Search

Reduced sheet resistance and longer film stability of oCVD (oxidative chemical vapour deposition) PEDOT films were achieved by including a post-process acid rinse step in the production of the thin films. PEDOT films were rinsed in multiple concentrations of hydrobromic acid, sulfuric acid, and hydrochloric acid to test the effect of acid rinsing on sheet resistance, doping concentration, chemical composition, optical transmittance, and film morphology. XPS, FTIR, Raman spectroscopy, and XRD measurements were taken to determine the morphology and composition of the rinsed films. On average, rinsing films in HCl, HBr, and H2SO4 produced conductivity increases of 37%, 135%, and 117%. The dc to optical conductivity ratio, σdc/σop, was increased to 6, 12, and 10, for HCl, HBr, and H2SO4 rinsed films respectively as compared to σdc/σop = 4 for MeOH rinsed films. This study found evidence of dopant exchange within the films facilitated by the acid rinsing step, as well as complete removal of residual iron chloride oxidant. The acid rinse step also resulted in improved film conductivity stability at elevated temperatures. The XRD measurements in particular show signs of semi crystallinity in the PEDOT film after acid rinsing in comparison to an amorphous structure observed before this step. In this study, acid rinsing applied as a post-process step alters thin PEDOT films in ways that enhance their ability to function as electrode materials in photovoltaic devices.

The properties and behavior of a surface as well as its interaction with surrounding media depend on the inherent material constituency and the surface topography. Structured surface topography can be achieved via surface wrinkling. Through the buckling of a thin film of stiff material bonded to a substrate of a softer material, wrinkled patterns can be created by inducing compressive stress states in the thin film. Using this same principle, we show the ability to create wrinkled topologies consisting of a highly structured gradient in amplitude and wavelength, and one which can be actively tuned. The mechanics of graded wrinkling are revealed through analytical modeling and finite element analysis, and further demonstrated with experiments.

Since its invention in ancient times, relief printing, commonly called flexography, has been used to mass-produce artifacts ranging from decorative graphics to printed media. Now, higher-resolution flexography is essential to manufacturing low-cost, large-area printed electronics. However, because of contact-mediated liquid instabilities and spreading, the resolution of flexographic printing using elastomeric stamps is limited to tens of micrometers. We introduce engineered nanoporous microstructures, comprising polymer-coated aligned carbon nanotubes (CNTs), as a next-generation stamp material. We design and engineer the highly porous microstructures to be wetted by colloidal inks and to transfer a thin layer to a target substrate upon brief contact. We demonstrate printing of diverse micrometer-scale patterns of a variety of functional nanoparticle inks, including Ag, ZnO, WO[subscript 3], and CdSe/ZnS, onto both rigid and compliant substrates. The printed patterns have highly uniform nanoscale thickness (5 to 50 nm) and match the stamp features with high fidelity (edge roughness, ~0.2 μm). We derive conditions for uniform printing based on nanoscale contact mechanics, characterize printed Ag lines and transparent conductors, and achieve continuous printing at a speed of 0.2 m/s. The latter represents a combination of resolution and throughput that far surpasses industrial printing technologies., Massachusetts Institute of Technology. Department of Mechanical Engineering, National Science Foundation (U.S.) (Grant CMMI-1463181), United States. Air Force Office of Scientific Research. Young Investigator Program (Grant FA9550-11-1-0089), National Institutes of Health (U.S.) (Grant 1R21HL114011-01A1)

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.

The concept of a neutral hole-transporting polymer is realized for the first time, by integrating patterned Cl−-doped poly(3,4-dimethoxythiophene) thin films into organic solar cells through a vacuum-based polymer vapor printing technique. Due to this novel polymer's neutrality, high transparency, good conductivity, and appropriate energy levels, the solar-cell efficiency and lifetime are significantly enhanced., Eni-MIT Solar Frontiers Center, Samsung Foundation of Culture (Samsung fellowship), Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract No. W911NF-13-D-0001)

