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Rayleigh-Taylor instability experiments with precise and arbitrary control of the initial interface shape
Z. Huang, A. De Luca, T.J. Atherton, M. Bird, C. Rosenblatt, and P. Carlès
Phys. Rev. Lett. 99 204502 (2007)
In a Rayleigh-Taylor instability a dense fluid sits metastably atop a less dense fluid, 
a configuration that can be stabilized using a magnetic field gradient when one fluid is
highly paramagnetic. On switching off the magnetic field, the instability occurs as
the dense fluid falls under gravity. By affixing appropriately shaped magnetically-permeable
wires to the outside of the cell, one may impose arbitrarily-chosen and well-controlled
initial perturbations on the interface. This technique is used to examine both the linear
and nonlinear growth regimes for which the perturbation amplitudes, growth rates,
and nonlinear growth coefficients are obtained.

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The importance of fluctuations in fluid mixing
 K. Kadau, C. Rosenblatt, J.L. Barber, T.C. Germann, Z. Huang, P. Carlès, and B.J. Alder
Proc. Nat. Acad. Sci. 104, 7741 (2007)
A ubiquitous example of fluid mixing is the Rayleigh-Taylor instability, in which a
heavy fluid initially sits atop a light fluid in a gravitational field. The subsequent
development of the unstable interface between the two fluids is marked by several
stages. At first, each interface mode grows exponentially with time, before
transitioning to a nonlinear regime characterized by more complex hydrodynamic
mixing. Unfortunately, traditional continuum modeling of this process has
generally been in poor agreement with experiment. Here we indicate that the
natural, random fluctuations of the flow field present in any fluid, which are
neglected in continuum models, can lead to qualitatively and quantitatively better
agreement with experiment. We performed billion-particle atomistic simulations
and magnetic levitation experiments with unprecedented control of initial interface
conditions. A comparison between our simulations and experiments reveals good
agreement in terms of the growth rate of the mixing front, as well as the new
observation of droplet breakup at later times. These results improve our
understanding of many fluid processes, including interface phenomena that
occur, for example, in supernovae, the detachment of droplets from a faucet, and
ink jet printing. Such instabilities are also relevant to the possible energy source
of inertial confinement fusion, in which a millimeter-sized capsule is imploded to
initiate nuclear fusion reactions between deuterium and tritium. Our results
suggest that the applicability of continuum models would be greatly enhanced by
explicitly including the effects of random fluctuations.
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Quasi-divergent nematic surface electroclinic coefficient
M.H. Zhu, G. Carbone, and C. Rosenblatt
Phys. Rev. E 73, 041701 (2006)
A polyimide coated substrate is treated so that vertical liquid crystal alignment (θ=0) obtains over the temperature range T_NA<T<T_a,
where T_NA is the nematic — smectic-A transition temperature.  When the cell is filled with a chiral liquid crystal, application of an
 in-plane electric field for T_NA<T<T_a induces a nonzero polar tilt θ ∝ E of the liquid crystal director at the surface,
where the tilted orientation propagates elastically into the bulk.  On heating toward T_a, this surface electroclinic response
becomes large, corresponding to the onset of a surface tilt transition from θ=0 to nonzero θ.
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Rayleigh-Taylor instability for immiscible fluids of arbitrary viscosities: Magnetic levitation investigation and theoretical model
P. Carlès, Z. Huang, G. Carbone, and C. Rosenblatt
Phys. Rev. Lett.  96, 104501 (2006)
A magnetic field gradient was used to draw down a low density but highly paramagnetic fluid below a more dense fluid in a Hele-Shaw cell. On
turning off the field a Rayleigh-Taylor instability was observed in situ, and the growth of the most unstable wavevector was measured as a
function of time.  A theory for the instability that permits different viscosities for two immiscible fluids was developed, and good agreement was
found with the experimental results.
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Smectic tilt susceptibility:  Anharmonic behavior in surface-induced smectic layers above the nematic -- smectic-A transition temperature
Z. Huang, G. Carbone, C. Xia, Ghanshyam P. Sinha, and C. Rosenblatt
Phys. Rev. E 72, 021708 (2005)
Freedericksz transition measurements were used to determine the quartic contribution to the
energy associated with molecular tilt relative to the layer normal in the surface-induced smectic
layers in the nematic phase above the smectic-A transition temperature T_NA.  Both the
