Supramolecularly Engineered Ï-Amphiphile - Langmuir (ACS

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)

Article

Supramolecularly Engineered #-Amphiphile Priya Rajdev, Saptarshi Chakraborty, Marc Schmutz, Philippe J. Mésini, and Suhrit Ghosh Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b00842 • Publication Date (Web): 20 Apr 2017 Downloaded from http://pubs.acs.org on April 26, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Langmuir is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 23 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

Langmuir

Supramolecularly Engineered π-Amphiphile Priya Rajdev, ‡a Saptarshi Chakraborty, ‡a Marc Schmutz, b Philippe Mesini*b and Suhrit Ghosh*a a

Polymer Science Unit, Indian Association for the Cultivation of Science, Kolkata, India-700032;

Email: [email protected] b

Institut Charles Sadron, 23 rue du Loess - BP 84047, 67034 Strasbourg Cedex 2, France;

Email: [email protected]

ABSTRACT. This article describes self-assembly of supramolecularly engineered naphthalenediimide (NDI) derived amphiphiles NDI-1 and NDI-2. They have the same hydrophobic/ hydrophilic balance but merely differ by a single functional group, amide or ester, respectively. They exhibit distinct self-assembly in water; NDI-1 form hydrogel which upon aging forms crystals while NDI-2 forms micelle as revealed by in-depth structural analysis using cryo-TEM, DLS and SAXS studies. These results suggest H-bonding among the amide groups fully regulates the self-assembly by overruling the packing parameters. Further the present study elucidates sharp lower critical solution temperature (LCST) exhibited by these π-amphiphiles which has been extensively studied for many important applications of water soluble polymers but hardly known in the literature of small molecule surfactants. Control experiments with the same water soluble hydrophilic wedge did not show such property confirming this to be a

ACS Paragon Plus Environment

1

Langmuir 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

Page 2 of 23

consequence of the supramolecular polymerization by extended amide-amide H-bonding and not inherent to the structure of the hydrophilic wedge containing oligo-oxyethylene chains.

INTRODUCTION Amphiphiles are versatile synthetic systems for creating self-assembled nanostructures with wide-ranging applications in biomedicine and nanotechnology. Over last few years, several new analogues including peptide-amphiphile,1 facial amphiphile,2 supra-amphiphile

3-4

or π-

amphiphile 5-6 have been investigated with great intensity as they bring new opportunities in the field of functional organic materials. Amongst these, π-amphiphiles are particularly promising 720

because the strong aromatic interaction among the hydrophobic π-systems in water contributes

to very robust self-assembly which elicits photoluminescence, percolated pathway for charge transport, bioimaging, light harvesting and so on. Therefore, it is of enormous importance to achieve molecular scale precision in structure formation of such emerging amphiphiles. As of now, it is possible to achieve tunable nanostructures from amphiphiles depending on the packing parameter (p) = v/a0d where v and d are volume and length of the hydrophobic segment, respectively, and a0 is the surface area of the hydrophilic head group. Generally spherical micelle, cylindrical micelle or vesicle are produced when p ≤ 1/3, 1/3 < p ≤ 1/2 and 1/2 < p ≤ 1, respectively.21 However, such packing parameter-dependent structure formation lacks molecular scale precision that exists in supramolecular assembly of π-systems by directional molecular interaction such as H-bonding.22-23 We have endeavored exploring directional supramolecular interaction (especially H-bonding) for enacting new design principles in structure formation of πamphiphiles. With this objective we have designed two naphthalene-diimide derived amphiphiles NDI-1 and NDI-2 (Scheme 1). They consist of hydrophobic NDI moiety linked with the


2

Page 3 of 23 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

Langmuir

hydrophilic tri-alkoxy wedge and both are structurally identical except a single functional group; ester or amide,24 respectively, for NDI-2 and NDI-1. Therefore in terms of packing parameter, there is almost no difference between them while H-bonding can be operative only in case of supramolecularly engineered 25-26 amphiphile NDI-1. The question that we asked is whether this single H-bonding functional group can overcome the packing parameter and fully dictate the self-assembly? In this article we disclose contrasting self-assembly of these amphiphiles, their thermo-responsive behavior, in-depth structural analysis (by SAXS, cryo-TEM and other studies) and relatively less explored gel to crystal transition by aging.

