Micro fabrication of microlens arrays by micro dispensing

In this study, master of the microlens arrays is fabricated using micro dispensing technology, and then electroforming technology is employed to replicate the Ni mold insert of the microlens arrays. Finally, micro hot embossing is performed to replicate the molded microlens arrays from the Ni mold insert. The resin material is used as the dispensing material, which is dropped on a glass substrate. The resin is exposed to a 380 W halogen light. It becomes convex under surface tension on the glass substrate. A master for the microlens arrays is then obtained. A 150‐nm‐thick copper layer is sputtered on the master as an electrically conducting layer. The electroforming method replicates the Ni mold insert from the master of the microlens arrays. Finally, micro hot embossing is adopted to replicate the molded microlens arrays. The micro hot embossing experiment employs optical films of polymethylmethacrylate (PMMA) and polycarbonate (PC). The processing parameters of micro hot embossing are processing temperature, embossing pressure, embossing time, and de‐molding temperature. Taguchi's method is applied to optimize the processing parameters of micro hot embossing for molded microlens arrays. An optical microscope and a surface profiler are utilized to measure the surface profile of the master, the Ni mold insert and the molded microlens arrays. AFM is employed to measure the surface roughness of the master, the Ni mold insert and the molded microlens arrays. The sag height and focal length are determined to elucidate the optical characteristics of the molded microlens arrays. Copyright © 2009 John & Sons, Ltd.     

Pyrolytic hydrolysis of polycarbonate in the presence of earth-alkali oxides and hydroxides

The rise in the use of polycarbonate (PC) calls for the development of after-use treatments. In this work, we describe a process for obtaining bisphenol A (BPA), phenol and isopropenyl phenol (IPP) from PC by hydrolysis at temperatures between 300 and 500 °C. The experiments were carried out in a steam atmosphere in the presence of MgO, CaO, Mg(OH)₂ or Ca(OH)₂ as catalysts, respectively. The results were compared with the hydrolysis of PC in the absence of any catalysts. All of these catalysts accelerated the hydrolysis of PC drastically, with MgO and Mg(OH)₂ being more effective than their Ca counterparts. The differences between oxides and hydroxides were negligible indicating the same mechanism for both, oxides and hydroxides. BPA was the main product at 300 °C, with a yield of 78% obtained in the presence of MgO. At 500 °C, BPA was mainly degraded to phenol and isopropenyl phenol (IPP). It can be shown that a combined process involving PC hydrolysis at 300 °C and BPA fission at 500 °C leads to high yields of phenol and IPP and the drastic decrease of residue.     

Dielectric studies of tetraaryl and triaryl polycarbonates and comparisons with bisphenol A‐polycarbonate

