Vapor deposition polymerization of synthetic rubber thin film in a plasma enhanced chemical vapor deposition reactor

Rubber is one of the most commonly used industrial materials worldwide. However, there is a gap in the literature on the production of rubber thin films in nanoscale. When the rubber thin films are produced in nanoscale, they can be used in high-tech applications where bulk rubbers have never been used before. This study is one of the first investigations to focus on the vapor-based production of the polyisoprene (PI), which is an important member of the synthetic rubber class. For this purpose, a single-step, rapid and environmentally friendly method based on plasma enhanced chemical vapor deposition (PECVD) was employed to produce PI thin films using 2-methyl-1,3-butadiene (isoprene). The high-vapor pressure of isoprene makes it a promising monomer for the production of chemical vapor deposition polymers. The effect of plasma processing parameters on the PI deposition rate was investigated. The deposition rate of PI thin film as high as 40 nm/min was achieved and the contact angle of PI coated bamboo surface was found to be 146.8°. The mechanical durability and laundering tests of PI thin films were performed. Based on this study results, PI thin films produced by PECVD can be used in a number of potential applications.     

聚酰胺酸液膜干燥行为研究

采用实验室的液膜干燥装置,考察了液膜干燥过程中溶剂初始含量、干燥温度、液膜厚度对溶剂含量的影响。结果表明,随着干燥温度的升高、溶剂初始含量的升高、液膜厚度的减少,溶剂含量下降加快。该方法实验重现性良好,在溶剂含量小于30%时,该实验的标准偏差小于0.0754,且操作方便,能为气相、液相扩散系数理论分析提供合理的实验数据。     

部分环化聚酰胺酸的湿法纺丝成形研究

采用三乙胺/乙酸酐混合液作环化剂对聚酰胺酸(PAA)进行部分环化,制备不同环化程度的聚酰胺酸/聚酰亚胺(PAA-PI)纺丝液,经湿法纺丝成形、高温拉伸得到PI纤维,通过红外光谱、热重分析、动态力学分析表征PI纤维的热稳定性和力学性能。结果表明:不同环化剂添加量的PAA-PI纺丝液的实际环化程度与理论值相符;预环化有利于提高PAA-PI初生纤维的热稳定性;部分环化的PAA-PI纺丝液有利于纤维的成形,且明显提高PI纤维的力学性能,但环化速度不宜过高;当环化程度为5%时,PI纤维的断裂强度最高达18.6 c N/dtex,相比未环化纤维提高16%。     

聚酰胺酸溶液的流变性能研究

采用锥板粘度计研究了聚酰胺酸溶液的流变性能及其粘度的影响因素。结果表明:聚酰胺酸溶液属于非牛顿假塑性流体,还具有负触变性流体的特征。聚酰胺酸溶液的粘度随剪切速率的增加而减小,随浓度的增加而增大,随温度的升高而降低,随存放时间的延长而下降;质量分数为15％的聚酰胺酸溶液的粘流活化能为20．83 kJ／mol。     

High-permeability fluorinated polyimide microcapsules by vapor deposition polymerization

Spherical microcapsules (∼1 mm in diameter and ∼1 μm in wall thickness) to be used as inertial confinement fusion targets were prepared from 6FDA-ODA polyimide by vapor deposition polymerization. Compared with the previously developed PMDA-ODA polyimide microcapsules, the 6FDA-ODA microcapsules were ∼50-fold more permeable to gases including He, D₂, O₂, N₂, Ar, and Ne, considerably more transparent in the UV-visible spectrum, and of marginally lower Young's modulus, tensile strength, and elongation at break. The microcapsules possessed amorphous morphology with an amorphous d-spacing of 5.8 Å as determined by wide-angle X-ray diffraction. The cryogenic permeability of helium was measured between 133 and 295 K, and the activation energy for permeation was determined to be 12.3 kJ/mol.     

ESR study of the radical polymerization of styrene

Summary The absolute rate constant of propagation (k_p) in styrene polymerization was determined on the basis of ESR detection of the polymer radical in the temperature range of 0 to 130°C. The Arrhenius plot of k_p gave a good linear relationship and the activation energy of the propagation was evaluated to be 39.7 KJ/mol. The termination rate constants over the same temperature range were also obtained by using the k_p values according to the standard kinetics of radical polymerization. Apparent activation energy of the termination was estimated to be 15.6 KJ/mol.     

ESR study on radical polymerization of styrene

Summary Propagation rate constant (k_p) for styrene was evaluated at different chain lengths of the polymer radical based on the steady-state concentration of the polymer radical determined by means of ESR spectroscopy at 70°C. Over a range of degree of polymerization of the polymer radical from 40 to 410, the value of k_p, 480±10 L/mol·s, remained constant. A considerable increase in viscosity of the polymerization mixture did not affect this value.     

