Initiated Chemical Vapor Deposition Kinetics of Poly(4-aminostyrene)

Vapor Deposition of Polymer Structures: From 2D Surface Coatings and Surface Microstructures to 3D Building Blocks and Structural Monoliths

Vapor deposition of polymers offers precise control over polymerization, enabling the creation of uniform thin films, conformal coatings, and complex geometries. These methods produce pinhole-free films with tailored physical and chemical properties while addressing the limitations of conventional solution-based techniques. Recent advancements have extended polymer fabrication beyond thin films to include surface patterns, microstructures, and 3D architectures. This review provides an overview of vapor deposition methods, polymerization mechanisms, and processes for fabricating microstructures and 3D architectures. This review highlights the progress of vapor-deposited polymers, from simple coatings to complex, multifunctional structures. By integrating precise structural control with chemical versatility, these advancements open new opportunities for innovative material design and address the growing demands of modern applications.

Analysis of the Vapor Phase Dynamics during iCVD: Free Radical Initiation by tert-Butyl Peroxide

While initiated chemical vapor deposition (iCVD) has been used in a wide range of fundamental and applied studies in the past two decades, little is known about the reactive vapor phase, leading to inconsistent treatment of the initiation process in the existing literature. Di-tert-butyl peroxide (TBPO) is commonly used as an initiator in iCVD by leveraging radical intermediates produced during thermal decomposition. Despite its widespread use, no models exist for TBPO decomposition in iCVD. To bridge this knowledge gap, we integrated the Pirani pressure gauge into the iCVD setup to measure the real-time vapor-phase composition in the reactor. After establishing the relationship between the Pirani gauge pressure and composition from batch data, we use it to quantify the fractional conversion of pure TBPO in the reactor in the continuous mode. We find that under iCVD conditions, TBPO fully decomposes to acetone and ethane following a first-order Arrhenius kinetics. This means that (i) the partial pressures of radicals are small (below the detection limit of the Pirani gauge) and (ii) there is a stoichiometric increase in the number of gas molecules in the reactor, which has not been accounted for in existing models. This causes the overestimation of monomer pressure, which is a key parameter in the current understanding of iCVD. We analyze the decomposition of TBPO in the presence of cyclohexyl methacrylate (CHMA) monomer suggesting that the monomer does not react appreciably in the vapor phase. To show how this model of the vapor phase is related to the deposition kinetics, we compare our data to the classical linear polymerization theory, which describes free radical polymerization of CHMA in solution and finds an acceptable fit. Notably, in Arrhenius plots of the deposition rate, there is a well-documented but unexplained decrease in the apparent activation energy at high filament temperature (>300 °C), which is predicted by our models.

Ion-conducting polymer thin films via chemical vapor deposition polymerization

Ion-conducting polymers (ICPs), benefiting from the movement of ions instead of electrons, have attracted significant interest in various scientific and technological fields, including drug delivery, water purification, and electrochemical devices. This review aims to highlight recent advances in the synthesis of ICP thin films, with a particular focus on chemical vapor deposition (CVD) technologies. Traditional solution-based methods for ICP thin film deposition face challenges, including non-uniformity, low-throughput manufacturing, and the generation of hazardous wastes. In comparison, CVD eliminates the drawbacks associated with solution-based processes. They offer precise control film properties, including high purity, conformal coating, delicate control over thickness, etc. This review organizes the latest developments in CVD-based ICP synthesis, based on material properties and the synthesis strategy, into direct deposition and post-polymerization modification, ionogels, hydrogels, and ultrathin siloxane or silazane-based polymer films. By providing an up-to-date review of the materials and synthesis, we aim to position CVD polymerization as an effective strategy for future materials development/production and device fabrication in energy, sustainability, and healthcare where ion conductivity is desired.

Advances in Antibacterial Polymer Coatings Synthesized via Chemical Vapor Deposition

Biofouling is a major issue across various industries ranging from healthcare to the production of food and water and transportation. Biofouling is often induced or mediated by environmental microbes, such as bacteria. Therefore, developing antibacterial coatings has been an essential focus of recent research on functional polymer thin films. To achieve high film quality, vapor-phase techniques represent promising alternatives to traditional solution-based methods, especially for the design and synthesis of antibacterial polymer coatings, as they enable highly uniform, chemically precise, and substrate-independent coatings. This Perspective examines the potential of vapor-phase polymerization techniques to create novel antibacterial polymer coatings. Current advancements in the design of antifouling, bactericidal, antibiofilm, and multifunctional coatings via vapor-phase techniques are organized based on their action mechanisms and design principles. The opportunities and challenges associated with implementing vapor-phase polymerization for developing antibacterial coatings are highlighted.

Enhancing the Kinetics of Vapor-based Polymerization by Pulsed Filament Approach

Initiated chemical vapor deposition is a versatile technique for synthesizing conformal polymer films on both planar and porous surfaces. It can retain functional groups and avoid undesired cross-linking. However, there is still room for enhancing its performance without altering the feed parameters. Here, we investigate a pulsed iCVD approach to improve the deposition process, achieved by switching on and off the resistively heated filament periodically. By strategically switching off the filament, a shortage of thermally activated primary radicals was created, which allowed uninterrupted chain propagation with fewer termination reactions and potentially increased monomer conversion rates. This has caused significantly faster deposition kinetics with a higher molecular weight and longer chain length for poly(glycidyl methacrylate) compared to continuous deposition. Spectra analyses confirmed that the functionality and stoichiometry ratios remained intact throughout the pulsed deposition process. The pulsed iCVD method is therefore a competitive and sustainable tool, demonstrating fast deposition kinetics and a well-preserved functionality.

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.

Glucose-Responsive Boronic Acid Hydrogel Thin Films Obtained via Initiated Chemical Vapor Deposition

Glucose-responsive materials are of great importance in the field of monitoring the physiological glucose level or smart insulin management. This study presents the first vacuum-based deposition of a glucose-responsive hydrogel thin film. The successful vacuum-based synthesis of a glucose-responsive hydrogel may open the door to a vast variety of new applications, where, for example, the hydrogel thin film is applied on new possible substrates. In addition, vacuum-deposited films are free of leachables (e.g., plasticizers and residual solvents). Therefore, they are, in principle, safe for in-body applications. A hydrogel made of but-3-enylboronic acid units, a boronic acid compound, was synthesized via initiated chemical vapor deposition. The thin film was characterized in terms of chemical composition, surface morphology, and swelling response toward pH and sucrose, a glucose–fructose compound. The film was stable in aqueous solutions, consisting of polymerized boronic acid and the initiator unit, and had an undulating texture appearance (rms 2.1 nm). The hydrogel was in its shrunken state at pH 4–7 and swelled by increasing the pH to 9. The pK_a was 8.2 ± 0.2. The response to glucose was observed at pH 10 and resulted in thickness shrinking.

Surfaces with Antifouling-Antimicrobial Dual Function via Immobilization of Lysozyme on Zwitterionic Polymer Thin Films

Due to the emergence of wide-spread infectious diseases, there is a heightened need for antimicrobial and/or antifouling coatings that can be used to prevent infection and transmission in a variety...