Rheology behavior of nematic side-chain polymers in blends with thermoplasts

Peculiarities of the rheological behavior of blends composed of thermoplasts and side-chain nematic polymers have been studied. The strong role of interface interactions associated with the polymer chemical structure on the effect of rheology is shown. The influence of the nematic ordering is shown to be effective in the mechanical characteristics of blend extrudates whereas the rheology effect does not depend on the liquid crystal ordering.     

Nanocrystalline LaYSrO films for liquid-crystal alignment via a solution process

The alignment of liquid crystals (LCs) has been widely studied to enable their use in high-quality displays. In addition to the deposition of an alignment layer, an alignment process to orient the LCs is also required. To accomplish self-alignment and to simplify the fabrication process, many alternatives have been proposed, including the doping of nanoparticles or organic/inorganic composites into LCs or the use of special treatments, such as ultra-violet (UV) irradiation or imprinting. However, an additional treatment is required to achieve proper LC orientation. Herein, we demonstrate the fabrication of an aligned LaYSrO (LYSO) via a solution process. Using this technique, we have generated a simple manufacturing method that eliminates the alignment process, and we have found that the quality of the LC cell is comparable to that of polyimide-rubbed films. The mechanisms of the film formation and the LC alignment were elucidated with a nanocrystalline LYSO film. In comparison with LCs, the nanocrystal is sufficiently large so that order in the LCs is induced along the direction of the nanocrystal. This approach allows for the fabrication of LC displays that meet specific goals such as high performance with a simple fabrication process.     

Rheology of concentrated blends with immiscible components

The rheology and morphology evolution of nondilute and concentrated immiscible blends were investigated in this paper. A theoretical model was established by a Hamiltonian formalism. The interactions between droplets were integrated in the morphology‐dependent drag coefficient. The phenomenological parameters in the model were determined by the comparisons with the dilute emulsion model and the Krieger–Dougherty model. The model showed better predictions in the shear viscosity and first normal stress difference than that of the dilute emulsion model. The effects of volume fraction on droplet deformation were also predicted and compared with the numerical simulations. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2534–2540, 2005     

Relationship between structure and rheological properties in the melt of polymers containing spherical inclusions

The linear viscoelastic behavior of model rubbertoughened polymer melts has been studied. The most significant influence of the dispersed crosslinked rubber phase on the melt rheology of the blends is the existence of a secondary plateau for the storage modulus G′ at low frequencies. This behavior was ascribed to a percolation phenomenon, leading to the formation of a threedimensional network of inclusions, and contributing to the elasticity at low frequencies of the blend. Two different systems were investigated: (a) a polystyrene matrix with crosslinked and structured latex particles and (b) silicon oil matrices with homogeneous crosslinked PMMA particles. An initial shearing history was found to influence the dynamic mechanical properties of the molten blends and in particular to lower the lowfrequency plateau value for G′. During a subsequent annealing, the plateau modulus increases again. These results are in agreement with the assumption of a particle network.     

Rheology of a polymer-based hybrid suspension composed of concentrated poly[(D,L-lactide)-co-glycolide] solution and inorganic salt particles

Suspensions composed of a solution of a biodegradable polyester in a volatile organic solvent, and solid inorganic particles of size in the order of hundreds of microns have been very important in the fabrication of porous scaffolds in the field of tissue engineering. This article reports the basic rheological investigations of this complex fluid type. A Couette geometry covered by silicon oil was found to be an appropriate geometry to retain stability of the rheological measurements. Suspension viscosity increased with the particle volume fraction, and the extent of the increase was much larger than that predicted by the Einstein suspension equation. Both start-up dynamics at the inception of steady shear and relaxation after an abrupt change of oscillatory shear frequency in the suspension showed significantly different behaviors from those in the associated polymer solution. Particle reorganization upon change of rheological state was anticipated.     