This paper reports on the fabrication of a pSi-based drug delivery system, functionalized with an initiated chemical vapor deposition (iCVD) polymer film, for the sustainable and temperature-dependent delivery of drugs. The devices were prepared by loading biodegradable porous silicon (pSi) with a fluorescent anticancer drug camptothecin (CPT) and coating the surface with temperature-responsive poly(N-isopropylacrylamide-co-diethylene glycol divinyl ether) (pNIPAM-co-DEGDVE) or non-stimulus-responsive poly(aminostyrene) (pAS) via iCVD. CPT released from the uncoated oxidized pSi control with a burst release fashion (∼21 nmol/(cm2 h)), and this was almost identical at temperatures both above (37 °C) and below (25 °C) the lower critical solution temperature (LCST) of the switchable polymer used, pNIPAM-co-DEGDVE (28.5 °C). In comparison, the burst release rate from the pSi-pNIPAM-co-DEGDVE sample was substantially slower at 6.12 and 9.19 nmol/(cm2 h) at 25 and 37 °C, respectively. The final amount of CPT released over 16 h was 10% higher at 37 °C compared to 25 °C for pSi coated with pNIPAM-co-DEGDVE (46.29% vs 35.67%), indicating that this material can be used to deliver drugs on-demand at elevated temperatures. pSi coated with pAS also displayed sustainable drug delivery profiles, but these were independent of the release temperature. These data show that sustainable and temperature-responsive delivery systems can be produced by functionalization of pSi with iCVD polymer films. Benefits of the iCVD approach include the application of the iCVD coating after drug loading without causing degradation of the drug commonly caused by exposure to factors such as solvents or high temperatures. Importantly, the iCVD process is applicable to a wide array of surfaces as the process is independent of the surface chemistry and pore size of the nanoporous matrix being coated. Refereed/Peer-reviewed

Chemical vapor deposition (CVD) methods are a powerful technology for engineering surfaces. When CVD is combined with the richness of organic chemistry, the resulting polymeric coatings, deposited without solvents, represent an enabling technology in many different fields of application. This article focuses on initiated chemical vapor deposition (iCVD), a new technique that utilizes benign reaction conditions to yield conformal and functional polymer thin films. The latest achievements in coating surfaces and 3D substrates with functional materials, and the use of the technique for biotechnology and selective permeation applications are reviewed, and future directions for iCVD technology are discussed.

Ordered herringbone patterns with deterministic long and short wavelengths are created using a sequential wrinkling strategy (SWS). Patterns with a prescribed zig-zag turning angle less than 90° are obtained upon sequential wrinkling of non-equi-biaxial prestrain for the first time. SWS provides a new method for measuring thin-film mechanical properties simply through the wrinkling metrology without measurement of film thickness.

Organic photovoltaics devices typically utilize illumination through a transparent substrate, such as glass or an optically clear plastic. Utilization of opaque substrates, including low cost foils, papers, and textiles, requires architectures that instead allow illumination through the top of the device. Here, we demonstrate top-illuminated organic photovoltaics, employing a dry vapor-printed poly(3,4-ethylenedioxythiophene) (PEDOT) polymer anode deposited by oxidative chemical vapor deposition (oCVD) on top of a small-molecule organic heterojunction based on vacuum-evaporated tetraphenyldibenzoperiflanthene (DBP) and C60 heterojunctions. Application of a molybdenum trioxide (MoO3) buffer layer prior to oCVD deposition increases the device photocurrent nearly 10 times by preventing oxidation of the underlying photoactive DBP electron donor layer during the oCVD PEDOT deposition, and resulting in power conversion efficiencies of up to 2.8% for the top-illuminated, ITO-free devices, approximately 75% that of the conventional cell architecture with indium-tin oxide (ITO) transparent anode (3.7%). Finally, we demonstrate the broad applicability of this architecture by fabricating devices on a variety of opaque surfaces, including common paper products with over 2.0% power conversion efficiency, the highest to date on such fiber-based substrates.

This report describes the preparation of superhydrophobic and oleophobic surfaces by grafting of poly(perfluorodecylacrylate) chains with initiated chemical vapor deposition on silicon substrates. The grafting enhances the formation of a semicrystalline phase. The crystalline structures reduce the polymer chain mobility, resulting in nonwetting surfaces with both water and mineral oil. On the contrary, the same contacting liquid easily wets the amorphous ungrafted polymer.

For the successful integration of graphene as a transparent conducting electrode in organic solar cells, proper energy level alignment at the interface between the graphene and the adjacent organic layer is critical. The role of a hole transporting layer (HTL) thus becomes more significant due to the generally lower work function of graphene compared to ITO. A commonly used HTL material with ITO anodes is poly(3,4-ethylenedioxythiophene) (PEDOT) with poly(styrenesulfonate) (PSS) as the solid-state dopant. However, graphene's hydrophobic surface renders uniform coverage of PEDOT:PSS (aqueous solution) by spin-casting very challenging. Here, we introduce a novel, yet simple, vapor printing method for creating patterned HTL PEDOT layers directly onto the graphene surface. Vapor printing represents the implementation of shadow masking in combination with oxidative chemical vapor deposition (oCVD). The oCVD method was developed for the formation of blanket (i.e., unpatterened) layers of pure PEDOT (i.e., no PSS) with systematically variable work function. In the unmasked regions, vapor printing produces complete, uniform, smooth layers of pure PEDOT over graphene. Graphene electrodes were synthesized under low-pressure chemical vapor deposition (LPCVD) using a copper catalyst. The use of another electron donor material, tetraphenyldibenzoperiflanthene, instead of copper phthalocyanine in the organic solar cells also improves the power conversion efficiency. With the vapor printed HTL, the devices using graphene electrodes yield comparable performances to the ITO reference devices (η(p,LPCVD) = 3.01%, and η(p,ITO) = 3.20%).

