Excess Epoxy Research Articles

Electrochemical impedance measurement of prostate cancer cells using carbon nanotubearray electrodes in a microfluidic channel

Highly aligned multi-wall carbon nanotubes were synthesized in the shape of towersand embedded into fluidic channels as electrodes for impedance measurement ofLNCaP human prostate cancer cells. Tower electrodes up to 8 mm high weregrown and easily peeled off a silicon substrate. The nanotube electrodes were thensuccessfully soldered onto patterned printed circuit boards and cast into epoxy underpressure. After polishing the top of the tower electrodes, RF plasma was used toenhance the electrocatalytic effect by removing excess epoxy and activating the openend of the nanotubes. Electrodeposition of Au particles on the plasma-treatedtower electrodes was done at a controlled density. Finally, the nanotube electrodeswere embedded into a polydimethylsiloxane (PDMS) channel and electrochemicalimpedance spectroscopy was carried out with different conditions. Preliminaryelectrochemical impedance spectroscopy results using deionized water, buffer solution, andLNCaP prostate cancer cells showed that nanotube electrodes can distinguish thedifferent solutions and could be used in future cell-based biosensor development.

Silane functionalization of perfluoroether oligomers for reaction management and morphology control of two‐phase epoxy networks

AbstractMixtures of an epoxy resin, hardener, and acid functionalized perfluoroether oligomers will readily undergo phase separation during curing. However, the conditions to bring about the growth of nuclei into microscopic particles have hitherto been found only for systems cured with anhydrides. In the present study perfluoroether oligomers were functionalized by established procedures to introduce both carboxylic acid groups and alkoxysilane groups in sites within the chain extended segments. The presence of alkoxysilane groups together with the prereaction step with an excess epoxy resin, prior to the addition of the aromatic amine hardener, induced phase separation by a nucleation‐and‐growth mechanism. The dual functionality in the perfluoroether oligomer was even more beneficial when the alkoxysilane groups were hydrolyzed prior to the addition of the amine hardener. Under such circumstances the precipitation of the perfluoroether oligomer occurred quantitatively, as indicated by the complete absence of any plasticization effects in the epoxy matrix. From electron microscopy examinations, thermal analysis, and measurements of mechanical properties it was possible to deduce a plausible mechanism for the formation of the typical core‐shell aggregates within the precipitated particles for these systems, which could also be applied to other systems, such as those using carboxylic‐acid‐terminated butadiene acrylonitrile oligomers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1036–1049, 2005

Acceleration of amine/epoxy reactions with N-methyl secondary amines

Kinetic studies established that the monomethylation of a primary amine leads to significantly higher reaction rates with glycidyl ethers. The relative rates for approximately 25 amines were determined in an alcohol solvent under pseudo-first-order conditions (excess epoxy). The rates were referenced to aniline. For the aliphatic amines, reactivity consistently increased upon going from a primary amine to the corresponding N-methyl secondary amine. This acceleration effect was not seen for aniline. The enhanced reactivity was also seen in curing systems, both with pure methylated amine curing agents and with complex mixtures obtained from the partial methylation of polyamines. Economically viable partially methylated amine curing agents were obtained by the reductive alkylation of commercial polyamines with formaldehyde and by the reaction of monomethylamine with 3-(N-methylamino)propionitrile in the presence of hydrogen and a hydrogenation catalyst. Although actual cure performance is based on a complex combination of several factors, the acceleration due to monomethylation could be a useful tool for enhancing amine/epoxy curing reactions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 921–930, 2000