A rheological and morphological study of a copolyester liquid crystal/polypropylene blend system

The effects of composition and shear rate on the rheology and morphology of blends of LC–3000, a thermotropic liquid crystalline polymer consisting of 60/40 of hydroxybenzoic acid and poly(ethylene terephthalate), with polypropylene were studied. It was found that the rheological properties depend in a complex manner on composition and applied shear. Both positive and negative deviations from the log-additivity rule were observed at low shear rates. Significant viscosity reduction was measured when the dispersed phase was a nematic TLCP. The accompanying microstructural transitions were characterized a posteriori, and it was found that the state of dispersion of the TLCP phase also influences the viscosity reduction phenomenon. A nematic, fibrillar TLCP phase shows a viscosity reduction of the order of fourfold with respect to the viscosity of the matrix. Another important finding was that the stability of these fibers would not be expected from work on other non-TLCP-containing immiscible blends. This suggests that the unique rheology of the TLCP minor phase is relevant to the formation of stable fibers. © 1996 John Wiley & Sons, Inc.     

Comb-shaped polymers as effective flow modifiers for thermoplastic polymers

Peculiarities of the rheological properties of blends composed of thermoplastic polymer and polyacrylates are studied. The comparison of blends containing comb-shaped polymers of differing side-chain lengths shows that the flow mechanism changes with shortening side-group length. This leads to higher viscosity and elasticity of the combshaped component and, at the same time, results in the dramatic decrease in the blend viscosity, even at combshaped additive low content.     

Electronically conductive polymers

A concise review of papers published during the last 3 years about the synthesis, blends, processing, and applications of electronically conductive polymers, is presented in this article. Copyright © 2002 John Wiley & Sons, Ltd.     

All-polymer solar cells utilizing low band gap polymers as donor and acceptor

All-polymer solar cells based on blends of the low band gap polymers poly{[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]} (PTB7) and poly{[N,N-9-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,59-(2,29-bithiophene)} (P(NDI2OD-T2)) are demonstrated. The use of the donor polymer PTB7 instead of poly(3-hexylthiophene) results in a higher open-circuit voltage and an overall spectral response better matched to the solar spectrum. A power conversion efficiency of 1.1% is reported with a peak external quantum efficiency of 18% at a wavelength of 680 nm. The microstructure of PTB7:P(NDI2OD-T2) blends is also investigated using a combination of grazing-incidence wide-angle X-ray scattering (GIWAXS), near-edge X-ray fine-structure (NEXAFS) spectroscopy, atomic force microscopy (AFM), and scanning transmission X-ray microscopy (STXM). GIWAXS measurements show that PTB7:P(NDI2OD-T2) blends contain P(NDI2OD-T2) crystallites with a (100) thickness of 9.5 nm dispersed in an amorphous PTB7 matrix. STXM measurements indicate a lack of mesoscale phase separation, with AFM and NEXAFS measurements revealing a P(NDI2OD-T2)-rich top surface with fibrillar morphology. These results indicate that the pairing of low band gap polymers as both donor and acceptor polymers in all-polymer solar cells may be an effective strategy for realizing high-efficiency all-polymer solar cells. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Melt spinning and mechanical properties of semirigid liquid-crystal copolyesters

Melt-spinning and mechanical properties of fibers of a new class of semirigid thermotropic liquid-crystal polymers are presented. These copolyesters are synthesized from 4-4′-dihydroxybiphenyl (B), 4-hydroxybenzoic acid (H), and flexible units provided by aliphatic diacids. The flexible units depress the melting temperature without strongly depressing the mechanical properties. These liquid-crystal polymers can be easily spun at high draw ratios. Indeed, unlike rigid liquid-crystal polymers, relatively high draw ratios are needed to attain high mechanical strength. Tensile moduli of about 28 GPa and tensile strengths of about 350 MPa are obtained. © 1993 John Wiley & Sons, Inc.     

