Re-entrant isotropic phase between lamellar and columnar mesophases

Tetradental cis-enaminoketone Ni (II) complexes with different molecular shape have been synthesized. Intramolecular hydrogen bonds, which stiffen the mesogenic core and restrict rotation of some molecular parts, have been introduced in these compounds. In the case of molecules with two hydrogen bonds and alkoxy terminal chains filling the inner molecular space, the uncommon phase sequence Iso-D(h)-Iso(re)-SmA (series III-3) was detected. For the first time, it was observed that the isotropic re-entrant (Iso(re)) phase (short-range order) is separating the columnar (D) (high-temperature) and the lamellar (SmA) (low-temperature) phases, both revealing long-range ordered structures.     

Gelation behavior of thermoplastic-modified epoxy systems during polymerization-induced phase separation

The rheological behavior and gelation characteristics of epoxy blends are of critical importance to property study and industrial application. In this work, we studied the rheological behavior and structural transition of different thermoplastics, including polyetherimide, polymethylmethacrylate, and polyethersulfone (PES), modified epoxy systems by using rheometry instrument, differential scanning calorimetry, time-resolved light scattering, and scanning electronic microscopes. At the same molecular weight level of thermoplastics, different epoxy blends show profound diversities on the rheological and gelation behavior due to the large differences in phase separation and curing process. For early phase-separation systems of PES-modified epoxy blends, two gel points are identified, which correspond to physical gelation and chemical gelation, respectively. With the variation of the PES molecular weight and curing rate, dramatic changes in gel time and critical exponent were observed. As the molecular weight of thermoplastics is increased, the gelation time becomes shorter and the gel strength gets lower, while the faster curing rate would increase the physical gel strength significantly.     

Study of micellar and phase separation behavior of mixed systems of triblock polymers

Cyclic voltammetric (CV) techniques have been employed to study the mixed micellar behavior of binary mixtures of triblock polymers (TBP) such as F127+P85, F127+P85, F88+P85, and F88+P123 using 2,2,6,6-tetramethyl-1-piperidinyloxy (Tempo) as an electroactive probe. Critical micellar concentration (cmc) has been obtained for pure triblock polymers and their mixed systems from the plots of peak current (i_p) variation versus the total concentration. Diffusion coefficients of the electroactive species have been determined from the Randles–Sevcik equation. The interaction parameter (β) for the mixed micelles was obtained from the regular solution theory. The values of β suggest that the synergism does exist especially with the F88+P123 system. Cloud point measurements have also been made on the binary mixtures of triblock polymers following similar mixing criteria. An effort has been made to correlate the micellar behavior and phase separation (cloud point) phenomenon. From the correlation, it can be concluded that in the systems studied, an increase in cmc increases the cloud point of mixed systems of triblock polymers.     

Organic-solvent-free systems with phase separation as efficient and safe systems for extraction of metal ions

The possibilities of using organic-solvent-free extraction systems with phase separation, based on antipyrine derivatives, are examined. Ionic associates with tin(II) and tin(IV) anionic complexes and mixed chelates of indium with antipyrine and sulfosalicylic acid are extracted into the organic phase. The suggested systems show promise for the recovery and determination of macro- and microamounts of indium, tin(II), and tin(IV) ions.     

Scaling behavior of nonisothermal phase separation

The phase separation process in a critical mixture of polydimethylsiloxane and polyethylmethylsiloxane (PDMS/PEMS, a system with an upper critical solution temperature) was investigated by time-resolved light scattering during continuous quenches from the one-phase into the two-phase region. Continuous quenches were realized by cooling ramps with different cooling rates kappa. Phase separation kinetics is studied by means of the temporal evolution of the scattering vector qm and the intensity Im at the scattering peak. The curves qm(t) for different cooling rates can be shifted onto a single mastercurve. The curves Im(t) show similar behavior. As shift factors, a characteristic length Lc and a characteristic time tc are introduced. Both characteristic quantities depend on the cooling rate through power laws: Lc approximately kappa(-delta) and tc approximately kappa(-rho). Scaling behavior in isothermal critical demixing is well known. There the temporal evolutions of qm and Im for different quench depths DeltaT can be scaled with the correlation length xi and the interdiffusion coefficient D, both depending on DeltaT through critical power laws. We show in this paper that the cooling rate scaling in nonisothermal demixing is a consequence of the quench depth scaling in the isothermal case. The exponents delta and rho are related to the critical exponents nu and nu* of xi and D, respectively. The structure growth during nonisothermal demixing can be described with a semiempirical model based on the hydrodynamic coarsening mechanism well known in the isothermal case. In very late stages of nonisothermal phase separation a secondary scattering maximum appears. This is due to secondary demixing. We explain the onset of secondary demixing by a competition between interdiffusion and coarsening.     