A new design paradigm for conformal, all-organic coatings that retain their flexibility and chemical functionality while displaying exceptional mechanical hardness and barrier properties is presented. Initiated chemical vapor deposition is used to synthesize a novel alternating copolymer thin film. Upon annealing, films display elastic moduli exceeding 20 GPa, excellent scratch resistance and flexibility, and very low oxygen permeability.

We demonstrate the use of a vacuum-based, vapor phase technique for the deposition of a donor polymer for use in polymer solar cells. Unsubstituted polythiophene (PT), which is insoluble and infusible and thus typically difficult to process, is easily prepared by oxidative chemical vapor deposition (oCVD). The oCVD process results in a conductive PT film that is heavily doped with FeCl 3 , which is used as the oxidizing agent. A post-deposition methanol rinse sufficiently dedopes the film and removes spent oxidant, leaving semiconducting PT with an optical bandgap close to 2 eV. Drastic changes in the film color, absorption spectra, and film composition confirm the dedoping process. The resulting semiconducting PT is then applied as an electron donor in bilayer heterojunction solar cells with a thermally evaporated C 60 electron acceptor layer, resulting in power conversion efficiencies up to 0.8%. The absorption edge of the PT at ∼620 nm closely matches the edge present in the external quantum efficiency spectra, indicating that the oCVD PT contributes to the photocurrent of the devices. This demonstrates that the oCVD technique can be used in the processing and design of polymer active layers for polymer solar cells and hybrid small molecular organic solar cells without solubility, temperature, or substrate considerations.

Preferred crystallographic orientation (texture) in thin fi lms of technologically important materials frequently has a strong effect on the properties of these fi lms and is important for stable surface properties. The deposition of organized molecular fi lms of a poly-perfl uorodecylacrylate, poly-(1 H ,1 H ,2 H ,2 H perfl uorodecyl acrylate) (p-PFDA), by initiated chemical vapor deposition (iCVD) is described. The tendency of p-PFDA to crystallize in a smectic B phase has been reported in fiprepared from solution but not for those using a CVD technique. The degree of crystallinity and the preferred orientation of the perfl uoro side chains, either parallel or perpendicular to the surface, are controlled by tuning the CVD process parameters (i.e., initiator to monomer fl ow rate ratio, fi lament temperature, and substrate temperature). Films with no observable X-ray diffraction patterns are also achieved. The observed differences in crystal texture strongly impact the observed water contact angles (150 ° to 130 ° , advancing) and corresponding hysteresis behavior. Low hysteresis ( < 7 ° ) is associated with high crystallinity, particularly when the orientation of the crystallites resulted in the perfl uoro side groups being oriented parallel to the surface. The latter texture resulted in smoother fi lm than the texture with the chains oriented perpendicular to the surface and this can be very advantageous for applications in which relatively smooth but still crystalline fi lms are needed.

Low band gap conjugated polymers are attractive for their applications in many devices including field-effect transistors, light-emitting diodes, electrochromic devices and photovoltaics. Selenophene-based polymers have many advantageous properties over polythiophene. However, poor solubility of solution-synthesized polyselenophene restricts its applications in the form of thin films. Electrochemical deposition of polyselenophene thin films is possible, but this process is limited to conductive substrates only. In this work, for the first time, we report deposition of polyselenophene (pSe) thin films on non-conductive substrates by a vapor based method, known as oxidative chemical vapor deposition (oCVD). oCVD synthesized pSe thin films were characterized by FT-IR, UV-Vis and X-ray photoelectron spectroscopies. Moreover, the oCVD made pSe shows 0.14 eV lower band gap than its calculated values. Vapor phase deposition of pSe by oCVD provides conformal thin films in a single and dry step. The conformal and dry nature of the pSe film deposition by oCVD may be employed for fabrication of devices on paper based substrates.

