From Tailored Supports to Controlled Nucleation: Exploring Material

Article pubs.acs.org/crystal

From Tailored Supports to Controlled Nucleation: Exploring Material Chemistry, Surface Nanostructure, and Wetting Regime Effects in Heterogeneous Nucleation of Organic Molecules Gianluca Di Profio,*,† Enrica Fontananova,† Efrem Curcio,‡ and Enrico Drioli‡ †

Institute on Membrane Technology (ITM-CNR), Rende, Italy Department of Chemical Engineering and Materials, University of Calabria, Rende, Italy

‡

ABSTRACT: In this study, the role of the material chemistry and the physical surface nanostructure (topography) of polymeric films to stimulate heterogeneous nucleation of three representative organic molecules, acetaminophen, acetylsalicylic acid and glycine, was investigated. Aim of the work was to enhance current knowledge of the mechanisms involved in heterogeneous nucleation and to enable rational design and fabrication on a large scale of materials useful to control nucleation processes for scientific, technological, and industrial applications. Experimental results demonstrated that while solute−polymer interaction dictated whether a surface would behave as an effective heteronucleant, roughness cannot be generally considered as an absolute and univocal parameter in directly enhancing its nucleating activity, as the specific surface topography has to be correlated with its wetting behavior, so that chemical and physical properties will cooperate or compete to address the process.

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INTRODUCTION There is increasing interest today in developing solid templates (heteronucleants) useful to control nucleation and crystal growth in the manufacture of advanced materials, such as active pharmaceutical ingredients (APIs)1 and semiconductors,2 and for the study of biomineralization phenomena,3,4 protein crystallization,5−7 droplets condensation,8 and so on. In spite of this, nucleation control still remains a major challenge, because the energetic barrier for nucleation is particularly susceptible to the operating conditions and to the various properties of the interfaces,9 thus affecting polymorphism,10 crystals orientation,11 and size.12 Furthermore, in addition to the chemical properties, surfaces structure (topography) has a remarkable influence on the nucleation rate,13 thus affecting crystal density, size, and size distribution. Therefore, uncontrolled heterogeneous nucleation might lead to unexpected and/or to irreproducible crystals features. On the other side, the possibility to exploit heterogeneous nucleation would afford significant advantages, like crystallizing in the metastable region,9 enhancing crystallization kinetics,14 inducing nucleation at lower supersaturation,7 or stimulating the formation of specific polymorphs.15,16 Accordingly, the present work aimed to develop appropriate preparative methodologies for the fabrication, on a wide scale, of tailored surfaces made with different polymeric materials (Figure 1) and displaying surface topography engineered at the nanometric range, and to investigate the role of their chemical−physical properties on the heterogeneous nucleation kinetics of three representative APIs: acetaminophen, acetylsalicylic acid, and glycine (Figure 2). © 2012 American Chemical Society

EXPERIMENTAL SECTION

Fabrication of Polymer Surfaces. Poly(vinylidenefluoride-cohexafluoropropylene) Kynarflex 2800 (co-PVDF) was supplied by Elf Autochem; Lenzing P84 co-Polyimide (PI) was purchased from HP polymer GmbH; sulphonated polyetheretherketone with cardo group (sPEEK-WC) with a sulphonation degree (SD) ranging from 0.1 to 1, and sulfonated polyetherethersulfone with cardo group (sPEES-WC) (SD 0.5) polymers were supplied by Prof. Trotta from the University of Torino (Turin, Italy). N-Methyl-2-pyrrolidone (NMP), dichlorometane (DCM), N,N-dimethylacetamide (DMA), 1,4-dioxane (Dioxane), methanol (MeOH) were acquired from Carlo Erba. 1,5Diamino-2-methylpentane (DAMP) and tetrabutilamonium bromide (TBABr) were purchased from Sigma-Aldrich. Nafion 117 membrane (EW 1100) was obtained from Quintech. Polypropylene (PP) (Accurel PP2EHF) and polyethersulfone (PES) (MicroPes 2F) membranes were purchased from Membrana GmbH. Cellulose acetate (CA) membranes were from Whatman Membrane filters. Polydimethylsiloxane (PDMS) was synthesized from a prepolymer (General Electric, RTV 615 A) and a cross-linker (General Electric, RTV 615 B) by Pt-catalyzed hydrosilylation reaction to form a densely cross-linked polymer network. An overview of the experimental conditions used to prepare the films is reported in Table 1. Homogeneous solutions were prepared dissolving the polymer (and, where indicated, TBABr or H2O) in the solvent or solvents mixture, at room temperature, by magnetic stirring until clear and homogeneous solutions were obtained. The solutions were cast onto a glass plate by an Elcometer 3570 micrometric film applicator with adjustable thickness (initial thickness 250 μm except in the case of the co-PVDF films which were 200 μm). In the case of the Received: April 23, 2012 Revised: May 14, 2012 Published: May 29, 2012 3749

