Mesophase Domains Research Articles

Bone-inspired stress-gaining elastomer enabled by dynamic molecular locking.

The limited capacity of typical materials to resist stress loading, which affects their mechanical performance, is one of the most formidable challenges in materials science. Here, we propose a bone-inspired stress-gaining concept of converting typically destructive stress into a favorable factor to substantially enhance the mechanical properties of elastomers. The concept was realized by a molecular design of dynamic poly(oxime-urethanes) network with mesophase domains. During external loading, the mesophase domains in the condensed state were aligned into more ordered domains, and the dynamic oxime-urethane bonds served as the dynamic molecular locks disassociating and reorganizing to facilitate and fix the mesophase domains. Consequently, the tensile modulus and strength were enhanced by 1744 and 49.3 times after four cycles of mechanical training, respectively. This study creates a molecular concept with stress-gaining properties induced by repeated mechanical stress loading and will inspire a series of innovative materials for diverse applications.

Morphology of poly-3-hexyl-thiophene blends with styrene-isoprene-styrene block-copolymer elastomers from X-ray and neutron scattering.

The nano- and micron scale morphology of poly(3-hexylthiophene) (P3HT) and polystyrene-block-polyisoprene-block-polystyrene (PS-PI-PS) elastomeric blends is investigated through the use of ultra-small and small angle X-ray and neutron scattering (USAXS, SAXS, SANS). It is demonstrated that loading P3HT into elastomer matrices is possible with little distortion of the elastomeric structure up to a loading of ∼5 wt%. Increased loadings of conjugated polymer is found to significantly distort the matrix structure. Changes in processing conditions are also found to affect the blend morphology with especially strong dependence on processing temperature. Processing temperatures above the glass transition temperature (Tg) of polystyrene and the melting temperature (Tm) of the conjugated polymer additive (P3HT) creates significantly more organized mesophase domains. P3HT blends with PS-PI-PS can also be flow-aligned through processing, which results in an anisotropic structure that could be useful for the generation of anisotropic properties (e.g. conductivity). Moreover, the extent of flow alignment is significantly affected by the P3HT loading in the PS-PI-PS matrix. The work adds insight to the morphological understanding of a complex P3HT and PS-PI-PS polymer blend as conjugated polymer is added to the system. We also provide studies isolating the effect of processing changes aiding in the understanding of the structural changes in this elastomeric conjugated polymer blend.

DPD Simulations of Homopolymer–Copolymer–Homopolymer Mixtures: Effects of Copolymer Structure and Concentration

AbstractBlends prepared by mixing incompatible homopolymers with a compatibilizing copolymer attract high technological interest due to their self‐assembling behavior. In the present work, 281 dissipative particle dynamics (DPD) simulations are performed in order to evaluate the influence of copolymer microstructure and concentration on properties of these systems. The results show that alternate copolymers are arranged between the homopolymeric phases while nanodomains rich in each of the components are formed in the copolymeric matrix. Dispersion in block lengths increases the size of these nanodomains, so that they can properly allocate homopolymer chains. Besides, dispersions in chain lengths and chemical compositions of diblock copolymers, which can form self‐assembled mesostructures, also lead to development of larger mesophase domains. Larger dispersions of chain lengths and chemical compositions cause the increase of the amount of copolymers necessary to bring about changes in the mixing behavior, when compared to non‐dispersed copolymers. It can be concluded that microstructural properties of the copolymer exert a decisive impact on molecular interactions and, consequently, on the characteristics of the mesophases generated during the blending process. Therefore, microstructure control methods, stemming from both polymer‐reaction engineering and polymer‐purification techniques, are important for the design and resulting performance of the analyzed blends.

Investigation on the development and orientation of mesophase microstructure during the two-stage pyrolysis of FCC decant oil

