Polymer Film Growth Research Articles

Surface Evolution of Polymer Films Grown by Vapor Deposition: Growth of Local and Global Slopes of Interfaces.

The kinetic roughening of polymer films grown by vapor deposition polymerization was analyzed using the widely accepted classification framework of "generic scaling ansatz" given for the structure factor. Over the past two decades, this method has played a pivotal role in classifying diverse forms of dynamic scaling and understanding the mechanisms driving interface roughening. The roughness exponents of the polymer films were consistently determined as α=1.25±0.09, αloc=0.73±0.02, and αs=0.99±0.06. However, the inability to unambiguously assign these roughness exponent values to a specific scaling subclass prompts the proposal of a practical alternative. This report illustrates how all potential dynamic scaling can be consistently identified and classified based on the relationship between two temporal scaling exponents measured in real space: the average local slope and the global slope of the interface. The intrinsic anomalous roughening class is conclusively assigned to polymer film growth characterized by anomalous "native (background slope-removed) local height fluctuations". Moreover, the new analysis reveals that interfaces exhibiting anomalous scaling, previously classified as intrinsic anomalous roughening, could potentially belong to the super-rough class, particularly when the spectral roughness exponent αs is equal to 1.

Biphasic nanocomposite films of polypyrrole and poly(3,4-ethylene dioxythiophene) using a surface-tethered dopant strategy

Using a newly invented surface-tethered dopant approach for the electrochemical polymerization growth of conductive polymer films, nanocomposites are created consisting of two distinct phases of polypyrrole (PPy) and Poly(3,4-ethylene dioxythiophene) (PEDOT). The growth of the conductive nanocomposite films takes advantage of the unique way in which a conductive polymer film forms when grown using a surface-tethered dopant, starting out as a highly nanoporous film that gradually becomes more and more solid as additional polymer deposition occurs preferentially within the nanopores rather than at the films outer surface. Nanocomposite films can thus be fabricated simply and controllably by first growing one nanoporous conductive polymer film followed by the deposition of a second conductive polymer within the nanopores of the first. This study investigates the morphological and electrochemical properties of nanocomposite films grown using a surface-tethered dopant and how these properties are affected by simple changes in electrochemical polymerization parameters.

Directional formation of microtubes by soft-template electropolymerization from fully conjugated triphenylamine-based monomers

Microtubular structures have been prepared by soft-template electropolymerization of conjugated organic monomers with the aim to mimic the strong water-adhesive forces of gecko foot or rose petals. Water-saturated solvent of low water solubility (dichloromethane) was used to form a micellar solution stabilized by tetrabutylammonium perchlorate as the electrolyte and the surfactant, in which case the formation of nanotubes was particularly efficient. The studied monomers were built from a triphenylamine core conjugated with three arms differing by their structure and positions: (i) 2- or 3-positions in the thiophene arms or (ii) carbazole arms attached to para, meta or ortho-positions of the benzene ring of the core. The formation of microtubes is due to preferential growth of polymer films and an aggregation of formed polymers/oligolymers in one direction (1D) facilitated by π–stacking interactions. The key factors influencing on the surface morphologies (monomer structures and reactivity, electrodeposition conditions, etc) are discussed. Impressive results have been obtained in studies of carbazole-containing monomers and the effect of regioisomerism in the monomers (the position of the carbazole attachment to the core). Extremely long microtubes (tens to >100 μm length, diameter ≈ 1.0–1.5 μm) were formed on the electrode surface from the monomer N-Ph-p-Cb with the carbazole attachment in the para-position. Wettability analysis showed highly hydrophobic surfaces with apparent contact angles up to 154.0° and extremely strong water adhesion comparable to rose petals or gecko feet. Such coatings can find applications in water-harvesting systems, sensing platforms or electrochemical analyses.

Ferroelectric polarization of β-polyvinylidene fluoride as control and mitigator of infectious organisms

In this work, Polyvinylidene fluoride (PVDF), a ferroelectric polymer thin film, was prepared by the solution casting method. The growth of polymer films was optimized to achieve the ferroelectric β–phase with PVDF and, most importantly, ferroelectric domains with dominant planar polarization components. The ferroelectric polarization of these polymers is known to hold surface charges with/without field. The polymer is expected to interact with microbial organisms whose physiological metabolism depends on surface charges. The current COVID-19 pandemic has motivated us to carry out a fundamental study of the interaction between the polarization of the ferroelectric polymers and microbes. The antimicrobial studies were performed, making these polymer films interact with bacterial, viral, and fungal growth environments. Electroded PVDF films were kept in contact with bacterial colonies, and a dc-voltage of 1.5 V was applied across the electrodes. The film was subjected to 1.5 V and kept in contact with the culture before the growth initiation, and the microbial growth was hindered entirely. It never occurred either beneath or over the surface of the films. Thus, in the presence of the electric field, the microbial growth was inhibited, even in a conducive environment.