dx.doi.org/10.1021/cg3005568 | Cryst. Growth Des. 2012, 12, 3749−3757

Crystal Growth & Design

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Figure 1. Chemical formula for the different polymeric materials used in this work. surface. The PI sample 25, after the NIPS process, was cross-linked by immersion in a 10 v/v% DAMP/MeOH solution for 24 h at 25 ± 1 °C. The imide group of the PI was in this way converted to an amidic group by the reaction with the DAMP.17 The chemically modified supports were washed with fresh methanol first and with water later, to flush away any residual unreacted cross-linker. The films prepared by vapor-induced phase separation (VIPS), and solvent evaporation (SE) methods were obtained by casting the solutions in a thermostatic box with controlled humidity and temperature (see Table 1 for the conditions) and left to evaporate for about 72 h. Then they were peeled off from the glass and washed in a water bath at room temperature for additional 24 h; finally films were dried at room temperature. For the fabrication of PDMS samples a solution (20 wt %) of the two components, prepolymer and cross-linker in a ratio 10:1, was prepared using DCM as solvent and stirred for 2 h at room temperature.18 This solution was cast and the solvent was left to evaporate for 24 h to allow the complete removal of DCM; next the film was treated under a vacuum at 150 °C for 1 h in order to complete the cross-linking reaction.19,20 Characterizations of Polymer Surfaces. Advancing (θa) and receding (θr) contact angles were measured by growing/shrinking sessile water drop, with the tangent method, according to the classical procedure,21 using a CAM 200 contact angle meter (KSV Instruments

Figure 2. Chemical formula of acetaminophen (ACM), acetyl salicylic acid (ASA), and glycine (GLY). samples prepared by the nonsolvent induced phase separation (NIPS) method, the cast films were immediately immersed in a coagulation bath containing distilled water at 23 ± 3 °C for 48 h. Then they were removed and dried at room temperature. Only the co-PVDF film 6 and the PI surface 25, before immersion in the coagulation bath, were evaporated for 60 s at 23 ± 3 °C and 15% relative humidity (RH). In this way it was possible to obtain a more dense skin and a smoother 3750



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Table 1. Composition of the Solutions and Conditions Used to Prepare the Polymeric Films surface n.

polymer (wt%)

1 2 3 4 5 6 9 11 12 13 14 15 16 17 20 21 22 23 24 25

co-PVDF (14%) co-PVDF (13.7%) co-PVDF (13.7%) co-PVDF (13.7%) co-PVDF (14%) co-PVDF (14%) PDMS (20%) sPEEK-WC SD 1.0 (15%) sPEEK-WC SD 0.8 (15%) sPEEK-WC SD 0.4 (15%) sPEEK-WC SD 0.2 (15%) sPEEK-WC SD 0.1 (15%) sPEEK-WC SD 0.1 (15%) sPEES-WC SD 0.5 PI (12%) PI (18%) PI (15%) PI (18%) PI (21%) PI (23%)

solvent (wt%) DMA (86%) DMA (84.3%) DMA (84.3%) DMA (84.3%) DMA (86%) DMA (86%) DCM (80%) DMF (85%) DMF (85%) DMF (85%) DMF (85%) DMF (85%) DMF (85%) DMF (85%) NMP (88%) NMP (82%) NMP (85%) DMA (82%) NMP (79%) NMP/dioxane (38.5%/ 38.5%)

additive (wt %) TBABr (2%) H2O (2%) TBABr (2%)

