Silica Microtubes Research Articles

Starch-Directed Synthesis of Worm-Shaped Silica Microtubes

Many strategies have been adopted to prepare silica materials with highly controlled structures, typically using sol-gel chemistry. Frequently, the alkoxysilanes used in sol-gel chemistry are based on monoalcohols, e.g., Si(OEt)4. The structural control over silica synthesis achieved by these precursors is highly sensitive to pH and solvency. Alkoxysilanes derived from the sugar alcohol glycerol (diglycerylsilane) react more slowly and with much less sensitivity to pH. We report that, in the presence of cooled aqueous starch solutions, glyceroxysilanes undergo transesterification with the sugars on starch, leading to (hollow) microtubules resembling worms of about 400 nm in diameter. The tubes arise from the pre-assembly of starch bundles, which occurs only well below room temperature. It is straightforward to treat the first-formed starch/silica composite with the enzyme amylase to, in a programmed fashion, increasingly expose porosity, including the worm morphology, while washing away untethered silica and digested starch to leave an open, highly porous materials. Sintering at 600 °C completely removes the starch silane moieties.

Mathematical Model for Flow of High-pressure Gas in Microscale

Fused silica micro-tubes, whose size is similar to the pore throat in a low permeability reservoir, simplify the complex and tortuous of channels and throats and are used in this study to stimulate the flow pattern with micro-scale methods. A high-pressure micro-tube holder (designed and developed independently with a patent for invention) has been used to study gas flow patterns within the pressure range of 0.1MPa-30MPa. Moreover, we establish a gas flow equation and analysis the applicability of different inlet pressure based on the experiment result. The result shows: First, the pressure drop in the micro-tube is predominantly induced by friction resistance at low inlet pressure. While under relatively high inlet pressure, the impact of kinetic energy conversion and throttling effect on pressure drop shall be considered. Second, we build up a gas-flow equation in a micro-tube considering friction resistance, kinetic energy loss, and throttling effect. We also analyze the applicability for different diameters and inlet pressure. These research achievements were enriched in microtubule flow; different conditions have been identified for a different equation which has significant meaning to gas flow regulation in tight sandstorm reservoirs.

Microscale wetting effect of oil-water in silica microtubes

Pore wetting is significant for understanding fluid behaviour in porous media. Due to the lack of measurement techniques, pore wettability was estimated by using contact angles measured on flat plate. This results in that the effect of pore size on wettability is rarely studied. In this paper, the oil-water static contact angles in the silica microtubes with inner diameter (ID) range of 1–523 μm were measured by the cryo-Focused Ion Beam-Scanning Electron Microscopy (cryo-FIB-SEM) and optical microscope. The experimental results show that the oil (silicone oil, hexadecane) and water contact angles in the silica microtubes have the microscale wetting effect, that is the contact angles increase monotonically with the decrease of the microtubular ID. Moreover, the oil-water contact angle of water-filled first is always smaller than that of oil-filled first. The static pore contact angle of oil-water in a silica microtube is different from the contact angle on a silica plate. This paper adds to our current understanding of the pore scale wettability phenomenon in the porous media and provides us with an experimental method for measuring micron scale pore wettability.

Experimental study on the effect of tube diameter on gas–liquid wettability in silica microtubules

In this paper, the gas–liquid static contact angles in silica microtubes (inner diameter range of 5–700 μm) are measured by optical microscope. The experimental results show that the gas–liquid contact angles in the microtube have microscale wetting effect, which decrease monotonically with the decrease of the tube diameter and regularly deviate from the contact angle measured on the plate. When the tube diameter decreases from 700 μm to 5 μm, the contact angles of water and hexadecane decrease from 42.87° to 13.22° and 15.94°–9.09°, respectively. Actual microscale wetting effect causes the gas–liquid capillary force and driving resistance of residual droplets in pore-throat to be bigger than the value determined by the contact angle on the plate. The smaller the pore radius, the greater the influence of the microscale wetting effect on the capillary force. The larger pore-throat ratio and smaller throat radius, the greater influence of the microscale wetting effect on the driving resistance. These results advance our current understanding of wettability in porous media and offer us directly measured contact angles from pore scale which are better representation of actual pores than flat plate to characterize the fluid wettability in porous media.

