Monomer Vapor Research Articles

Terminal conversion of polyamide membranes by homologous monomer vapors for chlorine-resistant desalination

Water scarcity is a global challenge and severely threatens human development. Membrane desalination shows great potential for producing freshwater from saltwater to alleviate this crisis. However, the dominating polyamide membranes suffer from the issue of poor chlorine resistance, which cause performance deterioration and shortens membrane lifespan. In this study, we report a concept of terminal conversion to design high-performance, antifouling, and especially chlorine-resistant polyamide desalination membranes. This amino-to-carboxyl conversion of commercial membranes can be simply performed by controllable and scalable chemical vapor deposition through exposure in homologous monomer vapor and hydrolysis of unreacted acyl chloride groups. We demonstrate that this conversion not only adjust the electronegativity and hydrophilicity of membranes to boost fouling resistance and reverse osmosis performance, but also tune the reactivity and electron cloud distribution of polyamide networks to restrain chlorine accessibility and substantially improve anti-chlorination property. After extreme chlorination for 240000 ppm h, the resultant membranes show limited rejection decline of only 7.2 %. For high-salinity (35000 ppm) and high-pressure (38 bar) desalination, the modified membranes before and after chlorination for 144000 ppm h still exhibit rejection of 94.5 % and 90.0 % and flux of 75.2 and 71.4 L m−2 h−1, respectively, which are much better than those of the pristine membranes (89.6 % and 63.5 %, and 64.2 and 57.5 L m−2 h−1). Our findings pave an alternative mechanism and strategy to reconstruct polyamide membranes for efficient water desalination.

Fabrication of Self-Wrinkling Polymer Films with Tunable Patterns through an Interfacial-Fuming-Induced Surface Instability Process.

Inspired by the superglue fuming method for fingerprint collection, this study developed a novel interfacial-fuming-induced surface instability process to generate wrinkled patterns on polymeric substrates. High-electronegativity groups are introduced on the substrate surface to initiate the polymerization of monomer vapors, such as ethyl cyanoacrylate, which results in the formation of a stiff poly(ethyl cyanoacrylate) capping layer. Moreover, interfacial polymerization resulted in the covalent bonding of the substrate, which led to the volumetric shrinkage of the composite and the accumulation of compressive strain. This process ultimately resulted in the development and stabilization of wrinkled surface morphologies. The authors systematically examined parameters such as the modulus of the epoxy substrate, prestrain, the flow rate of fuming, and operating temperature. The aforementioned technique can be easily applied to architectures with complex outer morphologies and inner surfaces, thereby enabling the construction of surface patterns under ambient conditions without vacuum limitations or precise process control. This study is the first to combine fuming-induced interfacial polymerization with surface instability to create robust wrinkles. The proposed method enables the fabrication of intricate microwrinkled patterns and has considerable potential for use in various practical applications, including microfluidics, optical components, bioinspired adhesive devices, and interfacial engineering.

Significant Progress of Initiated Chemical Vapor Deposition in Manufacturing Soft Non-spherical Nanoparticles: Upgrading to the Condensed Droplet Polymerization Approach and Key Technological Aspects

Initiated chemical vapor deposition is a unique solvent-free and completely dry vapor-phase deposition technique used to synthesize organic polymer films. In this process, an activated initiator, monomer, and carrier gas are introduced into the reaction chamber simultaneously. This technique has been widely adopted. However, if the monomer and initiator are introduced into the chamber in stages—allowing gas-phase monomer deposition and condensation first, followed by initiator introduction and controlling the monomer partial pressure to be higher than the saturated vapor pressure—non-spherical polymer nanoparticles with dome-like shapes can be obtained. This advanced iCVD technique is referred to as the “Condensed Droplet Polymerization Approach”. This high monomer partial pressure gas-phase deposition is not suitable for forming uniformly composed iCVD films; but interestingly, it can rapidly obtain polymer nanodomes (PNDs). Using CDP technology, Franklin polymerized multifunctional nanodomes in less than 45 s, demonstrating a wide range of continuous particle size variations, from sub-20 nanometers to over 1 micron. This rapid synthesis included a variety of functional polymer nanodomes in just a matter of seconds to minutes. This review discusses the crucial process conditions of the Condensed Droplet Polymerization (CDP) Approach for synthesizing PNDs. The main focus of the discussion was on the two-step method for synthesizing PNDs, where the nucleation mechanism of PNDs, factors influencing their size, and the effect of pressure on the distinct condensation of monomer vapor into polymer nanodomes and polymer films were extensively explored.