Self‐Wrinkling Vapor‐Deposited Polymer Films with Tunable Patterns

AbstractMaterials with complex curvature and micro‐structured surface topography allow scientists to replicate surfaces observed in nature. Initiated chemical vapor deposition is used to grow polymer films on substrates of various 3D shapes which exhibit wrinkling during film growth, termed self‐wrinkling. Self‐wrinkling avoids separate film growth and compression steps and more‐closely mimics processes observed in nature. The self‐wrinkling process is elucidated on flat elastic substrates, revealing control over the amount of compressive stress by changing deposition conditions. Next, a study of films grown on liquid substrates with interface profiles that either resemble cylinders or contain repeating concave cones, saddles, and bowls affirms the principle that the wrinkle roundness increases with interface curvature. The selection of high versus low stress generating conditions allows for the choice of the wrinkle pattern to be directed by either the stress concentration at boundaries or the substrate curvature. Experiments confirm the observation from simulations by other authors that on the inside of a torus, the lowest energy ridge wrinkle state is oriented around the major axis. The ability to control the character of wrinkle patterns via changes to the local and global substrate shape provides a route to generate materials with contrived surface topography.

Poly(safranine T)-deep eutectic solvent/copper oxide nanoparticle-carbon nanotube nanocomposite modified electrode and its application to the simultaneous determination of hydroquinone and catechol

This work presents the combined use of safranine (SF) as a redox polymer and multiwalled carbon nanotubes (MWCNT)-copper oxide nanoparticles (CuO) in the development of a novel sensor for the simultaneous analysis of hydroquinone (HQ) and catechol (CAT). Electropolymerisation of SF was carried out in acid-doped ethaline deep eutectic solvent to prepare poly(safranine) (PSFEthaline) film electrodes with three different nanostructured architectures on pencil graphite electrodes (PGE) as electrode substrate. The polymerisation was done after nanomaterial surface modification to obtain PSFEthaline-HCl/MWCNT/PGE, PSFEthaline-HCl/CuO/PGE, and PSFEthaline-HCl/MWCNT-CuO/PGE. The synthesis, preparation, and characterisation of PSF film-coated electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy to investigate the contribution of each nanomaterial on sensor performance. The best result for polymer film growth was obtained with PSF electrodeposited on MWCNT-CuO/PGE in HCl doped-ethaline. The analytical performance of the modified electrode was evaluated for electrochemical sensing of HQ and CAT by differential pulse voltammetry in aqueous Britton-Robinson buffer solution. Due to the combined effect of MWCNT-CuO nanocomposite film and PSF, the modified electrode sensor provided sensitive and selective detection of HQ and CAT with good peak separation. The simultaneousdetermination of HQ and CAT in both tap water and milk samples was successfully carried out to demonstrate the analytical applicability of the sensor. The sensor could be a promising analytical approach for monitoring the amount of HQ and CAT in real samples.

Electrochemical DNA Sensor Based on Poly(Azure A) Obtained from the Buffer Saturated with Chloroform.

Electropolymerized redox polymers offer broad opportunities in detection of biospecific interactions of DNA. In this work, Azure A was electrochemically polymerized by multiple cycling of the potential in phosphate buffer saturated with chloroform and applied for discrimination of the DNA damage. The influence of organic solvent on electrochemical properties of the coating was quantified and conditions for implementation of DNA in the growing polymer film were assessed using cyclic voltammetry, quartz crystal microbalance, and electrochemical impedance spectroscopy. As shown, both chloroform and DNA affected the morphology of the polymer surface and electropolymerization efficiency. The electrochemical DNA sensor developed made it possible to distinguish native and thermally and chemically damaged DNA by changes in the charge transfer resistance and capacitance.