Biofouling is a crucial consideration in a variety of applications including biosensors, biomedical implants and devices, food packaging, and industrial and marine equipment. On the other hand, the controlled adsorption of proteins is desired in certain fields such as bioassays and tissue engineering. As such, significant progress has been made in fabricating surface chemistries that are able to resist or regulate protein adsorption through the manipulation of the protein–water–surface interactions. However, a conformal, substrate-independent surface modification method is required in order to extend such chemistries to a wider range of applications including delicate substrates, nanostructured surfaces, and polymer nanotubes. Here, we review the chemical vapor deposition (CVD) of coatings to control protein adsorption. These CVD coatings can be classified into four categories: hydrophilic coatings or hydrogels, which resist protein adsorption through surface hydration; fluorinated coatings, which have especially been studied in the context of fouling release in marine environments; amphiphilic coatings involving a unique antifouling mechanism; and switchable or stimuli-responsive coatings. Many of the techniques in each group are compatible with the synthesis of surface or free-standing nanostructures, and can be easily integrated into the existing fabrication infrastructure.

A versatile solvent-free method for surface modification of various materials including both metals and polymers is described. Strong irreversible bonds were formed when substrates modified by initiated chemical vapor deposition (iCVD) of poly(1,3,5-trivinyltrimethylcyclotrisiloxane) or poly(V3D3) and exposed to an oxygen plasma were brought into contact with plasma-treated poly(dimethylsiloxane) (PDMS). The strength of these bonds was quantified by burst pressure testing microfluidic channels in the PDMS. The burst pressures of PDMS bonded to various coated substrates were in some cases comparable to that of PDMS bonded directly to PDMS. In addition, porous PTFE membrane coated with poly(V3D3) was successfully bonded to a PDMS microfluidic device and withstood pressures of over 300 mmHg. Bond strength was shown to correlate with surface roughness and quality of the bond between the coating and substrate. This work paves a methodology to fabricate microfluidic devices that include a specifically tailored membrane. Furthermore, the bonded devices exhibited hydrolytic stability; no dramatic change was observed even after immersion in water at room temperature over a period of 10 days.

Adsorption of biopolymers such as proteins and polysaccharides is known to expedite/facilitate microbial attachment and subsequent formation of biofilm on membrane surface that ultimately results in membrane biofouling. Therefore, surfaces that resist the adhesion of biopolymers can potentially block the irreversible attachment of microorganisms as well. Recently, it was shown that random copolymerization of the hydrophilic hydroxyethylmethacrylate (HEMA) monomer with the hydrophobic perfluorodecylacrylate (PFA) monomer leads to a surface that interferes with the adsorption of a representative protein, bovine serum albumin (BSA). In this work, we explore the feasibility of using these copolymer films as potential antifouling coatings on commercial RO membranes. The films were deposited using iCVD technique that allows good composition control, is solvent-free and can be done readily at room temperature. Characterization and performance evaluation of the coated membranes was carried out using different tec...

A chemiresistive biosensor for detecting an analyte can include a high specific surface area substrate conformally coated with a conductive polymer, and a binding reagent immobilized on the conductive polymer, wherein the binding reagent has a specific affinity for the analyte. The conductive polymer can be deposited on a substrate by oCVD.

Temperature-responsive p(N-isopropylacrylamide-co-ethylene glycol dimethacrylate) (p(NIPAAm-co-EGDMA) films, graded in composition to provide a NIPAAm-rich surface, were synthesized successfully via initiated chemical vapor deposition (iCVD). Their dynamic response to temperature changes as monitored using quartz crystal microbalance with dissipation monitoring (QCM-D) was clearly distinguishable from the response of control iCVD-prepared films of homogeneous composition. The lower critical solution temperature (LCST) of the homogeneous copolymer (15 °C) was less than that reported for pure NIPAAM (32 °C) due to the hydrophobicity of the comonomer, EGDMA. The graded films displayed a broader transition over the range from 16 to 28 °C. The time constants associated with the response to small step changes in temperature around the LCST transition were significantly smaller in the graded (

Membranes for a lung assist device must permit the exchange of gaseous O₂ and CO₂ while simultaneously acting as a liquid barrier, so as to prevent leakage of blood and its components from passing from one side to the other. Additionally, these membranes must be capable of being integrated into microfluidic devices possessing a vascular network. In this work, uniform, large-area, ultra-thin, polymeric free-standing membranes (FSMs) and composite membranes (CMs) are reproducibly fabricated by initiated Chemical Vapor Deposition (iCVD). The 5 μm thick FSMs remained intact during handling and exhibited a CO₂ permeance that was 1.3 times that of the control membrane (8 μm thick spun-cast membrane of silicone). The CMs consisted of a dense iCVD skin layer (0.5-3 μm thick) deposited on top of a polytetrafluoroethylene (PTFE) support membrane (20 μm thick, 100 nm pores). The CMs exhibited CO₂ and O₂ permeance values 50-300 times that of the control membrane. The FSMs were subjected to mechanical testing to assess the impact of the absence of an underlying support structure. The CMs were subjected to liquid barrier tests to ensure that while they were permeable to gases, they acted as barriers to liquids. Both FSMs and CMs were integrated into silicone microfluidic devices and tested for bond integrity.