The two-stage pyrolysis was proposed to effectively form uniaxially fibrous mesophase during pyrolysis of FCC decant oil. Detailed investigation focuses on main factors of regulating mesophase orientation and corresponding changes of mesogen stacks. The first-stage treatment under low temperature of 440 °C and high pressure of 2 MPa for 8 h ensures formation of bulk mesophase with well-coalesced texture and good molten fluidity; subsequently, fracture of residual alkyl side-chains together with devolatilization of trapped light molecules under high temperature (450–480 °C) and low pressure (0.2–1.0 MPa), mainly contributes to volatile evolution at solidification of two-stage pyrolysis. Thereby, the overlap between sufficient volatile evolution that provides enough shear force on mesophase and appropriate viscosity of bulk mesophase, high enough for maintenance of mesophase deformation but not too high to prevent penetration of gas bubbles, is readily achieved and then significantly promotes the transition from mesophase domain into acicular flow texture. Moreover, mesophase orientation at solidification is followed by transformation of mesogen stacks from columnar short-range order into nematic order, leading to decrease of stacked height and number of layer per stack. And further cracking and dehydroaromatization reactions at solidification of two-stage pyrolysis facilitate elimination of steric hindrance, relaxation of structural strains and heal of defects within the planar aromatic sheets, thus resulting into a more homogenous distribution of stacked mesogens and a smaller degree of disorder within the 2D mesogen lattice.

Nucleation‐controlled dual semicrystalline morphology of polyamide 11

AbstractCrystallization of polyamide 11 at low supercooling of the melt proceeds via heterogeneous nucleation and spherulitic growth of lamellae, while at temperatures close to the glass transition homogeneous nucleation prevails, preventing spherulite formation and leading to formation of a large number of nanometer‐sized mesophase domains. It is shown that spherulitic and non‐spherulitic crystallization at low and high supercooling of the melt, respectively, can be enforced by tailoring the cooling conditions, causing a twofold semicrystalline morphology at ambient temperature. Analysis of non‐isothermal crystallization as a function of the cooling rate, using fast scanning chip calorimetry, reveals that in the case of polyamide 11 such twofold semicrystalline morphology is predicted when cooling at rates between about 20 and 200 K s−1, since then two separate crystallization events are observed. The prediction has been confirmed by preparation of films crystallized during ballistic cooling at different rates which then were analyzed regarding their structure using optical microscopy, X‐ray diffraction and calorimetry. The study is completed by discussion of implications of twofold non‐isothermal crystallization for structure evolution in polymer processing, as well as by providing information that such behavior is not only typical for polyamide 11 but also for isotactic polypropylene or poly(butylene terephthalate) as two further examples. © 2018 Society of Chemical Industry

Interfacial liquid crystalline mesophase domain on carbon nanofillers in aromatic thermosetting copolyester matrix

ABSTRACTThis work presents the formation process and thermophysical characteristics of preferentially oriented interfacial liquid crystalline (LC) mesophase domain emerging around graphene nanoplatelet (GNP) particles within an amorphous aromatic thermosetting copolyester (ATSP) matrix. Acetoxy‐ and carboxylic acid‐capped matched oligomers of ATSP interact with oxygen‐bearing functional groups on the GNPs during the thermal polymerization process which tethers the nanofillers to the crosslinked polymer backbone. Upon curing, a nematic phase LC network develops at the nanoparticle and matrix interface via the crystalline carbonaceous structure induced local ordering effects. The LC region exhibits a thermally reversible phase transition characteristic; attains an isotropic morphology through a heating cycle and reverses to the nematic form following a subsequent cooling cycle. Solid‐state nuclear magnetic resonance spectroscopy analysis reveals the presence of a robust interfacial attachment between the GNPs and ATSP backbone. The strong covalent conjugation induces a marked upshift in the glass transition temperature (Tg) in the ATSP‐GNP nanocomposites. Introduction of an LC interlayer region surrounding the nanofillers facilitated by a strong interfacial attachment mechanism could help to optimize the performance of polymer nanocomposites. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46584.

Critical behaviour of optical birefringence in the vicinity of nematic–isotropic and smectic A–isotropic phase transitions of the eight members of alkyloxy-cyanobiphenyls

ABSTRACTWe report the measurements of birefringence (Δn) as a function of the temperature of a homologous series of alkyloxy-cyanobiphenyls (nOCB) liquid crystalline compounds by means of high-resolution optical transmission method. The temperature dependence of the birefringence has been determined from the transmitted intensity data for two different wavelengths. The order parameter critical exponent β, obtained by using a four-parameter fitting procedure consistent with the mean-field theory for a weakly first order transition, is found to be in good agreement with the theoretically predicted tricritical value. A weak birefringence has been found to develop on approaching the clearing temperature, which is tentatively attributed to the formation of a small mesophase domain within the isotropic phase. This striking behaviour leads to a further quantification of the critical fluctuation close to the transition. Finally, the order character of the nematic–isotropic (N–I) and smectic A–isotropic (SmA–I) phase transitions have been assessed by using the birefringence data. The critical exponent α (usually assigned to the heat capacity) extracted from Δn data describes the critical nature of N–I and SmA–I transitions and strongly supports the tricritical nature of the same.

