Impact of sequential surface-modification of graphene oxide on ice nucleation

Abstract

Base-washed graphene-oxide which has been sequentially-modified by thiol-epoxy chemistry, results in materials with ice-nucleation activity. The role of hydro-philic/phobic grafts and polymers was evaluated with the most potent functioning at just 0.25 wt %. These 2-D hybrid materials may find use in cryopreservation and fundamental studies on ice formation.The formation and growth of ice crystals presents problems in many fields from aerospace to cell cryopreservation to the automotive industry. Whilst ice formation is thermodynamically preferred below 0 °C, there exists a large barrier to this, such that pure water undergoes homogenous nucleation at ~ − 40 °C. For nucleation to occur above this temperature, a nucleator is necessary. In the environment, nucleators have been identified including dust,1 minerals, birch and conifer pollen2 and recently a species of fungus was found to be a potent nucleator.3 Ice nucleating proteins also exist in living species,4 for example Pseudomonas syringae produce ice nucleating proteins to promote frost formation on plant leaves, to release nutrients for feeding.5 However, the mechanisms of ice nucleation are not understood, and remain a significant challenge for modelling and theory.6,7 A key barrier to this understanding is the lack of sequentially modified materials to enable structure-activity relationships to be drawn. The few known nucleators are insoluble, inorganics such as kaolinite8 or bacterial proteins. Synthetic ice nucleators could play a key role in e.g. cellular cryopreservation, where control over the exact nucleation temperature could improve reproducibility in the cryopreservation process.9 In the past few years, significant progress has been made in the development of synthetic materials for ice recrystallization inhibition (IRI) -the growth of pre-formed ice crystals as mimics of antifreeze proteins (which sometimes, but not always, can influence ice nucleation also Considering the above, we hypothesised that the surface modification of base-washed graphene oxide would provide a versatile template to evaluate the potential of 2-dimensional carbon nanomaterials as ice-nucleating materials and also to provide a versatile scaffold to enable the role of surface chemistry to be probed. Base-washed GO (bwGO) was prepared using established methods16 to generate a 'clean' surface bearing epoxy groups available for orthogonal conjugation to thiols. For the surface modification, a small library of small molecule thiols was chosen, to give a range of hydrophilic/phobic functionalities. Watersoluble polymers with thiol-termini were also synthesised using RAFT (reversible addition fragmentation -transfer) polymerization. RAFT not only enables access to functional polymers of defined chain length and dispersity, but also introduces a thio-carbonyl at the ω-end-group, which can be reduced to a thiol. Using this method, poly(Nisopropylacrylamide), pNIPAM with degree of polymerization of 55 and 140 was synthesised, to use as a water soluble polymeric grafting age...

Mimicking the Ice Recrystallization Activity of Biological Antifreezes. When is a New Polymer “Active”?

“…There is also a report of graphene oxide inhibiting ice growth in this concentration range (all growth stopped at 5 mg mL −1 ) . Graphene oxide is also known to affect ice nucleation; such dual activity has also been observed for some AFPs …”

Laboratory study of the heterogeneous ice nucleation on black carbon containing aerosol

“…However, others (e.g. Whale et al, 2015;Lupi et al, 2014aLupi et al, , 2014bBiggs et al, 2017) suggested that a lower degree of oxidation leads to enhanced ice nucleation efficiency.…”

“…Moreover, molecular dynamics calculations show that hydrophilicity is not a sufficient condition for IN (Lupi et al, 2014a, 35 2014b). In fact, Biggs et al (2017) reported an increase in the ice nucleation activity due to a decrease in hydrophilicity.…”

Laboratory study of the heterogeneous ice nucleation on black-carbon-containing aerosol

“…Some studies (e.g., Koehler et al, 2009;Gorbunov et al, 2001;Marcolli, 2014) suggested that heterogeneous ice nucleation is favored on oxidized hydrophilic soot. However, others (e.g., Biggs et al, 2017) suggested that a lower degree of oxidation leads to enhanced ice nucleation efficiency. Our experiments explore the effect of oxidized surfaces.…”

“…A kinetically based PCF mechanism provides, at least in part, a possible explanation for the widespread IN activity observed for soot particles. This mechanism was formulated to explain ice nucleation by porous materials (Everett, 1961;Blachere and Young, 1972). The PCF mechanism proposes that empty spaces between aggregated primary particles fill with water due to capillary condensation at relative humidities (RH w ) below water saturation, which freezes homogeneously (Higuchi and Fukuta, 1966;Christenson, 2013;Marcolli, 2014;David et al, 2019).…”