The relative permittivity, loss, and breakdown strength are reported for a commercial sample of bisphenol A‐polycarbonate (comm‐BPA‐PC) and a purified sample of the same polymer (rp‐BPA‐PC) as well as for two new polycarbonates having low molecular cross‐sectional areas, namely a copolymer of tetraaryl polycarbonate and BPA‐PC (TABPA‐BPA‐PC) and a triaryl polycarbonate homopolymer (TriBPA‐PC). The glass transition temperatures of the new polymers are higher than the T_g of BPA‐PC (187 and 191 °C vs. 148 °C). Relative permittivity and loss measurements were carried out from 10 to 10⁵ Hz over a wide temperature range, and results for the α‐ and γ‐relaxation regions are discussed in detail. For the α‐relaxation, the isochronal peak position, T_α, scales approximately with T_g. On the other hand, the peak temperature for the γ‐relaxation is approximately constant, independent of T_g. Also, in contrast to what is observed for α, γ exhibits a strong increase in peak height as temperature/frequency increases and a significant difference is found between Arrhenius plots determined from isochronal and isothermal data analyses. Next, the γ‐relaxation region for comm‐BPA‐PC and associated activation parameters show strong history/purity effects. The activation parameters also depend on the method of data analysis. The results shed light on discrepancies that exist in the literature for BPA‐PC. The shapes of the γ loss peaks and hence glassy‐state motions for all the polymers are very similar. However, the intensities of the TriBPA‐PC and TABPA‐BPA‐PC γ peaks are reduced by an amount that closely matches the reduced volume fraction of carbonate units in the two new polymers. Finally, for comm‐BPA‐PC, the breakdown strength is strongly affected by sample history and this is assumed to be related to volatile components in the material. It is found that the breakdown strengths for TriBPA‐PC and TABPA‐BPA‐PC are relatively close to that for rp‐BPA‐PC with the value for TriBPA‐PC being slightly larger than that for rp‐BPA‐PC or the value usually reported for typical capacitor grade polycarbonate. Finally, it is shown that the real part of the relative permittivity remains relatively constant from low temperatures to T_g. Consequently, based on the dielectric properties, TriBPA‐PC and TABPA‐BPA‐PC should be usable in capacitors to at least 50 °C higher than BPA‐PC. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Effects of oxygen plasma treatment on the surface of bisphenol A polycarbonate: a study using SIMS,principal component analysis,ellipsometry, XPS and AFM nanoindentation

The effects of oxygen plasma treatment and the subsequent air exposure on the surface composition and properties of bisphenol A polycarbonate (BPA‐PC) were analysed by X‐ray photoelectron spectroscopy (XPS), ellipsometry, static time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) with principal component analysis (PCA) and nanoindentation using an atomic force microscope (AFM). PCA showed systematic changes in the film chemistry after short treatment times (0.1 s), with the main sites of attack being the carbonate and aromatic ring structure. On the basis of this multitechnique analysis, it was unambiguously determined that extended oxygen plasma treatment times resulted in the formation of low‐molecular‐weight material (LMWM) within the first 50 nm on the surface, and not in a cross‐linked skin as has been proposed by other researchers. The study shows that controlled surface modification of BPA‐PC polymers is possible, allowing surface oxygen incorporation without degradation of the polymer structure. This result is relevant for improved adhesion of coatings applied to BPA‐PC polymers. Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of plastic additives on depolymerization of polycarbonate in sub-critical water

The effects of plastic additives on depolymerization of polycarbonate (PC) in sub-critical water were examined. Depolymerization of PC with two additives was carried out in an autoclave at temperatures from 533 to 613 K for reaction times ranging from 15 to 60 min. The additives used were a flame retardant (decabromodiphenyl ether, DBDPO) and a plasticizer (di-n-octyl phthalate, DnOP). The main products of PC depolymerization in the presence or absence of the additives were bisphenol A (BPA) and phenol, which were identified by Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), and gas chromatography mass spectrometry (GC-MS), and quantified by gas chromatography (GC). The addition of DBDPO accelerated the hydrolysis of PC while the addition of DnOP had the opposite effect, and both additives reduced the yield of BPA. The activation energy for PC depolymerization in sub-critical water was found to be lower with DBDPO additive than with DnOP.     

亚临界水萃取-高效液相色谱法测定聚碳酸酯水杯中双酚A和苯酚的迁移量

建立了亚临界水萃取-高效液相色谱同时测定聚碳酸酯(PC)水杯中双酚A和苯酚迁移量的方法。选择萃取温度120 ℃、萃取压力6.89 MPa(1000 psi)、静态萃取时间1 h、萃取1次对11种样品进行测定。双酚A的迁移量为6.81～11.16 μg/g。5种样品中未检出苯酚,其余样品中苯酚迁移量为3.25～6.08 μg/g。在优化的测定条件下,双酚A和苯酚在8 min内达到基线分离。双酚A和苯酚分别在0.05～20 mg/L和0.02～20 mg/L范围内线性关系良好,相关系数(r)均大于0.9997,检出限分别为7.6 μg/L和2.0 μg/L。日内及日间的重复性(以RSD计)分别小于5.21%及11.63%。传统的浸提法结果表明长时间浸提会使PC材料发生微弱水解。相比传统的浸提法,该方法的萃取效率提高了49～106倍。该方法简便、快速、环保,可用来测定PC水杯中双酚A和苯酚的迁移量。     

