Supercooled liquids with enhanced orientational order

ABSTRACT The nature of the glass transition, the transformation of a liquid into a disordered solid, still remains one of the most intriguing unsolved problems in materials science. Recent

models rationalize crucial features of vitrification with the presence of medium-range ordered regions coexisting with the isotropic liquid. Here, in line with this prediction, we report an

extraordinary enhancement in bond orientational order in ultrathin films of supercooled polyols, grown by physical vapour deposition. By varying the deposition conditions and the molecular

size, we could tune the kinetic stability of the liquid phase enriched in bond orientational order towards conversion into the ordinary liquid phase. We observed a strong increase in the

dielectric strength with respect to the ordinary supercooled liquid and slower structural dynamics, suggesting the existence of a metastable liquid phase with improved orientational

correlations. You have full access to this article via your institution. Download PDF SIMILAR CONTENT BEING VIEWED BY OTHERS REVEALING THE ROLE OF LIQUID PREORDERING IN CRYSTALLISATION OF

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SPLAY NEMATIC PHASE Article Open access 16 August 2021 INTRODUCTION Isotropic liquids are characterized by the absence of any long-range positional order. Operationally, they are

distinguished from solids on the basis of their mechanical response as expressed by the structural relaxation time, _τ_, defined via Maxwell’s relation1 as the ratio between the shear

viscosity _η_ and the instantaneous shear modulus _G_∞. Materials in which _τ_ is shorter than the experimental observation time are considered liquids, whereas in the opposite case, they

are regarded as (disordered) solids. Upon cooling or pressurizing, liquids can transform into the solid state. Depending on their energy landscape and on the thermodynamic and kinetic path

they follow, they acquire a periodic structure with full translational order (crystals) or maintain a morphology lacking in long-range order (glasses)2,3,4,5. The structural relaxation time

increases upon cooling, and the glassy state is achieved when _τ_ exceeds the experimental observation time; upon quenching, this condition occurs at the glass transition temperature, _T_g.

Glasses are thus systems that are out of thermodynamic equilibrium. Although these materials are commonly regarded as disordered systems, crucial features of the glass transition, such as

the increase in heterogeneity and the larger cooperativity of the liquid dynamics approaching solidification6,7,8,9, can be rationalized by the presence of medium-range ordered regions (MRO)

in the liquid phase. Frustration models10,11,12, developed in the past few decades, ascribe this behaviour to the presence of icosahedra, locally preferred structures (LPSs) present in the

isotropic liquid at temperatures below the melting point, _T_m. The formation of these solid-like clusters is driven by maximizing the number of directional bonds that lock the system to

local minima in the free-energy landscape. As a consequence, LPSs are metastable, long-lived structures, showing bond orientational order (BOO) while lacking the long-range topological order

of the crystal. At low pressures, icosahedra are energetically favoured with respect to clusters with crystallographic symmetry, and the resulting geometric frustration prevents the

development of long-range order. In contrast, the two-order parameter model13 predicts that the frustration of crystallization is due to both kinetic and energetic factors: the presence of

an anisotropic potential of intermolecular interaction generates LPSs, whose spatial symmetry is not compatible with the structure of the equilibrium crystal. According both to the paradigm

of the frustration models and to the two-order parameter model, supercooled liquids consist of a heterogeneous mosaic of MRO regions, grown in proximity to LPSs and surrounded by the

isotropic ordinary liquid (OL). Evidence of such structures has been found in metallic glass formers14,15,16, where the presence of quasi-crystalline clusters with a few topological defects

has been detected by diffraction techniques, such as atomic-scale high-resolution transmission electron microscopy and by X-ray, neutron and electron diffraction. An enhanced degree of

topological order may be achieved via structural rearrangements, either by annealing below the glass transition temperature (physical aging)17 or pressurizing18, which permits the nucleation

of MRO regions in proximity to the quasi-crystalline clusters and the consecutive propagation of a similarly ordered structure. For some metallic glasses, this approach has allowed access