Hydrophilic nanoparticles stabilising mesophase curvature at low concentration but disrupting mesophase order at higher concentrations.

Using high pressure small angle X-ray scattering (HP-SAXS), we have studied monoolein (MO) mesophases at 18 wt% hydration in the presence of 10 nm silica nanoparticles (NPs) at NP-lipid number ratios (ν) of 1 × 10(-6), 1 × 10(-5) and 1 × 10(-4) over the pressure range 1-2700 bar and temperature range 20-60 °C. In the absence of the silica NPs, the pressure-temperature (p-T) phase diagram of monoolein exhibited inverse bicontinuous cubic gyroid (Q), lamellar alpha (Lα), and lamellar crystalline (Lc) phases. The addition of the NPs significantly altered the p-T phase diagram, changing the pressure (p) and the temperature (T) at which the transitions between these mesophases occurred. In particular, a strong NP concentration effect on the mesophase behaviour was observed. At low NP concentration, the p-T region pervaded by the Q phase and the Lα-Q mixture increased, and we attribute this behaviour to the NPs forming clusters at the mesophase domain boundaries, encouraging transition to the mesophase with a higher curvature. At high NP concentrations, the Q phase was no longer observed in the p-T phase diagram. Instead, it was dominated by the lamellar (L) phases until the transition to a fluid isotropic (FI) phase at 60 °C at low pressure. We speculate that NPs formed aggregates with a "chain of pearls" structure at the mesophase domain boundaries, hindering transitions to the mesophases with higher curvatures. These observations were supported by small angle neutron scattering (SANS) and scanning electron microscopy (SEM). Our results have implications to nanocomposite materials and nanoparticle cellular entry where the interactions between NPs and organised lipid structures are an important consideration.

Lipidic Cubic Phases as a Versatile Platform for the Rapid Detection of Biomarkers, Viruses, Bacteria, and Parasites

Rapid and affordable detection of analytes is critical in diagnostic technologies, but current methods are typically expensive and unsuitable for field detection. Lipidic cubic phases are optically isotropic, transparent lyotropic liquid crystals (LC), containing highly confined water nanochannels in‐between percolating lipid bilayers following defined space groups. Due to this nanoconfinement, the water in these systems provides a unique environment for chemical and enzymatic reactions. Here, it is shown that during the in meso peroxidase enzymatic reaction, the converted product crystallizes within the mesophase domains, generating a detectable birefringence signal and a new general assay principle is presented for the detection of an unprecedented vast class of analytes using such birefringence as sole optical output signal. By exploiting bienzymatic cascade reactions or introducing an enzyme‐linked immunosorbent assay based on birefringence (Birefringent‐ELISA), this approach is used for real‐time detection of exemplary analytes, such as glucose and cholesterol, model pathogenic microorganisms, Escherichia coli, and viruses such as Ebola and HIV. It is also shown how the same technology enables the rapid, naked‐eye screening of malaria infection via in meso detection of hemozoin crystallites. This new technology is general and readily adaptable to the rapid detection of virtually any type of analyte, such as disease biomarkers, viruses, bacteria, and parasites.

Dynamics of polyelectrolyte solutions under a constant gradient of base concentration.

Phase-separation dynamics of weakly charged polyacid solutions under a constant gradient of base concentration is studied both theoretically and numerically. The time-evolution equation of polymer volume fraction is derived by assuming that the chemical equilibrium of the dissociation reaction is locally established. Numerical simulations of the system in contact with two reservoirs in which the base concentrations differ are performed. The numerical results show that the polymer volume fraction can be transported by the concentration gradient of the base, which leads to the dynamic behavior of mesophase domain structures.

