Phase transitions of hexadecane in poly(alkyl methacrylate) core-shell microcapsules
Jeremy K Black1, Lauren E Tracy, Conor P Roche
1Department of Chemistry and Biochemistry, Santa Clara University, Santa Clara, California 95053, USA.
The Journal of Physical Chemistry. B
|March 9, 2010
Summary
Researchers studied n-hexadecane (HD) microcapsules, finding that polymer shell properties influence freezing. Bulkier side chains on poly(alkyl methacrylates) shells increase the supercooling required for HD to freeze.
Area of Science:
- Materials Science
- Physical Chemistry
- Nanotechnology
Background:
- Microencapsulation is crucial for controlling material properties.
- Understanding phase transitions in confined systems is key for applications.
- Polymer shell properties significantly affect encapsulated substance behavior.
Purpose of the Study:
- To investigate the effect of polymer shell surface tension on the freezing point of encapsulated n-hexadecane (HD).
- To explore the influence of microcapsule size and polymer side-chain structure on supercooling.
- To examine the aging behavior of these microcapsules.
Main Methods:
- Preparation of poly(alkyl methacrylates) microcapsules with subfemtoliter n-hexadecane (HD) cores (50-140 nm).
- Systematic variation of alkyl substituents in the polymer shell to tune surface tension.
- Analysis of freezing point depression and supercooling behavior.
- Investigation of capsule aging accelerated by heating.
Main Results:
- The size-dependent supercooling predicted by the G-T equation was not observed.
- Freezing of HD required greater supercooling in capsules with bulkier polymer side chains.
- Increased hydrophobicity and decreased glass transition temperature of the polymer correlated with increased supercooling.
- Microcapsule aging was observed and could be accelerated by heating.
Conclusions:
- Polymer shell chemistry, specifically side-chain bulkiness and hydrophobicity, significantly impacts the freezing behavior of encapsulated n-hexadecane.
- The observed supercooling effects deviate from standard size-dependent predictions, highlighting the role of interfacial properties.
- Microcapsule stability and aging are influenced by shell composition and thermal history.
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