Phase separation of the liquid crystal in the cholesterin phase

In the ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid [AA]/4-cyano-4'-n-heptyl biphenyl (TCB) solutions, 7CB acted as a diluting reagent when it was added into the (E-CE)C/AA cholesteric liquid crystalline solutions. The dispersed phase with 250–300nm in size appeared after the AA in the isotropic (E-CE)C/AA/7CB solutions with the 7CB concentration (C_7CB) between 27.4 – 41.2wt% was polymerized at 24°C. There was the dispersed phase rich with 7CB in the (E-CE)C/AA/7CB cholesteric liquid crystalline solutions when C_7CB was 43.0wt% at 24°C. The temperature at which the anisotropic phase in the dispersed phase transformed to the isotropic phase in the solutions was increased after the polymerization of the AA, but the transition temperature of the dispersed phase in both the solutions and the films was lower than that of the pure 7CB. Received: 6 October 2000/Revised version: 18 December 2000/Accepted: 28 December 2000     

Hydrotropic action of a diacid

An investigation to evaluate the mechanism of the hydrotropic action of a long chain diacid was made by determining the coassociation structures with a straight chain amphiphilic molecule of sufficient size to form long range order structures. The hydrotropic mechanism was found in the transition of a liquid crystalline struture to an isotropic solution. The mechanism was identical for aqueous solutions and water-poor inverse micellar solutions.     

Phasenumwandlungen von kristallin-flüssigen Modifikationen durch photochemische Isomerisierung

Phase Transitions of Liquid Crystalline Modifications by Photochemical Isomerisation On irradiating of liquid crystalline phases of aromatic azo- and azoxy-compounds, stilbenes or of derivatives of cinnamic acid by light of appropriate wave lengths the liquid crystalline phase will be converted into the isotropic liquid. In case of the azo- and azoxy-compounds studied this process is reversible, in case of the stilbene and cinnamic acid derivatives partially irreversible. The experimental results indicate that the photoinduced phase transition is caused by a trans-cis-isomerisation. For azo-compounds with more liquid crystalline phases also photoinduced transitions are possible between different liquid crystalline phases.     

ROLES OF CO-SURFACTANT AND CO-SOLVENT IN SURFACTANT WATERFLOODING

Residual oil displacement and surfactant retention were measured in Berea cores with well-characterized surfactant systems; phase and interfacial tension behavior was determined as well. The results, interpreted in terms of what is known about the different surfactant-rich microstructures present in aqueous sodium 4-(l'-heptylnonyl) benzenesulfonate (SHBS) alone or in conjunction with the co-surfactant sodium dodecylsulfate (SDS) or the co-solvent n-butanol (NBA), indicate that the large retention by Berea rock of liquid crystalline dispersions can be greatly reduced by sonicating them to produce tiny vesicles or by adding a suitable co-solvent or co-surfactant to dissolve the liquid crystallites.

The core tests show that high oil recovery with low retention can be achieved by injecting isotropic solutions of alcohol-solubilized surfactant or ultradispersions of vesicles, although the former performed better than the latter. These are able to form, in situ upon contact with residual oil, a surfactant-rich third phase with low interfacial tensions against both aqueous and oleic phases so that it can mobilize the oil.     

Development of co-continuous structure in liquid crystalline polyester

We investigated liquid crystallization of liquid crystalline polyester BB-5 during isothermal annealing by digital high-fidelity microscope and light scattering. A liquid crystalline spherical domain having a radius of micrometers appeared by annealing at around 180 °C. The domain grew dendritically in all directions. Neighboring liquid crystalline regions coalesced and then interconnected. The interconnected structure changed to a co-continuous two-phase structure with increasing ordering of the liquid crystalline phase, and the interface between the liquid crystalline phase and the isotropic phase became smoother over time. Liquid crystallization stopped before volume filling the whole space, and the liquid crystalline phase and isotropic phase coexisted. The liquid crystalline region became narrower with an increase in the temperature of the liquid crystallization. Such structural development is different from the liquid-liquid phase separation via spinodal decomposition, and it may be attributed to the segregation of non-liquid crystallizable low molecular weight molecules from the growth front by fractionation of the molecular weight distribution during the liquid crystallization in terms of the instability of the diffusion-controlled interface.     

