Multiple Glass Transitions of Microphase Separed Binary Liquids Confined in MCM-41

Abstract

International audienceThe confinement of fluids in channels of nanometer size presents unprecedented opportunities to reveal emergent physicochemical properties that have no equivalent in the corresponding bulk system. We present an experimental study of fully miscible binary low-molecular weight liquids confined in nanopores. Under these conditions, the mixtures form a microphase-separated state with two regions of different compositions forming the core and the shell of a concentric tubular nanostructure. We combine neutron diffraction and DSC measurements to assess the thermal behavior of this unusual phase. These results show that crystallization is suppressed, leading to glassy behaviors characterized by anomalies in the density and the heat capacity. We reveal the coexistence of two different glass transitions, providing the direct proof for two different enthalpic relaxation times. It leads to the conclusion that the subcomponents of the microphase-separated mixture each obey distinct dynamical behaviors. This phenomenon is all the more unusual considering that the thicknesses of the core and the shell are only one to three molecular sizes. These results have important implications for processes involving interfacial multicomponents fluids, including heterogeneous catalysis, microfluidic devices, nanofiltration or oil industry

Supramolecular Organization in Confined Nanospaces

“…observed a higher tendency of ethanol to selectively adsorb on the pore walls of boron nitride, and showed that the ethanol/water partial demixing was relatively unaffected by the pore width (Figure b) . Similar microphase‐separated tubular structures seem to be a recurrent feature of binary liquid mixtures in mesopores, and are also supported by experimental evidences . For example, neutron diffraction experiments on MCM‐41 filled with a tert‐butanol‐toluene mixture evidenced inhomogeneous distribution of the components, suggesting that the pore surface is covered by tert‐butanol molecules, while toluene preferentially locates in the central region of the pore …”

“…Recently, computational studies with slit‐pore models highlighted interesting organizational properties of confined fluids ,,,. According to Guo et al, an ethanol‐water mixture undergoes a partial demixing within the walls of an hydrophilic pore: while ethanol molecules tend to adsorb on surface silanols, water molecules preferentially interact among themselves, forming wires or clusters (Figure a) .…”

Dynamic Heterogeneities in Liquid Mixtures Confined in Nanopores

“…This direct experimental evidence of the core–shell organization represents a unique insight into allowing the investigation of the particular dynamical properties of these novel systems. Indeed, we evaluated the phase behavior and the glassy dynamics of TBA–TOL binary liquids confined in MCM-41 by the combination of neutron diffraction and differential scanning calorimetry (DSC) measurements in an attempt to examine the thermal behavior of this unusual phase in terms of density and heat capacity . Our studies revealed the coexistence of two different glass transitions, which suggests the existence of two spatially separated dynamics, likely attributed to the subcomponents of the microphase separated mixture.…”

Unprecedently large 37Cl/35Cl equilibrium isotopic fractionation on nano-confinement of chloride anion

“…A number of these differences originate in the confinement of the molecules in nano or sub-nano structures. Sulfur allotropy 1 , change in electrochemical reactivity 2 , and ferroelectric properties of polymers in narrow nanotubes 3 , solar cell operations 4 , liquid crystals properties in microdroplets 5 , hydrogen atom transfer in micelles 6 , or glass transitions in mesoporous nanochannels 7 , are among recently described examples of such phenomena. Confinement, by influencing molecular vibrations 8 – 10 , can also lead to isotopic fractionation.…”