Reversible Nucleation, Growth, and Dissolution of Poly (Î³-benzyl l

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Reversible Nucleation, Growth and Dissolution of Poly(#-benzyl L-glutamate) Hexagonal Columnar Liquid Crystals by Addition and Removal of a Nonsolvent Kaiwan Jahanshahi, Ioan Botiz, Renate Reiter, Harald Scherer, and Günter Reiter Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/cg400971g • Publication Date (Web): 23 Aug 2013 Downloaded from http://pubs.acs.org on August 31, 2013

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Crystal Growth & Design

Reversible Nucleation, Growth and Dissolution of Poly(γ-benzyl L-glutamate) Hexagonal Columnar Liquid Crystals by Addition and Removal of a Nonsolvent Kaiwan Jahanshahi†,‡, Ioan Botiz†,§, Renate Reiter†, Harald Scherer∥, Günter Reiter†,‡,§,* †

Institute of Physics, University of Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany; Freiburg Materials Research Center (FMF), Stefan-Meier-Str. 21, 79104 Freiburg, Germany; § Freiburg Institute for Advanced Studies (FRIAS), Albertstr. 19, 79104 Freiburg, Germany; ∥ Institut für Anorganische und Analytische Chemie, University of Freiburg, Albertstr. 21, 79104 Freiburg, Germany ‡

ABSTRACT We have investigated the process of nucleation and growth and its reversal, i.e. dissolution, of ordered poly(γ-benzyl-L-glutamate) (PBLG) objects in thin film solutions containing a few percent of α-helical PBLG dissolved in chloroform. Nucleation, growth and dissolution rate were controlled by adding and removing, respectively, defined amounts of a nonsolvent (methanol), introduced through the vapor phase by regulating its flow rate and vapor pressure. Adding methanol to the isotropic polymer solution allowed to induce nucleation and growth even polymer solutions of very low concentrations, which were significantly below the solubility limit (equilibrium volume fraction). The variation of the number density of nuclei with the supersaturation ratio was found to fit well the predictions of the classical nucleation theory, for all equilibrium concentrations. For a given supersaturation ratio, fewer objects were nucleated for lower equilibrium concentrations.

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INTRODUCTION In helicogenic solvents, polypeptides like poly(γ-benzyl L-glutamate) (PBLG) can adopt an α-helical conformation1-3. In this conformation, the polymer backbone is rigidified by intramolecular hydrogen bonds1. As a result, the molecules can be regarded as stiff, rod-like objects. For a sufficiently high aspect ratio and above a certain volume fraction, these rods can form liquid crystalline states in solutions, as has been predicted by the theories of Onsager4 and Flory5. These theories were partially confirmed by experimental data6, 7. However, systems of rod-like molecules can exhibit a rather complex phase behavior, including the occurrence of different liquid crystalline states, while theories by Onsager and Flory only treat states of orientational order. In particular, in solutions of polypeptides a chiral nematic phase7 and, at high volume fractions, a hexagonal columnar liquid crystalline phase8 have been found. This latter phase possesses a solid-like hexagonal order in two dimensions and a liquid-like in the third9. A hexagonal lateral order of the PBLG rods, with a spacing correlated to the volume fraction of solvent in the anisotropic phase, was already assumed in earlier studies10, 11. In a previous study12 we have shown that at low volume fractions of PBLG a highly ordered phase can grow in good solvent (chloroform) solutions, when small amounts of methanol, a nonsolvent, were added. The resulting ordered objects were shown to be in the hexagonal columnar liquid crystalline state, accompanied by the formation of a characteristic zigzag pattern during the process of drying (removal of solvent). The presence of methanol or other nonsolvents has been shown to decrease effectively the solubility of PBLG homopolymers11-15 and also rod-coil block copolymers with PBLG blocks as the rod parts15, 16. This is consistent with the Flory theory, where an increase of the Flory-Huggins parameter χ, a dimensionless measure of the interaction energy between solute and solvent,