Influence of thermal history on the formation of liquid crystalline phase of hydroxyethyl cellulose acetate

The influence of thermal history on the formation of HECA liquid crystalline phase was studied by DSC. It was found that the degree of ordering in the liquid crystalline phase was heterogeneous, and the multiphase transformation appears when the liquid crystalline phase transformed to the isotropic one. When HECA was annealed in the liquid crystalline state, the parts with the lower degree of ordering could transform to ones with the higher degree of ordering, and the temperature and the enthalpy of the phase transformation from the liquid crystalline phase to the isotropic phase increased. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1137–1142, 1998     

ROLES OF CO-SURFACTANT AND CO-SOLVENT IN SURFACTANT WATERFLOODING

Residual oil displacement and surfactant retention were measured in Berea cores with well-characterized surfactant systems; phase and interfacial tension behavior was determined as well. The results, interpreted in terms of what is known about the different surfactant-rich microstructures present in aqueous sodium 4-(l'-heptylnonyl) benzenesulfonate (SHBS) alone or in conjunction with the co-surfactant sodium dodecylsulfate (SDS) or the co-solvent n-butanol (NBA), indicate that the large retention by Berea rock of liquid crystalline dispersions can be greatly reduced by sonicating them to produce tiny vesicles or by adding a suitable co-solvent or co-surfactant to dissolve the liquid crystallites.

The core tests show that high oil recovery with low retention can be achieved by injecting isotropic solutions of alcohol-solubilized surfactant or ultradispersions of vesicles, although the former performed better than the latter. These are able to form, in situ upon contact with residual oil, a surfactant-rich third phase with low interfacial tensions against both aqueous and oleic phases so that it can mobilize the oil.     

Phase transition of LCP fluids confined in nanochannels through MD simulation

Manipulation of molecular orientation alignment in MCTLCPs (main-chain thermotropic liquid crystalline polymers) by pure shear at nano scale has been investigated for the first time using molecular dynamics (MD) simulation. Results indicate that high planar shear induces long-range uniform orientation ordering (liquid crystalline phase) of initially randomly orientated molecules of MCTLCP fluid confined in a nanochannel, which is confirmed by analyzing the orientation order parameter and the snapshots of MCTLCP liquid in a nanochannel under different shear rates. Insights into the origin of the phase transition phenomena are given at molecular level through investigating the thermodynamic density distribution of MCTLCP molecules in the nanochannel, suggesting that the energy shift due to a radical jump of system density affects both the magnitude and the orientation of the molecular ordering. Simulation results also show that there is a critical shear rate for transforming isotropic phase into liquid crystalline phase. The critical shear rate is dependent on the temperature of the MCTLCP system. Findings in this paper may present useful information for processing TLCP molecules at nano scale and the understanding of nanoflow.     

Study of in-situ photopolymerization of chiral liquid crystal acrylate

The effect of the smectic and isotropic phase on the photo-polymerization of the chiral liquid crystalline 4-acryloxy-undecanyloxy-4′-[S(?)-2-methylbutyloxy]-biphenyl (monomer ( I )) was studied using FTIR. The effect of temperature on the birefringence of surface-oriented monomer ( I ) and its polymer obtained by in-situ photopolymerization was also investigated. The results show that photopolymerization in the isotropic phase proceeds at a higher rate than in the smectic phase, when monomer conversion is less than 60%; however, when monomer conversion is above 60%, the photopolymerization rate is independent of the initial phase state of monomer ( I ), and a highly oriented liquid crystalline polyacrylate film can be prepared by in-situ photopolymerization of the surface-oriented chiral acrylate ( I ).     

