Srivatssan Mohan MSc

Ornstein Laboratory, room 14
Princetonplein 1, 3584 CC Utrecht
P.O. Box 80 000, 3508 TA Utrecht
The Netherlands
phone: +31(0)30 253 1287
secretariat: +31(0)30 253 2952
e-mail: s.mohan@uu.nl

Research

Supervisor: Dr. A.Imhof and Dr. K.P. Velikov
Promotor: Prof.dr. A. van Blaaderen

Employed since May 2014
Funded by FOM

Confocal Fluorescence Microscopy, Rheology
A mechanically rigid structure attains a marginal state when it is stripped of all
non-essential bonds, just before it ultimately loses its structural integrity and falls
apart. Recent theoretical work has brought to light that, materials at the vicinity
of their marginal state become highly sensitive; minute changes in temperature
or state of stress are shown to have an enormous effect on their mechanical
behavior [1,2]. This phenomena could lead to a new class of self-strengthening or
healing materials [2,3].
The main aim of the project is to design and understand real-life marginal soft
materials based on fibrous cellulose networks. The definition of a marginal state has been well established theoretically but has not been touched upon experimentally yet.
Establishing relationship between the
network microstructure and its  mechanical response would provide a lead to approach and
define the marginal state. The first step towards that would be to study the
inherently forming network structure of cellulose microfibrils (CMF). It is known
that dispersions of these shape anisotropic microfibrils form colloidal gels at low
concentrations due to their attractive nature [4]. Following the same procedure,
dispersions of CMF sourced from bacterial cellulose were made by high pressure
homogenization process. The microfibrils were then fluorescently labelled and
subsequently imaged with laser scanning confocal microscopy to study their
microstructure in 3D. Using image processing algorithms, quantitative information
about the network microstructure such as the average pore size could be
obtained which in turn can be used to correlate with mechanical measurements.
The mechanics of the fibre networks at their marginal state could be studied by
applying small local stresses by applying micro-rheological techniques owing to
their sensitivity. Further, methods to control the interaction between the fibrils
will be explored, which could help in manipulating the extent of fluctuation and
response of the resulting networks.
mohan_001
Fig 1: Projection of a 3-D image of cellulose microfibril network
[1] V. Vitelli et al., Nature 480 , 325-326 (2011)
[2] C. Broedersz et al., Nat. physics 7 , 983-988 (2011)
[3] M. Wyart et al., Phys. Rev. Lett., 101 , 215501 (2008)
[4] A. Kuijk et al., Langmuir 29 , 14356-14360 (2013)