Thermoreversible Gel-Dispersed Liquid Crystals.

A simple model is introduced to describe phase behaviours of binary mixtures of a thermoreversible gel and a low-molecular-weight liquid crystal (LC). We predict novel phase diagrams on the temperature-concentration plane, including sol-gel transition, nematic-isotropic phase transition, and phase separation. At high temperatures, the phase separation between the isotropic sol and gel phases appears. As the temperature decreases, we have the phase separation between nematic sol and isotropic gel phases, in which the nematic domains are dispersed in the isotropic gel phase. We suggest that thermoreversible gelation of reactive molecules mixed with LCs will become one of the new classes of polymer-dispersed liquid crystals.

Thermoresponsive mobility of liquid crystals and reactive mesogens during photopolymerization-induced phase separation.

Molecular interactions between liquid crystals (LCs) and reactive mesogens (RMs) at temperatures across the phase transition regions were comprehensively studied during photopolymerization-induced phase separation (PPIPS) beginning with raw mixtures until the formation of polymer network liquid crystals (PNLCs). Then, the molecules were found to be nonuniformly more and less mobile in response to temperature as PPIPS progressed. Optical birefringence and infrared absorption were carefully measured throughout PPIPS, using 4-cyano-4'-hexylbiphenyl (6CB) and 1,4bis-[4-(3-acryloyloxypropyloxy) benzoyloxy]-2-methylbenzene (RM257) as typical LCs and RMs. Microscopic views of thermoresponsive changes in the molecular orientation order of both LCs and RMs were obtained: LCs and RMs in raw mixtures interacted with one another but uniformly transformed their molecular orientation. Such interactions continuously change to become nonuniform with progress in PPIPS. At the incipient stages of PPIPS, RMs, which are polymerized but not completely networked, inhibit LCs from changing their molecular orientation and vice versa. As PPIPS progresses, some LCs become more mobile and some less mobile owing to RM constraints. The domain configuration of the submicrometer phase separation affects the thermoresponsive mobility of LCs and RMs, that is, LCs become more mobile in LC-richer areas. The quantitative knowledge here provides comprehensive insight that LCs and RMs are mutually constrained and that such interactive behavior varies nonuniformly as PPIPS progresses.

Volume Phase Transitions of Heliconical Cholesteric Gels under an External Field along the Helix Axis.

We present a mean field theory to describe cholesteric elastomers and gels under an external field, such as an electric or a magnetic field, along the helix axis of a cholesteric phase. We study the deformations and volume phase transitions of cholesteric gels as a function of the external field and temperature. Our theory predicts the phase transitions between isotropic (I), nematic (N), and heliconical cholesteric (ChH) phases and the deformations of the elastomers at these phase transition temperatures. We also find volume phase transitions at the I-ChH and the N-ChH phase transitions.

Phase transitions of heliconical smectic-C and heliconical nematic phases in banana-shaped liquid crystals.

A mean-field theory is introduced to describe heliconical nematic (N_{TB}), heliconical smectic-C (S_{m}C_{TB}), and biaxial heliconical smectic-C (S_{m}C_{TB,b}) phases with mirror symmetry breaking. We extend our previous theories of the N_{TB} phase to the heliconical smectic-C phases, by taking into account one-dimensional spatial ordering of smectic layers. The calculated phase diagrams on the temperature-alkyl chain length plane show a rich variety of phase transitions: first- and second-order N_{TB}-S_{m}C_{TB} transitions, etc., including tricritical, tetracritical, and multicritical points. Our theory is qualitatively consistent with an experimental phase diagram.

Normal- and Reverse-Mode Thermoresponsive Controllability in Optical Attenuation of Polymer Network Liquid Crystals.

