Formation Of Mesomorphic Phase Research Articles

The simultaneous control over the alternating sequence and the inner-core position of the mesogenic segments in side-chain liquid crystal polymers

Hydrosilylated 1,1-diphenylethylene (DPE-SiH/2SiH) are herein quantitatively and alternatingly incorporated during the living anionic copolymerization of isoprene with DPE-SiH/2SiH, which can efficiently control the Si-H densities and positions. The diversified mesogenic moieties containing azobenzene (Azo) or trifluoromethyl (F3C) groups, respectively, with the tuned inner-core position of the mesogenic segments are rationally designed and then fabricated into multiple alternatingly-arranged side-chain liquid crystal polymers (SCLCPs) along the alternating backbones. This study presents the novel SCLCPs with the simultaneous control over the sequence and the inner-core position of the mesogenic segment, providing the promising route and study model to develop the mechanistic investigations. The temperature range of mesomorphic phase formation (ΔT) and polarized optical morphologies are proved to be synergistically dependent on the diversified mesogenic moieties and the exactly controlled densities of the mesogenic segment.

Synthesis and properties of fluorinated terphenyl liquid crystals utilizing 5,6-dihydro-4H-cyclopenta[b]thiophene as core unit

5,6-dihydro-4H-cyclopenta[b]thiophene was incorporated to fluorinated terphenyl and six novel liquid crystals were designed and synthesized by Suzuki coupling reactions in high yields. These mesogens possessed wide smectic A or nematic phase ranges, which proved the usefulness of this core in the formation of liquid crystal phase as 1,4-disubstituted phenylene-based reference compound have no mesomorphic phase. Besides, the birefringence and dielectric anisotropy values of liquid crystals were also increased, making this core a practical candidate for the modification of terphenyl-typed mesogens. The density functional theory calculations were then used and whose reliability was ensured by comparison of the experimental and calculated absorption spectrum. The calculated length/width ratios of mesogens were improved after the introduction of this core unit, which might promote the formation of mesomorphic phases. The orders of calculated polarizability and dipole moment of two representative mesogens and their references were in agreement with the sequences of their birefringence and dielectric anisotropy values, respectively, providing some relationship information between microscopic molecular structures and macroscopic physical properties.

Mesomorphic Behavior in Silver(I) N-(4-Pyridyl) Benzamide with Aromatic π⁻π Stacking Counterions.

Organic semiconductor materials composed of π–π stacking aromatic compounds have been under intense investigation for their potential uses in flexible electronics and other advanced technologies. Herein we report a new family of seven π–π stacking compounds of silver(I) bis-N-(4-pyridyl) benzamide with varying counterions, namely [Ag(NPBA)2]X, where NPBA is N-(4-pyridyl) benzamine, X = NO3− (1), ClO4− (2), CF3SO3− (3), PF6− (4), BF4− (5), CH3PhSO3− (6), and PhSO3− (7), which form extended π−π stacking networks in one-dimensional (1D), 2D and 3D directions in the crystalline solid-state via the phenyl moiety, with average inter-ring distances of 3.823 Å. Interestingly, the counterions that contain π–π stacking-capable groups, such as in 6 and 7, can induce the formation of mesomorphic phases at 130 °C in dimethylformamide (DMF), and can generate highly branched networks at the mesoscale. Atomic force microscopy studies showed that 2D interconnected fibers form right after nucleation, and they extend from ~30 nm in diameter grow to reach the micron scale, which suggests that it may be possible to stop the process in order to obtain nanofibers. Differential scanning calorimetry studies showed no remarkable thermal behavior in the complexes in the solid state, which suggests that the mesomorphic phases originate from the mechanisms that occur in the DMF solution at high temperatures. An all-electron level simulation of the band gaps using NRLMOL (Naval Research Laboratory Molecular Research Library) on the crystals gave 3.25 eV for (1), 3.68 eV for (2), 1.48 eV for (3), 5.08 eV for (4), 1.53 eV for (5), and 3.55 eV for (6). Mesomorphic behavior in materials containing π–π stacking aromatic interactions that also exhibit low-band gap properties may pave the way to a new generation of highly branched organic semiconductors.

