Chemical Vapor Polymerization Research Articles

Fluorinated paracyclophane dimers for polymeric thin films via chemical vapor polymerization

Poly(para-xylylene) thin films from Gorham method via chemical vapor polymerization (CVP) process (so called Parylene) have been extensively utilized in various application fields. Specific functional groups can be also introduced into thin polymeric films via CVP process using functionalized paracyclophane dimer. There have been numerous efforts to fabricate parylene thin films using synthesized and functionalized paracyclophane dimers so far. Herein we report on synthesis of fluorine containing paracyclophane dimers and their polymeric thin films via Gorham method. Three different types of fluorine containing paracyclophane derivatives are synthesized and the CVP thin films are prepared in all cases by adjusting processing condition. Even though the functional groups on parylene thin films are similar, dramatic differences in surface energy can be observed. This work can provide extended material choices for whom want to precisely control surface properties with robust, pin-hole free, and conformal coatable polymeric thin films.

Fabrication of Zigzag Parylene Nanofibers in Liquid Crystals with Electric Field-Induced Defect Structures.

Liquid crystals (LCs) have been adopted to induce tunable physical properties that dynamically originated from their unique intrinsic properties responding to external stimuli, such as surface anchoring condition and applied electric field, which enables them to be the template for aligning functional guest materials. We fabricate the fiber array from the electrically modulated (in-plain) nematic LC template using the chemical vapor polymerization (CVP) method. Under an electric field, an induced defect structure with a winding number of -1/2 contains a periodic zigzag disclination line. It is known that LC defect structures can trap the guest materials, such as particles and chemicals. However, the resulting fibers grow along the LC directors, not trapped in the defects. To show the versatility of our platform, nanofibers are fabricated on patterned electrodes representing the alphabets 'CVP.' In addition, the semifluorinated moieties are added to fibers to provide a hydrophobic surface. The resultant orientation-controlled fibers will be used in controllable smart surfaces that can be used in sensors, electronics, photonics, and biomimetic surfaces.

Electrically‐assisted chemical vapor polymerization: A novel method for in situ polymerization of pyrrole

AbstractThis article offers a fast and innovative process for carrying out in situ polymerization of pyrrole onto a polyester fabric. This process is based on electrically‐assisted chemical vapor polymerization that takes around 180 s to produce an electroconductive fabric with a surface resistance of as low as 70 Ω. The ultrasonication carried out at 20 kHz frequency is quite effective in binding the polymer to the fabric. Fourier‐transform infrared spectroscopy and X‐ray diffraction studies confirm that the polymer formed is polypyrrole. The application of electric potential across an oxidant‐enriched fabric results in polymer add‐on of polypyrrole as high as 250%. The amount of polypyrrole formed and the surface resistance of the fabric are found to depend on the potential applied across the fabric. The concentrations of the oxidant and the dopant, the time of polymerization, and the rate of monomer vaporization are found to be critical in deciding the surface resistance of the fabric.

In situ deposition of conducting polymer on metal organic frameworks for high performance hybrid supercapacitor electrode materials

Metal organic frameworks (MOFs) attract great attention in electrochemical energy storage devices owing to high porosity, adjustable structure and abundant active sites. Nevertheless, their cycle stability and rate property are far unsatisfied to construct high performance devices due to the poor conductivity and structure ability. Herein, a high conductive and stable Ni-based metal organic framework (Ni-MOF)/poly(3,4-ethylenedioxythiophene) (PEDOT) composite is synthesized from Ni-MOF nanosheets and 3,4-ethylenedioxythiophene(EDOT) monomer via an in situ chemical vapor polymerization (CVP) method. The covering of conducting PEDOT on Ni-MOF results in significantly improved conductivity and electrochemical performance. The Ni-MOF/PEDOT composite exhibits an ultrahigh specific capacitance of 1401 F g−1 and the retention of specific capacitance is maintained over 80% subsequent to 1000 cycles at 10 A g−1. Moreover, an asymmetric supercapacitor (ASC) based on Ni-MOF/PEDOT and activated carbon (AC) is assembled, which achieves an energy density of 40.6 Wh kg−1 at a power density of 450 W kg−1.

