Design and fabrication of a shielded interdigital sensor for noninvasive In situ real‐time production monitoring of polymers

Interdigital sensors (IDS) have received great attention for production monitoring of polymers over the past decade. However, conventional IDS are limited by high noise to environment due to the dual side access of the sensor, low nominal capacitance, and sensitivity. In this study, a shielded IDS fabricated by flexible circuit board (FCB) technology is presented to overcome these challenges. Compared to conventional sensors, the environmental dependence of the new sensor is minimized by the copper shield. Furthermore, nominal capacitance of at least 350% higher, and an increase of sensitivity per unit area are achieved. To demonstrate the capabilities of the new IDS, a FCB comprising the proposed sensor is fabricated, attached to a mould, and successfully applied for in situ real‐time production monitoring of an epoxy resin. The resulting flexible sensor is noninvasive towards the fabricated parts, and measures the key stages along the production process. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2028–2037     

In situ monitoring of reaction-induced phase separation with modulated temperature DSC

A linearly polymerizing and network forming epoxy-amine system, DGEBA-aniline and DGEBA-MDA, respectively, will be modified with 20 wt% and 50 wt% of a high-T_g thermoplastic poly(ether sulphone) (T_g=223°C), respectively, both showing LCST-type demixing behavior. Reaction-induced phase separation (RIPS) in these modified systems is studied using Modulated Temperature DSC (MTDSC) as an in situ tool. Phase separation in the linear system can be probed by vitrification of the PES-rich phase, occurring at a higher conversion than the actual cloud point from light scattering measurements. The negative slope of the cloud point curve in a temperature-conversion-transformation diagram unambiguously shows the LCST-type demixing behavior of this system, while the relation between the composition/glass transition of the PES-rich phase and the cure temperature is responsible for the positive slope of its vitrification line. Phase separation in the network forming system appears as reactivity increases at the cloud point due to the concentration of reactive groups. Different mixture compositions alter the ratio between the rate of phase separation and the rate of reaction, greatly affecting the morphology. Information about this in situ developed structure can be obtained from the heat capacity evolutions in non-isothermal post-cures.     

Relaxations in thermosets. XVI. Dielectric studies of negative feedback during curing of an epoxide-ethylene-diamine thermoset

The complex dielectric permittivity of thermosets of diglycidly ether of bisphenol-A cured with ethylene diamine has been studied during their isothermal curing at several temperatures. As cross-linking progresses, the dc conductivity decreases. At the beginning of the cure the dc conductivity can be fitted to both the scaling laws with a critical exponent of about 4 and an equation indicating approach toward a singularity. In the later stage of the cure, the change in permittivity corresponds to dipolar relaxation of an infinitely connected network, and the Argand diagram for the complex permittivity measured at a fixed frequency obtained as the curing process proceeds at 305 K is similar to that for the complex permittivity as frequency is varied for a time-invariant system which obeys a stretched exponential relaxation function with the curing parameter or exponent, γ = 0.29. Increase in the temperature of isothermal curing lowers both γ and the net decrease in the equilibrium permittivity on curing. A plot of the calculated relaxation time with curing time is sigmoidal and shifts to shorter times on increasing the curing temperature. Measurement of the dielectric properties during the cure but for different frequencies show that the various parameters for the curing kinetics are independent of the frequency of measurement. These observations confirm the development of our concepts of thermoset curing in terms of a phenomenon of negative feedback between molecular diffusion and chemical reactions.     

New fluorescence probes for monitoring the kinetics of laser-initiated polymerization

Several new fluorescence probes useful for following photopolymerization have been characterized. Among these are probes which can be used in rapidly gelling monomer mixtures and for photochemical polymerization initiated by very high laser powers. Systems which can be used with polyolacrylates and either with visible initiators or with UV initiators are reported. © 1993 John Wiley & Sons, Inc.     