quadratic and quartic coefficients are consistent with the scaling relationship (T-T_NA)^-3nu,
where nu is the correlation length exponent, and their ratio was approximately constant.
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Effect of flexible bimeosgenic dopant on the stability of the anticlinic liquid crystal phase
M.H. Zhu, R.G. Petschek, L. Komitov, N. Olsson, B. Helgee, J.M. Kim, and M.E. Neubert
Phys. Rev. E. 72, 021702 (2005)
Small quantities of the floppy bimesogen di(4PPB5)3Si were dissolved in an anticlinic liquid crystal
consisting of a mixture of left- and right-handed TFMHPOBC, with enantiomer excess X=0.2.
The bimesogen dopant was found to promote anticlinic order with an anticlinic interaction coefficient
per molecule u_{dopant} smaller than, but of the same order as, the rigid bent-core dopant P-7PIMB
 For both dopants u_{dopant} was found to be much larger than that due to a pair of TFMHPOBC
molecules in adjacent layers.  The results are examined in terms of both the flexibility of the group
linking the two legs of each dopant, as well as their chemical structure.
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Planar degenerate substrate for micro- and nanopatterned nematic liquid crystals
I.M. Syed, G. Carbone, C. Rosenblatt, and B. Wen
J. Appl. Phys. 98, 034303 (2005)
A micro- or nanopatterned planar aligned cell ordinarily requires a pair of mirror-image patterned
substrates that must be aligned in register to ≪1 μm. As an alternative we examine the director
orientation profile of a nematic liquid crystal in a cell composed of one substrate whose easy axis is patterned
on micrometer length scales λ and a second substrate treated for planar degenerate alignment using
polymethyl methacrylate. For cell thickness <λ, the experimentally measured director profile in the
bulk corresponds approximately to that imposed at the micropatterned substrate.
The results are compared with theoretical calculations.  This method provides an excellent
alternative to the use of a pair of substrates aligned in close register.
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Polar anchoring strength of a tilted nematic:  Confirmation of the dual easy axis model
Giovanni Carbone and C. Rosenblatt
Phys. Rev. Lett. 94, 057802 (2005)
The polar anchoring strength coefficient W was measured as a function of polar pretilt angle
theta_0 for the liquid crystal 5CB.  It was found that W is proportional to (theta_0)^2 over the
range 0<theta_0<35 degrees.  The results provide a confirmation of the dual easy axis model,
wherein the liquid crystal director adopts an equilibrium orientation theta_0 at the substrate
that is determined by competition between a pair of preferred orienatation directions.
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Possible structures for the lameller-isotropic (Lam-I) and lameller-nematic Lam-N)  phases
N.M. Patel, I.M. Syed, C. Rosenblatt, M. Prehm, C. Tschiersek
Liquid Crystals 32, 55 (2005)
The three refractive indices of a liquid crystal that exhibits lamellar
analogs of the three dimensional isotropic, nematic, and smectic-A phases
are reported as a function of temperature for the Lam-I and Lam-N
phases.  Coupled with x-ray results, the data suggest a number of striking
behaviors: the orientational director n of the mesogenic moiety
is nearly three dimensionally disordered in the Lam-I phase; 
the two dimensional order associated with n in the Lam-N phase is
weak; and conformational changes in the sidechain result in an increase in
the refractive index perpendicular to the lamellae on decreasing temperature in
the Lam-N phase.
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International Collaborations in Liquid Crystal Research:  Personal Experiences
Charles Rosenblatt
Facets 4, No. 2, 14 (2005)
Collaborations.pdf
Liquid crystal research falls under the broad category of “soft materials,” and is conducted
at universities, government laboratories, and in industry around the
world.  The field has been particularly conducive to collaborative interactions,
with many national and regional liquid crystal societies operating under the broad umbrella of the International
Liquid Crystal Society.  In this article I shall describe a very small but representative slice of current liquid
crystal research — that performed by my own research group — and show how it
has been impacted by collaborations with colleagues around the world.
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Large polar pretilt for the liquid crystal homologous series alkycyanobiphenyl
Zhibin Huang and C. Rosenblatt
Appl. Phys. Lett. 86, 011908 (2005)
Sufficiently strong rubbing of the polyimide alignment layer SE-1211 (Nissan Chemical Industries, Ltd.)
 results in a large pretilt of the liquid crystal director from the homeotropic orientation. 