Sharing of Strain Between Nanofiber Forests and Liquid Crystals Leads to Programmable Responses to Electric Fields

AbstractFibers embedded in soft matrices are widely encountered in biological systems, with the fibers providing mechanical reinforcement or encoding of instructions for shape changes. Here, the mechanical coupling of end‐attached polymeric nanofiber forests and liquid crystals (LCs) is explored, where the nanofibers are templated into prescribed shapes by the chemical vapor polymerization of paracyclophane‐based monomers in supported films of the LCs. It is shown that the elastic energies of the nanofibers and LCs are comparable in magnitude, leading to reversible straining of nanofibers via the application of an electric field to the LC. This coupling is shown to encode complex electrooptical responses in the LC (e.g., optical vortices), thus illustrating how LC‐templated nanofiber forests offer the basis of fresh approaches for programming configurational changes in soft materials.

Integrated Evaporator for Efficient Solar-Driven Interfacial Steam Generation.

Solar-driven interfacial steam generation is a promising technique for clean water production because it can minimize thermal loss by localizing solar-to-heat conversion at the air/liquid interface. Here we report an integrated solar evaporator by partially growing 2D polypyrrole microsheets within a melamine foam through chemical vapor polymerization. These microsheets can induce multiple light reflections within the foam, enable omnidirectional light absorption, provide abundant surfaces to promote heat transfer, and achieve spatially defined hydrophobicity to facilitate vapor escape. Meanwhile, the inherent hydrophilicity of the bottom part of the foam promotes spontaneous upward water transport and suppresses heat loss. The composite foam exhibits an excellent apparent evaporation rate of ∼2 kg/(m2·h) and solar-to-vapor efficiency of ∼91%. The combined advantages of large surface area, high efficiency, low cost, all-weather application, excellent durability, and scalable manufacturing make our integrated design promising for fabricating large-scale solar steam generation systems that are suitable for practical clean water production.

Tuning of optical and electrical properties of polyaniline on flexible cellulose through Eosin Y dye interaction

Polyaniline, which is an attractive macromolecular system for electronic applications, has been chosen in this work in order to bring a tuning and alignment of energy levels for controlling its electrical and optical properties through Eosin Y dye interaction. Polyaniline has been synthesized over flexible cellulose substrate through a very simple oxidative chemical vapor polymerization technique. Prepared polyaniline incorporated cellulose was then allowed to interact with the anionic dye of Eosin Y to control its charge transport and optical properties. The dye interaction leads to better crystallinity of polyaniline over cellulose as revealed from x-ray diffraction pattern. From optical characterization, a remarkable change of band gap varying from 2.629 eV to 2.471 eV has been observed with increasing dye interaction time. The effects of dye interaction on charge transport and carrier dynamics were studied from I-V curve, which shows an excellent improvement of electrical conductivity. The color generating chromophores present in dye are likely to interact with positively charged polaron defect states present in polyaniline. Thus it opens a wider and simpler way of functionalizing π-conjugated polymers on flexible cellulose substrate in exploring their applications as electronic materials in sensor, memory devices and field effect devices.

Templated nanofiber synthesis via chemical vapor polymerization into liquid crystalline films.

Extrusion, electrospinning, and microdrawing are widely used to create fibrous polymer mats, but these approaches offer limited access to oriented arrays of nanometer-scale fibers with controlled size, shape, and lateral organization. We show that chemical vapor polymerization can be performed on surfaces coated with thin films of liquid crystals to synthesize organized assemblies of end-attached polymer nanofibers. The process uses low concentrations of radical monomers formed initially in the vapor phase and then diffused into the liquid-crystal template. This minimizes monomer-induced changes to the liquid-crystal phase and enables access to nanofiber arrays with complex yet precisely defined structures and compositions. The nanofiber arrays permit tailoring of a wide range of functional properties, including adhesion that depends on nanofiber chirality.

Conductive Shape Memory Microfiber Membranes with Core-Shell Structures and Electroactive Performance.