A new ultrasonic measurement system for the cure monitoring of thermosetting resins and composites

Measurements of the ultrasonic sound speed of thermosetting resins and composites can be used as an in-process cure monitoring technique. Ultrasonic measurements have an advantage over other in-process techniques in that ultrasonic sensors do not make contact with the part (thus leaving no imbedded sensor or witness mark) and can make true bulk measurements of the part. A new commercially available ultrasonic cure monitoring system has been developed which easily enables ultrasonic measurements to be made in compression molding, resin transfer molding, and autoclave processes. Advancements in ultrasonic sensor technology enable the sensor to maintain good coupling to the part during thermal cycling to 260C. Data is presented showing the change in ultrasonic sound speed during the compression molding of a graphite-epoxy prepreg. The data shows a good relationship to the ionic conductivity and resistivity data collected via dielectric cure monitoring.This effort was sponsored by the Manufacturing Technology Directorate, Wright Laboratory (WL/MTX), Air Force Material Command, USAF, under cooperative agreement award(s) to NCMS. The U. S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Wright Laboratory or the U.S. Government.     

Environmental monitoring and in situ gamma spectrometry

In situ gamma ray spectrometry is widely used for monitoring of natural as well as man-made radionuclides and corresponding gamma fields in the environment or working places. It finds effective application in the operational and accidental monitoring of nuclear facilities and their vicinity, spent fuel storages and waste depositories, radioactive contamination measurements and mapping, environmental, radiohygienic and radiation safety studies, geological prospecting and mapping, etc. Progressive spectrometric methods based on scintillation and semiconductor spectrometry and spectral deconvolution are discussed, including experimental arrangement as well as detection system responses/response matrixes simulation using stochastic (Monte Carlo) models. Methods for ground-level and airborne measurements are presented.     

Kinetics of phase separation in polymer blends. Calculations based on nonlinear theory

Suzuki's scaling theory for transient phenomena is applied to the calculation of the kinetics of phase separation in the early-to-intermediate stage based on a nonlinear theory proposed by Langer, Bar-on, and Miller (LBM). Calculated results are compared with experimental data on light scattering from a polymer blend system. Deviations from predictions of Cahn's linearized theory in the early time range of phase separation can be explained well by the proposed method of calculation. Nonlinear effects are found to play an essential role in characterizing the light scattering behavior of phase separation in the intermediate stage. Time evolutions of the single-point distribution function of composition are calculated, and the results are in good agreement with those reported in digital imaging analysis experiments and computer simulations of the time-dependent Ginzburg-Landau equation. The influence of asymmetry of free-energy on the single-point distribution function is also investigated in this study. © 1993 John Wiley & Sons, Inc.     

突发环境事件现场应急监测仪器技术现状及展望

突发环境事件现场应急监测是环境监测工作的重要组成部分.与常规实验室环境监测分析相比,现场应急监测的时效性要求更高,需要做到对环境污染物的快速定性与半定量分析.本文在分析现场应急监测仪器技术的基本特点基础上,从现场应急监测的环境介质、待监测项目、监测仪器技术分类等方面入手,重点对国内光谱法、色谱/质谱法和电化学法等类别的现场应急监测仪器技术现状进行了总结,最后对现场应急监测仪器技术的未来发展趋势进行了展望.     

Impedance spectroscopy of reactive polymers. 5. Impedance as a measure of chemical and physical changes in glass formers

A study was conducted aimed at establishing the nature of chemical and physical phenomena in polymeric and nonpolymeric glass formers that can be observed by impedance measurements. Various systems were investigated that undergo a temporal evolution of structure as a result of chemical reactions and physical processes such as crystallization, vitrification, or phase separation. Distinct and systematic changes in impedance during crystallization and vitrification confirmed that these events could be monitored by impedance spectroscopy. Of particular interest was the potential use of impedance measurements in detecting gelation in crosslinking polymers. It was shown that the experimentally observed “knee” in imaginary impedance during reaction shifts with frequency and, hence, cannot be used to measure gelation. But a new insight at the molecular level was obtained by employing a novel experimental approach based on simultaneous dielectric-infrared measurements. Evidence was generated to support the formation of a hydrogen-bonded complex in the vicinity of gel point in polymer networks, which affords a vehicle for the migration of intrinsic charges and provides a contribution to the overall conductivity. This finding should be explored further because it suggests the possibility of correlating dielectric response with gelation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 641–653, 1998     