Ltd.) equipped with a microsyringe, automatic dispenser, and software for image acquisition and processing. Advancing contact angle was measured with the increase in the volume of the droplet (initially 5 μL) by adding water with a constant dosing (1 μL/s) up to 15 μL while capturing images. During the entire measurement, the needle remained attached to the drop so that the portion of the needle inside the drop was maintained as small as possible to minimize adhesion of the droplet. Receding contact angle was achieved by reducing the volume of the drop, with the same dosing flow rate used in the advancing contact angle measurements.22 Between the growing/ shrinking stages, the equilibrium contact angle θeq was estimated without any fluid motion on the solid surface. Static contact angles for the three crystallizing solutions, θACM, θASA, and θGLY, were measured by depositing a droplet (5 μL) of the solutions onto the surface and measuring the contact angle after equilibration (10 s). Contact angles have been calculated as the average of three different measurements for each one of three slices of the same polymer surface. Contact angle hysteresis23 was calculated as difference between advancing and receding contact angles (H = θa − θr). Surfaces morphology was assessed by scanning electron microscopy (SEM) (Quanta 200 F FEI Philips) and a Nanoscope III atomic force microscope (AFM) (Digital Instruments, VEECO Metrology Group) in air, in tapping mode AFM imaging, as the average among three different measurements across 5 × 5 μm2 and 10 × 10 μm2 squares of the sample surfaces. Roughness analysis of surfaces were performed by SPIP 6.0 software (Image Metrology), by calculating average roughness (Sa), root-mean-square roughness (Sq), maximum height (Rmax), and density of summits (Sds). Roughness factor r was calculated as the ratio of the actual area of the rough surface to that of the projected area. Crystallization Tests. Stock solutions were prepared by dissolving acetaminophen, acetylsalicylic acid, and glycine (from Sigma-Aldrich) in bidistilled water at the concentration of 14.9, 5.4, and 180.2 mg/ gsolvent, respectively. These concentrations were selected to achieve crystals appearance on the surfaces but to avoid bulk nucleation in control experiments over the observation time. All solutions were filtered by 0.2 μm PES syringe filters. Two milliliters of each solution was inserted in the 24 wells of screw top hanging drop plates (Qiagen). 1 ×1 cm2 pieces of each film was completely submerged into the solutions so that, for each crystallizing molecule and for each surface, 24 tests were performed contemporaneously in the same conditions, for a total of 1800 trials for each experimental campaign. This extensive and time-consuming procedure ensures a statistical

technique

conditions

VIPS VIPS VIPS VIPS VIPS SE + NIPS SE SE SE SE SE VIPS SE SE NIPS NIPS NIPS NIPS NIPS SE + NIPS

23 ± 3 °C; 50 ± 5% RH 23 ± 3 °C; 50 ± 5% RH 23 ± 3 °C; saturated water vapor atmosphere 23 ± 3 °C; saturated water vapor atmosphere 23 ± 3 °C; saturated water vapor atmosphere SE: 23 ± 3 °C; 15 ± 1% RH; NIPS: liquid water at 23 ± 3 °C 23 ± 3 °C; 15 ± 1% RH 23 ± 3 °C; 15 ± 1% RH 23 ± 3 °C; 15 ± 1% RH 23 ± 3 °C; 15 ± 1% RH 23 ± 3 °C; 15 ± 1% RH 23 ± 3 °C; 50 ± 5% RH 23 ± 3 °C; 15 ± 1% RH 23 ± 3 °C; 15 ± 1% RH liquid water at 23 ± 3 °C liquid water at 23 ± 3 °C liquid water at 23 ± 3 °C liquid water at 23 ± 3 °C liquid water at 23 ± 3 °C SE: 23 ± 3 °C; 15 ± 1% RH; NIPS: liquid water at 23 ± 3 °C

