for capillary microextraction (CME). The sol-gel chemistry provided an efficient means to immobilize the CN-PDMS coating by establishing chemical anchorage between the coating and the fused silica capillary inner surface. This chemical bond provided excellent thermal and solvent stability to the created sol-gel coating. For the extraction of polar and nonpolar analytes, the upper allowable conditioning temperatures were 330 degrees C and 350 degrees C, respectively. To our knowledge, this is the first time when a CN-PDMS thick coating survived such a high operation temperature. The prepared sol-gel CN-PDMS coating provided effective extraction of polar and nonpolar analytes simultaneously from aqueous samples. The cyanopropyl moiety in sol-gel CN-PDMS coatings provided effective extraction of highly polar analytes such as free fatty acids, alcohols, and phenols without requiring derivatization, pH adjustment or salting out procedures. The PDMS moiety, on the other hand, provided efficient extraction of nonpolar analytes. The extraction properties of the sol-gel CN-PDMS coatings can be fine tuned via manipulation of relative proportions of 3-cyanopropyltriethoxysilane and hydroxy-terminated PDMS in the sol solution used to create the coatings. Detection limits of nanogram/liter (ng/L) were achieved for both highly polar and nonpolar analytes directly extracted from aqueous media using sol-gel CN-PDMS coated microextraction capillaries followed by GC analysis.     

Preparation and evaluation of stable coating for capillary electrophoresis using coupled chitosan as coated modifier

A coated capillary modified with a coupled chitosan (COCH) was developed by using a simple and fast (60 min) process that could be easily automated in capillary electrophoresis instrument. The COCH coating was achieved by first attaching chitosan to the capillary inner wall, and then coupling with glutaraldehyde, and rinsing chitosan again to react with glutaraldehyde. The COCH coating was stable and showed amphoteric character over the pH range of 1.8-12.0. When the pH value was lower than 4.5, the capillary surface possessed positive charges, which caused a reversal in the direction of the electroosmotic flow (EOF). The normal EOF direction could be obtained when the pH value was higher than 4.5. The COCH coating showed strong stability against 0.1 mol/L HCl, 0.1 mol/L NaOH and other solvents compared with conventional chitosan coating. The relative standard deviation of the run-to-run, day-to-day and capillary-to-capillary coating was all below 2% for the determination of EOF. The COCH-modified capillary was applied to acidic and basic proteins analyses and high efficiency could be attained. The comparison between unmodified capillary, chitosan-modified and COCH-modified capillary for the separation of real sample, extract from Elaphglossum yoshinagae with water, was also studied. Better results could be obtained on COCH-modified capillary than the other two capillaries.     

Some observations on dynamic coating of capillary columns

Summary The influence of the drying speed on dynamic coating of capillary columns was investigated. Fast drying speeds improve efficiency and increase film thickness.     

Direct observation of morphological development during the spin‐coating of polystyrene–poly(methyl methacrylate) polymer blends

We present results of the direct observation, in real‐space, of the phase separation of high molecular weight polystyrene and poly(methyl methacrylate) from ortho‐xylene using our newly developed technique of high speed stroboscopic interference microscopy. Taking a fixed concentration (3 wt % in o‐xylene) at a fixed composition (1:4 by weight) and by varying the rotational rate during the spin‐coating process, we are able to observe the formation of a range of phase separated bicontinuous morphologies of differing length‐scales. Importantly, we are able to show that the mechanism by which the final phase separated structure is formed is through domain coarsening when rich in solvent, before vitrification occurs and fixes the phase separated structure. The ability to directly observe morphological development offers a route toward controlling the length‐scale of the final morphology through process control and in situ feedback, from a single stock solution. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B Polym. Phys. 2013, 51, 875–881     

Preparation of poly(3, 4‐ethylenedioxythiophene)/poly(styrene sulfonate) (PEDT/PSS) composite and its applications in anti‐static coating

