BONLAB BLOG
Thoughts
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Scientific Fiction
BonLab collaborates to produce bacteria containing biocoatings
We have a long history of making polymer dispersions to be used in waterborne coatings. The polymer colloids, or latex particles, are made by emulsion polymerization. Prof. Joe Keddie from the Physics Department at Surrey University contacted us if we were interested to help out on a bio-coatings project that needed some bespoke polymer latexes and colloidal formulations. With the term bio-coatings we mean here the coating formulation has the ability to entrap metabolically-active bacteria within the dried polymer film.
We loved the concept. In BonLab, PhD student Josh Booth optimized the synthesis of acrylic polymer latexes at approximately 40wt% solids with a monomodal particle size distributions. Important was to use bacteria-friendly surfactants in the semi-batch emulsion polymerization processes. Important was also to have a dry glass transition temperature of the polymer latex binder around 34 ℃, so that film formation could occur at temperatures which preserved viability of the bacteria.
The latexes were formulated as mixtures with halloysite nanoclay (hollow tubes) and E coli bacteria back at Surrey. The tubular clay was introduced to create porosity inside the polymer nanocomposite films. The overall composition of the waterborne formulation was optimized for mechanical and bacterial performance.
We have a long history of making polymer dispersions to be used in waterborne coatings. The polymer colloids, or latex particles, are made by emulsion polymerization. Prof. Joe Keddie from the Physics Department at Surrey University contacted us if we were interested to help out on a bio-coatings project that needed some bespoke polymer latexes and colloidal formulations. With the term bio-coatings we mean here the coating formulation has the ability to entrap metabolically-active bacteria within the dried polymer film.
We loved the concept. In BonLab, PhD student Josh Booth optimized the synthesis of acrylic polymer latexes at approximately 40wt% solids with a monomodal particle size distributions. Important was to use bacteria-friendly surfactants in the semi-batch emulsion polymerization processes. Important was also to have a dry glass transition temperature of the polymer latex binder around 34 ℃, so that film formation could occur at temperatures which preserved viability of the bacteria.
The latexes were formulated as mixtures with halloysite nanoclay (hollow tubes) and E coli bacteria back at Surrey. The tubular clay was introduced to create porosity inside the polymer nanocomposite films. The overall composition of the waterborne formulation was optimized for mechanical and bacterial performance.
Prof. dr. ir. Stefan Bon says: “We are delighted to be part of this study, and are pleased with the outcomes. Credit goes to the teams at the University of Surrey for making it all a success. The concept of biocoatings fits well with the ethos of the BonLab to fabricate materials from colloidal building blocks. We hope to stay involved and work together on next generation advanced coatings, with a green twist”
The paper is published in the ACS Journal Biomacromolecules and shows that large free-standing films of bacteria containing biocoating composites can be made.
The work is a collaborative study with research teams at Surrey University: dr. Yuxiu Chen and prof. Joe Keddie (Soft Matter Group, dept. of Physics), and Simone Krings and dr. Suzanne Hingley-Wilson (dept. of Microbial Sciences).
New method to study chain transfer in radical polymerizations
Synthetic polymers in most cases do not have one bespoke molecular weight. A sample typically consists of a large number of individual polymer chains, each having a different molecular weight. The average molecular weights and the shape of the molecular weight distribution are a kinetic fingerprint of how to polymer material was made. The resulting molecular weight distribution dictates physical and mechanical properties.
In free radical polymerizations, four key mechanistic events need to be considered. These are initiation, propagation, termination, and chain transfer. The latter often gets brushed under the carpet in introductory textbooks, but is pivotal.
When one targets polymers of low molecular weight, chain transfer agents are often used. One prominent class of chain transfer agents are thiol compounds, for example n-dodecanethiol. To understand how the molecular weight distribution develops throughout the polymerization process, the ability to determine the reactivity of the chain transfer agent is crucial. This reactivity is often expressed in the form of a chain transfer constant, Ctr, which is the ratio of the rate coefficients of chain transfer and propagation.