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related to the interfacial tension between the two, is predicted to lead to a decrease of the equilibrium volume fraction φe of the rods dissolved in the isotropic phase, which may coexist with an anisotropic phase5, 11, e.g. an ordered or crystalline phase. In this paper, we present a study of the nucleation, growth and dissolution of ordered objects, hexagonal columnar liquid crystals, from semi-dilute PBLG solutions. It was convenient to induce nucleation by condensing methanol from the surrounding vapor phase onto a thin film of a chloroform solution. The experimental approach12, 15, 16 which was adopted here allowed to vary the quality of the mixed solvent by adding / removing methanol through the vapor phase by controlled condensation / evaporation. This was achieved by adjusting the vapor pressure of methanol in the surrounding vapor phase and by varying the temperature of the sample, i.e. the thin film solution. Using optical microscopy, we followed nucleation and growth of the ordered objects in situ, i.e. in real time and direct space. For a given volume fraction φp of PBLG, a sensitive control of the equilibrium volume fraction φe through the added methanol allowed to obtain objects of hundreds of micrometers in length. The observed number density of nuclei was analyzed on the base of CNT (see supporting information for theoretical approach). Based on our experimental approach of condensing a bad solvent from the surrounding vapor phase, we were able to grow objects even from rather dilute polymer solutions as the presence of methanol significantly decreased the solubility limit and thus the equilibrium volume fraction φe of PBLG. Using the surrounding vapor phase as a reservoir allowed to reverse the process; i.e ordered objects could be re-dissolved. This was achieved by improving the quality of the solvent through controlled evaporation of methanol from thin film solution by reducing the methanol flow rate and thus reducing the vapor pressure of the nonsolvent in the surrounding vapor phase.


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EXPERIMENTAL SECTION PBLG was purchased from Sigma-Aldrich with an average molecular weight Mw = 41000 g / mol and a polydispersity Mw / Mn ≈ 1.2, corresponding to an average degree of polymerization of 187 (resulting in an average molecular length of 28 nm for the α-helical conformation). Solid thin films of PBLG (initial thickness h0 = 50 ± 2 nm) were obtained by spincoating from chloroform solution (0.6 weight %) onto hydrophilic silicon substrates previously cleaned through a UV-ozone treatment. The high reflectivity of silicon substrates conveniently enabled to determine the film thickness by using an interference method described elsewhere.15, 16 Both, the experimental setup and the vapor condensation approach used to create a thin film solution, in which nucleation and growth of PBLG crystals could be studied in situ, were described in previous works.15, 16 In brief, the approach was based on placing the solid thin film of PBLG on a Peltier element enclosed in a homebuilt chamber (see Figure S1 in the Supporting Information) connected to two flow controllers. The chamber could be flushed either with dry nitrogen or with nitrogen saturated with solvent (chloroform) or nonsolvent (methanol) vapor. Before starting the experiment, the sample chamber was flushed with pure nitrogen for 5 minutes to remove any moisture or unwanted gas. In this way we established a dry and inert surrounding atmosphere. The Peltier element allowed controlling the temperature of the sample. Decreasing the sample temperature a few Kelvin below room temperature, i.e. below the condensation or dew point, led to condensation of solvent and nonsolvent present in the surrounding vapor onto the film and thus to swelling of the film. Passing through the vapor phase allowed us to control the ratio of solvent and nonsolvent within the film by regulating the vapor pressures of solvent and non solvent through controlling the flow rates of two gas streams. Hence, for a given sample temperature, we were able to control two key parameters, the polymer volume fraction φp and the


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equilibrium volume fraction φe, and thus could control in a time-resolved manner the process of nucleation and growth of PBLG crystals in a reversible manner. For constant flow rates, we measured the contributions of condensed chloroform (blue circles, hc) and methanol (red triangles, hm) to the total film thickness as a function of sample temperature (see Figure 1). The volume fraction of PBLG was deduced from the ratio of the initial film thickness h0 and the thickness of the swollen film h = h0 + hc + hm, i.e., φp = h0 / h. The volume fraction of methanol φm = hm / h was estimated in a separate experiment by condensing methanol on a dry PBLG film in the absence of chloroform under similar temperature conditions (Figure 1b). Here, h was derived from the interference colors.15, 16 For h > 1600 nm the number of interference fringes was counted. We note that the actual amount of the condensed methanol might be slightly different compared to experiments in the presence of chloroform. The growth of the ordered objects was observed using an optical microscope (Leitz, ORTHOLUX II POL-BK)

RESULTS AND DISCUSSION Figure 2 depicts a typical series of optical micrographs exemplarily showing growth and dissolution of objects by adding and removing, respectively, methanol from the thin film solution. A PBLG film of thickness of 50 nm was placed in the sample chamber, which was saturated with chloroform vapor. Cooling of the film led to condensation of chloroform vapor and thus swelling of the film. We have chosen a sample temperature for which the amount of condensed vapor led to an isotropic thin film solution of a specific polymer volume fraction φp = 1.2 ± 0.4 %. This solution did not show any signs of birefringence between crossed polarizers.


