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

Abstract

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.

Liquid crystal engineering – new complex mesophase structures and their relations to polymer morphologies, nanoscale patterning and crystal engineering

“…[202][203][204][205] Beside the organization of the T-shaped amphiphiles in thermotropic and lyotropic liquid crystalline phases these molecules have also a strong tendency to form well organized structures at surfaces, as for example at the air water interface. [206][207][208] 6 Summary LC research is a rapidly developing field which is just at the beginning and has a significant and not yet fully realized potential with significant impact on other disciplines of science. A whole zoo of new and complex mesophase structures has become available by appropriate designed of relatively simple polyphilic molecules.…”

Reversible collapse of the Langmuir films of a series of triphenylsilyl ether-terminated amphiphiles

“…These systems show a positive change in entropy exhibited upon collapse. The authors attribute the entropy increase to two driving factors: the shift from "a polar to an unpolar ordering" (from a monolayer at the air-water interface to a centrosymmetric liquid crystalline double layer on top of the monolayer), and the reordering of water [22].…”

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“…compound 18). 120 Such molecules have a significantly enhanced mesophase stability due to the increased intramolecular incompatibility between the fluorinated chains and the central parts. However, they show exclusively smectic A phases.…”