Crystal Growth Alignment of Î²-Polymorph of Resorcinol in Thermal

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Crystal growth alignment of beta polymorph of resorcinol in thermal gradient Piyush Panini, Basab Chattopadhyay, Oliver Werzer, and Yves Geerts Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b00143 • Publication Date (Web): 29 Mar 2018 Downloaded from http://pubs.acs.org on March 30, 2018

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Crystal Growth & Design

Crystal growth alignment of beta polymorph of resorcinol in thermal gradient Piyush Paninia, Basab Chattopadhyaya, Oliver Werzerb, Yves Geertsa* a

Laboratoire de Chimie des Polyméres, Faculte des Sciences, Université Libre de Bruxelles (ULB), CP 206/1, Boulevard du Triomphe, 1050 Bruxelles, Belgium. Email: [email protected] b

Institute of Pharmaceutical Sciences, Department of Pharmaceutical Technology, University of Graz, Universitätsplatz 1, 8010 Graz, Austria.

Supporting Information ABSTRACT: Crystallization of an organic compound, namely resorcinol, has been studied in a thermal gradient over a substrate where samples are, in addition, mechanically displaced at a constant rate. In such an experiment, nucleation and growth occur in well-defined dissipative conditions. The results show the capability of this method to produce thin films in the resorcinol β-form. Further, the alignment of the crystals within these films is along a preferred orientation. Employing polarized optical microscopy and X-ray diffraction measurements in terms of specular diffraction and pole figures shows that the crystals alignment follows the thermal gradient. Variation of the displacement rate, i.e. the sample velocity in the gradient field, shows additionally strong variation of the crystal orientations, showing that the kinetic of the crystal formation is crucial for the alignment in the thermal gradient.

Study of crystal structures of organic compounds is essential in scientific research since their physical, chemical and electronic properties derive from their molecular arrangements 1, 2 in the solid state . Polymorphism of molecular solids is defined as the occurrence of more than one type of crystal 3 packing of a specific chemical compound . Distinct polymorphs have typically different properties such as density, 3 4 solubility, bioavailability , superconductivity, magnetism or 5 optical properties while being chemical identical. Hence identification, characterization, stabilization and reproducible production of specific polymorphic forms of a compound are essential for industrial processes or fundamental research. In general, the control of the polymorphism of an arbitrary chemical is still very weak and it remains an unresolved scientific question. It remains up to now a topic of continuous discussions among research communities with a significant number of publications over past decade trying to 6, 7 identify a general valid theory . In recent years, there are growing evidences that the crystallization of organic compounds over a solid surface which can lead to stabilization of one particular polymorphic phase or even can lead to the

formation of new polymorphs, termed as substrate induced 8 phases (SIPs) . Among the many ways of crystallization, zone solidification offers an elegant way to crystallize a material under defined dissipative conditions otherwise hardly 9-12 achievable . The method itself is primarily used to crystallize metals along a thermal gradient wherein crystal growth rates are nearly equal to their displacement rate through the thermal gradient field. Surprisingly, this method of crystallization that decouples nucleation from growth is rarely used for organic compounds, except for zone refining or purification. Organic compounds behave differently from metals in many respects and especially in crystallization where the less symmetric unit cells and much lower anisotropic thermal 13 conductivity might be addressed to this behavior . Nevertheless, we could recently adopt a thermal gradient method for an organic compound. With this we could achieve uni-axially crystal alignment together with a selective stabilization of 14 one polymorphic form during crystallization . From the previous work one might conclude or even hypothesize that the lack of control of polymorph selection for many systems results often from ill-defined or ill-controlled 9, 10 non-equilibrium thermodynamic conditions . Hence we aim to understand the effect of the non-equilibrium dissipative condition on the crystal growth of organic compounds. By employing the thermal gradient methods the nonequilibrium condition can be controllably adjusted and its impact studied. In many other experiments this is hardly possible. In the current work, the crystallization of model substance resorcinol in a thermal gradient over a glass substrate has been performed. The role of molecular and crystal structure of the compound, thermal gradient magnitude, growth rate and polymorphism in the formation of preferably oriented or aligned thin film have been investigated using polarized optical microscopy, X-ray diffraction measurement 15 and pole figure analysis . Resorcinol occurs in three polymorphs at atmospheric pres16-20 sure, classified as α, β and recently observed, ε- resor21 cinol [see ESI]. These forms have been well studied in the 16-25 literature . Crystallization of resorcinol from melt provides β and ε- polymorphs wherein ε- resorcinol is obtained only