The threshold rubbing strength required to induce nonzero pretilt is found to be a monotonic
 function of the number of methylene units in the homologous liquid crystal series alkylcyanobiphenyl.
The results are discussed in terms of the dual easy axis model for alignment.
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Bent -core dopant in a liquid crystal having a reentrant synclinic phase
M.H. Zhu, C. Rosenblatt, J.M. Kim, and M.E. Neubert
Phys. Rev. E 70, 031702 (2004)
Small quantities of the bent-core mesogen P-7PIMB were dissolved in an
anticlinic liquid crystal consisting of a mixture of left- and right-handed
TFMHPOBC, with enantiomer excess X=0.2. The bent-core dopant promotes
anticlinic order at higher temperatures, but becomes less effective in
suppressing the synclinic phase at the reentrant synclinic transition due to
an orientational transition of the dopant within the calamitic TFMHPOBC
matrix. Measurements of the anticlinic-synclinic electric-field switching
threshold as a function of temperature and dopant concentration facilitate a
determination of the component of the anticlinic interaction coefficient $U$
that is due to the bent-core dopant.  It is found that the value of U per
bent-core molecule is much larger than the corresponding value for a pair of
TFMHPOBC molecules in adjacent smectic layers.
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Orientational transition of a bent-core dopant in an anticlinic liquid crystal matrix
M.H. Zhu, Mr.R. Dodge, T. Shioda, C. Rosenblatt, D.D. Parker, J.M. Kim, and M.E. Neubert
Liquid Crystals 31, 1381 (2004)
.Small quantities of the bent-core mesogen P-7PIMB were dissolved in an anticlinic liquid crystal
consisting of a mixture of left- and right-handed TFMHPOBC, with enantiomer excess X = 0.2.
 For bent-core concentrations above C=3 wt.-%, differential scanning calorimetry shows the disappearance
 of the higher temperature synclinic phase, as well as the appearance of a new peak at a low
 temperature Tc. Polarized infrared absorption measurements indicate that the new DSC
 peak is due to an orientational transition of the bent-core molecules, analogous to the transition
 observed by Pratibha, et al [Science, 288, 2184 (2000)] in a smectic-A matrix. For T>Tc the
 plane of the bent-core molecules lies in the plane of the anticlinic matrix, with the arrow 
(the symmetry axis) of the bent-core molecules parallel to the smectic layers. 
For T<Tc we deduce that the bent-core molecules lie within a single smectic layer, with the 
polar tilt of the arrow approximately equal to the polar tilt of the TFMHPOBC molecule and 
the vector connecting the two ends of the bent-core molecule perpendicular to the anticlinic tilt plane.
 Additionally, Tc was found to be an increasing function of bent-core concentration.
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Chiral-induced polarization at a tilted nematic - substrate interface
I.M. Syed and C. Rosenblatt
Ferroelectrics 311, 329 (2004)
An ac electric field at frequency omega  is applied to a chiral nematic liquid crystal
whose director is tilted by an angle theta _{i} with respect to the substrate normal. 
The nematic director is observed to oscillate at frequency omega  azimuthally about
the substrate normal, indicating the existence of a component of polarization P_{i}
at the substrate that is perpendicular to the director and parallel to the substrate. 
P_{i}, the anchoring strength coefficient, and the bulk viscosity are obtained by
 measurements of the oscillation amplitude as a function of omega .  In particular,
 it is found that the interfacial polarization, when scaled to a volumetric value,
 is two orders of magnitude smaller than in the same material in the smectic-C* phase.
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Nanostructured Surfaces:  Scientific And Optical Device Applications
Charles Rosenblatt
Mol. Cryst. Liq. Cryst.  412, 117 (2004)
Surfactant and polymer-coated substrates may be patterned on microscopic and nanoscopic length scales by the stylus of an atomic force microscope.  The resulting easy axes control the director orientation, facilitating both scientific studies and technological devices that were not possible using previous techniques.  In this talk I will present a review of work from my laboratory, performed in collaboration with Milind P. Mahajan, Wen Bing, Ghanshyam P. Sinha, and Rolfe G. Petschek, along with colleagues L.V. Mirantsev (St. Petersburg, Russia) and Jong-Hyun Kim and Hiroshi Yokoyama (Tsukuba, Japan).  Work includes a number of optical gratings for beam steering applications, gray scale images, anchoring strength studies, effects of controlled surface roughness on smectic order, and nanoscopic elasticity and anchoring effects on the nematic – isotropic phase transition.

