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The mechanisms of failure over time of a series of model acrylic pressure-sensitive adhesives under a moderate level of stress has been investigated with a probe method. Two competing mechanisms of failure have been observed: a progressive nucleation of cavities under stress and the propagation of existing cavities at the interface between the probe and the adhesive layer. Homogeneous creep of the adhesive was never observed as the only failure mechanism. In situations where the resistance to crack propagation was good relative to the resistance to cavitation, extensive nucleation of cavities was observed until a material-dependent and stable value of stress was achieved. On the other hand in situations were the resistance to crack propagation was weak, propagation led invariably to a complete failure of the adhesive bond. In addition to the stress relaxation, the energy dissipation was studied allowing to distinguish the different adhesives even further. This allowed determination of the optimal amount of a comonomer (acrylic acid) that had to be added to improve the long-term resistance of the adhesives under study. Further more we investigate the compliance of the confined adhesive layers and compare the obtained results to predictions from theoretical models.

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The binary phase diagrams are analyzed in aqueous solutions of monomeric, non-ionic surfactants and the corresponding polysiloxanes having attached the surfactants as side chains via the hydrophobic parts of the amphiphiles. In contrast to common surfactants these hydrophobic parts additionally contain a rigid, mesogenic biphenyl moiety. While the polymeric surfactants exhibit hexagonal and lamellar lyotropic liquid crystalline phases, similarly to the lowmolar-mass surfactants, two important results have to be emphasized: i) The liquid crystalline phase regions are markedly extended with respect to concentration and temperature compared with the corresponding monomers, as shown in a similar way for thermotropic polymer liquid crystals. ii) The phase sequence of the polymorphic liquid crystalline phases can be changed by polymerization. While for the systems under investigation the monomeric surfactant exhibits a cubic phase, the polymeric surfactant shows no cubic but a nemaficphase in front of the hexagonal phase at low surfactant concentration. The nematic phase of the polymeric surfactant is the first example for a nematic phase, which is formed for binary mixtures of non-ionic surfactants and water.