Influence of shear on the transient and the steady state properties of lyotropic bilayer systems

The work presented in this thesis comprises in-situ structural determination under shear using time-resolved scattering techniques and flow birefringence. These techniques were used to study transient structures occurring in surfactant bilayer systems under shear on length scales from a few nanometers up to several micrometers. The major concern of this thesis is the lamellar-to-MLV dynamic transition under shear, which is one of the unsolved mysteries in the area of complex fluids. In particular, details of the structural transition from a state of well aligned lamellae in parallel orientation to multilamellar vesicles (MLV) under the influence of a shear field were studied by a combination of time resolved small-angle neutron (SANS) and small-angle light scattering (SALS) using a nonionic surfactant lamellar phase. The study revealed five distinct transient states of bilayer organization and yielded strong support for a stress rather than a rate control of the transition. Reversible and irreversible parts of the transition, i.e., elastic storage of deformation on one hand and dissipation, which thus contributes to MLV formation, on the other, were determined in flow reversal experiments using the above mentioned time-resolved scattering techniques. Furthermore, the intriguing problem of particle inclusion in concentrated surfactant systems and its effect of the dynamic properties of such a sample was addressed by studying the incorporation of clay in a nonionic surfactant lamellar phase. Flow-SANS revealed a drastic decrease in lamellar spacing leading to the conclusion, that a micro phase separation takes place in such systems. The influence of shear on the bilayer organization was furthermore studied in a sponge- (or L3-) phase using flow-birefringence and transmission measurements. Here, the critical shear rates for the transition from the disordered sponge- to the shear aligned lamellar-phase displayed an unexpected scaling with membrane volume fraction and shear quench experiments revealed relaxation times for the structural recovery of the sponge-phase orders of magnitude slower than the inverse critical shear rate. Finally, a study of instrumental concern was carried out to solve the problem of the asymmetry of the tangential beam for a Couette or Searle-type shear cell used in Rheo-SANS experiments. In addition to considering the geometry of a tangential experiment, a practical method for experimentally accounting for the asymmetry is proposed

Influence of shear on the transient and the steady state properties of lyotropic bilayer systems

The work presented in this thesis comprises in-situ structural determination under shear using time-resolved scattering techniques and flow birefringence. These techniques were used to study transient structures occurring in surfactant bilayer systems under shear on length scales from a few nanometers up to several micrometers. The major concern of this thesis is the lamellar-to-MLV dynamic transition under shear, which is one of the unsolved mysteries in the area of complex fluids. In particular, details of the structural transition from a state of well aligned lamellae in parallel orientation to multilamellar vesicles (MLV) under the influence of a shear field were studied by a combination of time resolved small-angle neutron (SANS) and small-angle light scattering (SALS) using a nonionic surfactant lamellar phase. The study revealed five distinct transient states of bilayer organization and yielded strong support for a stress rather than a rate control of the transition. Reversible and irreversible parts of the transition, i.e., elastic storage of deformation on one hand and dissipation, which thus contributes to MLV formation, on the other, were determined in flow reversal experiments using the above mentioned time-resolved scattering techniques. Furthermore, the intriguing problem of particle inclusion in concentrated surfactant systems and its effect of the dynamic properties of such a sample was addressed by studying the incorporation of clay in a nonionic surfactant lamellar phase. Flow-SANS revealed a drastic decrease in lamellar spacing leading to the conclusion, that a micro phase separation takes place in such systems. The influence of shear on the bilayer organization was furthermore studied in a sponge- (or L3-) phase using flow-birefringence and transmission measurements. Here, the critical shear rates for the transition from the disordered sponge- to the shear aligned lamellar-phase displayed an unexpected scaling with membrane volume fraction and shear quench experiments revealed relaxation times for the structural recovery of the sponge-phase orders of magnitude slower than the inverse critical shear rate. Finally, a study of instrumental concern was carried out to solve the problem of the asymmetry of the tangential beam for a Couette or Searle-type shear cell used in Rheo-SANS experiments. In addition to considering the geometry of a tangential experiment, a practical method for experimentally accounting for the asymmetry is proposed