Kinetics of phase separation at the early stage of spinodal decomposition in epoxy resin modified with PEI blends

The behavior at the early stage of spinodal decomposition (SD) for polyetherimide (PEI)/epoxy blends was investigated. It was found that the phase separation of PEI/epoxy blends took place by SD mechanism. The development of molar mass in the epoxy resin was gradual and then the three blends could still be considered as concentrated solutions of thermoplastic. The kinetics at the early stage of phase separation for these blends could be described by the Cahn–Hilliard–Cook linearized theory.     

Advances in the Study of Gas Hydrates by Dielectric Spectroscopy

The influence of kinetic hydrate inhibitors on the process of natural gas hydrate nucleation was studied using the method of dielectric spectroscopy. The processes of gas hydrate formation and decomposition were monitored using the temperature dependence of the real component of the dielectric constant ε′(T). Analysis of the relaxation times τ and activation energy ΔE of the dielectric relaxation process revealed the inhibitor was involved in hydrogen bonding and the disruption of the local structures of water molecules.     

Dielectric relaxation spectroscopy and electro-optical studies of phase behaviour of a chiral smectic liquid crystal

Dielectric relaxation processes in various phases of a chiral smectic liquid crystal compound have been investigated over a wide range of frequencies from 10 to 300 kHz. Dielectric spectroscopy reveals the existence of two relaxation frequencies corresponding to the ferroelectric and ferrielectric Goldstone modes in the range of temperature where two different phases coexist. This phenomenon of coexistence is examined with respect to the cell thickness and reversal temperature.     

Influence of blend miscibility on the proton conductivity and methanol permeability of polymer electrolyte blends

The influence of miscibility on the transport properties of polymer electrolyte blends composed of a proton conductor and an insulator was investigated. The proton‐conductive component in the blends was sulfonated poly(ether ketone ketone) (SPEKK), while the nonconductive component was either poly(ether imide) (PEI) or poly(ether sulfone) (PES). The phase behavior of PEI‐SPEKK blends was strongly influenced by the sulfonation level of the SPEKK. At low sulfonation levels (ion‐exchange capacity (IEC) = 0.8 meq/g), the blends were miscible, while at a slightly higher level (IEC = 1.1 meq/g), they were only partially miscible and for IEC ≥ 1.4 meq/g they were effectively immiscible over the entire composition range. The PES‐SPEKK blends were miscible over the entire range of SPEKK IEC considered in this study (0.8–2.2 meq/g). At high IEC (2.2 meq/g) and at low mass fractions of SPEKK (<0.5), the miscible blends (PES‐SPEKK) had higher proton conductivities and methanol permeabilities than the immiscible ones (PEI‐SPEKK). The opposite relationship was observed for high mass fractions of SPEKK (>0.5). This behavior was explained by the differences in morphology between these two blend systems. At low IEC of SPEKK (0.8 meq/g), where both PEI‐SPEKK and PES‐SPEKK blend systems exhibited miscibility, the transport properties were not significantly different. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2253–2266, 2006     

Dielectric method for detection of phase separation and its kinetics in TMPC/PS blends

A new method for the detection of phase separation and its kinetics through real-time measurements is presented using the dielectric technique. The kinetics of phase separation were determined for a blend of tetramethyl bisphenol-A polycarbonate TMPC and polystyrene PS at different temperatures. The temperature dependence of the rate constant of phase separation was determined. The activation energy of phase separation process is found to be equal to 46 kcal/mole. In addition, it was possible to determine the variation in the composition of the TMPC-rich phase with time. The results obtained were compared with the literature data and were found to be in good agreement.     