Polyimide removal, cleaving, and fusion splicing of cylindrical and square fused silica capillaries for new separation and detection layouts in capillary electrophoresis and chromatography.

Fusion splicing is an already mature technology used to join the ends of optical fibers in the telecommunication industry. However, there is a lack of reliable and well-described protocols to join the ends of fused silica microtubes or capillaries using fusion splicing. In this work, a step-by-step procedure is proposed and demonstrated to find the optimal operation conditions to splice the ends of fused silica capillaries by fusion. The two most appropriate and known technologies were tested and optimized: the microfurnace technique (or hot filament technique) and the electric arc technique. It is shown that both produce good splices when the capillaries are well cleaved. For this reason, the removal of the external coating, which is important for good cleavage, was also revised. The cleaving techniques were also compared among themselves. As a result, fusion splices of cylindric-to-cylindric, cylindric-to-square, and square-to-square capillaries are demonstrated. They have potential applications in new detection schemes and separation layouts in capillary electrophoresis, electrophoresis-based hydrodynamic concentrators, chromatography, cell sorters, and microfluidics in general.

Magnetotactic Bacteria Powered Biohybrids Target E. coli Biofilms.

Biofilm colonies are typically resistant to general antibiotic treatment and require targeted methods for their removal. One of these methods includes the use of nanoparticles as carriers for antibiotic delivery, where they randomly circulate in fluid until they make contact with the infected areas. However, the required proximity of the particles to the biofilm results in only moderate efficacy. We demonstrate here that the nonpathogenic magnetotactic bacteria Magnetosopirrillum gryphiswalense (MSR-1) can be integrated with drug-loaded mesoporous silica microtubes to build controllable microswimmers (biohybrids) capable of antibiotic delivery to target an infectious biofilm. Applying external magnetic guidance capability and swimming power of the MSR-1 cells, the biohybrids are directed to and forcefully pushed into matured Escherichia coli (E. coli) biofilms. Release of the antibiotic, ciprofloxacin, is triggered by the acidic microenvironment of the biofilm, ensuring an efficient drug delivery system. The results reveal the capabilities of a nonpathogenic bacteria species to target and dismantle harmful biofilms, indicating biohybrid systems have great potential for antibiofilm applications.

EXPERIMENTAL VALIDATION OF LMTD METHOD FOR MICROSCALE HEAT TRANSFER

The s ingle phase fluid flow and heat transfer characteristic has been investigated experimentally. Experiments were conducted to cover transition zone for the Reynolds numbers ranging from 100 to 4800 by fused silica and stainless steel microtubes having diameters of 103-180 µm. The applicability of the Logarithmic Mean Temperature Difference (LMTD) method was revealed and an experimental method was developed to calculate the heat transfer coefficient. Moreover the scaling effects in micro scale such as axial conduction, viscous heating and entrance effects were discussed. The heat transfer coefficients were compared with data obtained by the correlations available in the literature in the study. The Nusselt numbers of microtube flows do not accord with the conventional results when the Reynolds number was lower than 1000. After that, the Nusselt number approaches the conventional theory prediction. On the aspect of fluid characteristics, the friction factor was well predicted with conventional theory and the conventional friction prediction was valid for water flow through microtube with a relative surface roughness less than about 4 %.

Facile One-Step Synthesis of Silica Micro- and Nanotubes and Their Functionalization

Rectangular silica nanotubes (NTs) and microtubes (MTs) were synthesized by a simple one-step sol-gel hydrolysis reaction. Although silica nanotubes are usually prepared in the presence of a template (e.g. metal rods), the proposed procedure eliminates the need for such template insertion and, subsequently, no further etching step is required.The Stöber silica nanoparticles (NPs) synthesis employs ammonium hydroxide solution as the base for tetraethyl orthosilicate (TEOS) hydrolysis, leading to the formation of discreet uniform NPs. Replacing ammonium hydroxide with sodium bicarbonate resulted in the formation of silica NTs with unique rectangular shape, both for the tube (external) and the lumen (internal cavity). On the other hand, replacing ammonium hydroxide with ammonium carbonate led to the formation of larger silica MTs with similar geometry. The influence of parameters such as: monomer concentration, base concentration, base:monomer ratio, temperature and solvent, on tube formation was investigated. This procedure was also utilized to prepare mesoporous and functionalized NTs and MTs with unique characteristics as omniphobic coatings.A proposed mechanism for the production of silica rectangular NTs and MTs via sheet folding is offered, based on our findings.