validation of the tests against the stochastic nature of the nucleation phenomena. Control experiments were performed by filling some wells with crystallizing solutions but without templates, to check that the possible homogeneous bulk nucleation or heterogeneous nucleation on the walls of the wells did not occur over the observation time. Plates were then introduced in a thermostat, so that the solution temperature was quenched from 25 to 5 °C (±0.1 °C) to achieve supersaturation, for a fixed period of time estimated by preliminary tests, consisting of 48, 72, and 200 h for ACM, ASA, and GLY, respectively. Nucleation Density Measurements. After incubation, polymer films were extracted from the wells and crystals attached to the surfaces were photographed under an optical microscope (DM 2500M, Leica Microsystems) for subsequent counting. Crystals occasionally present at the bottom of the wells, and supposedly detached from the surface during the incubation time, were not included in counting. It was verified that crystals did not appear in control tests over the incubation time. To make experimental results comparable for the three molecules, nucleation density was expressed as a fraction of crystal nucleated for each surface on the overall number of crystals counted. Namely, for a specific compound and for a specific polymer surface, nucleation density has been quantified by the ratio between the average number of crystals nucleated in the 24 wells of the same plate (containing the same surface and the same crystallizing molecule) over the sum of the averages of crystals nucleated in the 25 plates (25 different surfaces for the same molecule).

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RESULTS AND DISCUSSION Fabrication of Polymeric Surfaces. The appropriate design and fabrication of heteronucleants can exercise control over the nucleation stage by manipulating the nature of molecular recognition events occurring at the solute−template interface. Therefore, to investigate the effect of surfaces chemistry on solute−support interaction, polymers materials with specific properties were selected. The hydrophobic materials were co-PVDF (1−6), PP (7−8), and PDMS (9); the hydrophilic polymers were PES (18), CA (19), and PI (20−25). Furthermore, materials combining a hydrophobic main chain with extremely hydrophilic sulfonic groups directly linked on the main chain, that is, sPEEK-WC (11−16) and

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of the solvent. In the NIPS process, the mass transfer rates were usually higher than in VIPS, and the formation of a less porous and smoother layer at the liquid/polymer solution interface (the top surface of the film) was observed because of the rapid solvent−nonsolvent exchange which induced the polymer precipitation at the interface reducing the rate of exchanges in the sublayers. In this way, surface 6 was obtained with a low roughness value. On the contrary, in the VIPS method a more porous and rough surface was obtained because of the slow diffusion of the vapor phase to the film surface, which led to an uniform and flat concentration profile (in the cross section of the film) of the precipitant (water), the polymer, and the solvent, during the phase separation process.25 The rate of the diffusion processes in the VIPS process was modulated controlling the relative humidity of the atmosphere and the composition of the co-PVDF casting solution; this generated the surfaces 1−5 displaying a progressive decrease in roughness. Figure 4 show the SEM and AFM images of the co-PVDF templates. In addition, the porous and more rough sPEEK-WC film 15 (not shown), with the same SD (0.1) as for the dense and smoother sample 16, was prepared. The surface properties of the PI supports (20−25, displayed in Figure 5) were controlled by changing polymer concentration and type of solvent (Table 1). The different roughness spectrum achieved for the two sets of co-PVDF and PI films is evident from Figures 4 and 5. While for co-PVDF films Sa ranged from 475 to 520 nm (only for the sample 6 Sa was 184 nm) showing a sponge-like (porous) surface texture, PI samples’ roughness was more than 1 order of magnitude lower (from 2.8 to 32.2 nm), displaying a more dense (less-porous) structure. On what concerns wetting behavior, the hydrophilic PI (20− 25) and sPEEK-WC (15-16) surfaces demonstrated an increase of θeq when decreasing roughness (Figure 3), that is, the opposite performance with respect to the co-PVDF (1−6) and the PP (7−8) samples. According to Wenzel theory,26 hydrophilic (θ < 90°) surfaces, with a typical size of roughness details smaller than the size of the interacting droplet and without air pockets, referred to as a homogeneous interface with complete wetting, become more hydrophilic with an increase in roughness. For a rough hydrophobic (θ > 90°) surface, a nonwetting liquid may not penetrate into surface cavities, resulting in the formation of air pockets, leading to a composite solid−liquid−air interface. In this case, Cassie− Baxter27 model for the composite interface predicts that a hydrophobic smooth surface can be changed to superhydrophobic with an increase in roughness. Accordingly, the wetting behavior of the different surfaces fabricated in this work can be explained by the different wetting regime occurring for intrinsically hydrophilic or hydrophobic materials. Increasing roughness of co-PVDF and PP surfaces increased the contact angle (enhanced hydrophobicity) according with the Cassie− Baxter regime, while for sPEEK-WC and PI θeq decreased with increasing roughness, in agreement with Wenzel wetting conditions. In the present study, contact angles were measured by using droplets of 5 μL minimum, which corresponds to a droplet diameter of around 2000 μm. If considering that surface irregularities for the most rough co-PVDF film never exceeded 2.0 μm, the conditions used in this work satisfy well the requirements of validity of Wenzel and Cassie−Baxter models.28 Contact angle hysteresis reported in Figure 6 demonstrated that while for PI films H displayed the highest