Acceleration of amine/epoxy reactions withN-methyl secondary amines

Kinetic studies established that the monomethylation of a primary amine leads to significantly higher reaction rates with glycidyl ethers. The relative rates for approximately 25 amines were determined in an alcohol solvent under pseudo-first-order conditions (excess epoxy). The rates were referenced to aniline. For the aliphatic amines, reactivity consistently increased upon going from a primary amine to the corresponding N-methyl secondary amine. This acceleration effect was not seen for aniline. The enhanced reactivity was also seen in curing systems, both with pure methylated amine curing agents and with complex mixtures obtained from the partial methylation of polyamines. Economically viable partially methylated amine curing agents were obtained by the reductive alkylation of commercial polyamines with formaldehyde and by the reaction of monomethylamine with 3-(N-methylamino)propionitrile in the presence of hydrogen and a hydrogenation catalyst. Although actual cure performance is based on a complex combination of several factors, the acceleration due to monomethylation could be a useful tool for enhancing amine/epoxy curing reactions. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 921–930, 2000

Stepped spindle motor shaft to reduce disk drive acoustic noise

A spindle motor shaft having variable geometrical features for adjusting the torsion mode frequency of the shaft/stator assembly. The variable geometric features allow the torsion mode frequency to be tuned away from the driving force frequency of the motor. Variable geometrical features for the shaft may include circumferential grooves, radial slots cut through the shaft, or transverse holes disposed along the axis of the shaft. The radial slots have a longitudinal axis that is parallel to the axis of the shaft. Where circumferential grooves are used, the circumferential grooves may be designed to form a locator region along the shaft axis to promote axial alignment of the shaft and stator. Thermal track-misregistration (TMR) or screw torque problems are not introduced in the process of reducing or eliminating the acoustic problem thereby establishing a torsion mode frequency which is not subject to change due to temperature or time. Further, the removal of material from the shaft reduces the torsional stiffness of the shaft and lowers the torsion mode frequency of the shaft. Finally, the use of circumferential grooves prevents the wicking of excess epoxy up the shaft by the movement of the stator during the assembly/manufacturing process, which may lead to an undesirable increase in the stiffness.

A study on isothermal cure behavior of an epoxy-rich/anhydride system by differential scanning calorimetry

Cure behavior of a catalyzed epoxy/anhydride system was investigated for an epoxy-rich formulation using differential scanning calorimetry (DSC). The mixture was isothermally cured at different times and temperatures, and the cure behavior of the samples was analyzed by the peak exothermic temperature (Tpeak) and the extent of cure reaction (X) from DSC thermograms. For the excess epoxy sample, two exothermic peaks at a low temperature from esterification reaction and at a high temperature from etherification on DSC curves appeared in the early stage of cure and shifted to a lower temperature scale with curing. However, the esterification peak disappeared and the remaining etherification peak shifted to a higher temperature with further cure. The shift of the peaks may be attributed to the change of reaction mechanism from kinetically controlled to diffusion-controlled. The extent of cure of esterification and etherification was also considered separately in this article. The result shows that esterification reaction mainly occurs in the early stage of cure and then etherification slowly proceeds after the completion of the esterification. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:1101–1108, 1998

Direct monitoring of silane/epoxy interphase chemistry

Abstract Evanescent wave spectroscopy has been used to directly monitor the interactions between an epoxy resin and an amino silane coupling agent, γ-aminopropyltrimethoxy silane (γ-APS) adsorbed on silica fibers. First, it was shown that reactions of the adsorbed silane molecules could be monitored as a function of drying at elevated temperature. Next, the silane surface treated fibers were embedded in the epoxy resin and the primary amine reactivity of the silane at 70°C was measured by the decrease from the initial absorbance height of the combination band at 4925 cm −1 . It was found that there was a decrease of 13% in band absorbance when the silane was adsorbed from a 5% γ-APS solution. The percent decrease was 22% and 38% when the silane was adsorbed from 2% and 1% γ-APS solutions, respectively. The results show that a significant fraction of the amine groups remain unreacted, even in the presence of excess epoxy. Also, it was discovered that in no instance was there any indication of silane diffusion from the interphase during the course of the experiment, even when the adsorbed silane was not dried at elevated temperature, prior to placement in the epoxy resin.