Poly(3, 4‐ethylenedioxythiophene)/poly(styrene sulfonate) (PEDT/PSS) composite is prepared by solution polymerization at room temperature in the presence of 3, 4‐ethylenedioxythiophene as the monomer, PSS as the doping agent, potassium supersulfate (KPS) as the oxidant, and deionized water as the solvent. The color of the PEDT/PSS solution is dark blue and its solid content is 2.2%, its pH value is 1.5. By mixing alcohols, polar organic solvents, adhesives, and so on into PEDT/PSS solution, the anti‐static coating solution is prepared. The coating is conducted by bar‐coating (20 µm) at 40% relative humidity and 20°C. The influence of the content of each component on the coating surface resistivity is discussed, and a reasonable volume content of each component is obtained. The obtained coating has low surface resistivity (1 × 10⁶ Ω), excellent water resistance, and high transmittance of visible light together with a wide range of potential applications. Copyright © 2009 John Wiley & Sons, Ltd.     

Parameters affecting the quality of glass capillary columns prepared by the mercury plug dynamic coating method

Summary The paper presents examinations concerning the ways obtaining glass capillary columns. The mercury plug dynamic coating method used for coating capillary columns was investigated in order to establish haw the efficiency of the columns prepared can be related to the physical properties of stationary phase and the velocity of the coating solution through the capillary tube. It was found that there is an optimum range of the viscosity and velocity of the coating solution within which the highest column efficiency can be obtained. Moreover, the mechanism of the mercury plug dynamic coating method in which the thickness of the obtained film depends on interfacial tension between the mercury and the coating solution was confirmed.     

Controlled evaporative self-assembly of polymer nanoribbons using oscillating capillary bridges

Evaporative self-assembly (ESA), based on the “coffee-ring” effect, is a versatile technique for assembling particle solutions into mesoscale patterns and structures on different substrates. ESA works with a wide variety of organic and inorganic materials, where the solution is a combination of volatile solvent and nonvolatile solute. Modified ESA methods, such as “stop-and-go flow coating,” use a programmed meniscus “stick–slip” motion to create mesoscale assemblies with controlled shape, size, and architecture. However, current methods are not scalable for increased production volumes or patterning large surface areas. We demonstrate a new ESA method, where an oscillating blade controls the meniscus depinning and drives the evaporative assembly of solutes at the pinned meniscus. Results show that oscillation frequency and substrate speed control time/distance intervals between successive meniscus depinning, and the assembly dimensions depend on solution concentration, oscillation frequency, substrate speed, and meniscus height. We report the mechanism of the meniscus depinning and the control over assembly cross-sectional dimensions. This advance provides a scalable ESA method with faster processing times and maintained advantages. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1545–1551     

Breath figure patterns prepared by spin coating in a dry environment

We introduce a novel method for fabricating breath figure patterns on a homopolymer film by spin coating of polymer solutions with various solvents. The homopolymers employed in this study were cellulose acetate butyrate, monocarboxylated end-functional polystyrene, and poly(methyl methacrylate). Breath figure patterns were generated even when a water-miscible solvent such as tetrahydrofuran (THF) was used as a solvent. We even succeeded in generating breath figure patterns by spin coating even under a dry environment (relative humidity less than 30%), when water was directly added into THF solution. With the combination of the spin coating method, pores with a few hundred nanometers to several micrometers have been generated. We found that the pore size becomes larger with increasing water content in THF solution and decreasing rotating speed. This is equivalent to increasing humidity and decreasing evaporation speed, respectively, in the conventional method, which is direct solvent evaporation under a humid environment. Thus, compared with the conventional method for making breath figure patterns, this method would be very convenient for fabricating large-scale films with various pore sizes.     