Shear damping function measurements for branched polymers

We present results for step‐strain experiments and the resulting damping functions of polyethylene blends of different structures, including solutions of linear, star and comb polymers. Remarkably, an entangled melt of combs exhibits a damping function close to that for entangled linear chains. Diluting the combs with faster‐relaxing material leads to a more nearly constant damping function. We find similar behavior for blends of commercial low density polyethylene LDPE. Our results suggest a simple picture: on timescales relevant to typical damping‐function experiments, the rheologically active portions of our PE combs as well as commercial LDPE are essentially chain backbones. When strongly entangled, these exhibit the Doi‐Edwards damping function; when diluted, the damping function tends toward the result for unentangled chains described by the Rouse model – namely, no damping. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3117–3136, 2007     

Dissolution of rubbery and glassy polymers

A mathematical model is formulated for solvent dissolution of rubbery and glassy polymers. An exact solution to the problem is derived for the constant diffusivity case, and a weighted residual solution is developed for the case of a concentration-dependent diffusion coefficient. The solution is used to calculate concentration profiles, dissolution curves, dissolution half-times, and pseudointerface positions at various times. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2607–2614, 1998     

Morphology of Nylon-6 blends with styrenic polymers

The morphology of blends of styrenic polymers in a matrix of 75% Nylon-6 prepared in a Brabender Plasti-Corder was examined by scanning electron microscopy. Styrene/acrylonitrile copolymers (SAN) form smaller particles as the AN level increases owing to the corresponding decrease in the SAN–polyamide interfacial tension. Various styrenic polymers containing functional groups, maleic anhydride or oxazoline type, that can react with Nylon-6 during melt processing were added to the SAN phase which also led to a decrease in the particle size owing to the graft copolymer formed in situ. The effects of functional group type, amount of functional groups per chain, amount of functional polymer added, and the miscibility of the styrene/maleic anhydride (SMA) and SAN copolymers on the morphology of the styrenic phase in the Nylon-6 matrix are described. © 1992 John Wiley & Sons, Inc.     

Photoorientation in hydrogen-bonded blends of liquid-crystalline polymers with a low-molecular photochromic dopant

A series of hydrogen-bonded blends of nematic liquid-crystalline copolymers with a low-molecular photochromic dopant and their covalent analogs were prepared. Their phase behavior and photooptical properties were studied. The introduction of a dopant increases considerably the isotropization temperatures of the systems. A comparative study of photoorientation processes in the blends and copolymers analogous to them was carried out. The induced dichroism in covalent systems is more pronounced than in similar hydrogen-bonded blends. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 322–328, February, 2008.     

Degradable polymer blends. I. Screening of miscible polymers

Blends of biodegradable polymers having properties distinct from the individual polymer components, and that are suitable for use as carriers of pharmaceutically active agents, were prepared from two or more polyanhydrides, polyesters, and mixtures of polyanhydrides and low molecular weight polyesters. The blends have different properties than the original polymers, providing a mean for altering the characteristics of the polymeric matrix without altering the chemical structure of the component polymers. Aliphatic, aromatic, and copolymers of polyanhydrides were miscible in each other and formed less crystalline compositions with a single melting point which was lower than the melting point of the starting polymers. The polyesters: poly(lactide-glycolide), poly(caprolactone), and poly(hydroxybutyric acid) presented some miscibility in each other. However, the polyanhydrides were immiscible with the polyesters resulting in a complete phase separation both in solution or in melt mixing. Only low molecular weight polyesters (in the range of 2000) of lactide and glycolide, mandelic acid, propylenefumarate, and caprolactone presented some miscibility with polyanhydrides. Similarly, poly(orthoester) and hydroxybutyric acid polymers formed a uniform mixture with the anhydride polymers which had the two melting points of the original polymers. Drug release from polymer blends composed of poly(hydroxybutyric acid) or low molecular weight poly(lactic acid) with poly(sebacic anhydride) (PSA) showed a constant release of drug for periods from 2 weeks to several months as a function of the PSA content in the blend. Increasing the content of PSA, a fast degrading polymer, increases the release rate from the blend. © 1993 John Wiley & Sons, Inc.     