Random Copolymers from Polyamide 11 and Polyamide 12 by Reactive Extrusion: Synthesis, Eutectic Phase Behavior, and Polymorphism

Random copolymers from polyamide 11 (PA11) and polyamide 12 (PA12) were obtained from the parent homopolymers by transamidation reactions during high-temperature reactive extrusion. Concomitantly, the product molecular weight increased by postcondensation reactions. With both species being crystallizable, eutectic phase behavior was observed and explained in terms of the Flory theory for random copolymer melting. Close to the eutectic composition, both species crystallize in a competitive mode, which induces mesomorphic phase formation. Although the crystal centers most likely remain PA11 or PA12 pure, it is argued that foreign comonomer units might be tolerated at the crystal borders, at least for PA11 crystals. To understand the copolymer crystallization behavior in general, large amounts of rigid amorphous material need to be created alongside the crystallites. Because of their low melting point and since the crystallinity and mechanical performance typical of the parent homopolymers are preserved, ran...

Fast cooling of (non)-nucleated virgin and recycled poly(propylenes): Effect of processing conditions on structural and mechanical properties

In this study, the effect of processing parameters, i.e., the cooling rate and pressure, on the structure-property relationships for nucleated and non-nucleated i-PP from virgin and recycled sources was investigated. Special attention was given to the brittle-to-ductile transition of nucleated i-PP from plastic packaging waste. Differential fast scanning calorimetry and dilatometry were used to mimic industrial process conditions. From the calorimetric experiments, it was observed that under ambient pressure the mesomorphic phase was formed upon fast cooling, which was confirmed by WAXD analysis. The dilatometry results showed that by applying pressure also γ-phase crystals are formed. Nucleated samples showed an increased tendency for the γ-phase formation and a decreased tendency for mesomorphic phase formation. Up to now, recycled i-PP showed a brittle behavior, but this study showed that by applying a sufficiently high cooling rate, the yield stress can be reduced and a stabilization of the deformation can be obtained leading to a ductile behavior for recycled i-PP.

Influences of processing on the phase transition and crystallization of polypropylene cast films

ABSTRACTPhase transition and changes of properties of isotactic polypropylene (i‐PP) cast films with the processing conditions have been investigated by wide‐angle X‐ray diffraction, two‐dimensional small‐angle X‐ray scattering, and atomic force microscopy. It was found that chill roll temperature was a major factor, which influenced the formation of mesomorphic phase and its transition to spherulitic structure. Only mesomorphic phase was observed in the films produced under a chill roll temperature of below 40°C. When the roll temperature was increased to 60°C, mesomorphic phase coexisted with spherulitic crystal structure, and totally transformed to monoclinic structure at the roll temperature of 80°C. Differential scanning calorimetry, tensile, and optical tests were also performed on the films. The results showed that the observed structure changes were closely related to the thermal behavior, tensile, and optical properties of the PP films. The influence of die temperature on the films was also discussed, but the effect was much less than chill roll temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41100.

Mesomorphic phase formation of plasticized poly(l‐lactic acid)

