Side-chain Liquid Crystalline Polysiloxanes Research Articles

Orientational dynamics in the crystalline and amorphous states of side-chain liquid crystalline polysiloxane probed by second harmonic generation

The orientational behaviour of mesogenic chromophores in side-chain liquid crystalline polysiloxane subject to an external electric field was investigated by the measurement of second harmonic generation (SHG). The rise and decay rates of the electric-field-induced SHG intensity in the crystalline state were found to be slower than those in the amorphous state; furthermore, the SHG intensity in the crystalline state was found to be weaker than that in the amorphous state. Analysis of the rise and decay rates of the electric-field-induced SHG intensity suggested that the mesogenic chromophores in the amorphous state move independently with other mesogenic chromophores and with the siloxane backbone, whereas those in the crystalline state move cooperatively with them.

New hydrocarbon side chain liquid crystalline polysiloxane polymers: Synthesis, characterization, and thermotropic behavior

A series of new and high-purity hydrocarbon liquid crystal monomers were synthesized through the acylation reaction, deoxygenation reaction, and Grignard reaction. 1H-NMR spectra and elemental analyses were used to examine their purity. The liquid crystalline polysiloxane polymers were obtained by grafting the monomers onto poly(methylhydrosiloxane). The thermal transition temperature, mesomorphic properties, and mesophase textures of the monomers and the polymers were determined by differential scanning calorimetry (dsc), polarized optical microscopy, and X-ray diffraction analysis. Moreover, we observed the even–odd effect of the smectic/isotropic transition temperature with the length variation of the substituents. In this study, we found by X-ray diffraction that the liquid crystalline polysiloxane polymers undergo a transition from smectic B to smectic E mesophase. However, dsc has difficulty detecting the phase transition process. By considering the spin–lattice relaxation time (T1), we can systematically explain the relation between the flexibility of the substituent with the smectic/isotropic transition temperature. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2849–2863, 1998

Ferrocene- and Fullerene[60]- Containing Liquid-Crystalline Materials

This paper shows the versatility of ferrocene and fullerene for the design of thermotropic liquid-crystalline materials: i) the electrochemical properties of the ferrocene-ferrocenium system were exploited to design redox-active metallomesogens (1 and 2); ii) ferrocene-containing side-chain liquid-crystalline polysiloxane (3) and polymethacrylates (5 and 6) were synthesized by grafting a mesomorphic vinylferrocene monomer (4) onto commercially available polysiloxane and by free-radical polymerization of mesomorphic methacrylate-ferrocene monomers (7 and 8), respectively; iii) a first-generation ferrocene-containing liquid-crystalline dendrimer (9) was synthesized; and iv) liquid-crystalline fullerene (10) and mixed fullerene-ferrocene (11) derivatives were obtained by functionalizing the C60 core with a twin cholesterol moiety.

All-Hydrocarbon Liquid Crystalline Polysiloxane Polymer as Stationary Phase in Gas Chromatography Capillary Column for Separation of Isomeric Compounds of Polynuclear Aromatic Hydrocarbons

Two new and high-purity all-hydrocarbon side-chain liquid crystalline polysiloxane polymers were synthesized by grafting all-hydrocarbon liquid crystal monomers onto a polymethylhydrosiloxane backbone. The two polysiloxane polymers show both smectic B and E mesophases which were characterized by (differential scanning calorimetry and X-ray analysis. As stationary phases, these liquid crystalline polysiloxane polymers were coated on the inner surface of a capillary column (i.d. = 0.32 mm, film thickness d(f) ≈ 0.25 μm) using the static coating method. The capillary column was installed on a GC/MS instrument. We used a standard commercial mixture of 21 species of polynuclear aromatic hydrocarbons (purchased from Supelco Co. and Merck Co.) to test the chromatographic behavior of the coated stationary phase. Test results of the isomeric pair compounds show a better separation resolution than identical tests using the commercial HP-5 capillary column, which is a standard and state-of-the-art analytical tool for the chromatographic resolution of PAHs.

Mesogenic structural effects on monolayer behaviors of the liquid crystalline polysiloxanes at the air/water interface

The monolayer behavior of three newly synthesized side-chain liquid crystalline polysiloxanes and corresponding monomers have been investigated at the air/water interface. The surface pressure-area isotherms and Brewster angle microscopy (BAM) were used to study the influence by different mesogenic units in the side chains. The results indicate that difference in mesogenic unit structure, such as linkage bond and mesogen length, have marked effects on the liquid crystallinity and self-aggregation tendency of the molecular chains which determine the properties of the monolayers.

