Atomic force microscopy study for supermolecular microstructures in side-chain liquid crystalline polymer films

Atomic force microscopy (AFM) is employed to study the supermolecular microstructures of disclinations and inversion walls in thin films of a smectic side-chain liquid crystalline polymer. Two-dimensional nanostripes are formed in thin films when the material enters the smectic phase. A possible mechanism for their formation is also suggested. The stripes run parallel to the local director and thus decorate the overall patterns of nematic director around the disclinations and inversion walls. Three patterns involving radial, spiral, and circular supermolecular microstructures of a positive disclination with s = +1 and one hyperbolic pattern of a negative disclination with s = -1 are observed. The cores of all these microstructures exhibit circular dark centers in AFM height images. It is found that the specific configurations of a pair of (+1, -1) disclinations form during the late stage of annihilation and inversion walls always separate a pair of (+1, +1) disclinations. The analysis on the director fields around disclinations and inversion walls shows that the bend and splay elastic constants are of the same order of magnitude in the side-chain liquid crystalline polymer.     

Novel side-chain liquid crystalline polymer architectures produced by the Wittig-Horner reaction

We have investigated the use of the Wittig-Horner reaction in the preparation of novel side-chain liquid crystalline (SCLC) polymers. The simplicity and versatility of the Wittig-Horner methodology makes it another useful synthetic route in preparing SCLC polymers with polar groups being positioned along the polymer backbone. This new methodology will now be used to synthesise a range of novel ferroelectric SCLC polymers.     

An etching technique to reveal the supermolecular structure of crystalline polymers

Highly polished surfaces of nylon 6, nylon 66, polychlorotrifluoroethylene and polypropylene were etched by aromatic and chlorinated hydrocarbons at temperatures between 25 and 75°C to reveal surface morphology. Comparison with micrographs obtained with microtomed sections shows the absence of etching artifacts which are known to accompany the use of oxidizing etching agents.     

Cavitation and cavity-free deformation of filled crystalline polymer systems

Main mechanisms of tough response of polymers are described. In heterogeneous polymer systems due to mechanical misfit between heterogeneities and the matrix a high negative pressure (tri-axial stress) is generated. The excessive negative pressure is the main reason of material cavitation. Cavitation appears to be another mechanism of tough response of the material to loading. Cavitation is a massive phenomenon in crystalline polymers and in all filled polymers. Cavitation itself does not consume much energy but allows for further toughening by activating other mechanisms. Examples of polypropylene filled with chalk modified by liquid, rubber and mineral filled polypropylene and syndiotactic polypropylene filled with chalk are described. Modes of deformation with significant compressive component of stress prevents for cavitation. Materials deformed in a cavity-free manner show much higher strength. It is pointed out that high polymer crystal anisotropy is necessary for the formation of a network of easy crystallographic slip in the unusual toughening of highly filled polymers observed recently. An example of syndiotactic polypropylene filled with submicro-chalk particles is presented.     

Interpretation of light scattering from supermolecular structures in liquid systems by master curves

By a detailed analysis of light scattering curves, a more complete characterization of colloidal particles may be achieved. For this purpose, a fitting procedure based on theoretical master curves of models of polydisperse systems of homogeneous spheres and Gaussian coils is presented. The use of a suitable logarithmic distribution function makes it possible to separate the influence of polydispersity from that of particle size on the shape of the scattering curve. A double logarithmic plot of master curves reduces the fitting procedure to translations of the experimental curves. The reliability and accuracy of this procedure are demonstrated by light scattering results on solutions of a polyelectrolyte complex with variation of salt content.     