Kinetically Limited Bulk Polymerization of Polymer Thin Films by Initiated Chemical Vapor Deposition.

An experimental study and kinetic model analysis of the initiated chemical vapor deposition (iCVD) of polymer thin films have been performed at saturated monomer vapor conditions. Previous iCVD kinetic studies have focused on subsaturated monomer conditions where polymer deposition kinetics is known to be limited by monomer adsorption. However, iCVD kinetics at saturated conditions have so far not been systematically investigated, and it remains unclear whether the adsorption-limited phenomenon would still apply at saturation, given the abundance of monomer for reaction. To probe this question, a series of depositions of poly(vinylpyrrolidone) (PVP) thin films as a model system were performed by iCVD at substrate temperatures from 10 to 25 °C at both fully saturated (100%) and subsaturated (50%) conditions. While the deposition rates at subsaturated conditions exhibit the expected adsorption-limited behavior, the deposition rates at saturated conditions unexpectedly show two distinct deposition regimes with reaction time: an initial adsorption-limited regime followed by a kinetically limited steady-state regime. In the steady-state regime, the deposition kinetics is found to be thermally activated by raising substrate temperature with an overall activation energy of +86 kJ/mol, which agrees reasonably well with the experimentally determined value of +89 kJ/mol in the literature for bulk PVP polymerization and a mechanistically derived value of +91 kJ/mol based on the bulk free radical polymerization mechanism of PVP. These findings open new operating windows for iCVD polymerization and thin-film growth in which fast polymer deposition can be achieved without substrate cooling that can greatly simplify the iCVD scale-up to roll-to-roll processing and enable iCVD polymerization of highly volatile monomers relevant for diverse applications in biomedicine, smart wearables, and renewable energy.

Frequency-Tuned Porous Polyethylene Glycol Films Obtained in Atmospheric-Pressure Dielectric Barrier Discharge (DBD) Plasma

This study focuses on the fabrication of plasma-polymerized polyethylene glycol (pp-PEG) with porous morphology in a pulsed dielectric barrier discharge (DBD) plasma under atmospheric pressure. The signal frequency that modulates the plasma discharge was found to have a major influence on the pp-PEG film morphology. The recorded discharge current–voltage characteristic allowed us to establish a homogeneous regime of the DBD plasma operated in helium gas flow upon the frequency range 2–10 kHz. The as-prepared pp-PEG films were characterized by the Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and liquid-phase chromatography (HPLC) techniques. The performed analysis revealed that as the discharge frequency increases, the morphology of the obtained films becomes porous due to the plasma-induced stronger monomer fragmentation. To gain knowledge about the plasma species and the interaction processes that impact the film morphology, optical emission spectroscopy (OES) and intensified charge-coupled device (ICCD) fast imaging technique were applied. The determined vibrational (Tvib) and rotational (Trot) temperatures exhibit a decrease with the introduction of monomer vapors into the discharge gap. For instance, Trot drops from approximately 475 K to 350 K, and Tvib falls from 2850 K to 2650 K for a monomer vapor injection rate of 16 µL/min. This was attributed to the energy losses of the plasma-generated particles, as the inelastic collisions augment with the injection of a monomer. Concurrently with the change in temperature, the discharge current varies significantly for the investigated frequency range and exhibits a drop at high frequencies. This discharge current drop was explained by an enhancement of the recombination rate of charged particles and seems to confirm the prevalence of a plasma-induced monomer fragmentation process at high frequencies.

