Morphology change of asymmetric diblock copolymer micellar films during solvent annealing

The morphology change of an asymmetric polystyrene-block-poly(2-vinyl pyridine) (PS-b-PVP) diblock copolymer micellar film was investigated during solvent vapor annealing in chloroform. Initially, smaller islands in nanometer-length scale form at the film surface. Further annealing results in the growth of the islands composed of the PS-b-PVP cylinders above the bottom brush layer. For comparison, a film of the block copolymer prepared from THF solution (without micellar structure) was also studied. The surface morphology of the film from THF evolves via spinodal dewetting mechanism during solvent vapor annealing. At a long time solvent vapor annealing, the two kinds of the films display the same surface morphologies, which are determined by the interplay between the surface field and autodewetting.     

Study of the time evolution of the surface morphology of thin asymmetric diblock copolymer films under solvent vapor

The time development of the surface morphology of asymmetric polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) thin films ‘annealing’ in methanol vapor, a selective solvent for minority P4VP block, was investigated by atomic force microscopy(AFM). For PS-b-P4VP with cylindrical structure in bulk, as annealing time progressed, the surface morphology underwent structural transitions from featureless topography to hybrid morphology of cylindrical and spherical pits, to cylinders, to nanoscale depressions, back to cylinders again. The different film thickness made the number of the transitions observed, at any given annealing time, different. The thicker the film is the more transitions at a given annealing time can be observed. If the film was not thick enough, depressions appeared. For PS-b-P4VP with spherical structure in bulk, it displayed nanoscale depressions with the annealing time increasing. A possible mechanism of the transition of morphologies during solvent annealing was proposed.     

Solvent annealing thin films of poly(isoprene-b-lactide)

The use of solvent annealing to control the microdomain orientation and long-range ordering in poly(isoprene-b-d,l-lactide) thin films was investigated using scanning force microscopy and grazing incidence small angle X-ray scattering (GISAXS). Benzene and chloroform were used as annealing solvents. Both were found to improve the long-range order in the films. Additionally, at high concentrations of chloroform in the film, a perpendicular orientation of cylinders was observed where the solvent was able to mediate interfacial interactions sufficiently to prevent a preferential segregation of one of the blocks to the surface. In situ GISAXS measurements made during solvent swelling and evaporation allowed an examination of the film morphology over a wide range of solvent concentrations providing a efficient route to optimize conditions for morphology control by solvent annealing.     

A paradigm shift in morphological architecture of PEO-b-PFOMA semi-fluorinated block copolymer thin films upon facile solvent annealing

A systematical study on the morphological transition of the micelle films of semi-fluorinated poly(ethylene oxide)-b-poly(1H,1H-dihydro perfluorooctyl methacrylate) (PEO-b-PFOMA) diblock copolymers was carried out upon perfluroalkanes (PF-5080) or α,α,α-trifluorotoluene (TFT) solvent annealing. Poorly ordered short cylindrical structures of the PEO_5k-b-PFOMA_21k micelle film underwent a phase inversion with PEO cores in the PFOMA continuous phase with a short period of PF-5080 solvent annealing. In contrast, the highly ordered morphology of PEO_10k-b-PFOMA_21k with PFOMA cores in the PEO continuous phase developed into cylindrical microdomains presumably via the fusion process. Prolonged annealing of the film transformed its morphology into inverted-spherical domains of PEO in the PFOMA continuous phase through long-range ordering by following the fission process. In order to find out a synthetic application of the morphology inversion strategy, an attempt was undertaken by adding a gold precursor to the PEO_10k-b-PFOMA_21k micelle solution, and as-cast thin films were prepared accordingly. Upon PF-5080 solvent annealing, the nanoparticles populated in self-assembled thin films resulted in inverted-spherical domains having gold nanoparticles populated in PEO cores surrounded by the PFOMA continuous phase. When the annealing solvent was changed to TFT, a highly ordered in-plane cylindrical morphology with respect to the substrate was achieved from the poorly ordered cylindrical microdomains of the PEO_5k-b-PFOMA_21k thin film, whereas an uneven cylindrical structure was produced from PEO_10k-b-PFOMA_21k.     

