Amphitropic liquid crystals. Two lamellar phases in a surfactant containing thermotropic and lyotropic mesogenic groups

Fuller, Stuart; Hopwood, Jeremy D.; Rahman, A; Shinde, Neeta; Tiddy, G. J. T.; Attard, George S.; Howell, Owen; Sproston, S.

doi:10.1080/02678299208031065

Cited by 28 publications

(27 citation statements)

References 5 publications

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“…The mesogenic compound used is novel in that it possesses not only the usual flexible (alkyl chain) and rigid (biphenyl) moieties characteristic of low molar mass liquid crystals but also a polar head group located at the opposite end of one of the alkyl chains from the mesogen. These types of compounds are only recently receiving increased attention. ,,− …”

Section: Resultsmentioning

confidence: 99%

Mixtures of an Acid-Functionalized Mesogen with Poly(4-vinylpyridine)

and

Bazuin

1996

Chem. Mater.

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A thermotropic dialkoxy biphenyl liquid crystal, functionalized by a carboxylic acid group at one extremity, is mixed to varying proportions with poly(4-vinylpyridine) (P4VP). The liquid crystal, LC-4,6A, is characterized by a monotropic smectic A phase and a highly ordered or crystalline lamellar phase formed primarily of acid dimers. In the mixtures with P4VP (studied up to acid/pyridine molar ratios of 1.0), the fluid mesophase is suppressed. A solidisotropic phase transition is present above a molar ratio of about 0.2, whereas for lower LC-4,6A contents the mixtures form an apparently miscible, amorphous material. The glass transition temperature, T g , of the latter is strongly depressed, at a rate of 7 °C/mol % LC-4,6A up to a molar ratio of 0.1, after which the T g remains essentially constant. As supported by infrared analysis, the plasticization behavior is attributed to strong hydrogen bonding between the acid and pyridine moieties, which solubilizes the LC-4,6A molecules within the polymer matrix. When the solubility limit is reached, the excess small molecule solidifies into an ordered phase that is essentially identical to that of neat LC-4,6A. This phase can be modified by quenching from the melt, which freezes in a greater proportion of the acidpyridine interactions and leads to incorporation into this phase of significant amounts of P4VP.

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Section: Resultsmentioning

confidence: 99%

Mixtures of an Acid-Functionalized Mesogen with Poly(4-vinylpyridine)

and

Bazuin

1996

Chem. Mater.

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“…Twin-tailed, “gemini” surfactants are a specific class of molecules that have received considerable interest due to their desirable self-assembly properties and high surface activity. − Geminis exhibit significantly lower critical micelle concentration, enhanced tunability, and unique LLC phase behavior compared to single tail surfactants. Of particular interest to bilayer studies, geminis can form either L α or L β phases at room temperature, depending on the surfactant type. − These phases are distinguished by their X-ray diffraction spectra; L β phases generally exhibit additional scattering peaks corresponding to ∼4.1–4.2 Å spacing, − indicative of ordered hexagonal packing of alkyl chains in the bilayer. , This tunability for forming either L α or L β room temperature phases makes gemini surfactants ideal prototypical systems for studying the fundamental influence of surfactant tail ordering on the resulting bilayer properties. While such physics has been explored in corresponding gel and fluid phases of lipid bilayers, ,− the different temperature stability regimes of these phases render direct comparison of dynamical properties difficult.…”

Section: Introductionmentioning

confidence: 99%

“…Computational studies provide important microscopic detail of bilayer properties; while many such studies exist for biological lipid bilayers, ,,− to our knowledge, there are no computational studies that systematically compare the properties of gemini surfactant L α and L β phases. In addition, previous experimental characterization of ordered L β phases of gemini surfactants have primarily focused on cationic alkylammonium surfactants; − characterization of such phases in anionic gemini surfactants, which exhibit unique and interesting phase behavior, , is largely absent. In this work, we present a thorough computational study of the properties of both L α and L β phases of anionic, dicarboxylate gemini surfactants.…”

