Showing papers by "Volker Hessel published in 1993"
TL;DR: In this paper, a multilayers of photopolymerizable bolaform amphiphiles and polyelectrolytes self-assemble onto mica from aqueous solution using surface force measurement and atomic force microscopy.
Abstract: Monoand multilayers of photopolymerizable bolaform amphiphiles and polyelectrolytes self-assembled onto mica from aqueous solution were studied by surface force measurement and atomic force microscopy. Multiple layers of positively charged amphiphiles self-assemble if a negatively charged polyelectrolyte is inserted between them. The layers can be photopolymerized with a high-pressure UV lamp. The atomic force microscopy images indicate that the photopolymerized amphiphile monolayer has a higher degree of order than the unpolymerized monolayer, although the latter possesses some long-range order. Mechanical properties of the system measured by the surface force apparatus indicate that a photopolymerized layer is more robust and demonstrate that the rigidity and integrity of the first anchoring layer greatly influence the stability of the multilayer. The interaction between polyelectrolyte layers in water can be either attractive or repulsive depending on the coverage of the polyelectrolyte on the amphiphile layer. The mica separation of a pair of opposed monolayers in contact in the presence of water is surprisingly small (25 A) compared to the thickness (78 A) of a bilayer composed of fully extended amphiphiles.
81 citations
TL;DR: In this article, the thermotropic phase behavior of dipolar amphiphiles C 5 H 5 N + (CH 2 ) m OCOPhPHCOO(CH 2 ] 6 N + C 5H 5 )COO] n is described.
Abstract: The synthesis and the thermotropic phase behavior of the dipolar amphiphiles C 5 H 5 N + (CH 2 ) m OCOPhPHCOO(CH 2 ) m N + C 5 H 5 and the polymeric amphiphile [(CH 2 ) 6 OPhPhO(CH 2 ) 6 OCOCH([CH 2 ] 6 N + C 5 H 5 )COO] n are described
45 citations
TL;DR: In this paper, the authors showed that the incorporation of rigid units leads to a decrease in the critical micellar concentration (CMC), and a similar decrease was observed when chain ends were connected.
Abstract: Mono- and α,ω-dipolar amphiphiles with hydrophilic pyridinium head groups, and flexible and rigid hydrophobic parts have been synthesized. Surface tension and conductivity measurements proved that micellar aggregates for amphiphiles 1–4 are formed. The incorporation of rigid units leads to a decrease in the critical micellar concentration (CMC): the rigid monopolar amphiphile 2 aggregates at lower concentration than the flexible monopolar amphiphile 1. A similar decrease was observed when chain ends were connected: the flexible α,ω-dipolar amphiphile 3 has a lower CMC than the flexible monopolar amphiphile 1. The more flexible amphiphiles 1–3 allow the formation of micelles of different shape leading to both CMC and Ct values. For the α,ω-dipolar amphiphile 4 with a rigid azoxybiphenylene core, the possibility of different micellar shapes is reduced, leading only to a CMC value (CMC = Ct). For the flexible α,ω-dipolar amphiphile 3, only a small, but linear viscosity increase with concentration is found. Very viscous solutions were measured for the rigid α,ω-dipolar amphiphile 4 above a certain concentration. Phase diagrams of amphiphiles 3 and 4 were determined using polarization-microscopy and X-ray measurements. Flexible α,ω-dipolar amphiphile 3 shows a lyotropic mesophase only at very high concentration (83 mass %). In contrast, rigid analog 4 forms stable lyotropic mesophases at 16 mass %. Both nematic and higher ordered mesophases (probably lamellar) are found for the rigid α,ω-dipolar amphiphile 4.
11 citations