John Frostad

Assistant Professor

Research Interests

Emulsions
Fluid mechanics
Foams
Functional Foods
Interfacial Phenomena
Interfacial Rheology
Novel Instrumentation
Physics of Soft Matter
Agricultural Sprays

Relevant Degree Programs

Research Options

I am available and interested in collaborations (e.g. clusters, grants).
I am interested in and conduct interdisciplinary research.
I am interested in working with undergraduate students on research projects.
 
 

Research Methodology

Cantilevered-Capillary Force Apparatus
Instrument Development
Dynamic Fluid-film Interferometry
Langmuir-Pockels Trough
Pendant Drop Tensiometer
Dynamic Foam Analyzer
Rheometer
Interfacial Rheology
Particle Cohort Studies (ParCS) of food processing and digestions

Recruitment

Master's students
Doctoral students
Any time / year round

For more information, please see: http://food.chbe.ubc.ca/opportunities/

I support public scholarship, e.g. through the Public Scholars Initiative, and am available to supervise students and Postdocs interested in collaborating with external partners as part of their research.
I support experiential learning experiences, such as internships and work placements, for my graduate students and Postdocs.
I am open to hosting Visiting International Research Students (non-degree, up to 12 months).
I am interested in supervising students to conduct interdisciplinary research.

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Graduate Student Supervision

Master's Student Supervision

Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.

Polymer additive to enhance the retention of crop sprays (2021)

In pesticide and fertilizer applications, large spray droplet sizes (300-500 um)are commonly used in the field for reduced spray drift. However, retention of spraydroplets after they reach the target surface can be limited by droplets splashing,rebounding, or rolling off of the surface due to their high impacting velocity andinertial energy. While polymer additives were proposed to dissipate energy duringthe droplet impact process, whether they can enhance the retention efficiency of cropsprays in practical field conditions is still not clear. This research work focuses on enhancing the retention efficiency with polymer additives,which is carried out in four major steps: The first step is to screen polymerssuitable for spray applications. The second step is to develop an approach that providesdetailed physical insight in a setup that is representative of real spray conditionsto quantify retention efficiency. The third step determines the effect of extensionalrheological properties on retention efficiency at various spray conditions. The workcarried out in the first, second, and third steps forms a comprehensive study onthe relationship between extensional rheological properties of polymer solution andretention efficiency. Then the fourth step focuses on exploring the extensional rheologicalproperties of selected polymer additives at different solvent conditions and inagrochemical solutions.The results demonstrate that increasing the extensional relaxation time of thespray solution can increase the retention efficiency by up to 20% and in some casesachieve a total efficiency greater than 95%. It’s also suggested for a particular polymer,surface, and droplet size, the extensional relaxation time alone could be sufficientto predict retention efficiency. The results also relate the extensional relaxation timeto important influencing parameters including pH, ionic strength, type of ions, etc.

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The mechanical properties of neurospheres (2021)

Stem cell-derived 3D tissues such as spheroids are excellent models for investigating mechanisms of tissue formation and responses to physiological and mechanical cues. Neuronal spheroids, also known as neurospheres, have attracted particular interest. A lot is now known about the differentiation and maturation of neurospheres, as well as their responses to biochemical cues. However, understanding about their mechanical properties pales in comparison, which is all the more galling in light of newfound insights about how mechanical stimuli trigger the onset of neurodegenerative conditions. In the current study, we have taken formative steps to fill this knowledge gap. We generated neurospheres from murine neural stem cells, treated with hydrogen peroxide to simulate oxidative stress, and subjected them to compressive forces. We observed that neurospheres exhibit viscoelastic behaviour at low strains and plastic deformation at larger strains. We also evaluated the suitability of the Tatara model for characterizing the mechanical properties of neurospheres. There was an observable dependence of the mechanical properties of the neurospheres on the their sizes, with smaller samples being stiffer. When comparing neurospheres treated with a mild peroxide treatment to untreated samples, no significant differences in the mechanical properties were detected Our study is the first to investigate the mechanical properties of living neurospheres under uni-axial compression. However, the results demonstrate the need for further method development in order to account for biological variability and sample heterogeneity.

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Liquid content predictors for aqueous foams (2019)

Historically, foam studies have focused on foamability, foam stability, and foam inhibition as opposed to foam density. Hence, the impact of various factors on foam density is still not well understood. Previous experimental work shows that concentrated surfactant solutions with similar surface tensions produce foams with different liquid fractions. These results contradict the common assumption held that these foams would have near-identical liquid fractions. Therefore, this study probes for correlations between equilibrium and dynamic surfactant adsorption parameters at air-liquid interfaces for aqueous foams made from solutions well above the critical micelle concentration. A protocol was developed for measuring foam density using a cylindrical foaming apparatus with porous filter plate for gas sparging. The foams were created from aqueous solutions of small-molecule surfactants known to have negligible surface shear viscosity. Equilibrium parameters of the maximum surface concentration, equilibrium adsorption/desorption rate constant, and effectiveness (critical micelle concentration) showed weak evidence of a correlation as quantified by linear and ranked correlation coefficients. The surfactant efficiency (concentration needed to reduce the surface tension 20 mN/m) showed some evidence of linear correlation between the ranking of the variables. In contrast, the time required to reduce the surface tension 35% and 50% of the way from the pure water value to the equilibrium value (t_35 and t_50) showed strong evidence of correlation of increasing liquid fraction with faster surfactant adsorption times. The results of this study highlight the influence of dynamics even for highly concentrated surfactant solutions.

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