Density functional theory of polymer-polymer phase separation behavior

Polyatomic density functional theory is applied to a binary polymer blend. The polymer reference interaction site model (PRISM) liquid state theory provides the homogeneous state correlation functions necessary for the application of density functional theory. An effective chi parameter can be recognized from the density functional expression; however, the phase separation criteria does not depend solely upon the chi parameter, rather it depends upon various combinations of the species-dependent direct correlation functions of the blend. The Flory-Huggins chi parameter along with the associated phase diagram is obtained when the monomer volumes of the blend species are equal and for a range of monomer-monomer attractive interactions. Calculations are performed both with and without the assumption of incompressibility. The density functional theory along with the PRISM determined “input” predict that an isotopic polymer blend shows an upper critical solution temperature (UCST) phenomena. © 1995 John Wiley & Sons, Inc.     

Hydrogen isotope exchange and separation in gas-solid phase systems

Systems of two or more hydrogen-containing phases in solution equilibrium with hydrogen may not be in isotopic equilibrium. The resulting exchange of hydrogen isotopes between the phases is discussed with respect to both the kinetic behaviour and the final equilibrium state. The advantages of tracer experiments using tritium are discussed in terms of the experimental arrangement and the information attainable. It is shown that the equilibrium separation factor reflects the state of the dissolved hydrogen in different sorption states and that the exchange kinetics are affected by the state of the interphase. The effect of the total hydrogen pressure on the tracer exchange with tritium is discussed. The relationships developed are applied to the metal-hydrogen systems PdH_n and Ti_0.4Mn_0.6H_n. The results are supplemented by pressure-composition isotherms, neutron vibrational spectra, scanning electron micrographs, Auger electron spectra and Auger electron spectroscopy depth profiles obtained using argon ions.     

Monte Carlo simulation of the self-assembly and phase behavior of semiflexible equilibrium polymers

Grand canonical Monte Carlo simulations of a simple model semiflexible equilibrium polymer system, consisting of hard sphere monomers reversibly self-assembling into chains of arbitrary length, have been performed using a novel sampling method to add or remove multiple monomers during a single MC move. Systems with two different persistence lengths and a range of bond association constants have been studied. We find first-order lyotropic phase transitions between isotropic and nematic phases near the concentrations predicted by a statistical thermodynamic theory, but with significantly narrower coexistence regions. A possible contribution to the discrepancy between theory and simulation is that the length distribution of chains in the nematic phase is bi-exponential, differing from the simple exponential distribution found in the isotropic phase and predicted from a mean-field treatment of the nematic. The additional short length-scale characterizing the distribution appears to arise from the lower orientational order of short chains. The dependence of this length-scale on chemical potential, bond association constant, and total monomer concentration has been examined.     

Polymerization-induced viscoelastic phase separation in polyethersulfone-modified epoxy systems

The polymerization-induced phase-separation process of polyethersulfone (PES)-modified epoxy systems was monitored in situ continuously on a single sample throughout the entire curing process by using optical microscopes, time-resolved light scattering (TRLS), scanning electronic microscopes (SEM), and a rheometry instrument. At specific PES content a viscoelastic transformation process of phase inversion morphology to bicontinuous was found with an optical microscope. The rheological behavior during phase separation corresponds well with the morphology development. Light-scattering results monitoring the phase-separation process of systems with final phase inversion morphology show a typical exponential decay procedure of scattering vector qm. The characteristic relaxation time of phase separation can be described well by the WLF equation.     

