Solvent vapor annealing of block copolymer thin films: removal of processing history

The ordering processes of PS-b-P2VP block copolymer thin films with different processing histories were studied during solvent vapor annealing by in situ grazing incidence small-angle X-ray scattering (GISAXS). We compared cylinder-forming PS-b-P2VP thin films with 34 kg/mol molecular weight that were prepared in three different ways: spin coating, spin coating and subsequent solvent vapor annealing where the solvent vapor was removed instantaneously, and spin coating and subsequent solvent vapor annealing where the solvent vapor was removed slowly. Block copolymer thin films retained the morphology resulting from the different “processing histories” at smaller swelling ratios. This processing history was erased when the samples reached a higher swelling ratio (~1.4). After the solvent was slowly removed from the swollen film, the surface morphology was characterized by ex situ AFM. All samples showed the same morphology after solvent annealing regardless of the initial morphology, indicating the morphology of solvent annealed samples is determined by the polymer concentration in the swollen film and the solvent vapor removal rate, but not the processing history.     

PI-b-PMMA diblock copolymers: nanostructure development in thin films and nanostructuring of thermosetting epoxy systems

Poly(isoprene-block-methyl methacrylate) (PI-b-PMMA) block copolymers with different block ratios have been used to generate nanostructures both in thin films and by nanostructuring a thermosetting epoxy system. Obtained morphologies have been analyzed in terms of atomic force microscopy. The nanostructuring of thin films was carried out by thermal and solvent vapor annealing, in which the copolymer films were exposed to acetone vapors, selective solvent for methyl methacrylate (PMMA) block. By solvent vapor annealing thin films of both copolymers self-assembled into a hexagonally packed cylindrical morphology. Thermal annealing was carried out above the glass transition temperature of both blocks, obtaining worm-like and lamellar morphologies, depending on the block ratio. One of the copolymers has also been used for nanostructuring an epoxy thermosetting system. Morphologies consisting of spherical-shaped PI domains dispersed in a continuous epoxy matrix in which PMMA remained miscible were obtained, independently of the copolymer amount.     

Internal Architecture of Zwitterionic Polymer Brushes Regulates Nonfouling Properties

In this work, we study how film thickness and chain packing density affect the protein‐resistant properties of polymer brushes in complex media. Polymer brushes based on dual‐functional poly(carboxybetaine acrylamide) (pCB) were prepared via surface‐initiated photoiniferter‐mediated polymerization. By adjusting UV radiation time and solvent polarity, pCB films with different thicknesses can be achieved and characterized using an ellipsometer. The packing density of pCB polymer chains is directly related to the swelling ratio of swollen to collapsed film thicknesses. Results showed that the dry film thickness alone, used often in the literature, is not sufficient to correlate with nonfouling properties and the chain packing density must be considered for the design of nonfouling surface coatings.     

Investigation of polymer–solvent interactions in poly(styrene sulfonate) thin films

The swelling behavior of acid form poly(styrene sulfonate) (PSS‐H) thin films were investigated using in situ spectroscopic ellipsometry (SE) to probe the polymer–solvent interactions of ion‐containing polymers under interfacial confinement. The interaction parameter (χ), related to the polymer and solvent solubility parameters in the Flory–Huggins theory, describes the polymer‐solvent compatibility. In situ SE was used to measure the degree of polymer swelling in various solvent vapor environments, to determine χ for the solvent‐PSS‐H system. The calculated solubility parameter of 40–44 MPa^1/2 for PSS‐H was determined through measured χ values in water, methanol, and formamide environments at a solvent vapor activity of 0.95. Flory–Huggins theory was applied to describe the thickness‐dependent swelling of PSS‐H and to quantify the water‐PSS‐H interactions. Confinement had a significant influence on polymer swelling at low water vapor activities expressed as an increased χ between the water and polymer with decreasing film thickness. As the volume fraction of water approached ～0.3, the measured χ value was ～0.65, indicating the water interacted with the polymer in a similar manner, regardless of thicknesses. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1365–1372     