to smaller, pre-existing crystalline structures, otherwise undetectable by the aforementioned experimental techniques because the structure factor of an amorphous phase containing

topological order is virtually undistinguishable from the structure factor of a glass where molecules are randomly distributed19. A method used to grow extended ordered regions is physical

vapour deposition (PVD), which has been successfully employed to produce a large family of inorganic misfit layers20 (where the basic periodicities of one or two interpenetrating layers do

not coincide), which are otherwise impossible to obtain. A successive annealing step locks the system into local free-energy minima, dictated by the precursor obtained by PVD. Similarly, PVD

of organic glass formers below _T_g might yield ultradense glasses with highly efficient molecular packing, approaching the limit of the crystal21,22. Those new materials are characterized

by an extremely low excess enthalpy and by a thermodynamic and kinetic stability neither achievable in ordinary glasses, nor by physical aging, hence the name ‘ultrastable glasses’. In

contrast to approaching the glass transition by quenching or pressurizing the liquid, vapour deposition in the glassy state operates in thermodynamic equilibrium, taking advantage of the

enhanced molecular mobility at the free surface23, where evaporated molecules can rapidly sample the energetic landscape and reach deeper minima before being buried by the upcoming layers.

This preparation method thus proves to be, at present, the most efficient way to produce glasses with the lowest thermodynamic excess quantities (enthalpy, volume, entropy)24. In this

report, we present a new method to extend the investigation of medium-range order to organic glass-forming materials by the molecular beam deposition of polyols in the glassy state, followed

by annealing in the liquid state. The severe changes in the dielectric permittivity of samples prepared via our method is consistent with an enrichment of the isotropic liquid in

long-living MRO regions. RESULTS EXPERIMENTAL APPROACH TO ASSESSING HIDDEN ORIENTATIONAL ORDER We exploited the improved sampling of the energy landscape to obtain a liquid phase enriched in

regions with medium-range order, following an approach analogous to that introduced to produce misfit layers. We applied this method to prepare ultrathin films of glycerol, threitol and

xylitol, glass-forming materials known to form, already in the liquid state, temporary H-bonded networks that rely on highly directional, that is, anisotropic, intermolecular interactions25

(_E_OH···O=8–11 _k_B_T_ per bond)26. This feature, in combination with the improved sampling of the energy landscape, enhances the formation of precursor LPSs located at deep minima. The

resulting MRO regions are thus expected to survive long enough to be investigated. The main challenge was the choice of the experimental technique to detect the presence of local order in

organic glass-forming systems. In these materials, in contrast to metallic glasses, no evidence of MRO is seen by scattering and diffraction techniques because of the higher degree of

freedom, which causes a loss of symmetry in the molecular arrangement and thus prevents the generation of any measurable signal. We probed our films instead by dielectric spectroscopy to

gain information about the degree of correlation in the molecular orientation, that is the BOO. After depositing our films in the glassy state, we monitored their dielectric response during

annealing above _T_g, which permitted the measurement of their dielectric strength Δ_ε_, that is, the contribution of the orientational polarization to the dielectric constant (see below).

This quantity is a robust parameter for measuring the BOO, as it is sensitive to the orientation correlation among neighbouring dipoles, via the Kirkwood factor _g_. Indeed,

Δ_ε_≈_g_<_μ_2>/_k_B_T_ (ref. 27), where _μ_ is the molecular dipole moment and _g_ accounts for the correlation among neighbour molecular dipole moments. The value of g is given by

where _z_ is the number of correlated molecules around a given central molecule, and <cos _ψ_> is a statistically averaged cosine of the angle _ψ_ between two neighbouring dipoles.

