Phase Separation In Films Research Articles

High-diffraction-efficiency Fresnel lens based on annealed blue-phase liquid crystal–polymer composite

ABSTRACTWe demonstrated a relatively simple and effective method to fabricate a periodically isolated polymer wall of blue-phase liquid crystal Fresnel lens (BPLCFL) by employing a single-masking process of the ultraviolet (UV) irradiation, leading to excellent photopolymerisation-induced phase separation between blue -phase liquid crystal (BPLC) molecules and UV-curable monomers. Nevertheless, some uncured monomers would inherently reside in the BPLC-rich area and slightly inhibit the BPLC molecules realigned under the external electric field. To enhance the optical properties of the polymer-wall BPLCFL considerably, a novel technique for fabricating a pure BPLC zone is proposed that successfully expels the residual monomers from the BPLC volume using a thermal annealing process. Experimental results show that the maximum diffraction efficiency reaches ~36%, which approaches the theoretical limit of ~41%. Consequently, the annealing technique to purify phase-separated composite films has a strong potential to construct the BPLCFL in light of polarisation-free applications.

Ordered assemblies of Fe3O4 and a donor-acceptor-type π-conjugated polymer in nanoparticles for enhanced photoacoustic and magnetic effects

We report that the ordered structure in the assemblies of iron oxide nanoparticles in conjugated polymer nanoparticles is the key to achieve better properties to realize multimodal theranostic agents for magnetic resonance and photoacoustic imaging. Hybrid nanoparticles of a conjugated polymer (PCPDTBT), a phospholipid (D8PE) with a primary amine polar head, and iron oxide (Fe3O4) nanoparticles were prepared by a phase-separated film shattering process by varying the iron oxide concentration while maintaining a fixed mixing ratio of PCPDTBT and D8PE. Notably, the hybrid nanoparticles assembled at a molar mixing ratio of 1:1:0.8 (PCPDTBT/D8PE/Fe3O4) exhibited the shortest transversal relaxation time, T2, and a photoacoustic signal 22 times higher than that obtained at the 1:1:0 mixing ratio. Structural analysis by X-ray diffraction together with the measurements of energy transfer by transient absorption spectroscopy confirmed that the structural ordering of these hybrid nanoparticles was responsible for their enhanced photoacoustic and magnetic properties.

Magnetic-field-induced phase separation via spinodal decomposition in epitaxial manganese ferrite thin films

ABSTRACTIn this study, we report about the occurrence of phase separation through spinodal decomposition (SD) in spinel manganese ferrite (Mn ferrite) thin films grown by Dynamic Aurora pulsed laser deposition. The driving force behind this SD in Mn ferrite films is considered to be an ion-impingement-enhanced diffusion that is induced by the application of magnetic field during film growth. The phase separation to Mn-rich and Fe-rich phases in Mn ferrite films is confirmed from the Bragg’s peak splitting and the appearance of the patterned checkerboard-like domain in the surface. In the cross-sectional microstructure analysis, the distribution of Mn and Fe-signals alternately changes along the lateral (x and y) directions, while it is almost homogeneous in the z-direction. The result suggests that columnar-type phase separation occurs by the up-hill diffusion only along the in-plane directions. The propagation of a quasi-sinusoidal compositional wave in the lateral directions is confirmed from spatially resolved chemical composition analysis, which strongly demonstrates the occurrence of phase separation via SD. It is also found that the composition of Mn-rich and Fe-rich phases in phase-separated Mn ferrite thin films deposited at higher growth temperature and in situ magnetic field does not depend on the corresponding average film composition.