Solid-state synthesis of conductive polymer PEDOT whiskers

A long-standing goal in synthetic polymer chemistry is to synthesize polymers with a well-defined microstructure with desired properties. We have reported here a novel synthesis method to produce conductive polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) whiskers in vapor phase polymerization, in which the monomer vapor diffuses into the oxidant matrix to initiate polymerization. Pencil-like whiskers are projected vertically to the surface of the PEDOT-stuffed film. The whiskers are of 0.5–1.0 µm in width and 5–10 µm in length. It is speculated that the polymerized PEDOTs builds internal compressive stresses in the oxidant matrix. To compensate for the stress, the reacted oxidant molecules along with the entangled PEDOTs are being reorganized to a lower internal energy state, thus leading an anisotropic whisker growth. Crystallites formation of oxidant acts as a driving force and the crystal structure of the PEDOT molecules define the shape of the whiskers. This new route of polymer whiskers formation is simple and cost-effective. Importantly, the PEDOT whiskers can be produced onto a large area of any surface.

A consistent formation free energy definition for multicomponent clusters in quantum thermochemistry

Quantum chemical calculations have proven to describe the thermodynamics of sub-nanometre clusters more accurately than the liquid drop model used in classical nucleation theory (CNT). However, the standard quantum chemical free energies of multicomponent clusters are fundamentally incompatible with the quantity appearing in the exponential of the CNT expression for the nucleation rate. The origin of this incompatibility is known to be in the statistical thermochemistry, but it is also connected to a much debated issue of self-consistency within CNT. Although these issues do not affect the main results of previous theoretical studies of nucleation, a thorough analysis and discussion about the nature of free energy in quantum chemistry of cluster formation has been missing. In this study, we present a consistent definition for the formation free energy using the law of mass action and a general equilibrium cluster distribution function, and apply this definition to gas-phase quantum thermochemical calculations. This internal consistency allows us to integrate the high-level thermochemical data to the basic framework of CNT and the liquid drop model contained therein. Moreover, based on our analysis, we derive a simple analytical expression for the steady-state nucleation rate compatible with the widely used numerical acdc model. As an illustrative example, the consistent formation free energies and nucleation rates are presented and analysed for atmospherically relevant H2SO4–NH3 clusters at various temperature and monomer vapour pressure conditions.

Nanoarchitectonics for conductive polymers using solid and vapor phases.

Conductive polymers have been extensively studied as functional organic materials due to their broad range of applications. Conductive polymers, such as polypyrrole, polythiophene, and their derivatives, are typically obtained as coatings and precipitates in the solution phase. Nanoarchitectonics for conductive polymers requires new methods including syntheses and morphology control. For example, nanoarchitectonics is achieved by liquid-phase syntheses with the assistance of templates, such as macromolecules and porous materials. This minireview summarizes the other new synthetic methods using the solid and vapor phases for nanoarchitectonics. In general, the monomers and related species are supplied from the solution phase. Our group has studied polymerization of heteroaromatic monomers using the solid and vapor phases. The surface and inside of solid crystals were used for the polymerization with the diffusion of the heteroaromatic monomer vapor. Our nanoarchitectonics affords to form homogeneous coatings, hierarchical structures, composites, and copolymers for energy-related applications. The concepts using solid and vapor phases can be applied to nanoarchitectonics for not only conductive polymers but also other polymers toward a variety of applications.

Effects of Quenching Gas Feeding on Silver Nanoparticle Synthesis by the Inductively Coupled Plasma Torch

In this article, the synthesis of silver nanoparticles by a radio frequency inductively coupled plasma torch is numerically investigated. Gas temperature and velocity magnitude profiles have been obtained with a fluid model by changing the quenching gas flow, driving frequency, and coupled power. A combinational numerical scheme using the particle method for microparticles and the nodal method for nanoparticles has been merged to the fluid simulation results. The Lagrangian scheme calculates the dynamics of large particles, including the Coulomb force. In contrast, the Eulerian nodal method calculates the dynamics of small nanoparticles synthesized through the nucleation of supersaturated monomer vapors. The particle size distribution at the plasma torch outlet is controllable by adjusting the temperature profiles and the residence time to relocate the condensation, evaporation, and nucleation reactions with the variation of the control parameters.

