Synthesis and characterization of fluorine‐containing liquid crystalline polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens

Several novel side‐chain liquid crystalline (LC) polysiloxanes bearing cholesteryl cinnamate mesogens and trifluoromethyl‐substituted mesogens were synthesized by a one‐step hydrosilylation reaction with poly(methylhydrogeno)siloxane, a cholesteric LC monomer cholesteryl 3‐(4‐allyloxy‐phenyl)‐acryloate and a fluoro‐containing LC monomer 4‐[2‐(3‐trifluoromethyl‐phenoxy)‐acetoxy]‐phenyl 4‐allyloxy‐benzoate. The chemical structures and LC properties of the monomers and polymers were characterized by use of various experimental techniques, such as FTIR, ¹H‐NMR, ¹³C‐NMR, TGA, DSC, POM, and XRD. The temperatures at which 5% weight loss occurred were greater than 300°C for all the polymers, and the residue weight near 600°C increased slightly with increase of the trifluoromethyl‐substituted mesogens in the fluorinated polymer systems. The samples containing mainly cholesteryl cinnamate mesogens showed chiral nematic phase when they were heated and cooled, but the samples containing more trifluoromethyl‐substituted mesogens exhibited chiral smectic A mesophase. The glass transition temperature of the series of polymers increased slightly with increase of trifluoromethyl‐substituted mesogens in the polymer systems, but mesophase–isotropic phase transition temperature did not change greatly. In XRD curves, the intensity of sharp reflections at low angle increased with increase of trifluoromethyl‐substituted mesogens in the fluorinated polymers systems, indicating that the smectic order derived from trifluoromethyl‐substituted mesogens should be strengthened. These results should be due to the fluorophobic effect between trifluoromethyl‐substituted mesogens and the polymer matrix. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Characterization by Fourier transform infrared spectroscopy of polyethylene adipate/cholesteryl palmitate blends

FT‐IR spectroscopy has been employed to study compatibility, melting, and crystallization of the polyethylene adipate (PEA)/cholesteryl palmitate (CP) blends. The changes in FT‐IR spectra were followed by controlled rate of heating and cooling. The bands corresponding to the crystalline structure have been assigned. The accuracy of the transition temperature determination has been improved by fitting the curve of the integral absorbance dependence on temperature with a Boltzmann function. From dependence of the transition temperatures on the composition of the blend, it has been established that for each mixing ratio a certain mass fraction of CP should be dissolved in the PEA matrix. The PEA/CP blends behave as a phase‐separated system with partial miscibility. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1156–1163, 2004     

Cholesteryl sulfate-phosphatidylcholine interactions

The effect of cholesteryl sulfate, a natural membrane component, on the physical state of dipalmitoyl phosphatidylcholine multilamellar vesicles was investigated using fluorescence polarization and differential scanning calorimetry techniques. Cholesteryl sulfate increased the order of acyl chains for those temperatures higher than the gel-to-liquid crystalline transition temperature while it decreased the order for those temperatures below the phase transition temperature. At equimolar concentrations, cholesteryl sulfate suppressed the crystal liquid-to-gel phase transition of dipalmitoyl phosphatidylcholine. These data suggest that sterol sulfates may provide new tools for the elucidation of molecular mechanisms involved in sterollipid interactions.     

Effect of composition and molecular structure on the LC phase of PHB-PEN-PET ternary blend

Poly(p-hydroxybenzoic acid) (PHB)–poly(ethylene terephthalate) (PET) 8/2 thermotropic liquid crystalline copolyester, poly(ethylene 2,6-naphthalate) (PEN), and PET were mechanically blended to pursue the liquid crystalline (LC) phase of ternary blends. The torque values of blends with increasing PHB content abruptly decreased above 40 wt % of PHB content because the melt viscosity of ternary blends dropped. Glass transition temperature and melting temperature of blends increased with increasing PHB content. The tensile strength and initial modulus of blends were low at 10 and 20 wt % PHB. However, the blends containing above 30 wt % PHB were improved with increasing PHB content due to the formation of fibrous structure. The blend of 20 wt % PHB formed irregularly dispersed spherical domains, and the blends of 30–40 wt % PHB showed LCP ellipsoidal domains and fibrils. In the polarized optical photographs, the blends of 40 wt % PHB showed pseudo LC phases. The degree of transesterification and randomness of blends were increased with blending time. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1065–1073, 1998     