Characterization and Electro-Optical Properties of the Homopolymer and Copolymers of Ferroelectric Side-Chain Liquid Crystalline Polysiloxanes Containing Two Chiral Center Side Groups

Aggregation and electro-optical effects in the chiral smectic C phase of the ferroelectric liquid crystalline homopolymer and two copolymers were investigated. The smectic layers of homopolymer and copolymer were constructed by overlapping about 1.2 and 1.4 times the length of the side-chain mesogenic groups, respectively. The transient scattering mode was obtained by repeated voltage polarity reversal. Ferroelectric liquid crystalline polysiloxanes (FLCPs) exhibit large spontaneous polyarization (Ps) and Ps of homopolymers are larger than those of copolymers. The response times of homopolymers are longer than that of copolymers due to high viscosity. Reversible and bistable transparent-opaque change was successfully realized for the chiral smectic C phase upon applications of dc electric fields with a response time of several milliseconds at room temperature.

Transient Shear Flow Behavior of Dilute Solutions of Side-Chain Liquid-Crystalline Polysiloxanes in 4,4‘-(n-Pentyloxy)cyanobiphenyl

The transient stress response of homeotropic monodomains of dilute nematic solutions of side-chain liquid-crystalline polysiloxanes (LCPs) in 4,4‘-(n-pentyloxy)cyanobiphenyl (5OCB) is investigated. In contrast to the flow-aligning behavior of 5OCB, strong stress oscillations are observed for the dilute LCP solutions, characteristic of flow-tumbling behavior. The dependence of the oscillation periodicity on LCP concentration and LCP structure (molecular weight and spacer length) is presented. From analysis of the stress transients, the Leslie viscosity coefficients, α2 and α3, are calculated. For all LCP structures, the increment δα2 on dissolution of LCP is negative, whereas the increment δα3 is positive. The magnitude and signs of these viscosity increments are strictly inconsistent with earlier electrorheological measurements of the Miesowicz viscosity increments, δηb and δηc, of these solutions, using as a guide a hydrodynamic model that computes the contribution of the chains to viscous dissipation in a simple shear flow. We propose that an additional dissipation mechanism should be considered, which derives from the presence of an elastic torque between director rotation and LCP orientation. Corresponding modification of the theory leads to improved agreement with experiment.

New naphthalene containing side-chain liquid crystalline polysiloxane stationary phases for high-resolution gas chromatography

A new side-chain liquid crystalline polysiloxane (SCLCP) having a wide liquid crystalline range of 140°C to 315°C was used as a stationary phase in capillary column gas chromatography. A series of new SCLCPs was synthesized using olefins containing 2,6-disubstituted naphthalene. The olefins were attached to a hydromethylpolysiloxane backbone by a hydrosilylation reaction using a platinum catalyst. Reproducible fused-silica capillary columns were made from the new SCLCP stationary phase. The columns have high thermal stability, efficiency and isomer specificity for the separation of isomeric compounds. The separations on the SCLCP stationary phase column and on a dimethyl (5% phenyl)polysiloxane stationary phase column are compared. The applications of capillary columns made from the new SCLCP for the separation of isomeric polychlorinated dibenzo- p-dioxins, polycyclic aromatic hydrocarbons and pesticides are demonstrated as examples.

Terminally carboxyl oligo(ethylene oxide) monomethyl ethers-substituted side chain liquid crystalline polysiloxane polymer as stationary phase in capillary gas chromatography for the separation of polynuclear aromatic hydrocarbons

Through esterification, acyl halide addition and monomer-grafting reactions, three new side chain liquid crystalline polysiloxane polymers containing an oligo(ethylene oxide) monomethyl group as their respective terminal group, poly (4-[(2-methylethoxy)carbonyl]phenyl 4-[4-(allyloxyl)-phenyl]benzoate) (PBPBE1), poly (4-[(2-(2-methylethoxy)ethoxy)carbonyl]phenyl4-[4-(allyloxyl)-phenyl]benzoate) (PBPBE2) and poly (4-[(2-(2-(2-methylethoxy) ethoxy) ethoxy) carbonyl]phenyl 4-[4-(allyloxyl)-phenyl]benzoate) (PBPBE3) were synthesized. These liquid crystalline polysiloxane polymers were coated onto the inner surface of a capillary column (I.D.=0.32 mm, film thickness d f≈0.2 μm) to test the chromatographic behavior of the critical pairs 5–6, 9–10 and 11–12 from the Supelco 610M standard mixture polynuclear aromatic hydrocarbon compounds. Results show that the experimental columns give better separation resolution and can be employed over a wider temperature range than the commercial HP-5 capillary column (Hewlett–Packard).