Electronic phase separation in transition metal oxide systems

Electronic phase separation is increasingly getting recognized as a phenomenon of importance in understanding the magnetic and electron transport properties of transition metal oxides. The phenomenon dominates the rare-earth manganates of the formula Ln(1-x)A(x)MnO(3)(Ln = rare earth and A = alkaline earth) which exhibit ferromagnetism and metallicity as well as charge-ordering, depending on the composition, size of A-site cations and external factors such as magnetic and electric fields. We discuss typical phase separation scenarios in the manganates, with particular reference to Pr(1-x)Ca(x)MnO(3)(x= 0.3-0.4), (La(1-x)Ln(x))(0.7)Ca(0.3)MnO(3)(Ln = Pr, Nd, Gd and Y) and Nd(0.5)Sr(0.5)MnO(3). Besides discussing the magnetic and electron transport properties, we discuss electric field effects. Rare-earth cobaltates of the type Pr(0.7)Ca(0.3)CoO(3) and Gd(0.5)Ba(0.5)CoO(3) also exhibit interesting magnetic and electron transport properties which can be understood in terms of phase separation.     

Templating multiple length scales by combining phase separation, self-assembly and photopatterning in porous films

Patternable nanoporous silica thin films with pore sizes on multiple length scales are fabricated using preformed block copolymer/homopolymer blend films as templates. Previous work by Tirumala et al. [V.R. Tirumala, R.A. Pai, S. Agarwal, J.J. Testa, G. Bhatnagar, A.H. Romang, C. Chandler, B.P. Gorman, R.L. Jones, E.K. Lin, J.J. Watkins, Adv. Mater. 18 (8) (2008) 1603] has demonstrated that hydrogen bonding between an amphiphilic copolymer and a homopolymer leads to significant enhancements in the long range order of the template self assembly. However if the copolymer template is simply changed from Pluronic F127 to Brij78, a well ordered template is no longer always obtained; the blend phase separates with apparent selective partitioning of the photoacid generator (PAG) at the interface of the polymer phases. UV exposure selectively generates a photoacid, which is utilized to catalyze tetraethylorthosilicate (TEOS) condensation. The large disparity in diffusivity of the photoacid between the glassy poly(hydroxystyrene) (PHOSt) and rubbery Brij78 phases results in selective templating of the Brij mesostructure and limited reaction into the PHOSt. Calcination yields relatively monodisperse mesopores from the Brij phase and macropores from the PHOSt phase. Simple variations in processing parameters allow the macropore morphology to be tuned to create high surface area materials with structures on the order of 1 nm, 100 nm and microms from self assembly, phase separation and lithographic patterning respectively.     

Protein separation by nonsynchronous coil planet centrifuge with aqueous-aqueous polymer phase systems

Counter-current chromatographic separation of proteins was performed using a rotary-seal-free nonsynchronous coil planet centrifuge (CPC) fabricated in our laboratory. This apparatus has a unique feature that allows a freely adjustable rotational rate of the coiled separation column at a given revolution speed. The separation was performed using a set of stable proteins including cytochrome c, myoglobin and lysozyme with two different types of aqueous-aqueous polymer phase systems, i.e., PEG (polyethylene glycol) 1000-dibasic potassium phosphate, and PEG 8000-dextran T500 in 5 mM potassium phosphate buffer. Using a set of multilayer coiled columns prepared from 0.8 mm I.D. PTFE tubing with different volumes (11, 24, 39 ml), the effect of the column capacity on the partition efficiency was investigated under a given set of experimental conditions. Among these experiments, the best separation of proteins was attained using the 39 ml capacity column with a 12.5% (w/w) PEG 1000-12.5% (w/w) dibasic potassium phosphate system at 10 rpm of coil rotation under 800 rpm. With lower phase mobile at 0.2 ml/min in the head-to-tail elution, the resolution between cytochrome c and myoglobin was 1.6 and that between myoglobin and lysozyme, 1.9. With upper phase mobile in the head-to-tail elution, the resolution between lysozyme and myoglobin peaks was 1.5. In these two separations, the stationary phase retention was 35.0 and 33.3%, respectively. Further studies were carried out using a pair of eccentric coil assemblies with 0.8 mm I.D. PTFE tubing at a total capacity of 20 ml. A comparable resolution was obtained using both lower and upper phases as a mobile phase in a head-to-tail elution. The results of our studies demonstrate that the nonsynchronous CPC is useful for protein separation with aqueous-aqueous polymer phase systems.     