Phase separation and surface properties of poly(propyl methacrylate-b-methyl methacrylate) diblock copolymers

The phase separation and surface characteristics of poly(propyl methacrylate-b-methyl methacrylate) (PPrMA-b-PMMA) diblock copolymers were studied and compared to strongly phase-separated poly(pentyl methacrylate-b-methyl methacrylate) (PPMA-b-PMMA) block copolymers (BCPs). PPrMA-b-PMMA with varied compositions and molar masses was synthesized by living anionic polymerization. The phase separation was studied by DSC, SAXS, TEM and AFM. The experimental data were compared to the calculated phase diagram. PPrMA-b-PMMA BCPs were weakly phase-separated, and indications for the existence of a relative broad interface between the blocks were observed. Nevertheless, two ordered morphologies—hexagonally packed cylinders and lamellae—depending on the molar composition were distinguished. The phase separation in thin films was studied by AFM in comparison with PPMA-b-PMMA. The wetting behavior of the thin films was examined by contact angle measurements. The water contact angles on PPrMA-b-PMMA were clearly influenced by both blocks. XPS confirmed the presence of both blocks in the top surface layer, which was different to PPMA-b-PMMA diblock copolymers where the top layer consisted only of PPMA blocks. Thus, only the weakly phase-separated PPrMA-b-PMMA BCP system allowed the generation of phase-separated films with tunable wetting characteristics.

Polyurethane/polyphenylsilsequiloxane nanocomposite: From waterborne dispersions to coating films

Proper building of polymer/polysilsequioxane composite is determined by deep-rooted structural variables. This work focuses on the fabrication of silane-grafted waterborne polyurethane (DWPU)/polyphenylsilsequioxanes (PPSQ) composites by blending and in-situ methods, respectively. By using blending method, PPSQ nanoparticle latexes were dispersed in DWPU. By using in-situ method, as the precursor of PPSQ, phenyltrimethoxysilane was mixed in DWPU, and PPSQ was expected to be generated via in-situ sol-gel reaction during film formation. We systematically investigated the influences of PPSQ and its incorporation method on the phase separation of films. The competition between a heterophase-triggered phase separation and a silane-based crosslinking was found during film formation. The intrinsically local ordering permutation of PU segments was interrupted more or less with PPSQ. Both surface composition and morphology were altered in correspondence to the different addition amount of PPSQ. Furthermore, optical, mechanical, and thermal resistances of composite films were also investigated for potential applications as coatings.

Mapping nanoscale effects of localized noise-source activities on photoconductive charge transports in polymer-blend films

We develolped a method to directly image the nanoscale effects of localized noise-source activities on photoconducting charge transports in domain structures of phase-separated polymer-blend films of Poly(9,9-di-n-octylfluorenyl-2,7-diyl) and Poly(9,9-di-n-octylfluorene-alt-benzothiadiazole). For the imaging, current and noise maps of the polymer-blend were recorded using a conducting nanoprobe in contact with the surface, enabling the conductivity (σ) and noise-source density (NT) mappings under an external stimulus. The blend-films exhibited the phase-separation between the constituent polymers at domains level. Within a domain, high σ (low NT) and low σ (high NT) regions were observed, which could be associated with the ordered and disordered regions of a domain. In the NT maps, we observed that noise-sources strongly affected the conduction mechanism, resulting in a scaling behavior of σ ∝ in both ordered and disordered regions. When a blend film was under an influence of an external stimulus such as a high bias or an illumination, an increase in the σ was observed, but that also resulted in increases in the NT as a trade-off. Interestingly, the Δσ versus ΔNT plot exhibited an unusual scaling behavior of Δσ ∝ which is attributed to the de-trapping of carriers from deep traps by the external stimuli. In addition, we found that an external stimulus increased the conductivity at the interfaces without significantly increasing their NT, which can be the origin of the superior performances of polymer-blend based devices. These results provide valuable insight about the effects of noise-sources on nanoscale optoelectronic properties in polymer-blend films, which can be an important guideline for improving devices based on polymer-blend.

Reinforcing effect of graphene oxide reinforcement on the properties of poly (vinyl alcohol) and carboxymethyl tamarind gum based phase-separated film.