Thermotropic,side-chain ordered polymeric coatings: gas permeability switching via a thermal stimulus

Rapid access to large areas of stimuli-responsive materials is attractive in the field of membrane science for purification systems and molecular valves. Thermotropic liquid crystalline (LC) systems show sharp property changes through the smectic–LC transition induced by temperature. Comparison of similar amorphous and liquid crystalline systems allows for the elucidation of the characteristics of the LC phase. Lightly crosslinked C₆F₁₃ and C₈F₁₇ perfluorinated side-chain acrylate networks were UV cured as thin films resulting in amorphous and thermotropic liquid crystalline thin films, respectively. Thermal and morphological characterization indicates a restructuring of the liquid crystalline phase through the isotropic transition giving rise to an increase in transport and free volume properties. The amorphous film showed no dramatic change in transport or free volume properties.     

Kinetics of photopolymerization-induced phase separation and morphology development in mixtures of a nematic liquid crystal and multifunctional acrylate

Photopolymerization behavior and reaction kinetics for a series of multifunctional acrylate monomer(s) and eutectic liquid crystal blends were investigated with particular emphasis on determination of the reaction rate coefficients for propagation and termination steps of photopolymerization. Reaction rate coefficients were determined via real-time infrared spectroscopy and compared with those obtained by photo-differential scanning calorimetry. Effects of various parameters such as LC concentration, light intensity, and monomer functionality on the kinetics were investigated. Phase transition temperature versus composition phase diagrams were established by means of optical microscopy and differential scanning calorimetry for mixtures of triacrylate/liquid crystal (LC) before photopolymerization and after exposing to ultra violet (UV) irradiation under various reaction times. The snapshot phase diagram of the reacting mixtures exhibited isotropic gel, isotropic liquid + nematic, and narrow pure nematic coexistence regions. These coexistence regions were further confirmed by morphological changes of the polymer dispersed liquid crystal films as functions of temperature and concentration using polarized optical microscopy.     

Behaviour of the miscibility of poly(ethylene oxide)/liquid crystal blends

The microscopic behaviour of blends of poly(ethylene oxide) with two different low molecular weight liquid crystals (LC) was studied in order to evaluate miscibility. One of the liquid crystal components had a phase transition temperature lower than the melting temperature of poly(ethylene oxide) (PEO), and the other a higher value. The low molecular weight liquid crystal components were 4-cyano-4′-n-heptylbiphenyl (7CB) and p-cyanophenyl p-pentyloxybenzoate (pCP). Thermal analysis and polarized optical and scanning electron microscopy were employed. The melting temperature (T_m) depression of PEO increased with LC content in the blend, suggesting that the PEO was miscible with both liquid crystals in the isotropic phase. The spherulitic structural morphology of the semicrystalline components is affected by the presence of liquid crystals. © 1998 SCI.     

Nematic–isotropic transition in polymer‐confined and polymer‐free liquid crystal mixtures

Depending on the processing conditions in liquid crystal (LC) display manufacturing, LC/polymer composite films may exhibit unusual properties with respect to the compositional and phase behavior of the LC constituents. In particular, we have observed extraordinary large shifts of phase transition temperatures in LC/polymer composites, which can not be explained by preferential solvation or adsorption. Therefore, the influence of real manufacturing conditions such as thermal stress, storage in vacuum, and UV irradiation on the nematic–isotropic (n–i) transition temperatures of commercial nematic mixtures was investigated. Shifts of the clearing temperature of up to 88 K, presumably due to partial evaporation or UV degradation, were observed. Furthermore, we found that annealing may lead to the replacement of the nematic phase by the smectic A phase at room temperature in both LC/polymer composites and pure LC samples. Among the tested commercial LC blends, the mixtures E7, MLC‐6650, and L101 showed the smallest stress effects. Practical consequences of our results are discussed. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Self-assembly of bacterial and tunicate cellulose nanowhiskers