ABSTRACTThe effects of the crystallization temperature, Tc, on the crystal structure as well as its thermal behavior of plasticized poly(l‐lactic acid) were investigated by means of wide‐angle X‐ray diffraction (WAXD), Fourier‐transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). PLLA blended with succinic acid‐bis[2‐[2‐(2‐methoxyethoxy)ethoxy]ethyl] ester (SAE) showed clear difference in Tc dependence of crystalline form compared to PLLA homopolymer. PLLA with 26 wt % SAE crystallized into orthorhombic α form for Tc above 80°C, while a peculiar disordered structure (mesophase) was obtained for Tc at 40°C. A detailed FTIR analysis of the mesophase of PLLA, focusing on the intra‐ and inter‐chain interaction in the structure, indicated that mesophase had a large degree of disorder in 10/3 helical conformation as well as its packing manner of disordered 10/3 helical chain. Upon heating, mesophase showed a steep exothermic peak at 80°C in DSC thermogram, indicating the phase transformation from mesophase to a form crystal. FTIR results showed that the degree of interchain interaction of C=O in PLLA started to decrease above 60°C, followed by steep increase at 80°C due to the recrystallization into a form. Melt‐recrystallization process in mesophase‐α transformation was clarified. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39762.

2D WAXS/SAXS study on isotactic propylene-1-butylene random copolymer subjected to uniaxial stretching: The influence of temperature

The influence of temperature on the crystallization process of isotactic propylene-1-butylene (P–B) random copolymer with low comonomer concentration subjected to uniaxial tensile force was studied in-situ by using synchrotron-based wide- and small-angle X-ray scattering techniques (WAXS/SAXS). Data analysis was performed on the whole-pattern base. P–B copolymer was stretched at three temperatures, i.e., 100 °C, 60 °C and 25 °C. Before stretching, the static sample contained both γ- and α-phase of isotactic polypropylene (iPP) homopolymer, with the γ-phase being the dominant crystal modification. When subjected to uniaxial stretching, γ-phase adopted a tilted cross-β configuration, with the c-axis forming a tilting angle with respect to the fiber axis at all temperatures. At 100 °C and 60 °C, γ-phase was transformed to α-phase with parallel orientation of polymer chains. Daughter lamellae of the α-phase were observed at 100 °C but not at 60 °C. At room temperature, large lamellar crystals could not be formed due to strong tensile force applied to the polymer network. Low temperature stretching was featured with the formation of mesomorphic phase which was composed of tiny β-form crystals and of about 50% of oriented amorphous phase. The c-axis of the β-form crystal was in parallel to the fiber axis. The crystals were so small that no ordered texture was observed at the length scale of nanometers.

Studies on the influence of molecular weight and isotacticity of polypropylene on the formation of mesomorphic phase

AbstractPolypropylene (PP) blends with various molecular weight and isotacticity were prepared through solution blending and subjected to rapid melt quenching. Structural changes in the PP matrix during mesomorphic phase formation were measured by FTIR spectroscopy and wide‐angle X‐ray diffraction measurements. The blends with different molecular weight and isotacticity provided the pathway to understand their influence on mesomorphic phase formation. It is observed that low molecular weight PP with low isotacticity forms mesomorphic phase, whereas high molecular weight and low isotactic PP does not lead to the formation of mesomorphic phase. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Phase liquid-crystalline transitions in hydroxypropylcellulose-ethanol and hydroxypropylcellulose-acetic acid systems under deformation

The phase transitions and phase state of hydroxypropylcellulose mixtures with ethanol and acetic acid under static conditions and in the shear field have been studied by the turbidity-point method and polarization microscopy with the use of a polarization-photoelectric setup and a modified plastoviscometer. The deformation of solutions leads to a decrease in the temperature of mesomorphic phase formation and to a change in the type of liquid crystals from cholesteric to nematic.

Scanning Nanocalorimetry at High Cooling Rate of Isotactic Polypropylene

A wide set of cooling scans and subsequent melting behavior of isotactic polypropylene (i-PP) were investigated using differential scanning calorimetry and nanocalorimetry at very high cooling rate. The latter technique offers, indeed, the distinctive possibility to perform heat capacity measurements at rates of more than 1000 K/s, both in cooling and in heating, to characterize the crystallization. When the i-PP sample was solidified with cooling rate larger than 160 K/s, a novel enthalpic process was observed that was related to the mesomorphic phase formation. Furthermore, at cooling rates higher than 1000 K/s, the i-PP sample did not crystallize neither in the α nor in the mesomorphic form. The subsequent heating scan starting from −15 °C showed an exothermic event, between 0 and 30 °C, ascribed to the mesophase cold crystallization.

