Pattern formation in dewetting poly(tert-butyl acrylate)/polyhedral oligomeric silsesquioxane (POSS) bilayer films

The surface morphology of dewetting poly(tert-butyl acrylate) (PtBA) and trisilanolphenyl-POSS (TPP) bilayers has been studied as a function of time at 95 degrees C. For short annealing times, only the upper nanoparticle (TPP) layer dewets from the underlying PtBA layer. The number and lateral dimensions of the holes in the upper TPP layer increase with increasing annealing times, forming interconnected rim structures. At later annealing times, scattered holes that reach down into the PtBA layer are observed among the interconnected rim structures. Fractal nanofiller (TPP)-rich aggregates are found at the bottom of the scattered holes.     

Morphological evolution in dewetting polystyrene/polyhedral oligomeric silsesquioxane thin film bilayers

Morphological evolution in dewetting thin film bilayers of polystyrene (PS) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP), was studied as a function of annealing temperature and annealing time. The results demonstrate unique dewetting morphologies in PS/TPP bilayers at elevated temperatures that are significantly different from those typically observed in dewetting polymer/polymer bilayers. During temperature ramp studies by optical microscopy (OM) in the reflection mode, PS/TPP bilayers form cracks with a weak optical contrast at approximately 130 degrees C. The crack formation is attributed to tensile stresses within the upper TPP layer. The weak optical contrast of the cracks observed in the bilayers for annealing temperatures below approximately 160 degrees C is consistent with the cracking and dewetting of only the upper TPP layer from the underlying PS layer. The optical contrast of the morphological features is significantly enhanced at annealing temperatures of >160 degrees C. This observation suggests dewetting of both the upper TPP and the lower PS layers that results in the exposure of the silicon substrate. Upon annealing the PS/TPP bilayers at 200 degrees C in a temperature jump experiment, the upper TPP layer undergoes instantaneous cracking as observed by OM. These cracks in the upper TPP layer serve as nucleation sites for rapid dewetting and aggregation of the TPP layer, as revealed by OM and atomic force microscopy (AFM). X-ray photoelectron spectroscopy (XPS) results indicated that dewetting of the lower PS layer ensued for annealing times >5 min and progressed up to 90 min. For annealing times >90 min, OM, AFM, and XPS results revealed complete dewetting of both the layers with the formation of TPP encapsulated PS droplets.     

Compatibility studies of polystyrene and poly(vinyl acetate) blends using electrostatic force microscopy

The effect of thermal treatment on the phase separation process of the components of a polymer blend was investigated using electrostatic force microscopy (EFM). EFM technique is an advance on conventional atomic force microscopy, which enables us to measure locally the dielectric properties of the samples under investigation providing compositional information. In this work, we studied the phase separation process of the polymer blend thin films made of polystyrene and poly(vinyl acetate) (PS/PVAc) (75/25 weight fraction). The samples were subjected to different thermal treatments. It was found that at low annealing temperature, PVAc forms many small islands within PS matrix. As the annealing temperature increases, the number of PVAc islands decreases with an increase in the size of the islands. These islands take spherical‐like shape when annealed at a temperature well above the glass transition temperatures of both the component polymers. Despite these morphological/topographical changes, EFM images evidence that there is no interdiffusion which was further confirmed by quantitatively measuring the value of the dielectric permittivity across the interphase. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1332–1338, 2011     

Effect of annealing on self-organized gradient film obtained from poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate)/poly(methyl methacrylate-co-n-butyl acrylate) blend latexes

The effect of annealing on the self-organized morphology and component gradient distribution of films prepared from bimodal latexes blend containing 1:1 silicon-containing acrylate copolymer/silicon-free acrylate copolymer blend was studied using attenuated total reflectance–Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy with X-ray energy-dispersive (SEM-EDX) spectrometry, and atomic force microscopy (AFM). The distribution of silicon through the whole thickness of the film as a function of annealing was investigated using confocal Raman spectroscopy (CRS). AFM results show that poly(methyl methacrylate-co-n-butyl acrylate) latex fuses to form a continuous film at 25?°C. The wettability of the acrylate components and the heterogeneous composition of poly(3-[tris(trimethylsilyloxy)silyl] propyl methacrylate-co-methyl methacrylate) result in a graded block film. ATR-FTIR and SEM-EDX measurements reveal silicon-containing components segregate at the film–air interface upon annealing. CRS further shows that the nonlinear model gradient distribution of silicon is obtained, where the content of silicon component is enhanced and it gradually varies in the bulk. When the annealing temperature increases to 120 and 180?°C, blend latexes films demonstrate varying topography and phase images, indicating phase separation is induced by annealing. Furthermore, CRS implies that the destruction of the gradient structure is attributed to the phase separation of the two blend components.     

