Phase separation induced ordered patterns in thin polymer blend films

Strategies for the utilization of phase separation to generate ordered pattern in polymer thin film are reviewed. First, the fundamental theory and factors influencing phase separation in polymer thin film are discussed. That is followed by a discussion of the formation of ordered patterns induced by phase separation in polymer thin films under the influence of a chemical heterogeneous substrate, convection or breath figures. The mechanisms and the conditions for well-ordered structures generated by phase separation are then discussed to show that multi-scaled/multi-component patterns, stimuli-responsive patterns may be developed by controlling the preparation conditions or exposing the sample to different environments more complex structures. Finally, applications of fabricated patterns in pattern generation and reproduction, antireflecting coating, catalysis, bio-chips and optoelectronics are also discussed.     

Conformational,thermal, and ionic conductivity behavior of PEO in PEO/PMMA miscible blend: Investigating the effect of lithium salt

In this research, influence of incorporating LiClO₄ salt on the crystallization, conformation, and ionic conductivity of poly(ethylene oxide) (PEO) in its miscible blend with poly(methyl methacrylate) (PMMA) is studied. Differential scanning calorimetry showed that the incorporation of salt ions into the blend suppresses the crystallinity of PEO. The X‐ray diffraction revealed that the unit‐cell parameters of the crystals are independent of the LiClO₄ concentration despite of the existence of ionic interactions between PEO and Li cations. In addition, the complexation of the Li⁺ ions by oxygen atoms of PEO is investigated via Fourier transform infrared spectroscopy. The conformational changes of PEO segments in the presence of salt ions are studied via Raman spectroscopy. It is found that PEO chains in the blend possess a crown‐ether like conformation because of their particular complexation with the Li⁺ ions. This coordination of PEO with lithium cations amorphize the PEO and is accounted for suppressed crystallinity of PEO in the presence of salt ions. Finally, electrochemical impedance spectroscopy is used to characterize the ionic conductivity of PEO in the PEO/PMMA/LiClO₄ ternary mixture at various temperatures. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Composition effect on dewetting of ultrathin films of miscible polymer blend

Two kinds of dewetting and their transition induced by composition fluctuation due to different composition in blend [poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN)] films on SiO_x substrate at 145 °C have been studied by in-situ atomic force microscopy (AFM). The results showed that morphology and pathway of dewetting depended crucially on the composition. Possible reason is the variation in intensity of composition fluctuation resulted from the change of components in polymer blend. Based on the discussion of this fluctuation due to the composition gradient, parameter of U_q0/E, which describes the initial amplitude of the surface undulation and original thickness of film respectively, has been employed to distinguish the morphologies of spontaneous dewetting including bicontinuous structures and holes. Prior to the investigation of dewetting, it is confirmed that this blend is miscible at 145 °C using grazing incidence ultra small-angle X-ray scattering (GIUSAX).     

Studies on blends of binary crystalline polymers: Miscibility and crystallization behavior in PBT/PAr(I27-T73)

The miscibility and crystallization behavior of binary crystalline blends of poly(butylene terephthalate) [PBT] and polyarylate based on Bisphenol A and a 27/73 mole ratio of isophthalic and terephthalic acids [PAr(I27-T73)] have been investigated by differential scanning calorimetry (DSC). This blend system exhibits a single composition-dependent glass transition temperature over the entire composition range. The equilibrium melting point depression of PBT was observed, and Flory interaction parameter χ₁₂ = −0.96 was obtained. These indicate that the blends are thermodynamically miscible in the melt. The crystallization rate of PBT decreased as the amount of PAr(I27-T73) increased, and a contrary trend was found when PAr(I27-T73) crystallized with the increase of the amount of PBT. The addition of high-T_g PAr(I27-T73) would suppress the segmental mobility of PBT, while low-T_g PBT would have promotional effect on PAr(I27-T73). The crystallization rate and melting point of PBT were significantly influenced when the PAr(I27-T73) crystallites are previously formed. It is because not only does the amorphous phase composition shift to a richer PBT content after the crystallization of PAr(I27-T73), but also the PAr(I27-T73) crystal phase would constrain the crystallization of PBT. Thus, effects of the glass transition temperature, interaction between components, and previously formed crystallites of one component on the crystallization behavior of the other component were discussed and compared with blends of PBT and PAr(I-100) based on Bisphenol A and isophthalic acid.     