Conductive shape memory polymers as a class of functional materials play a significant role in sensors and actuators. A high conductivity and a high response speed are needed in practical applications. In this work, a conductive shape memory polylactic acid (PLA) microfiber membrane was synthesized by combining electrospinning with chemical vapor polymerization. The shape memory PLA was electrospun into microfibers with different diameters, and a conductive polypyrrole (PPy) coating was applied to the PLA microfiber membranes using vapor polymerization. The conductivity of the microfiber membrane was investigated as a function of different experimental parameters: FeCl3 concentration, PPy evaporation time, and PPy temperature. The maximum conductivity of the membrane prepared in a sub-zero environment is 0.5 S/cm, which can sustain a heat-generating electric current sufficient to trigger the electro-actuated behaviors of the membrane within 2 s at 30 V. Thermographic imaging was used to assess the uniformity of the temperature distribution during the shape recovery process. The low surface temperature is compatible with potential applications in many fields.

An amperometric glucose biosensor based on PEDOT nanofibers.

Here we present a simple, low cost approach for the production of PEDOT nanofiber biosensors using simple techniques. Firstly, nanofibers of PEDOT were produced by the chemical vapor polymerization of EDOT on FeCl3 containing electrospun PAN nanofiber mats. The nanofibers were characterized by SEM, FTIR, CV and conductivity studies, which indicated the formation of homogeneous, porous, electroactive PEDOT nanofibers. The fabrication of biosensors was achieved through the loading of various amounts of GOx on the nanofibers. To uncover their capability, the biosensors were operated under both hydrogen peroxide production and oxygen consumption conditions. For each biosensor current response versus glucose concentration calibration curves were plotted. The sensitivity, linear range, LOD, Km and Imax values of the biosensors were determined and the stabilities of all the sensors were investigated. The biosensor operating at 0.6 V revealed a lower LOD with a wider linear range, higher stability, good sensitivity and selectivity. For example, the PEDOT-NFs/GOx-3 nanofiber biosensor showed good sensitivity (74.22 μA mM−1 cm−2) and LOD (2.9 μM) with a response time of 2–3 s without any interference effects. The PEDOT-NFs/GOx-2 biosensor operating at −0.6 V exhibited extreme sensitivity of 272.58 μA mM−1 cm−2. Our studies have shown that having good sensitivity, LOD and stability makes these interference-free, easy to construct sensors viable candidates for commercialization.

The charge transport characterization of the polyaniline coated carbon fabric as a novel textile based counter electrode for flexible dye-sensitized solar cell

Implementation of textile based counter electrode with appreciable photovoltaic performances is a persistent objective for flexible dye-sensitized solar cells. The polyaniline (PANi) coated carbon fabric (CF) is launched as a novel flexible textile based counter electrode (CE) using different polymerization methods including chemical oxidation polymerization (COP), chemical vapor polymerization (CVP) and electropolymerization (EP) in current investigation. The electropolymerized PANi counter electrode exhibits lower charge transfer resistance (Rct) of 0.91ohm cm2 compared to CVP (1.89ohm cm2) and COP (12.18ohm cm2) techniques. As a result, electropolymerized PANi represents higher conductivity, more porosity and higher order of molecular structure which facilitates charge transfer on the counter electrode/electrolyte interface and provides sufficient electrocatalytic activity towards reduction of tri-iodide (I3−). In addition, electropolymerized PANi shows lower charge transfer than that of Pt (0.94ohm cm2) as well as an over 7% improvement in open circuit voltage at commendable overall power conversion efficiency (PCE) of 3.81%. Remarkably, the advantageous of low cost, easy and reproducible PANi synthesis, and flexible, cheap and chemical stable carbon fabric, opens up new opportunities in the development of high performance flexible textile based solar cell for energy supply in smart textiles applications.

