Control of Crystallization Pathways
by Electric Fields
Karolina Adrjanowicz and Ranko Richert
Abstract Polar molecular materials subject to high electric fields of magnitude
E lead to situations which are usually characterized by dipole energies (μE) that
remain small compared with the thermal energy, i.e., μE << k B T. As a result, typical
nonlinear dielectric effects are very small and electric fields are expected to have little
impact on the net molecular orientation and on thermodynamic potentials. Nevertheless, static electric fields in the range from 40 to 200 kV cm
−1 were observed to
impact the crystallization dynamics and pathway of a polar molecular glass-former:
vinyl ethylene carbonate (VEC), a derivative of propylene carbonate. Various temperature/field protocols have been employed to reveal the effect of a static electric field
on the crystallization behavior of VEC. The volume fraction of the liquid state is
measured via the dielectric permittivity. The rate of crystallization could be accelerated by more than a factor of 10, either by applying a field near the glass transition
temperature, T g , and then taking the sample to a higher crystallization temperature
T c without field, or by taking the sample directly from T > T m to T c , where T m is the
melting temperature, and then applying an electric field. Interestingly, crystallization
promoted by electric fields gave rise to a new polymorph that could not be obtained
in the absence of an electric field. The signature of this new structure is a melting
temperature that was observed to be 20 K below that of the ordinary crystal of VEC.
Because VEC is a simple polar molecule, these field-induced features are expected
to occur in many other materials having sufficient permanent dipole moments. Our
results highlight the important role of an external electric field as additional control
variable to influence the crystallization tendency of molecular glass-formers, and
provide new opportunities in pharmaceutical science or organic electronics.
Keywords High electric fields · Dielectric relaxation · Crystal polymorphs
K. Adrjanowicz
Institute of Physics, University of Silesia, 75 Pulku Piechoty 1a, Chorzow 41-500, Poland
e-mail: karolina.adrjanowicz@us.edu.pl
R. Richert (B)
School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, USA
e-mail: Ranko.Richert@asu.edu
© Springer Nature Switzerland AG 2020
T. A. Ezquerra and A. Nogales (eds.), Crystallization as Studied
by Broadband Dielectric Spectroscopy, Advances in Dielectrics,
https://doi.org/10.1007/978-3-030-56186-4_6
149
by Electric Fields
Karolina Adrjanowicz and Ranko Richert
Abstract Polar molecular materials subject to high electric fields of magnitude
E lead to situations which are usually characterized by dipole energies (μE) that
remain small compared with the thermal energy, i.e., μE << k B T. As a result, typical
nonlinear dielectric effects are very small and electric fields are expected to have little
impact on the net molecular orientation and on thermodynamic potentials. Nevertheless, static electric fields in the range from 40 to 200 kV cm
−1 were observed to
impact the crystallization dynamics and pathway of a polar molecular glass-former:
vinyl ethylene carbonate (VEC), a derivative of propylene carbonate. Various temperature/field protocols have been employed to reveal the effect of a static electric field
on the crystallization behavior of VEC. The volume fraction of the liquid state is
measured via the dielectric permittivity. The rate of crystallization could be accelerated by more than a factor of 10, either by applying a field near the glass transition
temperature, T g , and then taking the sample to a higher crystallization temperature
T c without field, or by taking the sample directly from T > T m to T c , where T m is the
melting temperature, and then applying an electric field. Interestingly, crystallization
promoted by electric fields gave rise to a new polymorph that could not be obtained
in the absence of an electric field. The signature of this new structure is a melting
temperature that was observed to be 20 K below that of the ordinary crystal of VEC.
Because VEC is a simple polar molecule, these field-induced features are expected
to occur in many other materials having sufficient permanent dipole moments. Our
results highlight the important role of an external electric field as additional control
variable to influence the crystallization tendency of molecular glass-formers, and
provide new opportunities in pharmaceutical science or organic electronics.
Keywords High electric fields · Dielectric relaxation · Crystal polymorphs
K. Adrjanowicz
Institute of Physics, University of Silesia, 75 Pulku Piechoty 1a, Chorzow 41-500, Poland
e-mail: karolina.adrjanowicz@us.edu.pl
R. Richert (B)
School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, USA
e-mail: Ranko.Richert@asu.edu
© Springer Nature Switzerland AG 2020
T. A. Ezquerra and A. Nogales (eds.), Crystallization as Studied
by Broadband Dielectric Spectroscopy, Advances in Dielectrics,
https://doi.org/10.1007/978-3-030-56186-4_6
149