A new method of growing crystalline networks in polymer matrices by simultaneous CT complex formation and in situ crystallization

A new method of preparing conductive polymer composites by growing crystalline networks of conductive additives in polymer matrices (reticulate doping) is described. The method consists of treating the polymer containing molecularly dispersed donor additive with acceptor/solvent vapors. In the swollen polymer layer simultaneously CT complex formation and crystallization takes place which for proper conditions leads to the formation of a network of the CT complex crystallites, making the film surface-conducting. The preparation and properties of surface conductive films using several electron donors and an iodine acceptor are described. The films obtained show surface resistivities of 10⁴–10⁶ ohm and are generally stable under ambient conditions.     

Porous structures of polymer films prepared by spin coating with mixed solvents under humid condition

We investigate the effects of interfacial energy between water and solvent as well as polymer concentration on the formation of porous structures of polymer films prepared by spin coating of cellulose acetate butyrate (CAB) in mixed solvent of tetrahydrofuran (THF) and chloroform under humid condition. The interfacial energy between water and the solvent was gradually changed by the addition of chloroform to the solvent. At a high polymer concentration (0.15 g/cm3 in THF), porous structures were limited only at the top surfaces of CAB films, regardless of interfacial energies, due to the high viscosity of the solution. At a medium concentration (approximately 0.08 g/cm3 in THF), CAB film had relatively uniform pores at the top surface and very small pores inside the film because of the mixing of the water droplets with THF solution. When chloroform was added to THF, pores at the inner CAB film had a comparable size with those at the top surface because of the reduced degree of the mixing between the water droplets and the mixed solvent. A further decrease in polymer concentration (0.05 g/cm3 in THF) caused the final films to have a two-layer porous structure, and the size of pores at each layer was almost the same.     

Polymer surfaces with reversibly switchable ordered morphology

Honeycomb macroporous films fabricated by the "breath figures" method were composed of poly2-vinylpyridine (P2VP) distributed in the holes of polystyrene (PS). The porous films exhibited reversible behavior responding to water and different solvent vapors. When the porous film was treated with water, the honeycomb pattern would change to the hexagonal islandlike pattern. Once heated to remove the water, the honeycomb pattern emerged again. When the porous film was exposed to different solvent vapors, the same reversible process appeared. Carbon disulfide (CS(2)), toluene (TOL), and tetrahydrofuran (THF) solvent vapors induced the honeycomb pattern into the ordered islandlike pattern, and ethanol, chloroform, methyl ethyl ketone (MEK), and dimethylformamide (DMF) solvent vapors made the islandlike pattern come back to the honeycomb pattern. The hygroscopic property of P2VP and the polymer-solvent interaction are the driving force for the reversibly switchable morphology. The appropriate control of the hole depth is very crucial in determining the reversible changes.     

Instabilities during the formation of electroactive polymer thin films

The solvent-induced film structure of poly(n-vinyl carbazole) (PVK) thin films on indium tin oxide (ITO)-coated glass was examined. PVK thin films were prepared via spin-coating using five different solvents. We investigated the relationship between the solvent characteristics and film properties, including surface roughness and structure, film thickness, and density. The spin-coated polymer thin films are not in thermodynamic equilibrium; rather, the film properties are affected by the dynamics of the spin-coating process. We found that water present in tetrahydrofuran (THF) induces dewetting of PVK films during the spin-coating process. Solvents with a high evaporation rate lead to high surface roughness due to Marangoni convection. The results show that the surface roughness and structure of the films are dominated by the dynamics of the film formation process, rather than thermodynamic interactions between the polymer and solvents.     