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Twist elasticity and anchoring in a lamellar  nematic phase
N.M. Patel, M.R. Dodge, M.Hu. Zhu, R.G. Petschek, C. Rosenblatt, M. Prehm, and C. Tschierske
Phys. Rev. Lett. 92, 015501 (2004)

Step-wise Fréedericksz transition in a nematic liquid crystal
T. Shioda, Bing Wen, and C. Rosenblatt
J. Appl. Phys.  94, 7502 (2003)
The stylus of an atomic force microscope is used to rub a polyimide-coated substrate with a spatial period of 10 microns.
 A spatial periodicity is thereby introduced  into the anchoring strength coefficient, resulting in a shoulder in the intensity -
voltage curve below the Fréedericksz transition threshold of a nematic liquid crystal.
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Light scattering investigation above the nematic-smectic A phase transition in binary mixtures of calamitic and bent-core mesogens
M.R. Dodge, R.G. Petschek, C. Rosenblatt, M.E. Neubert, and M.E. Walsh
Phys. Rev. E 68, 031073 (2003)
Quasielastic light scattering measurements were performed in the nematic
phase of mixtures consisting of the calamitic mesogen 8OCB doped with
small concentrations of the bent-core molecule P-7PIMB.  It was found
that the regular part of the bend elastic constant decreases strongly
with dopant concentration X.  Close to the nematic - smectic-A
phase transition, the divergent part of the bend elastic constant, which
is proportional to the bare correlation length parallel to
the layer normal, also decreases rapidly with X.  The effect of
the dopant on the bare correlation length is examined briefly theoretically.

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Surface-induced molecular tilt above the smectic-A -- smectic-C phase transition in a nonchiral liquid crystal
I.M. Syed and C. Rosenblatt
Phys. Rev. E 68, 031701 (2003)
A polyinide-coated substrate was rubbed in such a way as to
possess two competing easy axes for liquid crystal alignment.
On cooling a homeotropically-aligned liquid crystal through the smectic-A 
phase toward the smectic-C phase transition, an increasing tilt of
the molecules relative to the layer normal was observed.  The
tilt was localized to within a smectic-C correlation length of
the interface, and was found to increase monotonically with the rubbing
strength associated with the preparation of the polymer surface.  The
results are discussed in terms of the dual eas axis model, and suggest
that the two eas axes are not mutually orthogonal.

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Reentrant Synclinic Phase in an Electric Field - Temperature Phase Diagram for Enantiomeric Mixtures of an Antiferroelectric Liquid Crystal
N.M. Patel, C. Rosenblatt, and Yi-kuo Yu
Phys. Rev. E 68, 011703 (2003)
The threshold electric field E_th for a transition from the anticlinic to the synclinic phase of 
enantiomeric mixtures of the liquid crystal TFMHPOBC was measured as a function of 
temperature T and enantiomeric excess X. For small X the phase boundary curve on a temperature --
electric field phase diagram exhibits the phase sequence synclinic - anticlinic - reentrant synclinic 
on decreasing the temperature. At one point along the curve the quantity dT/dE diverges. 
For large values of enantiomeric excess a reentrant phase is not observed. The results are
discussed using a simple phenomenological theory that accounts for layer-layer interactions, such 
that the electric field-induced transition to the synclinic phase, although completed by solitary-wave propagation, 
is facilitated by a percolation mechanism. 
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Transverse surface-induced polarization at a chiral nematic - substrate interface
I.M. Syed and C. Rosenblatt
Phys. Rev. E 67, 041701 (2003)
A chiral nematic liquid crystal that is tilted by an angle theta with respect to a substrate is subjected to an ac electric field at frequency omega.  The nematic director is found to oscillate azimuthally about the normal to the liquid crystal - substrate interface at frequency omega, indicating that a nonzero polarization perpendicular to the molecular tilt plane exists at the interface.  The interfacial polarization, anchoring strength coefficient, and bulk viscosity are obtained by measurements of the oscillation amplitude as a function of omega.

Continuous nematic anchoring transition due to surface-induced smectic order
T. Shioda, Bing Wen, and Charles Rosenblatt
Phys. Rev. E 67, 041706 (2003)
A continuous transition from tilted to homeotropic alignment at an interface is observed at a temperature Ta for a nematic liquid crystal on cooling toward the nematic -- smectic-A phase transition temperature. Ta is found to depend on the treatment of the substrate.  The behavior is examined theoretically in terms of a pair of competing easy axes (homeotropic and planar) and the tilt elasticity associated with the growth of surface-induced smectic order.

Apparent tricritical behavior at a nearly-second-order nematic — isotropic phase transition of a cyclicliquid crystalline trimer
I.M. Syed, V. Percec, R.G. Petschek, and C. Rosenblatt
Phys. Rev. E 67, art. 011704 (2003)
The cyclic liquid crystalline trimer TPB-(c)9(3) was investigated by optical retardation and Freedericksz techniques to within a few tens of millikelvins of the superheating limit of the nearly second order nematic -- isotropic phase transition.  Both the optical retardation and the Freedericksz bend threshold voltage are in good agreement with tricritical behavior for the transition.

For a complete list of publicationsandpatents (1977 - Present), click here

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