Observation of Steady Shear-Induced Nematic Ordering of Selenium

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Observation of Steady Shear Induced Nematic Ordering of Selenium Chain Moieties in Arsenic Selenide Liquids Weidi Zhu, Galan Moore, Bruce G. Aitken, Simon Clark, and Sabyasachi Sen J. Phys. Chem. B, Just Accepted Manuscript • DOI: 10.1021/acs.jpcb.7b05115 • Publication Date (Web): 20 Jul 2017 Downloaded from http://pubs.acs.org on July 23, 2017

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The Journal of Physical Chemistry

Observation of Steady Shear Induced Nematic Ordering of Selenium Chain Moieties in Arsenic Selenide Liquids

Weidi Zhu1, Galan Moore2, Bruce Aitken2, Simon Clark3,4, Sabyasachi Sen1,*

1

Dept. of Materials Science & Engineering, University of California at Davis, Davis, CA 95616, USA

2 3

Science & Technology Division, Corning Incorporated, Corning, NY 14831, USA

Dept. of Earth and Planetary Sciences, Macquarie University, North Ryde, Sydney, NSW 2109, Australia. 4

Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC, NSW 2232, Australia.

*corresponding author (email: [email protected])

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Abstract

Structural anisotropy induced by steady shear and its mechanistic relation with shear thinning are investigated in AsxSe100−x glasses (5≤x≤30) quenched from parent liquids subjected to shear rates ranging between 0 and 104 s−1 using polarized Raman spectroscopy and twodimensional x-ray diffraction.

When taken together, the results demonstrate significant shear-

induced partial alignment of –Se-Se-Se- chain moieties in the flow direction of the extruded fibers. This alignment is reminiscent of nematic liquid crystals where orientational order exists without positional order. The degree of this structural alignment in quenched glasses appears to be practically independent of the shear rate, although the parent liquids undergo shear thinning at the highest shear rates.

It is conjectured that any causal relationship between structural

alignment and shear thinning in the liquid may be masked in the glassy state by the postextrusion structural relaxation of the parent liquid.


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1. Introduction All glass forming liquids exhibit Newtonian behavior at low shear rate where viscosity, defined as the ratio of shear stress to shear rate / , remains independent of shear rate. At sufficiently high stress and shear rates on the other hand, the viscosity becomes dependent on shear rate and the glass-forming liquids start to exhibit non-Newtonian behavior, usually in the form of shear thinning i.e. viscosity decreases with increasing shear rate.1-9 Such high stress and shear rate may be encountered in a wide range of industrial processing techniques including extrusion, injection molding and even fiberization. Structural changes in the liquid during such processing under high shear rate may affect the physical properties of the resulting glass product. At the same time, such structural changes must also be linked to the atomistic mechanism of shear thinning of the liquid. The liquid in the non-Newtonian regime may in fact explore structural configurations in its potential energy landscape that it would not explore otherwise in equilibrium, in the Newtonian regime. It must be noted in this regard that a variety of shear flow induced structural transitions including phase separation and eventual crystallization have indeed been reported in complex fluids, including liquid crystals and polymer solutions, as well as in inorganic glass-forming network liquids.3, 10-14 Therefore, an understanding of the high shearrate induced structural changes in glass-forming liquids is of great importance, not only in the optimization of the processing parameters in industry, but also in the fundamental understanding of the rheology of glass-forming liquids and glass transition. In the case of polymeric liquids shear thinning results from disentanglement of chain molecules due to their alignment in the flow direction under strong shear.15-16 On the other hand, shear thinning in particulate suspensions or emulsions may be controlled by one or more of the following processes: (i) deagglomeration of particles, (ii) axial alignment of particles with high



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aspect ratio, and (iii) breaking and size diminution of droplets in emulsions. Shear-induced structural ordering in the form of layering or string-like structures has been observed even in hard sphere liquids and colloidal suspensions.17 However, their mechanistic connection to shear thinning has recently been questioned.18