The current study deals with the preparation and the characterization of the PVA-CMT-GO films. The PVA-CMT film was translucent in nature and smooth to touch. The addition of GO resulted in the formation of agglomerated structures. XRD studies suggested that the incorporation of GO increased the average crystallite size. The mechanical properties of the films as determined by stress relaxation studies suggested that all the films were viscoelastic in nature. The drug release study showed a decrease in the amount of the drug release with the increase in the GO content. The PVA-CMT-GO films (without drug) showed certain degree of antimicrobial activity owing to the inherent antimicrobial property of GO. The drug loaded films also showed good antimicrobial property. It was found that the prepared films altered the cell proliferation of the human skin keratinocytes in a composition-dependent manner.

Morphology of phase-separated VO2 films deposited on TiO2-(001) substrate

The basic morphology of phase-separated VO2 films, in which the tetragonal (metallic) phase coexists with the monoclinic (insulating) phase, was studied using transmission electron microscopy. While the phase transformation temperature in an unstrained crystal is approximately 340 K, it was observed that at 298 K, elastic strain (caused by lattice mismatch with the TiO2-(001) substrate) stabilized the tetragonal phase near the VO2/TiO2 boundary. The observed zig-zag-shaped interface of the tetragonal phase was explained by the crystallographic orientation relationship between the tetragonal and monoclinic phases. The observations provide valuable information for future applications of VO2 films.

Investigation of a possible electronic phase separation in the magnetic semiconductors Ga1−xMnxAs and Ga1−xMnxP by means of fluctuation spectroscopy

We present systematic temperature-dependent resistance noise measurements on a series of ferromagnetic Ga$_{1-x}$Mn$_{x}$As epitaxial thin films covering a large parameter space in terms of the Mn content $x$ and other variations regarding sample fabrication. We infer that the electronic noise is dominated by switching processes related to impurities in the entire temperature range. While metallic compounds with $x>2$ % do not exhibit any significant change in the low-frequency resistance noise around the Curie temperature $T_\mathrm{C}$, we find indications for an electronic phase separation in films with $x<2$ % in the vicinity of $T_\mathrm{C}$, manifesting itself in a maximum in the noise power spectral density. These results are compared with noise measurements on an insulating Ga$_{1-x}$Mn$_{x}$P reference sample, for which the evidence for an electronic phase separation is even stronger and a possible percolation of bound magnetic polarons is discussed. Another aspect addressed in this work is the effect of ion-irradiation induced disorder on the electronic properties of Ga$_{1-x}$Mn$_{x}$As films and, in particular, whether any electronic inhomogeneities can be observed in this case. Finally, we put our findings into the context of the ongoing debate on the electronic structure and the development of spontaneous magnetization in these materials.

Evolution of Intrinsic and Magnetic Field-Induced Magnetic Anisotropies in Strongly Phase-Separated Manganite Thin Films

Single crystalline thin film (∼ 100 nm) of La0.18Pr0.40Ca0.42MnO3 is grown on (001) oriented LaAlO3 substrates and the evolution of anisotropy associated with the supercooling behaviour of the magnetic liquid is studied as a function of temperature and magnetic field. The angle-dependent magnetization measurements ascertain that the easy magnetic axis lies in the plane of the film while the hard axis is along the plane normal. The ratio of the easy and hard axes magnetizations (M|| and M⊥) measured at 10 K, viz., M||/M⊥ (10 K) = 2.6, confirms the strongly anisotropic nature of the film. The easy axis ferromagnetic (FM) transition temperature (TC) is smaller than that along the hard axis. The giant hysteresis in FCC–FCW M–T, which manifests the magnetic liquid behaviour of the strongly phase-separated manganites is appreciably narrowed along the hard axis. The strain glass state is also less dominant along the easy axis. The analysis of the M–H data brings out that the easy axis remanence (Mr||) shows a nonlinear temperature dependence, while the one corresponding to the hard axis (Mr⊥) shows a nearly linear behaviour. The coercivity (HC) follows a law of the type \(H_{\mathrm {C}}\left (T \right )\mathrm {=}H_{\mathrm {C}}\mathrm {(0)(1-}{\text {AT}}^{b}\mathrm {)}\). The value of exponent b ∼ 0.5 for single-domain particles, but in the present case, the best fit to the experimental data yields the exponent b ≈ 0.25 for both HC|| and HC⊥. The smaller value of the exponent is attributed to the non-canonical nature of the ferromagnetic state and the associated strongly phase-separated nature of the LPCMO thin film.