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As this value of φp is smaller than the equilibrium volume fraction φe, no nucleation of ordered objects was detected. However, when we added methanol (volume fraction φm = 8 ± 1 %) to this thin film solution at time t0, nucleation and growth of many objects was observed (see Figure 2, at t0 + 16 s). This can be explained by the fact that, for a constant polymer volume fraction φp, adding methanol, a protic nonsolvent for PBLG, led to supersaturation of the solution by decreasing the equilibrium volume fraction φe below φp. The decrease of φe caused also an increase of the interfacial tension σ between nuclei and the liquid surrounding phase.17 As a consequence, nucleation and growth of ordered objects occurred.12,

15, 16

Subsequent removal of methanol from the film

solution (by flowing pure nitrogen instead of methanol saturated nitrogen through the chamber) led to dissolution of all the previously formed objects (see Figure 2, at t0 + 58 s). Adding methanol again (this time less, φm = 6 ± 1 %) led again to nucleation and growth of objects (see Figure 2, at t0 + 94 s). However, compared to the previous case, their number density was lower due to the lower amount of methanol present in the film solution. Removing methanol once more (see Figure 2, at t0 + 174 s) led again to dissolution of all objects. Adding again methanol at even lower quantity (φm = 4 ± 1 %) reduced the number density of formed objects (see Figure 2, at t0 + 585 s). The experiments represented in Figure 2 show that nucleation, growth and dissolution of the objects are reversible. Moreover, increasing the amount of methanol added to the film solution decreased the time needed for inducing nucleation. For example, for 8% of methanol in the film, it took only about 6 seconds to detect growth while for 4 % of methanol it took about 2 minutes to observe the formation of the first nucleus. Figure 3 shows that we are able to control the nucleation rate J as well as the number density N of crystals by adjusting the volume fraction of methanol φm in the film solution through the


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vapor pressure above the thin film solution. To obtain values per unit area, we have multiplied J and N with the film thickness h. These quantities Jh and Nh, presented in Figure 3, were obtained by counting the number of nuclei per area of the optical micrograph, assuming that N was homogenous throughout the thickness of the thin film solution. Both, Jh and Nh were found to 1.2

increase with φm (Figure 3a and 3b). For example, a thin film solution of

0.4 %

containing about 8 % methanol led to a value of Nh = 3.3 x 109 m-2. In comparison, for φm = 4 % we obtained 1.8 x 108 m-2. Interestingly, the nucleation time t1 was less than 15 seconds for 8 % and 6 % of methanol but significantly longer for the solution containing 4 % of methanol. Accordingly, Nh saturated in less than 15 seconds for 8 % and 6 % of φm while for φm = 4 % saturation was reached only after about 60 seconds (not shown in Figure 3b). For a given polymer concentration, the amount of molecules contained in the ordered phase (which is proportional to the area times the number of nucleated objects) is determined by the supersaturation ratio, which, in turn, is controlled by the amount of non-solvent. However, the variation of the growth rate with super-saturation ratio may be different in the various spatial directions. Thus, the shape of the resulting ordered objects may differ with the amount of nonsolvent present. These results can be explained by the fact that φe decreased by adding methanol to the thin film solution, i.e. for

about constant, the supersaturation ratio (

⁄

) increased.

Therefore, the nucleation probability was higher and forming a nucleus needed less time. These experimental observations are in qualitative agreement with predictions of the classical nucleation theory and are also in accordance with previous results on copolymers.15,

16

As

expected, in all cases, Jh was maximal at the beginning and decreased to zero in time.