Thus, if the dipoles have a tendency for parallel orientation, then _g_>1, whereas 0<_g_<1 implies an antiparallel orientation. A random orientation of the dipoles, instead, results

in _g_=1. Accordingly, if an enrichment in MRO regions is finally obtained, the orientational correlation is locally enhanced, leading to an increase or a decrease in the value of _g_,

depending on the spatial organization of the molecules in the local clusters. We anticipate that in the specific case of our investigation, we found a clear enhancement of Δ_ε_ and a

consequent increase in _g_, indicating a parallel orientational correlation among the dipoles, which can be justified by the presence of (locally preferred) anisotropic structures. Moreover,

such an increase rules out the presence of long-range order and crystal-like BOO, which would instead cause a decrease in the dielectric response due to the suppression of the rotational

and translational modes in these clusters. Furthermore, as a consequence of a larger correlation length, the MRO regions are expected to have slower structural dynamics (corresponding to

~2–10 _τ_) with respect to the isotropic liquid28,29. DIELECTRIC RESPONSE OF A LIQUID WITH ENHANCED BOO In glycerol films (~10–130 nm), we found a tremendous enhancement in the dielectric

strength (Fig. 1), exceeding by more than threefold the value measured for bulk glycerol films deposited well above _T_g (ref. 30). Such a large value cannot be rationalized by a mere

increase in density, which would prompt non-physical changes, nor by a larger effective dipole moment, due to a very unlikely perfectly planar orientation in the direction of the electric

field. We ascribe this increase to a higher orientational correlation among the dipole moments, which is consistent with the concept of a liquid state having enhanced MRO and BOO, compared

with the OL. Hereafter, this particular liquid phase will be denoted as medium-range order enriched liquid (MROL). Concurrently, we observed structural relaxation times 4–5-fold longer than

the relaxation time of the OL, corresponding to a shift in _T_g of ~4 K. This finding is in line with the quantitative predictions proposed both for Lennard–Jones liquids28 and for model

polymeric systems29. To quantify the perturbation in the molecular orientation in the MROL, we analysed the temperature evolution of Δ_ε_N=Δ_ε_MROL/Δ_ε_OL. The isothermal dielectric spectra

acquired upon annealing showed that Δ_ε_N begins to decrease at an onset temperature depending on the material, on the thickness of the films and on the temperature of deposition (Figs 2 and

3), which indicates the metastable nature of the ordered structures. We were able to observe the MROL→OL transition via the temperature evolution of Δ_ε_N (Fig. 2, Methods and Supplementary

Fig. S1). The OL behaviour, that is, Δ_ε_N=1, is eventually recovered after prolonged annealing at _T_>_T_g. It must be noted that, compared with Δ_ε_, _τ_ is a less sensitive parameter

to the presence of MRO. The variation of Δ_ε_ with the concentration of MRO regions is remarkably larger with respect to the evolution of _τ_, which allows a better resolution in monitoring

the MROL→OL transition (Supplementary Fig. S2). Similar perturbations to the dielectric function have been observed for natural rubber, following the application of a tensile stress:

although the value of Δ_ε_ tripled, _τ_ remained unaffected by stretching31. In glycerol films (thicker than 20 nm), we observed an enhancement by a factor of 3.7 in Δ_ε_N and a simultaneous

increase of 4.5-fold in the relaxation time; during the MROL→OL transition, these alterations led to a broadening of the relaxation peak in the dielectric loss, without separation between

the contributions from the MRO regions and from the amorphous liquid (Supplementary Figs S1 and S3). For these reasons, we concentrated our investigation mainly on the dielectric strength.