Investigation of phase separated polyimide blend films containing boron nitride using FTIR imaging

Immiscible aromatic polyimide (PI) blend films and a PI blend film incorporated with thermally conductive boron nitride (BN) were prepared, and their phase separation behaviors were examined by optical microscopy and FTIR imaging. The 2,2′-bis(trifluoromethyl)benzidine (TFMB)-containing and 4,4′-thiodianiline (TDA)-containing aromatic PI blend films and a PI blend/BN composite film show two clearly separated regions; one region is the TFMB-rich phase, and the other region is the TDA-rich phase. The introduction of BN induces morphological changes in the immiscible aromatic PI blend film without altering the composition of either domain. In particular, the BN is selectively incorporated into the TDA-rich phase in this study.

Superhydrophobic Surfaces on Phase-separated Nanostructures of Polystyrene/Polymethyl Methacrylate Films Fabricated by the Double-spray Technique.

Rapid large-area printing techniques are required to fabricate superhydrophobic surfaces of polymer films on solid substrates. Here, we report a double-spray technique for fabrication of mixed phase-separated films of polystyrene (PS), poly(methyl methacrylate) (PMMA), and PS-b-PMMA. The surface wettability of the films changes to superhydrophobic by immersing the samples in cyclohexane, which is a good solvent for only PS. The rinsing process forms nanostructures in the remaining PMMA films that have flat surfaces before the rinsing treatment. The highest contact angle is about 150° on the film with a PMMA ratio of 0.2. X-ray photoelectron spectroscopy shows that a small amount of PS remains on the surface of the PMMA films, making the films superhydrophobic. Addition of PS-b-PMMA to the PS/PMMA films forms smaller phase-separated structures than those in the original PS/PMMA films because of an increase in the compatibility between PS and PMMA. The contact angle hysteresis in the films decreases with increasing PS-b-PMMA ratio, indicating an increase in the homogeneity of the phase-separated structures.

New insights on the influence of manufacturing conditions and molecular weight on phase-separated films intended for controlled release

The aim of this work was to investigate how manufacturing conditions influence phase-separated films of ethyl cellulose (EC) and hydroxypropyl cellulose (HPC) with different molecular weights of HPC. Two HPC grades, SSL and M, with weight average molecular weights (Mw) of 30×103g/mol and 365×103g/mol, respectively, were combined with EC 10 cps (70:30w/w EC/HPC) and spray-coated from ethanol solutions onto a rotating drum under well-controlled process conditions. Generally, a low spray rate resulted in a more rapid film drying process and, consequently, in smaller HPC-rich domains in the phase-separated film structure. For EC/HPC films with the low Mw HPC (SSL) the most rapid drying process resulted in a shift from a HPC-discontinuous to a partly bicontinuous structure and an increase in the permeability for water. In contrast, films containing the high Mw HPC (M) all showed bicontinuous structures, which resulted in overall higher water permeabilities and polymer release compared to the low Mw films. Interestingly, a maximum in permeability was observed for the high Mw films at intermediate spray rates. Below this spray rate the permeability decreased due to a lower amount of polymer released and at higher spray rates, the permeability decreased due to a loss of pore connectivity (or increased tortuosity). To conclude, this study shows that different Mw systems of EC/HPC can respond differently to variations in manufacturing conditions.

