Does Molecular Self-Association Survive in Nanochannels?

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Does Molecular Self-Association Survive in Nanochannels? Denis Morineau*,† and Christiane Alba-Simionesco‡ †

Institute of Physics of Rennes, CNRS-University of Rennes 1, UMR 6251, F-35042 Rennes, France, and ‡Laboratoire L eon Brillouin, CEA-Saclay, UMR 12, F-91191 Gif-Sur-Yvette, France

ABSTRACT tert-Butanol spontaneously forms supermolecular clusters in the liquid state. This phenomenon results from the balance between hydrogen(H)bonded self-association and steric repulsion, which is ubiquitous in complex supermolecular assemblies. Neutron scattering provides direct insight into this mesoscopic order through a distinct signature (prepeak) in the structure factor. Using MCM-41 molecular sieves, we show that the spatial correlations associated with micelle-like clusters are totally suppressed in nanoconfined geometry. This is direct evidence of a considerable variation of the structure at the mescoscopic scale of an associated liquid during its manipulation in nanostructured materials and illustrates to what extent nanoconfinement affects the formation of the highly directional hydrogen-bonded systems and the properties of confined liquids in general. SECTION Statistical Mechanics, Thermodynamics, Medium Effects

diffraction goes back to the 1930s.13-15 These systems are known to spontaneously form some long-lived micelle-like clusters of a few molecules in the liquid state. The clusters formation could provide a model for the mechanism of proteins aggregation or for the early stages of the formation of intermediate range order in network-forming systems such as water.3,7 As such, they have been the matter of constant active studies, with the aim to unravel the generic underlying mechanism of such association.16-23 The cluster formation results from the competition between strong and directional H-bond interactions of polar hydroxyl groups and the repulsion between the hydrophobic bulky parts of the molecules.18,19 On the basis of molecular simulations and X-ray and neutron scattering experiments, it has been shown that the formation of these microscopic arrangements has a clear experimental signature in terms of a prepeak in the static structure factor.13-17,24-30 tert-Butanol ((CH3)3-COH) is probably the simplest molecule among the variety of other systems, that display Hbonded clustering, such as aromatic amines like m-toluidine and m-fluoroaniline, or aromatic alcohols like m-cresol.26-31 For this reason and thanks to its globular form, it is also one of the most studied associating liquid investigated so far and can be considered as a model system for studying the generic features of mesoscopic H-bond-induced clustering. In the present letter, we report the analysis of liquid tert-butanol confined in the straight and monodisperse rigid channels of MCM-41 silica molecular sieves.32

M

olecular self-association is ubiquitous in hydrogen(H)-bonded liquids such as alcohols or amines, including chemical solvents and more complex fluids, found in material sciences and biology. The balance between hydrophobic interactions and H-bonds is an essential factor of self-association. It controls the microscopic segregation and supermolecular self-assembling of a variety of systems, from simple aqueous solutions to proteins.1-4 With the advance of nanotechnologies, the manipulation of fluids in nanochannels has offered new openings for fluidic applications and for material design. However, nanoconfinement can produce unanticipated structures. This is of particular importance since it can result in very different properties of the confined liquid. Although this aspect has not been systematically considered in the literature, there is an increasing amount of evidence that indicates that some properties of liquids in confinement should not be simply interpreted in terms of their bulk counterparts.5,6 This is especially important in the case of water, where confinement is considered as a possible strategy to extend the study of the liquid state or for the study of the cooperative nature of the dynamics of glass-forming materials.7,8 In the case of nanoconfined associating mixtures, interfacial macroclusters and new self-assembled phases have been reported in the literature.9-12 Many pure liquids exhibit supermolecular self-assembling in the bulk, which gives them special physical-chemical properties. We present in this letter a direct experimental observation of how nanoconfinement alters the formation of such mesoscopically ordered structures in a prototypical H-bonded liquid. A paradigm of mesoscopic H-bond-induced clustering is provided by globular alcohols, and its detection by X-ray

r 2010 American Chemical Society

Received Date: February 1, 2010 Accepted Date: March 11, 2010 Published on Web Date: March 18, 2010

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DOI: 10.1021/jz100132d |J. Phys. Chem. Lett. 2010, 1, 1155–1159