Influence of nanoparticle-polymer interactions on the apparent migration behaviour of carbon nanotubes in an immiscible polymer blend

We investigate the influence of nanoparticle-polymer interactions on the apparent migration behavior of multiwall carbon nanotubes (CNTs) in an immiscible polymer blend of ethylene-acrylate copolymer (EA) and polyamide 12 (PA). The polymer-CNTs interaction is tuned by using different surface modification strategies, comprising grafting and coating. Poly(methyl methacrylate) (PMMA) and polystyrene (PS) are chosen as surface modifiers. The nanocomposite materials are prepared by melt-blending polymer-modified-CNTs in EA and PA. Polymer-grafted-CNTs tend to concentrate at the PA/EA interface, even if predispersed in PA, as opposed to pristine CNTs, which stay inside PA under the same circumstances. This new behavior is consistent with the morphology of PA/EA/(PMMA or PS) ternary blends and suggest a dominance of interfacial thermodynamics on CNTs localization. If we use polymer-coated-CNTs instead, the behavior depends on molar mass of the coating polymer. For low molar mass, it is similar to that of pristine CNTs and indicates desorption of the coating, owing to the weak interaction with the CNTs surface. Interestingly, we observe that long PS chains do not desorb and can drive the CNTs to the interface of the PA/EA blend. Moreover, the influence of kinetics is clearly observed through the dependence of CNTs interfacial confinement on dispersed droplet size.     

Study on miscibility of PEO and PCL in blends with PHB by solution viscometry

Viscometric studies were carried out for polymer-blend solutions in chloroform, i.e. for solutions of two polymers in a common solvent. Polymer blends comprised poly(3-hydroxy butyrate) (PHB) in combination with poly(ethylene oxide) (PEO) and poly(ε-caprolactone) (PCL), respectively. Experimental results obey the Huggins equation to an excellent approximation in the concentration range studied. Intrinsic viscosities vary linearly with blend composition to a good approximation. Huggins coefficients display generally nonlinear dependencies on blend composition. Positive deviations from perfect behaviour are attributed to attractions between different chain molecules or miscibility of the constituents. The viscometric study demonstrates that PEO is miscible with PHB, whereas PCL is immiscible.     

Dendritic crystallization in thin films of PEO/PMMA blends: A comparison to crystallization in small molecule liquids

Dendritic crystallization of poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) thin films is reported. The film thickness is kept constant while the PMMA molar mass and blend composition are varied. Some basic features of dendritic growth, such as the diffusion length and tip curvature are discussed. The diffusion coefficient is tuned by varying the molar mass of the non-crystallizable PMMA and the blend composition. The observed dendrite tip radius is on the order of 50 nm and the shape of the growth envelope varies from square to needle-like as the PMMA molar mass or PMMA content is increased. The sidebranch spacing increases with the distance from the dendrite trunk with a power-law relationship that is also dependent on the PMMA molar mass and PMMA content. This coarsening process is similar to that reported for other classes of materials. These similarities (the curved dendrite tip, power-law relationship of the sidebranches, and the sidebranch coarsening processes) indicate that the large scale crystallization morphologies of the polymeric materials we study are similar to those found in crystallization of small molecules and metals.     

Effect of hydrodynamics on dynamics of phase separation in polystyrene/poly(vinyl methyl ether) blend

Polystyrene/poly(vinyl methyl ether) (PS/PVME) phase diagram was assessed by rheological tools and by on-line microscopy observations both under quiescent and shear flow conditions. Shear flow was found to induce both mixing and demixing of the mixture depending on the amplitude of the imposed shear rate. Viscoelastic properties of PS/PVME blends were also measured under steady shear flow near the phase separation temperature. At lower shear rate, flow enhances concentration fluctuation and induces phase segregation. At high shear rate, flow suppresses fluctuations and the polymer mixture keeps its miscible state. Several rheological signatures of phase transition were found. In steady shear flow, a secondary plateau in viscosity was observed when the temperature was close to T_s whereas, at the start-up shear flow, transient shear stress showed a second overshoot after a few minutes of shearing.     

