Structural information from the light scattered by solutions subjected to electric fields

Measurements of the intensity of the light scattered from polymer solutions lead to information about geometric parameters such as the molecular weight and radius of gyration of the solute. The intensity changes when an electric field is applied to the solutions, owing to the resulting orientation, deformation and alignment of the polymer molecules. Measurements of these intensity changes lead to the evaluation of such physical parameters as the permanent and induced dipole moments and the relaxation time of the particles. The theory of the effect is outlined briefly for rigid rod-like and for flexible randomly coiled molecules. Two attractive aspects of the theory are that, in favourable circumstances, some measures of both the solute flexibility and polydispersity are obtainable in addition to the determination of the electrical properties of the polymer. Details of the inexpensive and straightforward modification and operation of an existing photoelectric photometer are mentioned. Representative results are given for three systems. Aqueous dispersions of the needle-like clay mineral attapulgite illustrate the abundance of molecular information obtainable by the method. Results for polybenzyl glutamate in the helix-promoting solvent dichlorethane, demonstrate how an appraisal of the α-helical configuration can be made in terms of the molecular length and dipole moment. Finally, results for polyproline show that, even with poorly characterised samples, useful qualitative information is still readily available. In this case, the molecular flexibility and dipolar nature were clearly shown.     

Electrical and piezoresistive properties of multi-walled carbon nanotube/polymer composite films aligned by an electric field

Aligned multi-walled carbon nanotube (MWCNT)/polymer composite films are prepared by solution casting in the presence of an alternating electric field. Application of 7 kV/m at a frequency of 60 Hz to the polymer composite melt induces MWCNT alignment in the direction of the applied field, which is maintained after polymer crystallization. The electrical conductivity and piezoresistive response of electric-field-aligned and randomly oriented 0.1–0.75 wt% MWCNT/polysulfone films are evaluated. Electrical conductivity is 3–5 orders of magnitude higher for composites with electric-field-aligned MWCNTs than for randomly oriented composites. MWCNT alignment inside the polymer matrix also increases the film piezoresistive sensitivity, enhancing the strain sensing capabilities of the composite film.     

Pretransitional phenomena in the isotropic melt of a mesogenic side chain polymer

Pretransitional phenomena were characterized for a mesogenic side chain polymer using electric birefringence studies. The magnitude of the induced birefringence and its relaxation time were found to diverge in the isotropic melt as a hypothetical second order phase transition into the nematic phase is approached. The results are interpreted in terms of the Landau-de Gennes theory of the nematic phase transition.     

Molecular Imprinted Polymer of Methacrylic Acid Functionalised β-Cyclodextrin for Selective Removal of 2,4-Dichlorophenol

This work describes methacrylic acid functionalized β-cyclodextrin (MAA-βCD) as a novel functional monomer in the preparation of molecular imprinted polymer (MIP MAA-βCD) for the selective removal of 2,4-dichlorophenol (2,4-DCP). The polymer was characterized using Fourier Transform Infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) and Field Emission Scanning Electron Microscopy (FESEM) techniques. The influence of parameters such as solution pH, contact time, temperature and initial concentrations towards removal of 2,4-DCP using MIP MAA-βCD have been evaluated. The imprinted material shows fast kinetics and the optimum pH for removal of 2,4-DCP is pH 7. Compared with the corresponding non-imprinted polymer (NIP MAA-βCD), the MIP MAA-βCD exhibited higher adsorption capacity and outstanding selectivity towards 2,4-DCP. Freundlich isotherm best fitted the adsorption equilibrium data of MIP MAA-βCD and the kinetics followed a pseudo-second-order model. The calculated thermodynamic parameters showed that adsorption of 2,4-DCP was spontaneous and exothermic under the examined conditions.     

