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A Bubble Is Born: Nucleation and Early Growth of CO₂ Bubbles in Polymer Foams


Ylitalo, Andrew Samuel (2022) A Bubble Is Born: Nucleation and Early Growth of CO₂ Bubbles in Polymer Foams. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/cdgw-7c18.


Gas bubble nucleation is a fundamental phenomenon both throughout the natural sciences and in the production of foams for lightweight, functional materials; it is also the basis for many a bubbly beverage. Enhancing bubble nucleation in polyurethane insulating foams used for refrigeration can further reduce their low thermal conductivity without resorting to hazardous blowing agents used in the past. Experimental challenges of measuring the kinetics of the rapid, multiscale process of bubble nucleation pose a roadblock to investigation of suitable processing conditions, as well as the development of theoretical models of bubbles and foams.

Here, using a microfluidic flow-focusing technique developed for measurement of protein and chemical kinetics, we built a microfluidic cell to probe gas bubble nucleation of CO₂ in polyol, a model system for polyurethane insulating foams, at controlled pressure with millisecond resolution over acquisition times sufficient for optical, IR, and X-ray measurements. This technique allows for repeated measurements of bubble nucleation at any degree of supersaturation without the interference of heterogeneous nucleation from surfaces. By extrapolating a model fit to high-speed optical microscopy measurements of bubble growth backward in time, we estimated the degree of supersaturation at nucleation for thousands of bubbles. Estimates of the nucleation rate based on Poisson statistics were consistent with predictions by a string method model based on density functional theory and G-ADSA measurements. This model predicted that the addition of cyclopentane (a common physical blowing agent in polyurethane foams) can dramatically reduce the nucleation energy barrier due to the formation of a liquid-like layer of cyclopentane and CO₂ along the surface of the bubble that reduces the interfacial tension, which previous models have only predicted at significantly higher saturation pressures. This prediction was supported by thermodynamic measurement of a three-phase coexistence under similar conditions, which is a known fingerprint for such nucleation pathways, and measurement of significantly higher bubble nucleation rates upon the addition of cyclopentane. These findings shed light on the possibility of a previously unappreciated role of physical blowing agents like cyclopentane in enhancing bubble nucleation by opening up a qualitatively distinct and more favorable nucleation pathway.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:bubble nucleation carbon dioxide polymer foam microfluidics phase equilibrium high pressure polyurethane string method density functional theory PC-SAFT energy barrier flow instabilities bebop image processing diffusion
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemical Engineering
Awards:Constantin G. Economou Memorial Prize, 2018.
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Kornfield, Julia A. (advisor)
  • Wang, Zhen-Gang (co-advisor)
Thesis Committee:
  • Brady, John F. (chair)
  • Kornfield, Julia A.
  • Okumura, Mitchio
  • Ismagilov, Rustem F.
  • Flagan, Richard C.
  • Wang, Zhen-Gang
Defense Date:20 May 2022
Non-Caltech Author Email:ylitaand (AT)
Funding AgencyGrant Number
NSF Graduate Research Fellowship1745301
Record Number:CaltechTHESIS:03222022-221436705
Persistent URL:
Related URLs:
URLURL TypeDescription repository for G-ADSA analysis described in Ch. 2
Ylitalo, Andrew Samuel0000-0003-4086-3508
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14523
Deposited By: Andrew Ylitalo
Deposited On:02 Jun 2022 19:53
Last Modified:08 Nov 2023 00:30

Thesis Files

[img] PDF (Final version of thesis) - Final Version
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[img] PDF (Front Matter) - Final Version
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[img] PDF (Table of Contents) - Final Version
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[img] PDF (Chapter 1 - Introduction) - Final Version
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[img] PDF (Chapter 2 - Mother Phase) - Final Version
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[img] PDF (Chapter 3 - Apparatus) - Final Version
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[img] PDF (Chapter 4 - Image Processing) - Final Version
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[img] PDF (Chapter 5 - Bubble Growth) - Final Version
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[img] PDF (Chapter 6 - Bubble Nucleation) - Final Version
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[img] PDF (Chapter 7 - Effect of Additives on Nucleation) - Final Version
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[img] PDF (Chapter 8 - Elongated Bubbles, Merging, and Flow Instabilities) - Final Version
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[img] PDF (Closing Thoughts) - Final Version
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