Scheme 1. Structure of the two π-amphiphiles

RESULTS AND DISCUSSION Self-assembly studies: NDI-1 and NDI-2 were synthesized from commercially available starting materials in few synthetic steps (Scheme S1-S3) and characterized by NMR and mass spectrometry. Self-assembly was examined by solvent dependent UV/Vis studies (Figure 1a). In THF (good solvent) or polar medium like CH3OH and CH3CN, sharp absorption bands are noticed (Figure S1, SI) with characteristic vibronic peaks which indicate monomeric NDI. In water, for both the molecules there is a red shift accompanied by a hypochromic shift which can be attributed to off-set stacking among the NDI chromophores.27 Self-assembly could also be probed by solvent dependent 1H NMR studies (Figure 1b) that show sharp peaks in CDCl3 for


3

Langmuir 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

Page 4 of 23

the aromatic protons (from NDI and benzene rings) for both NDI-1 and NDI-2. But in D2O, significant up-field shift of all the aromatic proton peaks together with peak broadening clearly suggest aromatic stacking. Noteworthy that in the UV/Vis absorption spectra, the relative intensities of the two vibronic peaks at 382 and 362 nm, I382/ I362 differs in THF and water which further supports aromatic stacking.27 Concentration dependent UV/Vis studies show (Figure S2) that the value of I382/ I362 < 1 in concentrated solution for the aggregated NDI. With dilution the value remain invariant till certain concentration and then reaches to a value more than unity. From the inflection point of the I382/ I362 vs. concentration plot (Figure 1c-d) the critical aggregation concentration (CAC) was estimated to be 0.7 mM and 0.03 mM for NDI-1 and NDI2, respectively.28

Figure 1. a, b) Solvent dependent UV/Vis (c = 1.0 mM) and 1H NMR (c = 5.0 mM) spectra of NDI-1 and NDI-2. c, d) Variation of I382/ I362 (taken from the concentration dependent UV/Vis spectra shown in Figure S1) as function of concentration of NDI-1 (c) or (d)NDI-2


4

Page 5 of 23 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

Langmuir

Almost an order of magnitude higher CAC for NDI-1 is attributed to its less hydrophobicity due to the presence of the amide group. Thermoresponsive property: In order to verify the thermal stability, temperature-dependent UV/Vis experiments were attempted which surprisingly revealed precipitation at little above rt indicating these systems have a lower critical solution temperature (LCST). Considering large number of water soluble polymers exhibiting LCST behavior,29-30 similar observation in supramolecularly assembled systems are limited to a few.31-32 Therefore to study this systematically, the absorption at 450 nm (where neither NDI nor benzene ring has any absorption) was monitored as a function of temperature (Figure 2) which show a clear sigmoidal plot for both samples.

Figure 2. Temperature dependent absorbance (monitored at 450 nm) of aqueous solution of NDI-1, NDI-2 or the control molecule (structure shown as inset). c = 1 mM in all samples The sharp increase in absorbance intensity at 42 °C is attributed to the increased scattering at the cloud point due to the LCST of the self-assembled NDI-1 or NDI-2. Identical results in both cases is not surprising considering that the hydrophilic wedge consists of the same building


5

Langmuir 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

Page 6 of 23

blocks for both molecules. However the wedge (structure shown as inset Figure 2) alone lacking the NDI chromophore did not exhibit any cloud point within the tested temperature window (Figure 2). Infact even when the temperature dependent UV/Vis study was performed at ten times higher solute concentration, no cloud point was noticed even till 80 °C (Figure S4). It indicates the cloud point not only depends on the wedge structure but also on the hydrophobic/hydrophilic balance and/ or the self-assembly of the building block containing the temperature responsive segment. Mesoscopic structure: Although NDI-1 and NDI-2 exhibit identical physical properties, CryoTEM images (Figure 3) show contrasting morphologies. NDI-1 forms long fibrills with an average diameter of 4.2 ± 0.8 nm indicating elongated one dimensional assembly.18 Whereas NDI-2 shows micellar aggregates with an average diameter of 4.4 ± 1.0 nm (Figure 3b) which could also be verified by dynamic light scattering studies revealing a single sharp peak (Figure S5) with Dh = 5.0 nm.