Experimental study of microchannel flow for non-Newtonian fluid in the presence of salt

Hydraulic characteristics of non-Newtonian fluid flow in smooth fused silica microtubes with diameter ranging from 75 to 320μm are experimentally investigated. Hydraulic characteristics of deionized water (DI water), anion polyacrylamide (APAM) and nonionic polyacrylamide (NPAM) solution with sodium chloride (NaCl), calcium chloride (CaCl2) and magnesium chloride (MgCl2) over a wide range of flow rates are presented. The results show that the three types of electrolytes have important effect on the hydraulic characteristics of APAM solution flow in microchannels. However, the NPAM solution is hardly affected by the present electrolytes with different concentrations. Similar to the NPAM solution, no obvious electrolyte-effect is found for the DI water flow in smooth fused silica microchannels, and the experimentally obtained flow rate and friction factor agree well with conventional theory predictions.

Controlled‐release drug carriers based hierarchical silica microtubes templated from cellulose acetate nanofibers

ABSTRACTWe report a facile method to synthesize hollow silica microtubes (SMTs) from electrospun cellulose acetate fiber precursors. Specific surface areas of up to 765 m2/g (Brunauer–Emmett–Teller) were measured for the SMTs, which had a typical wall thickness of ∼100 nm and submicron inner diameters. An average pore size of 4.6 nm and pore volume of 0.41 cm3/g were derived from Barrett–Joyner–Halenda fitting, whereas Horvath–Kawazoe pore size distribution analysis revealed microporous median pore size and maximum pore volume of 0.7 nm and 0.18 cm3/g, respectively. The as‐prepared SMTs featuring micro‐ and mesoporous structures in the walls where amino‐functionalized to facilitate a very high drug loading (15% by weight). Drug release profile revealed sustained release rates (79% of acetylsalicylic acid was released after 6 h). It is concluded that the high drug loading and sustained release resulted from the advantageous integration of SMTs' hollow structure and wall mesoporosity. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42562.

Effect of the size and pressure on the modified viscosity of water in microchannels

The phenomenon that flow resistances are higher in micro scale flow than in normal flow is clarified through the liquid viscosity. Based on the experimental results of deionized water flow in fused silica microtubes with the inner radii of 2.5 μm, 5 μm, 7.5 μm, and 10 μm, respectively, the relationship between water flow velocity and pressure gradient along the axis of tube is analyzed, which gradually becomes nonlinear as the radius of the microtube decreases. From the correlation, a viscosity model of water flow derived from the radius of microtube and the pressure gradient is proposed. The flow results modified by the viscosity model are in accordance with those of experiments, which are verified by numerical simulation software and the Hagen-Poiseuille equation. The experimental water flow velocity in a fused silica microtube with diameter of 5.03 μm, which has not been used in the fitting and derivation of the viscosity model, is proved to be comsistent with the viscosity model, showing a rather good match with a relative difference of 5.56%.