Photophysical properties of [60]fullerenes and phthalocyanines embedded in ordered mesoporous silica films annealed at various temperatures

The photophysical properties of fullerene and/or phthalocyanine dyes embedded in ordered mesoporous silica films and the influence of annealing temperature on the nature of the immobilized dye molecules has been investigated using photoluminescence (PL) and diffuse reflectance (DR) studies. The PL and DR studies show that fullerene (C60) and/or zinc phthalocyanine (ZnPc) molecules incorporated into transparent mesoporous silica films, via either sol-gel or grafting routes, exist predominantly in monomeric form. Careful choice of annealing temperature, between 25 and 225 degrees C, can further enhance monomeric dispersion. For C60-containing films, monomeric dispersion of fullerene was observed for annealing temperatures up to 175 degrees C for sol-gel derived films and 225 degrees C for grafted films. Both sol-gel and grafted ZnPc-containing films showed evidence of monodispersed phthalocyanine for annealing temperatures up to 225 degrees C. In general, annealing temperatures in the range 125-175 degrees C were found to yield optimal monodispersion of the dye molecules. When both C60 and ZnPc were incorporated into the silica films, no evidence of interaction between the dyes, i.e., charge-transfer transitions or the formation of fullerene/phthalocyanine charge-transfer complexes, was observed. This suggests that embedded fullerene and phthalocyanine molecules may be used for the preparation of solid-state optical limiters, based on reverse saturable absorption, where monomeric dispersion of the dye molecules is important.     

Effects of POSS nanoparticles on glass transition temperatures of ultrathin poly(t‐butyl acrylate) films and bulk blends

As a model system, thin films of trisilanolphenyl‐POSS (TPP) and two different number average molar mass (5 and 23 kg mol^?1) poly(t‐butyl acrylate) (PtBA) were prepared as blends by Langmuir–Blodgett film deposition. Films were characterized by ellipsometry. For comparison, bulk blends are prepared by solution casting and the samples are characterized via differential scanning calorimetry. The increase in T_g as a function of TPP content for bulk high and low molar mass samples are in the order of ～10 °C. Whereas bulk T_g shows comparable increases for both molar masses (～10 °C), the increase in surface T_g for higher molar mass PtBA is greater than for low molar mass (～22 °C vs. ～10 °C). Nonetheless, the total enhancement of T_g is complete by the time 20 wt % TPP is added without further benefit at higher nanofiller loads. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 175–182     

An atomic force microscope study of thermal behavior of phospholipid monolayers on mica

We observed by using atomic force microscope (AFM) phospholipid (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) monolayers on mica being annealed and cooled to a selection of temperatures through steps of 2-4 degrees C/min. The annealed phospholipid monolayers started to disappear at 45-50 degrees C and disappeared completely above 60-63 degrees C under AFM observation. The phospholipid monolayers reformed when the samples were cooled below 60 degrees C and developed from fractal into compact monolayer films with decreasing temperatures. Simultaneously the height of the reformed phospholipid films also increased with decreasing temperatures from 0.4 nm to the value before annealing. The observed thermal features are attributed to a phase-transition process that upon heating to above 45-50 degrees C, the lipids condensed in the monolayers transform into a low-density expanded phase in which the lipids are invisible to AFM, and the transformation continues and completes at 60-63 degrees C. The lipid densities of the expanded phase inferred from the dissociated area of the condensed phase are observed to be a function of the temperature. The behavior contrasts with a conventional first-order phase transition commonly seen in the Langmuir films. The temperature-dependent height and shape of the reformed phospholipid films during cooling are argued to arise from the adjustment of the packing and molecular tilting (with respect to the mica surface) of the phospholipids in order to accommodate more condensed phospholipids.     