In contrast, little is known about shear-induced

structural changes in inorganic glass-forming liquids and their effect on shear thinning. Stress induced structural anisotropy has, however, been reported in inorganic glasses. For example, in a recent study Kaseman et al. reported alignment of -Se-Se-Se- chain moieties in uniaxially compressed Ge5Se95 supercooled liquid using one- and two-dimensional (2D)

77

Se nuclear

magnetic resonance (NMR) spectroscopy.19 A similar behavior of chain alignment in extruded metaphosphate glass fiber was also confirmed by Jäger et al. via 2D

31

P NMR spectroscopy.20

Yannopoulos et al. utilized polarized Raman spectroscopy to study structural “micro-ordering” in As2S3 glass fibers pulled under photoinduced fluidity condition.21 Although these studies demonstrated the existence and the nature of stress induced structural anisotropy in glassforming liquids, they did not explore to what extent such anisotropy is related to the flow behavior of the liquid. On the other hand, Brückner and coworkers reported an increase in the birefringence of metasilicate, metaphosphate and float glass with a concomitant decrease in viscosity as a function of compressive/tensile stress.22 The change in birefringence was ascribed to the formation of oriented flow units during the flow process. More interestingly, the metasilicate and metaphosphate glasses with chain-like structural moieties experienced a larger increase in birefringence than float glass that has a crosslinked network structure. This result implies a stronger tendency of the formation of structural anisotropy in structures with long chain segments. Yet, this study did not directly address the exact nature of the structural change under shear or its connection with the observed non-Newtonian behavior.


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Similar to oxide liquids, shear thinning behavior has also been reported, albeit relatively recently, in chalcogenide liquids.1-2,

5, 23-24

In the present work, we report the results of a

systematic study, based on polarized Raman spectroscopy and two-dimensional X-ray diffraction (2D-XRD), of the nature and extent of shear-induced structural changes in AsxSe100−x (5≤x≤30) glasses obtained via extrusion of the corresponding liquids at various shear rates in both the Newtonian and the non-Newtonian regime. As x varies from 5 to 30, the structure of these glasses transforms from one dominated by long selenium chains occasionally cross-linked by AsSe3 pyramids to one dominated by a three-dimensional corner-sharing network of AsSe3 pyramids with a small fraction of -Se-Se-Se- chains. This wide variation in the topology and connectivity provides an interesting opportunity to explore their effects on the structural mechanism behind the non-Newtonian behavior of chalcogenide glass-forming liquids.

2. Experimental 2.1 Sample Synthesis and Thermal Characterization AsxSe100−x glasses with x = 5, 10, 20 and 30 were synthesized in a 90 g batch via the typical melt-quench method. Constituent elements with ≥99.999% purity (metal basis) were melted in an evacuated fused quartz ampoule in a rocking furnace at 650°C for more than 24 hours to ensure homogeneity, followed by water quenching of the ampoule. The absence of crystalline phase was confirmed using powder X-ray diffraction. The samples were then remelted in a twin-bore capillary rheometer (Malvern Rosand RH2000) with a bore diameter of 9.5mm and equilibrated at a temperature corresponding to a Newtonian viscosity of approximately 103 Pa·s. The melts were subsequently extruded through a die (0.75mm diameter)



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at steady shear rates ranging between 50 s−1 and 104 s−1 during viscosity measurements in the rheometer. For each measurement, the piston was advanced at a constant speed corresponding to the desired shear rate while simultaneously monitoring the pressure at the entrance of the capillary with a transducer, as a function of time and piston speed.

The shear rate is

determined from the piston speed Vb as:

=

bore radius and Vb is the piston speed.

Details of the experimental setup and the viscosity

measurements can be found elsewhere.2

, where R is the radius of the die, Rb is the

Extruded fibers of diameter 0.75 mm were air-

quenched and collected for further characterization. Heat capacity measurements were carried out on these glass samples over a temperature range of ±50 K around the glass transition temperature Tg using a differential scanning calorimeter (Mettler Toledo DSC1 STAR) to determine their fictive temperature Tf using the equal-area method of Moynihan and coworkers.25 Sapphire single crystal was used as a heat-capacity standard for these measurements and a scanning rate of 10 K/min was used.