Phase Separation and Crystallization in High Hard Block Content Polyurethane Thin Films

Following studies of bulk behavior, the morphological evolution in thin films of linear TPUs with a high content of hard segment (HS) (from 70 to 100 wt %) on annealing is investigated. In contrast to melt-quenched bulk samples, a mixed phase was obtained for as-spin-cast films, and then, on annealing, a phase-separated mesophase domain, as previously observed by scattering and TEM in bulk samples, was observed by AFM to form directly from the mixed phase. In addition to this overall phase behavior, a crystallization behavior unique to thin films was observed: samples of thickness less than 120 nm and annealed at sufficiently high temperature developed large lamellar crystal blocks. Similar crystal blocks have also been found in thin films of a TPU with a more flexible chain extender, although in this case, with the greater HS/SS compatibility of this material, the phase separation behavior was not observed at all.

Hydrophobic nanoparticles promote lamellar to inverted hexagonal transition in phospholipid mesophases.

This study focuses on how the mesophase transition behaviour of the phospholipid dioleoyl phosphatidylethanolamine (DOPE) is altered by the presence of 10 nm hydrophobic and 14 nm hydrophilic silica nanoparticles (NPs) at different concentrations. The lamellar to inverted hexagonal phase transition (Lα-HII) of phospholipids is energetically analogous to the membrane fusion process, therefore understanding the Lα-HII transition with nanoparticulate additives is relevant to how membrane fusion may be affected by these additives, in this case the silica NPs. The overriding observation is that the HII/Lα boundaries in the DOPE p-T phase diagram were shifted by the presence of NPs: the hydrophobic NPs enlarged the HII phase region and thus encouraged the inverted hexagonal (HII) phase to occur at lower temperatures, whilst hydrophilic NPs appeared to stabilise the Lα phase region. This effect was also NP-concentration dependent, with a more pronounced effect for higher concentration of the hydrophobic NPs, but the trend was less clear cut for the hydrophilic NPs. There was no evidence that the NPs were intercalated into the mesophases, and as such it was likely that they might have undergone microphase separation and resided at the mesophase domain boundaries. Whilst the loci and exact roles of the NPs invite further investigation, we tentatively discuss these results in terms of both the surface chemistry of the NPs and the effect of their curvature on the elastic bending energy considerations during the mesophase transition.

Mesophase pitch-based carbon fiber spinning through a filter assembly and the microstructure evolution mechanism

A filter assembly in the upper stream of the spinneret was used to disturb the mesophase pitch (MP) melt flow during the spinning of precursor fibers. We studied the microstructure evolution mechanism of the MP-based carbon fibers during this process. Results showed that the use of filter assembly had a significant effect on the size of the split in the cross-section of carbon fibers. The split has been completely depressed in the carbon fibers spun with 50 layers of plain-weave. Selected area electron diffraction results showed that carbon fibers spun with 50 layers of plain-weave screens exhibited an apparent decrease of the orientational order of the (002) diffraction plane in both center and transition regions. The results of Raman spectroscopy indicated that, the size of graphitic microcrystalline domain in carbon fibers decreased with increasing the number of plain-weave screens in the filter assembly. Our studies confirmed the roles of the filter assembly in precursor fiber spinning to disrupt the mesophase domain formation in the MP melt and thus induce a reduced domain size.

Exclusion from Hexagonal Mesophase Surfactant Domains Drives End-to-End Enchainment of Rod-Like Particles

Anisotropic rod-like particles assemble end-to-end when the surfactant/water matrix in which they are dispersed is cooled from the isotropic to the lyotropic hexagonal phase. We demonstrate the formation of such end-to-end assemblies for gold nanorods, which are tens of nanometers in size, as well as for micrometer-sized ellipsoidal polystyrene particles. In both cases, the particles are well-dispersed in the low-viscosity surfactant/water phase above the isotropic-H1 transition temperature. On cooling into the H1 phase, mesophase domains form and the particles are expelled to the isotropic phase. As the H1 domains grow and finally impinge, the particles are localized at the domain boundaries where they reorient and assemble end-to-end. Remarkably, we observe the formation of end-to-end assemblies of gold nanorods even for volume fractions as low as 2 × 10(-6) in the initially dispersed state. The extent of particle "enchainment" increases with the particle concentration and with the aspect ratio of the particles.