sPEES-WC (17), or linked at the end of a side chain like in Nafion (10), were also used. In the case of sPEEK-WC, the nucleation rate was investigated using polymers with a sulfonation degree (SD) ranging from 0.1 to 1. From Figure 3, it is apparent that the reduction of equilibrium contact angle

Figure 3. Equilibrium contact angle θeq and average roughness Sa of the surfaces used in this work. Error bars indicate standard deviation over experimental data.

θeq when increasing the SD as a consequence of the increase in polar groups’ density in the polymer chain (from 16 to 11; sample 15 displaying a different structure is discussed later). The contribution of the physical properties of the surfaces on the heterogeneous nucleation activity was studied by preparing templates with tailored surface topography with co-PVDF, sPEEK-WC, and PI polymers. Surfaces structure was modulated by an appropriate choice of operating conditions for the realization of the films. For example, it was possible to change significantly the surface average roughness (Sa) and the wettability of the co-PVDF and the PI samples (Figure 3) by changing the state of the coagulation media (water) from vapor to liquid and/or the composition of the casting solution. In the case of co-PVDF (1−6), variation in the preparation procedure allowed surface features to range from smoother and moderately hydrophilic (6, θeq = 89.9°, Sa = 184 nm) to more rough and superhydrophobic (1, θeq ∼ 150°, Sa = 521 nm). Films 1−5 were prepared by vapor-induced phase separation (VIPS); sample 6 was prepared by NIPS.24 In the NIPS method, a film of the homogeneous polymeric solution was cast on a glass support and immersed in a nonsolvent bath. The polymer solution initially demixed in two liquid phases because of the exchange of the solvent and nonsolvent. The phase with the higher polymer concentration formed the solid part of a three-dimensional porous polymer network (the membrane), and the phase with the lower polymer concentration generated the pores. During the process, the exchange of solvent and nonsolvent in the demixed phases continued to cause an increase in the polymer concentration in the concentrated phase surrounding the pores. The polymer molecules rearranged their structure until the solidification of the concentrated phase occurred. As a consequence, the final film morphology was strongly dependent on the rate of the solvent/nonsolvent diffusion, which, in turns, was related to the chemical and physical properties of the systems involved and to the operative conditions.25 In the VIPS method the cast liquid film was exposed to water vapors, and the phase inversion was induced by the diffusion of the nonsolvent and the evaporation 3752



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Figure 4. From top to bottom: surfaces 1−6. From left to right: SEM micrographs, 3D height (Z = 1500 nm/div), and 2D amplitude 5 × 5 μm2 AFM images. AFM images. Unit bars in the main SEM micrographs 10 μm. Particulars in the SEM images at low magnification for samples 1−5.