Additional experiments on larger homologous molecules, such as threitol and xylitol, revealed the same trends as for glycerol, but to a lesser extent (smaller Δ_ε_N and lower onset

temperatures, Fig. 2), which further supports the H-bonding interaction as the origin of the enhanced orientational correlation. Indeed, the larger multiplicity of molecular conformations

that arise from the higher intramolecular degrees of freedom with increasing molecular size, likely reduces the efficiency of the formation of an ordered intermolecular network. Such a trend

is in further agreement with the idea that the more fragile glass formers (_m_xylitol>_m_threitol>_m_glycerol, (ref. 32) with _m_ the fragility) are characterized by lower

frustration, that is, by a lower concentration of (locally) ordered structures11,28, which explains the smaller increase in polarization with increasing molecular size. LIFETIME AND LENGTH

SCALE OF THE ENHANCEMENT IN POLARIZATION We gained further insight into the origin of the MRO regions and the related increase in Δ_ε_ of the MROL phase by investigating the dielectric

response of 30-nm-thick glycerol films, grown holding the substrate at different temperatures, _T_sub. After deposition, we measured Δ_ε_N during identical temperature scans, and we analysed

the impact of _T_sub on the maximum value of the increase in dielectric strengths, Δ_ε_Nmax, as observed before the onset of the transition to the OL (Fig. 3, red circles). To relate this

parameter to the kinetic stability of the MROL phase, we compared its temperature dependence with the temperature dependence of the conversion time _t_c normalized to the value of _τ_ at the

same temperature (blue stars). The excellent match between the trends of these two quantities proves that an enhancement in dielectric strength, that is, a higher orientational order, is

correlated with a greater stability of the MROL phase. The normalized dielectric strength and the value of log(_t_c/_τ_) remained almost constant up to _T_sub=206 K, where an abrupt

simultaneous drop in both parameters took place. Within the limits of our experimental method, we observed no enhancement in Δ_ε_N for films deposited at _T_sub≥213 K, which determined the

limiting temperature where we could detect a deviation from the OL. This behaviour suggests the onset of the stability of a liquid phase with enhanced orientational order below _T_*~213 K

(<_T_m). We conducted further experiments that verified that the increase in the dielectric susceptibility of the metastable liquid state also varies with the film thickness (Fig. 4). The

increase in Δ_ε_N exceeds 5.0 at 9 nm, and Δ_ε_Nmax decays progressively before settling to a constant value of 3.7, in films thicker than 15–20 nm. Given the purely additive contribution

of each layer to the dielectric strength in our experimental configuration33, we might imagine a higher BOO in proximity to the interfaces, penetrating for a few nanometres. Such a length

scale is larger than has been observed in metallic liquids in proximity to the crystal growth front34, where only a few atomic layers are affected. We were able to fit the interfacial excess

in Δ_ε_N with a single exponential with a characteristic decay length of 5.9±1.0 nm. This value can be treated as an upper bound for the actual spatial extent of the extra BOO in proximity

to the substrate, and thus also for the size of the region where the liquid dynamics is affected by the MRO35. To discern the impact of the interface-induced ordering caused by steric

effects from the possible impact of molecular interactions with the substrate36, we investigated MROL glycerol films grown on OL layers of the same material, previously deposited well above

_T_g (see Supplementary Methods for further details). We obtained quantitative agreement with the values measured in the single-layer films of comparable thickness, proving that the

interactions between the polyols and the substrate of the interdigitated electrodes (IDE) do not influence the structure of the MROL phase. To further analyse the transformation process, we

prepared glycerol films with different thicknesses, and we estimated the velocity _v_ of the conversion of the MROL into the OL by analysing the isothermal decay in Δ_ε_N at increasing

annealing temperatures. We found conversion rates on the order of 10−4 nm s−1 at _T_g+50 K for films thicker than 15 nm, while below this threshold, _v_ increases exponentially, with a

characteristic length of (7.2±2.0) nm, similar to the value found for Δ_ε_Nmax (Fig. 4). The outcome of this experiment, in which we kept _T_sub constant and we varied the layer thickness,

is in line with the data in Fig. 3, relative to measurements where we evaluated the conversion time at constant thickness, but at different _T_sub. Such behaviour, with the temperature

dependence observed for films of larger homologous molecules (Fig. 2), provides a further confirmation that higher values of Δ_ε_N correspond to a greater kinetic stability of the MROL.

