Martin Hagenbuechle - Academia.edu (original) (raw)

Uploads

Papers by Martin Hagenbuechle

Macromolecules, Aug 1, 1992

Aqueous solutions of poly(sodium p-styrenesulfonate) with molecular weights 100 000,400 000, and ... more Aqueous solutions of poly(sodium p-styrenesulfonate) with molecular weights 100 000,400 000, and 1 200 000 were examined by the transient and dynamic electric birefringence method. On the basis of the results it is demonstrated that the investigated polyelectrolyte solutions have to be divided into four different concentration ranges (I-IV). In the dilute concentration range (range I) the buildup and decay of the electric birefringence proceed by a single process (TJ. In this concentration range the interactions between the different molecules can be neglected, and the polyelectrolytes are present in a more or less stretched conformation. The birefringence in this concentration region is negative, and the molecules are oriented with their long axis in the direction of the electric field. The concentration range I1 starts at the concentration c1* where the rotational volumes of the rods begin to overlap. A second effect (T~) with opposite sign of the first effect is present together with the T~ process. The time constant T Z of the second effect is longer than the time constant of the first effect. Its amplitude can also be larger than the amplitude of the first effect, and the total sign of the birefringence becomes positive. It is concluded that during this second process the macromolecules are oriented perpendicular to the electric field. At even higher concentrations (range 111) a third effect (~3) with the same sign as the first effect becomes visible. This effect is likely due to the cooperative motion of an entangled transient network structure, which again can be oriented parallel to the electric field. In a very small concentration range the three processes can be observed simultaneously. At even higher concentrations the birefringence vanishes. This seems to be a consequence of the coiling of the macromolecules (range IV). The observed results on the polyelectrolytes are very similar to results that have been obtained previously on ionic surfactants that form rodlike micelles. The principal results on the two different systems are the same, but rodlike micelles possess an inherent stiffness in comparison to the investigated polyelectrolytes. The concentration-dependent flexibility of the polyelectrolytes causes some special features of the anomalous birefringence behavior. It can be concluded that all systems with charged anisometric particles show the anomaly of the electric birefringence.

Macromolecules, Jun 1, 1994

Previous results on the electrophoretic mobility of aqueous suspensions of polystyrene latices at... more Previous results on the electrophoretic mobility of aqueous suspensions of polystyrene latices at low ionic strengths are controversial. We have reexamined and extended mobility measurements as a function ofpolyion concentration down to salt concentrations smaller than ns = 10-6 M, where the polyions are liquid-like ordered due to screened Coulomb forces. A significant increase in mobility is found below ns 10-4 M. To discuss mobilities as a function of small ion concentration, for the first time electrophoretic mobility and electric conductivity data are combined to estimate salt content. Static light scattering is used to support the latter results and to characterize the structure of the suspensions. The weak polyion concentration dependence and the increase in mobility are discussed in the light of recently published calculations.

Journal De Physique, 1994

The Journal of Physical Chemistry, 1994

Aps March Meeting Abstracts, Mar 1, 1996

Macromolecules, 1992

The structural order in the isotropic phase of charged rodlike TMV solutions (length L = 300 nm) ... more The structural order in the isotropic phase of charged rodlike TMV solutions (length L = 300 nm) has been investigated by static light scattering (SLS) and small-angle neutron scattering (SANS) experiments. We present measurements of the static structure factor S(q) as a function of the ionic strength over the concentration regimes c < c* and c > c* (c* = 1 particle/13). SANS results in the semidilute regime c > c* show that strong interparticle correlations are present even at concentrations as high as 25c*, in contrast to results for hard-rod systems. The magnitudes of the correlations depend on both the macroion concentration and the Debye screening length K-1. As expected the position of the first maximum of S(q) is found to scale with concentration as qmm-c1/3 below the overlap concentration c* but surprisingly to turn over to a c1l2 behavior above c*. With increasing salt, at constant macroion concentration a decrease in structure is observed and the first-maximum position q-is shifted to larger scattering vectors. In the absence of any adequate theory we compare our results to SLS measurements and HNC calculations of a spherical particle system. The influence of added salt on TMV solutions is examined by Monte Carlo simulations at c < c*.

SPIE Proceedings, 2002

In the collimator array development effort for MEMS applications, the ability to align devices au... more In the collimator array development effort for MEMS applications, the ability to align devices automatically that meets industry target specifications of power throughput for multiple channels has been demonstrated. Results show eight-channel devices have been successfully aligned and attached within 2-dB power loss. Three key factors of success include: (1) Automated Pitch/Yaw using virtual pivot, (2) initial mirror alignment to verify parallelism between fiber array and lens array, (3) channel balance algorithm to compensate for lens array pitch and focal length variations.

A ferrofluid emulsion is used as a model magnetorheological fluid. Due to the dipole-dipole inter... more A ferrofluid emulsion is used as a model magnetorheological fluid. Due to the dipole-dipole interaction induced by an applied magnetic field the ferrofluid droplets in the emulsion form chains. In a dilute emulsion chain formation is a very slow process and therefore can be easily studied in contrast to concentrated emulsions where it occurs on a timescale of milliseconds. We use light scattering, especially dynamic light scattering, to study the formation and dynamics, i.e. diffusion and internal motion, of the chains as a function of the magnetic field. Changing the scattering vector q allows us to probe the sample on different length scales.

Journal of Colloid and Interface Science, 1991