2.2. Raman spectroscopy Unpolarized Raman spectra were collected using a Bruker RFS 100/S Fourier transform Raman spectrometer in a backscattering geometry at ambient temperature. The spectrometer is equipped with an Nd:YAG laser operating at 1064 nm and a liquid nitrogen cooled solid-state Ge detector. The bulk glass samples were crushed and pelletized while the fibers were cut and packed densely onto the sample holder with double-sided tape.

All unpolarized Raman

spectroscopic measurements were performed using a laser power of 30 mW and a resolution of 3 cm-1. 64 scans were taken and averaged for all spectra. 6 ACS Paragon Plus Environment

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The polarized Raman spectra of As5Se95, As10Se90 and As30Se70 glasses were collected in VV and VH configuration using a Horiba LabRam Evolution HR Micro-Raman spectrometer in a backscattering configuration. The spectrometer utilizes a Nd:YAG laser operating at 1064 nm and a liquid nitrogen cooled IGA detector. All polarized spectra were performed using a laser power of 25 mW, x10 microscope objective, 3min exposure time, and a resolution of 1.8 cm-1. For each composition measurements were carried out on the unsheared bulk glass sample and fibers extruded at steady shear rates of 100, 1000 and 10000 s−1 that approximately correspond for these materials to the Newtonian regime, the onset of shear thinning and well within the nonNewtonian regime of shear thinning, respectively (Fig. 1).2

Fiber samples were aligned

perpendicular to the incident light with the plane of polarization aligned to be parallel to the extrusion direction.

2.3. 2D Synchrotron X-ray Diffraction 2D-XRD experiments were carried out on As10Se90 and As20Se80 fibers extruded at the highest shear rate of 104 s−1 to investigate the feasibility of this technique in identifying structural anisotropy in sheared liquid/glass. Experiments on a more extensive set of samples are currently underway and will be reported in a future publication. The 2D-XRD data were collected on beamline 12.2.2 at the Advanced Light Source in the Lawrence Berkeley National Laboratory. This beamline benefits from hard x-rays generated by a superconducting bending magnet and focused by a set of brightness preserving optics to a 10 µm x 10 µm spot at the sample position.26 An x-ray wavelength of 0.41327 Å (30 keV) was selected using a Si(111) double bounce monochromator. A CeO2 standard was used to calibrate the sample to detector distance using the



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FIT2D software package.27 Data were collected from both samples with the fibers oriented parallel to the plane of polarization of the incident X-ray beam. An exposure time of 120 s was found to be sufficient to obtain data with adequate signal to noise ratio. The diffraction patterns were unrolled using the cake feature in the FIT2D software. Starting and ending azimuths of 31o and −31o were selected in order to avoid including the area of reduced intensity caused by absorption by the backstop mount.

3. Results and Discussion The measured heat capacity Cp of the bulk (unsheared) glass and sheared fiber samples is used to determine the Tf using the relation proposed by Moynihan and coworkers:25

∗ − = ∗ −

(1)

where T* is a temperature well above Tg, T' is a temperature well below Tg and Cpe and Cpg are the heat capacities of equilibrium supercooled liquid and glass, respectively. This procedure is demonstrated in Fig. 2 where the representative Cp data for the bulk As20Se80 glass and for the corresponding fiber extruded at a shear rate of 104 s−1 are plotted against temperature. According to Eqn.1, Tf can be determined from Cp(T) plots by simply matching the two shaded areas that represent the two integrals on either side of Eqn. 1 as is demonstrated in Fig. 2. The Tf thus determined for both the bulk glass and the corresponding fibers extruded at the highest shear rates for all four compositions are listed in Table 1. It is clear from Table 1 that the Tf for a specific composition does not change significantly between the unsheared bulk glass and the extruded fiber. This result eliminates the possibility of any thermal history induced differences between the two kinds of glass samples. This hypothesis is corroborated by the strong similarity 8 ACS Paragon Plus Environment