Incidence, disease onset and short-term outcome in urea cycle disorders – cross-border surveillance in Germany, Austria and Switzerland

Background: Urea cycle disorders (UCDs) are a group of rare inherited metabolic disorders. Affected individuals often present with hyperammonemic encephalopathy (HE) and have an increased risk of severe neurologic disease and early death. The study aims to provide epidemiologic data and to describe the disease manifestation and short-term outcome. Method: Cross-border surveillance of newly diagnosed patients with UCDs - below 16 years of age - was performed from July 2012 to June 2015 in Germany and Austria and from January 2012 to December 2015 in Switzerland. Inquiries were sent monthly to all Pediatric Departments in Germany and Switzerland, and quarterly to the Austrian Metabolic Group. In addition, data were collected via a second source (metabolic laboratories) in all three countries. Results: Between July 2012 and June 2015, fifty patients (Germany: 39, Austria: 7, Switzerland: 4) with newly diagnosed UCDs were reported and later confirmed resulting in an estimated cumulative incidence of 1 in 51,946 live births. At diagnosis, thirty-nine patients were symptomatic and 11 asymptomatic [10 identified by newborn screening (NBS), 1 by high-risk-family screening (HRF)]. The majority of symptomatic patients (30 of 39 patients) developed HE with (n = 25) or without coma (n = 5), 28 of them with neonatal onset. Despite emergency treatment 15 of 30 patients with HE already died during the newborn period. Noteworthy, 10 of 11 patients diagnosed by NBS or HRF remained asymptomatic. Comparison with the European registry and network for intoxication type metabolic diseases (E-IMD) demonstrated that cross-national surveillance identified a higher number of clinically severe UCD patients characterized by earlier onset of symptoms, higher peak ammonium concentrations in plasma and higher mortality. Conclusion: Cross-border surveillance is a powerful tool to identify patients with UCDs demonstrating that (1) the cumulative incidence of UCDs is lower than originally suggested, (2) the mortality rate is still high in patients with neonatal onset of symptoms, and (3) onset type and peak plasma ammonium concentration predict mortality

Effect of flow reversal on the shear induced formation of multi lamellar vesicles

The influence of rate controlled flow reversal on the transition from planar lamellae to multilamellar vesicles (MLV) using a nonionic lamellar phase consisting of 40 wt % triethylene glycol monodecyl ether (C10E3 in D2O) is investigated by means of time-resolved rheo-small-angle light and neutron scattering (SALS, SANS). Flow reversal provides the possibility to control the kinetics of the transition substantially, and states occurring very early during the transition can be studied. A slowing down of the transition on an absolute strain axis is observed as the strain amplitude of the flow reversal is decreased. This retardation is attributed to the partial recovery of an earlier state as shear is inverted. This can nicely be demonstrated by the width of the azimuthal intensity distribution, which shows oscillations upon flow reversal. >From the slowing down of the process a loss term is defined, which provides insight in the very early stages of the experiment, namely the minimum strain that is needed to induce irreversible structural changes in the sample. This quantity is for the present sample found to be 6.5 strain units. Furthermore, the exponential scaling of the strain needed to reach characteristic states of the transition with strain amplitude seems to hold for all length scales involved in the process

Shear-induced sponge–to–lamellar phase transition studied by rheo-birefringence

We report on the shear induced transition from the L-3- to the L-alpha-phase studied by means of flow birefringence using the system pentaethyleneglycol monododecylether (C12E5), decane, water. The dependence of the critical shear rate, at which the transition from the isotropic state to the anisotropic takes place, on membrane volume fraction was studied in temperature ramp experiments at different constant shear rates and in isothermal shear ramp experiments. These results are compared with relaxation experiments from the shear aligned state back to the isotropic. For all these experiments power law exponents in the membrane volume fraction between 1.6 and 2.8 were found, which are rather low compared to values of current theories. The values found for the inverse critical shear rate and the decay times from the relaxation experiments differ by four orders of magnitude