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ing solidification a defined solid film results, which was monitored by polarized optical microscopy (POM) in-situ. After crystallization, the samples are dismounted and careful removal of the upper glass slide allowed then further analysis using X-ray diffraction measurements. Further details about materials, experiments and instruments are provided in the supporting information. In short, the initial bulk material is observed to be purely consisting of α-form of resorcinol (see ESI). Results from DSC [Fig. S4] and PXRD [Fig S6 -S7] experiments confirm the phase transition at 100°C from the bulk phase of resorcinol (which is α – form) to another phase and it remains unchanged during the subsequent heating cycle. In the literature, irreversible phase transition from α-form to β–form of resorcinol above 98°C is 25 very well documented . Figure 1. Schematic representation of the thermal gradient (∇T) experimental setup. in the presence of an additive. Furthermore, it was established recently that there exists asymmetric growth along polar axis i.e. +c or –c – axis in case β – form wherein growth 21 along {011} was observed to be faster than {01 -1} . These characteristics in the crystallization of polymorphs of resorcinol are a selection criterion of this compound here, wherein the role of thermal gradient in this asymmetric growth along the polar axis can be controlled precisely. Thermal gradient experiments were performed with an LINKAM GS350 setup which is schemed in Figure 1. It consists of two independent heating stages which are controlled separately using individual temperature controllers. These stages are separated by a defined gap of 2.5mm to obtain a well-defined temperature gradient field in between them. For a crystallization experiment, one stage is set at a temperature Th, well above the melting temperature of resorcinol (hot side) while the other is set below the crystallization temperature, Tc (cold side). The sample is first placed over the hot side until the sample is completely melted. Then the sample is translated towards the cold side with a constant speed [termed as “sample velocity (v)”], thus eventually leading to crystallization of the compound at a certain point. For sake of easier sample movement between the two sides/plates 3 during the experiment, a 76 x 26 x 1 mm microscopic glass slide is positioned between hot/cool stage and the sample [c.f. Fig. 1]. For a single thermal gradient (∇T) experiment, about 3-4 mg of resorcinol was deposited onto cleaned glass substrate located on the hot plate side and melted. Another identical glass slide was then carefully placed onto the melt ensuring the melt uniformly distributes. The sample which was initially located only on the hot side was then slowly translated towards the cold side at a constant velocity. Dur-

POM images of solids obtained after melt crystallization over a glass slide and sandwiched between two glass slides before the thermal gradient experiment are shown in figure S9 in ESI. In first case [Fig. S9(a)], spherulites growth is observed whereas crystallization between two sandwiched glass slides [Fig. S9(b)] demonstrates randomly oriented small crystals. Comparison of PXRD patterns [Fig. S10] of such samples, with that of an ideal powder consisting of resorcinol β – form confirms the solely presence of this form. Having many peaks present in a pattern typically means that a powder like arrangement exists with spatial random crystalline arrangement. As there is a deviation of the peak intensities between those of an ideal powder and our results this means that a partial preferred orientation of the 200 planes (peaks for 120 and 111 planes are also missing) exists. Hence, this may be the intrinsic property of β-resorcinol and commonly observed for 26 27 many other substances including paracetamol , ibuprofen amongst many others. The effect of the thermal gradient in directional crystallization of β – form of resorcinol has been studied by varying the velocity and a list of all experiments is provided in Table 1. According to DSC experiments, the melting point of β – form of resorcinol is 109°C whereas crystallization was observed only below 45°C. Hence for all the ∇T experiments, hot stage temp (Th) was set at 120°C while cold stage temp (Tc) was at 30°C. The magnitude of thermal gradient (∇T) was determined using a reference compound. This is important, as the actual gradient typically deviates from those expected from simple slab geometry due to the complex setup. Employing the compound C8-BTBT-C8 under similar experimental conditions the gradient value (∇T) was determined to be 7.2 °C/mm [Fig. S8]. This value was kept identical for all experiments. The sample was then moved under constant velocity, v, from the hot to cold region. Using v in the range from 5 μm/s to 100 μm/s this sets cooling rates ranging from 2.16°C/min to 43.2 °C/min (see Table 1).