A platform for fabrication of conductive copolymer based resistive biosensor on nonconductive substrate is demonstrated. The −COOH functional groups in the copolymer of thiophene-3-acetic acid (TAA) and 3,4-ethylenedioxythiophene (EDOT) was employed for immobilization of a biomolecule. The sheet resistance of the conductive copolymer thin films significantly increased upon immobilization of the biomolecule. In terms of the fabrication method, application of bromine as an oxidant in this oxidative chemical vapor deposition (oCVD) technique considerably improved the conductivity of the copolymer and also notably reduced the polymer synthesis steps. This low temperature oCVD process shows promises for coating any substrate, for example, paper, plastics, silicon and glass with highly conducting, conformal polymeric films for the future applications in fabricating flexible biosensor devices.

High-aspect ratio hydrophobic, cylindrical nanopores having diameters as low as 5 nm are rapidly fabricated using conformal vapor deposition of fluorinated polymeric layers into porous track-etched polycarbonate membranes. The resultant selectivity of these membranes for pairs of small molecules of similar size, but of different hydrophobicity, arises from solute-pore wall interactions emphasized by confinement. Increasing selectivity was observed as pore diameter decreased and as the surface of the pore became more hydrophobic. Cylindrical pores provided higher selectivity than bottleneck-shaped pores having the same minimum diameter. A maximum selectivity of 234 was achieved between mesitylene and phloroglucinol by the best performing membrane. Membranes with small fluorinated pores exhibited an effective cutoff based on the polar surface area of the molecules, with limited correlation with solute size. This technology could lead to a new generation of membrane separations based on specific interactions.

Poly[2-(dimethylamino)ethyl methacrylate-co-ethylene glycol dimethacrylate] (PDE) thin films were synthesized via initiated chemical vapor deposition (iCVD) and reacted with 1,3-propane sultone to obtain the zwitterionic structure. The cross-linker ethylene glycol dimethacrylate (EGDMA) was utilized to make the copolymer insoluble in water. The composition of the copolymer was tuned by varying the flow rates of precursors and calculated from Fourier transform infrared spectroscopy (FTIR) spectra. The zwitterionic coatings were covalently grafted on to reverse osmosis (RO) membranes, and surface characterizations were carried out. Scanning electron microscope (SEM) and atomic force microscope (AFM) revealed that the iCVD zwitterionic coatings were conformal and smooth over the RO membrane, and the coating thickness can be measured by using ellipsometry. Salt rejection was not impaired by the coating. Permeation tests were carried out under different feed pressures, film thicknesses, and film compositions, ...

Polymeric nanofilms which change dimensions in response to environmental stimuli, such as temperature, open the possibility for the development of smart surfaces. We demonstrate the synthesis of a coaxial nanofilm with a hydrogel core and a shape memory shell to form temperature activated nanotubes. The nanofilm is fabricated by conformally coating the pores of anodic aluminium oxide membranes with a shape memory polymer shell and a hydrogel core using initiated chemical vapor deposition. The temperature response of the coaxial nanofilm is studied through the time release of a fluorescent dye encapsulated and adsorbed by the hydrogel layer. It is demonstrated that the burst release of the fluorescent dye occurs due to the stress applied by the shape memory outer layer when activated at elevated temperature.

A novel thermally responsive copolymer p(NIPAAm-co-DEGDVE) is synthesized using the substrate independent method of iCVD and exhibits a sharp lower critical solution temperature (LCST) transition centered at ≈28.5 ± 0.3 °C determined via quartz crystal microbalance measurements with dissipation monitoring (QCM-D). Swelling with water below the LCST produces a reversible change of ≈3 x in film thickness. The layer is conformal on nanostructured surfaces including MWCNT forests and electrospun nanofiber mats. Modified planar substrates exhibit ≈30°change in static contact angle over the LCST, while through conformal coating on nanostructured substrates changes in static contact angle up to 135° are achieved. Additionally, coated surfaces exhibit temperature sensitive BSA adsorption measured by QCM-D and is reversible as shown through fluorescence imaging of a coated electrospun nanofiber mat.