Utilization of Polypyrrole Nanofibers in Glucose Detection

The present work demonstrates a novel, simple approach for fabrication of sensitive and selective glucose biosensors based on polypyrrole (PPy) nanofibers without using price-rising mediator or nanoparticles. The nanofibers were produced by chemical vapor polymerization of pyrrole on FeCl3 containing PAN nanofiber mats. Amperometric biosensors were constructed by entrapment of glucose oxidase on the nanofibers with the help of glutaraldehyde. The operational parameters such as pH, working potential, enzyme amount were optimized. For every biosensor sensitivity, linear range, limit of detection (LOD), and Michaelis-Menten constant values were determined and the stabilities of some of the sensors were tested. Our studies underlined the clear effect of enzyme content where the biosensors tend to show widened the linear detection range as the enzyme loadings increased +0.65V. PPy-NFs/GOx-1 biosensor showed good sensitivity (68.95 μA/mM.cm2) and LOD (7.8 μM) without any interference effect at +0.65V. On the other hand, when it was operated at −0.65V (oxygen consumption) the biosensor exhibited enhanced sensitivity of 116.42 μA/mM.cm2 with modest LOD and operational stability. Due to utilization of biocompatible, large surface area, nanoporous PPy nanofibers; an improved analytical performance was achieved with a very short response time, good stability and high selectivity, which make them feasible candidates for commercialization.

Manganese dioxide nanoparticle enrichment in porous conducting polymer as high performance supercapacitor electrode materials

We demonstrated preparation of porous conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT)/MnO2 nanoparticles (NPs) composites as high performance electrochemical energy storage electrode. NPs-enriched PEDOT porous structures are prepared by simple thermal treatment and chemical vapor polymerization (VPP) methods. The incorporation of MnO2 NPs in PEDOT is characterized by scanning electron microscopy, X-ray photoelectron spectroscopy and infrared spectroscopy, which indicate the uniform dispersion of MnO2 NPs into porous PEDOT matrix. This porous composite contains large and highly opened surface area with excellent electrochemical activity. A specific capacitance of as high as 321.4F/g at a 0.5A/g current density was achieved. The highly conductive and porous PEDOT matrix facilitates fast charge/discharge of the MnO2 NPs and prevents them from agglomerating. These synergic properties enable the metal oxide nanoparticle-enriched porous conducting polymer with both high specific capacitance and good cycling stability as promising electrode materials for electrochemical energy storages.

Gas Sensors Based on Deposited Single-Walled Carbon Nanotubes-Polypyrrole Networks for Ammonia Detection

In this work, we demonstrate excellent gas sensors based on single-walled carbon nanotubes (SWNTs)-polypyrrole (PPy) networks for the detection of ammonia (NH3) gas. The SWNTs networks were deposited on oxidized silicon surface functionalized with 3-aminopropytrimethysilane. The Fe3+ions were easily adsorbed on the surface of SWNTs by ion exchange process. After deposition of PPy molecules on the surface of SWNTs by chemical vapor polymerization process in a sealed container with pyrrole vapors, SWNTs-PPy networks were formed. By the combination of traditional silicon processes, SWNTs-PPy networks-based gas sensors were fabricated at a wafer scale. The sensitive properties of the resultant gas sensors for the detection of NH3gas were investigated at room temperature. And the results suggested that the gas sensors based on SWNTs-PPy networks exhibited excellent sensitivity to NH3gas. This new method is very simple, which holds great potential in the wide spread practical production.

The application of the fast multivariant fitting procedure of the LBET models to the analysis of carbon foams prepared by various methods from furfuryl alcohol

The paper presents the numerical analysis based on the low temperature N 2 adsorption isotherms of carbon foam microporous structures prepared by various methods from furfuryl alcohol by employment of the fast multivariant fitting procedure of the thermodynamical LBET class models. Various techniques, including chemical vapor polymerization, were employed to produce microporous carbons. To perform the analysis of the porous structure, the fast multivariant fitting procedure with the new adsorption numerical models of the LBET class was used. The results of the analyses carried out with the use of the fast multivariant fitting procedure of the LBET class models have provided valuable information concerning the microporous structure of the analyzed materials, with the determination of the reliability of the defined parameters of the LBET class models. Those studies have been completed by microscopic research aimed at visualization of the macroporous structure as a framework for the formation of micropores.