Nanocomposite polymer electrolyte comprising PEO/LiClO4 and solid super acid: effect of sulphated-zirconia on the crystallization kinetics of PEO

A novel PEO-based nanocomposite polymer electrolyte is prepared by using solid super acid sulphated-zirconia (, SZ) as the filler. Polarized optical microscopy (POM) and differential scanning calorimeter (DSC) results show that part of SZ particles may act as the nucleus of PEO spherulites and thus increase the amount of PEO spherulites. On the other hand, other SZ particles, which do not act as the nucleus, can restrain the recrystallization tendency of PEO chains through Lewis acid-base interaction and hence decrease the growth speed of PEO spherulites. As a result, the PEO component in PEO-LiClO₄-SZ can maintain a high amorphous state for a long time. The room temperature ionic conductivity of PEO-LiClO₄-SZ is relative high and stable compared with pristine PEO-LiClO₄, indicating that it is promising for all solid-state rechargeable lithium ion batteries.     

Surface energy inducing asymmetric phase distribution in films of a bynary polymeric blend

The phase morphology of blends of low density polyethylene (PE) with low molecular weight copolyamide (CPA) was investigated in films having 50-100 μm thickness. Films were prepared by compression moulding between two surfaces with different polarity, namely teflon and aluminium sheets, in a parallel plate heating press. The film surface characterization and surface energy deduction were performed by FT-IR/ATR spectroscopy and contact angle measurements, respectively. Moreover, the morphology and phase distribution were investigated by scanning electron microscopy both on the surfaces and on the cryogenic section of the films.The copolyamide resulted to be the dispersed phase in all compositions (90/10, 95/5, 97.5/2.5 and 99/1 PE/CPA) and the shape, dimension and distribution of the domains depending on temperature, pressure, time and nature of the surfaces used during the compression stage.The experimental evidences were discussed with respect to the different surface energies of the type of moulding material during the film preparation and related compatibility of the components.     

Solid-state NMR studies on phase behavior and motional mobility in binary blends of polystyrene and poly(cyclohexyl methacrylate)

The phase behavior and motional mobility in binary blends of polystyrene (PS) and poly(cyclohexyl methacrylate) (PCHMA) have been investigated by solid state ¹³C NMR techniques. The blend miscibility has been studied by examining the ¹H spin-relaxation times in the laboratory frame (T₁^H) and in the rotating frame (T_1ρ^H) for the PCHMA/PS blends with various compositions and pure components. The T_1ρ^H results show that PCHMA and PS are intimately mixed at the molecular level within the blends at all compositions. In addition, according to the results of carbon T_1ρ relaxation time measurements, we conclude that mixing is intimate enough to cause a reduction in local chain mobility for PS, but an increase in side chain mobility for PCHMA.     

Compatibilisation of heterogeneous acrylonitrile-butadiene rubber/polystyrene blends by the addition of styrene-acrylonitrile copolymer: effect on morphology and mechanical properties

Compatibility of polystyrene (PS) and acrylonitrile-butadiene rubber (NBR) blend is poor, hence technological compatibilisation was sought by the addition of styrene-acrylonitrile copolymer (SAN). The interfacial activity of SAN was studied as a function of compatibiliser concentration by following the morphology of three different blend series, viz. PS/NBR 30/70, 50/50 and 70/30. Incorporation of SAN into PS/NBR blends improved tensile, tear, hardness and impact properties. Addition of SAN beyond the saturation level (critical micelle concentration) adversely affected the ultimate properties. Attempts were made to understand the conformation of the compatibiliser at the interface. The protocol of mixing was varied, and, its effect on the mechanical properties was investigated. The experimental results were compared with the theoretical predictions of Noolandi and Hong.     

Molecular weight influence on shape memory effect of shape memory polymer blend (poly(caprolactone)/styrene-butadiene-styrene)

The shape memory effect (SME) does not only concern the macroscopic structure. It concerns also the polymer structure at morphological, macromolecular, and molecular scales. This effect may depend on different physicochemical properties like morphology heterogeneity, chain rigidity, steric hindrance, chain polarity, free volume, cross-linking or entanglement density, molecular shape and weight, and so on. Hence, finding the relationship between the SME and these properties is very important. This can help to obtain the knowledge about the phenomenon origin and mechanism. One of the basic polymer properties, which can have direct SME, may be the molecular weight (M_w ). The question here is: If the M_w of a shape memory polymer (SMP) changes, for different reasons like degradation, what will be the effect of this change on its SME. In order to answer to this question, the investigation is focused on an SMP blend of 40% poly(ɛ-caprolactone) (PCL) and 60% styrene-butadiene-styrene (SBS). Then, enzymatic hydrolysis is performed on this blend to change its M_w . It is shown that this change is only related to the variation in the M_w of PCL. After that, different samples with a distinct average M_w are prepared and characterized by various experimental methods. Shape memory tests are performed on these blends, and the recovery rate (R_r ) for each of them is determined. It is found that when M_w of PCL decreases, its degree of crystallinity, its glass transition, and its melting temperatures, corresponding to the PCL phase, increase. However, the elongation at break of the blend declines with the reduction in M_w . The tests show that the alteration in the blend's M_w influences its SME. Indeed, R_r of the (PCL/SBS) mixture drops with the decrease in M_w of PCL.     