Chemical Vapor Deposition (CVD) methods significantly augment the capabilities of traditional surface modification techniques for designing polymeric surfaces. In CVD polymerization, the monomer(s) are delivered to the surface through the vapor phase and then undergo simultaneous polymerization and thin film formation. By eliminating the need to dissolve macromolecules, CVD enables insoluble polymers to be coated and prevents solvent damage to the substrate. Since de-wetting and surface tension effects are absent, CVD coatings conform to the geometry of the underlying substrate. Hence, CVD polymers can be readily applied to virtually any substrate: organic, inorganic, rigid, flexible, planar, three-dimensional, dense, or porous. CVD methods integrate readily with other vacuum processes used to fabricate patterned surfaces and devices. CVD film growth proceeds from the substrate up, allowing for interfacial engineering, real-time monitoring, thickness control, and the synthesis of films with graded composition. This article focuses on two CVD polymerization methods that closely translate solution chemistry to vapor deposition; initiated CVD and oxidative CVD. The basic concepts underlying these methods and the resultant advantages over other thin film coating techniques are described, along with selected applications where CVD polymers are an enabling technology., Massachusetts Institute of Technology. Institute for Soldier Nanotechnologies (Contract DAAD-19-02-D-0002)

A new nanoscale sensing concept for the detection of nitroaromatic explosives is described. The design consists of nitroaromatic-selective polymeric layers deposited inside microfabricated trenches. As the layers are exposed to nitroaromatic vapors, they swell and contact each other to close an electrical circuit. The nitroaromatic selective polymer, poly(4-vinylpyridine) (P4VP), is deposited in the trenches using initiated chemical vapor deposition (iCVD). P4VP is characterized for the first time as a selective layer for the absorption of nitroaromatic vapors. The Flory–Huggins equation is used to model the swelling response to nitroaromatic vapors. The Flory–Huggins interaction parameter for the P4VP–nitrobenzene system at 40 °C is 0.71 and 0.25 for P4VP–4-nitrotoluene at 60 °C. Sensing of nitrobenzene vapors is demonstrated in a prototype device, while techniques to improve the performance of the design in terms of response time and sensitivities are described. Modeling shows that concentration and mass limits of detection of 0.95 ppb and 3 fg, respectively, can be achieved.

Poly(3,4-ethylenedioxythiophene) (PEDOT) thin films were obtained through oxidative chemical vapor deposition (oCVD) by using a new oxidant—bromine. The use of bromine eliminates any post processing rinsing step required with other oxidants like iron chloride and hence makes the process completely dry. Film properties are further compared with the PEDOT films deposited using iron chloride as the oxidant. Accelerated aging experiments show longer retention of electrical conductivity for the PEDOT films obtained using bromine as the oxidant. Conductivities as high as 380 S/cm were obtained for PEDOT films deposited using bromine as the oxidant at 80 °C, which is significantly higher than that for PEDOT films deposited using iron chloride as the oxidant at the same temperature. Cross-sectional SEM of the PEDOT films deposited using bromine on silicon trench wafers demonstrates high conformal deposition of the films. All the results show the possibility of depositing highly conducting, conformal PEDOT films o...

Bifunctional surfaces are micropatterned using a self-aligned, dual-purpose lithographic mask and pairs of conformally deposited iCVD polymers. A first layer is deposited, then physically masked and etched in oxygen plasma. A second layer is deposited with the mask still in place. Lift-off reveals the micropatterned surface. The thicknesses of the two layers are independently controlled so that the resultant surface displays both chemical and topographical contrast. The patterning scheme is independent of the polymers used and order of deposition. We use this scheme to create surfaces that spatially confine microcondensation, as well as chemical functionality. We also demonstrate microwells whose depth can be altered in response to a water stimulus.

Grafting (g)CVD from the monomer 1-vinyl-2-pyrrolidone (VP) and the Type II initiator benzophenone (BP) under 254 nm UV irradiation yields durable hydrophilic coatings on substrates of poly(methacrylic acid) (PMA) derivatives, desirable for scleral lens applications. The gCVD polymerization of the VP monomer is essentially complete, and little excess BP remains in the film. Process optimization, through single variable and two fractional factorial experiments, result in retention of >90% of the as-deposited film thickness after rinsing. Increasing the initiator dosing time beyond 10 min, or the UV exposure time beyond 5 min, has little effect on the as-deposited thickness, or percentage of film retained after rinsing. This suggests that UV irradiation rapidly transforms most of the BP absorbed on the surface to initiating radicals. Once sufficient initiator dosage and UV exposure have been achieved, the initial deposition thickness is controlled primarily by the total flux of monomer to the surface, which is consistent with previous studies. For all samples, thickness loss occurs primarily during the first 30 days of saline soak-testing with no statistically significant loss (p > 0.25) during the next 90 days of soak testing. While the additional UV exposure time has a limited effect on initial film thickness, it does increase long term thickness retention, most likely by forming crosslinked and branched structures within the film. All samples tested retain sufficient gCVD coating thickness to impart improved hydrophilicity at the surface throughout the entire 120 day saline soak-testing period. The fractional factorial experiments correlate improved hydrophilicity with an interaction between initiator dosage time and UV exposure time. Indeed, decreasing these two process variables in tandem provides the greatest reduction in contact angle. While the uncoated PMA displayed 92.3° ± 2.1° advancing and 86.7° ± 3.0° receding contact angles with water, the most hydrophilic gCVD coating lowers the advancing and receding contact angles to 39.5° ± 2.6° and 36.2° ± 1.6°, respectively.