Phase separation and rheological behavior in thermoplastic modified epoxy systems

The relationship between rheological behavior and phase separation in polyesterimide modified epoxy systems was studied by rheometry, time-resolved light scattering (TRLS), and Differential Scanning Calorimetry (DSC). The rheological behaviors of blends during phase separation showed an exponential grow of complex viscosity, while the phase separation was inhibited by the vitrification of the polyesterimide-rich matrix phase rather than gelation of dispersed epoxy-rich particles. The characteristic relaxation time obtained by the simulation of complex viscosity could be described well by the Williams–Landel–Ferry equation, which corresponded well with the light scattering results. Therefore, this work would further provide the experimental proofs that the exponential relaxation behavior of complex viscosity could be attributed to the viscoelastic flow of epoxy-rich escaping from polyesterimide-rich matrix during phase separation.     

Temperature-dependent phase behavior of polyelectrolyte-mixed micelle systems

The effect of temperature on the phase behavior of a polycation-anionic/nonionic mixed micelle system, poly(dimethyldiallylammonium chloride)-sodium dodecylsulfate/Triton X-100, was studied over a wide range of surfactant compositions, ionic strengths, and polycation molecular weights using turbidimetry and dynamic light scattering. Soluble complexes become biphasic upon heating through either liquid-liquid (coacervation) or liquid-solid (precipitation) separation. The biphasic boundary comprises two regions: a coacervate domain exhibiting a lower critical solution temperature and a second superimposed domain in which either solids or very dense and viscous fluids are formed upon heating. The position of the first region is symmetrically centered around conditions corresponding to charge neutralization of complexes and their aggregates at incipient phase separation. The second region, observed at high micelle charge, corresponds to the collapse of polycation onto micelle surfaces and expulsion of counterions and can produce either dense coacervate or precipitate. The two regions exhibit different dependences on ionic strength, polyelectrolyte molecular weight, and concentration, from which inferences about the mechanisms of phase separation may be drawn. Preliminary observations of the dense liquid phases isolated after coacervation disclose a number of interesting optical and rheological properties, possibly arising from shear-induced phase separation.     

Polymerization-induced phase separation in silica sol-gel systems containing formamide

Silica gels with well-defined pores both in micrometer and nanometer ranges were obtained by acid-catalyzed hydrolysis and polymerization of tetramethoxysilane in the presence of formamide. The micrometer-range structures of these gels are studied in terms of the phase diagram of the quasi two-component system, namely solvent-rich and silica-rich end compositions. The resulting interconnected structures and aggregates of particles are related to the occurrence of spinodal phase separation. The composition region that gave interconnected structures for the present system was much more limited and their characteristic sizes were much smaller than those for the previously reported systems containing an organic polymer. These results could be explained qualitatively by the effect of the degree of polymerization on the Flory-Huggins' type free energy change of mixing.     

PVT behavior of thermoplastic poly(styrene-co-acrylonitrile)-modified epoxy systems: relating polymerization-induced viscoelastic phase separation with the cure shrinkage performance

The volume shrinkage during polymerization of a thermoplastic modified epoxy resin undergoing a simultaneous viscoelastic phase separation was investigated for the first time by means of pressure-volume-temperature (PVT) analysis. Varying amounts (0-20%) of poly(styrene-co-acrylonitrile) (SAN) have been incorporated into a high-temperature epoxy-diamine system, diglycidyl ether of bisphenol A (DGEBA)-4,4'-diaminodiphenyl sulfone (DDS) mixture, and subsequently polymerized isothermally at a constant pressure of 10 MPa. Volume shrinkage is highest for the double-phased network-like bicontinuous morphology in the SAN-15% system. Investigation of the epoxy reaction kinetics based on the conversions derived from PVT data established a phase-separation effect on the volume shrinkage behavior in these blends. From subsequent thermal transition studies of various epoxy-DDS/SAN systems, it has been suggested that the behavior of the highly intermixed thermoplastic SAN-rich phase is the key for in situ shrinkage control. Various microscopic characterizations including scanning electron microscopy, atomic force microscopy, and optical microscopy are combined to confirm that the shrinkage behavior is manipulated by a volume shrinkage of the thermoplastic SAN-rich phase undergoing a viscoelastic phase separation during cure. Consequently, a new mechanism for volume shrinkage has been visualized for the in situ polymerization of a thermoplastic-modified epoxy resin.     

The phase behavior of microemulsion systems containing kerosene

The phase behavior of microemulsion systems containing an anionic surfactant (SDS) as well as a nonionic surfactant (Triton X-100) along with cosurfactant (1-pentanol) and using kerosene as an oil phase is reported. The unusual features observed are explained.