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Evidence of microphase separation in controlled pore glasses
A Vyalikh1, Th Emmler, E Gedat
1Freie Universität Berlin, Institut für Chemie, Takustrasse 3, 14195 Berlin, Germany.
Solid State Nuclear Magnetic Resonance
|August 3, 2005
Summary
Phase separation of water and isobutyric acid (iBA) in porous glass was observed. This confined liquid mixture exhibits a distinct phase separation temperature range, differing from bulk behavior.
Area of Science:
- Physical Chemistry
- Materials Science
- Chemical Engineering
Background:
- Phase separation in liquid mixtures is a critical phenomenon.
- Confinement effects can significantly alter phase behavior compared to bulk systems.
- Understanding confined phase separation is vital for applications in porous materials.
Purpose of the Study:
- To investigate the phase separation of a water-isobutyric acid (iBA) mixture within Controlled Pore Glass (CPG) pores.
- To determine the temperature window and characteristics of phase separation under confinement.
- To develop a model explaining the observed confined phase separation behavior.
Main Methods:
- 1H NMR relaxometry was employed to probe molecular dynamics.
- 1H-pulsed field gradient (PFG) diffusion measurements quantified molecular mobility.
- Controlled Pore Glass (CPG) with a pore size of 10-75 nm was used as the confining medium.
Main Results:
- Evidence of phase separation was observed for an acid-rich (54 wt% iBA) mixture in CPG pores.
- The confined phase separation occurred within a specific temperature window (32-39°C).
- Anomalous diffusion coefficients and bi-exponential relaxation decays indicated the phase transition.
Conclusions:
- The phase separation temperature in CPG pores is lower than in the bulk (41°C).
- Confined phase separation occurs over a finite temperature range, suggesting heterogeneity.
- A model involving temperature-dependent domain structures explains the observed phenomena.