In this work we demonstrate that the concentration of vinyl bonds present in monomers adsorbed onto the surface determines the degree of conformality achieved by polymeric films grown over substrate topology by initiated (i)CVD. For microtrenches of varying aspect ratio, a ballistic model correlates the observed step coverage to a range of sticking coefficients of the initiating radicals, γ, between 0.01 and 0.05. Increasing the surface concentration of the monomer results in higher values of γ. In the deposition regime studied, γ is independent of the concentration of radical initiators. Furthermore, γ is insensitive to substrate temperature if the surface concentration of monomer is fixed. Using this knowledge, conformal coverage on microtrenches is demonstrated from both ethylene glycol diacrylate (EGDA) and neopentyl methacrylate (npMA). Additionally, the conformality permits templating of nanotubes of the mechanically robust and solvent-resistant iCVD-produced p(EGDA) crosslinked polymer.

Simultaneous improvement of mechanical properties and lowering of the dielectric constant occur when films grown from the cyclic monomer tetravinyltetramethylcyclotetrasiloxane (V4D4) via initiated chemical vapor deposition (iCVD) are thermally cured in air. Clear signatures from silsesquioxane cage structures in the annealed films appear in the Fourier transform IR (1140 cm−1) and Raman (1117 cm−1) spectra. The iCVD method consumes an order of magnitude lower power density than the traditional plasma-enhanced CVD, thus preserving the precursor's delicate ring structure and organic substituents in the as-deposited films. The high degree of structural retention in the as-deposited film allows for the beneficial formation of intrinsically porous silsesquioxane cages upon annealing in air. Complete oxidation of the silicon creates ‘Q’ groups, which impart greater hardness and modulus to the films by increasing the average connectivity number of the film matrix beyond the percolation of rigidity. The removal of labile hydrocarbon moieties allows for the oxidation of the as-deposited film while simultaneously inducing porosity. This combination of events avoids the typical trade-off between improved mechanical properties and higher dielectric constants. Films annealed at 410 °C have a dielectric constant of 2.15, and a hardness and modulus of 0.78 and 5.4 GPa, respectively. The solvent-less and low-energy nature of iCVD make it attractive from an environmental safety and health perspective.

Performance stability of electrochemically active polymers (EAPs) remains one of the greatest and long-standing challenges with regard to EAP-based technologies for a myriad of energy, biomedical, and environmental applications. The performance instability of EAPs originates from their structural alteration under repeated charge–discharge cycling and/or flexing. In this work, a conceptually new “soft confinement” strategy to enhance EAP performance stability, including cyclic and mechanical, by using rationally designed, vapor-deposited organic networks is presented. These chemically cross-linked networks, when in contact with an electrolyte solution, turn into ultrathin, elastic hydrogel coatings that encapsulate conformally the EAP micro-/nanostructures. Such hydrogel coatings allow easy passage of ions that intercalate with EAPs, while simultaneously mitigating the structural pulverization of the EAPs and/or their detachment from substrates. Fundamentally distinct from extensively studied “scaffolding” or “synthetic” approaches to stabilizing EAPs, this soft confinement strategy relies on a postmodification step completely decoupled from the EAP synthesis/fabrication, and enjoys the unique advantage of substrate-independency. Hence, this strategy is broadly applicable to various types of EAPs. The proposed stability enhancement strategy is demonstrated to be effective for a range of EAP systems with differing chemical and morphological characteristics under various testing conditions (repeated charging/discharging, bending, and twisting).

Poly(4-aminostyrene) (PAS) thin films were synthesized via initiated chemical vapor deposition (iCVD) with tert-butyl peroxide as the initiator, representing the first time that a library of iCVD functional groups has been extended to amine moieties. The retention of the pendent amine chemical functionality was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) reveals that the iCVD PAS coatings are conformal over nonplanar structures. Fluorescence microscopy and photoluminescence of quantum dot functionalized surfaces confirm that the reactive amine functional group density at the surface of iCVD PAS is ∼1 order of magnitude greater than for films grown by plasma-enhanced chemical vapor deposition (PECVD). The higher amine density of the iCVD films enables the formation of a robust nanoadhesive with complementary epoxy functional groups. Prototype microfluidic structures were fabricated using the low-temperature (50 °...