Quantifying phase separation in terms of magnetoresistive hysteresis loops in strongly phase-separated manganite thin films

The present work reports the scaling behaviour of thermomagnetic hysteresis in temperature and magnetic field-dependent resistivity [(ρ–T) and (ρ–H)] measured during cooling/warming and H increasing/decreasing cycles in single crystalline La0.21Pr0.42Ca0.37MnO3 thin films. The zero-magnetic field (H = 0) insulator–metal transition temperature (IMT) measured in warming cycle ( $$T_{{{\text{IM}}}}^{{\text{W}}}$$ ~ 163 K) is higher than that in the cooling cycle ( $$T_{{{\text{IM}}}}^{{\text{C}}}$$ ~ 116 K) and the difference between the two IMTs shrinks as H is increased. The magnetic field dependence of the two IMTs is well fitted by the equation $${T_{{\text{IM}}}}=T_{{{\text{IM}}}}^{0}+\beta {H^\alpha }$$ . Here, $$T_{{{\text{IM}}}}^{0}$$ is the H-independent contribution and the constants, pre-factor $$\beta$$ and exponent $$\alpha$$ determine the H-dependent part of the IMT. The ρ–T loop area diminishes with the increasing H and its scaling with H in the regime which is akin to a magnetic liquid and unstable towards external H (H < 30 kOe) is nicely described by $${A_T}={A_{T0}}{e^{ - {\Gamma}H}}$$ . Here, $${A_{T0}}$$ is the zero-field normalized area and Γ is a constant related to the degree of phase separation. The analysis of the isothermal ρ–H loop area, which increases with H shows a scaling behaviour of the type $$A(H)=a{(H - {H_{{\text{IM}}}})^\eta }$$ . Here, the constant HIM corresponds to the induced AFMI–FMM phase transition and decreases with temperature, while the exponent ‘η’ measures the degree of phase separation.

Conjugated Polymer Nanoparticles in Aqueous Media by Assembly with Phospholipids via Dense Alkyl Chain Packing

Revealing the nature of chain packing in conjugated polymer nanoparticles (CPNs) is one of the important issues to polymer physics research. Surfactant-stabilized CPNs in water show significantly enhanced luminescence intensity in comparison to small molecular organic dyes and single polymer chains dissolved in solvents. The importance of the conjugated polymer structure in nanomaterials is undoubted. However, details of the relationship between alignment of conjugated polymer backbone in CPNs and its luminescent property have not been established. Furthermore, there are yet no methods that can predict the atom-resolved structure of conjugated polymer in the CPNs. Herein, we employ coarse-grained (CG) molecular dynamic simulations to investigate the structure of phase-separated film and the film shattering process for a mixture of poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta[2,1-b;3,4-b′]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and 1,2-dioctanoyl-sn-glycero-3-phosphocholine (D8PC). The π...

Poly(N‐vinylpyrrolidone)–polydimethylsiloxane amphiphilic ABA triblock copolymers

ABSTRACTTriblock copolymers of N‐vinylpyrrolidone (NVP) and polydimethylsiloxane (PDMS) were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization using two different types of difunctional telechelic PDMS‐based dixanthate macroinitiators. The incorporation of PDMS into the triblock copolymers was evidenced by 1H NMR spectroscopy and varied between 4 mol % and as high as 20 mol %, dependent on reaction time and monomer conversion. The copolymer homogeneity was characterized in terms of molecular weight distribution determined by GPC to estimate the level of control over the chain length. Monomodal molecular weight distributions were observed, and 1H NMR spectroscopy indicated the copolymers had number average molecular weights (Mn) ranging between 28,000 and 160,000 g/mol. In addition, thin film phase separation and critical micelle concentrations for these copolymers were analyzed via transmission electron microscopy and surface tension measurements, respectively. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3387–3394

Water-induced phase separation of miconazole-poly (vinylpyrrolidone-co-vinyl acetate) amorphous solid dispersions: Insights with confocal fluorescence microscopy