A New Series of Kinked Liquid Crystals: 2-(6-Alkoxynaphthalen-2-yl)-6-methoxyquinolines

A new series of 2-(6-alkoxynaphthalen-2-yl)-6-methoxyquinolines (nO-NpQOMe, n = 3–8) liquid crystal compounds, a linear molecular structure with two kinks, were synthesized using a short two-step reaction with overall yields between 43% and 58%. Spectral analyses were in accord with the expected structures. Thermotropic behavior of these liquid crystal compounds were investigated using polarized optical microscopy and differential scanning calorimetry. All compounds exhibited purely enantiotropic nematic phase at the medium–high temperature range of 162.4–234.2 °C. However, short ranges of nematic phase, 20.5–16.6 °C at heating and 46.7–37.0 °C at cooling, were observed in these linear liquid-crystalline compounds with two kinks.     

Possible reasons that piezoelectricity has not been found in bulk polymer of polyvinylidene cyanide

The structure, energy, internal rotation, dipole moments and molecular polarizabilities of poly(vinylidene cyanide) (PVDCN) of - and β-chain models were studied with density functional theory at B3PW91/6-31G(d) level. The effects of chain length on the polymer chain stabilities, chain conformations and electric properties were examined and compared with those of the piezoelectric PVDF in order to explore the possible reasons that the piezoelectricity has not been observed in the bulk polymer of PVDCN experimentally. The results show that the energy barriers (11.5 and 6.9 kJ/mol) of PVDCN in its - → β-chain and β- → -chain transitions are smaller than those (16.3 and 8.2 kJ/mol) of PVDF, which promises an easier transition between the two conformations. This may be one of the reasons that the preparation of the stable piezoelectric phase will be difficult. However, an extremely important feature of the ideal β-chain is that the PVDCN chain is curved with a radius of only about 8.5 Å, which is much smaller than that (30.0 Å) in PVDF and is smaller than that (12.6 Å) in polymethylvinylidenecyanide (PMVC). This suggests that the bulk polymer of PVDCN is difficult to be prepared into crystal phase, and the contribution of the dipole moment per unit to the total dipole will be cancelled if the chain is longer than 12 units (hemicycle). Therefore, the reasons that the piezoelectricity has not been found may be due to the orientation difficulties of chains and dipoles.     

Controlled local organization of lyotropic liquid crystalline polymer thin films with electric fields

The ability of electric fields to induce the controlled alignment of lyotropic liquid crystalline polymer thin films on microfabricated substrates is demonstrated. These devices allow for variations in electric field geometry on the polymer alignment to be examined systematically. The polymers studied included poly(hexyl isocyanate) (PHIC) and poly(benzyl l-glutamate). The polymers were oriented by the electric field while in solution and solidified into a stable, oriented structure by solvent evaporation. Optical microscopy and transmission electron microscopy experiments make it possible to directly image the disclinations that mediate molecular alignment. The defect type and density in the solidified films are a function of the electric field geometry.     

Effect of electric field on the structure and piezoelectric properties of poly(vinylidene fluoride) studied by density functional theory

The geometry and piezoelectric properties of chain in PVDF under different electric fields are studied by density functional theory (DFT). The simulation gives optimized geometry of PVDF of α chain and β chain, with rotation angle around ±50° and arbitrary angle between 175° and 185° respectively. The energy barrier is about 16.16 kJ/mol in the chain transition from α chain to β chain, and the one of reverse transition is about 6.24 kJ/mol. The positive electric decreases the energies of α chain and β chain. There would be a critical positive electric field inducing the transition from α chain to β chain. Positive electric field increases dipole moment of the β chain and has few effects on mean molecular polarizibility. It is found that the change of geometry increases dipole moment and the change of electronic properties decrease dipole moment under positive electric field and the geometry plays an important role.     