Surface relief terraces and self-assembled nanostructures in thin block copolymer films with solvent annealing

We have investigated the temporal evolution of relief terraces and microphase-separated nanodomains in poly(styrene-block-ethylene oxide) P(S-b-EO) on silicon substrates (SiO_x/Si) annealed under toluene/butanol vapors. For thin films, solvent annealing causes the formation of relief terraces. With solvent annealing for 12 h, hexagonal arrays of nanospheres of three sizes are dominant over the surface morphology of relief-terraced microstructures with epitaxial packing. The coexistence of nanospheres of three sizes is ascribed to a morphology triggered by the constraint of the film thickness. Upon exposure to toluene/butanol vapors for 16 and 20 h, these nanospheres become metastable and grow further into nanocylinders lying on the surface. During dewetting, the undulations of the local thickness and the nanodomain transitions are inseparable, consequently forming relief terraces comprising multiple layers of lying nanocylinders. The mechanisms and causes of nanodomain transitions of varied routes in solvent-annealed P(S-b-EO) films are analyzed and discussed.     

Water-induced morphology evolution of block copolymer micellar thin films

Morphology evolution of diblock copolymer polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) micellar thin film in the presence of water was investigated. Surface holes with nanoscale cavities in hexagonal order could be induced by water treatment for certain periods. The nanoscale surface cavities could be transformed into isolated nanospheres in a dry environment or back to protruding densely packed spheres by toluene (a selective solvent for PS coronae) treatment. The morphology evolution of micellar thin film strongly depended on the slow evaporation of toluene solvent, the swelling of P4VP cores in the humid environment, and the subsequent movement of PS chains induced by air and toluene. The incompatibility between solvent and block, and that between the unlike blocks also played an important role in the morphology evolution.     

Dewetting and microphase separation in symmetric polystyrene‐block‐polyisoprene diblock copolymer ultrathin films

The kinetics of surface structure evolution in ultrathin films of low‐molecular‐weight polystyrene‐block‐polyisoprene (M_w: 7300 g mol^?1–7300 g mol^?1) diblock copolymer at temperatures below the bulk order‐to‐disorder transition temperature are presented. Films with two different thicknesses were studied as a function of annealing temperature using atomic force microscopy. These film thicknesses enabled the investigation of the competition between microphase separation and dewetting that resulted in two different morphologies: long‐range bicontinuous structures and random holes. Three distinctive stages of structure evolution were observed in bicontinuous structure, with the underlying mechanism compared with spinodal dewetting. Thicker films presented holes on their surfaces upon annealing at elevated temperatures, and kinetics of formation of the holes were discussed. We found that the molecular mobility determined the rates of dewetting, while the microphase separation hardly affected the dewetting process. © 2015 Society of Chemical Industry     

Growth of highly c-axis oriented LaNiO3 films with improved surface morphology on Si substrate using chemical solution deposition and rapid heat treatment process

LNO (LaNiO₃) thin films were directly deposited onto Si substrates with a thin layer of amorphous natural oxide (SiO₂) using three different precursor solutions. Effects of the constitution of precursor solution and the annealing heating rate on the surface morphology and the orientation were investigated. The LNO film derived from the mixture of a methanol solvent and an acetylacetone chelating agent had the flat surface with no cracks and pinholes. The heating rate of rapid annealing process had a critical effect on the oriented growth of the LNO film, and its c-axis orientation degree increased with the annealing heating rate. The LNO film with the heating rate of 40 ℃/s exhibited the highest degree of c-axis orientation (99.57%) and the lowest resistivity (9.35 × 10^?4 Ω cm). It would be a potential bottom electrode and/or seed layer to integrate perovskite-type films on it for functional devices.     

Association of stereoregular poly(methyl methacrylates): 2. Formation of stereocomplex in bulk

Blends of isotactic and syndiotactic poly(methyl methacrylate) (i- and s-PMMA) are obtained by precipitation from chloroform and acetone solutions. By differential scanning calorimetry and dynamicmechanical measurements the formation of stereocomplexes from i- and s-PMMA in bulk is demonstrated. After annealing of the blends at 130–160°C a melting endotherm is detected and it is established by X-ray analysis that this endotherm is caused by formation of crystalline stereocomplex. The rate of complex formation is maximal at 140°C and the extent of complex formation is maximal at an isotactic-rich composition. It appears that the difference in solvent history can be removed by heating to 240°C. The subsequent S-shaped course of glass transition temperature, T_g, with composition is explained by the occurrence of some complex formation during cooling from 240°C. Asymmetry and shift of the dynamic-mechanical damping curves after annealing are also explained by the formation of complexes. A mechanism is proposed with helical isotactic chains acting as nuclei for a fringed micelle type of complex formation.     