Thickening mechanism of associative polymers

Steady state viscosity and viscoelasticity of HMHEC solutions were studied. Viscosity increases with concentration due to a reinforcement of the micellar network. High shear rate viscosities are independent of temperature. Two relaxation processes were observed, the long one related to the lifetime of the hydrophobic junction and the short related to rapid Rouse-like relaxations of the free chains. When SDS is added, mixed micelles form that reinforce the network up to an optimum [SDS]/[HMHEC] ratio. Above this ratio, the micelles in excess isolate the polymer chains, the long relaxation process disappears and Rouse-like relaxations occur, corresponding to rapid movements of free chains.     

Interfacial tension in a lower critical solution temperature blend: Effect of temperature,blend composition,and deformation of the interphase

Interfacial tension is a very important material parameter in two‐phase polymer blends. It determines the morphology development during processing, which is crucial for the end‐use properties of the material. Although different techniques for interfacial tension measurement give comparable results for immiscible polymers, the determination of the interfacial tension in lower critical solution temperature blends is not straightforward. This is illustrated for poly(α‐methyl styrene acrylonitrile)/poly(methyl methacrylate)(PαMSAN/PMMA), a slightly incompatible polymer pair. Interfacial tension has been measured with three different techniques: small‐amplitude oscillatory shear, recovery after elongation, and elongation of a multilayer sample. The large differences in these results can be attributed to the fact that most experimental techniques determine an apparent value, rather than the thermodynamic equilibrium value, of the interfacial tension. The latter is only obtained if the measurement is performed under quiescent conditions on a system that is composed of the coexisting PαMSAN‐rich and PMMA‐rich phases. The apparent interfacial tension depends on the actual composition of the phases and on the deformation of the interface. An order of magnitude approximation for such effects has been derived from theoretical considerations. Finally, each of these apparent values can be of practical importance. If a blend is prepared by melt mixing of the pure polymers, a high apparent value of interfacial tension should be considered. If, however, a blend is prepared by phase separation of a homogeneous mixture, the thermodynamic value is important. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 679–690, 2002     

Rheology of polystyrene/poly(vinyl methyl ether)blends near the phase transition

Mixtures are expected to show anomalous behavior in their viscoelastic properties close to a critical point. In this study, the reheological behavior of blends of polystyrene and poly (vinyl methyl ether) below, close to, and above the phase separation temperature T_s was investigated. Rheological measurements were carried out at three different compositions in the melt. Below and far from T_s, a satisfactory superposition of the storage and loss moduli G' and G″ was observed at all temperatures and frequencies. Close to T_s deviations were observed for G' at low frequencies (the so-called terminal zone). Above T_s G″ values was still observed over the whole range of frequencies and temperatures. The deviations observed for G' near T_s can be interpreted as due to the presence of significant concentration fluctuations. Plots of log (G'/G″²) as a function of temperature were shown to be sensitive to this anomalous behavior.     

Morphological development and rheological changes of phenoxy/SAN blends during in‐situ polymerization

This article reports the results of an investigation into the time‐dependent morphological and rheological changes that accompany the in‐situ polymerization of blends composed of poly(hydroxyether of bisphenol A) (phenoxy) and poly(styrene‐co‐acrylonitrile) (SAN). The rheological behavior was monitored continuously during the in‐situ polymerization, whereas the miscibility and phase structure of blends formed in situ were examined at discrete stages of polymerization by differential scanning calorimetry and transmission electron microscopy. In the blend with 30 wt % SAN, a co‐continuous blend morphology was associated with gradual changes in the dynamic moduli, suggesting that phase separation proceeded by spinodal decomposition (SD). In contrast, phenoxy‐rich dispersions were uniformly dispersed in a continuous SAN‐rich matrix in the blend with 50 wt % SAN, and the corresponding rheological signature revealed a sharp initial increase in the dynamic moduli, followed by slower growth after long times, indicative of phase separation via nucleation and growth (NG). The rheological property changes are closely related to morphology development and mechanisms of phase separation induced duringin‐situ polymerization. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2614–2619, 2007