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Figure 3c depicts the evolution of the area of individual objects with time, referring to the marked objects in Figure 2 with correspondingly colored ellipses. The longest length of these objects as a function of time was deduced from in situ observations by OM and is indicated in the in-set of Figure 3c. For a given

, the objects were larger when grown in PBLG film

solutions containing less methanol, i.e. for higher φe and thus lower Nh. Thus, more PBLG molecules were available per nucleus. Surprisingly, while the maximum area depended on

,

the largest length of the objects was found to be nearly the same for all investigated values of

φm. During growth, the PBLG concentration φp,surr in the solution surrounding the growing objects decreased. Thus, the growth rate decreased to zero when equilibrium was reached for a concentration of φp,surr = φe. In additional experiments (not shown here), we extended the growth process through a continuous but slow increase of the amount of condensed methanol. Thus, φe slowly but continuously decreased and equilibrium was continuously shifted to lower values of φp,surr. This approach allowed to include more molecules into the ordered objects which thus increased the lengths to more than 200 µm.12 In Figure 4a, for constant values of φm, we show the evolution of N with polymer volume fraction φp. Here, we included also data from previous studies15, 16 on solutions of PBLG star block copolymers in chloroform with trace amounts of methanol. We observed a similar nucleation behavior for the here studied homopolymer. Adding protic nonsolvents to the block copolymer solution had the same effect on φe. Moreover, data for N(φp) for PBLG homopolymer and star block copolymer solutions could both be fitted to the same equation exp

(eqn. 2 in the supporting information), yielding values of the

equilibrium volume fraction φe (see Table 1). Using the values of φe from Table 1, we could


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present the number density N as a function of the supersaturation ratio S (Figure 4b) for the three data sets with differing amounts of methanol in the film solution. In Figure 4c, the dimensionless quantity interfacial tension

⁄

⁄

, which is proportional to the

between the nuclei and the surrounding solution (see eqn. 2 in the

supporting information), is shown as a function of the equilibrium volume fraction φe.17 For comparison, the interfacial tension obtained in previous studies15, 16 on chloroform solutions of PBLG star block copolymers with various amounts of water added, using a similar way of analyzing the data, are also represented. The best fit yields a slope of -0.52±0.01. Differences in the values of the slopes for the here studied homopolymer and the previously studied star block copolymer are attributed mainly to the differences in the nonsolvents used and also to uncertainties in determining the values of , , and the way used to extract values of

.

The presence of a nonsolvent influences the solubility limit or equilibrium volume fraction. This can be explained in two complementary ways: Calculations11 on ternary systems of PBLG, solvent and nonsolvent on the base of Flory’s theory5 show that the equilibrium volume fraction of dissolved PBLG in the isotropic phase can strongly decrease by increasing the volume fraction of the nonsolvent, in accordance with experimentally obtained phase diagrams13, 14. Alternatively, we may assume the formation of a complex between polypeptide molecules and protic nonsolvent molecules (water or methanol15,18). These complexes have a different solubility. We tried to check for such possible complexation between methanol and PBLG molecules by NMR measurements (see supplementary information). However, the results obtained so far only confirm that addition of methanol to the PBLG solution induces phase separation. No direct interaction between protons of methanol and PBLG molecules was detected in the isotropic solutions. However, as the resolution of the NMR measurements was limited, this does not


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represent an unambiguous proof against such complexation in the anisotropic part of the solution. For more discussion, see Figure S3 in supporting information.

CONCLUSIONS In summary, we have presented an experimental study on nucleation, growth and dissolution of ordered PBLG objects in dilute thin film solutions, induced by adding or removing, respectively, controlled amounts of methanol through the surrounding vapor phase. With this approach, we were able to control the rate of nucleation and the number density of nucleated objects. We showed that adding methanol to isotropic polymer solutions decreased the equilibrium volume fraction of dissolved polymers and hence, promoted nucleation and growth of ordered PBLG objects. Based on classical nucleation theory, we described the dependence of nucleation probability on polymer concentration and the amount of nonsolvent in the solution. The decrease of the equilibrium volume fraction with increasing content of methanol can be attributed to an increase of the interfacial tension between ordered phase and surrounding solution, in line the effect predicted by Flory for adding a nonsolvent to a binary solution. Complementary NMR experiments confirmed phase separation induced by the addition of methanol. While we do not have evidence for complexation between methanol and PBLG in the isotropic phase as the origin for the increase in interfacial tension, we cannot exclude yet such complexation in the ordered, anisotropic phase.