Synthetic polymers in most cases do not have one bespoke molecular weight. A sample typically consists of a large number of individual polymer chains, each having a different molecular weight. The average molecular weights and the shape of the molecular weight distribution are a kinetic fingerprint of how to polymer material was made. The resulting molecular weight distribution dictates physical and mechanical properties.
In free radical polymerizations, four key mechanistic events need to be considered. These are initiation, propagation, termination, and chain transfer. The latter often gets brushed under the carpet in introductory textbooks, but is pivotal.
When one targets polymers of low molecular weight, chain transfer agents are often used. One prominent class of chain transfer agents are thiol compounds, for example n-dodecanethiol. To understand how the molecular weight distribution develops throughout the polymerization process, the ability to determine the reactivity of the chain transfer agent is crucial. This reactivity is often expressed in the form of a chain transfer constant, Ctr, which is the ratio of the rate coefficients of chain transfer and propagation.
The most famous method to determine values for the chain transfer constant, Ctr, is referred to as the Mayo method. It is an excellent method, but over time its assumptions and boundary conditions have been eroded. The Mayo method is only valid if there is no marked composition drift, that is a drift in concentration ratio of chain transfer agent and monomer. In essence it makes use of the instantaneous molecular weight distribution, here in the form of the number average molecular weight. Whereas this is easy to achieve in experiments where Ctr < 1 by keeping monomer conversion low, this is less easy to do in cases where Ctr > 1.
In the same time period (1940s) Smith already reported a solution. Whereas elegant, in this method there is no direct link with the molecular weight distribution, which may sit uncomfortably.
In our paper entitled When Mayo falls short (Ctr ≫ 1): the use of cumulative chain length distribution data in the determination of chain transfer constants (Ctr) for radical polymerizations published in the RSC journal Polymer Chemistry we propose a new method. Here we make use of the cumulative molecular weight distribution, hereby taking into account composition drift.
The validity of our method is demonstrated using Monte Carlo simulations and its experimental usefulness is shown studying one of the most challenging systems of all: the free radical polymerization of vinyl acetate in presence of thiols as chain transfer agent. We are happy to report a value for the chain transfer constant of dodecanethiol of 223, at 333 K.
Prof. dr. ir. Stefan Bon says: “ I am delighted with the final version of the manuscript. The hard work by PhD student Matt Donald to carry out the experiment and his dedication in bringing together wet science with Monte Carlo simulations paid off. We both hope that our method will be embraced, tested, and used by others. “
Details on the paper can be found here:
BonLab wins awards and prizes for Innovative Research
The BonLab team has recently won a number of awards and prizes in recognition for their innovative research in the field of polymer colloid science.
In April 2019 at the RSC/SCI Rideal Lecture in honour of prof. Peter Lovell Sam Wilson Whitford won the RSC Soft Matter poster prize for his work on microcapsules based on supramolecular waxes. At the same meeting Matt Donald won the RSC Polymer Chemistry poster prize for his work on the mechanistic aspects of vinyl acetate emulsion polymerization.
In May 2019 Wai Hin Lee was awarded a prestigious Warwick International Chancellor’s Scholarship to continue his PhD in complex 2D colloidal materials. Brooke Longbottom was awarded a Warwick University faculty of science PhD thesis prize for his outstanding contributions to the field of “active” colloidal particles.
In June 2019 Andrea Lotierzo was awarded best PhD student presentation at the International Polymer Colloids Group Conference in Singapore, for his work on the synthesis of Janus, patchy and armored latex particles.
Prof.dr.ir. Stefan Bon, leader of the BonLab, says: “ I am delighted with our recent awards and prizes and I am proud of the achievements of Sam, Matt, Wai, Brooke and Andrea. They all have worked tremendously hard with dedication and enthusiasm and all are the reason why BonLab continues to innovate in science”