Surface-Initiated Ring-Opening Metathesis Polymerization (SI-ROMP): History, General Features, and Applications in Surface Engineering with Polymer Brushes

Surface-Initiated Ring-Opening Metathesis Polymerization (SI-ROMP) has attracted great attention in the past two decades because of its high efficiency in decorating material surfaces with functional polymer brushes. To fill the vacancy of review articles in SI-ROMP, this article is aimed at giving an overview of the history, the general features and procedures, and applications of SI-ROMP, guiding future researchers in this field. In general, SI-ROMP consists of three main steps: surface functionalization with olefin anchors, attachment of catalyst to the surface, and polymerization from the surface. Several metal-based catalysts for ROMP in solution have been developed, but most SI-ROMP reactions use the ruthenium-based Grubbs catalysts. SI-ROMP enables the rapid growth of polymer films on a large variety of substrates such as silica, gold, graphene oxides, carbon nanotubes, metal oxide nanowires, and composite polymer membranes. There are many methods to characterize these polymer brushes. In addition, some novel techniques have been developed to precisely control the surface polymer growth and lead to polymer films with unique structures and functions. Up to this day, SI-ROMP can be applied to the surface engineering of many novel materials, including ultrahydrophobic surfaces, microfluidic channels, electric devices, ion exchange media, and responsive surfaces.

Effects of Standing Waves on the Growth and Stability of Vapor Deposited Polymer Films

We demonstrate that liquid substrates can be agitated in situ via sound during vapor phase polymerization. The effects of standing waves on the growth of polymer films at the vapor–liquid interface were studied by depositing poly(1H,1H,2H,2H-perfluorodecyl acrylate) and poly(1H,1H,2H,2H-perfluorodecyl acrylate-co-ethylene glycol diacrylate) onto an agitated silicone oil lens. It was found that continuous polymer films could be formed by the addition of a cross-linker. We also tested the mechanical stability of the polymer films on agitated liquids and found that the robustness of the films increased with the addition of cross-linker and increasing film thickness.

Superwettability-Based Interfacial Chemical Reactions.

Superwetting interfaces arising from the cooperation of surface energy and multiscale micro/nanostructures are extensively studied in biological systems. Fundamental understandings gained from biological interfaces boost the control of wettability under different dimensionalities, such as 2D surfaces, 1D fibers and channels, and 3D architectures, thus permitting manipulation of the transport physics of liquids, gases, and ions, which profoundly impacts chemical reactions and material fabrication. In this context, the progress of new chemistry based on superwetting interfaces is highlighted, beginning with mass transport dynamics, including liquid, gas, and ion transport. In the following sections, the impacts of the superwettability-mediated transport dynamics on chemical reactions and material fabrication is discussed. Superwettability science has greatly enhanced the efficiency of chemical reactions, including photocatalytic, bioelectronic, electrochemical, and organic catalytic reactions, by realizing efficient mass transport. For material fabrication, superwetting interfaces are pivotal in the manipulation of the transport and microfluidic dynamics of liquids on solid surfaces, leading to the spatially regulated growth of low-dimensional single-crystalline arrays and high-quality polymer films. Finally, a perspective on future directions is presented.

Molecular engineered conjugated polymer with high thermal conductivity.

Traditional polymers are both electrically and thermally insulating. The development of electrically conductive polymers has led to novel applications such as flexible displays, solar cells, and wearable biosensors. As in the case of electrically conductive polymers, the development of polymers with high thermal conductivity would open up a range of applications in next-generation electronic, optoelectronic, and energy devices. Current research has so far been limited to engineering polymers either by strong intramolecular interactions, which enable efficient phonon transport along the polymer chains, or by strong intermolecular interactions, which enable efficient phonon transport between the polymer chains. However, it has not been possible until now to engineer both interactions simultaneously. We report the first realization of high thermal conductivity in the thin film of a conjugated polymer, poly(3-hexylthiophene), via bottom-up oxidative chemical vapor deposition (oCVD), taking advantage of both strong C=C covalent bonding along the extended polymer chain and strong π-π stacking noncovalent interactions between chains. We confirm the presence of both types of interactions by systematic structural characterization, achieving a near-room temperature thermal conductivity of 2.2 W/m·K, which is 10 times higher than that of conventional polymers. With the solvent-free oCVD technique, it is now possible to grow polymer films conformally on a variety of substrates as lightweight, flexible heat conductors that are also electrically insulating and resistant to corrosion.

In situ investigation of poly(3,4-ethylenedioxythiophene) film growth during liquid phase deposition polymerization

Liquid phase deposition polymerization (LPDP) is a recently reported method suitable for preparation of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT), with some similarities to vapor phase polymerization except the polymer film growth at the gas-solid boundary is replaced with growth at the liquid-solid interfacial layer. Film growth process by LPDP method is largely unexplored compared to vapor phase polymerization and it is essential to understand the film formation process in order to use the full potential that this new method entails in preparation of highly conductive PEDOT films. In this study, in situ measurements of electrical resistance and transmittance were used to monitor these key parameters of the polymerizing films during LPDP, revealing a three-stage polymerization process. Films with conductivity of 362 S/cm were prepared and the detailed information from in situ measurements opens up research directions to further improve the properties of the PEDOT films. Cyclic voltammetry was used for investigating the electrochemical behavior of the PEDOT films.