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FIGURES

a

b 8

1

0

0.1

0.01

0.01

m

4

0.1

p

4

8.5

1

8

hm (祄 )

hc (祄 )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0 9.0

9.5

10.0

8.5

o

9.0

9.5

10.0

o

T ( C)

T ( C)

Figure 1. (a) Dependence of thickness of a PBLG thin film solution on sample temperature due to the contributions of condensed chloroform (hc) and methanol (hm) from the surrounding vapor phase at room temperature. (b) PBLG volume fraction φp (blue circles) and methanol volume fraction, φm (red triangles) as a function sample temperature.


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a

b

t0

t0+16 s

No methanol

φ m = 8 ± 1 %

No methanol

t 0+94 s

t0+174 s

t0+585 s

φ m = 6 ± 1 %

No methanol

φ m = 4 ± 1 %

m [volume %]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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t0+58 s

10 5 0 0

100

200

300

t - t0 [s] Figure 2. (a) Typical series of optical micrographs demonstrate reversible growth and dissolution of ordered PBLG objects when adding or removing, respectively, methanol from the thin film solution. Initially, the dry thin film had a thickness h0 = 50 nm. It was then swollen to a polymer volume fraction of φp = 1.2 ± 0.4 % by condensing chloroform. All micrographs have a size of 230

120

.

(b) Temporal evolution of the volume fraction of methanol φm for the experiment displayed in (a). The length of the thick red lines represents the waiting time required for observing the formation of the first nuclei after adding methanol to the thin film solution.


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a

b 9

10

8

0

15

30

Time (s)

45

2

Time (s)

200

0

0

15

30

45

Time (s)

100

200

300

40

100 0

6

10

300

Length (祄 )

7

10

10

8±1% 6±1% 4±1%

Area (祄 )

8

10

10

-2

8±1 % 6±1 % 4±1 %

Nh (m )

10 -2 -1

c 10

9

Jh (m s )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


20

0

0

100

200

300

Time (s)

Figure 3. Temporal evolution of (a) nucleation rate J and (b) number density N of nuclei multiplied by the thickness of the thin film solution h, observed after adding φm = 8 %, 6 % and 4 % of methanol, respectively, to an initial polymer concentration of φp = 1.2 ± 0.4 %. (see Figure 2). (c) Temporal evolution of the area (in-set: longest length) of individual objects (marked with correspondingly colored ellipses in Figure 2). The length was measured along the long axis of these objects.


13


b 18

10



18

7±2% 4±2% 

15

10

12

1

p (%)

10

10

15

10

12

2 1/3

10

(Q )

-3

-3

N (m )

10

7±2% 4±2%

c / (kT)

a N (m )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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10

1

10

3

10

15 10 5 0 -4

5

-2

1E-4 10 1E-30.01 10 0.1 1

e (%)

S

Figure 4. Number density N of nuclei as a function of (a) polymer volume fraction

10 100

and (b)

supersaturation ratio S obtained for selected amounts of methanol in the thin film solution. The solid lines represent fits to

exp

(see eqn. 2 in the supporting information)

by assuming Q = 3/5 for a diffusion controlled growth process, β =

for spherical nuclei (β is

a shape factor introduced by Nielsen to account for different nucleus geometries), υ = ln

(which is the volume of a spherical molecule of radius r) and

.17 The obtained

values of φe and P are represented in Table 1. The dark circles in represent results taken from previous investigations15,

16

on chloroform solutions of rod-coil block PBLG copolymers,

containing only trace amounts of methanol. The green star in (a) represents the result of an analogous experiment on a chloroform solution of the here studied PBLG homopolymer, containing only a trace amount of methanol. As can be seen in a), a fit of exp

to this data point in combination with results for PBLG copolymers

yields satisfactory agreement. (c) Interfacial tension σ between nuclei and surrounding solution, represented by the dimensionless quantity

⁄

⁄

(see supporting information and

reference [17]), as a function of the equilibrium volume fraction

, consistent with previous


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studies.17 The triangles represent results for previous investigations15, 16 on chloroform solutions of rod-coil block PBLG copolymers, containing different amounts of water as the protic nonsolvent for PBLG.