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dominant supermolecular clusters involve a limited number of molecules (typically between 4 and 10 according to the different studies), which rather form cyclic H-bonded structures and small winding chains surrounded by the hydrophobic parts of the corresponding molecules.22,24-30 It has been demonstrated that the presence of micelle-type clustering in tert-butanol induces a large density deficit at intermediate distances, which shows up in certain partial pair correlation functions and takes the appearance of a prepeak in the structure factor.24,25 This feature is obviously not specific to tert-butanol since it has been observed for many other associating molecules, including aliphatic or aromatic alcohols and amines (see, for instance, the prepeak of m-fluoroaniline in the inset of Figure 1).26-31 It is rather a generic characteristic of sufficiently large H-bonding molecules, whose association is frustrated by hydrophobic and steric interactions. At variance, self-association does not lead to this experimental signature for network-forming liquids, such as water or methanol (see methanol in the inset of Figure 1).26-28 Neutron diffraction offers a unique opportunity to probe directly H-bonded molecular association inside nanochannels by a detailed inspection of the static structure factor at low and intermediate Q values. Figure 2 shows that mesoporous confinement profoundly affects the static structure factor of liquid tert-butanol. The main diffraction peak is broadened and its total intensity is strongly reduced (by about 30%). The second major effect concerns the prepeak, which disappears under confinement. Note that other differences at lower Q values, i.e., a negative intensity for Q < 0.5 Å-1, are related to the mesoporous structure and are not relevant to the present discussion.6,33,34 The large changes of S(Q) in the region of the prepeak and the main diffraction peak suggest that the local order of the liquid phase is fundamentally disrupted by nanoscale confinement. More specifically, the absence of any correlation peak at the position of the prepeak means that supermolecular clusters, which are an essential ingredient of tert-butanol and many other associated liquids, are unstable in nanopores. Different reasons can be invoked to interpret the absence of prepeak in the structure factor of nanoconfined tert-butanol. Supermolecular self-assembling in H-bonded liquids results from a delicate balance between hydrophobic and H-bond interactions, which has been shown to be sensitive to external parameters such as temperature or pressure.20-22,26-28 Because of the huge surface-to-volume ratio of nanoconfined systems, the energetic interactions between the molecules and the matrix dominate a significant part of the thermodynamic properties of the confined system. This is in fact a recurrent issue in the physics of confined systems. For instance, an extensive number of studies have revealed the large influence of surface energy on the relative stability of the different phases of a confined system.35-38 Surface interaction could also modify the stability of structural entities or fluctuations in the liquid state as it does for associating mixtures.9-12 Changing the nature of the surface interaction, for instance by tuning the hydrophobicity by chemical grafting would be a possible way to address this issue more specifically, although it would also change the

Figure 1. Neutron static structure factor S(Q) and intramolecular form factor f1(Q) of bulk tert-butanol. Inset: structure factor of two different types of H-bonded liquids: methanol (light gray) and m-fluoroaniline (dark gray).

Figure 2. Low-Q neutron static structure factor S(Q) of tertbutanol in bulk and confined in nanochannels of pore size D = 2.4 nm and D = 3.5 nm.

The experimental structure factor S(Q) of bulk liquid tertbutanol is shown in Figure 1. The computed intramolecular form factor f1(Q) has been added as a dashed line. A direct comparison between S(Q) and f1(Q) indicates that the scattered intensity at large Q values (i.e., above 3 Å-1) is essentially related to intramolecular contributions. Short-range intermolecular correlations and intermediate range supermolecular assembly show up in the region of smaller Q values. The use of a high-resolution spectrometer allows for an improved description of this small and intermediate Q-range where two essential features are observed, as shown in Figure 2. First, the main diffraction peak appears in the range from 1.1 to 1.5 Å-1 with a maximum at about QMP = 1.3 Å-1. This relatively broad peak at intermediate Q-range is typically observed in liquids and amorphous solids and mostly reflects short-range intermolecular correlations. In addition, the structure factor of liquid tert-butanol clearly exhibits a prepeak (or inner peak) at QPP = 0.7 Å-1. This prepeak in diffraction data is the signature of H-bonded association.13-15 It has been unambiguously ascribed to the formation of H-bond-induced clusters of mesoscopic size.16,17,24-30 According to the abundant literature on the matter, the existence of a prepeak in associated fluids is closely related to the amphiphilic nature of the alcohol molecules, more specifically to a competition between hydrophobic hard-core repulsive and H-bond interactions. It requires packing and steric effects, which do not favor the formation of extended structures in terms of H-bonds chains or networks.16-22 Hence,


