Abstract
Nature has evolved many elegant solutions to enable life to flourish at low temperatures by either allowing (tolerance) or preventing (avoidance) ice formation. These processes are typically controlled by ice nucleating proteins or antifreeze proteins, which act to either promote nucleation, prevent nucleation or inhibit ice growth depending on the specific need, respectively. These proteins can be expensive and their mechanisms of action are not understood, limiting their translation, especially into biomedical cryopreservation applications. Here well-defined poly(vinyl alcohol), synthesized by RAFT/MADIX polymerization, is investigated for its ice nucleation inhibition (INI) activity, in contrast to its established ice growth inhibitory properties and compared to other synthetic polymers. It is shown that ice nucleation inhibition activity of PVA has a strong molecular weight dependence; polymers with a degree of polymerization below 200 being an effective inhibitor at just 1 mg.mL–1. Other synthetic and natural polymers, both with and without hydroxyl-functional side chains, showed negligible activity, highlighting the unique ice/water interacting properties of PVA. These findings both aid our understanding of ice nucleation but demonstrate the potential of engineering synthetic polymers as new biomimetics to control ice formation/growth processes
Highlights
Ice formation via heterogeneous nucleation is crucial in the context of atmospheric science,[1] cryopreservation,[2] cryomedicine,[3] cryosurgery,[4] and food science.[5]
Previous reports on the role of Poly(vinyl alcohol) (PVA) on ice nucleation have been in vitrified solutions and using poorly defined materials with broad molecular weight distributions and variable degrees of acetate hydrolysis
Using a xanthate chain transfer agent (Scheme 1), the molecular weight of the polymer can be tuned by controlling the monomer to initiator ratio
Summary
Ice formation via heterogeneous nucleation is crucial in the context of atmospheric science,[1] cryopreservation,[2] cryomedicine,[3] cryosurgery,[4] and food science.[5]. The presence of impurities in water (dust, salts, bacteria, etc.) provide nucleation sites enabling nucleation to occur typically in the range of 0 to −20 °C in bulk samples This complex phase behavior has proven to be challenging to understand, in part due to nucleation being a rare event, meaning computational modeling of the process is very challenging. The ability to predictably control ice nucleation temperature, would be technologically significant in applications ranging from the seeding of rain clouds to controlling ice build-up on wind turbines. Several inorganic minerals, such as kaolinite[8] and feldspar, have been shown to be very potent ice nucleators and may play a role in rain cloud formation via Saharan dust clouds.[9,10]
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