非对称双嵌段共聚物薄膜在平板受限和溶剂蒸发下自组装行为的分子模拟研究

采用模拟退火和Monte Carlo方法研究体相形成柱状相的双嵌段共聚物薄膜在平板受限和溶剂蒸发条件下的自组装,特别关注柱状相形貌的取向.对于平板受限下的薄膜,研究了表面选择性、溶剂选择性和膨胀程度对柱状相取向的影响.对于溶剂蒸发的薄膜,研究了表面选择性和薄膜厚度对柱状相取向的影响,并讨论了柱状相取向的机理.结果表明,薄膜内存在中性溶剂时形成垂直柱形貌的表面选择性范围较小;存在亲长嵌段的溶剂时形成垂直柱形貌的表面选择性范围较大.溶剂蒸发后薄膜生成垂直柱形貌的参数范围较热退火下增大;柱状相取向取决于蒸发过程中体系由球状相演化为柱状相时的薄膜厚度与体相周期的匹配性.     

Modification of the structure of cellulose triacetate films in the course of solvent vapor sorption

Intermolecular interaction and structure of cellulose triacetate films in the course of sorption of dimethylsulfoxide, nitromethane, and tetrachloroethane vapors were studied by Fourier IR spectroscopy, X-ray diffraction analysis, and polarization microscopy. Quantitative ratio of different types of intra- and intermolecular hydrogen bonds in polymer films was estimated. Changes in the structure of cellulose triacetate films in the course of solvent vapor sorption were discussed from the viewpoint of competition between the interchain interactions via OH and C=O groups of the macromolecules and their solvation with the solvent molecules.     

Effect of humidity and solvent vapor phase on cellulose esters films

In the present study the effect of relative humidity (RH) during spin-coating process on the structural characteristics of cellulose acetate (CA), cellulose acetate phthalate (C-A-P), cellulose acetate butyrate (CAB) and carboxymethyl cellulose acetate butyrate (CMCAB) films was investigated by means of atomic force microscopy (AFM), ellipsometry and contact angle measurements. All polymer solutions were prepared in tetrahydrofuran (THF), which is a good solvent for all cellulose esters, and used for spin-coating at RH of (35 ± 5)%, (55 ± 5)% or (75 ± 5)%. The structural features were correlated with the molecular characteristics of each cellulose ester and with the balance between surface energies of water and THF and interface energy between water and THF. CA, CAB, CMCAB and C-A-P films spin-coated at RH of (55 ± 5)% were exposed to THF vapor during 3, 6, 9, 60 and 720 min. The structural changes on the cellulose esters films due to THF vapor exposition were monitored by means of AFM and ellipsometry. THF vapor enabled the mobility of cellulose esters chains, causing considerable changes in the film morphology. In the case of CA films, which are thermodynamically unstable, dewetting was observed after 6 min exposure to THF vapor. On the other hand, porous structures observed for C-A-P, CAB and CMCAB turned smooth and homogeneous after only 3 min exposure to THF vapor.     

Formation of nonextinct ring-banded textures and multistacked lamella of tetra-aniline-block-poly(L-lactide) rod-coil diblock oligomer films induced by solvent vapor treatment

The self-assembly processes of the rod-coil diblock oligomer thin film of tetra-aniline (TANI)-block-poly(L-lactide) (PLLA) with different film thicknesses induced in the coil-selective solvent of acetone vapor at room temperature were studied. The morphologies of the oligomer films were determined by the film thickness. For the thicker film (232 nm), the nonextinct concentric ring-banded textures could form. While for the thinner and appropriate film (about 6 nm), multistacked diamond-shaped appearances with the periodic thickness being about 8.5 nm(6-nm-thick extended PLLA chain and 2.5-nm-thick p-pi conjugating TANI bimolecular layer) formed. The possible formation models of those two regular morphologies were presented in detail.     