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between the unpolarized Raman spectra of the bulk and fiber samples of these glasses (Fig. 3), which suggests that the directionally averaged structure of these glasses remains unaltered upon quenching from their parent melts even when they are subjected to rather high shear rates that are well inside the non-Newtonian regime. However, the compositional evolution of the structure of these glasses can be clearly observed in these unpolarized Raman spectra. The intensity of the A1 symmetric stretching mode of the selenium chain moieties near 250 cm-1 decreases with increasing As content, while that of the symmetric intra-pyramid As-Se stretching mode of the AsSe3 pyramidal units at ~ 220 cm-1 increases, indicating a progressive cross-linking of selenium chains with AsSe3 pyramids.28 In contrast with the spatially and directionally averaged structural information available from the unpolarized Raman spectra, analysis of the polarized Raman spectra allows for probing of the presence and extent of any shear-induced orientational order in these glasses. The VV and VH polarized Raman spectra of the unsheared bulk glass and of the fibers extruded under different shear rates for As5Se95, As10Se90 and As30Se70 compositions are shown in Fig. 4. While the shapes of the VV spectra for each composition remain almost identical between different shear rates, the shapes and intensities of the VH spectra relative to the VV spectra changes, which implies a concomitant change of depolarization ratio ρ = IVH/IVV, where IVH and IVV are the intensities of the VH and VV spectra, respectively. In general, ρ for a vibrational mode is a measure of the symmetry of the polarizability tensor of the associated structural moiety and, consequently, any orientational order in the latter can be probed by measuring ρ as a function of sample orientation (see below). Here we focus on the shear rate dependence of ρ for the two major bands at ~ 250 and 220 cm−1, corresponding to the symmetric stretching modes of the selenium chain and the AsSe3 pyramidal moieties, respectively, in these glasses. Since the high9 ACS Paragon Plus Environment


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frequency band in the Raman spectra of these glasses contains overlapping contributions from multiple bands, it was fitted with four Gaussian peaks at ~220 cm−1, 235 cm−1, 250 cm−1 and 268 cm−1 (Fig. 5), in order to isolate the ρ for the two major bands for various compositions and shear rates. It may be noted here that the constituent bands near 235 and 267 cm−1 are likely composite in nature, containing contributions from both Se-Se and As-Se stretching in chain and pyramidal units, respectively. However, the 235 cm−1 band primarily corresponds to Se-Se stretching in selenium chain moieties with strong inter-chain interaction, while the 268 cm−1 band arises from the bridging As-Se-As inter-pyramid asymmetric stretching modes, respectively.29,30 The variation of ρ with shear rate for the 250 cm−1 band is shown in Fig. 6 for As5Se95, As10Se90 and As30Se70 glasses. Interestingly, in comparison with the unsheared bulk glass, the sheared glass fibers are always characterized by a significantly smaller ρ. This lowering of ρ can be linked to a shear-induced partial alignment of the associated structural moieties in the extruded fibers along the direction of shear. For example, the symmetric stretching mode of the Se-Se-Se- chain segment (i.e. the 250 cm−1 band), which is similar to a uniaxial cylindrical molecule, has a polarizability tensor where the off-diagonal elements are much smaller than the diagonal elements. In an idealized case where the off-diagonal elements are all zero and the diagonal elements are α1, α2 and α3, the depolarization ratio is expressed as 〈 !"#$"(&' (& )* 〉

' ! ",& #$ ") 〉

= 〈(&

(2)

where α1 and α3 are the diagonal tensor elements in the laboratory frame and θ is the angle between the z axes of the laboratory and the molecular frames. The depolarization ratio ρ reaches 10 ACS Paragon Plus Environment

