Synthesis of Polymer Nanoparticles via Vapor Phase Deposition onto Liquid Substrates

Accessing Thin Film Wetting Regimes during Polymer Growth by Initiated Chemical Vapor Deposition

We investigate the growth of a fluorinated polymer via initiated chemical vapor deposition onto a suite of isotropic and mesogenic liquids with a range of refractive indices. The polymer morphology at fluid interfaces was found to deviate from conformal films predicted by the positive spreading coefficient, and the resulting morphology is attributed to long-range van der Waals interactions during the deposition process. Experiments systematically vary the deposition conditions and compare the liquid phase (isotropic or nematic) to evaluate the effect of kinetic factors and the liquid substrate phase on the interfacial polymer morphology and spatial organization.

Vapor Deposition of Silicon-Containing Microstructured Polymer Films onto Silicone Oil Substrates

In this study, a silicon-containing cross-linked polymer, poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane-co-ethylene glycol diacrylate) (p(V4D4-co-EGDA)), was deposited onto high-viscosity silicone oil using initiated chemical vapor deposition (iCVD). The ratio of the feed flow rate of V4D4 to EGDA was systematically studied, and the chemical composition and morphology of the top and bottom surfaces of the films were analyzed. The films were microstructured, and the porosity and thickness of the films increased with increasing V4D4 content. The top of the film was composed of densely packed and loosely packed microstructured regions. X-ray photoelectron spectroscopy on the top and bottom surfaces of the films showed a heterogeneous chemical composition along the thickness of the film, with higher silicon content on the top surface compared to that on the bottom surface. To the best of our knowledge, this is the first study of iCVD deposition of a silicon-containing polymer film onto silicone oil. The results of this study can be used for the synthesis of polymer precursor films for the fabrication, via pyrolysis, of silicon-based inorganic membranes for use in hydrogen production using silicone oil to prevent infiltration of monomer into the underneath membrane support structure during vapor deposition.

Plasma Processing of Low Vapor Pressure Liquids to Generate Functional Surfaces

The concept of depositing solid films on low-vapor pressure liquids is introduced and developed into a top-down approach to functionalize surfaces by attaching liquid polyethylene glycol (PEG). Solid-liquid gradients were formed by low-pressure plasma treatment yielding cross-linking and/or deposition of a plasma polymer film subsequently bound to a flexible polydimethylsiloxane (PDMS) backing. The analysis via optical transmission spectroscopy (OTS), optical, confocal laser scanning (CLSM) and scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) as well as by water contact angle (WCA) measurements revealed correlations between optical appearance, chemical composition and surface properties of the resulting water absorbing, covalently bound PEG-functionalized surfaces. Requirements for plasma polymer film deposition on low-vapor pressure liquids and effective surface functionalization are defined. Namely, the thickness of the liquid PEG substrate was a crucial parameter for successful film growth and covalent attachment of PEG. The presented method is a practicable approach for the production of functional surfaces featuring long-lasting strong hydrophilic properties, making them predestined for non-fouling or low-friction applications.

Synthesis of Functional Particles by Condensation and Polymerization of Monomer Droplets in Silicone Oils

We studied the synthesis of poly(4-vinylpyridine) and poly(2-hydroxyethyl methacrylate) polymer particles in silicone oil using a sequential vapor phase polymerization method in which monomer droplets were first condensed onto a layer of silicone oil and subsequently polymerized via a free radical mechanism. The viscosity of the silicone oil was systematically varied. At lower viscosities, a heterogeneous particle size distribution was produced where small particles were formed by engulfment of the monomer droplets at the liquid surface and large particles were formed by coalescence of the monomer droplets inside the liquid layer. Coalescence could be inhibited by increasing the viscosity of the silicone oil leading to a decreased average radius and a narrower size distribution of the polymer particles. The advantages of our method for the fabrication of polymer particles are that it does not require surfactants or organic solvents.

Polymer Thin Films and Surface Modification by Chemical Vapor Deposition: Recent Progress

Chemical vapor deposition (CVD) polymerization uses vapor phase monomeric reactants to synthesize organic thin films directly on substrates. These thin films are desirable as conformal surface engineering materials and functional layers. The facile tunability of the films and their surface properties allow successful integration of CVD thin films into prototypes for applications in surface modification, device fabrication, and protective films. CVD polymers also bridge microfabrication technology with chemical and biological systems. Robust coatings can be achieved via CVD methods as antifouling, anti-icing, and antihydrate surfaces, as well as stimuli-responsive or biocompatible polymers and novel nanostructures. Use of low-energy input, modest vacuum, and room-temperature substrates renders CVD polymerization compatible with thermally sensitive substrates and devices. Compared with solution-based methods, CVD is particularly useful for insoluble materials, such as electrically conductive polymers and controllably crosslinked networks, and has the potential to reduce environmental, health, and safety impacts associated with solvents. This review discusses the relevant background and selected applications of recent advances by two methods that display and use the high retention of the organic functional groups from their respective monomers, initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization.

Two-Stage Growth of Polymer Nanoparticles at the Liquid-Vapor Interface by Vapor-Phase Polymerization

In this article, we study the growth of polymer nanoparticles that are formed on the surface of silicone oils via initiated chemical vapor deposition. The average radius of the particles can be increased by decreasing the silicone oil viscosity, increasing the deposition time, or increasing the deposition rate. The time series data indicates that there are two stages for particle growth. Particle nucleation occurs in the first stage and the particle size is dependent on the liquid viscosity and deposition rate. Particle growth occurs in the second stage, during which the particle size is dependent only on the amount of deposited polymer. This two-step process allows us to make core-shell particles by sequentially depositing different polymers. The benefits of our nanoparticle synthesis process are that solvents and surfactants are not required and the size of the nanoparticles can be controlled over a wide range of radii with a relatively narrow distribution.

Fabricating Polymer Canopies onto Structured Surfaces Using Liquid Scaffolds

In this work, we study the use of initiated chemical vapor deposition in conjunction with liquid scaffolds to deposit polymer canopies onto structured surfaces. Liquid is applied to micropillar and microstructure surfaces to act as a scaffolding template such that the deposited polymer films take the shape of the liquid surface. Two methods for directing the location of the scaffolding liquid were examined. In the first method, high surface tension liquids rest in a Cassie-Baxter state over the structured surfaces, allowing for control over the canopy location and size by varying the position and volume of the liquid. In the second method, the structured surfaces are inverted onto a thin layer of low surface tension liquid, allowing the coverage and height of the canopy to be controlled by varying the area and thickness of the liquid layer. Although the canopies demonstrated in this study were fabricated using initiated chemical vapor deposition, the generality of our scaffolding method can easily be translated to other vapor deposition processes.

Microstructured Films Formed on Liquid Substrates via Initiated Chemical Vapor Deposition of Cross-Linked Polymers

We studied the formation of microstructured films at liquid surfaces via vapor phase polymerization of cross-linked polymers. The films were composed of micron-sized coral-like structures that originate at the liquid-vapor interface and extend vertically. The growth mechanism of the microstructures was determined to be simultaneous aggregation of the polymer on the liquid surface and wetting of the liquid on the growing aggregates. We demonstrated that we can increase the height of the microstructures and increase the surface roughness of the films by either decreasing the liquid viscosity or decreasing the polymer deposition rate. Our vapor phase method can be extended to synthesize functional, free-standing copolymer microstructured thin films for potential applications in tissue engineering, electrolyte membranes, and separations.