PT Unknown
AU Krasnov, I
TI Mechanical properties of Bombyx mori silkworm silk: viscoelasticity, structural and molecular origin
PY 2013
PU Christian-Albrechts-Universität zu Kiel
WP https://macau.uni-kiel.de/receive/diss_mods_00013595
LA en
DE Material science; viscoelasticity; molecular dynamics; trasition state theory; x-ray and neutrons scattering; silk rheology
AB This thesis is a comparative experimental and theoretical  work focused on the mechanical properties 
of Bombyx mori silk on macroscopic and molecular levels. We did study the response of silk to a mechanical perturbation by monitoring changes of the microscopic structure in the crystalline regions as well as
the molecular dynamics of the amorphous phase. In order to achieve this goal \insitu scattering 
experiments were performed: synchrotron X-ray radiation and cold neutrons were used as probes of 
the structure and dynamics, respectively. 

Much attention was devoted to the less studied temporal evolution  of the surveyed phenomena.  
Accordingly our stretching experiments covered several time intervals, ranging from fractions of a 
second up to several days.  Because such environmental parameters as temperature and humidity  
strongly influence the thermo-mechanical properties of silk the measurements were done at 
controlled environmental conditions and were repeated at several humidities.

The theoretical analysis of our experimental data resulted in the development of a set of interrelated
 viscoelastic, structural and dynamical models. These models allow to describe the behaviour of 
stretched silk in the examined range of forces and elongations over almost the whole range of humidity. Particularly, they help to clarify the basic principles of the viscoelastic linear and 
non-linear behaviour of silk as well as the geometrical and structural aspects of the elongation 
in the crystalline regions. 

Generally, a link between the macroscopic viscoelastic behaviour and the mechanism at the molecular 
length scales has been established. With our experimental techniques and analyses we could 
separate the mechanical properties of the crystalline region of silk from those of the amorphous part,
 as well as show their interplay.

In our opinion, interesting novel results were also obtained concerning the long-time mechanical relaxation of silk and molecular diffusion processes. Both phenomena exhibit definitive memory 
effects and can be well described by the models based on fractional calculus.
Despite the fact that these phenomena belong to very different temporal and spacial levels the 
fractional characteristics of these phenomena are very similar.
PI Kiel
ER