Phase separation in potassium-doped ZnPc thin films

In this study synchrotron radiation was used to investigate the electronic properties of a thin film of zinc-phthalocyanine (ZnPc) deposited on Si(001)-2x1 and progressively doped with K atoms. The molecular orientation was probed by angular-dependent x-ray absorption spectroscopy and the molecules were found to lie with the macrocycle plane roughly perpendicular to the surface. The evolution of the electronic properties of the film was then followed by measuring the photoemission spectra upon in situ evaporation of K atoms on the pristine ZnPc film. The results show that doping proceeds through charge donation from the K atoms to the molecular units whose lowest unoccupied molecular orbital (LUMO) becomes progressively filled. Despite the fact that the LUMO spectral weight increases as the stoichiometry x in the K(x)ZnPc compound varies from about 1 to 4 (as determined by core level photoemission), no detectable density of states was observed at the Fermi level, showing that the film remains insulating for all the investigated stoichiometries. On the other hand the C 1s spectra, which appear merely broadened at the earliest stages of doping (x approximately 1), clearly develop two distinct components when x exceeds 2, suggesting that the charge state is not the same for all the molecules. At the same time, the modification of the valence band points towards the coexistence of two distinct phases with x=2 and x=4.     

振荡剪切流场下PS/PVME/SiO2复合物的相行为

利用光学显微镜-剪切台联用系统研究了振荡剪切流场下聚苯乙烯（PS）/聚甲基乙烯基醚（PVME）/二氧化硅（SiO₂）纳米粒子复合物的热力学稳定性. 结果表明,小振幅振荡剪切可导致PS/PVME共混物出现类似在稳态流场下的剪切诱导相容及剪切诱导相分离现象. 共混体系存在临界振荡频率ω_c,当振荡频率低于ω_c时,发生剪切诱导相分离（SID）行为,反之发生剪切诱导相容（SIM）行为. SiO₂纳米粒子的加入使复合体系的相容性提高. 存在一个临界SiO₂纳米粒子含量φ_c,当SiO₂纳米粒子含量高于φ_c时,复合体系中不存在临界振荡频率ω_c,低振荡频率下的剪切诱导相分离得到抑制. 此外,复合体系的上述行为与升温速率和共混物组成密切相关.     

Phase separation of polymer blends in thin films

Films of polystyrene-poly(vinylmethyl ether) blends of various compositions are formed by a dip-coating procedure, the thickness of the film being controlled by the concentration of the solution. The substrates used are glass and gold. The phase separation process is followed by a laser light scattering experiment in which the total forward scattering intensity is monitored as a function of temperature. Morphological examination shows that phase separation occurs by a spinodal decomposition mechanism. A thickness effect on the phase separation temperature is noticeable when film thickness is smaller than 1 μm. This effect is substrate dependent. In all films formed on gold the spinodal temperature increases as film thickness decreases. Films formed on glass exhibit a destabilizing effect on decreasing film thickness. This effect is slight in films of composition poorer in polystyrene than the critical composition, and is enhanced in films richer in polystyrene. The stabilizing effect of decreasing the thickness of films formed on the gold substrate is considered to reflect mainly a purely geometrical effect. The decreasing dimensionality is shown by simple theoretical considerations to increase the phase-separation temperature. However, the phase separation behavior of thin films on glass appears to be the result of two kinds of substrate-polymer interactions in addition to the geometrical effect: (a) electrostatic interaction of the charged glass surface (a destabilizing effect at all film compositions) and (b) selective adsorption of polystyrene on glass.     

Phase separation morphology of thin films of polystyrene/polyisoprene blends

We present the results of a study of the morphology of phase separation in a thin film blend of polystyrene (PS) and polyisoprene (PI) in a common solvent of toluene. The blend is quenched by rapid solvent evaporation using a spincoating technique rather than a temperature quench. The mass fraction of polystyrene is varied to determine the effect of the substrate on thin film phase separation morphology. We compare the phase separation morphology for very thin films of the PS/PI blend cast onto three different substrates: Si(001) with a native oxide layer (Si (SINGLEBOND) SiO_x), Si(001) etched in hydrofluoric acid (Si-H), and a Au/Pd alloy sputtered onto Si(001). We observe large differences between the morphologies of 1000 Å thick blend films on the Si(SINGLEBOND) SiO_x and Si-H substrates as the mass fraction is varied due to the difference in the wetting properties of PS on the two substrates. Smaller differences are observed between the films on the Si(SINGLEBOND) SiO_x and Au/Pd substrates only for film thicknesses h < 600 Å. © 1996 John Wiley & Sons, Inc.     