Dependence of the interfacial reaction and morphology development on the functionality of the reactive precursors in reactive blending

PMMA containing 50 wt% of anthracene-labeled PMMA chains end-capped by a phthalic anhydride group (anth-PMMA-anh) has been melt blended at 180°C with PS containing 33 wt% of chains end-capped by an aliphatic primary amine (PS-NH₂) and PS bearing 3.5 pendant amine groups (as an average) along the chains (PS-co-PSNH₂), respectively. The reactive chains have been synthesized by atom transfer radical polymerization. Conversion of anth-PMMA-anh into PS-b-PMMA and PS-g-PMMA copolymers has been monitored by SEC with a UV detector. The interfacial reaction mainly occurs in the initial melting and softening stage (<1.0 min.), although at a rate which strongly depends on the number of reactive groups attached to PS chains, the higher conversion being observed for the PS-co-PSNH₂ containing blends. The phase morphology depends on the architecture of the in-situ formed copolymer. Indeed, a coarser phase dispersion is observed in case of the graft copolymer compared to the diblock.     

Modification of the cation exchange resin properties by impregnation in polyethyleneimine solutions: application to the separation of metallic ions

A commercial cation exchange resin Amberlite 200 has been modified after immersion in solutions of polyethyleneimine (PEI). The kinetic of fixation of the metallic ions have been determined. The modification of the surface of the resin deals with a change in the order of the affinities of the resins towards cations. The retention is the function of the formation and the stability of the complex. The conditions of modification (pH, PEI concentration and time of immersion) have been examined and the modification was confirmed by the determination of the exchange capacities, the distribution coefficient (P) and the selectivity factors (S). The obtained results revealed the effect of PEI on the exchange properties of the resin. The pH range selected (6-8) permitted a good adherence of PEI onto the resin surface. The quantity of the adsorbed PEI was increased by raising the initial concentration and the immersion period. The exchange capacity for copper ion passed from 2.6 mmol g⁻¹, in the case of unmodified resin, to 3.9 mmol g⁻¹ for the modified one.     

Liquid phase oxidation of alcohols with oxygen: in situ monitoring of the oxidation state of Bi-promoted Pd/Al2O3

In situ, time-resolved XAS studies on a Bi-Pd/Al2O3 catalyst indicate that Pd, and Bi located on the Pd surface, are in a reduced, metallic state during the oxidation of 1-phenylethanol with molecular oxygen--a key for understanding the role of promoter in the reaction mechanism.     

Characterization of copolyesteramides from reactive blending of PET and MXD6 in the molten state

Poly(ethylene terephthalate)‐poly(m‐xylylene adipamide) PET‐MXD6 copolymers were prepared by reactive blending of equimolar PET/MXD6 blends at 285 °C for different times in presence of terephthalic acid (1 wt %). First, the partial hydrolysis of PET and MXD6 occurs, yielding oligomers terminated with the reactive aromatic carboxyl groups. These oligomers quickly react with ester and amide inner groups producing a PET‐MXD6 copolymer that may compatibilize the initial biphasic blend. In this homogeneous environment, the aliphatic carboxyl‐terminated MXD6 chains, inactive in the initial biphasic blend, may promote the exchange reactions determining the formation of a random copolymer at longer reaction time (120 min). The progress of exchange reactions, and the microstructure of the formed copolyesteramides, versus the reaction time was followed by ¹H and ¹³C NMR analyses using a CDCl₃/TFA‐d/(CF₃CO)₂O mixture as solvent and applying appropriate mathematical models. Dyads and triads sequences were thoroughly characterized by NMR. Semicrystalline block copolymers were obtained at reaction time lower than 45 min. All PET‐MXD6 copolymers show a single T_g that change as a function of the dyads molar composition in the copolymers. The measured T_g values match with those calculated by a proposed modified Fox equation that take into account the weight fraction of the four dyad components of the PET‐MXD6 copolymers. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010