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Figure 2. (a) In-situ polarized optical microscopy (POM) image of a sample hosted between two glass slides during a thermal gradient experiment at speed 25μm/sec. Blue arrow indicates the direction of crystal growth. The thermal gradient and sample velocity (v) coincide and are indicated by the colored arrow. (b) Specular X-ray diffraction and (c) grazing incidence X-ray diffraction patterns obtained as well as an X-ray diffraction pole figure measurement (d) for the sample crystallized using the gradient technique. Illustrations of the corresponding (e) derived orientation 1 versus substrate and (f) top view alignment 1 along the thermal gradient (∇T). Diagrams for other velocities (v) are presented in ESI.



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Figure 3. (a) POM image of sample prepared by ∇T experiments with velocity (v) = 75μm/sec and its corresponding (b) out-ofplane/specular-XRD and (c) GIXD measurement patterns along with (d) pole figures measurement for {110} set of planes (others are presented in ESI) . Schematic representations of (e) orientation 2 versus substrate and (f) alignment 2 along the thermal gradient ∇T (Top view). Diagrams for other velocities (v) are presented in figures S13 - S14. The small bump after the intense peak at 2θ = 14.3° in s-XRD is an instrumental artifact.


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All the samples were analyzed using different techniques including POM and X-rays. The results reveal two distinct behaviors in terms of crystal alignment (see Table 1) in the ∇T. These two cases are discussed in detail in the following. In Figure 2 the various results of an exemplarily sample, prepared at v = 25 μm/sec, is shown. The image displays the formation of unidirectional homogenous crystalline domains which extend over large distances exceeding even mm size. The morphology of this but also of all the other samples crystallized in the thermal gradient appears strongly altered when compared to samples crystallized without (c.f. S9). Similar morphological results are obtained for samples crystallized at other speeds (Figs. S11-S16). Surprisingly the crystal growth front direction is inclined so that it is not parallel to the ∇T – field. An angle of 30° is observed for the sample shown in Figure 2a. Repeated measurements using the same velocities show that inclinations vary from sample to sample from 15 - 40°. Such a diagonal growth is usually not observed upon crystallization in thermal gradient. For example, in case 14 of terthiophene and also for the reference compound C8BTBT-C8, parallel growth with ∇T results [Fig. S8]. To gain further insight into the crystallographic orientation of the samples various X-ray diffraction techniques were applied. Specular X-ray diffraction experiments were performed to determine the plane which is in contact with the substrate (glass) surface. In Fig. 2b the results of the sample prepared at 25µm/s is shown. Over the entire measurement range from 10 - 30° the pattern reveals one peak at 22.5°. From a comparison with the powder pattern of the α and β form, it follows that this sample consisted of resorcinol in its β form. Further, a single peak in such a scan strongly suggests that these crystals contact the glass only with their 200 planes, hence displaying the presence of a prefered orientation (termed hereafter as “orientation 1” in the manuscript) with respect to the substrate plane. While a specular scan allows judging the texture there is no way to allow deciding for the alignment in other directions. To gain more information on the preferred orientation with respect to the thermal gradient field (or velocity direction), two additional measurements were performed. Grazing incidence X-ray diffraction (GIXD) measures net planes which are oriented perpendicular to the surface normal. In this measurement, the sample was placed over the diffractometer such that thermal gradient produced in the experiment (to prepare the thin film) remains parallel with incident X-ray and then in-plane measurement was performed by moving the detector along chi (χ) angle. The result is shown in Figure 2c, with one strong peak. This peak corresponds to the 011 net plane which verifies the 200 orientation. For selected samples also polefigures are measured [Figs. 2(d), S11-S12]. In such a measurement a single net plane distance is evaluat15 ed in term of its spatial directions . Setting the measurement for a strong peak like the 120 peak, this results in two poles (areas of high intensity) to be measured. These poles are located at the azimuthal direction of 80 and 260° and are inclined to the surface normal by about 50°. More importantly, from this measurement, the direction of the 011 peaks can be directly determined (see figure 2). These peaks are located in-plane, as already determined from GIXD, and are rotated by 30° off the temperature gradient directions. A comparison of the inclination angles from the POM results in Fig. 2a