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roughness of the surface. Moreover, the proximity of a solid surface often promotes specific organizations in the interfacial fluid, such as layering, linear aggregate, or hexatic order.9-11,35-38 This ordering of the interfacial fluid can compete with the inherent structures of the bulk liquid. In principle, such interactions between the fluid and the matrix should show up in the neutron structure factor. Finally, in addition to surface effects, the spatial restriction introduced by the porous geometry imposes severe constraints on the extension of medium-range ordered structures. Such effect does not only depend on the pore size (finite size effect) but also on the details of the pore shape. In order to get a deeper understanding of the possible origin of our experimental observations, we have compared them with the quantitative predictions of a simple model that accounts for spatial confinement effects on the static structure factor. This model was introduced by Soper et al. for Vycor,39,40 and later generalized for MCM-41 types of materials by Morineau et al.6,33,34 It primary accounts for the fact that the static structure factor S(Q) of a nanoconfined fluid is not simply related to the pair correlation function gL(r), R as it is the case in the bulk state (i.e., S(Q) = f1(Q) þ (4π/Q)F ( gBulk L (r) - 1)r sin(Qr)dr, where F is the liquid density). Indeed, S(Q) includes both fluid-fluid and fluid-matrix cross-correlations in a confined system, and it is additionally distorted by excluded volume effects. Excluded volume effects basically express the topological constraint introduced by spatial confinement, which imposes an inhomogeneous distribution of density within the sample. Only the porous volume is accessible to molecules. Static correlations in a confined phase are sensitive to both the local structure of the fluid (inherent intermolecular correlations) and the requirement that a fraction of space is inaccessible to the molecules (out of pore volume). This can be expressed quantitatively in eq 1, which is the sum of an intramolecular term, an intermolecular fluid-fluid term, and a fluid-matrix cross-term.6,33,34 Z 4π SðQÞ ¼ f1 ðQÞ þ xLiq F ½ð~gLiq ðrÞ -1ÞgðppÞintra ðrÞ u Q þ gðppÞ u ðrÞ -1r sinðQrÞdr ^bSiO2 4π Z -1Þr sinðQrÞdr þ 2xSiO2 F ð~gLiq-SiO2 ðrÞgðpwÞ u ^bLiq Q ð1Þ

Figure 3. Simulated low-Q static structure factor S(Q) of tertbutanol confined in nanochannels of pore size D = 2.4 nm and D = 3.5 nm, and the experimental neutron structure factor of the bulk.

molecular order. The modification of S(Q) due to excluded volume effects, assuming they are the only contribution, can be fully computed. This implies setting ~gLiq(r) = ~gBulk L (r) and ~gLiq-SiO2(r) = 1. The resulting structure factors are shown in Figure 3. The simulated structure factors provide a fair description of the experimental variation of the intensity of the main diffraction peak, while some essential trends are partly reproduced for the prepeak. Indeed, excluded volume effect predicts a significant broadening of the prepeak, and a considerable decrease of its intensity. One can conclude that the topological constraint induced by spatial confinement is the dominant ingredient leading to the destruction of H-bond induced supermolecular correlations. At variance to experiments however, there remains a distinguishable shoulder at QPP = 0.7 Å-1. Such a discrepancy is conceivable given the simplicity of the model used. Accordingly, the remaining differences between the predicted and the experimental structure factors can be viewed as the upper bound for the influence of other contributions such as nontrivial interfacial cross-correlations in ~gLiq-SiO2(r) or modifica6 tions of the inherent fluid-fluid pair correlations ~gLiq(r) ¼ ~gBulk L (r). This finding would profit from more microscopic information, for example, gained by molecular simulations. In conclusion, our neutron scattering experiments show that the signature of H-bonded supermolecular micelle-like clusters in terms of a prepeak in the structure factor of liquid tert-butanol is suppressed by nanoconfinement. We show that the topological constraint induced by spatial confinement plays a dominant role in the loss of intermediate range correlations, while some calculations of excluded volume effects allow us to provide an upper bound for other possible contributions. The change (or the control) of the local and intermediaterange H-bonds structure under confinement is a crucial aspect of some topical issues, such as the anomalous phase behavior of nanoconfined water.7 In the latter case, molecular simulation and careful methodological developments in the data reduction of neutron scattering experiments have been required to emphasize some differences between bulk and confined water.5 Beyond the very important specific case of water, our results provide the first direct observation of the instability of molecular self-assemblies in a prototypical