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Figure 5. From top to bottom: surfaces 20−25. From left to right: 3D height (Z = 1500 nm/div), 2D amplitude and 3D amplitude (Z = 2 V/div) 10 × 10 μm2 AFM images.

values and an increasing trend with surface roughness factor r, typical of a Wenzel wetting behavior,29 in the case of co-PVDF samples, lower hysteresis supports a Cassie−Baxter wetting condition, although it was not clearly observed the expected reduction of H with increasing surface roughness.29 Crystallization Experiments. The nucleation activity of the samples 1−25 for the three molecules ACM, ASA, and GLY has been approximated with the nucleation area density,9 that is, the number of crystals per unit area per unit time detectable under the microscope at a certain stage of the crystallization

process (Figure 7). Results clearly demonstrate that heterogeneous nucleation is highly sensitive to surface chemistry, and it is directly related to the binding potential of the target molecules to specific chemical functionalities existing in the polymer structure. GLY did not display significant nucleation activity with hydrophobic surfaces made of co-PVDF and PP, while a strong nucleation activity was observed in the case of the more hydrophilic sPEEK-WC, sPEES-WC, PI, and, to a lower extent, PES and CA. Because GLY brings an acidic (COOH; Ka 4.57 × 10−3) and a basic (NH2; Kb 3.98 × 10−5) 3754



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Figure 6. Contact angle hysteresis H as function of the roughness factor r, for the co-PVDF (squares) and the PI (circles) samples. Error bars indicate standard deviation over experimental data.

functionality, it can effectively interact via acid−base interactions with the basic groups of PI and the acid functionalities of the sPEEK-WC and sPEES-WC. The nucleation rate of GLY on the sPEEK-WC surfaces increased with the SD (from 16 to 11). The formation of acid−base interactions and hydrogen bonds with GLY is also possible on the PDMS and Nafion surfaces, despite the hydrophobic nature of these two materials. In the case of the more hydrophobic ACM and ASA, van der Waals interactions were possible between the aromatic groups of these molecules and the hydrophobic co-PVDF, PP, PDMS, and Nafion surfaces. The formation of hydrogen bonds is common to all the three target molecules with the polar surface including CA and PES, as well as, with sPEEK-WC and sPEES-WC samples. Concerning the last two materials, the nucleation activity was in the order GLY > ASA > ACM, a trend that is coherent with the order of acidity of the OH groups of the molecules (Ka 4.57 × 10−3, 3.27 × 10−4, and 3.20 × 10−10, respectively). The same nucleation trend was also visible, and even more pronounced, for the interaction with PI surfaces which bring basic functionalities. The ACM molecule, in analogy with GLY, can also form acid− base interactions between its basic group and the acid groups of sPEEK-WC and sPEES-WC; however, the amidic group of the ACM is less basic than the aminic group of the GLY, thus reducing the extent of these interactions. These observations clearly demonstrate that the chemical affinity between functional groups existing on a target molecule and solid support is a crucial condition in dictating whether the latter would act as effective heteronucleant, corroborating previous findings.6,10,16,30,31 When exploring the effects of the physical structure of the surfaces on the nucleation activity, it can be seen that in the case of ACM and ASA, increased nucleation area density occurred with decreasing roughness of the hydrophobic surface 1−6 (Figure 7a,b), indicating that increasing roughness discourages heterogeneous nucleation. A similar effect was visible with the two commercial PP surfaces (7−8). As GLY did not display significant chemical affinity with the hydrophobic co-PVDF and PP polymers, the contribution of surface topography was not observed for this molecule. In the case of PI (20−25) and sPEEK-WC (15−16), the opposite tendency was observed for the three target molecules, although

Figure 7. Crystal’s nucleation area density on the different surfaces for ACM (a), ASA (b), and GLY (c) and static contact angles measured for the respective crystallizing solutions. Surfaces have been numbered according to a decreasing roughness order for surfaces 1−6, 7−8, 15− 16, and 20−25, and with a decreasing SD for surfaces 11−16 (surfaces 15 and 16 have the same SD = 0.1). Error bars indicate standard deviation over experimental data.

