Sandipan Chattaraj | IIT Bombay (original) (raw)

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Papers by Sandipan Chattaraj

Densely crosslinked glassy epoxies such as SU-8, are increasingly being used as thin films and mi... more Densely crosslinked glassy epoxies such as SU-8, are
increasingly being used as thin films and micro-sized and
nano-sized cantilevers for sensing applications. Hence,
there is a need to develop a robust understanding of
localized and contextual mechanical response of such
epoxies. Nanoindentation experiments, and their
appropriate data interpretation, can provide for such an
understanding. However, refinements are necessary to the
conventionally employed Oliver-Pharr method, to
estimate accurately the elastic modulus and hardness; e.g.,
accurate estimates of the time-varying contact area, or
direct modeling of the load-displacement relationship. We
propose here preliminary development of a constitutive
model, containing direct load-displacement (instead of
stress, strain and strain rate) mechanical elements: springs,
dashpots, and slider. This model aims to capture the functional form as well as the multiple nonlinear, time dependent phenomena occurring during SU-8 nanoindentation. We also report here preliminary DSC, XRD, and Laser-Raman spectroscopy characterization of our samples.

In densely crosslinked glassy thermosets, at yield, bond length and bond angle deformations, tran... more In densely crosslinked glassy thermosets, at yield, bond length and bond angle deformations, transition
to cooperative deformation of multiple effective network chains via bond torsions. We introduce here the
activation number, n, the ratio of the Eyring activation volume, V*, to the network chain volume, Vc, as a
measure of the number of network chains, ‘activated’ at yield for cooperative deformation. We find that
n ~ 2-4, at room temperature, for DGEBA-based epoxies including SU-8 and DGEBA-amine networks,
over a range of network junction functionalities and V*. This first reported analysis of yield at various
strain rates, of the octafunctional epoxy, SU-8, is via our compression experiments on fabricated
micropillars. Molecular validation of our bulk density based analysis to determine Vc, is achieved by
mapping to the eight-chain network model of Arruda and Boyce. We thus identify the activation number
as a universal molecular descriptor of yield in densely crosslinked glassy thermosets.

Densely crosslinked glassy epoxies such as SU-8, are increasingly being used as thin films and mi... more Densely crosslinked glassy epoxies such as SU-8, are
increasingly being used as thin films and micro-sized and
nano-sized cantilevers for sensing applications. Hence,
there is a need to develop a robust understanding of
localized and contextual mechanical response of such
epoxies. Nanoindentation experiments, and their
appropriate data interpretation, can provide for such an
understanding. However, refinements are necessary to the
conventionally employed Oliver-Pharr method, to
estimate accurately the elastic modulus and hardness; e.g.,
accurate estimates of the time-varying contact area, or
direct modeling of the load-displacement relationship. We
propose here preliminary development of a constitutive
model, containing direct load-displacement (instead of
stress, strain and strain rate) mechanical elements: springs,
dashpots, and slider. This model aims to capture the functional form as well as the multiple nonlinear, time dependent phenomena occurring during SU-8 nanoindentation. We also report here preliminary DSC, XRD, and Laser-Raman spectroscopy characterization of our samples.

In densely crosslinked glassy thermosets, at yield, bond length and bond angle deformations, tran... more In densely crosslinked glassy thermosets, at yield, bond length and bond angle deformations, transition
to cooperative deformation of multiple effective network chains via bond torsions. We introduce here the
activation number, n, the ratio of the Eyring activation volume, V*, to the network chain volume, Vc, as a
measure of the number of network chains, ‘activated’ at yield for cooperative deformation. We find that
n ~ 2-4, at room temperature, for DGEBA-based epoxies including SU-8 and DGEBA-amine networks,
over a range of network junction functionalities and V*. This first reported analysis of yield at various
strain rates, of the octafunctional epoxy, SU-8, is via our compression experiments on fabricated
micropillars. Molecular validation of our bulk density based analysis to determine Vc, is achieved by
mapping to the eight-chain network model of Arruda and Boyce. We thus identify the activation number
as a universal molecular descriptor of yield in densely crosslinked glassy thermosets.