Controlling Anisotropic Drug Diffusion in Lipid-Fe3O4 Nanoparticle Hybrid Mesophases by Magnetic Alignment

We present a new strategy to control the anisotropic diffusion of hydrophilic drugs in lyotropic liquid crystals via the dispersion of magnetic nanoparticles in the mesophase, followed by reorientation of the mesophase domains via an external magnetic field. We select a lipid reverse hexagonal phase doped with magnetic iron oxide nanoparticles and glucose and caffeine as model hybrid mesophase and hydrophilic drugs, respectively. Upon cooling through the disorder-order phase transition of the hexagonal phase and under exposure to an external moderate magnetic field (1.1 T), both the nanoparticles and the hexagonal domains align with their columnar axes along the field direction. As a result, the water nanochannels of the inverted hexagonal domains also align parallel to the field direction, leading to a drug diffusion coefficient parallel to the field direction much larger than what was measured perpendicularly: in the case of glucose, for example, this difference in diffusion coefficients approaches 1 order of magnitude. Drug diffusion of the unaligned reverse hexagonal phase, which consists of randomly distributed domains, shows values in between the parallel and transversal diffusion values. This study shows that modifying the overall alignment of anisotropic mesophases via moderate external fields is a valuable means to control the corresponding transport tensor of the mesophase and demonstrates that the orientation of the domains plays an important role in the diffusion process of foreign hydrophilic molecules.

In Situ Observation of Mesophase Formation and Coalescence in Catalytic Hydroconversion of Vacuum Residue Using a Stirred Hot-Stage Reactor

A microreactor equipped with a view window and a stirrer was used to observe mesophase formation in Athabasca vacuum residue with and without catalyst. The effect of stirring on mesophase formation and its growth and coalescence was studied during the cracking of vacuum residue under hydrogen at 4.8 MPa and 440 °C. Stirring can result in a bimodal distribution of size of mesophase domains. The forced coalescence of mesophase droplets by the stirrer led to the formation of very large mesophase regions (bulk mesophase), which coexisted with a large number of small micrometer-sized mesophase domains. The addition of catalyst likely had both chemical and physical effects on the formation and growth of mesophase. The catalyst gave a delay in the onset of mesophase formation as a chemical effect and a decrease in the amount of bulk mesophase regions by suppressing the coalescence of smaller mesophase domains as a physical effect. The analysis of the resulting cokes by scanning electron microscopy (SEM) showed that catalyst particles agglomerated and stuck to the outer surface of the mesophase domains and suppressed their coalescence. The agglomeration of catalyst particles likely decreased their ability to suppress the formation of small mesophase domains, in the range of a few micrometers in size. However, catalyst was effective in suppressing the formation of bulk mesophase domains with areas over 2000 μm2. The results showed that the onset of observable mesophase initially increased with the addition of catalyst, but then decreased at higher catalyst concentrations. SEM observation confirmed that the significant agglomeration of catalyst particles at higher concentrations was likely responsible for the decreased effectiveness of the catalyst in suppressing mesophase formation.

Fractionated crystallization of α‐ and β‐nucleated polypropylene droplets

AbstractA layer multiplying coextrusion process was used to produce multilayered polypropylene/polystyrene (PP/PS) films with various nucleating agents. When heated into the melt, the thin PP layers broke up into submicron PP droplets that exhibited fractionated crystallization. If the initial PP layers were 20 nm or less, the resulting droplets exhibited exclusively homogeneous nucleation. If a nucleating agent was added, the systematic departure from homogeneous nucleation provided insight into the nature of the heterogeneous nucleation. In this study, we used thermal analysis, atomic force microscopy (AFM), and wide angle X‐Ray scattering (WAXS) to examine the effect of two nucleating agents. We confirmed with WAXS and AFM that a soluble sorbitol nucleating agent for the PP α‐form operates in three concentration regimes as proposed in a previous study. Morphologically, homogeneous nucleation of the submicron droplets produced a granular texture. The correlation length from small‐angle X‐Ray scattering (SAXS) suggested that the grains contained 1–3 mesophase domains. Drawing on classical nucleation theory, the critical size nucleus of an individual mesophase domain was estimated to be about 2 nm3, which was considerably smaller than the mesophase domain. This pointed to mesophase crystallization that included the processes of nucleation and growth. Additional experiments were performed with nucleating agents for the PP β‐form. However, they were not effective in nucleating crystallization of the droplets, presumably because they were essentially insoluble in PP and the nucleating particles were too large to be accommodated in the PP droplets. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Structural and morphological changes during UV irradiation of the trans-planar form of syndiotactic polypropylene