Pyrrole derivatives for electrochemical coating of metallic medical devices

Electropolymerization of medical devices such as cardiovascular stents may posses advantages including a simple and reproducible process with the ability to control the thickness, adherence, and composition of the coating by the duration and intensity of the applied current, the monomer composition and concentration, the solvent, and the reaction conditions. The properties of the polymer can also be controlled by copolymerization of different monomers, grafting substituents to a functionalized polymer, and by entrapping biomolecules. This article describes the synthesis of a range of pyrrole‐based monomers and their electrocoating onto stainless steel surfaces. N‐substituted pyrrole monomers with C1–C18 alkyl chains and poly (ethylene glycol) chains were synthesized in good yields and purity. Electropolymerization of these monomers provided uniform coatings with different hydrophobicities. Studies now focus on the incorporation of drugs in the coated device for release from the surface. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1658–1667, 2004     

Influence of polyelectrolyte coating conditions on capillary coating stability and separation efficiency in capillary electrophoresis

Polyelectrolytes are widely used in capillary electrophoresis as coating agents of silica capillaries to prevent adsorption phenomena and improve the repeatability of peptide and protein analysis. A systematic study of the coating experimental conditions has been carried out to optimize coating stability and performance. The main experimental parameters studied were the type and concentration of polyelectrolytes used in several monolayer and multilayer coatings, the ionic strength of coating and stabilizing solutions, and the procedures used for coating and capillary storage. Electroosmotic flow magnitude, direction and repeatability were used to monitor coating stability. Coating ability to limit adsorption was investigated by monitoring variations of migration times, time-corrected peak areas and separation efficiency of test peptides. Capillary-to-capillary and batch-to-batch reproducibility was also studied. In addition, the separation performance of polyelectrolyte coatings were compared to those obtained with bare silica capillaries.     

Sol-gel methyl coating in capillary microextraction hyphenated on-line with high-performance liquid chromatography Counterintuitive extraction behavior for polar analytes

A sol-gel coating with anchored methyl groups was developed for capillary microextraction hyphenated on-line with high-performance liquid chromatography (HPLC). This was accomplished by using methyltrimethoxysilane as the sol-gel precursor. The methyl group on the sol-gel precursor ultimately turned into a pendant group on the created sol-gel coating and was primarily responsible for the extraction of nonpolar analytes. A 40-cm segment of 0.25mm I.D. fused silica capillary containing the sol-gel methyl coating on the inner surface was installed as a sampling loop in an HPLC injection port. The analytes were extracted by the coating when an aqueous sample containing the analytes was passed through this capillary. The extracted analytes were then transferred to the HPLC column using isocratic elution with an acetonitrile/water mobile phase. This capillary demonstrated excellent extraction capability for polycyclic aromatic hydrocarbons and ketones. Unexpectedly, this coating also provided good extraction for polar analytes, including aromatic phenols, alcohols, and amines. Considering the fact that the methyl group is nonpolar in nature, such an extraction behavior of sol-gel methyl coating toward polar analytes is counterintuitive. Thus, sol-gel sorbents with short alkyl side chains have the potential to offer a polymer-free alternative to traditional sol-gel capillary microextraction (CME) media commonly prepared with the use of polymers in the sol solution. Elimination of polymers from the sol-gel coating solution is conducive to improving thermal stability and solvent tolerance of the created sol-gel extracting phase. This also makes the preparation of sol-gel coatings facile and cost-effective. Possessing excellent solvent stability, such sol-gel coatings offer the opportunity for effective on-line hyphenation of capillary microextraction with HPLC and other liquid-phase separation techniques that employ organo-aqueous mobile phases.     

Effects of solvent polarity on mutual styrene grafting onto polypropylene by electron beam irradiation

Radiation induced mutual grafting of styrene onto polypropylene has been carried using several grafting solutions with different organic solvents and polarity levels. In the mixture of styrene and protic polar solvents high grafting yields were obtained. This behavior suggests that grafting process does not have dependence on swelling of the substrate, something that is expected when a non-polar substrate and a non-polar media are in contact. In this case, the grafting yield may be related to the free radical generation at protic polar solvent; these reactive specimens start the reaction on substrate surface to allow the accessibility of monomer species to active sites. Some reaction mechanisms are proposed.