Density effect on mixing and segregation processes in a vibrated binary granular mixture

The mixing and segregation processes of binary granular mixture with identical sizes but different densities particles subjected to vertical oscillatory excitation are investigated in this study. The spatial distributions of vibrated binary steel-glass beads mixture are visualized by simulation and the results are similar to the experimental data. The time evolution of pattern formations show that the heavy particles first move toward the center of the bed and then concentrate near the centers of the two convection cells of the vibrated system. The mechanism causing the mixing and segregation is strongly dependent on the momentum exchange of each species which is related to the granular temperature gradients of mixture components. The influences of solid fraction and granular temperature profiles on the mixing of the mixture are examined under different operating conditions. The simulation results show that the granular temperatures of heavy particles are higher than those of light particles, indicating that the granular temperatures do not equilibrate for the mixture system. The convection motion also plays an important role in determining the mixing of the system. For understanding the extent of granular mixing, the segregation intensity was determined to quantify the mixing rate of binary mixtures. The segregation intensity shows that the mixing rate increases with the vibration strength, but decreases with the initial heights of mixture.     

Investigation of different crystal habits without chemical additives in a three-phase reactor

A lot of powders with fine particle sizes and specific crystal habits are produced by precipitation processes, in which growth and morphology of the particles are controlled by a wide range of chemical agents. This study investigates alternative ways to limit crystal growth and influence crystal morphology. Experiments are carried out in an ultrasound levitator, where a single droplet can be suspended against gravity by an acoustic levitation force. The ultrasound leviator is a three-phase reactor, which allows the investigation of precipitation with applying specific shear forces at growing crystals within the droplet. The investigated system is calcium carbonate. By variation of physical reaction parameters as temperature and level of applied shear forces it is possible to obtain different crystal habits and morphologies. The morphology of calcium carbonate produced in the leviator can vary between prismatic, shell-like and spherical shape. Also the particle size distribution of the precipitated product is influenced. Increasing mechanical stress leads to a shift of the particle size distribution to smaller sizes.     

Molecular weight effect on swelling of polymer gels in homopolymer solutions: a fluorescence study

A novel technique based on in situ steady state fluorescence measurements is introduced for studying swelling processes of gels formed by free radical crosslinking copolymerization of methyl methacrylate (MMA) and ethylene glycol dimethacrylate (EGDM) in homopolymer solutions. Gels were prepared at 55±2 °C for various EGDM contents. After drying these gels, swelling experiments were performed in chloroform solution of anthracene labeled poly(methyl methacrylate) (An-PMMA) in various molecular weights at room temperature by real time monitoring of anthracene fluorescence intensity. Anthracene labeled PMMA chains having various molecular weights were prepared by atom transfer radical polymerization at 90 °C. During the swelling experiments, it was observed that anthracene emission intensities increased due to trapping of An-PMMA chains into the gel as the swelling time is increased. The trapping of An-PMMA chains in swollen gel, increase by obeying parabolic law in time. Penetration time constant, τ of PMMA chains were measured and found to be increased as the crosslinker density of gel is increased. It is observed that τ values are much higher for high molecular weight An-PMMA chains than low molecular weight chains in all gel samples.     