Syndiotactic polypropylene films, obtained in the trans-planar mesophase, were exposed to accelerated weathering in a UV device at 45 °C for increasing times. A different series of films, characterized by the same structural organization, was annealed at 45 °C for the same times, to discern the thermal effects from those due to UV irradiation. The influence of UV irradiation and thermal treatments on the structural changes in terms of phase composition, crystallite sizes, and chain conformations was studied. Diffractometric and thermal analyses show that UV radiation causes a strong increase of helical crystallinity (189% with respect to the initial value), leaving the trans-planar mesophase unchanged. The mesophase domains have a higher rigidity and hinder the oxygen diffusion slowing down the photooxidative degradation. The chain scission in the amorphous phase produces a higher mobility, allowing crystallization. The crystallinity also increases in the thermally treated samples, but the increase is limited to the first 48 h and reaches about 89% of the initial value. Both in the thermally treated and UV irradiated samples the crystallite coherence length perpendicular to the 200 planes increases with time. The amorphous chains do crystallize at the beginning near the already formed crystals, thus increasing their dimensions. The carbonyl index shows an induction period of 48 h, before a rapid increase which apparently is inversely proportional to the percentage of mesomorphic and crystalline phases of the irradiated samples, indicating that the photooxidative reactions took place mainly in the amorphous region. A comparison with data already published on the photooxidative behavior of samples crystallized in form I shows that the presence of compact domains in trans-planar mesophase led to an increase in the induction period and to a greater stability of the material in the first 150 h of UV treatment.

Plastic Deformation of the γ Phase Isotactic Polypropylene in Plane−Strain Compression at Elevated Temperatures

Plastic deformation behavior of iPP homopolymer crystallized exclusively in the γ modification was studied. Samples of γ-iPP were obtained by isothermal crystallization under pressure of 200 MPa. Deformation experiments in plane−strain compression were performed in the temperature range of 55−100 °C. Samples of γ-iPP demonstrated higher modulus, higher yield stress, and flow stress, yet slightly lower ultimate strain comparing to α-iPP in the entire range of temperature studied. During plastic deformation numerous fine shear bands, initiated by the interlamellar shear of the amorphous layers, start to develop already at the yield point. Their propagation across the sample causes a limited destruction of γ lamellae oriented perpendicularly to the direction of the band. Destroyed fragments of crystallites partially reconstruct into either mesophase (smectic) domains or crystals of α phase, depending on the deformation temperature. Mesophase is produced upon deformation at room temperature, while at 55 °C and above the crystalline α phase is formed instead. With increasing strain shear bands multiply and tilt toward the flow direction. Fragmented lamellae undergo kinking and rotation, which results in formation of a chevron-like lamellar morphology. This leads also to the development of a weak crystalline texture. Both crystalline texture and lamellae orientation emerge due to the same deformation mechanism of interlamellar slip, produced by the shear within interlamellar amorphous layers. The activity of any crystallographic deformation mechanism within the crystalline component was not detected at any temperature. The interlamellar amorphous shear appears to be the primary deformation mechanism of γ-iPP. The other identified mechanisms, i.e., γ−smectic and γ−α transformations, play a supplementary role in the deformation sequence.

Crystallization kinetics and morphology of the mesomorphic form of syndiotactic polypropylene

AbstractFor the first time the kinetics of formation of syndiotactic polypropylene mesophase close to 0 °C through differential scanning calorimetry has been investigated. The calorimetric data have been analyzed through the well‐known Avrami analysis. We have obtained Avrami coefficients less or at most equal to 2, which are likely to indicate a nearly bidimensionality of the crystallites. The morphology of the mesophase, not known up to now, has been examined through atomic force microscopy (AFM): lamellar structures have been observed. The fractal dimension of the AFM images has been evaluated through the box counting method. It resulted about 2, in a very good agreement with the calculated Avrami coefficients. An infrared and diffractometer analysis on samples kept for increasing times at 0 °C has also been performed to confirm the calorimetric data. The experimental results allow one to better clarify the kinetics of mesophase‐formation. It has been found that a time of 3 h at 0 °C is actually necessary for the complete crystallization of the trans‐planar mesophase, a longer time is needed to stabilize the mesophase domains when the sample is extracted from 0 °C at room temperature. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 936–944, 2007