Solid-State Precursor Impregnation for Enhanced Capacitance in Hierarchical Flexible Poly(3,4-Ethylenedioxythiophene) Supercapacitors.

Increasing capacitance and energy density is a major challenge in developing supercapacitors for flexible portable electronics. A thick electrode with a high mass loading of active electronic material leads to high areal capacitance; however, the higher the loading, the higher the mechanical stiffness and ion diffusion resistance, thereby hampering development of flexible supercapacitors. Here, we show a chemical strategy that leads to a hierarchical electrode structure producing devices with both an exceedingly high areal capacitance and superior flexibility. We utilize α-Fe2O3 particles as an oxidant precursor for controlling oxidative radical polymerization of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) from the vapor phase. Our approach impregnates carbon cloth with α-Fe2O3 particles prior to monomer vapor exposure, resulting in state-of-the-art flexible nanofibrillar PEDOT supercapacitors possessing high areal capacitance (2243 mF/cm2 for two-electrode vs 6210 mF/cm2 for three-electrode) and high areal energy density (412 μWh/cm2).

Formation of a Polymer Shell of a Given Thickness on Surfaces of Submicronic Particles

A method using a vapor phase approach to formation of a polymer shell on the surfaces of submicron particles (SP) has been investigated. The method is based on the condensation of monomer vapors and their subsequent polymerization on surfaces of charged and dispersed SP. This method makes it possible to vary the thickness of the polymer shell from a few to hundreds of nanometers. This is achieved by choosing the ratio of the flow rates of SP and monomer in two miscible two-phase flows. It is shown that the polymer shell possesses good adhesion to the surfaces of the SP. Apparently, this will make it possible to introduce encapsulated particles, while maintaining the polymer shell, into the polymer matrix of thermoplastics at their softening temperature.

In-Situ Iodine Doping Characteristics of Conductive Polyaniline Film Polymerized by Low-Voltage-Driven Atmospheric Pressure Plasma.

In-situ iodine (I2)-doped atmospheric pressure (AP) plasma polymerization is proposed, based on a newly designed AP plasma reactor with a single wire electrode that enables low-voltage-driven plasma polymerization. The proposed AP plasma reactor can proceed plasma polymerization at low voltage levels, thereby enabling an effective in-situ I2 doping process by maintaining a stable glow discharge state even if the applied voltage increases due to the use of a discharge gas containing a large amount of monomer vapors and doping materials. The results of field-emission scanning electron microscopy (FE-SEM) and Fourier transformation infrared spectroscopy (FT-IR) show that the polyaniline (PANI) films are successfully deposited on the silicon (Si) substrates, and that the crosslinking pattern of the synthesized nanoparticles is predominantly vertically aligned. In addition, the in-situ I2-doped PANI film fabricated by the proposed AP plasma reactor exhibits excellent electrical resistance without electrical aging behavior. The developed AP plasma reactor proposed in this study is more advantageous for the polymerization and in-situ I2 doping of conductive polymer films than the existing AP plasma reactor with a dielectric barrier.

Effect of monomer concentration on adhesive strength of PTFE films treated with atmospheric-pressure nonthermal plasma graft polymerization

The effect of monomer concentration on the adhesive strength of polytetrafluoroethylene (PTFE) films treated with atmospheric-pressure nonthermal plasma (NTP) graft polymerization is investigated. In this study, we use acrylic acid (CH2=CHCOOH) as the monomer, and two types of evaporation vessels (named vessel I and vessel II) are prepared to generate the monomer vapor. Vessel II consists of a pair of evaporation containers that have half the evaporation area of vessel I. The monomer concentration in the treatment chamber is adjusted by controlling the monomer temperature. After purging the chamber with Ar, a jet of NTP is applied to the PTFE film surface at an Ar flow rate of 40 L/min. The treated PTFE films are then adhered to stainless steel plates using double-sided tape, and 90° peeling tests are conducted. It is found that the peeling strength increases with decreasing monomer concentration. When the acrylic acid temperature in vessel II is set to 55 °C, the monomer concentration is estimated to be 980 ppm, and the highest peeling strength per unit width of 4.85 N/mm is obtained under this condition. Despite the same monomer temperature used (60 °C), the peeling strength of the PTFE films treated in vessel II is higher than that of films treated in vessel I. Additionally, smaller data variation is observed when vessel II is used. This result is due to the uniform distribution of monomer concentration achieved when vessel II is used to generate the monomer vapor. Furthermore, information regarding the chemical bonding and elemental composition of the untreated and treated films is obtained using X-ray photoelectron spectroscopy measurements and the graft-polymerized surface morphologies are studied using scanning electron microscopy.