A simple nonuniform irradiation method for photopolymerization-induced phase separation (PPIPS) was developed to produce unconventional mesoscale domain structures composed of liquid crystal (LC) and reactive mesogen (RM) phases. The LC/RM phase formations and their molecular orientation ordering through PPIPS were comprehensively investigated as a function of LC/RM molar ratio, curing temperature, and the use of uniform or nonuniform irradiation. Then, two different optical-anisotropic structures that can cause normal- or reverse-mode thermoresponsive light attenuation were formed by nonuniform irradiation at different curing temperatures at the same molar ratios. These two structures consist of mesoscale domains organized with multiaxially orientation-ordered LCs and orientation-disordered RMs for normal-mode thermoresponse and uniaxially orientation-ordered LCs and RMs for reverse-mode thermoresponse. Phase-separation nuclei were generated by nonuniform irradiation at the incipient stage during the PPIPS process under nonuniform irradiation and subsequently coalesced to form mesoscale polymer networks while maintaining their molecular orientation order. This is a promising method to overcome the restraint of structural controllability due to intrinsic material properties and thus to provide unconventional optical and photonic devices, such as thermoresponsive smart windows and thermometric sheets.

Multiple Bragg Diffractions with Different Wavelengths and Polarizations Composed of Liquid Crystal/Polymer Periodic Phases.

We first fabricated holographic polymer-dispersed liquid crystals (HPDLCs) that produce multiple Bragg diffractions with different polarization states for every angle of incidence, through a photopolymerization-induced phase separation by one-time interferential exposure. The polarizations of the Bragg diffractions were well-controlled at individual wavelengths in the fabrication process by the compositional ratio of LCs to monomers. The raw mixtures of extremely low-functionality monomers having very different viscosities were used to reduce the domain size in phase separation and subsequently to form elaborate periodic structures of the LC and polymer phases. A cross-linker (1-vinyl-2-pyrrolidione) and a prepolymer with urethane groups were employed to strengthen the polymer network. Note that the diffractions of our HPDLCs are regarded as not purely but mostly Bragg type, according to the evaluation with the established criteria. The devices, which are monolithic but versatile in diffractive behaviors, have advantages of simple manufacturing and handling.

Volume phase transitions of cholesteric liquid crystalline gels.

We present a mean field theory to describe anisotropic deformations of a cholesteric elastomer without solvent molecules and a cholesteric liquid crystalline gel immersed in isotropic solvents at a thermal equilibrium state. Based on the neoclassical rubber theory of nematic elastomers, we derive an elastic energy and a twist distortion energy, which are important to determine the shape of a cholesteric elastomer (or gel). We demonstrate that when the elastic energy dominates in the free energy, the cholesteric elastomer causes a spontaneous compression in the pitch axis and elongates along the director on the plane perpendicular to the pitch axis. Our theory can qualitatively describe the experimental results of a cholesteric elastomer. We also predict the first-order volume phase transitions and anisotropic deformations of a gel at the cholesteric-isotropic phase transition temperature. Depending on a chirality of a gel, we find a prolate or oblate shape of cholesteric gels.

Phase diagrams of mixtures of a polymer and a cholesteric liquid crystal under an external field.

We present a mean field theory to describe phase behaviors in mixtures of a polymer and a cholesteric liquid crystal under an external magnetic or electric field. Taking into account a chiral coupling between a polymer and a liquid crystal under the external field, we examine twist-untwist phase transitions and phase separations in the mixtures. It is found that a cholesteric-nematic phase transition can be induced by not only the external field but also concentration and temperature. Depending on the strength of the external field, we predict cholesteric-paranematic (Ch+pN), nematic-paranematic (N+pN), cholesteric-nematic (Ch+N) phase separations, etc., on the temperature-concentration plane. We also discuss mixtures of a non-chiral nematic liquid crystal and a chiral dopant.

Theory of polymer-dispersed cholesteric liquid crystals.