Studies on the Phase Separation of Poly(Ether Imide)‐Modified Cyanate Ester Resin

Abstract

A high temperature thermosetting bisphenol‐A dicyanate (BADCy) was blended with a novel thermoplastic poly(ether imide) (PEI) at various composition. The phase separation behavior during isothermal curing was studied by differential scanning calorimeter (DSC), time‐resolved light scattering (TRLS), scanning electron microscopy (SEM), and rheological measurements. The results suggested that the phase structure changed from separated phase, via co‐continuous phase, to phase inversion with the increase of the PEI content. The curing conversion of BADCy was slightly affected by the composition in the blend and the curing rate was decreased with the increase of PEI content. The co‐continuous phase morphology was attributed to a spinodal decomposition. The initial concentration of PEI had an effect on the rheological behavior during phase separation. It was found by tensile test that the blend with 15 wt.% PEI had higher tensile strength and elongation at break than that without PEI.     

Scaling tests of late stages of spinodal decomposition in PC/PMMA blends

Time-resolved light scattering studies were undertaken to elucidate the kinetics of phase separation in polycarbonate (PC)/polymethyl methacrylate (PMMA) blends. The 40:60 PC/PMMA blend undergoes thermally induced phase separation through spinodal decomposition. Temperature jump experiments were carried out from a single-phase to a two-phase temperature region. The general trend of spinodal decomposition in this blend system is nonlinear in character and obeys the power laws. The time evolution of scattering curves was analyzed in accordance with dynamical scaling laws for self-similarity and the shape of scaled structure functions.     

等规聚丙烯/二元乙丙橡胶合金相分离对结晶动力学的影响

用小角激光光散射(SALLS)、相差显微镜(PCM)、示差扫描量热仪(DSC)和偏光显微镜(POM)研究了聚丙烯/二元乙丙橡胶(iPP/EPR)共混体系的相分离行为和等温结晶行为.发现iPP/EPR(50/50,W/W)发生的液-液相分离遵循spinodal机理.通过Cahn-Hilliard方程求得了不同实验温度下iPP/EPR的表观扩散系数(Dapp)以及spinodal温度(Ts).考察了不同相分离程度的iPP/EPR体系结晶动力学,发现延长相分离时间(tps)或提高相分离温度(Tps)均会导致半结晶时间(t1/2)增大,即结晶速率降低.这被归于EPR成核作用的降低.动力学分析结果表明Avrami模型适用于描述该体系的等温结晶过程,其结晶机理基本不受相分离程度的影响,结晶均以瞬时成核和三维生长为主.     

Phase separation and phase dissolution in poly(ε-caprolactone)/poly(styrene-co-acrylonitrile) blend

A blend of poly(ε-caprolactone) (PCL) and poly(styrene-co-acrylonitrile) (SAN) containing 27.5 wt% of acrylonitrile having the critical composition (80/20 PCL/SAN) was studied. This PCL/SAN blend having a lower critical solution temperature (LCST) phase boundary at 122 °C offered an excellent opportunity to investigate, firstly the kinetics of phase separation above LCST (125-180 °C), and secondly the kinetics of phase dissolution below LCST (50-115 °C). The blend underwent a temperature-jump above LCST where spinodal decomposition (SD) proceeded, yielding a regularly phase-separated structure (SD structure). Then, it was quenched to the temperatures below LCST when the phase dissolution proceeded. Optical microscopy was used to observe the spinodal decomposition qualitatively while light scattering was used to characterize the phase separation and phase dissolution quantitatively. It was found that during phase dissolution the peak maximum moved towards a smaller angle (wavelength of concentration fluctuations increased) while the peak intensity decreased. This behavior was explained by a model. Also it was found that the fastest phase dissolution kinetics at 80 °C, which was characterized by an apparent diffusion coefficient, was about 10 times slower than the kinetics of phase separation at 180 °C.     