Fluorescence study of film formation from PS/Al2O3 nanocomposites

Steady state fluorescence (SSF) and UV–vis (UVV) techniques were used to study the film formation behavior of pyrene (P) labeled polystyrene (PS) latex and Al₂O₃ (PS/Al₂O₃) composites depending on PS particles size and Al₂O₃ content. The close-packed arrays of PS spheres (SmPS: 203 nm; LgPS: 382 nm) templates on clean glass substrates were covered with various layers of Al₂O₃ by dip-coating method. Two different film series (SmPS/Al₂O₃ and LgPS/Al₂O₃) were prepared in various Al₂O₃ layer content. The film formation behavior of these composites were studied by annealing them at a temperature range of 100–250 °C and monitoring the scattered light intensity (I_sc), fluorescence intensity (I_P) from P and transmitted light intensity (I_tr) through the films after each annealing step. Optical results indicate that classical latex film formation was occurred for all Al₂O₃ content films and film formation process was unaffected by the Al₂O₃ content for both film series. Extraction of PS template produced highly ordered porous structures for high Al₂O₃ content in both film series. SEM images showed that the pore size and porosity could be easily tailored by varying the PS particle size and the Al₂O₃ content.     

退火处理对钛酸钡微弧氧化铁电薄膜物相的影响

以工业纯钛板作为阳极,在Ba(OH)2溶液中微弧氧化制得BaTiO3薄膜。研究了BaTiO3薄膜的表面形貌和物相组成,着重研究了退火处理对BaTiO3薄膜物相的影响。微弧氧化所得薄膜表面凹凸不平,且存在大量分布不均的孔洞,主要由六方相BaTiO3组成,经不同温度退火后,其物相组成发生很大变化。在1 100°C下退火1 h后,薄膜中开始出现四方相BaTiO3;随着热处理温度的升高和保温时间的延长,更多的BaTiO3由六方相向四方相转变。但高温退火过程中基体Ti与微弧氧化膜反应形成的氧化物层会影响薄膜的铁电性能。     

Self-reorganization of mixed poly(methyl methacrylate)/polystyrene brushes on planar silica substrates in response to combined selective solvent treatments and thermal annealing

This article reports reversible changes in surface morphology and surface wettability of mixed poly(methyl methacrylate) (PMMA)/polystyrene (PS) brushes with PS M_n slightly lower than that of PMMA in response to combined selective solvent treatments and thermal annealing. The mixed brushes were synthesized from asymmetric difunctional initiator-terminated monolayers by controlled radical polymerizations. Two sets of experiments were performed. The first set involved treating the samples with glacial acetic acid (AA), a selective solvent for PMMA, followed by treatment with cyclohexane, a selective solvent for PS, or thermal annealing. The surfaces were rough and composed of relatively ordered nanodomains after AA treatment. Subsequent cyclohexane treatment or thermal annealing made the surfaces flattened and surface analysis indicated that the outermost layers were occupied by PS. The second set of experiments involved treating the samples with cyclohexane or thermal annealing, followed by AA treatment. The surfaces were smooth after cyclohexane treatment or thermal annealing and became very rough in the subsequent AA treatment. The nanodomains formed in AA treatment were speculated to be micelles with PS forming the core shielded by PMMA chains.     

Taguchi optimization of device parameters for fullerene and Poly (3-octylthiophene) based heterojunction photovoltaic devices

Photovoltaic devices were fabricated with the structure ITO/fullerene/Poly (3-octylthiophene)/Au and device parameters were optimized using Taguchi optimization technique. Optimized parameter such as fullerene and Poly (3-octylthiophene) film thickness, annealing temperature and annealing duration are found to be as 110 nm, 45 nm, 120° C and 15 min respectively. Fabricated device with optimized parameters shows short circuit current density (J_sc), open circuit voltage (V_oc) and fill factor (FF) as 2 × 10^− 4 mA/cm², 0.47 V and 0.25 respectively. Effect of solvent casting on C₆₀ layer was studied which shows formation of uneven surface providing large interfacial area.     