Figure 3. Cryo-TEM images of (a) NDI-1 and (b) NDI-2 in D2O.


6

Page 7 of 23 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

Langmuir

As expected from the morphology, the NDI-1 spontaneously forms a transparent hydrogel33-35 at C > 3.0 mM but contrastingly no such gelation could be noticed for NDI-2 (Figure 4a). While large number of examples are known on organogels and spherical assemblies,27 NDI-derived hydrogelator are less common.36 As the volume fraction of the hydrophobic and hydrophilic segments are identical in both cases, the contrasting morphology and gelation ability could be related to the H-bonding interaction among the amide groups in NDI-1. To confirm this, FT-IR spectra of NDI-1 was compared in THF and water (Figure 4b). In THF several peaks appear in the range of 1640-1740 cm-1 which can be attributed to ester carbonyl (1708 cm-1), imide carbonyl (1720 and 1672 cm-1) and the amide carbonyl (1695 cm-1). The assignment of this particular peak for the amide carbonyl can be confirmed as it is missing in the spectrum of NDI2. Now in D2O, the amide peak shifted to 1645 cm-1 directly supporting H-bonding among the amide groups.

Figure 4. (a) Gel and sol images of NDI-1 (left) and NDI-2 (right) in H2O (5.0 mM). (b) Solvent dependent FT-IR spectra of NDI-1 and NDI-2, the arrow indicates the carbonyl stretching peak of the amide group in NDI-1; c = 5.0 mM Further insight on the structural detail of self-assembled NDI-1 and NDI-2, was gained by small angle X-ray scattering (SAXS) experiments. The intensities scattered by a gel of NDI-1 and


7

Langmuir 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

Page 8 of 23

solution of NDI-2, recorded under identical concentration and conditions, strongly differ by their shape at lower q (Figure 5). For NDI-1 it varies as q-1, whereas for NDI-2 it is invariant. The first dependence corresponds to particles with fibrillar shape, while the second dependences correspond to spherical particles and thus are in good agreement with the results obtained from cryo-TEM (Figure 3). For a dispersion of particles without inter-particle correlation, the scattered intensity (cm-1) can be expressed as: I(q) = φV ∆ρ 2VP P(q)

(1)

where φV is the volume fraction of the particles, ∆ρ is the difference in scattering length density (SLD) (cm-2) of the particle and the solvent, VP is the volume (cm3) of the particle and P(q) is the form factor of the particles. The curves for NDI-1 could not be modeled by the form factor of the homogeneous cylinder. Thus they were fitted with the form factor of a core-shell cylinder.37-40 2 π 1  2J1 (qr1 ) 2J1 (qr2 )  P(q) = + ( ρ s − ρ solv ) VP ( ρc − ρ s ) Vc  qr1 qr2  qL ∆ρ 2Vp 

(2)

where q is the scattering vector, L is the length of the cylinder (L >> r2); r2 is the outer radius of the cylinder, r1 is the radius of the core; ρc, ρs and ρsolv are the scattering length densities of the core, shell and solvent, respectively; Vc is the volume of the core, Vp is the volume of the particle including core and shell. Similarly the intensities from NDI-2 were fitted by the form factor of the core-shell sphere: sin(qr1 ) − qr1 cos(qr1 )] 1  [sin(qr2 ) − qr2 cos(qr2 )]  3Vc ( ρc − ρ s ) [ + 3Vp ( ρs − ρsolv ) 3 3 2 2 ∆ρ Vp   ( qr1 ) ( qr2 )

2

P(q) =

(3)


8

Page 9 of 23 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

Langmuir

In these equations, ∆ρ is the volume average SLD. We assumed that the core consists of the hydrophobic parts of the molecules. ρc was evaluated and fixed (values reported in table S1), while ρs was adjusted by the fit. The best fit for NDI-1 obtained with equations (1) and (2) is represented in Figure 5. The model matches well with the curve, except at low q where it has a lower slope. It was refined by taking into account a fraction f of the cylinders that are aligned and in contact with each other, which is also noticed in the TEM image (Figure 6). We have modeled it by pairs of cylinders in close contact, which adds a correcting factor:

Pcorr (q) = P(q) f (1+ J0 (2qr2 ))+ (1− f )

(4)

The best fits were obtained for the following values of the parameters ρs = 10.1 ± 0.003 1010 cm2

, r1 = 10.8 ± 0.1 Å, r2-r1 = 19.4 ± 0.1 Å, Φv = 0.049 ± 0.002 and f = 0.20 ± 0.02. The diameter of

the core is about 22 Å while the diameter of the cylinder is 60 Å which roughly matches with the width of the fibers obtained from cryo-TEM.