GIUSAXS and AFM studies on surface reconstruction of latex thin films during thermal treatment

The structural evolution of a single-layer latex film during annealing was studied via grazing incidence ultrasmall-angle X-ray scattering (GIUSAXS) and atomic force microscopy (AFM). The latex particles were composed of a low-Tg (-54 degrees C) core (n-butylacrylate, 30 wt %) and a high-Tg (41 degrees C) shell (t-butylacrylate, 70 wt %) and had an overall diameter of about 500 nm. GIUSAXS data indicate that the q(y) scan at q(z) = 0.27 nm(-1) (out-of-plane scan) contains information about both the structure factor and the form factor. The GIUSAXS data on latex films annealed at various temperatures ranging from room temperature to 140 degrees C indicate that the structure of the latex thin film beneath the surface changed significantly. The evolution of the out-of-plane scan plot reveals the surface reconstruction of the film. Furthermore, we also followed the time-dependent behavior of structural evolution when the latex film was annealed at a relatively low temperature (60 degrees C) where restructuring within the film can be followed that cannot be detected by AFM, which detects only surface morphology. Moreover, compared to AFM studies GIUSAXS provides averaged information covering larger areas.     

Formation and dissolution of phase-separated structures in ultrathin blend films

The phase separation of ultrathin polymer blend films of deuterated poly(styrene)/poly(vinylmethylether) leads to a variety of film morphologies, depending on polymer composition. Phase-separation measurements are made at a constant temperature difference from the critical temperature, leading to a bicontinuous spinodal decomposition pattern for near-critical blend compositions and to “mounds” and “holes” for PVME-rich and dPS-rich off-critical mixtures, respectively. Reverse temperature jumps of the phase-separated blend films into the one-phase region result in dissolution of the undulating surface patterns, confirming the phase-separation origin of the film patterns. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36 : 191–200, 1998     

Dynamic aspects of phase decomposition in reactive blends of polycarbonate and syndiotactic polymethyl methacrylate

Dynamics of phase separation in bisphenol-A polycarbonate (PC)/syndiotactic polymethyl methacrylate (sPMMA) blends has been investigated by means of time-resolved light scattering. Solvent-cast films of the PC/sPMMA blends were transparent, suggestive of miscible character. Several temperature jumps were carried out at a 50/50 PC/sPMMA composition from a homogeneous state (room temperature) into a two-phase regime. The process of phase separation first occurred for some considerable period, then it was followed by phase dissolution driven by chemical reaction. The thermodegradative reaction of sPMMA triggered the dissolution process by probably forming PC/sPMMA graft or random copolymers at the interface, which eventually resulted in a single phase. However, annealing at elevated temperatures for an extended period could lead to cross-linking, and thus a two-phase structure could be fixed permanently. The early stage of spinodal decomposition was interpreted in terms of the linearized Cahn-Hilliard theory. In the late stages of spinodal decomposition, the relationship between scattering peak wavenumber and time was found to obey a power law, but the exponents showed a strong dependence on temperature jumps. The temporal universal scaling failed due to the influence of the chemical reaction. © 1995 John Wiley & Sons, Inc.     

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     

Effect of pressure on phase behavior in polymer blends of poly(2,6-dimethyl-1,4-phenylene oxide) and poly(styrene-co-p-fluorostyrene) copolymers

The effect of pressure on the miscibility of blends of poly(2,6-dimethyl-l,4-phenylene oxide) (PPO) with a random copolymer of styrene and para-fluorostyrene, P(S-co-p-FS), has been studied by high pressure differential thermal analysis (HPDTA). P(S-co-p-FS) copolymers less than 36 mole % p-FS are miscible with PPO in all proportions irrespective of pressure up to 200 MPa, using the customary criterion of a single calorimetric glass relaxation. P(S-co-p-FS) copolymers containing 40 to 50 mole % p-FS undergo phase separation upon annealing at elevated temperatures, indicating the existence of a lower critical solution temperature (LCST). In these blends, pressure displaces the phase boundary associated with the LCST to higher temperatures causing an apparent increase in polymer miscibility. The phase diagram for the blend of PPO and P(S-co-p-FS) containing 46 mole % p-FS, shows that the critical composition at about 50 wt % PPO does not change with pressure, but the consolute temperature T_c increases with increasing pressure. The pressure dependence of the LCST (dT_c/dP) of this system is about 0.35°C/MPa.     