Vapor deposition of stable copolymer thin films in a batchiCVDreactor

AbstractThis study demonstrates the deposition of poly(ethylhexyl acrylate‐co‐ethylene glycol dimethacrylate) (P(EHA‐co‐EGDMA)) copolymer thin films in a batch type initiated chemical vapor deposition (iCVD) reactor. Crosslinked copolymers are desired for many applications because of their high stable properties. iCVD polymers derived by monomers bearing only one vinyl bond are usually linearly structured polymers and hence they are not durable, which is unfavorable for many real‐world applications. Robust crosslinked iCVD films can be produced with the help of crosslinkers. In a typical iCVD process, copolymer thin film is produced by constantly feeding monomer vapor and crosslinker into the reactor. The monomer/crosslinker ratio should be precisely controlled for fabrication of reproducible thin films. In order to eliminate problems caused by adjusting the flowrates of precursors, a closed‐batch type iCVD reactor was used for the first time in this study to produce copolymer thin films. The variation of precursors' partial pressures allowed control over the copolymer thin film structures. As compared with homopolymer, copolymers showed the better chemical and thermal stable properties. Almost 40% of the copolymer thin film remained on the substrate surface at an annealing temperature of 300°C, whereas the homopolymer film was completely removed at an annealing temperature of 280°C.

Oblique angle initiated chemical vapor deposition for patterning film growth

Initiated chemical vapor deposition (iCVD) can be used to deposit thin polymer films on a variety of substrates. In this work, the monomer precursor was introduced at an oblique angle to the substrate using an inlet extension, and the pattern of the resulting polymer film was studied as a function of deposition time, substrate temperature, monomer flow rate, reactor pressure, and vapor flow angle. The polymerizations of n-butyl acrylate, methacrylic acid, and 2-hydroxyethyl methacrylate were examined to determine the generality of the trends across several monomers. It was found that the monomer flow rate significantly affected the pattern of the deposited polymer by shifting the location of the thickest point in the films. Increasing the deposition time, decreasing the substrate temperature, and increasing the reactor pressure all increased the polymer deposition rate consistent with conventional iCVD; however, the pattern of the deposited polymer did not vary with these parameters. Computational analysis was used to determine how the inlet extension affects the pressure and velocity profiles within the reactor. The data demonstrate that the introduction of a monomer precursor at an oblique angle can be used to pattern polymer films during iCVD.

Integration of Polymer Synthesis and Self‐Assembly for Controlled Periodicity and Photonic Properties

AbstractMaterials chemistry and self‐assembly properties are usually treated separately, largely limiting the real‐time control of their nanostructures and resulting macroscopic properties in advanced self‐assembled materials. This study shows a model system that integrates synthesis and self‐assembly to achieve controlled periodicity and photonic properties in block copolymers (BCPs) at defined locations. First, the BCP thin films containing a pre‐dissolved photo‐initiator are swollen with monomer vapors. Upon exposure to UV light, the photoreaction synthesizes homopolymers within the film, which simultaneously blend with the BCPs and modify the periodicity in the exposed regions. This technique is successfully adapted to cylindrical polystyrene‐b‐polyisoprene‐b‐polystyrene and lamellar polystyrene‐b‐poly(2‐vinyl pyridine) BCP thin films. This capability is especially useful in the practical application of photonic crystals, where it is shown that the stop band position of polystyrene‐b‐quaternized‐poly(2‐vinyl pyridine) photonic gel films can be successfully modulated in situ. A large‐scale pattern is then fabricated by using a photomask. This study provides a model system for integrating materials synthesis and self‐assembly to achieve spatially defined control over structural periodicity and macroscopic properties in self‐assembled materials.