Moreover, the linear decay of Δ_ε_N during isothermal transformation, indicating a constant transformation rate, is consistent with the scenario of a growth front-like transformation process

where the liquid–liquid interface between the two phases propagates through the film at a constant velocity, inversely proportional to the increase in orientational polarization of the

structural process in the liquid state37. DISCUSSION Further investigations will be necessary to unveil the molecular origin of the transformation process and the origin of such high kinetic

stability. A rationalization of the observed values of _t_c/_τ_ would require determining the lifetime of the LPSs and their stability against annealing. The MRO enrichment should persist

as long as the LPSs have not recovered their equilibrium concentration at a given temperature. Until the achievement of this condition, the MRO regions continuously destroy and nucleate,

driven by the minimization of local free energy, achieved via spatial reorganization at the time scale of _τ_ (refs 11, 28). This long-lasting behaviour permitted us to detect the

differences in the orientational polarization. At present, no simulation methods are available to compute the distribution and the exact lifetime of these metastable structures, even using

state-of-the-art computer resources11. However, recent Monte Carlo simulations have verified that metastable states associated with lower inherent structure energy (that is, LPSs) can

survive for lifetimes longer than the lifetimes predicted by simple diffusion models and can thus coexist with the isotropic liquid38. We speculate that our preparation method permitted us

to obtain similar long-lived structures, ensuring the persistence of the enhanced MRO in our systems. This success was possible because, as anticipated, performing PVD below _T_g has been

proven to be the most efficient way to age glasses. In the supporting information, we analyse the similarities between the results from our experiment and previous investigations of ordinary

and ultrastable glasses (Supplementary Figs S4–S6). Because of the importance of such domains in determining the properties of the glass transition, we believe that the procedure described

in this work, which allows the preparation of isotropic liquids enriched in conformations present in the glassy state, represents a possible method of achieving hidden liquid phases with

intriguing materials properties. We hope that our work will stimulate further investigation of this new liquid phase via different experimental approaches, which will make it possible to

test theoretical models to clarify the nature of the glass transition. METHODS MOLECULAR BEAM DEPOSITION IN THE GLASSY STATE Films of glycerol, threitol and xylitol (degree of purity

>99%, purchased from Aldrich), were prepared by organic molecular beam deposition directly on the IDE30,39,40, which made it possible to probe their dielectric response. The bulk material

was heated above its melting temperature in a crucible connected, via a pneumatic valve, to a vacuum chamber maintained at a pressure _p_~10–8 mbar. The thickness of the films, monitored

via a quartz crystal microbalance (QCM), was varied by switching the valve; the temperature of the crucible was adjusted to keep the evaporation rate below 3 × 10−2 nm s−1. During

evaporation, the temperature of the substrate, _T_sub, was maintained at 0.88_T_g; this value was very close to the temperature providing the best thermal and kinetic stability of the MROL,

as indicated by additional experiments performed on 50-nm-thick glycerol films grown at different _T_sub in the range from 0.75_T_g to _T_g. To prepare the glycerol bilayers, layers of

different thickness (6 and 36 nm) were deposited at 223 K (1.2_T_g) and immediately after deposition cooled to 0.88_T_g, where the evaporation of an 11-nm capping layer followed the same

protocol used for the single layers. DIELECTRIC MEASUREMENTS To perform _in situ_ dielectric spectroscopy while permitting a continuous evaporation of material on the target substrate, we

employed IDE structures, which present an open-electrode configuration. The sensors, produced by UV lithography, were composed of 100 gold fingers (height=200 nm; width=15 μm) deposited on a

quartz substrate. Each pair of fingers is spaced 1.25 μm apart, resulting in a total capacitance of 5 pF. Silver wires were glued on the connectors of the IDE via a thermally and

electrically conductive epoxy resin filled with silver nanoparticles (Ecolit E 325) and soldered to a high-vacuum feedthrough, which allowed connection to an impedance analyser (ALPHA,