Vertical phase separation and liquid-liquid dewetting of thin PS/PCL blend films during spin coating

Thin films of an amorphous polymer, polystyrene (PS), and a crystalline polymer, poly(ε-caprolactone) (PCL), blend were prepared by spin coating a toluene solution. Surface chemical compositions of the blend films were measured by X-ray photoelectron spectroscopy (XPS), and the surface and interface topographical changes were followed by atomic force microscopy (AFM). By changing the PS concentration and keeping the PCL concentration of the solution at 1 wt %, a great variety of morphologies were constructed. The results show that the morphology of the blend films can be divided into three regions with increasing PS concentration. In region I, PS island domains are embedded in PCL crystals when the PS concentration is lower than 0.3 wt % and the size of the PS island increases with increasing PS concentration. In region II, holes with different sizes surrounded by a low rim are obtained when the concentration of PS is between 0.35 and 0.5 wt %. After selectively washing the PS domains, we studied the interface morphology of PS/PCL and found that the upper PS-rich layer extended into the bottom PCL layer, forming a trench surrounding the holes. In region III, an enriched two-layer structure with the PS-rich layer on top of the blend films and the PCL-rich crystal layer underneath is obtained when the concentration of PS is higher than 0.5 wt %. Last, the formation mechanism of the different surface and interface morphologies is further discussed in terms of the vertical phase separation to a layered structure, followed by liquid-liquid dewetting and crystallization processes during spin coating.     

Phase separation dynamics of a poly(vinyl methyl ether)/polystyrene (PVME/PS) blend studied by ultrafast differential scanning calorimetry

In this work, ultrafast differential scanning calorimetry (UFDSC) is used to study the dynamics of phase separation. Taking poly(vinyl methyl ether)/polystyrene (PVME/PS) blend as the example, we firstly obtained the phase diagram that has lower critical solution temperature (LCST), together with the glass transition temperature (T_g) of the homogeneous blend with different composition. Then, the dynamics of the phase separation of the PVME/PS blend with a mass ratio of 7:3 was studied in the time range from milliseconds to hours, by the virtue of small time and spatial resolution that UFDSC offers. The time dependence of the glass transition temperature (T_g) of PVME‐rich phase, shows a distinct change when the annealing temperature (T_a) changes from below to above 385 K. This corresponds to the transition from the nucleation and growth (NG) mechanism to the spinodal decomposition (SD) mechanism, as was verified by morphological and rheometric investigations. For the SD mechanism, the temperature‐dependent composition evolution in PVME‐rich domain was found to follow the Williams–Landel–Ferry (WLF) laws. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1357–1364     

Phase separation in thin films of end‐grafted block copolymers

An atomic force microscopy investigation was carried out on various thick (30–120 nm) polymethyl methacrylate‐b‐polystyrene and poly(2‐(dimethyl amino)ethyl methacrylate)‐b‐polystyrene films prepared via a grafting‐from method. The structure of the films was examined with both topographic and phase imaging. Several different morphologies were observed including a perforated lamellar phase with irregular perforations. In addition, complementary small‐angle X‐ray scattering and reflectometry results measurements on a non‐grafted polymer are presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Phase Separation,Wetting and Dewetting in PS/PVME Blend Thin Films: Dependence on Film Thickness and Composition Ratio

The effects of film thickness and composition ratio on the morphology evolution of polystyrene (PS)/poly(vinyl methyl ether) (PVME) blend thin films were investigated. Diverse morphology evolutions including droplet-matrix structure, hole emergence, bicontinuous structure formation, percolation-to-droplet transition could be observed under annealing in two-phase region, depending on film thickness and composition ratio. The mechanism for these morphology variations was related to the complex effects of phase separation, dewetting and preferential wetting. The comparison between the thickness of bottom PVME layer and the twice of gyration radius 2R_g(PVME) played a dominant role in morphology control. Only when the PS/PVME film had specific film thickness and compositional symmetry, phase separation and dewetting could happen in sequence.     