The self-assembly and phase transition diagrams of cellulose nanowhiskers derived from tunicates, food grade bacterial cellulose (nata-de-coco) and lab cultured bacterial cellulose are reported. The phase transition diagram for isotropic to liquid crystalline phase transition has been developed for cellulose nanowhiskers obtained from all these sources by recording phase separation behaviour and polarised optical microscopy (POM). The phase separation stops at 10, 4, and 12 wt% for tunicate cellulose, food grade and lab cultured bacterial cellulose, respectively, which also corresponds to the transition seen by POM. The phase diagrams and transition behaviours are explained on the basis of aspect ratio distributions. The liquid crystalline phase obtained after transition shows characteristics of both nematic and chiral nematic phases.     

Aromatic thermotropic polyesters based on 2,5-furandicarboxylic acid and vanillic acid

This paper addresses a route to synthesize bio-based polymers with an aromatic backbone having a liquid crystalline (LC) phase in the molten state. The LC phase is employed to achieve uniaxial orientation during processing required in e.g. fiber spinning. For this purpose 2,5-furandicarboxylic acid (2,5-FDCA) and O-acetylvanillic acid (AVA), obtained from natural resources, are used as monomers. Similar to the 2,6-hydroxynapthoic acid used to perturb the crystalline packing of poly(oxybenzoate) in the Vectran^® series, these bio-based monomers are used to lower the crystal to liquid crystal transition temperature. Considering that the poly(oxybenzoate) can also be obtained from natural resources, the adopted route provides the unique possibility to synthesize bio-based polymers that can be used for high performance applications. To obtain the desired polymers, a synthetic route is developed to overcome the thermal instability of the 2,5-FDCA monomer. Experimental techniques, such as optical microscopy, FTIR spectroscopy, DSC, and TGA are employed to follow the polymerization, phase transitions and evaluate thermal stability of the synthesized polymers.     

Incommensurate phase transition of cholesteryl 2,2,3,3-tetrafluoropropionate (CTFP)

This paper describes a paraelectric-incommensurate phase transition of cholesteryl 2,2,3,3-tetrafluoropropionate(CTFP) found at about -94°C by means of X-ray diffraction and dielectric constant studies performed with the single crystal.     

Hydrogen bonding interactions and miscibility studies of poly(amide)/poly(vinyl pyrrolidone) blends containing mangiferin

Miscibility studies of amorphous poly(amide)/poly(vinyl pyrrolidone) (PA/PVP) blends containing a crystalline phytochemical called “mangiferin” have been carried out using differential scanning calorimetry, Fourier transformed infrared spectroscopy and polarized optical microscopy. The binary blends of PA/PVP prepared from dimethylsulfoxide solutions were found to be completely miscible showing a systematic movement of a single glass transition temperature over the entire composition range. The FTIR study indicated the occurrence of cross-hydrogen bonding interactions between PA and PVP, which may be responsible for complete miscibility of the PA/PVP pair. Moreover, cross-hydrogen bonding promotes miscibility in binary blends of PA/mangiferin and PVP/mangiferin. However, the addition of mangiferin to PA/PVP blends has resulted in liquid-liquid phase separation between PA/mangiferin and PVP/mangiferin phases due to the preferential affinity of mangiferin to PVP than to PA. With increasing mangiferin concentration, liquid-liquid phase segregations occur between PA + mangiferin and PVP + mangiferin phases in addition to the solid-liquid phase transition of mangiferin crystals. Lastly, a ternary morphology phase diagram of the PA/PVP/mangiferin blends was established, which exhibited various coexistence regions such as isotropic, liquid + liquid, liquid + crystal, liquid + liquid + crystal, and solid crystal regions.     