where xLiq and xSiO2 are the molar fractions of fluid and silica within the nanocomposite system, respectively. ^ bLiq (^ bSiO2) is the sum of the atomic correlation lengths over one liquid molecule (silica unit respectively). The intrinsic pair correlations within the fluid and between the fluid and the matrix are described by ~gLiq(r) and ~gLiq-SiO2(r), respectively. At variance, g(pp)intra (r), g(pp) and g(pw) are uniform fluid pair u u u correlation functions that account for the excluded volume effects and only depend on the geometry of the porous matrix. They are defined as the pair correlation functions of a system of noninteracting particles confined in the same restricted geometry.6,33,34,39,40 The above model allows one to extract purely topological effects, which constrain the extension of fluid static correlations, from other hypothetical changes of the inherent


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H-bonded liquid. They emphasize that some inherent properties of nanoconfined fluids cannot be simply deduced from the understanding of the bulk phase. Given the fact that selfassociation is the characteristic factor determining the physical-chemical properties of many solvents and biological systems, we anticipate that our conclusions are also relevant to other supermolecular assemblies and their manipulation in nanostructured devices.41

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EXPERIMENTAL METHODS

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Two MCM-41 matrices with cylindrical pore diameters D = 2.4 and D = 3.5 nm were synthesized according to a procedure already detailed in previous works.8,42,43 The structural parameters of the matrices were checked by neutron diffraction, scanning electron microscopy, and by nitrogen adsorption isotherms at liquid nitrogen temperature. Fully deuterated tert-butanol (99.8%) was purchased from Eurisotop, Saclay and used with no further purification. The same procedure as described in refs 8, 42, and 43 was used to achieve a nearly complete filling of the porous volume with tert-butanol by impregnation from the liquid phase. The obtained materials were loaded in a sealed vanadium cell prior to neutron scattering experiments. The neutron scattering experiments were performed at T = 300 K on two different double-axis spectrometers G6.1 and 7C2 of the Laboratoire L eon Brillouin neutron source facility (CEA-CNRS, Saclay) using a monochromatic incident wavelength of 4.7 Å and 0.7 Å, respectively. Standard calibration and data reduction procedures were applied.26-28 The static structure factor of the confined tert-butanol was derived from a difference between the experimental differential cross sections of the confined system and an empty MCM-41.6,33,34 The scattered intensity arising from the empty matrix corresponds to less than one-third of the total intensity like in previous studies.6,33 We combined the normalized spectra obtained from these complementary spectrometers to cover an extended range of momentum transfer Q (from 0.1 to 16 Å-1) with an improved resolution at low Q (Q < 1.8 Å-1). This region of the structure factor contains essential information about the intermolecular order that exists in the liquid at the short (nearest neighbors) and intermediate distances.

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AUTHOR INFORMATION Corresponding Author: *To whom correspondence should be addressed. E-mail: denis. [email protected].

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REFERENCES (1)

(2) (3)

(4)

Dixit, S.; Crain, J.; Poon, W. C. K.; Finney, J. L.; Soper, A. K. Molecular Segregation Observed in a Concentrated AlcoholWater Solution. Nature 2002, 416, 829. Chandler, D. Interfaces and the Driving Force of Hydrophobic Assembly. Nature 2005, 437, 640. Stradner, A.; Sedgwick, H.; Cardinaux, F.; Poon, W. C. K.; Egelhaaf, S. U.; Schurtenberger, P. Equilibrium Cluster Formation in Concentrated Protein Solutions and Colloids. Nature 2004, 432, 492. Guo, J.-H.; Luo, Y.; Augustsson, A.; Kashtanov, S.; Rubensson, J.-E.; Shuh, D. K.; Agren, H.; Nordgren, J. Molecular Structure of Alcohol-Water Mixtures. Phys. Rev. Lett. 2003, 91, 157401.