Phase separation in thin films of polymer blends: The influence of symmetric boundary conditions

Using nuclear reaction analysis composition‐depth profiling, we investigate the influence of symmetric/asymmetric confining walls on the equilibrium configuration of thin films of phase‐separated polymer blends. Depth profiles of samples annealed under symmetric boundary conditions show a laterally averaged concentration, while samples confined by nonsymmetric walls show (as in earlier studies) clear separation into two thin layers of coexisting phases. This suggests that for phase separation under symmetric boundary conditions the interface between the two phases is orthogonal to the sample plane, in line with recent theoretical discussion. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 831–837, 2000     

Phase transitions in calcium nitrate thin films

Calcium carbonate is a ubiquitous mineral and its reactivity with indoor and outdoor air pollutants will contribute to the deterioration of these materials through the formation of salts that deliquesce at low relative humidity (RH). As shown here for calcium nitrate thin films, deliquescence occurs at even lower relative humidity than expected from bulk thermodynamics and lower than the recommended humidity for the preservation of artifacts and antiques.     

Hexagonal-to-cubic phase transformation in composite thin films induced by FePt nanoparticles located at PS/PEO interfaces

The organization process of asymmetric poly(styrene-block-ethylene oxide) (PS-b-PEO) copolymer thin films blended with FePt nanoparticles is studied. In a first step, it is shown that FePt nanoparticles stabilized by oleic acid ligands are distributed within the PS matrix phase, whereas the same particles partially covered with short dopamine-terminated-methoxy poly(ethylene oxide) (mPEO-Dopa) are located at PS/PEO interfaces. The swelling of PS domains, induced by FePt_oleic acid nanoparticles during the solvent annealing process, results in formation of a disordered microstructure in comparison to the well-organized hexagonally close-packed (HCP) cylinder phase formed in the neat PS-b-PEO copolymer. The evolution of the microstructure of PS-b-PEO/FePt_mPEO-Dopa composite has been investigated for different solvent annealing treatments. Under high-humidity conditions during the vapor annealing process, the addition of FePt nanoparticles results in formation of spheres in the film split into terraces. The upper and lower terraces are occupied by spheres organized in an unusual square and HCP phases, respectively. Under low-humidity conditions, undulated PEO cylinders oriented parallel to substrate are formed in the presence of FePt nanoparticles. In this case, we observe that most of the nanoparticles accumulate within the core of topological defects, which induces a low nanoparticle concentration at the PS/PEO interfaces and so stabilizes an intermediate undulated cylinder phase.     

Highly selective multilayer polymer thin films for CO2/N2 separation

Multilayer thin films of poly(ethylene oxide) (PEO) and poly(methacrylic acid) (PMAA), deposited via layer‐by‐layer (LbL) assembly from aqueous solutions, are investigated for CO₂/N₂ separation. Eight and ten bilayer (217 and 389 nm thick, respectively) PEO/PMAA thin films deposited on a 25 μm polystyrene substrate exhibit CO₂/N₂ selectivities of 142 and 136, respectively. These are the highest reported to‐date for this gas pair separation using a homogeneous polymer film. While further work remains to improve CO₂ permeability, these results indicate the potential of LbL assemblies as standalone CO₂ separation membranes for low‐flux/high‐purity applications, or as part of a composite and/or mixed‐matrix membrane for high‐flux applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1730–1737     

Phase behavior in thin films of confined colloid-polymer mixtures

Using self-consistent-field and density-functional theories, we first investigate colloidal self-assembly of colloid-polymer films confined between two soft surfaces grafted by polymers. With increasing colloidal concentrations, the film undergoes a series of transitions from disordered liquid --> sparse square --> hexagonal (or mixed square-hexagonal) --> dense square --> cylindrical structures in a plane, which results from the competition between the entropic elasticity of polymer brushes and the steric packing effect of colloidal particles. A phase diagram displays the stable regions of different in-layer ordering structures as the colloidal concentration is varied and layering transitions as the polymer-grafted density is decreased. Our results show a new control mechanism to stabilize the ordering of structures within the films.     