Transient shear response of liquid crystal-forming hydroxypropyl cellulose solution in dimethylacetamide. I. Stress growth and relaxation behavior

The stress growth and relaxation behavior of liquid crystalline hydroxypropyl cellulose solutions in dimethylacetamide was characterized by using exponential functions. The parameters evaluated for the stress growth and relaxation processes were compared and the shear history effect on the parameters was determined. The exponential functions proposed were valid for our system. The isotropic solutions had one retardation time and one relaxation time, whereas the liquid crystalline solutions had plural retardation and relaxation times. The concentration dependence of the parameters for the stress growth process was similar to that for the stress relaxation process and to that for the steady-state shear viscosity. The stress growth and relaxation behavior for the liquid crystalline solutions was originated from the change (deformation or decrease) in liquid crystalline domains. The deformation of liquid crystalline domains with shear seemed to be slower than the recovering of the domains to original shape. The stress growth process was a progressive event, whereas the relaxation process was a sudden event. Stress relaxation behavior for the liquid crystalline solutions was sensitive to the shear history. © 1994 John Wiley & Sons, Inc.     

Thermotropic liquid crystalline halatopolymers

Divalent metal (I.e.) Ba(2+), Ca(2+i), Mg(2+), Mn(2+), Cd(2+), Zn(2+), Pb(2+), and Sn(2+) salts of monovalent organic acids (i.e. p-methoxycinnamic, cinnamic, p-methoxybenzoic, and 4-n-butoxybenzoic) were synthesized via the double decomposition reaction from aqueous solution. Optical microscopy and differential scanning calorimetry (DSC) analysis showed that this series of salts formed nematic liquid crystals. DSC thermograms were characterized by broad nematic-to-isotropic transitions indicative of biphasic regions in which the nematic and isotropic phases coexist. These liquid crystalline salts were polymeric when melted due to ionic crosslinking which took place through the coordination of the divalent metal ion. Except Sn (2+) and Pb(2+), all the liquid crystalline halato-polymers were spun into fibers.     

Cholesteric order in aqueous solutions of the polysaccharide Xanthan

Summary Measurements of birefringence, optical rotation and laser light diffraction show that aqueous solutions of the polyelectrolytic polysaccharide Xanthan at a concentration of 7.5 % (vol/vol) have long range order very similar to cholesteric liquid crystals. The cholesteric screw is left handed implying a rod-like conformation and right handed helicity of individual molecules. The cholesteric phase separates from a less concentrated isotropic solution and spherolites are formed.     

Structure and liquid crystalline phases of amphiphilic side chain polymers in aqueous solution

Functional amphiphilic molecules which form liquid crystalline (l.c.) phases in aqueous solutions, can be polymerized to amphiphilic side chain polymers. Depending on the formation of the polymer backbone via the hydrophobic (type A) or hydrophilic part (type B) of the monomer, it can be differentiated between two polymers. For both types of polymers a model is proposed which explains their micellar association in solution. In aqueous solutions polymers of type A should form normal spherical, rodlike and disc-like micelles, while polymers of type B should form the corresponding reversed micelles. The phase behavior in aqueous solutions is investigated with two model systems of monomer/side chain polymer of type A. It is shown that the polymers exhibit l.c. phases, which are stable within a broader concentration range, as well as to higher temperatures compared to the corresponding monomers. The structures of the l.c. phases are in accordance with the model considerations.     