shows that this agrees well with the fast-growing direction for the crystal in this very sample. This result may indicate the presence of (011) plane perpendicular to substrate i.e along with thermal gradient [Fig. 2(f)]. This is termed hereafter as “alignment 1” in the manuscript. This means that the unit cell is an upright standing direction with respect to the surface as indicated from Figure 3e. Hence in the orientation 1, as depicted in figure 3e, axis a of unit cell is being perpendicular to the substrate and the 100 plane lies parallel with substrate. This leads to the molecular plane of β-resorcinol being tilted with approximately 40° with the 100 plane i.e with substrate plane. In this orientation, either both of –OH groups or none are appeared to be pointed towards the substrate plane. Figure 2f depicts (viewed down the a-axis) the presence of 011 planes along the thermal gradient, along which crystal growth was observed. Using identical thermal gradient fields but with slower velocity (below and equal to 35μm/sec) reveals similar behavior but with the texture remaining either 100 [mostly observed; Figs S11 - S12], 020 or an intermixed (see Table 1 and ESI). This is independent on the velocity and happened on an arbitrary basis meaning that this process is stochastic. Nevertheless, other textures are not identified so that one might conclude that the gradient field impeded the growth when the contact plane is different. To demonstrate this distinct growth in more detail, another setup of the experiment is used. In this new experiment a polycrystalline sample containing the β – form is used as a seed. Typically, this should result in the many different directions growing simultaneously. But the results reveal different properties when analyzed with POM and s-XRD [Fig. S13]. It was observed that as soon as the sample starts moving towards the cold region in the thermal gradient field, crystals start growing, again diagonally with the direction of sample movement over the substrate [Fig. S13 (a)] The s-XRD pattern of this sample further also confirm about the preferential orientation of (200) and some 020 planes over the entire substrate. These results corroborate the fact that growth alignment is induced by the growth condition, i.e. the thermal gradient. Employing higher translation velocities, so that the crystal growth rate increased, results in the morphology remaining similar but with the crystallographic behavior being changed significantly which now explains the second situation often observed. The crystal growth front remains unchanged to those prepared from lower speeds. Exemplarily the sample prepared at speeds of 75µm/sec shows diagonal needle directions running multiple mm over the surface (c.f. Fig. 2a and Fig. 3a). The s-XRD measurements show that unlike the previous case, this sample prepared at higher speeds has changed its preferred orientation; now a 010 texture is present which we label as orientation 2 [see Fig (3b)]. As a consequence this means that the in-plane direction also changed. GIXD and pole figure show that now the 201 plane is in-plane [Fig 3(c)]. Further, this 201 plane is perpendicular to the gradient field or velocity direction [Fig 3(d)]. This means that this sample also has a uni-axially alignment but now with its direction being changed. As this behavior is distinct we label this as alignment 2 [Figs. 3(e) & 3(f)]. In this orientation, the longer b-axis of the unit cell as well as molecular plane is ob-