Novocontrol). The intensity of the applied electric field _E_ was <106 V m−1, a regime in which the polarization response is linearly proportional to _E_. The IDE was mechanically

attached to a metallic plate located inside the vacuum chamber and held at the desired temperature by the combined action of a resistance heating and a cooling flux of gaseous nitrogen. A

Pt100 sensor was glued to the substrate of the IDE with Elecolit E 325 to constantly monitor _T_sub. In addition to the direct QCM measurements, the thickness of the film could also be

checked based on the dielectric signal, according to the equation Δ_C_∞=_N ε_0(_ε_∞−1)(_p_/_d_) _L_, where _L_ is the thickness of the film; Δ_C_∞ is the resulting change in the capacitance

of the system; _ε_0 is the vacuum permittivity; _ε_∞ is the dielectric constant of the material; _N_ is the total number of fingers; and _p_ and _d_ indicate the length of the fingers of the

IDE and their mutual distance, respectively. Such a procedure was used below 30 nm, where the error in determining the thickness by QCM, due to the different position of the two sensors,

exceeded 10%. The measured increase of the dielectric strength is a strong proof of the lack of bubbles inside our films, which, acting as dielectric cavities (_ε_∞vacuum<_ε_∞glycerol)

would reduce the polarization and thus the dielectric signal. CHARACTERIZATION OF THE MROL PHASE After deposition, the films were heated to a temperature _T_=_T_g+10 K and subsequently

annealed up to _T_g+50 K in steps of 1 K. Isothermal dielectric spectra were acquired at each temperature, in the frequency range between 10−1 and 106 Hz. The values of the relaxation time

_τ_ were derived from the relation _τ_=2_π_/_f_max, where _f_max is the frequency at which the imaginary part of the dielectric permittivity _ε_″(_ω_) shows a maximum. The values of the

dielectric strength were obtained by analysing the isothermal spectra via the empirical Havriliak–Negami (HN) function: where Δ_ε_, _τ_HN, _α_, and _β_ are the dielectric strength, the

relaxation time and the shape parameters, respectively, accounting for the width and the asymmetry of the loss curves. Further isothermal measurements were performed on glycerol films of

different thicknesses (9, 15, 18, 26, 30, 55, 89 nm): the temperature of the IDE was varied in the same range as above, but in steps of 5 K. The sample was held at each annealing temperature

for 2 h. The conversion rate into the OL phase, _v_, was estimated by fitting isothermal scans with linear decays _v_=Δ_l_/(_t_−_t_0), where Δ_l_ is the fraction of transformed film, and

_t_0 indicates the onset of measurement. The value of Δ_l_ is obtained from the time evolution of the dielectric strength under the assumption that Δ_ε_ is the sum of the contribution of the

two liquid phases averaged over their volume fractions according to Δ_ε_TOT=_x_OL·_R_Δ_ε_OL+_x_MROLΔ_ε_OL=_R_Δ_ε_OL(_L_−Δ_l_)/_L_+Δ_ε_OL·Δ_l_/_L_, where _x_ is the volume fraction,

_R_=Δ_ε_Nmax/Δ_ε_OL. The dielectric strength of the film normalized by the value in the OL, Δ_ε_OL, is thus given by Δ_ε_N(_t_−_t_0)=Δ_ε_TOT(_t_−_t_0)/(Δ_ε_OL·_L_)=_R_−(_R_−1)·Δ_l_/_L_,

which simplifies to Δ_ε_N (_t_0)−Δ_ε_N(_t_−_t_0)=(_R_−1)·Δ_l_/_L_. Finally, _v_=_L/_(_t_−_t_0)·[Δ_ε_N (_t_0)−Δ_ε_N(_t_−_t_0)]/(_R_−1). We ruled out the possibility that the larger values of