(22)

(23)

(24) (25)

1158

Mancinelli, R.; Imberti, S.; Soper, A. K.; Liu, K. H.; Mou, C. Y.; Bruni, F.; Ricci, M. A. Multiscale Approach to the Structural Study of Water Confined in MCM41. J. Phys. Chem. B 2009, 113, 16169. Morineau, D.; Gu egan, R.; Xia, Y.; Alba-Simionesco, C. Structure of Liquid and Glassy Methanol Confined in Cylindrical Pores. J. Chem. Phys. 2004, 121, 1466. Soper, A. K. Structural Transformations in Amorphous Ice and Supercooled Water and Their Relevance to the Phase Diagram of Water. Mol. Phys. 2008, 106, 2053. Alba-Simionesco, C.; Dumont, G.; Frick, B.; Geil, B.; Morineau, D.; Teboul, V.; Xia, Y. Confinement of Molecular Liquids: Consequences on Thermodynamic Static and Dynamical Properties of Benzene and Toluene. Eur. Phys. J. E 2003, 12, 19. Mizukami, M.; Moteki, M.; Kurihara, K. Hydrogen-Bonded Macrocluster Formation of Ethanol on Silica Surfaces in Cyclohexane. J. Am. Chem. Soc. 2002, 124, 12889. Mizukami, M.; Nakagawa, Y.; Kurihara, K. Surface Induced Hydrogen-Bonded Macrocluster Formation of Methanol on Silica Surfaces. Langmuir 2005, 21, 9402. Yilmaz, N.; Mizukami, M.; Kurihara, K. Molecular Macrocluster Formation on Silica Surfaces in Phenol-Cyclohexane Mixtures. Langmuir 2007, 23, 6070. Kotelyanskii, M.; Kumar, S. K. Surface Transitions for Confined Associating Mixtures. Phys. Rev. Lett. 1998, 80, 1252. Stewart, G. W.; Skinner, E. W. X-ray Diffraction in Liquids: A Comparison of Certain Primary Normal Alcohols and Their Isomers. Phys. Rev. 1928, 31, 1. Warren, B. E. X-ray Diffraction in Long Chain Liquids. Phys. Rev. 1933, 44, 969. Pierce, W. C.; MacMillan, D. P. X-ray Studies on Liquids: The Inner Peak for Alcohols and Acids. J. Am. Chem. Soc. 1938, 60, 779. Karmakar, A. K.; Sarkar, S.; Joarder, R. N. Molecular Clusters in Liquid tert-Butyl Alcohol at Room Temperature. J. Phys. Chem. 1995, 99, 16501. Karmakar, A. K.; Krishna, P. S. R.; Joarder, R. N. On the Structure Function of Liquid Alcohols at Small Wave Numbers and Signature of Hydrogen-Bonded Clusters in the Liquid State. Phys. Lett. A 1999, 253, 207. Bowron, D. T.; Finney, J. L. Anion Bridges Drive Salting Out of a Simple Amphiphile from Aqueous Solution. Phys. Rev. Lett. 2002, 89, 215508. Bowron, D. T.; Finney, J. L.; Soper, A. K. The Structure of Pure Tertiary Butanol. Mol. Phys. 1998, 93, 531. Sassi, P.; Palombo, F.; Cataliotti, R. S.; Paolantoni, M.; Morresi, A. Distributions of H-Bonding Aggregates in tert-Butyl Alcohol: The Pure Liquid and Its Alkane Mixtures. J. Phys. Chem. A 2007, 111, 6020. Durov, V. A.; Shilov, I. Y.; Tereshin, O. G. Modeling of Supramolecular Structure and Dielectric Properties of Butanols from Melting Point to Supercritical State. J. Phys. Chem. B 2008, 112, 8076. Andanson, J. M.; Soetens, J. C.; Tassaing, T.; Besnard, M. Hydrogen Bonding in Supercritical tert-Butanol Assessed by Vibrational Spectroscopies and Molecular-Dynamics Simulations. J. Chem. Phys. 2005, 122, 174512. Kusalik, P. G.; Lyubartsev, A. P.; Bergman, D. L.; Laaksonen, A. Computer Simulation Study of tert-Butyl Alcohol. 1. Structure in the Pure Liquid. J. Phys. Chem. B 2000, 104, 9526. Perera, A.; Sokolic, F.; Zoranic, L. Microstructure of Neat Alcohols. Phys. Rev. E 2007, 75, 060502(R). Zoranic, L.; Sokolic, F.; Perera, A. Microstructure of Neat Alcohols: A Molecular Dynamics Study. J. Chem. Phys. 2007, 127, 024502.