Chemical vapor deposition (CVD) polymerization utilizes the delivery of vapor-phase monomers to form chemically well-defined polymeric films directly on the surface of a substrate. CVD polymers are desirable as conformal surface modification layers exhibiting strong retention of organic functional groups, and, in some cases, are responsive to external stimuli. Traditional wet-chemical chain- and step-growth mechanisms guide the development of new heterogeneous CVD polymerization techniques. Commonality with inorganic CVD methods facilitates the fabrication of hybrid devices. CVD polymers bridge microfabrication technology with chemical, biological, and nanoparticle systems and assembly. Robust interfaces can be achieved through covalent grafting enabling high-resolution (60 nm) patterning, even on flexible substrates. Utilizing only low-energy input to drive selective chemistry, modest vacuum, and room-temperature substrates, CVD polymerization is compatible with thermally sensitive substrates, such as paper, textiles, and plastics. CVD methods are particularly valuable for insoluble and infusible films, including fluoropolymers, electrically conductive polymers, and controllably crosslinked networks and for the potential to reduce environmental, health, and safety impacts associated with solvents. Quantitative models aid the development of large-area and roll-to-roll CVD polymer reactors. Relevant background, fundamental principles, and selected applications are reviewed.

Highly cross-linked but flexible polyhexavinyldisiloxane (p-HVDSO) thin films were deposited by initiated chemical vapor deposition (iCVD) for applications where smooth, adhesive, and flexible coat...

Smooth surfaces with compositional heterogeneities at a molecular-length scale are presented with the goal of disrupting surface-protein interactions. These surfaces are synthesized by utilizing photoinitiated chemical vapor deposition (piCVD) to deposit thin films of random copolymers consisting of highly hydrophilic and highly hydrophobic comonomers. Swellability, wettability, and surface roughness could be systematically controlled by tuning the copolymer composition. The surface composition was dynamic, and the surface reconstructed based on the hydration state of the film. Proteins adsorbed to the copolymer films less readily than to either of the respective homopolymers, indicating a synergistic effect resulting from the random copolymer presenting molecular-scale compositional heterogeneity. These results provide direct evidence that protein adsorption can be disrupted by such surfaces and a simple analytical model suggests that the heterogeneities occur over areas encompassing 4-5 repeat units of the polymer. The synthetic method used to create these films can be used to coat arbitrary geometries, enabling practical utility in a number of applications.

In this work, initiated chemical vapor deposition (iCVD) of the poly(ethylene glycol diacrylate) is reported and the effects of process parameters on the deposition rates are investigated. The systematic studies of depositions performed at different filament temperatures showed that the deposition rates increased with the temperature due to the increase in the radical concentration which was monitored with a gas-phase Fourier transform infrared spectroscopy. For temperatures below 242±3 and 224±2°C for 2 and 1SCCM (SCCM denotes cubic centimeter per minute at STP) of monomer flowrates, respectively, a reaction-kinetics limited regime was observed, where the deposition kinetics was limited by the decomposition of the radicals. In this regime, the deposition rates were highly dependent on the filament temperature and the apparent activation energy was found to be 166±5kJ∕mol, consistent with the cleavage of the O–O bond in the tert-butyl peroxide initiator as the rate limiting reaction in the deposition mech...

The fabrication of prototype composite membranes consisting of permeable, size-selective hydrogel thin films on porous alumina membrane supports is described. Smooth hydrogel films with sub-100 nm thicknesses lacking micrometer-sized pinholes were readily synthesized using initiated chemical vapor deposition (iCVD). iCVD was a convenient technique for membrane applications as it enabled control over the coating conformality by modulating surface concentrations of the polymer precursors and film thickness through in situ monitoring of the deposition process. Scanning electron microscopy confirmed that the deposited film bridged the pore openings of the alumina supports, and little pore infiltration occurred. Membrane permeability was controlled through variation of the thickness and composition of the iCVD poly[maleic anhydride-co-dimethylacrylamide-co-di(ethylene glycol) di(vinyl ether)] (PMaDD) film. The combination of swelling and stability was achieved for a film composition of 76% N,N-dimethyl acrylam...

Vapor based polymer deposition methods have evolved to address the limitations of solution polymerization. However this field of vapor based polymerization suffers from varied nomenclature and would benefit from a review article that brought together the different approaches to vapor based polymerization with an effort to present existing nomenclature, clearly identify the various approaches within this field and summarize recent results. This review article is written with the purpose of compiling recent advances in vapor based deposition methods of polymers with a focus on applications that will continue to drive research in this field. We hope that this article encourages researchers engineering novel polymer applications to give vapor based polymerization a serious consideration apart from solution polymerization methods.