全芳香族热致液晶聚合物与热塑性树脂聚砜的原位复合材料

用自制的四种全芳香族热致液晶聚合物ＢＰ ＬＣＰ、ＢＰＭ ＬＣＰ、ＢＰＡ ＬＣＰ、ＢＰＳ ＬＣＰ与热塑性树脂聚砜（ＰＳＦ）熔融共混，制备了一系列原位复合材料．研究了所得材料的微观形态、热性能、力学性能等，结果显示：四种液晶聚合物中，ＢＰ ＬＣＰ，ＢＰＳ ＬＣＰ在所用加工条件下可在ＰＳＦ中取向成纤，而且这两种共混物断面上存在皮 核效应；ＢＰＭ ＬＣＰ和ＢＰＡ ＬＣＰ未成纤，均以球状存在于ＰＳＦ中．这四种液晶聚合物与ＰＳＦ的相容性较差，各共混物的Ｔｇ均分别接近于二纯组分的Ｔｇ值，ＳＥＭ照片上明显的相界面也能说明以上问题．液晶聚合物对ＰＳＦ有增强作用，但增强效果不很显著，这可能是二者相容性较差所致     

Thermal behaviour of teflon/phenolic liners in self-lubricating bearings

The gun system of the M1 series tank rides on a pair of self-aligning spherical bearings that allows the elevation and depression of the cannon. Because these bearings are encapsulated within the rotor housing, periodic lubrication or maintenance is impossible. To overcome this problem self-lubricating bearings were incorporated into the system. There are two basic liner designs, molded and fabric. Molded liners are produced by applying a formulation of teflon and typically asbestos into a phenolic resin, which is applied to the bearing surface, then cured. Fabric liners utilize a woven fabric bonded to the bearing surface, then teflon which is mixed into phenolic resin is applied to the bearing surface and cured. Initial studies of the existing bearing liner were completed to determine the liner composition and establish a baseline or standard to compare thermal and mechanical properties with potential vendors. DSC revealed an average teflon content of 39.53%, which varied significantly throughout the liner. TG analysis showed an asbestos concentration of 12.22%. The remainder of the liner was phenolic resin. Physical testing of the bearing from ?20 to 120?C under normal loading conditions demonstrated excellent thermal stability with little wear. Bearings from each vendor were tested and compared to the standard properties of the baseline bearing. Some properties were difficult to compare or insignificant due to the design differences between molded and fabric liners. The testing program resulted in the qualification of two bearings, which met or exceeded the established standards. Both of these bearings were designed with fabric liners.     

Phenol-Crotonaldehyde Resins. III. Curing Behavior with Hexamethylenetetramine

Solid thermoplastic resins were prepared by acid-catalyzed condensation of phenol and crotonaldehyde (both crude and distilled). The thermal and curing properties were compared with the conventional phenol-formaldehyde (PF) novolak resins. Phenol-crotonaldehyde (PC) resins were found to be thermoplastic even after curing with the crosslinking agent hexamethylenetetramine up to 160°C. This curing behavior was observed irrespective of the purity of the crotonaldehyde or the phenol-to-crotonaldehyde mole ratio in the resin. Postcuring of these resins at elevated temperatures yielded insoluble and infusible thermoset products. This unique thermal characteristic could lead to interesting processing possibilities for the resins. The technical feasibility of thermoplastic processing of the PC resins followed by postcure heat treatment for transforming the molded part into a thermoset has been demonstrated.     