Development of nanofibrous morphology in LDPE/LLDPE/PP blends and its effect on mechanical properties of blend films

Nanofibrous morphology has been observed in ternary blends of low density polyethylene (LDPE), linear low density polyethylene (LLDPE), and isotactic polypropylene (PP) when these were melt‐extruded via slit die followed by hot stretching. The morphology was dependent on the concentration of the component polymers in ternary blend LDPE/LLDPE/PP. The films were characterized by wide angle X‐ray diffraction (XRD), scanning electron microscopy (SEM), and testing of mechanical properties. The XRD patterns reveal that the β phase of PP is obtained in the as‐stretched nanofibrillar composites, whose concentration decreases with the increase of LLDPE concentration. The presence of PP nanofibrils shows significant nucleation ability for crystallization of LDPE/LLDPE blend. The SEM observations of etched samples show an isotropic blend of LDPE and LLDPE reinforced with more or less randomly distributed and well‐defined nanofibrils of PP, which were generated in situ. The tensile modulus and strength of LDPE/LLDPE/PP blends were significantly enhanced in the machine direction than in the transverse direction with increasing LLDPE concentration. The ultimate elongation increased with increasing LLDPE concentration, and there was a critical LLDPE concentration above which it increased considerably. There was a dramatic increase in the falling dart impact strength for films obtained by blow extrusion of these blends. These impressive mechanical properties of extruded samples can be explained on the basis of the formation of PP nanofibrils with high aspect ratio (at least 10), which imparted reinforcement to the LDPE/LLDPE blend. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Microphase separation in ABA triblock copolymer-based model conetworks in the bulk: Effect of loop formation

This work estimates the free energy and domain size and predicts the phase diagram of microphase-separated model polymer conetworks, consisting of end-linked ABA triblock copolymers with cross-link points of relatively low functionality, in the strong segregation limit (highly incompatible A and B). Considering the case when these conetworks were prepared in the disordered state, their microphase separation is accompanied by extensive loop formation, with the fraction of loops depending on the morphology. The free energy of these conetworks is approximated using the expressions for linear block copolymers, modified to take into account the presence of loops whose free energy is estimated in two different approaches. The domain sizes in the conetwork system are found to be larger than those of the same morphologies in the linear system because of the reduction of the retractive force due to loop formation in the former system. The conetwork phase diagram is very sensitive to the expression used to describe the energy for loop formation.     

Synthesis of reactor blend of linear and branched polyethylene using metallocene/Ni‐diimine binary catalyst system in a single reactor

This work reports the synthesis of a series of reactor blends of linear and branched polyethylene materials using a combination of [1,4‐bis(2,6‐diisopropylphenyl) acenaphthene diimine nickel(II) dibromide] ( 1 )/MMAO, known as an active catalyst for the production of branched polyethylene, and [rac‐ethylenebis(indenyl) zirconium dichloride] ( 2 )/MMAO, which is active for the production of linear polyethylene. The polymerization runs were performed at various levels of temperature, pressure, and catalyst 2 molar fractions. At 5°C, there was very low influence of catalyst 2 molar fraction on the overall catalyst activity. However, at 30°C and 50°C, the overall catalyst activity increased linearly with catalyst 2 molar fraction. The same linear dependency was also found for the polymerization reactions carried out at 60°C and 100°C. At various levels of temperature and ethylene pressure, higher melting temperature and crystallinity were observed with an increase in catalyst 2 molar fraction. At 60°C and 100 psig, the DSC thermograms of the polymers produced with 1 / 2 /MMAO exhibited two distinct peaks with melting temperatures closely corresponding to the melting temperatures of the polymers produced with the individual catalysts, 1 /MMAO and 2 /MMAO. The GPCV analysis of all polyethylene samples showed monomodal molecular weight distributions with low polydispersities. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2212–2217, 2005     

Epoxidation of surface-bound polynorbornene films on silicon: Preventing degradation via solvent effect

We describe a strategy to prevent the detachment of polymer chain during the epoxidation of covalently grafted polynorbornene (PNb) films. Surface-bound PNb was prepared by surface-initiated ring-opening metathesis polymerization (SIROMP) from Si/SiO₂ substrates, and then epoxidized with meta-chloroperoxybenzoic acid by taking advantage of the double bonds along the polymer chains. The polymer-solvent interactions of three model solvents (dichloromethane, ether and methanol) with grafted PNb and grafted epoxidized PNb were studied by measuring the intrinsic viscosity of the free counterparts in solutions with a capillary viscometer. Oxidative degradation of the films was evaluated by ellipsometric thicknesses. The change in surface morphology was characterized with atomic force microscopy (AFM). Reactions of degradation and epoxidation of grafted PNb in three model solvents were studied. Kinetics study revealed that the surface-bound PNb is epoxidized gradiently from the surface toward the silicon substrate in ether. Through the solvent control, epoxidation of surface-bound PNb film without degradation was achieved under relatively mild condition.