Crystallization of polypropylene at various cooling rates

Crystallization of polypropylene (PP) can result in formation of different crystal modifications depending on external conditions. The mechanisms of formation of various crystal modifications in polypropylene are still under discussion. We have investigated non-isothermal melt crystallization of isotactic polypropylene at cooling rates ranging from 1 up to 180,000 K/min using two types of differential scanning calorimeters-standard device Perkin–Elmer DSC Pyris-1 and ultra-fast calorimeter. Additional results were obtained by means of wide angle X-ray scattering and optical microscopy. At cooling rates below 6000 K/min there is only one exothermic peak corresponding to simultaneous crystallization of α- and β-modifications. At cooling rates higher than 6000 K/min there is additional low temperature DSC peak corresponding to formation of mesomorphic phase. At the rates higher than 36,000 K/min there is no trace of formation of any ordered phase. In our opinion this complex behavior observed during crystallization of polypropylene can be explained using the concept of metastable phases. An increase of β content in samples with quinacridone pigment has been observed only at very low cooling rates, corresponding to high temperatures of crystallization and low homogeneous nucleation rate.

Effect of Isotacticity on Formation of Mesomorphic Phase of Isotactic Polypropylene

The effect of isotacticity on the mesomorphic phase-forming properties of isotactic polypropylene (iPP) is reported. Only iPP having high isotacticity (iPP-HT) can form the mesomorphic phase by a rapid quench, but iPP having low isotacticity (iPP-LT) cannot form the mesomorphic phase though it crystallizes by the same quenching rate. These results suggest that the mesomorphic phase of iPP is closely related to the stereoregularity of the polymer chain. The mesomorphic phase in the iPP-HT shows longer regular 3/1 helices than in the crystalline iPP-LT. The structure and formation mechanism of the mesomorphic iPP are considered analogous to those of liquid crystals since the average length of the long regular 3/1 helices in the mesomorphic iPP acting as rodlike segments is sufficiently large to fulfill a criterion for the formation of liquid crystalline phase. From this criterion, the minimum requirement of isotacticity to form the mesomorphic phase is also estimated.

Mesomorphic phase formation of poly(macromonomer)s of ω-vinylbenzyl and ω-methacryloyloxyethyl polystyrene macromonomers

Liquid crystalline phase formation and the related molecular properties of poly(macromonomer)s of ω-vinylbenzylpolystyrene macromonomers, poly(VB-PSt)s, were investigated. The results were compared with those of the poly(macromonomer)s of ω-methacryloyloxyethyl polystyrene macromonomers, poly(MA-PSt)s. Poly(VB-PSt)s having a polystyrene backbone formed a mesomorphic phase, depending on the branching architecture of the poly(macromonomer)s as in the case of poly(MA-PSt)s. The branch density as well as the branch length strongly influenced the formation of the mesomorphic phase. The values of the chain stiffness parameter, the Kuhn statistical segment length, estimated from the radius of gyration vs. molecular weight curves were very consistent with the observation of the mesomorphic phase under the assumption that the poly(macromonomer)s behave as a worm-like polymer. Wide-angle X-ray diffraction (WAXD) data obtained from solutions as well as cast films for both types of poly(macromonomer)s showed only an amorphous halo, indicating that the inside of each poly(macromonomer) molecule is amorphous-like and that the observed mesomorphic phase is due to the orientational ordering of poly(macromonomer) molecules.