Plasma Polymer Surfaces Compatible with a CMOS Process for Direct Covalent Enzyme Immobilization

AbstractPlasma polymerized surfaces, prepared using a CMOS compatible plasma enhanced chemical vapor polymerization technique, are found to covalently immobilize enzymes without the need for intermediate chemical linker groups. The polymerized surfaces are smooth, strongly adherent to substrates, and have a long shelf life for storage. After incubation with enzymes, a densely packed monolayer is attached. We report the effects of both oxygen etching and annealing post‐processing showing that they can be implemented so as not to affect the enzyme binding performance. The fully compatible polymerization method with CMOS device manufacture processes is a potential candidate for integration into nano‐CMOS biochemical sensors for direct immobilization of enzymes.magnified image

Ferroelectric Poly(vinylidene fluoride) Thin Films Grown by Low‐Pressure Chemical Vapor Polymerization

AbstractFerroelectric poly(vinylidene fluoride) polymer (VDF2)n thin‐film formation by a low‐pressure chemical vapor polymerization (CVP) process is described. The process involves polymerization of an isotropic vinylidene fluoride monomer condensate layer by cleavage of C double bonds using :CF2 initiators derived from hot‐filament, thermochemical decomposition of the hexafluoropropylene oxide C3F6O. Two different growth modes on the film surface and in the bulk are identified by Fourier transform infrared (FTIR) and X‐ray photoelectron spectroscopy (XPS) studies. Surface impingement of :CF2 induces lateral growth of molecular chains in trans conformation. Due to the initiation of polymerization at random surface sites, amorphous β‐phase growth is also observed. Bulk growth of polymer film involves chain formation dominated by gauche conformations having a predominance of the α‐phase. Ferroelectric investigations of (VDF2)n films show spontaneous polarization and hysteresis effects, which improves on crystallization. Typical polarization values of 3.5 and 1.5 μC cm–2 in the planar and normal directions, respectively, are observed after crystallization. Structural defects in the molecular chains give rise to space charge conduction which affects polarization switching properties. The low‐pressure CVP technique is compatible with sub‐micrometer semiconductor device fabrication and also provides a novel method for incorporating additional functional units into the molecular chains to control the film properties.

Poly(tetraflouro-p-xylylene), a low dielectric constant chemical vapor polymerized polymer

A low dielectric constant polymer, poly(tetrafluoro-p-xylylene) (VT-4) was synthesized by a chemical vapor polymerization process using 4,5,7,8,12,13,15,16-octafluoro-[2.2]-paracyclophane as a precursor. The VT-4 polymer has a dielectric constant of 2.42 and a dielectric loss of 0.008 at 1 MHz, perpendicular to the plane of the film. Thermal stability of VT-4 satisfied the SEMATECH criteria, exhibiting an onset of degradation at 460 °C, and 1% weight loss at 480 °C in an argon environment. The x-ray diffraction data suggest a disordered semicrystalline polymer as-deposited (at ∼12 °C). The crystalline phase became more ordered due to a decrease in the d spacing from 4.850 to 4.594 Å and an increase in the percent crystallinity from 39% as-deposited to 66% after successive postdeposition anneals to 300 °C. Optical measurements showed a highly anisotropic thin film with ne @630 nm=1.601 and n0 @630 nm=1.471, progressively becoming more negatively birefringent after postdeposition anneals, reaching a plateau at ∼250 °C, due to the polymer chain becoming more conformationally ordered.

A new method for fabricating high performance polymeric thin films by chemical vapor polymerization

A vacuum deposition method is presented in which copolymer films are grown from a vinylic monomer chosen for desirable properties and paraxylylene. The concentration of paraxylylene in the final copolymer can be negligibly small if proper deposition conditions, presented here for the first time, are employed. Films of paraxylylene with N-phenyl maleimide deposited at 40 °C, for example, showed thermal stability and FTIR spectra nearly identical with homopolymers of poly(N-phenyl maleimide). Different rate-limiting steps are proposed to explain film composition; paraxylylene is under surface reaction control, while the comonomer obeys mass flow control. This results in a deposition environment extremely rich in comonomer. Growth rates and compositions were consistent with predictions. The initiation reaction did not appear different from homopolymerization of paraxylylene. The general method presented here allows fabrication of vapor-deposited thin films with properties limited primarily by the comonomer employed.