Alignment and reordering of a block copolymer by solvent-enhanced thermal laser direct write

Block copolymer (BCP) thin films have shown high potential as a pattern transfer medium for ultra-fine (<20 nm) features. We introduce an effective approach for performing rapid local annealing of BCP films by focused laser spike (FLaSk) zone annealing, using a moving highly-focused circularly polarized visible wavelength laser spot. A poly(styrene-b-dimethylsiloxane) BCP was transformed from a metastable spherical micelle morphology to the bulk equilibrium cylindrical morphology aligned along the write direction within a region controlled by manipulation of the laser focal plane, even for curved paths. This simultaneous microdomain reordering and alignment was accomplished on the tens of millisecond time scale by creating a very large driving thermal gradient (estimated as 100–750 K/μm or, temporally, 3000–75,000 K/s), enhanced by incorporation of solvent vapor (here toluene) swelling of the BCP film. The extent of the thermal effects suggests that the role of solvent may extend beyond increasing the mobility of the BCP film to enhancing both the thermal gradient and also potentially the surface energy gradients, providing a thermocapillary shear mechanism. Further, enhanced domain alignment is greatest at higher scan speed, indicating as well the importance of the temporal thermal gradient.     

Effect of annealing on the properties of nanostructured CuO thin films for enhanced ethanol sensitivity

Copper oxide (CuO) thin films were grown on glass substrates by low cost spray pyrolysis technique for three different molar concentrations (0.05 M, 0.10 M and 0.15 M), at a substrate temperature of 350 °C, and subsequently annealed at 400 °C for 2 h. The effects of precursor concentration and annealing on the structural, electrical and morphological properties of the crystallized films were investigated. X-ray diffractograms of the films showed the formation of single phase CuO with tenorite structure. The electrical properties of the films like carrier concentration, Hall co-efficient (R_H), mobility and conductivity were studied from Hall effect measurements. The positive values of R_H confirmed the p-type conductivity of the films. Resistivity decreased drastically by two orders of magnitude for the annealed films. The microstructures characterized by a scanning electron microscope for 0.15 M concentration of the precursor revealed that the morphology of the films was substantially affected by annealing. The film surface revealed uniformly distributed cluster of peanut shaped grains after annealing. The response of the as deposited and annealed CuO sensor to low concentration of ethanol (10 ppm) was compared. The annealed CuO film showed higher sensor response than the as-deposited CuO film did. The result suggested that annealing causes significant effect on the sensing performance of CuO to ethanol.     

Residual solvent removal and n-hexane sorption in blends of atactic and isotactic polystyrene

Atactic polystyrene, isotactic polystyrene, and intermediate polyblend films of the homopolymers were cast from solutions of 1,3,5-trimethylbenzene (mesitylene) or o-chlorotoluene. Residual solvent content, glass transition temperatures, and densities of the polyblends were determined. Consequent to these preliminary characterizations, n-hexane absorption kinetics and equilibria in unannealed blends were determined; maxima in the plots of weight change versus time were apparent for all compositions. The maximum is a consequence of the ‘unlocking’ of previously trapped residual casting solvent consequent to plasticizing invasion by the n-hexane in the unannealed film specimens. Neutron activation analysis for chlorine confirmed that the o-chlorotoluene content in the films was reduced dramatically consequent to n-hexane absorption. Residual solvent content was also reduced by thermally annealing the films at 110°C for 48 h under a vacuum and, therefore, no maximum in the sorption/time behaviour was observed in thermally annealed samples nor in films previously contacted with n-hexane vapour and subsequently vacuum stripped. Both the rate of sorption and the apparent sorption equilibrium are greatly reduced as the isotactic polystyrene content is increased. Predominantly Case II or relaxation controlled absorption kinetics were observed in the polyblends consequent to thermal annealing and/or ‘solvent’ annealing. Although the form of the sorption kinetics was quite similar for absorption of n-hexane in thermally annealed or ‘solvent-annealed’ films, the sorption rate and amount of penetrant sorbed at apparent equilibrium were both larger for the thermally annealed films. These results suggest that the history dependence, which so frequently affects polymeric glasses, appears to confound a simple interpretation of the sorption experiments reported here. Consistent with observations in related systems, Super Case II kinetics were observed for the more slowly sorbing films which, in this case, contained isotactic polystyrene. Moreover, film whitening related to micro-voiding accompanied n-hexane sorption in blends containing atactic polymer; however, the whitening in the isotactic polymer was less pronounced and densification, presumably related to solvent induced crystallization, occurred consequent to long term exposure of the isotactic polymer to n-hexane.     

