The coexisting phase behavior of thermo-responsive copolymer solutions
Chao Feng1, Chun-lai Ren, Yu-qiang Ma
1National Laboratory of Solid State Microstructures, Department of Physics, Nanjing University, Nanjing 210093, China. chunlair@nju.edu.cn.
Soft Matter
|June 24, 2014
Summary
This study explores how temperature affects polyethylene oxide-block-poly(N-isopropylacrylamide) (PEO-b-PNIPAm) self-assembly. We found that micelles and vesicles can coexist, revealing temperature-induced transitions in thermoresponsive polymers.
Area of Science:
- Polymer science
- Materials science
- Physical chemistry
Background:
- Polyethylene oxide-block-poly(N-isopropylacrylamide) (PEO-b-PNIPAm) is a thermoresponsive copolymer.
- Understanding its self-assembly behavior is crucial for applications.
Purpose of the Study:
- To investigate the impact of temperature on PEO-b-PNIPAm self-assembly in aqueous solutions.
- To quantitatively describe the changes in water affinities of PEO and PNIPAm blocks with temperature.
- To determine the phase behavior and co-existence of different aggregate structures.
Main Methods:
- Utilizing a molecular theory for dilute PEO-b-PNIPAm solutions.
- Accounting for hydrogen bond formation between copolymer monomers and water.
- Applying the equilibrium criterion of excess grand potential under grand canonical ensemble conditions.
- Calculating potentials of mean force for aggregates.
Main Results:
- Increased temperature breaks hydrogen bonds in PNIPAm, making it hydrophobic while PEO remains hydrophilic.
- Both micelles and vesicles are stable and can coexist in aqueous solutions.
- A phase diagram was generated, showing distinct regions for micelles, vesicles, and their coexistence.
- Two types of micelle-vesicle transitions were identified: spontaneous and temperature-induced.
Conclusions:
- The study provides a theoretical framework for understanding thermoresponsive polymer self-assembly.
- The findings are valuable for designing PEO-b-PNIPAm based materials for various applications.
- The coexistence of micelles and vesicles highlights complex phase behavior influenced by temperature.
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