Section: Introductionmentioning

confidence: 99%

Coupling between the Dynamics of Water and Surfactants in Lyotropic Liquid Crystals

McDaniel

Yethiraj

2017

J. Phys. Chem. B

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Bilayers composed of lipid or surfactant molecules are central to biological membranes and lamellar lyotropic liquid crystalline (LLC) phases. Common to these systems are phases that exhibit either ordered or disordered packing of the hydrophobic tails. In this work, we study the impact of surfactant ordering, i.e., disordered L and ordered L LLC phases, on the dynamics of water and sodium ions in the lamellar phases of dicarboxylate gemini surfactants. We study the different phases at identical hydration levels by changing the length of the hydrophobic tails; surfactants with shorter tails form L phases and those with longer tails form L phases. We find that the L phases exhibit lower density and greater compressibility than the L phases, with a hydration-dependent headgroup surface area. These structural differences significantly affect the relative dynamic properties of the phases, primarily the mobility of the surfactant molecules tangential to the bilayer surface, as well as the rates of water and ion diffusion. We find ∼20-50% faster water diffusion in the L phases compared to the L phases, with the differences most pronounced at low hydration. This coupling between water dynamics and surfactant mobility is verified using additional simulations in which the surfactant tails are frozen. Our study indicates that gemini surfactant LLCs provide an important prototypical system for characterizing properties shared with more complex biological lipid membranes.

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“…The nanoconfinement length scale and topology in LLCs are readily determined by sharp X-ray scattering peaks, , and this confinement can be precisely tuned on the basis of the surfactant weight percent. LLCs may exhibit a variety of morphologies, including hexagonally packed cylinders, bicontinuous cubic networks, or lamellar structures, depending on the type of surfactant and water composition; ,, in this regard, lamellar phases are the closest analogue to biological membrane bilayers, whereas other morphologies may be more desirable for technological applications. − As with biological membranes, lamellar LLCs may exhibit either ordered or disordered packing of hydrophobic tails within the bilayers, resulting in either L β or L α phases, respectively. − Furthermore, the relative stability of L α and L β LLCs can be controlled through synthetic modification of the surfactants, − which allows systematic characterization of water and ion dynamics for these different bilayer phases over a range of nanoconfinement length scales.…”

Section: Introductionmentioning

confidence: 99%

Proton Diffusion through Bilayer Pores

McDaniel

Yethiraj

2017

J. Phys. Chem. B

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The transport of protons through channels in complex environments is important in biology and materials science. In this work, we use multistate empirical valence bond simulations to study proton transport within a well-defined bilayer pore in a lamellar L phase lyotropic liquid crystal (LLC). The LLC is formed from the self-assembly of dicarboxylate gemini surfactants in water, and a bilayer-spanning pore of radius of approximately 3-5 Å results from the uneven partitioning of surfactants between the two leaflets of the lamella. Local proton diffusion within the pore is significantly faster than diffusion at the bilayer surface, which is due to the greater hydrophobicity of the surfactant/water interface within the pore. Proton diffusion proceeds by surface transport along exposed hydrophobic pockets at the surfactant/water interface and depends on the continuity of hydronium-water hydrogen bond networks. At the bilayer surface, there is a reduced fraction of the "Zundel" intermediates that are central to the Grotthuss transport mechanism, whereas the fraction of these species within the bilayer pore is similar to that in bulk water. Our results demonstrate that the chemical nature of the confining interface, in addition to confinement length scale, is an important determiner of local proton transport in nanoconfined aqueous environments.

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Amphitropic liquid crystals. Two lamellar phases in a surfactant containing thermotropic and lyotropic mesogenic groups

Cited by 28 publications

References 5 publications

Mixtures of an Acid-Functionalized Mesogen with Poly(4-vinylpyridine)

Mixtures of an Acid-Functionalized Mesogen with Poly(4-vinylpyridine)

Coupling between the Dynamics of Water and Surfactants in Lyotropic Liquid Crystals

Proton Diffusion through Bilayer Pores

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