Δ_ε_ and of _τ_ observed in the medium-range crystalline order phase are actually induced by the presence of water or other contamination in the films. Water molecules would instead enhance

the structural relaxation time (plasticizing effect) and reduce the dielectric strength by breaking the OH bonds.41,42 Contamination by other impurities would also break the intermolecular

OH bonds, whose fluctuations contribute to the Δ_ε_ of polyols, and consequently reduce the dielectric strength. Furthermore, we considered whether the observed enhancement in the dielectric

strength and its thermal evolution could be due to the presence of ionic impurities intruded into the films during deposition, and subsequently desorbing at higher temperatures, during

annealing. Such a mechanism could mimic the conversion of the MROL phase into the OL. In addition to increase in the value of the dielectric strength, ionic contaminants would, in fact, also

yield a larger conductivity _σ_, see Supplementary Methods and Supplementary Equation S2. To verify the validity of this conjecture, we performed isothermal experiments at 228 K, a

temperature high enough to simultaneously observe the evolution of the dielectric strength and of the conductivity. The results (Supplementary Fig. S7) show that the dielectric strength

decays linearly with the annealing time, whereas the conductivity remains at a constant value, comparable with that of films deposited at _T_ »_T_g. This evidence strongly excludes the

possibility that the observed enhancement in dielectric strength is due to the presence of contaminants. ADDITIONAL INFORMATION HOW TO CITE THIS ARTICLE: Capponi, S. _et al._ Supercooled

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and fast dynamics in glycerol-water mixtures. _J. Non-Cryst. Solids_ 352, 4696–4703 (2006). Article  CAS  ADS  Google Scholar  Download references ACKNOWLEDGEMENTS We thank Haijme Tanaka

(Institute of Industrial Science, University of Tokyo) for a fruitful discussion. S.C. and M.W. acknowledge financial support from the Research Council of the K.U. Leuven, projects No.

OT/06/30 and OT/11/065, and financial support from FWO (Fonds Wetenschappelijk Onderzoeks—Vlaanderen) within the project G.0642.08. AUTHOR INFORMATION Author notes * Simona Capponi Present

address: Present address: School of Physics, University College Dublin, Belfield, Dublin, Ireland., AUTHORS AND AFFILIATIONS * Department of Physics and Astronomy, Laboratory of Acoustics

and Thermal Physics, Katholieke Universiteit Leuven, Celestijnenlaan 200D, Leuven, 3001, Belgium Simona Capponi & Michael Wübbenhorst * Laboratory of Polymer and Soft Matter Dynamics,

Faculté des Sciences, Université Libre de Bruxelles (ULB), Boulevard du Triomphe, Bâtiment NO, Bruxelles, 1050, Belgium Simone Napolitano Authors * Simona Capponi View author publications

You can also search for this author inPubMed Google Scholar * Simone Napolitano View author publications You can also search for this author inPubMed Google Scholar * Michael Wübbenhorst

View author publications You can also search for this author inPubMed Google Scholar CONTRIBUTIONS S.C., S.N. and M.W contributed equally to this work. CORRESPONDING AUTHOR Correspondence to

Simone Napolitano. ETHICS DECLARATIONS COMPETING INTERESTS The authors declare no competing financial interests. SUPPLEMENTARY INFORMATION SUPPLEMENTARY METHODS Supplementary Figures S1-S7,

Supplementary Methods and Supplementary References (PDF 867 kb) RIGHTS AND PERMISSIONS Reprints and permissions ABOUT THIS ARTICLE CITE THIS ARTICLE Capponi, S., Napolitano, S. &

Wübbenhorst, M. Supercooled liquids with enhanced orientational order. _Nat Commun_ 3, 1233 (2012). https://doi.org/10.1038/ncomms2228 Download citation * Received: 30 August 2012 *

Accepted: 26 October 2012 * Published: 04 December 2012 * DOI: https://doi.org/10.1038/ncomms2228 SHARE THIS ARTICLE Anyone you share the following link with will be able to read this

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