Kinetic study of lipid distribution after washing with lipases: Microscopy analysis

AbstractEffect of lipase on removal of lard from a cotton fabric by detergency was studied in detail by radioisotope and X‐ray microanalysis over 60‐min washing. Osmium tetroxide was used to label the soil for microscopy. Backscattred electron images were used to study residual soil present on and within the cotton fibers and in the interfiber spaces of the yarn bundle. Lard‐soiled samples had large deposits on the fabric surfaces; oil was present in the crenulation, secondary walls, and the lumen of the fibers. Relative concentrations of oil were determined for selected morphological locations within the fiber structure and at the fiber surface using X‐ray microanalysis. Specimens soiled with lard and tagged with osmium tetroxide immediately from the wash bath at 0, 5, 10, 20, and 60 min provide snapshots of the washing process. Within the yarn structure, domains with high oil concentration developed during washing. These domains were not adsorbed onto the fiber surfaces, but were contained within the twisted yarn structure. The inclusion of lipase “accelerates” the washing process with the dislodgment of the soil from the fiber surface being more complete for the yarn specimens washed with lipase for 20 and 60 min. The three main stages of the soil‐removal process—transport of water and detergent to the soil on the substrate, separation of soil and substrate, and transport of dislodged soil into the wash bath—were observed. Lipase functions in detergency by hydrolysis of triglycerides forming mono‐ and diglycerides and fatty acids that are more soluble in water, can undergo soap formation, enhance mesomorphic phase formation, and increase emulsification. The quantification of the mass of the residual oil is well‐defined using the radioisotope methodology. The effectiveness of lipase on removal of lard stains is observed at all points in the washing cycle (5, 10, 20, 60 min). Our data fit a classical kinetic description of the soil‐removal process described by an exponential decay, with the presence of lipase greatly increasing the rate of oil removal during the early period of washing (0 to 20 min). With the use of lipase in the washing bath, the amount of soil removal after 10 min is about the same as observed after washing 60 min with detergent only. Washing removes soil located on the fibers and yarns on the fabric surfaces early in the process and more completely. Soil that is located within the yarn structure is removed by washing but this requires more time, and lard removal from these interfiber capillaries is greatly enhanced by use of lipase. Washing does remove soil from within the cotton fiber, i.e. secondary wall and lumen, and this is also more complete with the use of lipase. After washing with a detergent for 60 min, the highest concentration of residual soil is in the lumen, although the concentration has been reduced by a factor of two. It appears that the lumen is the last region of the cotton fabric structure to be cleaned by laundering. The use of lipase in the wash bath increased the rate of soil removal for all locations with the cotton fabric and fiber structures.

Bimetallomesogens: formation of calamitic or columnar mesophases by μ-exogenous-bridged groups in N,N ′-(propan-2-ol)-bis(4-alkoxysalicylaldimine)copper(II) complexes †

A new type of dicopper(II) complex derived from μ-exogenous 3,4,5-trialkoxybenzoate- or acetate-bridged N,N′-(propan-2-ol)-bis(4-alkoxysalicylaldimines) prepared by the condensation of 2-hydroxy-4-alkoxybenzaldehydes with 1,3-diaminopropan-2-ol are reported; the formation of mesomorphic phases was found to be dependent upon the bridging groups used, acetate-bridged compounds formed a smectic A (SmA) phase and benzoate-bridged compounds formed a hexagonal columnar (Colh) phase.

Mesomorphic phase formation of poly (macromonomer)s of polystyrene macromonomers

The liquid crystalline phase formation of poly(macromonomer)s associated with the specific multibranched architecture of high branch density was investigated. The poly(macromonomer)s were prepared by radical chain polymerizations of ω-methacryloyloxyethyl polystyrene macromonomers. It was confirmed that the mesomorphic phase formation depended on the branching architecture, where sufficient length of the branch chains as well as the backbone chain is crucial for the formation of the mesomorphic phase. Formation of the optically anisotropic mesophase also depended on the nature of solvent. The mesophase was observed in the cast films prepared from p-xylene, toluene, tetrahydrofuran, carbon disulfide and chloroform but not observed for cyclohexane. The effects of the branched structure and the solvent nature were explained by repulsive interaction between the polystyrene branch chains of high branch density. The repulsive interaction increases the chain stiffness of the central backbone and also prevents the interpenetration of the polystyrene branches of different molecules in solution, which allow poly(macromonomer) molecules to arrange with the orientational order. Copyright © 2000 John Wiley & Sons, Ltd.