TABLES

φm (%)

P (m-3)

φe (%)

7±2

1.3

1.8

10

6.1

1.8

10

4±2

3.0

1.8

10

15

2.9

10

9.9

5.3

10

1

14.6 ± 1

Table 1. Fitted values of φe for the different methanol content. Parameters deduced from the fits shown by the solid lines in Figures 4a and 4b. The equilibrium volume fraction φe for trace amount of methanol was obtained by using data from previous works15, 16 on chloroform solutions of rod-coil block PBLG copolymers.


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ASSOCIATED CONTENT Supporting Information Available. A schematic representation of the set up used in order to

microscopically observe thin film samples, a plot showing the relative number density N / P of nuclei as a function of equilibrium volume fraction φe and a discussion about possible complexation between methanol and PBLG molecules by NMR measurements are presented in the supporting information. This material is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * Prof. Günter Reiter Institute of Physics, Faculty of Mathematics and Physics, Albert-Ludwigs-University of Freiburg, Hermann-Herder-Str. 3, 79104 Freiburg, Germany Tel: +49-761-2035857

Fax: +49-761-2035855

Email: [email protected]

ACKNOWLEDGMENT The authors thank Prof. Gert Strobl, Prof. Achim Kittel, Dr. Werner Stille, Dr. Mohammad Razavi-Nouri, Dr. Khosrow Rahimi and Dr. Roozbeh Shokri for invaluable discussions. We are grateful for the Deutsche Forschungsgemeinschaft (DFG) for the financial support. I. B. and G. R. acknowledge the Freiburg Institute for Advanced Studies (FRIAS) for financial support.


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New York, 1993.


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(10) Robinson, C.; Ward, J. C.; Beevers, R. B., Liquid crystalline structure in polypeptide solutions. part 2. Discuss. Faraday Soc. 1958, 25, 29-42. (11) Russo, P. S.; Miller, W. G., On the Nature of the Poly(γ-benzyl glutamate)Dimethylformamide "Complex Phase". Macromolecules 1984, 17, 1324-1331. (12) Jahanshahi, K.; Botiz., I.; Reiter, R.; Thomann, R.; Heck, B.; Shokri, R.; Stille, W.; Reiter, G., Crystallization of Poly(γ-benzyl L-glutamate) in Thin Film Solutions: Structure and Pattern Formation. Macromolecules 2013, 46, 1470-1476. (13) Nakajima, A.; Hayashi, T.; Ohmori, M., Phase equilibria of rodlike molecules in binary solvent systems. Biopolymers 1968, 6, 973-982. (14) Wee, E. L.; Miller, W. G., Liquid Crystal-Isotropic Phase Equilibria in the System poly γ-benzyl-α, L-glutamate - Dimethylformamide. J. Phys. Chem. 1971, 76, 1446-1452. (15) Botiz, I.; Schlaad, H.; Reiter, G., Processes of Ordered Structure Formation in Polypeptide Thin Film Solutions. In Adv. Polym. Sci.: Self-Organized Nanostructures of Amphiphilic Block Copolymers, ed.; Springer Berlin-Heidelberg, 2011; Vol. 242, pp 117-149. (16) Botiz, I.; Grozev, N.; Schlaad, H.; Reiter, G., The influence of protic non-solvents present in the environment on structure formation of poly(γ-benzyl-L-glutamate in organic solvents. Soft Matter 2008, 4, 993-1002. (17) Nielsen, A. E.; Söhnel, O., Interfacial tensions electrolyte crystal-aqueous solution, from nucleation data. J. Cryst. Growth 1971, 11, 233-242. (18) Malcolm, B. R., Studies of Synthetic Polymer-Water Interactions using Monolayer Techniques. J. Polymer Sci. Part C: Polymer Symposia 1971, 34, 87-99.


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For Table of Contents Use Only

REVERSIBLE NUCLEATION φm = 0 %

φm = 8 ± 1 %

φm = 0 %

φm = 4 ± 1 %

120 x120 µm2 TOC. Optical micrographs showing the growth process of reversible nucleation of PBLG hexagonal columnar liquid crystal through adding/removing methanol via the surrounding vapor phase.

Manuscript title: Reversible nucleation, growth and dissolution of poly(γ-benzyl L-glutamate) hexagonal columnar liquid crystals by addition and removal of a nonsolvent

Authors: Kaiwan Jahanshahi; Ioan Botiz; Renate Reiter; Harald Scherer; Günter Reiter


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Reversible Nucleation, Growth, and Dissolution of Poly (Î³-benzyl l

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