Evidence of Sticky Contacts between Wormlike Micelles in Viscoelastic Surfactant Solutions

Abstract

Many cationic surfactants form highly viscoelastic solutions at concentrations of only a few percent. These solutions contain wormlike micelles (WLM) which can be several micrometers long. The structural relaxation time, τ s in these solutions can be as long as many seconds, and the zero-shear viscosity can be in the range of 10 6 Pas. Electric birefringence measurements on such solutions showed four different relaxation times with increasing concentration. The two shortest ones, τ 1 and τ 2 in the μs region were due to the alignment of small rodlike or ringlike micelles. The third one, τ 3 , was observed in the viscoelastic region in the ms region and finally, a fourth one, τ 4 , which was the same as the structural relaxation time, τ s . In this article, it is shown that the τ 3 process is due to the formation and opening of contacts between the WLM. The reason for the contacts is the attraction between the WLM which is due to the hydrophobic surfaces of the micelles. The contacts crosslink the WLM and thus form a threedimensional network. This network is the reason for the high viscosity and viscoelastic properties of the samples. If the attraction between the WLM is reduced by adding glycerol to the solution, the viscosity of the solution breaks down. The same happens if the surface of the WLM is made hydrophilic by the addition of small amphiphilic molecules. The WLM are not destroyed by these procedures.

Unraveling an Alternative Mechanism in Polymer Self-Assemblies: An Order–Order Transition with Unusual Molecular Interactions between Hydrophilic and Hydrophobic Polymer Blocks

“…Solvent-exposed pPheOzi blocks could be interpreted as sticky patches, which help to mechanically connect different worm-like micelles, adding to the high storage modulus of the gels . The evidence of such sticky contacts in worm-like micelles was recently discussed by Thurn and Hoffmann . However, we cannot completely rule out that these patches result (in part) from an insufficient number of polymers in our model, as the exact composition of the micelle was not available as a priori input from experimental data.…”

“… 22 The evidence of such sticky contacts in worm-like micelles was recently discussed by Thurn and Hoffmann. 32 However, we cannot completely rule out that these patches result (in part) from an insufficient number of polymers in our model, as the exact composition of the micelle was not available as a priori input from experimental data. In silico , about 53% of all pMeOx, 62% of all pEtOx, and 83% of all pMeOzi repeat units keep a minimum average distance of more than 5 Å to the pPheOzi blocks over the last 100 ns (including hydrogen atoms for calculation).…”

Unravelling a Novel Sol-Gel Transition Mechanism in Polymer Self-Assemblies: An Order-Order Transition Based on Specific Molecular Interactions Between Hydrophilic and Hydrophobic Polymer Blocks

“…22 The evidence of such sticky contacts in worm-like micelles was recently discussed by Thurn and Hoffmann. 62 On the other hand, this could also result from an insufficient number of polymers in our model, as the exact composition of the micelle was not available as input a priori from experimental data. For the pPheOzi residues analyzed during density calculation, we measured distances to the nearest polymer moieties, as well as the angle ω between the planes of nearby N-(C=O)-C amide groups and the aromatic ring (Figure S7).…”

Investigação >i<ab initio>/i< dos mecanismos de formação de nanoflocos de dicalcogenetos de metais de transição

“…1 Este esforço se deve à importância que este tipo de interação possui em sistemas fundamentais para a química, biologia e estudos de estado sólido. Além do mais, interações de vdW estão presentes em sistemas iônicos ou covalentes, sendo, no entanto, preponderantes em sistemas que apresentem partes fracamente ligadas, como em DNA, [136,137] micelas [138,139] ou interações verticais envolvendo dicalcogenetos de metais de transição. [50,62] As interações de van der Waals são de natureza eletrostática e surgem de flutuações quânticas e térmicas, [140,141] o que faz com que estas possuam correspondência com o movimento dos elétrons de um sistema, uma vez que as flutuações que dão origem às interações de vdW podem ser associadas com flutuações da densidade de carga.…”