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served of being perpendicular with the substrate plane. Unlike the previous case, here, one of the –OH group is pointed towards substrate plane. Figure 3f shows the orientation of 201 planes, which are present parallel with the gradient field and perpendicular with substrate plane. The alignment 2 together with orientation 2 was exclusively observed when the speed exceeded 35µm/sec [Figs. S14 – S16]. At lower speeds some samples crystallized differently, i.e. orientation 1 alignment 1 [Figs. S11 & S12]. However, it can be concluded that when orientation 1 is found always the alignment 1 follows and for orientation 2 alignment 2 follows. A mixture of this situation like orientation 1 / alignment 2 or vise versa was never observed (see Table 1). Hence from the overall analysis of outcome, it was observed that resorcinol hesitates between orientation 1 and 2 upon crystallization in ∇T with sample velocity below and equal to 35μm/sec. However orientation 1 (with the alignment of (011) along ∇T) is often observed in this case with a minor tendency towards orientation 2. In case of sample velocity, v > 35μm/sec, orientation 2 is exclusively observed. Due to a higher rate, the undercooling at the growth front is probably larger and the system is driven further away from equilibrium, forcing it to choose exclusively orientation 2 along with alignment along (201) versus ∇T. Further, to get a better understanding of this phenomenon, we have calculated heat flux flowing across the sample at the growth front for both the cases of orientation 1 and 2 (Table S1). The details of the calculation are given in ESI. The total heat flux (Jtotal) is observed to vary linearly as a function of sample velocity (v) [Fig. S17]. Jtotal for orientation 2 was observed to be more than that for orientation 1 (Table S1). This means that the crystallization of β-resorcinol in orientation 2 releases more heat at the growth front than its crystallization in orientation 1. The difference between two values (∆Jtotal) was also observed to be increasing linearly when the sample was moving faster in ∇T [Fig. 4]. For the sample velocity, v > 35 µm/sec, the difference become more (greater than 75 W/m2) and hence sample prefer to crystallize in orientation 2 whereas, for slower velocities, it hesitates between the two orientations. The reason may lie in the fact that β – resorcinol does show the presence of partial preferred orientation of 200 planes (i.e. orientation 1) when crystallizes from the melt. Since for slower v, the value of ∆Jtotal is so much less that it does not always prefer to crystallize in orientation 2. Furthermore, the tilt angle of the growth direction with ∇T was appeared to vary randomly within a range from 15 to 70° which has no correlation with orientation or alignment preferences. This tilt angle at the crystal growth front of resorcinol may be due to the anisotropy of surface tension of the interfaces during crystallization. This behavior was also observed during thin-sample directional solidification of eutec28

tic alloys . We have at this stage no other explanation for these intriguing results. Moreover, in order to investigate the role of the substrate in the preferential growth of β – form by ∇T experiments, PDMS coated substrates were prepared [Fig. S18]. PDMS was selected because it is opposite in nature when it comes in contact with a liquid. For example, it is hydrophobic in