Electrorheological creep response of tumbling nematics

The shear creep response of homeotropic monodomains of 4,4′-n-octylcyanobiphenyl (8CB) and dilute solutions of a side-chain liquid-crystalline polysiloxane (LCP) in N-(4-methoxybenzylidene)- 4-butylaniline (MBBA) is studied in the absence and presence of electric fields applied along the director. In the absence of the field, oscillations in strain rate are observed for 8CB and the LCP/MBBA solutions, indicative of director-tumbling flow. In the presence of electric fields, the tumbling flow is suppressed and, with increasing field strength, a systematic evolution is observed toward flow-aligning, the apparent viscosity being determined by the balance in hydrodynamic and electric torques. Due to a larger dielectric anisotropy, the tumbling flow of 8CB is suppressed at a critical field strength much lower than that of the LCP/MBBA solution. Moreover, a field-induced asymmetry of the doublet peaks is observed in the creep deformation for 8CB at 34 °C. Based on Ericksen’s transversely isotropic fluid theory, simulation of the influence of electric fields on the flow-tumbling behavior is performed and qualitative agreement with the experimental results is obtained.The shear creep response of homeotropic monodomains of 4,4′-n-octylcyanobiphenyl (8CB) and dilute solutions of a side-chain liquid-crystalline polysiloxane (LCP) in N-(4-methoxybenzylidene)- 4-butylaniline (MBBA) is studied in the absence and presence of electric fields applied along the director. In the absence of the field, oscillations in strain rate are observed for 8CB and the LCP/MBBA solutions, indicative of director-tumbling flow. In the presence of electric fields, the tumbling flow is suppressed and, with increasing field strength, a systematic evolution is observed toward flow-aligning, the apparent viscosity being determined by the balance in hydrodynamic and electric torques. Due to a larger dielectric anisotropy, the tumbling flow of 8CB is suppressed at a critical field strength much lower than that of the LCP/MBBA solution. Moreover, a field-induced asymmetry of the doublet peaks is observed in the creep deformation for 8CB at 34 °C. Based on Ericksen’s transversely isotropic fluid theory,...

Guest-host ferroelectric side-chain liquid crystalline polymeric materials with improved electro-optical properties

A ferroelectric side-chain liquid crystalline polysiloxane (FLCP) containing azobenzene dyes as guest molecules for electro-optics has been investigated. The intensity and frequency of the Goldstone mode for the FLCP were increased remarkably after doping with azobenzene dyes. Larger fluctuation of the spontaneous polarization vector in each smectic layer under an applied electric field can be brought about with the addition of a strong dipole-moment guest molecule. This leads to a larger spontaneous polarization and shorter response time. It was found that the doping of a suitable amount of a strong dipole-moment azobenzene dye in the LC phase of the FLCP is helpful for the improvement of the electro-optical properties.

Effect of lateral substituents on the mesomorphic properties of side-chain liquid crystalline polysiloxanes containing 4-[(S)-2-methyl-1-butoxy]phenyl 4-(alkenyloxy)benzoate side groups

The synthesis of side-chain liquid crystalline polysiloxanes containing ei- ther 4-((S)-2-methyl-1-butoxy)phenyl 4-(alkenyloxy)benzoate or laterally fluoro-, chloro-, bromo-, and methoxy-substituted 4-((S)-2-methyl-1-butoxy)phenyl 4-(alkenyl- oxy)benzoate mesogenic side groups is presented. The mesomorphic properties of the synthesized polymers have been characterized by optical polarizing microscopy, differ- ential scanning calorimetry, and X-ray diffraction measurements. The effects of spacer length and lateral substituent on the mesomorphic properties of the obtained polymers are examined. The five polymers which contain three methylene units in the spacers show no mesophase, while the five polymers which contain eleven methylene units in the spacer display smectic mesomorphism. Among the other fifteen polymers which contain respectively four, five, or six methylene units in the spacers, those with small fluoro and chloro substituents reveal respectively an SA phase, while those with bulky bromo and methoxy substituents show no liquid crystalline behavior. The experimental results demonstrate that introducing a bulky lateral substituent into the mesogenic core of a polymer depresses the tendency to form a mesophase. Furthermore, the tech- nique of thermally stimulated current has been used to study the dipolar relaxation mechanisms in a side-chain liquid crystalline polysiloxane. q 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2793-2800, 1997