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(26)

(27)

(28)

(29)

(30)

(31)

(32)

(33)

(34)

(35)

(36) (37)

(38)

(39)

(40)

(41)

(42)

(43)

Morineau, D.; Alba-Simionesco, C.; Bellissent-Funel, M. C.; Lauthie, M.-F. Experimental Indication of Structural Heterogeneities in Fragile Hydrogen-Bonded Liquids. Europhys. Lett. 1998, 43, 195. Alba-Simionesco, C.; Morineau, D. Hydrogen-Bond-Induced Clustering in the Fragile Glass-Forming Liquid m-Toluidine: Experiments and Simulation. J. Chem. Phys. 1998, 109, 8494. Alba-Simionesco, C.; Morineau, D.; Frick, B.; Higonenq, N.; Fujimori, H. An Analysis of the Short and Intermediate Range Order in Several Glass-Forming Liquids from the Static Structure Factor Under Pressure. J. Non-Cryst. Solids 1998, 235-237, 367. Chelli, R.; Cardini, G.; Procacci, P.; Righini, R.; Califano, S. Molecular Dynamics of Glass-Forming Liquids: Structure and Dynamics of Liquid Metatoluidine. J. Chem. Phys. 2002, 116, 6205. Chelli, R.; Cardini, G.; Procacci, P.; Righini, R.; Califano, S. Dynamical and Structural Correlation in Supercooled Liquids: A Molecular Dynamics Investigation of m-Toluidine. J. Chem. Phys. 2003, 119, 357. Descamps, M.; Legrand, V.; Guinet, Y.; Amazzal, A.; Alba, C.; Dore, J. “Pre-Peak” in the Structure Factor of Simple Molecular Glass Formers. Prog. Theor. Phys. 1997, 126, 207. Kresge, C.; Leonowicz, M.; Roth, W.; Vartuli, J.; Beck, J. Ordered Mesoporous Molecular Sieves Synthesized by a Liquid-Crystal Template Mechanism. Nature 1992, 359, 710. Morineau, D.; Alba-Simionesco, C. Liquids in Confined Geometry: How to Connect Changes in the Structure Factor to Truly Different Structures. J. Chem. Phys. 2003, 118, 9389. Guegan, R.; Morineau, D.; Alba-Simionesco, C. Interfacial Structure of an H-Bonding Liquid Confined into Silica Nanopore with Surface Silanols. Chem. Phys. 2005, 317, 236. Gelb, L. D.; Gubbins, K. E.; Radhakrishnan, R.; SliwinskaBartkowiak, M. Phase Separation in Confined Systems. Rep. Prog. Phys. 1999, 62, 1573. Christenson, H. K. Confinement Effects on Freezing and Melting. J. Phys.: Condens. Matter 2001, 13, R95. Alcoutlabi, M.; McKenna, G. B. Effects of Confinement on Material Behaviour at the Nanometre Size Scale. J. Phys.: Condens. Matter 2005, 17, R461. Alba-Simionesco, C.; Coasne, B.; Dosseh, G.; Dudziak, G.; Gubbins, K. E.; Radhakrishnan, R.; Sliwinska-Bartkowiak, M. Effects of Confinement on Freezing and Melting. J. Phys.: Condens. Matter 2006, 18, R15. Bruni, F.; Ricci, M. A.; Soper, A. K. Water Confined in Vycor Glass. I. A Neutron Diffraction Study. J. Chem. Phys. 1998, 109, 1478. Soper, A. K.; Bruni, F.; Ricci, M. A. Water Confined in Vycor Glass. II. Excluded Volume Effects on the Radial Distribution Functions. J. Chem. Phys. 1998, 109, 1486. Lucent, D.; Vishal, V.; Pande, V. S. Protein Folding under Confinement: A Role for Solvent. Proc. Natl. Acad. Sci. U.S.A. 2007, 104, 10430. Morineau, D.; Xia, Y.; Alba-Simionesco, C. Finite-Size and Surface Effects on the Glass Transition of Liquid Toluene Confined in Cylindrical Mesopores. J. Chem. Phys. 2002, 117, 8966. Xia, Y.; Dosseh, G.; Morineau, D.; Alba-Simionesco, C. Phase Diagram and Glass Transition of Confined Benzene. J. Phys. Chem. B 2006, 110, 19735.


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Does Molecular Self-Association Survive in Nanochannels?

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