Bio-template-assisted synthesis of hierarchically hollow SiO2 microtubes and their enhanced formaldehyde adsorption performance

The indoor air quality is crucial for human health, taking into account that people often spend more than 80% of their time in houses, offices and cars. Formaldehyde (HCHO) is a major pollutant and long-term exposure to HCHO may cause health problems such as nasal tumors and skin irritation. In this work, for the first time, hierarchically hollow silica microtubes (HHSM) were synthesized by a simple sol–gel and calcination method using cetyltrimethyl ammonium bromide (CTAB) and bio-template poplar catkin (PC) as co-templates and the PC/SiO2 weight ratio R was varied from 0, 0.1, 0.3 and 1. The prepared samples were further modified with tetraethylenepentamine (TEPA) and characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR), X-ray photoelectron spectroscopy (XPS), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), and N2 physisorption techniques. This was followed by formaldehyde adsorption tests at ambient temperature. The results showed that all the prepared HHSM samples contained small mesopores with peak pore size at ca. 2.5nm and large several tens of nanometer-sized pores on the tube wall. The R exhibited an obvious influence on specific surface areas and the sample prepared at R=0.3 exhibited highest specific surface area (896m2/g). All the TEPA-modified samples exhibited enhanced formaldehyde adsorption performance. The maximum HCHO adsorption capacity (20.65mg/g adsorbent) was achieved on the sample prepared at R=0.3 and modified by 50wt.% TEPA. The present study will provide new insight for the utilization of bio-template used for the fabrication of inorganic hollow tubes with high HCHO adsorption performance for indoor air purification.

Pseudomorphic transformation of amorphous silica microtubes into mesoporous MCM-41 type silica tubes. Synthesis, characterization and surface functionalization with titania, vanadia and zirconia

Silica tubes with MCM-41 type mesostructures were successfully synthesized by a combination of the Stoeber process and a pseudomorphic transformation using electrospun macrosized polystyrene fibres as structure directing templates. Two different morphologies of mesoporous silica tubes are accessible with this method: a hollow morphology with tunable silica wall thickness and with a mesoporous silica shell structure and a core containing amorphous silica. All one dimensional tube like porous silica materials have a high specific surface area of approximately 1000 m(2) g(-1) with well-ordered hexagonal mesopores. Grafting of Ti, V and Zr metallocene dichloride molecular complexes has been employed resulting in the deposition of titanium-, vanadium-, zirconium-oxide in the interior of the silica tubes after ceramisation of the green body composites. The respective oxides were coated on top of the inner mesoporous silica surface of the tubes. Such silica based hybrids might be potential support materials in heterogeneous catalysis (e.g. vanadia) as well as interesting catalysts for photocatalysis (for TiO(2), ZrO(2)). All materials were characterised by X-ray diffraction (SAXS and XRD), nitrogen adsorption at 77 K, UV/VIS diffuse reflectance spectroscopy (UV-DRS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

Experimental investigation of non-Newtonian liquid flow in microchannels

Investigation on non-Newtonian fluid flow in microchannels is of both fundamental interest and practical significance. Flow characteristics of deionized water and the PAM solution over a wide range of Reynolds numbers in fused silica microtubes with diameters from 75 to 250μm, fused silica square microchannels with equivalent diameters of 75 and 100μm, and stainless steel microtubes with diameters from 120 to 300μm, were studied experimentally. The obtained mass flow rate and friction factor for deionized water in smooth fused silica microchannels were in good agreement with theoretical predictions for conventional-sized channels while the deviation for stainless steel microtubes was observed due to the roughness. Friction factors of the PAM solution were much higher than conventional theoretical predictions. Flow behaviors of deionized water and the PAM solution under hydrophobic condition are also studied experimentally. The mass flow rate increased in hydrophobic microchannels compared to untreated microchannels. The drag reduction in hydrophobic channels is greater for rough stainless steel microtubes than for smooth fused silica channels. The effect of surface wettability on the shear thinning PAM solution is also observed to be more evident than on the Newtonian deionized water.

ChemInform Abstract: Synthesis and Catalytic Applications of Sulfonic Acid Group‐Functionalized Nano‐ and Microsilica Structures.

AbstractSulfonic acid group‐functionalized silica nanospheres and microtubes are synthesized, which efficiently catalyze the synthesis of dihydropyrimidines (IV) via the Biginelli reaction.

Synthesis and Catalytic Applications of Sulfonic Acid Group–Functionalized Nano- and Microsilica Structures

Sulfonic acid group–functionalized nano- and microsilica with different sizes and shapes were synthesized. Silica nanospheres with an average size of 225 nm, silica microtubes, and fine silica gel were prepared and functionalized by sulfonic acid. Their catalytic activity was investigated in the three-component Biginelli reaction for the synthesis of dihydropyrimidinones.