Continuous aerosol photopolymerization to coat de-agglomerated nanoparticles

A novel continuous aerosol photopolymerization technique to coat nanoparticles that have been previously de-agglomerated is presented. After de-agglomeration in a jet-impactor assisted fluidized bed, monomer vapors are condensed onto the surface of aerosolized nanoparticles via heterogeneous condensation. Photopolymerization is initiated through exposure to UV light. To demonstrate the process, titanium dioxide (TiO2) and methyl methacrylate (MMA) were selected as nanoparticle and organic monomer, respectively. We demonstrated this light-based technique, operated at ambient pressure and room temperature, is able to graft a PMMA-like film with a thickness of 1.5 nm on the surface of nanoparticles, confirmed by TEM and FTIR. XPS analysis confirmed formation of covalent bonds with the TiO2 surface, indicating a surface-initiated photopolymerization. Particle size measurements in suspension illustrated the efficiency of the de-agglomeration and subsequent coating process, as coated particles remained smaller than bare particles. UV–Vis absorbance spectra show that the coating facilitates dispersion in non-polar solvents. Finally, long-term stability experiment confirmed the suspension stability is enhanced not only because of the reduction of agglomerate sizes, but also as a result of the carbon coating that improves the interfacial interactions among particles, and between particles and solvent. This technique can be easily combined with any continuous inorganic nanoparticle generation process as a solvent-free post-synthesis approach to impart a functional coating.

Vapor Deposition of Functional Porous Polymer Membranes

The fabrication of porous polymer membranes is currently dominated by solution-phase processing techniques. We recently developed a versatile solventless method to deposit porous polymer membranes. In this paper, we will review the mechanism that governs the fabrication process, the advantages and capabilities of the technique, and potential applications for these membranes. In the fabrication process, low substrate temperatures are used to transition the monomer vapor into solid microstructures which are then polymerized using a thermally cleavable vapor-phase initiator. This paper covers the effect of processing parameters such as time and temperature on the molecular weight distribution of the polymer and the porosity of the membranes. We will discuss several methods for patterning and cross-linking the membranes, and we will demonstrate that asymmetric membranes with varying chemical functionalities and thicknesses can be fabricated. Finally, we will review potential applications for these membranes.

Synthesis of Submicron PEDOT Particles of High Electrical Conductivity via Continuous Aerosol Vapor Polymerization.

Current state-of-the-art synthetic strategies produce conducting polymers suffering from low processability and unstable chemical and/or physical properties stifling research and development. Here, we introduce a platform for synthesizing scalable submicron-sized particles of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The synthesis is based on a hybrid approach utilizing an aerosol of aqueous oxidant droplets and monomer vapor to engineer a scalable synthetic scheme. This aerosol vapor polymerization technology results in bulk quantities of discrete solid-state submicron particles (750 nm diameter) with the highest reported particle conductivity (330 ± 70 S/cm) so far. Moreover, particles are dispersible in organics and water, obviating the need for surfactants, and remain electrically conductive and doped over a period of months. This enhanced processability and environmental stability enable their incorporation in thermoplastic and cementitious composites for engineering chemoresistive pH and temperature sensors.

Sonochemically Initiated RAFT Polymerization in Organic Solvents

Sonochemically initiated RAFT polymerization (sonoRAFT) in organic solvents is presented for the first time. Acoustic cavitation, induced by high-frequency ultrasound (US) (490 kHz), caused pyrolysis of organic solvent molecules providing a source of initiating radicals. In this way, polymers could be prepared without conventional radical initiators (e.g., AIBN) or additives (e.g., piezoelectric nanoparticles). The polymerization of acrylates and acrylamides was well controlled with the prepared polymers displaying good agreement between theoretical and experimental molecular weights with low dispersities. Methacrylates were found to be less controlled. Several factors were found to influence the final monomer conversion (25–92%) and the upper limit of molecular weight (20–30 kDa) such as the monomer vapor pressure and solubility, solvent choice, and polymer type. No polymerization occurred in the absence of US demonstrating excellent temporal control, and the polymer products were found to possess high c...