Effects of various factors on the formation of high molecular weight polyamic acid

The reaction of pyromellitic dianhydride (PMDA) and aromatic diamine in an aprotic solvent such as dimethylacetamide (DMAc) gives a solution of poly(amic acid). The effects of certain variables on the polymerization and some additives on the stability and imidization of the poly(amic acid)s were studied. It was found that the addition of PMDA portionwise to the solution of diamine always keeps the excess diamine in solution and enables one to obtain the highest molecular weight of poly(amic acid). When the addition process was reversed, either by the change or dehydration of solvent, a high molecular weight was not attained. The inevitable water in the solvent or the reaction medium is the major factor, and the more the water content in the solvent or the reaction medium, the larger is the probability of destruction of PMDA during the reaction and hence low molecular weight is obtained. If very pure monomers were used in the polymerization, the 1:1 of molar ratio is the optimum value. Excess diamine or dianhydride results in the exchange reaction with poly(amic acid) and causes a rapid degradation of polymer chain. This exchange reaction was proved by NMR measurements. The presence of electrophilic agents or the nucleophilic agents containing active protons in the poly(amic acid) solution promotes the decomposition of polymer and causes the brittleness of polyimide film in the curing process. Using acetic anhydride (A) to convert the poly(amic acid) to polyimide, pyridine (P) can protect the polymer chain from the nucleophilic attack by the anhydride. The mixture with proper ratio of A/P (1/1–15/1) can be used as good dehydrating agents. Meanwhile, according to the results to the results of experiments, we suggested the probable reaction mechanisms about how the water, amine, and anhydride destroy the polyamic acid chains.     

Morphological characterization and kinetics study of polyaniline film formation by emulsion polymerization

The kinetics and morphology of polyaniline film prepared by using ammonium persulfate (APS) as oxidant and dodecylbenzoyl sulfonic acid (DBSA) as both emulsifier and dopant were studied in this paper. The kinetics of the formation of polyaniline film was determined by using the quartz crystal microbalance (QCM), and the film morphology was characterized by scanning electron microscopy (SEM). The reaction exhibited half-order kinetics with respect to APS concentration and first-order kinetics with respect to aniline concentration. The activation energy is 41.15 kJ/mol, and the growth rate of PANI film increased with increasing temperature and decreased with increasing concentration of DBSA.     

High-quality diamond film deposition on a titanium substrate using the hot-filament chemical vapor deposition method

Diamond film on titanium substrate has become extremely attractive because of the combined properties of these two unique materials. Diamond film can effectively improve the properties of Ti for applications as aerospace and biomedical materials, as well as electrodes. This study focuses on the effects of process parameters, including gas composition, substrate temperature, gas flow rate and reactor pressure on diamond growth on Ti substrates using the hot-filament chemical vapor deposition (HFCVD) method. The nucleation density, nuclei size as well as the diamond purity and growth tendency indices were used to quantify these effects. The crystal morphology of the material was examined with scanning electron microscopy (SEM). Micro-Raman spectroscopy provided information on the quality of the diamond films. The growth tendency of TiC and diamond film was determined by X-ray diffraction analysis. The optimal conditions were found to be: CH₄:H₂ = 1%, gas flow rate = 300 sccm, substrate temperature T_sub = 750 °C, reaction pressure = 40 mbar. Under these conditions, high-quality diamond film was deposited on Ti with a growth rate of 0.4 μm/h and sp² carbon impurity content of 1.6%.     

Properties of polyamic acid ionomers

Polymers containing amic acid units were produced by reacting an oligomer based on polytetramethylene oxide (PTMO) with 1,2,4,5-benzenetetracarboxylic dianhydride (BTDA). Neutralization by a metal salt produced amic acid ionomers. Similar to other ionomer systems, neutralization from the acid to the ionomer led to the formation of a separate ionic phase as determined by dynamic mechanical analysis. Phase separation resulted in a substantial increase in mechanical properties. The effect of neutralization level, cation, soft-segment molecular weight, and soft-segment end group on mechanical and thermal properties was investigated. © 1993 John Wiley & Sons, Inc.     

2,6-二甲氧基苯胺的合成与结构表征

研究2,6-二甲氧基硝基苯催化加氢制备2,6-二甲氧基苯胺的工艺。结果表明,室温条件下及乙醇介质中,氢气压强为1．0MPa的条件下,选择Pd/C催化剂（2％,w／w）,可以高活性的催化合成2,6-二甲氧基苯胺,收率可达80％。其结构经过1H NMR鉴定。     

Characterization of particle contamination in process steps during plasma-enhanced chemical vapor deposition operation

The occurrence time and the contribution level of particle contamination on the wafer in individual steps during plasma-enhanced chemical vapor deposition (PECVD) operation were investigated. A method was proposed to determine the occurrence time of particle contamination by making use of the capability of thermophoresis to shield the wafer from particle deposition. The level of particle contamination on the wafer was determined by a scanning electron microscopy (SEM) and the particle behavior in the reactor was observed using a laser light scattering (LLS) technique. The particles were continuously injected into the plasma reactor from the outside. Using this technique, the effect of particle size on the particle behavior can be studied with high certainty. It was found that the particle contamination occurred during the postplasma when the injected particles were trapped in the sheath region below the powered electrode. On the other hand, when the injected particles were not trapped due to a strong inertial effect of particle, the contamination occurred during plasma operation. There is a regime of operation condition in which the lowest level of contamination occurs. Most particles retained their negative charge in the postplasma as shown by their movement and deposition on the wafer in the presence of either a negative or positive dc field. The charge on these particles was determined from particle motion with high certainty using the current experimental technique.     