the influence of PI surfaces topography on nucleation rate of ACM was only slightly evident, due to reduced interaction with this polymer. In this case, increased surface roughness supported the nucleation rate as also reported by some authors.13,14,32−41 Observations of co-PVDF and PP samples substantiate instead those results demonstrating the inefficacy, or even the reduction, of the nucleation activity of a solid support in some circumstances when increasing roughness.33,35,36,42 The opposite effect of surface roughness on the nucleation activity for intrinsically hydrophobic and more 3755



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represent a potential interesting application in the field of controlled crystallization processes.

hydrophilic polymer surfaces, correlates well with the wetting behavior of the different polymeric templates by the crystallizing solutions, as demonstrated by static contact angles θACM, θASA, and θGLY (right-hand axes in Figure 7). Results show that wetting behavior of the surface dictates whether enhanced roughness would positively affect nucleation rate, in accordance with classical nucleation theory (CNT),43 and explain the different impact of roughening on nucleation density displayed in Figure 7. In the case of hydrophobic polymers, the reduction in wetting tendency with increasing roughness justifies the reduced nucleating activity demonstrated by co-PVDF and PP samples. On the other side, increasing roughness of the hydrophilic sPEEK-WC and PI films induced a reduction in the solution contact angle, thus enhancing the active interface available for interaction between solute molecules and the support, so increasing the nucleation activity. This effect would be even more strengthened by the physical entrapment of solute molecules in certain nanometric domains of the irregular surface, thereby enhancing local supersaturation.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: g.diprofi[email protected]. Tel: +390984492010. Fax: +390984402103. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Professor Francesco Trotta from Università di Torino (Turin, Italy) is acknowledged for providing sPEEK-WC and sPEESWC powders.

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REFERENCES

(1) Chadwick, K.; Chen, J.; Myerson, A. S.; Trout, B. L. Cryst. Growth Des. 2012, 12, 1159. (2) Briseno, A. L.; Mannsfeld, S. C. B.; Ling, M. M.; Liu, S.; Tseng, R. J.; Reese, C.; Roberts, M. E.; Yang, Y.; Wudl, F.; Bao, Z. Nature 2006, 444, 913. (3) Hammer, J. E.; Sharp, T. G.; Wessel, P. Geology 2010, 38, 367. (4) Xiao, J.; Wang, Z.; Tang, Y.; Yang, S. Langmuir 2010, 26, 4977. (5) Saridakis, E.; Chayen, N. E. Trends Biotechnol. 2008, 27, 99. (6) Shah, U. V.; Allenby, M. C.; Williams, D. R.; Heng, J. Y. Y. Cryst. Growth Des. 2012, 12, 1772. (7) Shah, U. V.; Williams, D. R.; Heng, J. Y. Y. Cryst. Growth Des. 2012, 12, 1362. (8) Lazaridis, M.; Hov, Ø.; Eleftheriadis, K. Atmosph. Res 2000, 55, 103. (9) Kashchiev, D. Nucleation: Basic Theory with Applications; Butterworth Heinemann: Oxford, 2000. (10) Lang, M.; Grzesiak, A. L.; Matzger, A. J. J. Am. Chem. Soc. 2002, 124, 14834. (11) Berman, A.; Ahn, D. J.; Lio, A.; Salmeron, M.; Reichert, A.; Charych, D. Science 1995, 269, 515. (12) Lee, A. Y.; Lee, I.-S.; Dette, S. S.; Boerner, J.; Myerson, A. S. J. Am. Chem. Soc. 2005, 127, 14982. (13) Dean, J. R.; Jones, A. M.; Holmes, D.; Reed, R.; Weyers, J.; Jones, A. Practical Skills in Chemistry: Prentice Hall:, Harlow, U.K., 2001. (14) Chayen, N. E.; Saridakis, E.; El-Bahar, R.; Nemirovsky, Y. J. Mol. Biol. 2001, 312, 591. (15) Ha, J. M.; Wolf, J. H.; Hillmyer, M. A.; Ward, M. D. J. Am. Chem. Soc. 2004, 126, 3382. (16) Price, C. P.; Grzesiak, A. L.; Matzger, A. J. J. Am. Chem. Soc. 2005, 127, 5512. (17) Choi, S.-H.; Jansen, J. C.; Tasselli, F.; Barbieri, G.; Drioli, E. Sep. Purif. Technol. 2010, 76, 132. (18) Vankelecom, I. F. J.; Jacobs, P. A. Catal. Today 2000, 56, 147. (19) Bonchio, M.; Carraro, M.; Scorrano, G.; Fontananova, E.; Drioli, E. Adv. Synth. Catal. 2003, 345, 1119. (20) Fontananova, E.; Di Profio, G.; Curcio, E.; Giorno, L.; Drioli, E. J. Incl. Phenom. Macroc. Chem. 2007, 57, 537. (21) Johnson, R. E.; Dette, R. H. Surf. Colloid Sci. 1969, 2, 85. (22) Waghmare, P. R.; Mitra, S. K. Langmuir 2010, 26, 17082. (23) Patankar, N. A. Langmuir 2010, 26, 7498. (24) Mulder, M. Basic Principles of Membrane Technology; Kluwer: Dordrecht, The Netherlands, 1991. (25) Strathmann, H.; Kimmerle, K. Desalination 1990, 79, 283. (26) Wenzel, R. N. J. Ind. Eng. Chem. 1936, 28, 988. (27) Cassie, A.; Baxter, S. Trans. Faraday Soc 1944, 40, 546. (28) Marmur, A.; Bittoun, E. Langmuir 2009, 25, 1277. (29) Wang, L.; Wei, J.; Su, Z. Langmuir 2011, 27, 15299. (30) Delmas, T.; Roberts, M. M.; Heng, J. Y. Y. J. Adhes. Sci. Technol. 2011, 25, 357.