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its minimum value of zero when θ = 0°, i.e. the z axis of the tensor coincides with the electric field of the incident laser beam. Any deviation or randomization from this perfect alignment would result in an increase in ρ. Therefore, the lowering of ρ in the sheared glass fibers (Fig. 5), when these fibers are aligned with the plane of polarization of the incident light, can be explained by the appearance of structural anisotropy in the form of shear-induced partial alignment of selenium chain fragments. A lowering of ρ has also been reported in previous studies on other systems such as stretched polymer films and organic monolayers where it was related to the formation of unique structural anisotropy compared to their randomly distributed amorphous counterparts.31-33 However, it is important to note that, despite the difference in ρ between the unsheared bulk glass and sheared fibers, there is no significant variation of ρ as a function of shear rate in the latter (Fig. 6). As noted earlier, there is a clear relation between the viscosity and the shear rate and the shear rates of 100 s−1, 1000 s−1 and 10000 s−1 in these AsxSe100−x liquids correspond to the Newtonian region, onset to non-Newtonian flow and the non-Newtonian region, respectively. Therefore, the lack of any significant variation of ρ with shear rate in extruded AsxSe100−x fibers may be interpreted to suggest that the shear-induced alignment of structural moieties in these liquids may not be mechanistically related to shear thinning.

However, it can also be argued that the degree or extent of alignment of the structural

moieties in the extruded fibers is limited by the post-extrusion structural relaxation of the liquid before it is quenched to the glassy state. Finally, the variation of ρ with shear rate for the 220 cm−1 band is shown in Fig. 7 for the As30Se70 composition, where the intensity of this band corresponding to the symmetric As-Se stretch of AsSe3 pyramids becomes strong enough to reliably estimate its depolarization ratio. Unlike the 250 cm−1 band, the ρ of the 220 cm−1 band does not show any significant variation with shear rate (Fig. 7). Although it is tempting to 11 ACS Paragon Plus Environment


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interpret this result as an indiactor of the lack of alignment of AsSe3 pyramidal units in the structure, further fiber-orientation dependent polarized Raman studies are needed to test the validity of this hypothesis. The raw 2D-XRD patterns collected from the As10Se90 and As20Se80 glass fibers extruded at the highest shear rate of 104 s−1 and oriented horizontal and parallel to the plane of polarization of X-ray are shown in Fig. 8. X-ray scattering from amorphous materials usually produces a series of smooth and diffuse but continuous rings with intensities that are independent of the azimuthal angle, which is indicative of the absence of any positional and orientational structural order. Although the diffraction patterns in Fig. 8 can be seen to contain these diffuse rings, the ring intensities are not constant along the ring but show periodic maxima and minima including diffuse arcs near the poles (Fig. 8a). The unrolled patterns (Fig. 8b) make this visualization easier and show that all of the diffuse scattering rings are characterized by periodic sections of high and low scattering. Due to the different intensities of the rings and the small amplitude of the periodic scattering, it is difficult to show the intensity variation adequately for each ring in a single image; an annotated version of Fig. 8b (Fig. 8c) marks the location of these maxima in each ring. These x-ray scattering patterns are similar to those reported from systems containing strongly aligned molecules such as DNA, stretched polymer films or liquid crystals with nematic or orientational molecular ordering.34-37 Location of the maxima in the diffraction rings on the equator of the scattering patterns gives a Hermans-Stein orientation factor close to 1 for the aligned moieties.36,37 It should be noted that the periodic scattering in each ring is only a small proportion of the total scattering intensity and hence, diffraction is still dominated by the general positional and orientational disorder of the amorphous state. Therefore, the results presented in Fig. 8 imply the presence of significant orientational order for a fraction of structural moieties in 12 ACS Paragon Plus Environment

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these extruded fibers, parallel to the fiber axis. When taken together, the results from 2D-XRD and Raman spectroscopy provide unequivocal evidence in favor of shear-induced orientational ordering of structural moieties such as -Se-Se-Se- chain fragments parallel to the direction of flow in the extruded AsxSe100−x fibers. This orientational order in the absence of positional order is strongly reminiscent of nematic ordering observed in liquid crystals.