Figure 4. Plot of difference between heat flux for orientation 2 and orientation 1 (∆Jtotal) versus sample velocity (v). nature, related to water (due to the presence of methyl group) so that water does not wet the PDMS surface whereas 29 water wets hydrophilic glass surfaces . The melt of a polar molecule like resorcinol behaves similarly as water. As per expectation, melted does not wet the PDMS surface and remains as a solvent-like droplet over it. The thermal gradient (∇T) experiment of β – form over a PDMS coated substrate was performed with identical conditions as in case of bare glass substrates. A POM image of this sample shows again diagonal growth of crystal [Fig. S18(a)]. Further a preferential orientation of the (200) plane was found. Hence this result confirms that a preferential orientation of (200) plane of β – form is obtained in thermal gradient, irrespective of the nature of the substrate tested. This result appears to be constant for sample velocity ranging from v = 5μm/sec to 100 μm/sec. All the thin films were characterized by s-XRD, GIXD and pole figure measurements. Here the results show the presence of “orientation 1” and “alignment 1”, which means the 200 plane of β – form sits over the PDMS-coated substrate and 011 planes of crystallites are aligned along the ∇T. It was observed that PDMS coated substrate does not induce similarly growth as a glass substrate. For the entire velocity range, β-resorcinol prefers to crystallize in orientation 1, which is an intrinsic property of resorcinol. Orientation 2 was never found. The possible reason may be the difference in wetting property of melt-resorcinol when in contact with PDMS coated substrate compared with merely glass substrate. The role of wetting in the crystallization of 30 thin film is very well established . Moreover, the role of hydrogen bonding with the substrate cannot be ruled out which is not possible with PDMS surface due to the presence of bulky methyl group. Selection of one preferred orientation may be the resultant of many effects like magnitude of thermal gradient, sample movement, wetting, intrinsic nature of material and hydrogen bonding or other forces, which are acting simultaneously during the ∇T experiment. It is of interest to relate the molecular packing and hydrogen bonding in β –form of resorcinol with the two orientations (1 and 2) which were observed upon crystallization of resorcinol in ∇T. It is to be noted that there are two sets of hydrogen bond present in the crystal structure of β –form (space


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group: Pna21). One strong O-H…O hydrogen bond along caxis utilizing 21-screw whereas another consists of a strong O-H…O hydrogen bond along with weak C-H…O hydrogen bond, utilizing n - glide normal to a-axis or parallel with 011 plane [Fig. 5]. In orientation 1, it was observed that the crystallographic a-axis is perpendicular with the substrate plane i.e. bc plane (100) is parallel with the substrate and crystal growth in ∇T along {011} is observed to be normal with substrate plane. In figure 5(a), packing of molecule parallel with the substrate plane i.e. bc plane (viewed along the a-axis) has been depicted. It is observed that strong OH…O hydrogen bond along with weak C-H…O hydrogen bond leads to the formation of the molecular layer down to the bc plane [Fig. 5(a)]. The molecular plane is also observed to be parallel with the substrate in case of orientation 1. It can be observed that crystal growth along [011] direction is possibly assisted by both sets of hydrogen bonds as one of these is acting parallel with [011] direction while the other is parallel with the c- axis. Further, in orientation 2, plane 020 (ac plane) was observed to sit over the substrate while crystal growth in thermal gradient along (201) plane is normal with the substrate. Figure 5(b) represents crystal orientations and molecular packing characteristics in this case. It is observed that the orientation of the molecular plane of β-resorcinol is normal with the substrate in orientation 2. The strong O-H…O hydrogen bond along with weak C-H…O hydrogen bonds, utilizing nglide normal to a-axis (along 011), pack the molecule in such a way that it extends along b-axis [Figs. 5(a) & 5(b)]. This could be one of the reasons for the exclusive growth of 020 plane over the substrate in these cases, particularly for faster sample velocity. Further, the growth along [201] is supported