Influence of different polyesters and their molecular weight on the textural and electrooptical behavior of polymer‐dispersed liquid crystals

The textural and electrooptical behavior of a nematic liquid crystal (LC) dispersed in a flexible and rigid polyester was studied. The dispersion of LC in the polymer matrix and light transmission through the polymer‐dispersed liquid crystal (PDLC) is governed by the nature of the polymer, its molecular weight, and the applied voltage. It was observed that the transmission of light and the dispersion of LC maximizes their respective values at the minimum molecular weight irrespective of the nature of the polymer and at the maximum voltage. The reason is the predominance of chain alignment over entanglement at the minimum molecular weight. As molecular weight increases, the transmission of light as well as the dispersion of LC in the polymer may increase or decrease depending on the predominance of chain entanglement or chain alignment. The alignment of LC droplets in the direction of the applied voltage is increased by an increase in the applied voltage, causing enhancement of the light transmission. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 284–289, 2003     

Bistable light scattering effects in a (side chain liquid crystalline polymer)/(low molecular weight liquid crystal) composite and in a ferroelectric liquid crystalline polymer

The electro-optical effects and aggregation states of liquid crystalline polymer (LCP)/ low molecular weight liquid crystal (LC) composite and ferroelectric liquid crystalline copolymer (FLCP) have been investigated. The nematic LCP was observed to be miscible with the nematic LC over wide ranges of concentration and temperature. The binary mixture showed an induced smectic phase in the range of 80/20-20/80 mol%. The electro-optical effects of the LCP/LC composite in an induced smectic phase could be classified into the turbid (light- scattering) and the transparent states upon application of AC and DC electric fields, respectively. The transient scattering mode was obtained by repeated voltage polarity reversal in the chiral smectic C phase of FLCP. The reversible transparent-opaque (light scattering) change was observed in the chiral smectic C state upon application of DC and AC electric fields, respectively. Both transparent and light-scattering states of the LCP/LC composite and the FLCP could be maintained, even after the electric field had been turned off (memory effect). The bistable effects of LCP/LC composite and FLCP are opposite under the same conditions. A novel type of electro-optical effect on light scattering was obtained for liquid crystalline polymer in the smectic states.     

Optical biaxiality of nematic LC-side chain polymers with laterally attached mesogenic groups

Summary Liquid crystalline polymers with mesogenic groups laterally attached to the polymer backbone were investigated by polarizing microscopy with respect to their optical properties. The nematic polymers were macroscopically oriented in a magnetic or electric field. Polarization microscopic investigations with convergent polarized light show optical biaxial behavior of the nematic phase.     

Alignment of carbon nanotubes in polyimide under electric and magnetic fields

Usually alignment of carbon nanotubes (CNT) in polymer composites can be induced by a single electrical or magnetic field. Here we report a comparison between the results of simultaneous application of both fields to the polyimide composite and a single field. Alignment of CNT in polyimide was performed under a 2 Tesla magnetic field and various electric fields (150, 300, 450, and 600 V/cm). Polarized Raman spectroscopy was used for assessing the degree of alignment of the nanotubes in the composites and many details of the alignment were examined. The results indicated that at the same electric field strength, incorporation of a magnetic field in a given direction will enhance the level of alignment as compared with only using an electric or magnetic field alone. The best alignment condition was for the CNT samples under parallel magnetic and electric fields. Optical microscopy observations also indicated that nanotube alignment appeared at the highest field strength and decreased when the field strength decreased. A possible mechanism for field alignment is presented. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Role of network nematicity in swelling and phase equilibria of polymer networks in nematic solvents

Swelling and phase equilibria of polymer networks in a low molecular mass liquid crystal (LC) have been investigated as a function of network nematicity. LC networks with varying nematicity were prepared by copolymerization of mixtures of mesogenic monomers and non-mesomorphic (styrene) monomers with various compositions. Molar fraction of mesogenic monomer (x) in copolymer network strongly influences the swelling behavior as well as the nematic-isotropic (N-I) transitions in both dry and swollen states. The swollen networks of sufficiently high x with strong nematicity exhibit a sharp N-I transition and simultaneously undergo a discontinuous change in gel volume, i.e. volume phase transition. Meanwhile, the swollen networks of x≤0.8 with less nematicity show a broad N-I transition, and the resulting volume change proceeds continuously over a finite temperature range. When x decreases further down to less than 0.5, the nematicity of the dry networks vanishes. The nematic ordering in the swollen copolymer networks of x<0.5 occurs at the same temperature as the N-I transition temperature of the pure nematic solvent (T_NI^S), which yields the inflection in the swelling-temperature curve. A mean field theory considering network nematicity as a variable describes the effects of x on volume phase transition such as a shift of T_NI^G and a change in the magnitude of volume transition, apart from the emergence of continuous volume transition due to the broad N-I transition. The purely isotropic network of x=0 appreciably swells in the nematic solvent. The solvent inside the gel forms the nematic phase at the temperatures below which conflicts with the classical theoretical prediction that nematic ordering of LC solvent in fully swollen isotropic network never occurs.     

