Formation Of Liquid Crystalline Mesophases Research Articles

Influence of the amphiphilicity profile of copolymers on the formation of liquid crystalline mesophases in microemulsions

In bicontinuous microemulsions, the increase of the solubilization capacity of a surfactant, e.g., by the addition of amphiphilic block copolymers (“boosting effect”), is normally accompanied by the formation of liquid crystalline mesophases. We studied a new class of amphiphilic polymers as “boosters,” so-called gradient polymers, with a gradual change from the hydrophilic to the hydrophobic part. Phase diagram measurements and static and quasielastic neutron scattering experiments reveal that the polymers cause a stiffening of the amphiphilic film while simultaneously the saddle splay modulus decreases such that the formation of liquid crystalline mesophases, normally present with diblock polymers as “boosters,” is suppressed, while bicontinuous structures are geometrically favored. In addition, these findings are supported by theoretical calculations following the works of Lipowsky. Hence, gradient amphiphilic polymers not only increase the efficiency of surfactants but simultaneously suppress the formation of liquid crystalline phases thereby greatly increasing their application potential.

Organized molecular systems in structured non-aqueous solvents. Is formamide a water like solvent?

Abstract We have investigated the aggregation of surfactants in formamide (FA) instead of water. Qualitatively, the general behavior with FA is similar to the corresponding aqueous systems. Micelle formation has been demonstrated in this solvent as well as the formation of liquid crystalline mesophases at higher surfactant concentration. However, there were some quantitative differences, for example: the much higher Krafft temperature and critical micellar concentration (cmc) values with FA solvent compared to the aqueous systems, and the possibility to utilize amphiphilic molecules insoluble in water. Vesicles and liposomes have been observed, similar to those obtained in water. Also, in microemulsions, water may be replaced by formamide and such non-aqueous microemulsions are reaction media very efficient for organic synthetic processes.

Ionic liquids as amphiphile self-assembly media

In recent years, the number of non-aqueous solvents which mediate hydrocarbon-solvent interactions and promote the self-assembly of amphiphiles has been markedly increased by the reporting of over 30 ionic liquids which possess this previously unusual solvent characteristic. This new situation allows a different exploration of the molecular "solvophobic effect" and tests the current understanding of amphiphile self-assembly. Interestingly, both protic and aprotic ionic liquids support amphiphile self-assembly, indicating that it is not required for the solvents to be able to form a hydrogen bonded network. Here, the use of ionic liquids as amphiphile self-assembly media is reviewed, including micelle and liquid crystalline mesophase formation, their use as a solvent phase in microemulsions and emulsions, and the emerging field of nanostructured inorganic materials synthesis. Surfactants, lipids and block co-polymers are the focus amphiphile classes in this critical review (174 references).

Self-Assembly of Nonionic Surfactants into Lyotropic Liquid Crystals in Ethylammonium Nitrate, a Room-Temperature Ionic Liquid

The stability of a variety of lyotropic liquid crystals formed by a number of polyoxyethylene nonionic surfactants in the room-temperature ionic liquid ethylammonium nitrate (EAN) is surveyed and reported. The pattern of self-assembly behaviour and mesophase formation is strikingly similar to that observed in water, even including the existence of a lower consolute boundary or cloud point. The only quantitative difference from water is that longer alkyl chains are necessary to drive the formation of liquid crystalline mesophases in EAN, suggesting that a rich pattern of "solvophobic" self-assembly should exist in this solvent.

The kinetics of solvolysis of phosphorus acid esters in the ternary sodium dodecyl sulfate-ethylene glycol -La 3+ micellar system

By methods of conductivity measurements, micellization of sodium dodecyl sulfate in ethylene glycol at the concentration above 0.18 M is shown. The La 3+ ion catalysis of solvolysis of phosphorus acid ester both in the absence of surfactant and in the micellar sodium dodecyl sulfate solution in ethylene glycol is found. The influence of the other lanthanide ions on the kinetics is also studied. The La 3+ and Pr 3+ are found to exert an identical effect while Sm 3+ is less effective. By methods of polarizing microscopy, the formation of liquid crystalline mesophase at high lanthanum (tris(dodecyl)sulfate concentrations in ethylene glycol is revealed. The investigation of the catalytic effect of the sodium dodecyl sulfate -La 3+ (3 : 1 molar) composition has shown a sharp acceleration of the reaction at high surfactant concentration.