Growth Processes and Morphological Evolution of Polyaniline Film During Potentiostatic Growth

We have investigated the potentiostatic growth processes and morphological evolution of polyaniline film on an indium tin oxide (ITO) electrode. The current‐time transient shows the existence of three stages in two growth regimes. As the initial formation of polyaniline is extremely fast, the current increases rapidly with time. Subsequently, the current increase is slowed down due to the decomposition reaction competes with polymerization. Polyaniline film grown rapidly on a bare ITO electrode shows a compact two‐dimensional layer with a granular structure. The granules start to grow upward on the first layer, with one‐dimensional growth resulting in a loosely bound and open fibrous structure. Further polymer film growth results in surface aggregates due to the increased degradation rate. Visualization of the surface morphology and the roughness of the grown film are consistent with the proposed growth processes.

Conducting polymer microcontainers for biomedical applications.

Advancement in the development of metallic-based implantable micro-scale bioelectronics has been limited by low signal to noise ratios and low charge injection at electrode-tissue interfaces. Further, implantable electrodes lose their long-term functionality because of unfavorable reactive tissue responses. Thus, substantial incentive exists to produce bioelectronics capable of delivering therapeutic compounds while improving electrical performance. Here, we have produced hollow poly(pyrrole) microcontainers (MCs) using poly(lactic-co-glycolic) acid (PLGA) as degradable templates. We demonstrate that the effective surface area of the electrode increases significantly as deposition charge density is increased, resulting in a 91% decrease in impedance and an 85% increase in charge storage capacity versus uncoated gold electrodes. We also developed an equivalent circuit model to quantify the effect of conducting polymer film growth on impedance. These MC-modified electrodes offer the potential to improve the electrical properties of implantable bioelectronics, as well as provide potential controlled release avenues for drug delivery applications.

Influence of organic surface chemistry on the nucleation of plasma deposited SiOx films

The nucleation and film growth of SiOx plasma polymer films as a function of the substrate surface chemistry are analysed by a combination of microscopic, spectroscopic and electrochemical techniques. Self-assembled organothiol monolayers (SAMs) surfaces with different terminating groups (methyl, carboxyl- and trimethoxysilane groups) on Au(111) serve as a model system. Ultra-thin SiOx films with thickness ranging from 0.4 to 1.4 nm were deposited by microwave plasma in a mixture of HMDSO and O2. The changes in surface, interface and thin film chemistry are characterized by PM-IRRAS. Cyclic voltammetry with ferricyanide as a redox system is used to probe the defect density of the bare SAMs and the SiOx-covered SAMs. Furthermore, the evolution of the SiOx surface morphology for increasing film thickness as function of the substrate chemical termination is investigated by AFM. A strong influence of the surface chemistry on the SiOx nucleation and film growth is observed. While the methyl and carboxyl terminated SAMs are degraded during the nucleation leading to defect rich ultrathin films, the trimethoxysilane group protects the aliphatic chain of the SAM and leads to much better barrier properties of the ultra-thin SiOx-films. A mechanistic explanation of the results is provided.

In Situ Growth of Flexible Polyphenylene-Conjugated Microporous Polymer Films for Fluorescence Detection of the Total Quantity of Developing Agents and Their Oxidation Products

Conjugated microporous polymers (CMPs) are a kind of porous skeleton polymers, which are characterized by extended conjugated skeletons, large specific surface area and structure stability. In this work, a facile and versatile method was developed to fabricate flexible conjugated microporous polymer films for fast detecting the total quantity of developing agents and their oxidation products. Conjugated microporous polymer films were synthesized through in situ one-step approach by Suzuki coupling reaction. With such merits such as intense luminescence, easy synthesis and disposability, the polymer films were employed to detect developers based on fluorescence quenching in the printing wastewater. A linear response to p-benzoquinone, oxidation product of developers, was obtained in the range of 0.05–0.5 μmol·L−1, with a detection limit of 0.015 μmol·L−1. The strategy for in situ growth of flexible polyphenylene-conjugated microporous polymer (PP-CMP) films seems to be a very portable and general method for meeting different analytic purposes.