A mean field theory is presented to describe cholesteric phases in mixtures of a polymer and a cholesteric liquid crystal. Taking into account an anisotropic coupling between a polymer and a liquid crystal, we examine the helical pitch, twist elastic constant, and phase separations. Analytical expressions of the helical pitch of a cholesteric phase and the twist elastic constant are derived as a function of the orientational order parameters of a polymer and a liquid crystal and two intermolecular interaction parameters. We also find isotropic-cholesteric, cholesteric-cholesteric phase separations, and polymer-induced cholesteric phase on the temperature-concentration plane. We demonstrate that an anisotropic coupling between a polymer and a liquid crystal can stabilize a cholesteric phase in the mixtures. Our theory can also apply to mixtures of a nematic liquid crystal and a chiral dopant. We discuss the helical twisting power, which depends on temperature, concentration, and orientational order parameters. It is shown that our theory can qualitatively explain experimental observations.

Theory of liquid crystalline micelles.

A theory is introduced to describe self-assembly of liquid crystalline AB diblock copolymers, consisting of a homopolymer (A) and a side-chain liquid crystalline polymer (B). We derive the free energy of the liquid crystalline micellar solutions and examine the equilibrium solution properties: critical micelle concentration (CMC), nematic-isotropic phase transition (NIT) of the rigid side-chains inside the micelle core, and phase separations. It is shown that there is a critical micelle size below which the NIT becomes continuous due to a packing effect. We also find re-entrant micellizations near the NIT temperature. The phase diagrams, including binodal, spinodal, CMC, and NIT curves are also examined on the temperature-concentration plane.

Novel biaxial nematic phases of side-chain liquid crystalline polymers.

We present a mean field theory to describe biaxial nematic phases of side-chain liquid crystalline polymers, in which rigid side-chains (mesogens) and rigid-backbone chains favor mutually perpendicular orientations. Taking into account both excluded volume and attractive interactions between rigid rods, novel biaxial nematic phases are theoretically predicted. We calculate uniaxial and biaxial orientational order parameters as a function of temperature and the length of backbone chains. We find a first-order biaxial-biaxial phase transition and a first (or second)-order uniaxial-biaxial one, depending on the length of mesogens and backbone chains.

Phase diagrams of binary mixtures of liquid crystals and rodlike polymers in the presence of an external field.

We theoretically study phase separations in mixtures of a low molecular-weight-liquid crystalline molecule (LC) and a rigid-rodlike polymer (rod) under an external field, such as magnetic or electric fields. By taking into account two orientational order parameters of the rod and the LC, we define four nematic phases (N(0), N(1), N(2), N(3)) on the temperature-concentration plane. Depending on the sign of the dielectric anisotropy Δε(i) of the rod (i = 1) and LC(i = 2), we examine the phase behavior of rod/LC mixtures in the case of Δε(1) > 0, Δε(2) > 0 (a), Δε(1) < 0, Δε(2) > 0 (b), Δε(1) > 0, Δε(2) < 0 (c), and Δε(1) < 0, Δε(2) < 0 (d). We predict a variety of phase separations induced by an external field.

Volume phase transitions of biaxial nematic elastomers.

We present a mean-field theory to describe biaxial nematic phases of side-chain liquid crystalline elastomers. Novel biaxial nematic phases are theoretically predicted in a side-chain liquid crystalline polymer and gel, where side chains (mesogens) and rigid-backbone chains favor mutually perpendicular orientations. We calculate uniaxial and biaxial orientational order parameters and examine deformations of the gel and stable biaxial nematic phases of the liquid crystalline gel dissolved in isotropic solvents. We predict first-order uniaxial-biaxial nematic phase transitions of the gel and the volume of the gel is discontinuously changed at the phase transition temperature.

Presence of older thrombus in patients with late and very late drug-eluting stent thrombosis.

