Effect of a Siloxane Moiety on the Anchoring of Ferroelectric Liquid Crystals at the Air−Water Interface

Ibn‐Elhaj, Mohammed; Cherkaoui, M. Z.; Zniber, R.; Möhwald, Helmuth

doi:10.1021/jp980153x

Cited by 8 publications

(8 citation statements)

References 24 publications

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“…The positive entropy change indicates the establishment of disorder upon compression. In analogy to the explanations given for the multilayer formation in thin films of weakly amphiphilic calamitic molecules, 33,36 it can be ascribed to the entropy change in going from a polar to an unpolar ordering (centrosymmetric double layer on top) and to the change of water ordering. Furthermore, the proposed multilayer formation requires the removal of the amphiphiles from the surface.…”

Section: Plateaulike Transition Regionsmentioning

confidence: 92%

“…14 Rodlike mesogens with weakly polar terminal groups (e.g., -CN or -OOCCHClR) have been investigated in more detail recently. 3,[31][32][33][34][35][36] Here the plateau regions are due to an ordered smectic multilayer formation upon compression of the smectic monolayer. [34][35][36] It was proposed that the transition from smectic monolayers to triple layers can be described as a first-order phase transition.…”

Section: Plateaulike Transition Regionsmentioning

confidence: 99%

“…3,[31][32][33][34][35][36] Here the plateau regions are due to an ordered smectic multilayer formation upon compression of the smectic monolayer. [34][35][36] It was proposed that the transition from smectic monolayers to triple layers can be described as a first-order phase transition. Because the phase at higher pressure is not the original one, this transition was described as a re-entrant phenomenon.…”

Section: Plateaulike Transition Regionsmentioning

confidence: 99%

“…Because the phase at higher pressure is not the original one, this transition was described as a re-entrant phenomenon. 36 A negative slope of dπ/dT is characteristic for these plateaulike transition regions. 36 Also the transition regions of compounds 1 and 2 represent temperature-dependent horizontal lines, and therefore they could be described as first-order phase transitions.…”

Section: Plateaulike Transition Regionsmentioning

confidence: 99%

“…36 A negative slope of dπ/dT is characteristic for these plateaulike transition regions. 36 Also the transition regions of compounds 1 and 2 represent temperature-dependent horizontal lines, and therefore they could be described as first-order phase transitions. 19 Interestingly, the surface pressure in the plateau regions of 1 and 2 decreases upon an increase of the temperature with a slope dπ/dT = -0.03 mN/m‚K (20 and 35 °C isotherms).…”

Section: Plateaulike Transition Regionsmentioning

confidence: 99%

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Influence of the Position of the Hydrophilic Group on the Monolayer Properties of Rigid Amphiphiles with Laterally Attached Headgroups

1999

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The π/A isotherms of rodlike 4,4‘ ‘-didecyloxy-p-terphenyl derivatives incorporating hydrophilic 1,2-diol groups in different lateral positions were recorded with dependence on the temperature, and the thin films were investigated by Brewster angle microscopy. Depending on the position of the hydrophilic groups and on the type of spacer between the hydrophilic group and the rigid core, different types of isotherms with different temperature dependences have been found. Two sharp breaks separated by a large plateau occur along the π/A isotherms of the 2-substituted and 2‘-substituted compounds. In the plateau region a defined formation of a triple layer is proposed. For the 3-substituted compounds with a peripheral position of the hydrophilic groups, the type of isotherm largely depends on the type and the length of the spacer unit between the hydrophilic group and the rigid core. Two transition regions can be found in the slope of their isotherms. A tentative model of the organization of these molecules with dependence on the lateral pressure is proposed. Accordingly, the first transition is attributed to a transition of the rigid cores from a flat arrangement on the surface to a tilted arrangement. In the second transition region either formation of a defined triple layer (short spacer) or transition to a more densely packed monomolecular film with the rigid cores arranged parallel or tilted to the surface normal (long polyether chains) should take place. If the hydrophilic groups are coupled via lipophilic alkyl chains, the molecules are organized immediately after spreading and π/A isotherms similar to those of amphiphiles with terminal hydrophilic groups have been found. Thus, by slight changes of the molecular structure completely different supermolecular organizations at the water surface can be realized.

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Section: Plateaulike Transition Regionsmentioning

confidence: 92%