Crystallization morphology of a thermotropic liquid crystalline polymide

Crystallization morphology of an aromatic thermotropic liquid crystalline polyimide was studied by means of polarized light microscopy. The polyimide was synthesized from 1, 2, 4, 5-benzenetetracarboxylic dianhydride (PMDA) and 1, 3-bis[4'(4′ aminophenoxy) cumyl] benzene (BACB), which exhibited three exothermic peaks at onset temperatures of 292, 279, and 250°C in the DSC cooling curve. The results of polarized light microscopy revealed that the polyimide quenched from 350°C in air exhibited fine structure, frozen liquid crystalline texture. The liquid crystalline texture disappeared when the sample was heated to 298°C. However, the polymer melt still exhibited, to some degrees, birefringence until the temperature reached 340°C, where the polyimide was in the truly isotropic state. Isothermal crystallization experiments were carried out at both the isotropic temperature range and the non-isotropic temperature range. Two types of negative spherulites with lamellar structure and positive needle-like crystals formed from the isotropic melt have been observed. Interestingly, with a further decrease of the crystallization temperature to the liquid crystalline state temperature, the whole field was covered by the liquid crystalline texture. However, if the sample was kept at 286°C for a long time, and then reheated to 305°C to melt the liquid crystalline phase, negative spherulites with loose structures formed from the liquid crystalline state could be observed. Surprisingly, if the sample was kept at 305°C for a period of time, further crystallization could be observed using the spherulites formed at 286°C as nuclei. Composite spherulites were developed if the low-high temperature crystallization process was repeated.     

Structural transitions in liquid crystalline solutions of some cellulose derivatives

It was found that the domains of the mesophase of the investigated systems have cylindrical symmetry and a different direction of the maximum polarizability: for ethylcellulose and cellulose diacetate, the polarizability is directed along the axis of the cylinder, while it is at an angle of 45‡ for hydroxypropylcellulose. Formation of liquid-crystalline spherulites in the thermotropic transition of isotropic solutions of ethylcellulose in formic acid to the mesophase was demonstrated. In the liquid crystal—isotropic liquid phase transition, a characteristic extreme of the intensity of light scattering is observed near the region of melting of the liquid crystalline matrix, so that this method can be used for identifying the region of the existence of a two-phase “corridor”. Translated from Khimicheskie Volokna, No. 5, pp. 25–27, September–October, 1997.     

Lipid crystallization: from self-assembly to hierarchical and biological ordering

Lipid crystallization is ubiquitous in nature, observed in biological structures as well as in commercial products and applications. In a dehydrated state most of the lipids form well ordered crystals, whereas in an aqueous environment they self-assemble into various crystalline, liquid crystalline or sometimes macroscopically disordered phases. Lipid self-organization extends further to hierarchical levels including structured emulsions and nanostructured particles. Many consumer products including cosmetics, foods and medicines account for such lipid architectures. Cell membranes primarily consist of planar lipid bilayers; however sub-cellular biomembranes are more of a convoluted type. Some of the biological entities have lipids in truly crystalline form; yet liquid crystalline lipid phases are prevalent, in general. Crystallization of fats - triglyceride lipids - has been relatively well documented and reviewed more often, but this review features other areas where lipid organization is crucial and diverse. Some recent advances along with a few explicit examples of model lipid phases and biological evidences are also reported.     

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.     

Characterization of the orientational order in liquid crystalline polymers

Polymers which display liquid crystalline phases are characterized by an orientational order already in the isotropic melt. This order which increases with decreasing temperature involves a parallel local alignment of neighbouring molecules as well as an orientation correlation between molecular axes and the vector, connecting molecular centers. Pretransitional effects take place both at the nematic phase transition and at a second phase transition, occurring at low temperatures.     

Liquid crystalline poly(enamine ketone)s formed through hydrogen bonding

A series of poly(enamine ketone)s (PEAKs) which exhibit liquid crystalline phases has been synthesized. The enamine ketone groups are able to exist in the cis and trans conformations. Molecular modelling results show that the cis conformation is energetically more favorable due to intramolecular hydrogen bonding. Model compound studies indicate that the formation of the mesogen requires the cis conformation in the enamine ketones to stabilize the liquid crystalline phase. This liquid crystalline phase is nematic for the model compound and the polymers. The heats of liquid crystal transition in the model compound and in PEAKs are very close (4.7 kJ/mol in model compound and 4.0 kJ/mol of repeating units in polymers). This is not only an indication of a similar percentage of the cis conformation in both cases, but also an example that the flexible ethyleneoxy spacers in the polymers do not contribute to the orientational order of this liquid crystalline phase. PEAKs can crystallize through either quenching from the isotropic melt or from the liquid crystalline phase. Crystallization kinetics exhibit the effect of pre-ordering when these two different kinetics are compared.