Growth of carbon dendrites on cathode above liquid ethanol using surface plasma

The newly developed method presented in this paper allows growth of carbon dendrites, which exhibit glassy carbon- and pyrocarbon-like structures, using surface plasma on the cathode surface above dehydrated ethanol. The process is based on the polarization of polar organic molecules under the influence of external high electric field strength. Ethanol molecules have a dipole moment, they were aligned in the direction of the electric field, and the process of electronic/dipole-relaxation polarization started to occur in liquid ethanol. The dipole density was maximized in the cathode region located at 7–10 mm above the liquid ethanol owing to the non-uniform electric field. The electronic breakdown started in the region experiencing the maximum electric field strength. The decomposition of ethanol molecules changed the condition of the gas phase in the breakdown region a resultant current started to flow in the circuit. The growth of carbon dendrites on the Pt cathode, possible under the stability of surface plasma discharges, was characterized by formation of carbon nuclei on the cathode surface. Another advantage of the plasma surface process is that it enables growth of carbon dendrite on dielectric surfaces without increasing of plasma power generation.     

Directed crystallization of poly(3-hexylthiophene) in micrometre channels under confinement and in electric fields

We present two methods for controlling the in-plane alignment of polymer chains in poly(3-hexylthiophene) (P3HT) films within the channel of a field effect transistor device. Solvent-induced dewetting into the transistor channels of a prepatterned, bottom-gate bottom-contact transistor channel followed by controlled, low nucleation density recrystallization under confinement resulted in a preferential orientation of the π-stacked nanocrystalline lamellae parallel to the resulting P3HT micrometre-sized lines. The contrasting alignment, of perpendicular lamellae, was induced by application of an electric field during recrystallization. Preliminary measurements of the dependence of charge transport mobility on the global orientation of the polymer chain direction are consistent with faster charge transport perpendicular to the π-stacked lamellae (direction parallel to the polymer chains) compared to along the π-stacking direction in the common edge-on oriented morphology.     

Electro-optical properties of poly(ε-carbobenzosy-l-lysine) in organic solvents

The electric birefringence of poly(ε-carbobenzoxy-l-lysine) (PCBL) in various helicogenic organic solvents and solvent mixtures has been measured over a wide range of field strengths by application of rectangular pulses. The apparent permanent dipole moment and the optical anisotropy factor were separately determined from the field strength dependence of the steady-state birefringence. The apparent dipole moment per residue for a PCBL sample with molecular weight close to 1 × 10⁵ fell in the range of 4.7 to 5.9 D in spite of the large variation of the solvent dielectric constant. The optical anisotropy factor was appreciably small and changed its sign depending upon the solvent. The intrinsic birefringence of PCBL was found to be negative in sign on the basis of the Peterlin-Stuart theory. This was interpreted in terms of the orientation of the side chains with respect to the helical backbone. The apparent dipole moment per residue for high molecular weight PCBL samples was much smaller, indicating a considerable flexibility of the helix.     

Cloud Point Extraction of Parabens Using Non-Ionic Surfactant with Cylodextrin Functionalized Ionic Liquid as a Modifier