聚碳酸酯在亚临界水中解聚的研究

采用间歇式高压反应装置研究聚碳酸酯(PC)在亚临界水中的解聚.在温度260～340℃、压力4.8～14.8 MPa、反应时间5～60min的反应条件下,考察了反应温度及反应时间对PC解聚率及主产物双酚A(BPA)和苯酚(PhOH)回收率的影响.产物分别采用傅里叶红外光谱(FTIR)、扫描电子显微镜(SEM)、气质联谱(...     

Electrochemical sensor based on f-SWCNT and carboxylic group functionalized PEDOT for the sensitive determination of bisphenol A

A simple,sensitive,and reliable method for the voltammetric determination of bisphenol A(BPA) by using carboxylic group functionalized single-walled carbon nanotubes(f-SWCNT)/carboxylic-functionalized poly(3,4-ethylenedioxythiophene)(PC4) complex modified glassy carbon electrode(GCE) has been successfully developed.The electrochemical behavior of BPA at the surface of the modified electrode is investigated by electrochemical techniques.The cyclic voltammetry results show that the as-prepared electrode exhibits strong catalytic activity toward the oxidation of BPA with a well-defined anodic peak at 0.623 V in PBS(0.1 mol/L,pH 7.0).The surface morphology of the 3D network of composite film is beneficial for the adsorption of analytes.Under the optimized conditions,the oxidation peak current is proportional to BPA concentration in the range between 0.099 and 5.794 μmol/L(R~2 = 0.9989),with a limit of detection of 0.032 μmol/L(S/N = 3).The enhanced performance of the sensor can be attributed to the excellent electrocatalytic property of/-SWCNT and the extraordinary conductivity of PC4.Furthermore,the proposed modified electrode displays high stability and good reproducibility.The good result on the voltammetric determination of BPA also indicates that the asfabricated modified electrode will be a good candidate for the electrochemical determination and analysis of BPA.     

Tuning the optical clarity of glass fiber‐reinforced polycarbonates by reactive blending with alternatives from biorenewable isosorbide

Optically transparent and mechanically strong glass fiber (GF)‐reinforced polycarbonate (PC) composites were fabricated via reacting with biorenewable isosorbide (ISB) moiety. While direct copolymerization of ISB and bisphenol A (BPA) by melt transesterification with diphenyl carbonate remained difficult due to the large discrepancy of reactivity and low thermal stability of ISB, we demonstrated in this work that ISB and BPA copolycarbonates with high molecular weight, low discoloration, and excellent optical transparency can be fabricated at 250 °C within 2.5 min by reactive blending of commercially available ISB‐based PC and BPA‐PC. A systematic study of synthesis, thermal degradation, and reactive blending of ISB‐containing PCs was performed to distinguish the reactivity between ISB and BPA, elucidate the effect of catalyst on chain scission, and testify the reaction mechanism of the unexpected asymmetrical inner–inner carbonate exchange. We clarified that the hydroxyl group on BPA exhibited a low reactivity and Lewis acid‐catalytic transesterification played a key role in preventing from the chain scission during the asymmetrical inner–inner exchange. Another unexpected factor that effectively suppressed the further chain scission was the miscibility of the ISB‐based PC with BPA‐PC once each chain on average was carbonate exchanged with its counterpart to form a “biblock” PC. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1670–1681     