4. Conclusions The polarized Raman spectra and 2D-XRD patterns of extruded AsxSe100−x (5 ≤ x ≤30) glass fibers provide unequivocal evidence of shear-induced structural anisotropy in the form of significant, nematic-like, orientational ordering of –Se-Se-Se– chain moieties. Such structural changes are not accompanied by any change in the fictive temperature. These results indicate that glass-forming liquids under steady shear explore rather unique configurations in the potential energy landscape. However, measurements on fibers quenched from the parent liquid subjected to a wide range of shear rates in the Newtonian and the non-Newtonian regime do not display significant change in the degree of structural anisotropy. Hence, one possibility is that shear thinning in these liquids may not have any causal relationship with the observed alignment of structural moieties. On the other hand, it is also possible that the extent of the structural alignment that can be quenched in the glassy state is limited by the post-extrusion loss of such alignment during the structural relaxation of the parent liquid, before it enters the glassy state.



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Acknowledgments This work was supported by a GOALI grant from the National Science Foundation (NSF-DMR 1505185). The authors wish to acknowledge the assistance of Sara Cole in the collection of polarized Raman spectra. Advanced Light Source is supported by the Department of Energy under contract no. DE-AC02-05CH11231.


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(21) Kastrissios, D. T.; Papatheodorou, G.; Yannopoulos, S., Vibrational modes in the athermally photoinduced fluidity regime of glassy As2S3. Phys. Rev. B 2001, 64, 214203. (22) Habeck, A.; Brückner, R., Direct connection between anisotropic optical properties, polarizability and rheological behaviour of single-phase glass melts. J. Non-Cryst. Solids 1993, 162, 225-236. (23) Zhu, W.; Aitken, B.; Sen, S., Communication: Non-Newtonian rheology of inorganic glass-forming liquids: Universal patterns and outstanding questions. J. Chem. Phys. 2017, 146, 081103. (24) Wang, S.; Jain, C.; Wondraczek, L.; Wondraczek, K.; Kobelke, J.; Troles, J.; Caillaud, C.; Schmidt, M. A., Non-Newtonian flow of an ultralow-melting chalcogenide liquid in strongly confined geometry. Appl. Phys. Lett. 2015, 106, 201908. (25) Moynihan, C. T.; Easteal, A. J.; BOLT, M. A.; Tucker, J., Dependence of the fictive temperature of glass on cooling rate. J. Amer. Ceram. Soc. 1976, 59, 12-16. (26) Kunz, M.; MacDowell, A. A.; Caldwell, W. A.; Cambie, D.; Celestre, R. S.; Domning, E. E.; Duarte, R. M.; Gleason, A. E.; Glossinger, J. M.; Kelez, N. et al. A beamline for highpressure studies at the Advanced Light Source with a superconducting bending magnet as the source. J. Synchrotron Radiat. 2005, 12, 650-658. (27) Hammersley, A.; Svensson, S.; Hanfland, M.; Fitch, A.; Hausermann, D., Twodimensional detector software: from real detector to idealised image or two-theta scan. High Press. Res. 1996, 14, 235-248. (28) Yang, G.; Bureau, B.; Rouxel, T.; Gueguen, Y.; Gulbiten, O.; Roiland, C.; Soignard, E.; Yarger, J. L.; Troles, J.; Sangleboeuf, J.-C. et al. Correlation between structure and physical properties of chalcogenide glasses in the AsxSe1-x system. Phys. Rev. B 2010, 82, 195206/1-8. (29) Li, W.; Seal, S.; Rivero, C.; Lopez, C.; Richardson, K.; Pope, A.; Schulte, A.; Myneni, S.; Jain, H.; Antoine, K., Role of S∕ Se ratio in chemical bonding of As–S–Se glasses investigated by Raman, x-ray photoelectron, and extended x-ray absorption fine structure spectroscopies. J. Appl. Phys. 2005, 98, 053503. (30) Lucovsky, G.; Martin, R. M., A molecular model for the vibrational modes in chalcogenide glasses. J. Non-Cryst. Solids 1972, 8, 185-190. (31) Voyiatzis, G.; Petekidis, G.; Vlassopoulos, D.; Kamitsos, E. I.; Bruggeman, A., Molecular orientation in polyester films using polarized laser Raman and Fourier transform infrared spectroscopies and x-ray diffraction. Macromolecules 1996, 29, 2244-2252. (32) Liu, Y.-C.; McCreery, R., Raman spectroscopic determination of the structure and orientation of organic monolayers chemisorbed on carbon electrode surfaces. Anal. Chem. 1997, 69, 2091-2097. (33) Zhao, J.; McCreery, R. L., Polarized Raman spectroscopy of metallophthalocyanine monolayers on carbon surfaces. Langmuir 1995, 11, 4036-4040. (34) Collins, B.A. et al., Polarized x-ray scattering reveals non-crystalline orientational ordering in organic films. Nat. Mater. 2012, 11, 536-543. (35) Fan, Z.X.; Chiang, L.Y.; Haase, W., X-ray diffraction study on liquid crystals from 4hexylphenyl 4-cyanobenzoyloxybenzoate and 4-heptyloxyphenyl 4-cyanobenzoyloxybenzoate. Liq. Cryst., 1995, 18, 13-19. (36) Hermans, P., Physics and chemistry of cellulose fibres. Elsevier (New York) 1949. (37) Stein, R. S.; Norris, F. H., The x‐ray diffraction, birefringence, and infrared dichroism of stretched polyethylene. J. Polym. Sci. 1956, 21, 381-396. 16 ACS Paragon Plus Environment