A cloud point extraction (CPE) process using non-ionic surfactant (DC193C) to extract selected paraben compounds from water samples was investigated using reversed phase high performance liquid chromatography (RP-HPLC). The CPE process with the presence of β-cyclodextrin (βCD) functionalized ionic liquid as a modifier (CPE-DC193C-βCD-IL) is a new extraction technique that has been applied on the optimization of parameters, i.e., pH, βCD-IL concentration and phase volume ratio. This CPE-DC193C-βCD-IL method is facilitated at 30 °C, showing great losses of water content in the surfactant-rich phase, resulting in a high pre-concentration factor and high distribution coefficient. The developed method CPE-DC193C-βCD-IL did show enhanced properties compared to the CPE method without the modifier (CPE-DC193C). The developed method of CPE-DC193C-βCD-IL gives an excellent performance on the detection of parabens from water samples with the limit of detection falling in the range of 0.013–0.038 μg mL⁻¹. Finally, the inclusion complex formation, hydrogen bonding, and π–π interaction between the βCD-IL, benzyl paraben (ArP), and DC 193C were proven using ¹H NMR and 2D NOESY spectroscopy.     

Influence of polarization,reorientation, and coupling of dipole on electrocaloric effect in ferroelectrics

Electrocaloric effects due to entropy change and dipole coupling upon electric field in second-order phase transition (tetragonal-cubic) ferroelectrics are investigated by a three-dimensional Devonshire's theory and statistic method. In diabatic condition, increase in vibration entropy to heat the ferroelectric is due to decreases in polarization entropy and configuration entropy of dipole reorientation in the specific directions. Coupling effect originated from the reorientation of dipoles accompany with electric hysteresis loop happens in the nearest neighbor dipoles parallel to electric field direction. Numerical simulations exhibit that polarization effect causes electrocaloric peak at the Curie's temperature independent of electric field, reorientation effect of dipole causes a shift of electrocaloric peak to high temperature with electric field, and coupling effect between dipoles gives rise to increase in electrocaloric effect with decreasing temperature. A method to predetermine the excellent electrocaloric effect of ferroelectrics from dielectric and/or polarization experimental results is proposed.     

Mesogen-jacketed liquid crystalline polymers substituted with oligo(oxyethylene) as peripheral chain

Mesogen-jacketed liquid crystalline polymer (MJLCP) is a typical rod-shaped macromolecule. Its unique molecular architecture allows one to tune the geometric parameters of the macromolecular rod. Moreover, the rod surface chemistry can be controlled by designing the peripheral groups of the lateral mesogens. In previous work in this system, short alkyl chains have been used and the resultant macromolecular rods therefore have a hydrophobic surface. In this paper, we report using oligo(oxyethylene) groups as the peripheral groups of the lateral mesogens. Poly{{2,5-bis[4-methoxyoligo(oxyethylene)phenyl]oxycarbonyl}styene} (PnEOPCS) with different oligo(oxyethylene) chain length has been synthesized. These oligo(oxyethylene) groups led to macromolecular rods with hydrophilic surface. Differential scanning calorimetry, polarized light microscopy, and one-/two-dimensional wide-angle X-ray diffraction experiments were carried out to study the phase structures and phase behaviors of this series of polymer. The existence of flexible polar groups lowered the glass transition temperatures of PnEOPCS. All polymers studied showed supramolecular columnar nematic or hexatic columnar nematic phase, which arose from the parallel alignment of the polymer supramolecular rods. The diameter of the cylindrical building block increased with increasing the length of the oligo(oxyethylene) groups. The macromolecular rod surface can be further tuned by complexation the oligo(oxyethylene) with lithium salts. Detailed study showed that this complexation also tremendously affected the liquid crystalline phase of the polymer.     

Pd/C纳米结构的尺寸调控及液相高效加氢脱氯性能

在甲酰胺体系下,利用KBr调控合成了Pd粒径为2 nm、3 nm、4 nm和6 nm的不同水溶性Pd/C催化剂,采用TEM、XRD和XPS对催化剂进行表征,并以4-氯苯酚为反应物,测试了催化剂的液相加氢脱氯性能。结果表明,相比于商业Pd/C催化剂,在甲酰胺体系中合成的Pd/C催化剂具有更高的水溶性,催化效果提高了约40%以上。同时研究了不同溶剂对催化剂加氢脱氯效果的影响,结果表明,随着溶液极性、溶剂的介电常数(ε)、偶极矩(μ)和归一化极性参数(ETN)的增强,催化效果越好。