Electrorheological Behavior of Side-Chain Liquid-Crystalline Polysiloxanes in Nematic Solvents

The electrorheological properties of well-characterized side-chain liquid-crystalline polysiloxanes with different backbone and spacer lengths were studied in two nematic solvents: 4‘-(pentyloxy)-4-biphenylcarbonitrile (5OCB), which has positive dielectric anisotropy, and N-(4-methoxybenzylidene)-4-butylaniline (MBBA), which has negative dielectric anisotropy. Specifically, we measured the steady-shear viscosities, ηoff and ηon, in the absence and presence, respectively, of a saturation electric field. For 5OCB solutions, the electrorheological (ER) effect is positive, i.e., ηon > ηoff. For the intrinsic viscosities, we find [ηoff] ≫ [ηon], and [ηoff] shows a strong dependence on molecular weight ([ηoff] ∼ M0.4) and spacer length, whereas [ηon] is insensitive to the change of molecular weight and spacer length. In contrast, the ER effect of MBBA solutions is very small and slightly negative, i.e., ηon < ηoff. In addition, [ηoff] and [ηon] are of comparable magnitude and each shows a strong dependence on molecular weight ([ηoff] ∼ [ηon] ∼ M0.3). These distinctive patterns of ER behavior can be explained by a hydrodynamic model which assumes the side-chain liquid-crystalline polysiloxane has an asymmetric conformation, such that the root-mean-square end-to-end distance parallel to the director, R∥, is different from that perpendicular to the director, R⊥. R∥ is aligned along the shear gradient in 5OCB when the field is on but is tilted toward the flow direction with the field off. In MBBA, R∥ is oriented perpendicular to the shear gradient both with the field on and with the field off.

New side chain liquid crystalline polysiloxanes containing 1,3-dithiane or 1,3-dioxane rings as mesogenic side groups

New liquid crystal materials: 2-\\[p-(9-decenyloxy)phenyl]-5-(p -alkoxyphenyl)-1,3-dioxane(11) and 2-\\[p-(9-decenyloxy)phenyl]-5-(p -alkoxyphenyl)-1,3-dithiane(12) were synthesized. The mesomorphic behaviour of these compounds was determined. Though the 1,3-dioxane-type monomer exhibited both SmA and nematic phases, the 1,3-dithiane-type monomer only exhibited a nematic phase. By the hydrosilylation of poly(methylhydrosiloxane) and these monomers, side chain polysiloxanes were synthesized. For the monomers, the transition temperatures of the nematic to isotropic transitions of 1,3-dioxane-type compounds are higher than those of the corresponding 1,3-dithiane-type compounds. However, in the polysiloxane polymer this relation reversed.

Synthesis of Liquid Crystalline Polysiloxanes Containing Naphthalene-Based Mesogens and Chiral Side Chains

The synthesis and characterization of side-chain liquid crystalline polysiloxanes containing (2S)-2-chloro-4-methylpentyl 4-[(6-alkanyloxynaphthyl-2-yl)carbonyloxy]benzoate and (2S, 3S)-2-chloro-3-methylpemtyl 4-[(6-alkanyloxynaphthyl-2yl)carbonyloxy]benzoate side groups are presented. All of the obtained polymers reveal respectively an enantiotropic smectic A phase. The phase transition temperatures of the obtained polymers depend on the spacer length. As the spacer length increases the glass transition temperature decreases while the isotropization temperature increases. The thermal stability of the obtained polymers increases as the spacer length increases. All of the obtained polymers present no chiral smectic C phase. The result seems to demonstrate that incorporation of a naphthalene ring in the mesogenic core decreases the tendency to form a chiral smectic C phase.

Effect of a lateral substituent on the mesomorphic properties of ferroelectric side chain liquid crystalline polysiloxanes

The synthesis of side chain liquid crystalline polysiloxanes containing oligooxyethylene spacers and (S)-2-methylbutyl 4-\\[(4-oxybiphenyl-4-yl)carbonyloxy]-3-fluorobenzoate mesogenic side groups is presented. Differential scanning calorimetry, optical polarizing microscopy and X-ray diffraction measurements reveal liquid crystalline properties for all synthesized monomers and polymers. All three precursor olefinic monomers reveal cholesteric and smectic A phases. The olefinic monomer which contains two oligooxyethylene units in the spacer is the only one which reveals a twist grain boundary A phase and a blue phase, besides the cholesteric and smectic A phases. All three polysiloxanes present enantiotropic smectic A and chiral smectic C phases. The mesomorphic behaviours of the monomers and polymers are compared with those of the corresponding monomers and polymers without the lateral fluoro substituent. The results seem to demonstrate that incorporating a lateral fluoro substituent in the mesogenic cores of the monomers affects not only the mesophase thermal stability, but also the nature of the mesophases formed. However, incorporating a lateral fluoro substituent in the mesogenic cores of the polymers affects only the thermal stability of the mesophases formed. The lateral fluoro substituent has a more profound effect on the mesomorphic behaviour for the monomers than that for the polymers.