Silica microcapsules and microtubes prepared from rod‐like and needle‐like polyaniline templates

AbstractRod‐like or needle‐like particles of polyanilinium p‐toluene sulfonate have been used as templates for the formation of silica microcapsules or microtubes. Thus, an alkaline aqueous suspension of the needles was treated with tetraethyl orthosilicate to form silica‐coated needles, which were subsequently calcined to remove the polyanilinium templates. The rod‐like or needle‐like polyaniline particles, their silica‐coated derivatives and silica microcapsules or microtubes have been characterized by thermogravimetric analysis, Fourier transformation infrared spectroscopy, scanning electron microscopy (SEM), field emission scanning electron microscopy (FE‐SEM), and transmission electron microscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Preparation of silica microtubes by surface-initiated atom transfer radical polymerization from microfiber templates

Poly(methyl methacrylate-co-vinylbenzyl chloride), P(MMA-co-VBC) microfibers (with submicron diameters) of about 1 μm in size were prepared by electrospinning. Silyl-functional groups were introduced onto the P(MMA-co-VBC) microfibers templates via surface-initiated atom transfer radical polymerization of 3-(trimethoxysilyl)propyl methacrylate. The silyl groups were then converted into a silica shell, approximately 0.25 μm thick, via a reaction with tetraethoxysilane in ethanolic ammonia. Hollow silica microfibers were finally generated by thermal decomposition of the P(MMA-co-VBC) template cores. Scanning electron microscopy and transmission electron microscopy were used to characterize the intermediate products and the hollow microtubes. Fourier-transform infrared spectroscopy results indicated that the polymer cores were completely decomposed. The microfibers were characterized by X-ray photoelectron spectroscopy, X-ray diffraction and the thermal gravimetric analysis.

Monitoring of liquid flow through microtubes using a micropressure sensor

The pressure-driven liquid flow through microtubes was studied in a range of very low Reynolds numbers (<0.15) by monitoring the pressure change in situ. Cylindrical microtubes with diameters ranging from 50 μm to 500 μm were examined and two types of tube material, namely PEEK polymer and fused silica were compared. A good linear relation for the pressure drop versus flow rate was obtained. Apparent deviations between the measured slopes with those calculated using conventional theory were attributed to uncertainties in the calculated values which are dominated by the uncertainties in the microtube diameters. It was found that a period of stabilisation time was required for reaching a steady flow after the syringe pump was switched on/off or to a different flow rate. The stabilisation time was likely due to the compressibility of the fluid. Insignificant difference between PEEK polymer and fused silica microtubes in terms of flow resistance was observed. The in-situ measurement of pressure drops provides a convenient approach for monitoring fluid flow through microtubes and detecting dimensional changes within microchannels in Lab-on-a-Chip and microreactor systems.

Friction Numbers and Viscous Dissipation Heating for Laminar Flows of Water in Microtubes

The friction numbers for laminar flows of water in microtubes, determined from the temperature rise due to the viscous dissipation heating assuming a velocity slip, show a strong dependence on the diameter and aspect ratio. The calculated values compare well with those determined from experimental data for water flows in glass and diffused silica microtubes (16–101μm in diameter D and aspect ratios L∕D=499–1479). With a slip, the friction number almost exponentially decreases as D decreases and, to a lesser extent, as L∕D increases. For D&gt;400μm, the friction number approaches the theoretical Hagen–Poiseuille for macrotubes (64) when L∕D&gt;∼1500, but higher values at smaller L∕D. The developed semiempirical analytical expression for calculating the friction number is in good agreement with the numerical and experimental results. The results suggest the presence of a velocity slip in the experiments and the plausible presence of a thin nanolayer at the walls of the microtubes. For D&gt;200μm, this layer, if exists, is estimated to be ∼18.9nm, but increases to ∼21.5nm for D&lt;200μm, when R¯e=800 and L∕D=1479.