BACKGROUND: Although drug-eluting stents (DES) have considerably reduced the incidence of in-stent restenosis, late and very late stent thrombosis (ST) after DES implantation have emerged as major safety concerns. We morphologically investigated the age of DES thrombi aspirated during percutaneous coronary intervention (PCI) from patients with either late or very late ST that resulted in acute myocardial infarction (AMI). METHODS AND RESULTS: We obtained DES thrombi during PCI from 16 consecutive patients with ST (late and very late ST, n=4 and n=12, respectively), who presented with AMI within 24 h of the onset of anginal symptoms. Thrombi were morphologically classified as fresh, lytic, and organized. Fresh thrombus was identified in 5 (31%) of the 16 patients and lytic thrombus was found in 3 (19%). Organized thrombus was notably found in 8 (50%) patients, of whom 5 (31%) had only the organized type and 3 (19%) had both fresh and organized thrombi. The frequency of fresh thrombus tended to be higher in patients with stent failure such as stent malapposition and fracture, but the difference did not reach significance (p=0.06). CONCLUSIONS: Although the study group is small, about two-thirds of DES thrombi in late and very late ST were days or weeks old. These findings suggest an important discrepancy between the time of onset of the intra-stent thrombotic process and the occurrence of acute clinical symptoms, and provide further information about another potential mechanism of DES thrombosis.

Late restenosis following sirolimus-eluting stent implantation.

OBJECTIVES: This serial angiographic study evaluated the incidence and predictors of late restenosis after sirolimus-eluting stent (SES) implantation. BACKGROUND: Previous studies showed late restenosis (i.e., late catch-up phenomenon) after implantation of 7-hexanoyltaxol-eluting stents and nonpolymeric, paclitaxel-eluting stents. METHODS: Between August 2004 and December 2006, SES implantation was performed in 1,393 patients with 2,008 lesions, in whom 8-month and 2-year follow-up coronary angiography were planned. RESULTS: Of 2,008 lesions, 1,659 (83%) underwent 8-month follow-up angiography (8.3 ± 2.2 months). Restenosis was observed in 122 lesions (7.4%). Coronary angiography 2 years (1.9 ± 0.4 years) after SES deployment was performed in 1,168 lesions (74% of lesions without restenosis at 8-month follow-up angiography). Late restenosis was observed in 83 lesions (7.1%). There was significant decrease in minimum luminal diameter (MLD) between 8-month and 2-year follow-up (2.56 ± 0.56 mm vs. 2.35 ± 0.71 mm, p < 0.001). Multivariate analysis showed in-stent restenosis before SES implantation and MLD at 8-month follow-up as independent predictors of late restenosis. CONCLUSIONS: Between 8-month and 2-year follow-up after SES implantation, MLD decreases, which results in late restenosis in some lesions. In-stent restenosis before SES implantation and MLD at 8-month follow-up are independent predictors of late restenosis.

Repeated sirolimus-eluting stent implantation to treat sirolimus-eluting stent and bare-metal stent restenosis.

BACKGROUND: In-stent restenosis (ISR) remains a persistent, unresolved issue even in the era of percutaneous coronary intervention (PCI) using drug-eluting stents. The present study compares the clinical and angiographic outcomes of using sirolimus-eluting stents (SES) for re-intervention against ISR that was originally treated with sirolimus-eluting or bare-metal (BMS) stents. METHODS AND RESULTS: This prospective single-center registry investigated 179 ISR lesions in 158 consecutive patients (53 lesions in 49, and 126 in 109 patients originally treated with SES and BMS, respectively), who had undergone re-intervention with SES. The patients were clinically and angiographically followed up at 8 months after re-PCI. The incidence of re-restenosis (29 vs 12%, P<0.01), ischemia-driven target lesion revascularization (TLR; 21 vs 8%, P<0.05) and major adverse cardiac events (MACE; 21 vs 9%, P<0.05) were significantly greater in ISR lesions originally treated with SES than in those originally treated with BMS at 8 months after re-PCI. Moreover, late luminal loss was significantly greater in the group with post-SES restenosis (P<0.05). Even after adjustment, post-SES restenosis was the only independent predictor of re-restenosis and MACE (P<0.05, each). CONCLUSIONS: Although the re-restenosis rate is acceptable, the incidence rates of late restenosis, ischemia-driven TLR and MACE are higher after repeated SES implantation to treat SES, than BMS restenosis. These results might affect the mid-term clinical outcomes of re-intervention with SES.