Phase Transition and Liquid Crystalline Structures of Side-Chain Liquid-Crystalline Polysiloxanes Containing Acetoyl Group as a Mesogenic Terminal Substituent

Phase Transition and Liquid Crystalline Structures of Side-Chain Liquid-Crystalline Polysiloxanes Containing Acetoyl Group as a Mesogenic Terminal Substituent

Influence of dilution by polydimethylsiloxane on electrorheological effect of side-chain liquid crystalline polysiloxane

A liquid crystalline polysiloxane (LCP), having an ether bond in the spacer between its siloxane main chain and its mesogenic-group side chains, exhibited a very small electrorheological (ER) effect or increase in shear stress upon application of an electric field, but mixtures of the LCP and polydimethylsiloxane (PDMS) exhibited a sharply increasing ER effect with increasing PDMS content throughout the tested range of up to 0.5 of PDMS weight fraction. When phenyl-substituted PDMS (Ph-PDMS) at a weight fraction of 0.3 was used instead of PDMS, however, the ER effect decreased with increasing phenyl content and became nearly undetectable with Ph-PDMS having a phenyl content (ratio of substituted phenyl groups to initial methyl groups) of approximately 15%. DSC analyses showed that the ER effect of the LCP/PDMS mixtures occurred undiminished throughout a temperature range in which LCP itself is an isotropic liquid in the absence of an applied electric field and suggested that the LC structure of the LCP was maintained even when it was diluted with PDMS in weight fractions of 0.5 or higher, but disrupted when diluted by a 0.3 weight fraction of Ph-PDMS having a 15% phenyl content. Optical microscopic observation of the mixtures of the LCP with a 0.3 weight fraction of PDMS or Ph-PDMS (15% phenyl content) showed that both consisted of uniformly dispersed micron-sized droplets which became elongated in the direction of the applied electric field when it was applied alone but became smaller when both the electric field and shear were applied. These results suggest that the phase separation between the LCP and the dilution oil, as well as the existence and orientation of LC domains, is essential for the generation of a large ER effect. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1319–1328, 1997

Effects of the Degree of Substitution on the Properties and Structures of Side Chain Liquid Crystalline Polysiloxanes

Poly[6-(4-cyanobiphenyl-4'-oxy)-hexylmetylsiloxanes] (PCS-n) with various degrees of substitution (DS) were prepared, and the effects of the degree of substitution on the phase transition, structures, and liquid crystallization of PCS-n were investigated. PCS-n showed S Ad in the temperature range from glass transition temperature (T s ) to clearing temperature (T i ) in spite of various DS. T 2 and increased linearly with DS, and the temperature range of S A phase between T g and T i expanded with DS. The layer spacing d L of the S A structure decreased with increasing DS, since the non-mesogenic flexible backbones were squeezed between smectic layers. d L of the sample with lower DS highly decreased with increasing temperature, due to entropy relaxation of backbones between the S A layers. DS remarkably influenced the liquid crystallization of PCS-n. PCS-n with higher DS exhibited faster growth rates of liquid-crystalline textures compared with lower DS.

Synthesis and characterization of sidechain liquid cryastalline polysiloxanes containting either cholesteryl or cyanobiphenyl mesogenic groups

A series of side-chain liquid crystalline polysiloxanes containing either cholesteryl or cyanobiphenyl mesogenic groups were synthesized by the hydrosilylation reaction of a polysiloxane containing Si−H group with a vinyl-terminated compound containing the mesogenic group. Their chemical structures were confirmed by IR,1H NMR, and elemental analysis, Their phase behaviors were investigated by differential scanning calorimetry, optical polarizing microscope, and X-ray diffraction technique. The results show that all these polysiloxanes except P V display smectic or nematic mesonorphism or both. The dependence of phase transition temperature on the rigidity of mesogenic unit. the length of spacer group, and the flexibility of\(\rlap{--} (Si(CH_3 )_2 O\rlap{--} )\) chain is also described.