Film instability induced evolution of hierarchical structures in annealed ultrathin films of an asymmetric block copolymer on polar substrates

With an atomic-force microscope and a grazing-incidence small-angle X-ray scattering we studied ex situ the evolution of hierarchical structures in isothermally annealed ultrathin films of asymmetric polystyrene-block-poly(methyl methacrylate) P(S-b-MMA) that dewetted on polar substrates via a mechanism involving nucleation and growth. Film instability causes the surface to acquire an undulating thickness through incommensurability, producing not only the relief structures on a micrometer scale but also mesophase-separated domains on a nanometer scale. The dewetted morphologies strongly influence the ordering behavior of the nanoscale domains. The noncylindrical nanostructures become stable at the curved edges of the relief microstructures in the destabilized P(S-b-MMA) films, for which a preferential wetting of the PS block with the free surface is prohibited. Additionally, the shape of relief structures as result of film instability correlates with the formation of mesophase-separated nanodomains. At early stages of film instability, the formation of parallel-oriented PMMA cylindrical nanodomains increases the deformation energy and it further persists to force the shape of relief structures between irregular holes to have a facet-wedge shape. However, those relief structures are expected to be not at equilibrium. At high temperatures, the relief structures between irregular holes progressively developed to form hemispherical-cap drops accompanied by a transformation of cylindrical into noncylindrical nanodomains at curved surfaces.     

Enhancement of integrity of graphene transferred by interface energy modulation

We report on the systematic studies of the parameters governing the integrity of graphene film during general “wet” transfer from a thermodynamic point of view. We chose polystyrene (PS) as a test carrier material and attempted to use eight different solvents to find optimal conditions for the graphene transfer from a catalyst film to a desired substrate without defects. When parameterizing the conventional chemical properties of solvents, the boiling points and surface tension were found to be critical in determining the quality of the transferred graphene. During the formation step of a conformal PS film on a graphene surface before catalyst etching, a solvent with a boiling point over ∼140 °C was essential. During the following PS film removal step, a solvent with surface tension higher than approximately 29 dyn/cm led to the formation of a continuous graphene film without cracks and holes. In addition, a high spin-coating velocity and lower concentration of PS in the solvent enhanced the quality of a transferred graphene film. The UV treatment of Si/SiO₂ (100 nm) was also found to improve the adhesion of the graphene on substrates. By electrical characterization, morphological differences were found to affect the electrical properties markedly.     

Films formed from polystyrene latex/clay composites: A fluorescence study

This study reports a steady-state fluorescence (SSF) technique for studying film formation from surfactant-free polystyrene (PS) latex and Na-montmorillonite (SNaM) composites. The composite films were prepared from pyrene (P)-labeled PS particles and SNaM clay at room temperature and annealed at elevated temperatures in 10-min intervals above glass transition temperature (t₃) of polystyrene. During the annealing processes, the transparency of the film improved considerably. Scattered light (I_s) and fluorescence intensity (I_p) from P were measured after each annealing step to monitor the stages of film formation. Evolution of transparency of composite films was monitored by using photon transmission intensity, I_tr. Scanning electron microscopy (SEM) was used to detect the variation in physical structure of annealed composite films. Minimum film formation temperature, T_q, and healing temperatures, T_h, were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It was observed that both activation energies increased as the percent of SNaM was increased in composite films.     

Surface morphology evolution of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP)(H) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA) supramolecular film

Well-ordered nanostructured polymeric supramolecular thin films were fabricated from the supramolecular assembly of poly(styrene-block-4-vinylpyridine) (PS-b-P4VP)(H⁺) and poly(methyl methacrylate)-dibenzo-18-crown-6-poly(methyl methacrylate) (PMCMA). A depression of cylindrical nanodomains was formed by the block of P4VP(H⁺) and PMCMA associates surrounded by PS. The repulsive force aroused from the incompatibility between the block of P4VP(H⁺) and PMCMA was varied through changing the molecule weight (M_w) of PMCMA, the volume fraction of the block of P4VP(H⁺), and annealing the film at high temperature. Increasing the repulsive force led to a change of overall morphology from ordered nanoporous to featureless structures. The effects of solvent nature and evaporation rate on the film morphology were also investigated. Further evolution of surface morphologies from nanoporous to featureless to nanoporous structures was observed upon exposure to carbon bisulfide vapors for different treatment periods. The wettability of the film surface was changed from hydrophilicity to hydrophobicity due to the changes of the film surface microscopic composition.