Supramolecular structure of certain amphiphilic liquid crystalline polymers

Poly(maleic anhydride) was reacted with long-chain aliphatic amines in a 1:1 molar ratio (as per monomer unit) resulting in the formation of amphiphilic polymers bearing the carboxylic group on their polymer backbone. On the other hand, poly(acryloyl chloride) was interacted with ω-amino or ω-hydroxy carboxylic acids affording polyamphiphiles with the carboxylic polar group at the tail of the pendant group. In addition, the carboxylic group was replaced by the extremely polar quaternary group at the end of the lipophilic chain. Liquid crystalline textures were exhibited by these polymers as determined by optical microscopy and d.s.c. studies while the supramolecular structures, formed through hydrogen bonding of carboxylic groups, were responsible for the formation of mesomorphic phases.

Are theoretical surface chemistry measurements really practical?

AbstractThe principles and concepts of surface chemistry can be of enormous aid in the application of surfactant chemicals to practical cleaning and foaming problems. The use of surfactants for foam stability was seen to be dependent on rheological properties of the foam (bulk and surface viscosity) and to the energetics of the adsorbed surfactant monolayer (area/surfactant molecule, monolayer clasticity modulus, rate of monolayer spreading and rate of surfactant adsorption into the interface). From these principles, an equation predicting foam volume in the presence or absence of soil was derived and found to be in good agreement with experiment. In detergency, the performance was dictated by the thermodynamic work of adhesion between the soil and substrate. The adhesion was a function of surface properties (soil/water interfacial tension and soil/water/substrate). The role of agitation in detergency was shown to be that energy which was needed to overcome the adhesive bond between soil and substrate. The implicit form of the agitation term was discussed (dependent on substrate configuration, agitator system geometry and mechanics) but not explicitly deduced. The role of interfacial tension was discussed in relation to foam stability and detergency. In both applications, low interfacial tension is beneficial to performance. However, because other surface chemical effects play a role in performance in detergency and foam stability, it was noted that interfacial tension is not the sole correlating parameter with performance. The situations in which low interfacial tension is not sufficient to give improved detergency and foam stability performance were delineated. A possible new method of aiding in optimizing oil/surfactant performance also was discussed. Finally, the role of micelles in detergency was examined in light of very recent experimental work which suggests that micelles may be detrimental to detergency and foam stability performance. This study suggests that surfactants which form mesomorphic phases with soil give better performance. Micelles, instead of solubilizing soil in their hydrophobic cores, are said to be competing with the mesomorphic phase formation process, thereby hindering detergency performance. It is suggested by the sheer weight of new theoretical and innovative approaches to surface chemistry applied to detergency and foam stability performance that “theoretical surface chemistry measurements really (are) practical!”

Mechanism of fatty soil removal

AbstractThe effects of temperature, detergents, electrolyte, agitation and fabric structure on the removal from cotton of octadecane, tripalmitin, stearyl alcohol and stearic acid labelled with carbon‐14 have been studied. The following mechanisms appear to be operative in the removal of these materials: (1) the rolling‐up mechanism; (2) mesomorphic phase formation; (3) soap formation; (4) break‐up of polycrystalline aggregates.In general, the addition of electrolyte in the presence of surface‐active agents increases the amount of fatty soil removed. The magnitude of the electrolyte effect depends on (a) the degree of ionisation, (b) the pH of the solution and (c) the valency of the added cation.By means of a chopped fibre technique it has been possible to show that about 35% of the fatty soil is held on the surface of the threads, about 30% between the fibres of which the threads are composed, about 30% inside the tubular fibres while about 5% is held in the fibrile structure of the fibres.