Understanding and controlling the morphology of styrene–isoprene side-group liquid crystalline diblock copolymers

In side-chain liquid crystalline diblock copolymers, driving forces for ordering of the material may be provided by the chemical incompatibility between the blocks and by the liquid crystalline nature of one of the blocks. We study the microstructure and its development from initially isotropic solutions in side-group liquid crystalline copolymers based on styrene–isoprene diblocks. Hierarchical structure from the 5Å to the 500Å length scale is observed, the product of coherent block copolymer microphase separation and liquid crystalline mesophase formation. The presence of cylindrical microdomains of either the poly(isoprene-LC) or poly(styrene) block markedly increased the thermal stability of the LC. Confinement of the LC to cylindrical microdomains strongly inhibited defect formation within the mesophase after suitable orientation and thermal treatment, readily manifested by the significantly improved optical clarity of these samples versus LC matrix or LC lamellar samples. We consider the relative stabilities of parallel–transverse, perpendicular–parallel, parallel–parallel and transverse–perpendicular arrangements of the microdomain and mesophase structures in interpreting the development of structure in these materials under oscillatory shear.

Spatial configuration of chain molecules incorporated in liquid crystals and thermodynamic significance

AbstractThe conformation of chain molecules participating variously in the formation of liquid crystalline mesophase has been elucidated. Two examples are mentioned: (1) the side chain flanking the α‐helical backbone of polypeptides, and (2) the spacer joining mesogenic units in mainchain liquid crystals. Flexible segments play an important role in determining thermodynamic properties of these systems.

Cholesterol (thermodynamic) activity determinations in bile salt-lecithin-cholesterol systems and cholesterol-rich liquid crystalline mesophase formation.

Previous in vitro studies have shown that tauroursodeoxycholate (TUDC)-lecithin (L) micellar solutions solubilize cholesterol (Ch) poorly compared to its 7 alpha-epimer, taurochenodeoxycholate (TCDC). However, in clinical studies ursodeoxycholic acid (UDC) has been found to be as effective as chenodeoxycholic acid (CDC) in Ch gallstone dissolution, and it has been suggested that, during UDC therapy, liquid crystalline mesophase formation may be involved in enhancing micellar Ch dissolution and dispersion. The purpose of the present study was to investigate whether measurements of the Ch thermodynamic activity (A(T) would provide new insights into the problem of Ch solubilization and mesophase formation in bile salt-lecithin-Ch systems. Using the silicone polymer uptake method developed in this laboratory, A(T) was measured as a function of Ch concentration in the TUDC-L-Ch and TCDC-L-Ch model bile systems. In the TCDC systems Henry's law was obeyed almost up to unit activity (i.e., A(T) was proportional to Ch concentration almost up to A(T) = 1.0). However, in many of the TUDC-containing systems negative deviations from Henry's law were observed well below unit activity and these systems became visibly turbid before saturation with respect to cholesterol monohydrate (ChM) was reached. The effects of varying the TCDC/TUDC ratio upon the A(T) behavior were also studied. With increasing TCDC/TUDC ratio, the onset of mesophase formation was shifted to higher A(T) values. A(T) measurements were also conducted in BS-L-Ch mixtures simulating biles of patients undergoing UDC therapy. The results obtained suggest that mesophase formation may not always occur in biles of patients undergoing UDC therapy.(ABSTRACT TRUNCATED AT 250 WORDS)

On the nature of polymeric liquid crystals

AbstractStarting from the theory of formation of liquid crystalline mesophases in solutions of rod‐like rigid chain macromolecules, developed by Flory and DiMarzio, the situation is analyzed where the flexibility parameter, f, which is essential in this theory, is variable and concentration dependent. It is shown that energetic factors of physical‐chemical origin expressed by the polymer‐solvent interaction parameter, χ1, and connected with the selectivity of these interactions may influence substantially f, changing its value from the supercritical ( > 0.63), when self‐organization in an ordered mesophase is impossible, to the subcritical, i.e., values down to f→ 0, when a spontaneous formation of a liquid crystalline phase occurs. In quite a similar manner (the analogy encompassing even the corresponding formulae) f is affected by external fields, as a result, in a stationary orienting field a system of flexible chain macromolecules may become equivalent to a unperturbed system of rigid chain macromolecules. The external field can also decrease the critical concentration of the formation of the liquid crystalline phase in rigid chain systems and liquidate the domain structure, thus transforming such a system into a unique “liquid single crystal”. This is shown to be true for the behavior of a rigid chain polymer polyparabenzamide in strong magnetic fields.The analysis leads to the conclusion that a purely entropic formalism for the description of the formation of extended chain liquid crystals is neither necessary nor sufficient, and purely energetic factors most certainly must be taken into account. However, following incorporation of these data, it becomes possible to reduce the formation of the ordered phase to the “entropic” mechanism of Flory‐DiMarzio.

Thermokinetics of formation of ordered structures in polymer solutions and gel

Abstract