Chemical resistance of waterborne epoxy/amine coatings

Waterborne epoxy/amine coatings, compared to solvent-based, show considerably lower chemical resistance. This fact is often blamed on hydrophilic emulsifiers or crosslinking agents remaining inside the coating after curing. To judge this assertion, the influence of surfactants and hardeners, as well as various other parameters were investigated. Surfactants appear just to influence the solvent resistance slightly. The main responsibility for the poor resistance to other chemicals – especially acids – lies with unreacted amine curing agents and/or water trapped inside the coating, and, most important, an inhomogeneous film structure due to insufficient coalescence during the curing process. Incremental improvements are possible by using excess epoxy, increasing the film thickness, or curing at elevated temperatures. The latter forces water out of the coating, drives the epoxy/amine reaction to completion, and also somewhat improves the coalescence. However, the resistance can still not be enhanced to the level of a solvent-based system. But although there seem to be inherent limitations to the chemical resistance of waterborne epoxy systems, for many practical applications it is adequate.

Polymer networks derived from the anhydride curing of tetraepoxides

The cure of a technical-grade TGDDM (N,N,N′N′-tetraglycidyl-4,4′-diaminodiphenylmethane) with two different anhydride hardeners (hexahydrophthalic anhydride [HHPA] and tetrahydrophthalic anhydride [THPA]) is reported. The reaction was followed by differential scanning calorimetry (DSC), in situ infrared spectroscopy (FTIR), and viscosity measurements at constant temperature. Onset values of the glass transition temperatures of fully reacted networks under stoichiometric conditions were 206°C with HHPA and 184°C with THPA. THPA was more reactive than was HHPA but it was necessary to heat the mixture above its melting point to generate a homogeneous solution (HHPA remained in solution at room temperature). A first-order kinetics was observed after an induction period necessary to establish a pseudo-steady-state concentration of OH and COOH groups. A catalytic effect of the KBr used in the FTIR measurements was found, in agreement with other authors. Formulations containing an epoxy excess exhibited a higher reactivity due to the increase in the hydroxyl concentration introduced by the epoxy monomer. An increase in the heat of reaction expressed per anhydride equivalent was ascribed to the presence of the epoxy homopolymerization as a side reaction. It was estimated that about 38% of excess epoxy groups over the anhydride groups are homopolymerized in the case of HHPA and 17% in the case of THPA. Full conversions of both epoxy and anhydride groups are obtained for formulations with stoichiometric ratios, r (anhydride/epoxy groups) = 0.72 in the case of HHPA and 0.85 in the case of THPA. These values are in the range where the maximum glass transition temperature has been reported for epoxy-anhydride formulations. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 157–166, 1997

Cure Behavior of an Epoxy-Anhydride-Imidazole System

The cure behavior of an epoxy-anhydride system with one of imidazole derivatives as an accelerator was investigated for both stoichiometric and epoxy-rich formulations. The mixtures were isothermally cured for different times at various temperatures, and the glass transition temperature (Tg) was determined by differential scanning calorimetry (DSC). There was a considerable increase in the Tg during curing, and master curves were formed by shifting and superposing the Tg vs. cure time curves. The activation energies obtained by the shift were 15.2 kcal mol−1 and 16.5 kcal mol−1 for the stoichiometric and epoxy-rich systems, respectively. For the epoxy-rich one, plateaus were observed on the Tg vs. cure time curves, and two exothermic peaks appeared on DSC curves in the early stage of cure and became one thereafter. This phenomenon is related to the competitive reactions between esterification and etherification reactions. We found that the maximum Tgs were 80°C for esterification and 125°C for etherification in the excess epoxy system.