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Table 1. Fictive temperatures of unsheared bulk glasses and corresponding fibers extruded at a shear rate of 104 s−1. Composition

Unsheared glass (±2°C)

Extruded fiber (±2°C)

As5Se95

50.6

52.6

As10Se90

67.5

64.8

As20Se80

99.9

100.9

As30Se70

125.7

128.0



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Figure 1. Shear rate dependence of viscosity for the four AsxSe100−x liquids, as reported in Reference [2].


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Figure 2. Representative heat capacity vs. temperature curves for the unsheared bulk As20Se80 glass (top) and corresponding fibers extruded at a shear rate of 104 s−1 (bottom). The dashed lines are extrapolated from the glass and liquid heat capacities and the vertical line indicates the Tf. The fictive temperature, which is marked by the vertical solid line, is determined by matching the two shaded areas. The curves are offset for a clear demonstration.



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Figure 3. Unpolarized Raman spectra of the unsheared bulk AsxSe100−x glasses (red lines) and corresponding fibers extruded at a shear rate of 104 s−1 (black lines). The glass compositions are listed alongside each spectrum.


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Figure 4. Polarized VH (red) and VV (black) Raman spectra of unsheared bulk AsxSe100−x glasses and corresponding fibers extruded at different shear rates indicated alongside each spectrum. (a) As5Se95. (b) As10Se90. (c) As30Se70.



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Figure 5.

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Representative simulation (red dashed line) of the high-frequency band in the

experimental polarized (a) VV and (b) VH Raman spectra (solid black line) of unsheared bulk As30Se70 glass. Individual Gaussian simulation components are shown in teal, blue, green and purple.


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Figure 6. Shear rate dependence of the depolarization ratio IVH/IVV of the 250 cm−1 band for As5Se95 (squares), As10Se90 (circles) and As30Se70 (inverted triangles) glasses.



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Figure 7. Shear rate dependence of the depolarization ratio IVH/IVV of the 220 cm−1 band for As30Se70 glass.


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Figure 8a. Raw 2D-XRD patterns of As10Se90 (left) and As20Se80 glass (right) fibers extruded at 104 s−1 shear rate. Fiber orientation is horizontal and parallel to the plane of polarization of X-ray.



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Figure 8b.

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Unrolled 2D-XRD patterns of As10Se90 (left) and As20Se80 glass (right) fibers

extruded at 104 s−1 shear rate showing intensity variation with scattering and azimuthal angles.


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Figure 8c. Same as in Fig. 7b except with scattering maxima highlighted.

Note periodic

variation in intensity with azimuthal angle implying structural anisotropy, superimposed on constant intensity (along azimuth) pattern corresponding to isotropic disorder.



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TOC Graphics


Observation of Steady Shear-Induced Nematic Ordering of Selenium

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