Phase behavior and structure formation for diblock copolymers composed of side-chain liquid crystalline and glassy amorphous components

Phase behavior and structure formation in liquid crystallization of a side-chain liquid crystalline (LC) block copolymers composed of poly[11-(4′-cyanophenyl-4″-phenoxy)undecyl acrylate] (PA₁₁OCB) and polystyrene (PSt) were investigated by using a time-resolved small-angle X-ray scattering technique (SAXS), differential scanning calorimetry and polarizing optical microscopy. PA₁₁OCB homopolymer formed smectic (Sm) liquid crystal. Liquid crystallization behavior of the block copolymers depended on the molecular weight and the block composition. When molecular weight was relatively low, order-disorder transition (ODT) was observed. In cooling of such block copolymers, liquid crystallization seemed to wait for the formation of LC-rich microphase by ODT. For the block copolymers with relatively high molecular weight, liquid crystallization slightly enlarged the domain spacing without changing the microphase separation structure in the melt. The order of the LC phase was lowered with decreasing dimensionality of the LC microdomains, that is, the LC blocks formed smectic liquid crystal in the matrix or lamellar microphase while liquid crystallization in the cylindrical microdomains did not show smectic but maybe nematic liquid crystal. Moreover, the LC blocks within the spherical microdomains did not liquid crystallize. From the 2-D SAXS with applying shear flow, the Sm layers were orientated perpendicularly to the interface of the microphase separation. The relation between the layer thickness of the LC phase and the molecular weight suggested that the main chain was extended normally to the interface of the microphase separation.     

Comparative study of the tribological properties of polyamide 6 filled with molybdenum disulfide and liquid crystalline additives

The effect of adding a 1 wt % proportion of thermotropic liquid crystals 4,4′‐dibutylazobenzene (LC1) and 4‐octyl, 4′‐cyanobiphenyl (LC2) on the tribological properties of polyamide 6 (PA 6) is compared with that of the addition of MoS₂ in different concentrations (1 and 5 wt %). Friction and wear are determined in a pin‐on‐disk tribometer by using injection‐molded additivated nylon disks against steel or aluminum pins, below (25°C) and above (80°C) glass transition temperature. Polymeric blends are characterized by differential scanning calorimetry and by optical and scanning electron microscopy and microanalysis. Concentration of liquid crystalline additives is higher at the surface than in the bulk of PA 6 disks. Crystallinity degree of PA‐6 is not significantly changed by the presence of additives. Addition of 1 wt % LC1 improves processibility of PA 6 by increasing its melt flow rate. Cyanoderivative liquid crystal (LC2) shows the best wear‐reducing ability for PA 6/steel contacts at all temperatures. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2426–2432, 2001     

Synthesis and cure of liquid crystalline diallyl modifiers for bismaleimide resin

Three kinds of liquid crystalline aromatic azomethine modifiers were synthesized with high yield, and the modification of bismaleimide resin (BMI) with them was studied by scanning electron microscope, polarizing optical microscope, thermogravimetric analyzer, differential scanning calorimetry, and rheolometry. Blends cured at the temperature of liquid crystalline phase were found to have oriented liquid crystal‐rich phase and improved mechanical properties. The addition of o,o′‐diallyl bisphenol A in the blends of BMI decreases thermal properties but shows little effect on phase structures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4366–4371, 2006     

Characterization and free radical polymerization of liquid crystalline acrylic acid/cellulose diacetate and N-vinyl-2-pyrrolidinone/cellulose diacetate solutions

Polymerizations of liquid crystalline solutions of cellulose diacetate (CDA) in acrylic acid (AA) and N-vinyl-2-pyrrolidinone (NVP) were conducted in an attempt to prepare molecular composites (polymer blends) processing a rigid rod polymer with liquid crystalline orientation. CDA was found to form liquid crystalline solutions in both AA and NVP at concentrations avove 40 wt% CDA. Polymerization of anisotropic 50 wt% CDA-AA and CDA-NVP solutions occurred with considerable retention of the starting solution anisotropy and yielded homogeneous blends (1 T_g) when the rate of polymerization was fast relative to the phase separation of the free radically polymerizing AA or NVP with CDA. Slow polymerizations lead to phase separated blends (2 T_g).     