Effect of novel compatibilizers on the properties and morphology of PP/PC blends

A series of compatibilizers, including polypropylene (PP) grafted with 2‐tertbutyl‐6‐(3‐tertbutyl‐ 2‐hydroxy‐5‐methylbenzyl)‐4‐methylphenyl acrylic ester (BPA), glycidyl methacrylate (GMA), GMA/styrene (GMA‐st), and 2‐allyl bisphenol A (2A) were investigated for the purpose of improving the compatibility of PP/polycarbonate (PC) blends. PP‐g‐BPA shows a remarkable compatibilizing effect on PP/PC blends since it has similar group‐benzene ring with PC, and it is a sort of heat‐resistant antioxidant in the meantime, which can reduce the molecular degradation of PP during grafting and blending under high temperatures. Its compatibilizing effect was examined in terms of the mechanical, thermal properties, and morphologies. PP/PC blends show a decreasing and much more homogeneous size of dispersed PC particles through addition of a small amount of PP‐g‐BPA, and dynamic mechanical analysis (DMA) reveals a noticeable approach of T_g between PP and PC, indicating the improvement of the compatibility of PP/PC blends. Furthermore, styrene‐ethylene‐butylene‐styrene (SEBS) as a toughening rubber and a compatibilizer was applied to PP/PC blends. Around 25 wt% SEBS and 20 wt% PC lead to high toughness and strength of PP. Copyright © 2008 John Wiley & Sons, Ltd.     

Sub-Tg dynamics in polycarbonate by neutron scattering and its relation with secondary gamma relaxation

We have investigated the dynamics of phenylene rings in glassy bisphenol-A (BPA) polycarbonate (PC) by means of quasielastic neutron scattering. Taking advantage of selective deuteration of the samples, we have studied the incoherent scattering of hydrogens in phenylene rings on the one hand, and on the other hand the coherent quasielastic scattering of all the atoms in the sample. Two different types of neutron spectrometers, time of flight and backscattering, were used in order to cover a wide dynamic range, which extends from microscopic (approximately 10(-13) s) to mesoscopic (approximately 10(-9) s) times. Moreover, neutron-diffraction experiments with polarization analysis were carried out in order to characterize the structural features, and the relative coherent and incoherent contributions of the samples investigated. In contrast with previous studies of phenylene ring dynamics in BPA polysulfone performed by us also by neutron scattering, phenylene rings in BPA PC exhibit an "extra" motion in addition to those found for BPA polysulfone's phenylene rings. This extra motion of the rings in PC perfectly correlates with the main carbonate group motion followed by dielectric spectroscopy and allows us to (i) consistently interpret the PC's gamma relaxation in terms of two different motions; and (ii) experimentally confirm the relation between the motion of phenylene rings and carbonate groups within BPA PC formerly predicted by computational methods.     

Polycarbonate-modified epoxies. I. Studies on the reactions of epoxy resin/polycarbonate blends prior to cure

An epoxy resin based upon the diglycidyl ether of bisphenol-A was modified with poly(bisphenol A carbonate) (PC). Prior to aromatic amine cure, the possible reactions in the epoxy resin/PC blend were investigated using GPC and FTIR techniques. It was shown that at 150°C, the epoxy resin acted as a plasticizer and promoted the crystallization of PC. In addition, a transesterification between the secondary hydroxyl groups in the epoxy resin with the carbonate groups in PC occurred. This reaction resulted in degraded PC chains with phenolic hydroxyl end groups. There was no evidence of reaction of epoxide groups at 150°C in this blend. At 200°C, the secondary hydroxyl groups acted as a catalyst converting most of the aromatic–aromatic carbonates to the aromaticndash;liphatic and aliphaticndash;aliphatic carbonates through transesterification. At this elevated temperature, the secondary hydroxyl groups were regenerated by the addition reaction between the epoxide groups and the phenolic hydroxyl end groups, either from the transesterification or the hydrolysis of PC. This addition reaction combining the PC chains and epoxy chains eventually resulted in a crosslinked polymer if the extent of reaction was high. Thus, by using a melt blending process at high temperature, e.g., 200°C, a copolymer network structure of PC-modified epoxy could be formed. The fracture toughness should be increased by increasing the capability for plastic deformation due to the incorporation of PC chains into the network; results will be reported in a future study. © 1996 John Wiley & Sons, Inc.     