by another set of strong O-H…O hydrogen bond along the caxis utilizing 21-screw [Figs. 5(b)]. Therefore, in both orientations, hydrogen bonds play an important role in deciding the direction of crystal growth perpendicular to the substrate and along the thermal gradient. Further the diagonal growth of β-form when the sample was moved in ∇T, could be related to the direction of (011) and (201) plane with respect to the substrate plane in both cases. However, this phenomenon needs to be tested with a compound that forms no H - bonding. In any condition used, uni-axial alignment is observed. Thus resorcinol does not demonstrate any tendency towards asymmetric growth along (0 1 1) or (0 -1 -1) or along (2 0 1) or (- 2 0 -1). In conclusion, highly textured thin films of only β resorcinol were obtained by the thermal gradient technique. It was observed that in most cases the 010 plane sits parallel to the substrate and the 201 plane is observed to be normal with the substrate. This is repetitive when the sample is prepared with faster sample velocity (> 35um/sec). For slower sample velocity, a new orientation of crystallites with the substrate was observed along with the previous result. In this outcome, the 200 plane was observed to be parallel with the substrate while 011 planes are normal to the substrate. In both cases, growth direction is observed to be tilted by a positive angle (25 - 70°C) with respect to the thermal gradient (∇T). Further, the role of the substrate surface in the generation of the orientated thin film has been observed as in case of PDMS coated surfaces, only the 200 plane sits on the substrate for all the range of sample velocities. To get further comprehensible understanding of this phenomenon, new experiments with varieties of compounds (molecules with or without Hbonding capabilities) would be our upcoming research focus.



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Figure 5. Packing of beta form (a) for the case of orientation 1, down the (100) plane (top view) along with depiction of four sets of {011} planes in pink color and (b) for the case of orientation 2, down the (020) plane (top view) along with depiction of four sets of {201} planes in light blue color.

ASSOCIATED CONTENT Supporting Information Experimental details and contents are available as supporting information. This information is available free of charge via the Internet at http: //pubs.acs.org

AUTHOR INFORMATION Corresponding Author Email: [email protected].

ACKNOWLEDGMENT We acknowledge the funding from FNRS projects POLYGRAD 22333186 and PDRT.0058.14. B.C. is an FRSFNRS fellow. We are thankful to Prof. Roland Resel, Institute of Solid State Physics, Graz University of Technology (Austria) for the pole figure measurements.

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(4) Ganin, A. Y.; Takabayashi, Y.; Jeglic, P.; Arcon, D.; Potocnik, A.; Baker, P. J.; Ohishi, Y.; McDonald, M. T.; Tzirakis, M. D.; McLennan, A.; Darling, G. R.; Takata, M.; Rosseinsky, M. J.; Prassides, K. Polymorphism control of superconductivity and magnetism in Cs(3)C(60) close to the Mott transition. Nature, 2010, 466, 221 – 225. (5) Salammal, S. T.; Balandier, J. –Y.; Arlin, J. –B.; Olivier, Y.; Lemaur, V.; Wang, L.; Beljonne, D.; Cornil, J.; Kennedy, A. R.; Geerts, Y. H.; Chattopadhyay, B. Polymorphism in Bulk and Thin Films: The Curious Case ofmDithiophene-DPP(Boc)Dithiophene. J. Phys. Chem. C, 2014, 118, 657−669. (6) Cruz-Cabeza, A. J.; Bernstein J. Conformational Polymorphism. Chem. Rev. 2014, 114, 2170 −2191 and references therein. (7) Aitipamula S. Polymorphism in Molecular Crystals and Cocrystals. In: Tamura R., Miyata M. (eds) Advances in Organic Crystal Chemistry. Springer, Tokyo, 2015 and references therein. (8) Jones, A. O. F.; Chattopadhyay, B.; Geerts, Y. H.; Resel, R. Substrate-Induced and Thin-Film Phases: Polymorphism of Organic Materials on Surfaces. Adv. Funct. Mater. 2016, 26, 2233–2255. (9) Jackson, K. A.; Kinetic processes: Crystal growth, Diffusion, and Phase transition in Materials 2nd edition, Wiley – VCH Verlag GmbH & Co., 2012. (10) Kondepudi, D.; Prigogine, I. Modern Thermodynamics From Heat Engine to Dissipative Structures, John Wiley & Sons, 2007. (11) England, J. L. Dissipative adaptation in driven selfassembly. Nat. Nanotech. 2015, 10, 919 – 923.