The aim of this study was to evaluate the utility of confocal fluorescence microscopy (CFM) to study the water-induced phase separation of miconazole-poly (vinylpyrrolidone-co-vinyl acetate) (mico-PVPVA) amorphous solid dispersions (ASDs), induced during preparation, upon storage at high relative humidity (RH) and during dissolution. Different fluorescent dyes were added to drug-polymer films and the location of the dyes was evaluated using CFM. Orthogonal techniques, in particular atomic force microscopy (AFM) coupled with nanoscale infrared spectroscopy (AFM-nanoIR), were used to provide additional analysis of the drug-polymer blends. The initial miscibility of mico-PVPVA ASDs prepared under low humidity conditions was confirmed by AFM-nanoIR. CFM enabled rapid identification of drug-rich and polymer-rich phases in phase separated films prepared under high humidity conditions. The identity of drug- and polymer-rich domains was confirmed using AFM-nanoIR imaging and localized IR spectroscopy, together with Lorentz contact resonance (LCR) measurements. The CFM technique was then utilized successfully to further investigate phase separation in mico-PVPVA films exposed to high RH storage and to visualize phase separation dynamics following film immersion in buffer. CFM is thus a promising new approach to study the phase behavior of ASDs, utilizing drug and polymer specific dyes to visualize the evolution of heterogeneity in films exposed to water.

Spin Filtering in Epitaxial Spinel Films with Nanoscale Phase Separation.

The coexistence of ferromagnetic metallic phase and antiferromagnetic insulating phase in nanoscaled inhomogeneous perovskite oxides accounts for the colossal magnetoresistance. Although the model of spin-polarized electron transport across antiphase boundaries has been commonly employed to account for large magnetoresistance (MR) in ferrites, the magnetic anomalies, the two magnetic phases and enhanced molecular moment, are still unresolved. We observed a sizable MR in epitaxial spinel films (NiCo2O4-δ) that is much larger than that commonly observed in spinel ferrites. Detailed analysis reveals that this MR can be attributed to phase separation, in which the perfect ferrimagnetic metallic phase and ferrimagnetic insulating phase coexist. The magnetic insulating phase plays an important role in spin filtering in these phase separated spinel oxides, leading to a sizable MR effect. A spin filtering model based on Zeeman effect and direct tunneling is developed to account for MR of the phase separated films.

Specular and Diffuse Reflectance of Phase‐Separated Polymer Blend Films

Diffuse reflectors have various applications in devices ranging from liquid crystal displays to light emitting diodes, to coatings. Herein, specular and diffuse reflectance from controlled phase separation of polymer blend films, a well-known self-organization process, are studied. Temperature-induced spinodal phase separation of polymer blend films in which one of the components is selectively extracted is shown to exhibit enhanced surface roughness as compared to unextracted films, leading to a notable increase of diffuse reflectance. Diffuse reflectance of UV-visible light from such selectively leached phase-separated blend films is determined by a synergy of varying lateral scale of phase separation (≈200 nm to 1 μm) and blend film surface roughness (0-40 nm). These critical parameters are controlled by tuning annealing time (0.5-3 h) and temperature (140, 150, 160 °C) of phase separation. Angle-resolved diffuse reflection studies show that the surface-roughened polymer films exhibit diffuse reflectance up to 40° from normal incident light in contrast to optically uniform as-cast films that exhibit largely specular reflectance. Furthermore, the intensity of the diffusively reflected light can be enhanced (300-700 nm) or reduced (220-300 nm) significantly by coating the leached phase-separated films with a thin silver over layer.

Intermixed Donor/Acceptor Region in Conjugated Polymer Blends Visualized by Conductive Atomic Force Microscopy

The charge-transport characteristics of phase-separated blend films of poly(3-hexylthiophene) (P3HT; electron donor) and poly[2,7-(9,9-didodecylfluorene)-alt-5,5-(4′,7′-bis(2-thienyl)-2′,1′,3′-benzothiadiazole)] (PF12TBT; electron acceptor) were visualized by conductive atomic force microscopy (C-AFM). The C-AFM hole-current images clearly showed two phases: an electrically conductive region assigned to the P3HT-rich donor domain and a nonconductive region assigned to the PF12TBT-rich acceptor domain. The hole current in the conductive region was small compared with that of a neat P3HT film with similar thickness, indicating that the P3HT-rich domain contained a large fraction of PF12TBT as a minor component. Thermal annealing initially increased the hole current throughout the P3HT-rich domain because of reorganization of the P3HT chains from their as-cast configurations. Further annealing increased the hole current mainly in the middle of the P3HT-rich domain, but it decreased the hole current in the bo...