A role for sulfation-desulfation in the uptake of bisphenol a into breast tumor cells

Bisphenol A (BPA) is a widely used plasticizer whose estrogenic properties may impact hormone-responsive disorders and fetal development. In vivo, BPA appears to have greater activity than is suggested by its estrogen receptor (ER) binding affinity. This may be a result of BPA sulfation/desulfation providing a pathway for selective uptake into hormone-responsive cells. BPA is a substrate for estrogen sulfotransferase, and bisphenol A sulfate (BPAS) and disulfate are substrates for estrone sulfatase. Although the sulfated xenobiotics bind poorly to the ER, both stimulated the growth of receptor-positive breast tumor cells. Treatment of MCF-7 cells with BPAS leads to desulfation and uptake of BPA. No BPAS is found inside the cells. These findings suggest a mechanism for the selective uptake of BPA into cells expressing estrone sulfatase. Therefore, sulfation may increase the estrogenic potential of xenobiotics.     

Influence of photo-Fries reaction products on the photodegradation of bisphenol-A polycarbonate

The photodegradation of BPA polycarbonate (PC) can be described as an autoaccelerating process initiated by the formation of biphenol products arising from a formal photo-Fries reaction pathway. Evidence comes from spiking PC films with model compounds of photo-Fries reaction products, pre-exposure of films to generate photo-Fries products, and kinetic analysis. Published data on products formed during natural PC weathering are consistent with this pathway.     

Development of Photochromic Coatings on Polycarbonate

New photochromic materials based on heteropolyoxometallates (HPOM) incorporated into a hybrid organic-inorganic binder were prepared and coated onto polycarbonate (PC) substrates. The hybrid binder was formed through the controlled hydrolysis and condensation of 3-glycidoxypropyl-trimethoxysilane (GPTMS) and bisphenol A (BPA) by the sol–gel technique. The photochromic behavior of the materials was investigated by using ultraviolet-visible (UV-Vis) absorption spectroscopy and color index values. The results indicated that the films were reduced photochemically to yield a blue species under UV irradiation, with the film color changing to deep blue with increasing time, and HPOM and BPA content. The photosensitivity of several films with molybdenum HPOM showed faster coloration and much slower bleaching than the tungsten HPOM. A photochromic mechanism involving electron transfer between the GPTMS matrix with BPA, and PWO is proposed. After UV irradiation, the O–H and bonds decomposed gradually and W^{6 +} was reduced gradually with increasing time. The photochromic coatings on PC substrate showed reversible transmittance change before and after UV irradiation, making then efficient light protectors under UV irradiation.     

Effect of Candida antarctica lipase B immobilization on the porous structure of the carrier

A series of poly(GMA-co-EGDMA) resins with identical composition but varying particle sizes, pore radii, specific surface areas and specific volumes are studied to assess how Candida antarctica lipase B immobilization affects the porosity of the copolymer particles. Mercury porosimetry reveals a significant change in the average pore size (up to 6.1-fold), the specific surface area (up to 3.2-fold) and the specific volume (up to 2.1-fold) of the epoxy resin. A similar behaviour is observed for glutaraldehyde-modified epoxy resins. The influences of the resin porosity properties on the loading of Candida antarctica lipase B during immobilization and on the hydrolytic activity (hydrolysis of p-nitrophenyl acetate) of the immobilized lipase are studied.     

Synthesis and properties of isosorbide based epoxy resin

Isosorbide based epoxy resin (IS-EPO) of epoxy number: 0.44 mol/100 g was synthesised in the one step reaction from 1,4:3,6-dianhydro-d-glucitol (isosorbide) and epichlorohydrin in the presence of concentrated aqueous NaOH. The product obtained was characterised by means of NMR, FT-IR and ESI MS spectroscopy. Compositions with typical hardeners were prepared and cured. The thermal and mechanical properties of the resulting materials were evaluated. Comparison with commercially available epoxy resin Epidian 5 shows relatively good mechanical performance of IS-EPO which makes isosorbide a promising candidate to replace bisphenol A (BPA).