Kinetic models of pregelation stages for epoxy resins cured with mixed amine systems

The systems of epoxy resins cured with primary amines with the substitution effect and etherification have been analyzed by the kinetic method. The average molecular weight, witch changed with reaction time or conversion, and the gel time were calculated, and the results agree well with those by another combined kinetic and statistical theory and experimental data. Then a more complex system, epoxy resins cured with mixed amines, was analyzed for various reactivity ratio of two kinds of amines. For a system in witch the reactivity of one kind of amine unit is rather higher than another, the average degree of polymerization profile versus epoxy conversion is close to those system with only one kind of amine and excess epoxy units

Stoichiometric and heating-rate effects on DSC-evaluated kinetics for a high-performance epoxy system

Dynamic DSC experiments on a high-performance amine-cured epoxy system have shown that the kinetic parameters determined assuming an overall reaction for the system are dependent on the heating rate of the scan. The high-performance system examined in this investigation is the TGDDM—DDS epoxy system. Changes in the number, location, and magnitude of the transitions in the thermograms which occur with changes in the heating rate were interpreted through the definition of two reaction regimes: one in which the primary-amine addition reaction predominates; and the other in which the secondary-amine addition, hydroxyl—epoxide, and homopolymerization reactions become significant. To elucidate these regimes, three compositions were examined: epoxy alone; excess epoxy; and excess amine. The activation energies for the two reaction regimes were determined to be 16.7 and 42.3 kcal mol −, respectively. A model proposed by Prime for the heating rate dependence of the kinetic parameters as determined by DSC is also analyzed for its applicability for the kinetic analysis of this reaction system. Further, analysis of isothermal data is considered as an integral part of the kinetic analysis for this system.

Control of Sand Production in the Underground Storage of Natural Gas

Production of sand during withdrawal of gas from a storage field can cause Production of sand during withdrawal of gas from a storage field can cause reservoir damage, loss of deliverability and damage to subsurface tubular goods and to surface equipment. It can even jeopardize the safety of personnel by causing fires and blow-outs. Sand consolidation helped to personnel by causing fires and blow-outs. Sand consolidation helped to reduce these problems in the Redfield and Vincent storage fields in Iowa. Introduction Gas storage wells completed in unconsolidated or poorly consolidated sandstone aquifers have presented a problem to the underground gas storage industry for many years. Of primary concern is the production of sand during a withdrawal season, and the inherent problems it causes such as blow-outs and fires, eroded surface and subsurface equipment and reservoir damage. Sand production hampers the development of new storage fields because it makes it impossible to secure adequate water pumping data for caprock and aquifer evaluation. Initially, sand screens and slotted liners for controlling sand production were evaluated, but the liners either plugged or had holes eroded in them by the sand. The slotted liners allowed too much sand to be produced and had to be removed when the wells needed stimulating and cleaning out. Therefore, the method of plastic sand consolidation was investigated. The low bottom-hole temperature of about 60F in the aquifers presented a problem because the resin used in the oil fields presented a problem because the resin used in the oil fields was designed for higher temperatures. Thus it was necessary to develop an ultra-low-temperature consolidation system for the 60 to 90F range. The patented three-step process that was adopted produces the desired properties in a resin-consolidated formation, i.e., high compressive strength and retained permeability. Although the desired characteristics have been attained, there are a few disadvantages to all plastic sand consolidation methods, such as high costs and the difficulty of controlling placement of chemicals in the reservoir. placement of chemicals in the reservoir. Presented here are some of the parameters that were considered in developing a satisfactory injection system for plastic sand consolidation and an evaluation of wells consolidated plastic sand consolidation and an evaluation of wells consolidated by this process. The Process of Sand Consolidation During the sand consolidation process each sand grain is coated with an epoxy resin so that pendular rings of the resin harden to form a connecting bond for the sand grains. The consolidation treatment consists of five basic steps:pumping a diesel preflush into the formation to reduce the water saturation to a preflush into the formation to reduce the water saturation to a minimum,pumping acetone into the formation to remove the remaining water saturation,pumping the epoxy resin containing a patented additive that increases the resin's affinity for the sand grains,pumping a diesel solution into the formation to displace the excess epoxy resin from the pore channels to re-establish permeability, andpumping a diesel-activator mixture to polymerize the resin in the form of pendular rings bonding the sand grains. JPT P. 581