Vapochromic behavior of polycarbonate films doped with a luminescent molecular rotor

We report on vapochromic films suitable for detecting volatile organic compounds (VOCs), based on polycarbonate (PC) doped with 4‐(triphenylamino)phthalonitrile (TPAP), a fluorescent molecular rotor sensitive to solvent polarity and viscosity. PC films of variable thickness (from 20 up to 80 µm) and containing small amounts of TPAP (0.05 wt%) were prepared and exposed to a saturated atmosphere of different VOCs. TPAP/PC films showed a gradual decrease and red‐shift of the emission during the exposure to solvents with high polarity index and favorable interaction with the polymer matrix such as THF, CHCl₃, and acetonitrile. In the case of the most interacting solvents (THF and CHCl₃), TPAP/PC films also showed a fluorescence increase at longer exposure times, as a consequence of an irreversible, solvent‐induced crystallization process of the polymeric matrix. The vapochromism of TPAP/PC films is rationalized on the basis of alterations of the rotor intramolecular motion upon solvent uptake by PC and polarity effects of the microenvironment. Interestingly, the fluorescence response of the TPAP/PC films shows a non‐trivial, tuneable dependence on film thickness during the second solvent‐exposure stage. The latter effect is attributed to a variable extent of the crystallization process occurring in the PC films. This observation promptly suggests, in turn, an effective procedure to modulate the spectroscopic response in such functionalized polymeric materials through the precise control of the film thickness. Copyright © 2015 John Wiley & Sons, Ltd.     

Electron beam irradiation of poly(vinyl methyl ether) films: 1. Synthesis and film topography

Temperature-sensitive hydrogel layers on silicon (Si) substrates were synthesized by electron beam irradiation of spin-coated poly(vinyl methyl ether) (PVME) films. The influences of the used solvent, the polymer concentration, and the spinning velocity on the homogeneity and the thickness of the PVME film were investigated. In the range of concentration c(p) = 1-15 wt% PVME in ethanol solution, homogeneous films with a thickness between d = 50 nm and 1.7 mum were obtained. The films were cross-linked by electron beam irradiation under inert atmosphere and analyzed by sol-gel-analysis. The results were compared with bulkgels formed by electron beam irradiation of PVME in the dry state. The film topography was analyzed by high-resolution field emission scanning electron microscopy and atomic force microscopy. An islandlike structure in the dry, swollen, and shrunken state of the hydrogel films was observed.     

PEG／PED-g-CB化学敏电阻材料的制备及其气敏性能的研究

以不同分子量聚乙二醇(PEG)为基体，PEG接枝改性的炉法炭黑(PEG-g-CB)为导电裁流子，采用溶液分散工艺制得一种新鞭的气敏传感器材料。研究了PEG分子量对接枝率及对各种溶剂蒸气的响应性、响应灵敏度的影响；用透射电子显微镜(TEM)和紫外—可见分光光度计考察了两种炭黑粒子分散行为、袁面特性差异及其对响应重复性、稳定性的影响。结果表明，PEG／PEG-g-CB复合材料化学敏电阻体对其良溶剂蒸气如THF、氯仿、丙酮具有很强的响应性，其电阻值可提高到初始电阻的10^4～10^6倍。将这种材料再放入干燥空气中时，电阻又恢复到初始值；而对其不良溶剂如正己烷、甲苯几乎不响应。随PEG分子量的提高，响应灵敏度下降；响应的重复稳定性受炭黑粒子分散行为的影响，从聚合物溶胀行为及逾渗导电理论解释了实验结果。     

Polymer-coated gold island films as localized plasmon transducers for gas sensing

Ultrathin (typically < or = 10-nm thick) gold island films evaporated on transparent substrates show a prominent localized surface plasmon (SP) extinction in the visible-to-NIR range. Changes in the dielectric properties of the contacting medium influence the SP absorption band, providing a scheme for optical sensing based on refractive index change. In the present work, the gas sensing capability of gold island based localized surface plasmon resonance (LSPR) transducers was explored using polymeric coatings as the active interface. LSPR transducers were fabricated by spin-coating of polystyrene (PS) or polystyrene sulfonic acid, sodium salt (PSS) onto 5-nm-thick (nominal thickness) gold island films evaporated on silanized glass and annealed. Detailed characterization of the transducers was carried out using high-resolution scanning electron microscopy, cross-sectional transmission electron microscopy, and in situ atomic force microscopy under controlled atmosphere. The hydrophobic PS film exhibits swelling and significant thickness increase upon exposure to chloroform vapor and little or no change in water vapor, whereas the hydrophilic PSS film shows the opposite behavior when exposed to the same vapors. Polymer swelling upon absorption of vapors of good solvents shows a net effect of lowering the effective refractive index in the vicinity of the gold islands, manifested as a characteristic decrease of the SP band intensity and a blue shift of the band maximum. The response, measured for four different vapors, is fast (approximately 15 s) and reversible. It is shown that gold island systems coated with polymeric films can be applied to vapor recognition in an array configuration.     