Figure 5. SAXS intensities of NDI-1 gel () and NDI-2 solution () at 2.5 wt. %; a) I(q) vs q. The intensity of NDI-2 has been multiplied by 10 for clarity. The dashed lines represent q-1 and q-4 variations. b) Kratky representation (q2I(q) vs q) for NDI-1. c) Kratky representation for NDI2. In all figures, the continuous lines are the fits; NDI-1 is modeled with core-shell cylinders partially paired (eq. 1, 2 and 4). NDI-2 is modeled with core-shell spheres (eq. 1 and 3). The dotted lines are the fits for NDI-1 without pairing (eq. 1 and 2)


9

Langmuir 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

Page 10 of 23

The dark areas in Cryo TEM correspond to a higher electronic density than water. The contrasts in TEM are therefore proportional to the SLD calculated for X-rays. Especially the shell should be less visible than the core. The observed diameters in TEM are between the diameters of the shell and the cores as observed by SAXS. This may be explained by the fact that close to the core, the density of the EO is higher or by a more complex model. The diameter of the core matches the length of the hydrophobic core, and the thickness of the shell matches the length of the ethylene oxides (17 Å). (Figure S6). Therefore, it is proposed (Scheme 2) that NDI-1 stacks with rotational displacement along the long axis leading to a closely packed cylindrical structure. Moreover, the estimated value for ρs (10.1 ± 0.003) is close to the SLD of EO (table S1) and confirms that ethylene-oxides belong in the shell. For NDI-2, the parameters for the best fits (from eq. 3) are ρs = 10.1 ± 0.003 1010cm-2, r1 = 15.3 ± 0.1 Å, r2-r1 = 17.2 ± 0.1 Å and Φv = 0.034 ± 0.001. The SLD found for the shell in micelles is about the same as in NDI-1, which confirms the models. In the micelles of NDI-2 the diameter of the core is 50% larger than the core in the cylinders of NDI-1, which can be attributed to the absence of the amide group which yields a looser packing of the hydrophobic parts. However, the estimated diameter of the particle is ~ 65 Å which corroborates with the DLS or cryo-TEM data. For both self-assemblies, the found volume fraction is higher than the one calculated from the molar volumes (0.02). It suggests that the peripheral oligo-oxyethylene chain are spread and hydrated. The effective volume is therefore much larger than the one occupied by the mere gelator.


10

Page 11 of 23 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

Langmuir

Scheme 2. Proposed packing of NDI-1 (left) and NDI-2 (right) Gel to crystal transformation: It is generally believed that gel phase is a meta-stable state and may not be the thermodynamic minimum of the system. However despite large number of examples known on hydrogelators, it is limited to only few examples where the internal order of the gelator molecules in fibrillar assembly has been studied in detail as a function of aging or an external stimulus. We noticed NDI-1 derived homogeneous hydrogel after few hours produced a supernatant liquid and a crystalline solid in a viscous liquid indicating evolution of another selfassembled state. TEM images (Figure 6) show a fibrillar network for the freshly prepared sample which is consistent with the cryo-TEM. However in contrast for the aged sample discrete short objects are noticed indicating generation of the crystal-like structure form the gel after aging.41-45 Atomic Force Microscopy (AFM) images also show (Figure S7) fibrillar structure for the freshly prepared solution of NDI-1 which upon aging transforms to sheet like structure (height ~3.0 nm, width ~ 100 nm) and therefore corroborate with the TEM results.This was further evident from the time dependent SAXS studies. The recorded intensities reflect with increasing time, the intensity at low angle lowers, a Bragg peak appears at 0.11 Å-1 (Figure 6), which corresponds to a distance of 57 ± 2 Å, comparable to the external diameter of the cylinder as measured by SAXS (60 Å). The precipitate may result from the crystalline packing of the cylinders, which will be studied in detail in the future. However the curves corresponding to the first three hours of measurements are constant and the Braggs peaks could be neglected. These first curves were summed and averaged and showed satisfactory statistics to conduct our study and get structural information of the gel fibers.


