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Interfacial Molecular-level Structures of Polymers and Biomacromolecules Revealed via Sum Frequency Generation Vibrational Spectroscopy
Published on: August 13, 2019
Modeling polymer-induced interactions between two grafted surfaces: comparison between interfacial statistical
Shekhar Jain1, Valeriy V Ginzburg, Prasanna Jog
1Department of Chemical and Biomolecular Engineering, Rice University, Houston, Texas 77005, USA. sjain@rice.edu
The Journal of Chemical Physics
|August 7, 2009
Summary
The study shows that free polymers can cause attraction between grafted polymer surfaces, depending on chain lengths. This finding is crucial for understanding nanocomposite behavior and thermodynamics.
Area of Science:
- Polymer Science
- Physical Chemistry
- Materials Science
Background:
- Interactions between polymer grafted surfaces are vital for applications like nanocomposites and colloid stabilization.
- Previous work established interfacial statistical associating fluid density theory (iSAFT) for calculating grafted polymer chain structures.
Purpose of the Study:
- To apply iSAFT to calculate the interaction forces between two grafted polymer monolayers in good solvent conditions.
- To investigate the influence of differing segment sizes between free and grafted polymers on these interactions.
Main Methods:
- Utilized density functional theory, specifically iSAFT, to model polymer grafted surfaces.
- Analyzed interaction forces under implicit good solvent conditions.
- Considered scenarios with varying segment sizes (sigma(f), sigma(g)) and chain lengths (N(f), N(g)) of free and grafted polymers.
Main Results:
- In the absence of free polymers, interactions are always repulsive.
- In the presence of free polymers, interactions can be repulsive or exhibit an attractive minimum.
- An attractive minimum occurs when the ratio of free to grafted polymer chain lengths (alpha = N(f)/N(g)) exceeds a critical value.
- A scaling relation was derived: rho(g) * sqrt(N(g)) * beta^3 is proportional to alpha^(-lambda), where beta = sigma(f)/sigma(g) and lambda is the scaling exponent.
- Results for beta = 1 align with previous self-consistent field theory (SCFT) studies.
Conclusions:
- The presence and characteristics of free polymers significantly alter the interaction forces between grafted surfaces.
- The derived scaling relation provides a predictive tool for understanding these interactions.
- iSAFT offers a valuable approach for modeling nanocomposite thermodynamics, with detailed comparisons to SCFT validating its accuracy.
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