Theory of binary mixtures of a rodlike polymer and a liquid crystal.

We present a mean field theory to describe phase separations in mixtures of a low molecular-weight-liquid crystalline (LC) molecule and a rigid-rodlike polymer (rod) such as carbon nanotubes (CNTs) and LC polymers. By taking into account two orientational order parameters of the rod and the LC, we find three nematic phases (N(0),N(1),N(2)) on the temperature-concentration plane, depending on the attractive or repulsive interactions between the rod and the LC. We discuss the phase behavior of the systems where the rod and the LC are oriented to be parallel or perpendicular with each other and find that the phase diagrams of the parallel alignment are different from that of the perpendicular one. We predict the appearances of a lower critical solution temperature (LCST) and an upper one, a tricritical point, a critical point, and the first- and the second-order nematic-isotropic phase transitions. The theory can qualitatively describe the phase diagram with a LCST observed in a rod/LC mixture. We also predict a variety of phase separations in CNT/LC mixtures.

Three stage-volume phase transitions of a side-chain liquid crystalline elastomer immersed in nematic solvents.

We theoretically study volume phase transitions of a side-chain liquid crystalline elastomer (LCE) immersed in nematic solvents. Six different uniaxial nematic phases (N(1 parallel), N(1 perpendicular), N(2 parallel), N(2 perpendicular), N(3 parallel), and N(3 perpendicular)) are defined by using orientational order parameter S(m) of a side-chain mesogen, S(b) of a backbone chain, and S(0) of a nematic solvent inside the gel. We derive the free energy of a side-chain LCE dissolved in nematic solvents and calculate the swelling behavior of the LCE, the order parameters, and the deformations of the LCE as a function of temperature. We find various phase transitions of the LCE, such as the isotropic (I)-N(1 parallel)-N(3 perpendicular) and the I-N(2 parallel)-N(3 parallel), etc., accompanied by volume phase transitions. These results present new concepts in the structure of a side-chain LCE dispersed in nematic solvent molecules.

Phase separations in mixtures of a liquid crystal and a nanocolloidal particle.

We present a mean field theory to describe phase separations in mixtures of a liquid crystal and a nanocolloidal particle. By taking into account a nematic, a smectic A ordering of the liquid crystal, and a crystalline ordering of the nanoparticle, we calculate the phase diagrams on the temperature-concentration plane. We predict various phase separations, such as a smectic A-crystal phase separation and a smectic A-isotropic-crystal triple point, etc., depending on the interactions between the liquid crystal and the colloidal surface. Inside binodal curves, we find new unstable and metastable regions, which are important in the phase ordering dynamics. We also find a crystalline ordering of the nanoparticles dispersed in a smectic A phase and a nematic phase. The cooperative phenomena between liquid-crystalline ordering and crystalline ordering induce a variety of phase diagrams.

Volume phase transitions of smectic gels.

We present a mean-field theory to describe volume phase transitions of side-chain liquid crystalline (LC) gels, accompanied by isotropic-nematic-smectic- A phase transitions. Three different uniaxial nematic phases ( N1 , N2 , and N3 ) and smectic- A phases ( S1 , S2 , and S3 ) are defined by using orientational order parameter S_{m} of side-chain liquid crystals (mesogens), S_{b} of semiflexible backbone chains, and a translational order parameter sigma for a smectic- A phase. We derive the free energy for smectic- A phases of side-chain LC gels dissolved in an isotropic solvent and examine the swelling curve of the LC gel, the orientational order parameters, and the deformation of the LC gel as a function of temperature. We find that the LC gel discontinuously changes the volume at an isotropic-nematic, an isotropic-smectic- A , and a nematic-smectic- A phase transition.