Catalyzed radical polymerization of styrene vapor on nanoparticle surfaces and the incorporation of metal and metal oxide nanoparticles within polystyrene polymers

We present a novel approach to polymerize olefin vapors on the surfaces of metallic and semiconductor nanoparticles. In this approach, a free radical initiator such as AIBN is dissolved in a volatile solvent such as acetone. Selected nanoparticles (prepared separately using the laser vaporization-controlled condensation method) are used to form initiator-coated nanoparticles placed on a glass substrate. The olefin (styrene) vapor is polymerized by the thermally activated initiator on the nanoparticle surfaces. Our approach also provides structural and mechanistic information on the early stages of catalyzed gas-phase polymerization, which can be used to correlate the gas-phase structural properties with the bulk properties and the performance of the polymer nanocomposites. This correlation is the key step in controlling the properties of the polymer nanocomposites. Our results clearly demonstrate the success of this method in preparing polymer coated nanoparticles for a variety of interesting applications. The precise control of the chemical functionality, thickness, and morphology of the polymer film and the size, size distribution, and properties of the core nanoparticles (photoluminescence, magnetic) may lead to major technological breakthroughs in a variety of applications including drug delivery, ultrasensitive detectors, and chemical and biological sensors.     

Dewetting Behavior of Random Copolymer Films Induced by Solvent Vapor Annealing

In recent years, the dewetting behavior of block copolymer films has been studied a lot, but that of random copolymer films was rarely studied. In this study, effects of film thickness and solvent vapor annealing duration (0 s–24 h) on the dewetting behavior of the spin-coated poly(styrene-co-acrylonitrile) (SAN) random copolymer films were mainly investigated by atomic force microscopy and contact angle method for the first time. The film thicknesses of the SAN films prepared at different concentrations were characterized by X-ray reflectometry to be 6–34 nm. With the annealing of acetone vapor, the SAN films first appear holes and then rupture into droplets which fuse and break periodically. The periodic evolutions of the droplets are due to the preferred affinity of acetone molecules with the AN segments and the change of surface energy. This phenomenon is different from the single evolutions in the spin-coated polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) block copolymer films. This illustrates the interactions between AN segments and the substrate are stronger than those between PMMA segments and the substrate in the spin-coated films.     

Roughening of gold atomic steps induced by interaction with tetrahydrofuran

Exposure of a clean gold surface to tetrahydrofuran (THF) under ambient conditions was observed to cause roughening of atomic step edges. This change was followed in situ using a scanning tunneling microscope during the exposure of a gold surface to a controlled stream of THF vapor. THF is a common solvent used in depositing molecules, self-assembled monolayers, and polymer films on surfaces, in electrochemistry, and in chemical reactions. Unlike other solvents, such as methanol, ethanol and diethyl ether, however, we found that THF itself has a profound effect on the surface morphology that needs to be taken into account when reporting on the interactions of solutes with a gold surface. At the same time, this finding may present new opportunities in catalysis or nanostructuring of surfaces.     

Complex aggregates of silica microspheres by the use of a polymer template

Evaporation of a droplet of silica microsphere suspension on a polystyrene and poly(methyl methacrylate) blend film with isolated holes in its surface has been exploited as a means of particles self-assembly. During the retraction of the contact line of the droplet, spontaneous dewetting combined with the strong capillary force pack the silica microspheres into the holes in the polymer surface. Complex aggregates of colloids are formed after being exposed to acetone vapor. The morphology evolution of the underlying polymer film by exposure to acetone solvent vapor is responsible for the complex aggregates of colloids formation.