11

Langmuir 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

Page 12 of 23

Figure 6. TEM images (after negative staining) of (a) freshly prepared NDI-1 hydrogel and (b) after 6 h of aging. (c) Intensity scattered by a freshly prepared NDI-1 gel (2.5 wt %) at different times (The first measurement is done after 3 h maturation). The intensity is not sensibly modified after 3 h. Then a Bragg peak at 0.11 Å-1 appears

CONCLUSION In this article we have shown H-bonding driven distinct self-assembly pattern of two πamphiphiles which have identical packing parameters. It suggests directional molecular interaction have a great role to play in precision structure formation of amphiphiles by overruling the hydrophilic/ hydrophobic ratio dependent morphology variation. The paper also discloses a relatively less studied phenomenon of gel to crystal transition upon aging which is of relevance to the fundamental interest of structure and dynamics of gel phase.46-47 Furthermore, similar to thermo-responsive water soluble polymers, the present example indicates, supramolecular polymers can also exhibit LCST behaviour which is less explored till date. Together with adaptability and reversibility, such stimuli responsive behaviour will be of importance in emerging interest in supramolecular biomaterials.48 EXPERIMENTAL


12

Page 13 of 23 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

Langmuir

Materials and Methods: Solvents and reagents were received from commercial sources and used as it is unless otherwise mentioned. 1H NMR spectra were all recorded on a Bruker DPX400 or DPX-500 MHz NMR spectrometer and all the spectra were calibrated using TMS as the internal standard. Dynamic light scattering (DLS) measurements were carried out in a Malvern instrument at a scattering angle of 173°. UV/Vis absorption spectra were recorded on a PerkinElmer Lamda 25 spectrophotometer, attached with a temperature controlled Peltier. FT-IR spectra were recorded in a PerkinElmer Spectrum 100FT-IR spectrometer. Sample Preparation: Stock solutions of individual compounds (NDI-1 or NDI-2) were prepared in water or D2O. For NDI-1, water was added to the solid sample followed by cycles of sonication and heating till a clear transparent solution was obtained. In case of NDI-2, direct addition of water/D2O resulted in clear transparent solution. For determination of CAC, directly prepared solutions of varying concentrations and those prepared by dilution of a single concentrated solution were examined (data shown in Figure 1 and Figure S3) when comparable results were obtained. LCST Studies by UV/Vis Spectroscopy: For LCST studies, aqueous solution of a sample was placed in a quartz cuvette of 1.0 cm path length and heated from 25 to 70 °C with intervals of 1°C. 1.0 min of equilibration time for each temperature was allowed before the measurements were done. Absorbance at 450 nm was noted at various temperatures. The absorbance at 450 nm was plotted against temperature, and LCST was obtained from the inflection point. SAXs experiment: Sample of NDI-1 in water (2.5 wt %) were heated until a light precipitate appears and then cooled at room temperature. The mixture became transparent again and


13

Langmuir 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

Page 14 of 23

eventually formed a gel. The gel was let stand at room temperature. After 3 hours from the beginning of the preparation, the SAXS experiments were started. The SAXS experiment were performed with an Elexience spectrometer, equipped with a Rigaku microfocus rotating anode generator (MicromaxTM-007 HF) operating at 40 kV and 30 mA (CuKα radiation (λ=1.54 Å). The X-ray beam was monochromatized and focused using a confocal Max-Flux OpticsTM developed by Osmics, Inc. together with a three pinholes collimation system. Scattered intensity was measured with a 2D multiwire detector located at 0.7 m from the sample. This configuration allowed q vectors to be investigated in the range 0.0108 Å-1

Supramolecularly Engineered Ï-Amphiphile - Langmuir (ACS

Recommend Documents

Supramolecularly Engineered Ï-Amphiphile - Langmuir (ACS