Surface phase separation, dewetting feature size, and crystal morphology in thin films of polystyrene/poly(ε-caprolactone) blend

Thin films of polystyrene (PS)/poly(ε-caprolactone) (PCL) blends were prepared by spin-coating and characterized by tapping mode force microscopy (AFM). Effects of the relative concentration of PS in polymer solution on the surface phase separation and dewetting feature size of the blend films were systematically studied. Due to the coupling of phase separation, dewetting, and crystallization of the blend films with the evaporation of solvent during spin-coating, different size of PS islands decorated with various PCL crystal structures including spherulite-like, flat-on individual lamellae, and flat-on dendritic crystal were obtained in the blend films by changing the film composition. The average distance of PS islands was shown to increase with the relative concentration of PS in casting solution. For a given ratio of PS/PCL, the feature size of PS appeared to increase linearly with the square of PS concentration while the PCL concentration only determined the crystal morphology of the blend films with no influence on the upper PS domain features. This is explained in terms of vertical phase separation and spinodal dewetting of the PS rich layer from the underlying PCL rich layer, leading to the upper PS dewetting process and the underlying PCL crystalline process to be mutually independent.     

Thermal stability of cubic boron nitride films deposited by chemical vapor deposition

Thermal stability of well-crystallized cubic boron nitride (cBN) films grown by chemical vapor deposition has been investigated by cathodoluminescence (CL), Raman spectroscopy, and scanning electron microscopy (SEM) with the cBN films annealed at various temperatures up to 1,300 degrees C. The crystallinity of the cBN films further improves, as indicated by a reduction of the relevant Raman line width, when the annealing temperature exceeds 1,100 degrees C. Structural damage or amorphization was observed on the grain boundaries of the cBN crystals when annealing temperature reaches 1,300 degrees C. The CL spectra are found to be unchanged up to 1,100 degrees C after annealing at 500 degrees C, showing the stability of the cBN films in electronic properties up to this temperature. New features were observed in the CL spectra when annealing temperature reaches 1,200-1,300 degrees C.     

Fractional crystallization behavior of PCL and PEG in blends

The crystallization behavior of poly(e-caprolactone)/poly(ethylene glycol) (PCL/PEG) blend was investigated by differential scanning calorimetry (DSC) and polarized microscopy (POM). Individual phase transition peaks in the DSC curves for both PEG and PCL in all the polymer blends with different PCL contents were observed. The crystallization and melting peak temperatures of PEG were at 41 and 65°C, respectively; while the crystallization and melting temperatures of PCL located at 28 and 56°C, respectively. In-situ POM results demonstrated that spherulites crystalline morphology was formed for both PCL and PEG homopolymers. In PEG/PCL blend, however, both the phase separation morphology and spherulitic morphology can be observed. In blends with 30 or 50 wt % PCL, the PCL component formed dispersed phase and crystallized at lower temperature. However, in blends with 70% PCL, the phase inversion behavior occurred. The continuous PCL phase crystallized at 35°C, while the PEG dispersed phase crystallized at a lower temperature. Fractional crystallization behavior of PEG and PCL was controlled by temperature. The spherulites growth rate of PEG was greatly influenced by temperature, instead of the content of PCL component in the PCL/PEG blends.     

The effect of phase‐separated morphology on the rheological properties of polystyrene/poly(vinyl methyl ether) blend

The effect of phase‐separated morphology on the rheological properties of polystyrene/poly(vinyl methyl ether) (PS/PVME) blend was investigated by optical microscopy (OM), light scattering (LS) method, and rheology. The blend had a lower critical solution temperature (LCST) of 112°C obtained by turbidity experiment using LS at a heating rate of 1°C/h. Three different blend compositions (critical 30/70 PS/PVME by weight) and two off‐critical (50/50 and 10/90)) were prepared. The rheological properties of each composition were monitored with phase‐separation time after a temperature jump from a homogeneous state to the preset phase‐separation temperature. For the 30/70 and 50/50 blends, it was found that with phase‐separation time, the storage and loss moduli (G′ and G″) increased at shorter times due to the formation of co‐continuous structures resulting from spinodal decomposition. Under small oscillatory shearing, shear moduli gradually decreased with time at longer phase‐separation times due to the alignment of co‐continuous structures toward the flow direction, as verified by scanning electron microscopy. However, for the 10/90 PS/PVME blend, the rheological properties did not change with phase‐separation times. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 889–906, 1999