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Surfactant in a Polyol-CO₂ Mixture: Insights from a Classical Density Functional Theory Study

Mantha, Sriteja and Chao, Huikuan and Ylitalo, Andrew S. and Fitzgibbons, Thomas C. and Zhou, Weijun and Ginzburg, Valeriy V. and Wang, Zhen-Gang (2022) Surfactant in a Polyol-CO₂ Mixture: Insights from a Classical Density Functional Theory Study. Langmuir, 38 (51). pp. 16172-16182. ISSN 0743-7463. PMCID PMC9798868. doi:10.1021/acs.langmuir.2c02913.

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Silicone–polyether (SPE) surfactants, made of a polydimethyl-siloxane (PDMS) backbone and polyether branches, are commonly used as additives in the production of polymeric foams with improved properties. A key step in the production of polymeric foams is the nucleation of gas bubbles in the polymer matrix upon supersaturation of dissolved gas. However, the role of SPE surfactants in the nucleation of gas bubbles is not well understood. In this study, we use classical density functional theory to investigate the effect of an SPE surfactant on the nucleation of CO₂ bubbles in a polyol foam formulation. We find that the addition of an SPE surfactant leads to a ∼3-fold decrease in the polyol–CO₂ interfacial tension at the surfactant’s critical micelle concentration. Additionally, the surfactant is found to reduce the free energy barrier and affect the minimum free energy pathway (MFEP) associated with CO₂ bubble nucleation. In the absence of a surfactant, a CO₂-rich bubble nucleates from a homogeneous CO₂-supersaturated polyol solution by following an MFEP characterized by a single nucleation barrier. Adding a surfactant results in a two-step nucleation process with reduced free energy barriers. The first barrier corresponds to the formation of a spherical aggregate with a liquid-like CO₂ core. This spherical aggregate then grows into a CO₂-rich bubble (spherical aggregate with a vapor-like CO₂ core) of a critical size representing the second barrier. We hypothesize that the stronger affinity of CO₂ for PDMS (than polyether) stabilizes the spherical aggregate with the liquid-like CO₂ core, leading to a lower free energy barrier for CO₂ bubble nucleation. Stabilization of such an aggregate during the early stages of the nucleation may lead to foams with more, smaller bubbles, which can improve their microstrustural features and insulating abilities.

Item Type:Article
Related URLs:
URLURL TypeDescription CentralArticle
Mantha, Sriteja0000-0001-7813-0903
Chao, Huikuan0000-0001-9930-3586
Ylitalo, Andrew S.0000-0003-4086-3508
Fitzgibbons, Thomas C.0000-0002-8330-1102
Ginzburg, Valeriy V.0000-0002-2775-5492
Wang, Zhen-Gang0000-0002-3361-6114
Additional Information:The authors acknowledge Dow, Inc., for the financial support through the Dow–Caltech university partnership initiative (UPI). The authors benefited greatly from the discussions with our UPI experimental collaborators, Prof. Julie Kornfield and Prof. Richard Flagan. S.M. thanks Chris Balzer for discussions and useful comments. A.S.Y. acknowledges the support of the National Science Foundation Graduate Research Fellowship Program under Grant DGE-1745301.
Funding AgencyGrant Number
Dow Chemical CompanyUNSPECIFIED
NSF Graduate Research FellowshipDGE-1745301
Issue or Number:51
PubMed Central ID:PMC9798868
Record Number:CaltechAUTHORS:20230117-369491100.6
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:118810
Deposited By: Research Services Depository
Deposited On:10 Feb 2023 20:20
Last Modified:10 Feb 2023 20:20

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