Two‐step cavitation in semi‐crystalline polymer during stretching at temperature below glass transition

Cavitation behavior in poly(4‐methyl‐1‐pentene) upon stretching below glass transition temperature was investigated by in situ ultra‐small angle X‐ray scattering technique. Strong stress‐whitening was observed indicating an extensive occurrence of cavitation in the material during tensile deformation below Tg. The X‐ray scattering patterns suggest oriented disc‐shaped cavities with normal mostly parallel to the stretching direction occurred. Structural parameters of such cavities such as thickness, radius, and tilting angle of the normal of the disc with respect to the stretching direction have been successfully calculated using a model fitting procedure. The results exhibited a two‐step process of cavitation that small amount of large cavities appeared first and then small cavities were triggered extensively in the samples at larger strains. This two‐step cavitation phenomenon can be weakened after the quenched sample was annealed or the sample was prepared by slow cooling. This peculiar two‐step cavitation process can be understood as a result of high frozen in internal stress in quenched sample that led to local failure of the materials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2007–2014     

Raising the conductivity of crystalline polymer electrolytes by aliovalent doping

Polymer electrolytes, salts dissolved in solid polymers, hold the key to realizing all solid-state devices such as rechargeable lithium batteries, electrochromic displays, or SMART windows. For 25 years conductivity was believed to be confined to amorphous polymer electrolytes, all crystalline polymer electrolytes were thought to be insulators. However, recent results have demonstrated conductivity in crystalline polymer electrolytes, although the levels at room temperature are too low for application. Here we show, for the first time, that it is possible to raise significantly the level of ionic conductivity by aliovalent doping. The conductivity may be raised by 1.5 orders of magnitude if the SbF6- ion in the crystalline conductor poly(ethylene oxide)6:LiSbF6 is replaced by less than 5 mol % SiF6(2-), thus introducing additional, mobile, Li+ ions into the structure to maintain electroneutrality.     

On the mechanism of crystalline polymorph selection by polymer heteronuclei

The phase-selective crystallization of acetaminophen (ACM) using insoluble polymers as heteronuclei was investigated in a combined experimental and computational effort to elucidate the mechanism of polymer-induced heteronucleation (PIHn). ACM heteronucleates from supersaturated aqueous solution in its most thermodynamically stable monoclinic form on poly(n-butyl methacrylate), whereas the metastable orthorhombic form is observed on poly(methyl methacrylate). When ACM crystals were grown through vapor deposition, only the monoclinic polymorph was observed on each polymer. Each crystallization condition leads to a unique powder X-ray diffraction pattern with the major preferred orientation corresponding to the crystallographic faces in which these crystal phases nucleate from surfaces of the polymers. The molecular recognition events leading to these outcomes are elucidated with the aid of computed polymer-crystal binding energies using docking simulations. This investigation illuminates the mechanism by which phase selection occurs during the crystallization of ACM using polymers as heteronuclei, paving the way for the improvement of methods for polymorph selection and discovery based on heterogeneous nucleation promoters.     

New apparatus for studies on supermolecular structures of thin polymer films by small-angle light scattering

The construction and principle of operation of small-angle light scattering apparatus for studies of supermolecular structure in thin polymer films is described. The apparatus can be used to study changes in spherulite structure during crystallization and changes in films subjected to steady or sinusoidal strain. Typical results with polyethylene films are given.     

Microsphere organization of nanorods directed by PEG linear polymer

We demonstrate the sphere organization of ZnO, Bi2S3, MnO2, and La(OH)3 nanorods directed by PEG linear polymer. Our study shows that zinc, bismuth, manganese, or lanthanum species added to PEG solutions, in which PEG molecules are well dissolved in a coil state, convert the polymer coils to aggregate structures, which further aggregate into micrometer-sized M(n+)-PEG globules. The concentration of metallic species is higher in the globules than in bulk solutions. The surfaces of the globules act as soft templates for the initial nucleation and thereafter the growth of the nanorods. Finally, echinus-type assemblies of single-crystalline nanorods form by the metallic species hydrolyzing or reacting with deposition agents. This approach opens the possibility of using polymers as soft templates to control the organization of nano building units into designed structures.     