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CONCLUSION Experimental evidence demonstrated that roughness cannot be considered as an absolute and univocal parameter in directly modulating the nucleating activity of heteronucleants regardless of their chemical properties. While the chemical nature of the surfaces dictates whether it would act as an effective nucleationactive substrate, increased surface roughness will positively or negatively affect nucleation density depending on the extent of interaction between the crystallizing solution and the surface (wetting properties). Accordingly, both chemical and physical factors cooperate/compete to improve/discourage heteronucleation. In the case of hydrophilic templates, a significant fraction of interacting solute molecules are likely to accumulate at the solid−solution interface via adsorption, where molecular recognition events may induce partial realignment in the solute enriched layers. In addition, molecules can further concentrate in certain heterogeneous domains by physical entrapment. In these conditions, increasing surface roughness would enhance the active interface available for interaction/entrapment, thereby increasing supersaturation and hence nucleation density. Hydrophobic supports, displaying reduced wetting tendency by crystallizing solution, demonstrated increased contact angle and reduced nucleation activity when increasing topographical heterogeneity, in accordance with CNT, regardless of their pronounced porous and spongelike structure. Furthermore, the present research provides substantial technological insights into the fabrication of polymeric surfaces displaying tailored physical features, useful as effective tools for the control of heterogeneous nucleation. While microfabrication methods have been developed to produce on small-scale patterned supports with special surface topography (e.g., ref 36), here we described routes for the production of macroscopic and easily maneuverable films, using common polymeric materials with a wide range of chemical functionalities. Using polymeric films as heteronucleants offers a promising alternative to metal, inorganic, or biomaterials, since their structure and chemistry are easily tunable over a wide range by a variety of established fabrication methods conventionally used for membranes preparation. Moreover, combining the function of tailored polymeric surfaces, to stimulate controlled heterogeneous nucleation mechanisms, with simultaneous solvent removal in the vapor phase, like it is in membrane crystallization technology,44 would 3756



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From Tailored Supports to Controlled Nucleation: Exploring Material

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