Synthesis and characterization of novel liquid crystalline cholesteryl-modified hydroxypropyl cellulose derivatives

Two new series of cholesteryl-modified hydroxypropyl cellulose (HPC) derivatives were synthesized by performing reactions involving HPC, a cholesterol-based mesogenic dimer (HPC-G1-Chol), or cholesteryl chloroformate (HPC-Chol), all with different degrees of substitution (D _Chol). All of the compounds obtained were characterized by conventional spectroscopic methods. The D _Chol values of the modified HPCs was obtained using ¹H NMR spectroscopy. Thermogravimetric analysis and differential scanning calorimetry (DSC) in combination with polarizing optical microscopy (POM) were used to investigate the thermal properties of the compounds obtained. The glass transitions of the modified HPCs occurred at lower temperatures than the glass transition temperature for HPC, but the glass transition temperatures increased with increasing D _Chol. All of the synthesized polymers formed thermotropic liquid crystalline phases. Polymers with a mesogenic side chain (i.e., the HPC-G1-Chol series) had wider mesophases than HPC and polymers that were derived from HPC-Chol. These compounds were found to be soluble in a variety of organic solvents, so they formed lyotropic liquid crystal mesophases in acetone. The critical concentrations above which liquid crystalline order was observed were 20 and 25 wt% for a sample from each series (HPC-G1-Chol and HPC-Chol, respectively) in acetone. It can therefore be hypothesized that HPC-G1-Chol has a greater propensity to exhibit specific chain–chain association phenomena than HPC-Chol in acetone.     

Blends of liquid crystalline polyester–polyurethane and epoxy: Preparation and properties

A novel liquid crystalline polyester–polyurethane (LCPU) that contains polyester mesogenic units was synthesized in the present work. Through a careful investigation of the structure and morphology of the LCPU, it was found that the home‐synthesized LCPU is a highly birefringent thermotropic nematic liquid crystal. After being blended with bisphenol‐A epoxy, the liquid crystalline polymer can, simultaneously, improve the impact strength and the glass transition temperature as well as the tensile strength and the tensile modulus of the blends. It was proved to be an efficient toughening agent for epoxy without the expense of other properties. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 783–787, 2003     

Miscibility and crystallization of biodegradable poly(butylene succinate-co-butylene adipate)/poly(vinyl phenol) blends

Miscibility, crystallization kinetics, crystal structure, and microstructure of biodegradable poly(butylene succinate-co-butylene adipate) (PBSA)/poly(vinyl phenol) (PVPh) blends were studied by differential scanning calorimetry, optical microscopy, wide angle X-ray diffraction, and small angle X-ray scattering in detail in this work. PBSA and PVPh are miscible as evidenced by the single composition dependent glass transition temperature and the negative polymer-polymer interaction parameter. Isothermal crystallization kinetics of PBSA/PVPh blends was investigated and analyzed by the Avrami equation. The overall crystallization rates of PBSA decrease with increasing crystallization temperature and the PVPh content in the PBSA/PVPh blends; however, the crystallization mechanism of PBSA does not change in the blends. Furthermore, blending with PVPh does not modify the crystal structure of PBSA. The microstructural parameters, including the long period, thickness of crystalline phase and thickness of amorphous phase, all become larger with increasing the PVPh content, indicating that PVPh mainly resides in the interlamellar region of PBSA spherulites in the blends.