Relaxation of liquid‐crystalline polymer fibers in polycarbonate–liquid‐crystalline polymer blend system

The relaxation of liquid‐crystalline polymer (LCP) fibers in the polycarbonate (PC)/LCP blend was examined under various conditions on a hot‐stage microscope. LC5000 is a thermotropic LCP consisting of 80/20 hydroxybenzoic acid and poly(terephthalate). The geometry of the fibers is not an important factor in the relaxation process. Fibers of different aspect ratios and lengths relaxed at the same rate and exhibited identical onset times. Increasing the temperature caused the fibers to relax faster, especially near the nematic‐transition temperature. The fibers relaxed almost immediately when subjected to a temperature of 285 °C. At 280 °C the fibers were stable for 43 min, whereas at 270 °C no noticeable relaxation was evident. Addition of compatibilizer stabilized the fibers by enhancing the interfacial adhesion between the fibers and the PC matrix. Consequently, LCP fibers in the compatibilized system relaxed at a much higher temperature (294 °C) as compared with the uncompatibilized system (275–280 °C). © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2307–2312, 2003     

Flow-induced structure in a thermotropic liquid crystalline polymer as studied by SANS

Small-angle neutron scattering is utilized to determine the flow induced alignment of a model thermotropic liquid crystalline polymer (LCP) as a function of shear rate and temperature. The results demonstrate that the flow-induced structures in thermotropic liquid crystalline polymers have similarities and differences to those in lyotropic liquid crystalline polymer solutions. The shear rate dependence of the alignment shows that the flow-induced alignment correlates very well to the viscosity behavior of the LCP in the shear thinning regime, while temperature variation results in a change in the extent of alignment within the nematic phase. Relaxation results also demonstrate that the flow-induced alignment remains essentially unchanged for up to an hour after the shear field has been removed. Last, there exists a regime at low shear rate and low temperature where alignment of the LCP molecule perpendicular to the applied shear flow is stable. These results provide important experimental evidence of the molecular level changes that occur in a thermotropic liquid crystalline polymer during flow, which can be utilized to develop theoretical models and more efficiently process thermotropic polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 3017–3023, 1998     

Anisotropy of the dielectric relaxation of a crystalline polymer

A theory which relates the change in the strength of absorption to the change in crystal orientation function is presented for the anisotropy of dielectric relaxation for the dipolar orientation change in an oriented crystalline polymer. Experimental measurements are presented for the α dielectric absorption of a stretched ethylene–carbon monoxide copolymer and compared with the orientation of crystals of this copolymer as determined by x-ray diffraction.     

Free-volume estimates in heterogeneous polymer systems. I. Diffusion in crystalline ethylene–propylene copolymers

Apparent thermodynamic diffusion coefficients were obtained from carbon tetrachloride, benzene, and n-hexane sorption-desorption kinetics in crystalline and amorphous ethylene-propylene copolymers (with propylene content from 1 to 70 wt. %, and crystallinity from 0% to 77%), in high-density and low-density polyethylene, and in polypropylene. The dependence of the diffusion coefficient vs. concentration curves on crystallinity and propylene content in the copolymers is reported. The diffusion coefficient at zero penetrant concentration increases with decrease in crystallinity. The apparent diffusion activation energies in the temperature interval investigated (25 to 75°C) are independent of temperature and are constant for crystalline copolymers. A modified Fujita-like free-volume theory for diffusion in crystalline polymer systems is introduced, and the theoretical estimates of diffusion coefficients show satisfactory agreement with experiment.     

Fractionation of bone-marrow cells by counter-current distribution in aqueous polymer two-phase systems. Relation between settling time and the efficiency of separation

The fractionation of heterogeneous populations of rat and human bone-marrow cells has been studied by counter-current distribution in a charged 5% dextran-4% poly(ethylene glycol) two-phase system. The subfractionation into two broad populations has been achieved at a low top/bottom phase volume ratio by increasing (up to 20 min) the settling time allowed for the phases to be separated after each mixing step. No effect of this parameter on a homogeneous population of erythrocytes has been observed. However, heterogeneous cell separations can be improved by exploiting different phase settling times.     

Nanostructure control in polymer solar cells by self‐organization

Recently, polymer solar cells (PSCs) based on “bulk heterojunctions” using a simple mixture of electron donor and acceptor materials in thin films have been extensively studied. Although relatively high power conversion efficiencies have been achieved by using this approach, further improvement is necessary to precisely construct stable, reproducible nanostructures that are suitable for both efficient charge separation and transport inside such films. For this purpose, it is highly desirable to utilize a bottom‐up approach, such as the self‐organized formation of inorganic and organic nanostructures. In this review, an overview of our recent studies on the control of nanostructures in PSCs is presented. DOI 10.1002/tcr.201000015