Surfactants in heterophase polymerization: A study of film formation using force microscopy

Film formation of three different latices was studied using atomic force microscopy. The latices were made from a mixture of butyl acrylate, styrene, and acrylic acid using either a polymerizable or an unreactive anionic surfactant as an emulsifier. Sodium 11-crotonoyloxyundecan-1-ylsulfate and sodium 3-(sulfopropyl)tetradecylmaleate were used as a reactive surfactant and the unreactive surfactant was sodium dodecylsulfate (SDS). The conventional surfactant was found to migrate to the surface of the latex film to a much greater extent than did the reactive surfactants; however, also, the latter were incompletely anchored to the particle. The maleate surfactant was bound to a higher degree than was the crotonate, a finding which is in line with the relative reactivities of the two surfactants. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 187–198, 1997     

聚酰胺酸粒子亚胺化的研究

以均苯四酸二酐(PMDA)和4,4,-二氨基二苯醚(ODA)为原料合成了均苯型的聚酰胺酸(PAA)粒子.并以乙酸酐/吡啶为脱水剂,对PAA粒子进行化学亚胺化和不同温度下进行热亚胺化处理.通过红外光谱(IR),紫外光谱(UV),示差热量扫描(DSC)探讨了PAA的亚胺化条件.     

Controlled mesoporous film formation from the deposition of electrosprayed nanoparticles

Thin films of controlled morphology were fabricated by electrospray drying a colloidal nanoparticle suspension using a conductive and volatile solvent and impacting the nanoparticles on a substrate. Three parameters were used for control: impact velocity, size of the nanoparticles or nanoparticle agglomerates, and solvent volatility. The impact velocity was controlled by charging nanoparticles through electrospray dispersion and varying the electric field driving the particle impaction. It was found that the structure is governed by the relative importance of charged particle drift imposed by the external electric field and the thermal velocity due to Brownian motion. Peclet number correlates with the morphology of the deposit where columnar structures result from high Pe, corresponding to ballistic deposition and porous, fractal-like structures result from small Pe. These patterns match predictions based on Monte Carlo simulations in the literature. For dispersions with higher nanoparticle concentrations, droplet evaporation causes densification of the particle ensemble to form a spherical aggregate that deposits in a predominantly ballistic manner, with smaller aggregates forming denser films. If the droplet evaporation lifetime is altered for the aggregates to be partially wet upon impacting the substrate, the subsequent rapid evaporation of the remaining solvent on the substrate leads to formation of films with high interconnectivity. Films formed by the electrospray technique have large-scale uniformity and their structure is independent of thickness. The interpretation of the observed morphologies in terms of Peclet number and Damkhöler number provides a conceptual framework for a rational design of film structures as required by many applications.

Copyright © 2017 American Association for Aerosol Research     

An energy balance approach to solvent removal in polyamic acid coatings

Using an energy balance approach incorporating a Flory-Huggins expression for free energy and the strain energy of the material, the solvent removal process in liquid-based coatings was shown to depend on stress and temperature. An equilibrium is obtained between residual solvent content and stress in the coating at a given temperature. Such stress-dependent solvent removal behavior was observed with a polyamic acid coating solution-cast using N-methylpyrrolidinone.     

Synthesis of substituted poly (arylene vinylene) films by vapor deposition polymerization

Summary An efficient method for the synthesis of PPV based polymers, poly ( 2,5-dimethyl-1,4-phenylene vinylene) (DMe-PPV) and poly (2,5-dimethoxy-1,4-phenylene vinylene) (DOMe-PPV) were developed using 2,5-dimethyl-1,4-bis ( chloromethyl ) benzene and 2,5-dimethoxy 1,4-bis ( chloromethyl ) benzene via vapor phase pyrolysis and followed by vapor deposition polymerization. The structure of polymer films were confirmed by FT-IR, solid state NMR and elemental analysis. Thermal gravimetry analysis reveals that the precursor polymer films form a conjugated polymer after thermal conversion at 250°C. The optical and electrical properties of the polymer films were investigated by UV-Vis absorption and photoluminescence spectroscopies. Electroluminescent devices were fabricated using these polymers. Received: 18 May 2000/Revised version: 21 July 2000/Accepted: 28 July 2000     

The control of graphene double-layer formation in copper-catalyzed chemical vapor deposition

The growth of graphene during Cu-catalyzed chemical vapor deposition was studied using ¹²CH₄ and ¹³CH₄ precursor gasses. We suggest that the growth begins by the formation of a multilayer cluster. This seed increases its size but the growth speed of a particular layer depends on its proximity to the copper surface. The layer closest to the substrate grows fastest and thus further limits the growth rate of the upper layers. Nevertheless, the growth of the upper layers continues until the copper surface is completely blocked. It is shown that the upper layers can be removed by modification of the conditions of the growth by hydrogen etching.