Phase separation and disorder in half metallic ferromagnetic manganite thin films: A theoretical study looking forward low noise nano-devices

The resistivity of thin La_0.7Sr_0.3MnO₃ films was first investigated in a wide temperature (T) range (10–750 K). Films grown by different techniques and on several substrates enabled to analyze samples with different amounts of disorder. The aim of this work was to elucidate the nature of the metal–insulator (M–I) transition occurring at T = T_p in these films and its relation with the different kinds of inhomogeneities they could present like intrinsic electric disorder and co-existence of two different electrical and/or magnetic phases. The low-temperature resistivity state was described mostly by a law which scales as T with  ≈ 2.5. This supports the theoretical proposal of single magnon scattering in presence of minority spin states localized by the disorder. In the whole range of temperatures the experimental data are found to be consistent with a phase separation (PS) scenario. In order to go through the origin of the characteristic length scale of inhomogeneity found, preliminarily low frequency noise measurements as a function of T in a range of temperature around the M–I transition were made. The samples used were patterned using photolithography into bridges with various widths and lengths. No clear sign of separation phase dynamic has been observed in our noise measurements. Unexpectedly the normalized Hooge parameter _H/n was found not to be volume (Ω) independent. The LSMO electrical properties may strongly be driven by disorder and new design for magnetoresistance sensors may have to take into account their intrinsic PS.     

Ordered porous ZnO thin films formed by dip-coating method using PS templates

Monolayer polystyrene spheres (∼400 nm) array templates were assembled orderly on clean glass substrates by dip-coating method from emulsion of polystyrene (PS). Porous ZnO thin films were also prepared by dip-coating method to fill the interstices among the close-packed PS templates with ZnO and annealing to remove the PS templates. Results showed that ZnO sol concentration and dipping time of PS templates in sol had great influences on the morphology of ordered porous ZnO thin films. There was a shrinkage ratio of about 30% from pore to PS. SEM observation showed that the PS array templates had face-centered cubic close-packing. X-ray diffraction (XRD) spectra showed the porous ZnO thin film was wurtzite structure. The optical transmittance decreased with decreasing wavelength of lights, but was kept above 80% beyond the wavelength of 550 nm. Optical band-gap of the porous ZnO thin film annealed at 500°C was 3.22 eV.     

An AFM, XPS and wettability study of the surface heterogeneity of PS/PMMA-r-PMAA demixed thin films

A series of homopolymer/random copolymer blends was used to produce heterogeneous surfaces by demixing in thin films. The chosen homopolymer is polystyrene (PS) and the random copolymer is poly(methyl methacrylate)-r-poly(methacrylic acid) (PMMA-r-PMAA), whose acidic functions could be used as reactive sites in view of further surface functionalization. The proportion of each polymer at the interface was deduced from X-ray photoelectron spectroscopy (XPS) data using, on the one hand, the O/C ratio, and on the other hand, decomposition of the carbon peak of the blends in two components corresponding to the carbon peaks of PS and PMMA-r-PMAA. Combining the information from XPS with atomic force microscopy (AFM) images, water contact angle measurements and PS selective dissolution, it appears that the surfaces obtained from blends with a high PS content (90/10 to 70/30) display pits with a bottom made of PMMA-r-PMAA, randomly distributed in a PS matrix. On the other hand, the surfaces obtained from blends with a low PS content (30/70 to 10/90) display randomly distributed PS islands surrounded by a PMMA-r-PMAA matrix. The characteristics of the heterogeneous films are thought to be governed by the higher affinity of PMMA-r-PMAA for the solvent (dioxane), which leads to the elevation of the PS phase compared to the PMMA-r-PMAA phase, and to surface enrichment in PMMA-r-PMAA.     

Morphological phase separation in unstable thin films: pattern formation and growth

We present results from a comprehensive numerical study of morphological phase separation (MPS) in unstable thin liquid films on a 2-dimensional substrate. We study the quantitative properties of the evolution morphology via several experimentally relevant markers, e.g., correlation function, structure factor, domain-size and defect-size probability distributions, and growth laws. Our results suggest that the late-stage morphologies exhibit dynamical scaling, and their evolution is self-similar in time. We emphasize the analogies and differences between MPS in films and segregation kinetics in unstable binary mixtures.     

Microphase separation transition and ordering kinetics in thin films of diblock copolymers

Using x-ray reflectivity measurements, we have investigated the structure of films of a symmetric diblock copolymer of polystyrene-b-polyisoprene (M _w =15700). The film thickness is in the range of 1 m. In equilibrium the films consist of lamellae with a thickness of 15.3 nm. They are nearly completely oriented parallel to the substrate. The evolution of oriented structure is studied by time-dependent experiments. The time constants of the structure formation depend strongly on the annealing temperature. An enhancement of the diffuse intensity in the range of Yoneda scattering is evidence for an additional surface structure.