Kafirin polymer film for enteric coating on HPMC and Gelatin capsules

Protein-based materials have attracted a tremendous attention to the growth of polymer films and protein-based coating. Efficiency of Kafirin film and effect of Kafirin film as an enteric coating for drug release was studied. The cast films with varying plasticizer concentrations (polyethylene glycol-300) were tested for mechanical tests (Tensile, Young’s, Elongation) and further analyzed with DSC and TGA analysis. Swelling behavior and FTIR were performed to ensure medium uptake and inter- and intra-molecule structural changes. All together for enteric coating, capsules filled with Paracetamol were dip coated in Kafirin solution with 20, 30, and 40% of PEG plasticizer of drug release study. Dissolution studies demonstrated zero release upon exposure to 0.1 N HCl of pH 1.2 for initial 2 h, and gradual release was observed upon exposure to phosphate buffer of pH 6.8. The effect of plasticizer concentration was noticeable in the case of HPMC capsules, and drug release declined with the increasing plasticizer content. Whereas, in case of Gelatin opposite results were obtained. This work has shown that Kafirin protein has a potential for use as an enteric coating for drug delivery application.

Entropy-Driven Conformational Control of α,ω-Difunctional Bidentate-Dithiol Azo-Based Adsorbates Enables the Fabrication of Thermally Stable Surface-Grafted Polymer Films.

Thermally stable radical initiator monolayers were prepared from uniquely designed α,ω-difunctional adsorbates with bidentate headgroups for the growth of nanoscale polymer films on metal surfaces. The length of the spacer separating the bidentate headgroups was varied to afford 4,4'-(diazene-1,2-diyl)bis(N-(16-(3,5-bis(mercaptomethyl)phenoxy)hexadecyl)-4-cyanopentanamide) (B16), 4,4'-(diazene-1,2-diyl)bis(N-(16-(3,5-bis(mercapto-methyl)phenoxy)decyl)-4-cyanopentanamide) (B10), and 4,4'-(diazene-1,2-diyl)bis(N-(4-(3,5-bis(mercaptomethyl)phenoxy)butyl)-4-cyanopentanamide) (B4). The structural features of the self-assembled monolayers (SAMs) derived from B16, B10, and B4 were characterized by X-ray photoelectron spectroscopy (XPS), ellipsometry, and polarization modulation infrared reflection-absorption spectroscopy (PM-IRRAS) and compared to those derived from an analogous α,ω-difunctional adsorbate with monodentate headgroups, 4,4'-(diazene-1,2-diyl)bis(4-cyano-N-(16-mercaptohexadecyl)pentanamide (M). These studies demonstrate that the conformation (i.e., hairpin vs standing up) of the bidentate initiator adsorbates on gold surfaces was easily controlled by adjusting the concentration of the adsorbates in solution. The results of solution-phase thermal desorption tests revealed that the radical initiator monolayers generated from B16, B10, and B4 exhibit an enhanced thermal stability when compared to those generated from M. Furthermore, a study of the growth of polymer films was performed to evaluate the utility of these new bidentate adsorbate SAMs as film-development platforms for new functional materials and devices. Specifically, surface-grafted polystyrene films were successfully generated from SAMs derived from B16. In contrast, attempts to grow polystyrene films from SAMs derived from M under a variety of analogous conditions were unsuccessful.

Additive Growth and Crystallization of Polymer Films

We demonstrated a polymeric thin film fabrication process in which molecular-scale crystallization proceeds with additive film growth, by employing an innovative vapor-assisted deposition process termed matrix-assisted pulsed laser evaporation (MAPLE). In comparison to solution-casting commonly adopted for the deposition of polymer thin films, this physical vapor deposition (PVD) methodology can prolong the time scale of film formation and allow for the manipulation of temperature during deposition. For the deposition of molecular and atomic systems, such a PVD manner has been demonstrated to facilitate molecular ordering and delicately manipulate crystalline morphology during film growth. Here, using MAPLE, we deposited thin films of a model polymer, poly(ethylene oxide) (PEO), atop a temperature-controlled substrate with an average growth rate of less than 10 nm/h. The mechanism of deposition is sequential addition of nanoscale liquid droplets. We discovered that the deposition process leads to the form...

Kinetics of growth and plasma destruction of polymer films deposited in a glow discharge in methane

The kinetics of the deposition of polymer films in methane plasma and the kinetics of their plasma destruction in argon and oxygen has been investigated experimentally. It has been shown that, in the studied range of conditions, both processes are stationary and proceed in the kinetic mode; moreover, the dependences of the deposition rate on the external parameters of the discharge correspond to a radical or radicalionic polymerization mechanism. It has been proposed that the rate of polymer film destruction in the argon and oxygen plasma is controlled by heterogeneous processes with the participation of intrinsic plasma ultraviolet radiation.