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Page 10 of 11

Table 1. List of Thermal gradient experiments Experiments

Sample velocity (v) in TG experiment

Gradient magnitude (∇ ∇T) (°C/mm)

(μm/sec)

[Fig. S8]

Cooling rate (°C/min) = (v x ∇T)

Heat Flux (J/m .sec)

Orientation versus Substrate

[see ESI]

(hkl)

2

Alignment versus Thermal gradient (∇ ∇T)

Approximate Tilt angle versus ∇T (°)

(hkl) 1

5

7.2

2.16

2374

(2 0 0)

(0 1 1)

25

2

5

7.2

2.16

2385

(0 2 0)

(2 0 1)

30

3

5

7.2

2.16

2385

(0 2 0)

(2 0 1)

60

4

5

7.2

2.16

2374

(2 0 0)

(0 1 1)

20

5

10

7.2

4.32

3596

(0 2 0)

(2 0 1)

70

6

10

7.2

4.32

3574

(2 0 0)

(0 1 1)

20

7

10

7.2

4.32

3574

(2 0 0)

(0 1 1)

30

8

15

7.2

6.48

4775

(2 0 0)

(0 1 1)

25

9

15

7.2

6.48

4775

(2 0 0)

(0 1 1)

20

10

15

7.2

6.48

4807

(0 2 0)

(2 0 1)

50

11

25

7.2

10.80

7176

(2 0 0)

(0 1 1)

30

12

25

7.2

10.80

7229

(0 2 0)/(2 0 0)

(2 0 1)

40

13

25

7.2

10.80

7176

(2 0 0)

(0 1 1)

15

14

25

7.2

10.80

7176

(2 0 0)

(0 1 1)

20

15

35

7.2

15.12

9652

(0 2 0)

(2 0 1)

30

16

35

7.2

15.12

9576

(0 2 0)/(2 0 0)

(2 0 1)

25

17

35

7.2

15.12

9652

(0 2 0)

(2 0 1)

60

18

35

7.2

15.12

9652

(0 2 0)

(2 0 1)

40

19

35

7.2

15.12

9652

(0 2 0)

(2 0 1)

35

20

45

7.2

19.44

12074

(0 2 0)

(2 0 1)

45

21

45

7.2

19.44

12074

(0 2 0)

(2 0 1)

50

22

45

7.2

19.44

12074

(0 2 0)

(2 0 1)

30

23

45

7.2

19.44

12074

(0 2 0)

(2 0 1)

30

24

45

7.2

19.44

12074

(0 2 0)

(2 0 1)

40

25

60

7.2

25.92

15707

(0 2 0)

(2 0 1)

35

26

60

7.2

25.92

15707

(0 2 0)

(2 0 1)

40

27

60

7.2

25.92

15707

(0 2 0)

(2 0 1)

40

28

60

7.2

25.92

15707

(0 2 0)

(2 0 1)

35

29

75

7.2

32.40

19340

(0 2 0)

(2 0 1)

35

30

75

7.2

32.40

19340

(0 2 0)

(2 0 1)

30

31

75

7.2

32.40

19340

(0 2 0)

(2 0 1)

35

32

100

7.2

43.20

25396

(0 2 0)

(2 0 1)

40

33

100

7.2

43.20

25396

(0 2 0)

(2 0 1)

50

34

100

7.2

43.20

25396

(0 2 0)

(2 0 1)

30


10

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For Table of Contents Use Only

Crystal growth alignment of beta polymorph of resorcinol in thermal gradient Piyush Paninia, Basab Chattopadhyaya, Oliver Werzerb, Yves Geertsa*

TOC Graphic:

SYNOPSIS: Crystallization of resorcinol in thermal gradient (∇T) results in the formation of a highly textured thin film of its β-polymorph which is observed to be preferentially oriented over the substrate and aligned along the thermal gradient. Selection between two different orientations by the crystals of β-polymorph is found to be dependent upon the magnitude of sample velocity in ∇T.


11

Crystal Growth Alignment of Î²-Polymorph of Resorcinol in Thermal

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