An aquamelt is a naturally hydrated

polymeric A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

material that is able to solidify at environmental temperatures through a controlled stress input (be it mechanical or chemical). They are unique in being able to “lock in” work applied to them through an alteration in

hydrogen bond In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a ...

ing, which enables them to be processed with approximately 1000 times less energy than standard polymers. This has been recently shown for an archetypal

biopolymer Biopolymers are natural polymers produced by the cells of living organisms. Like other polymers, biopolymers consist of monomeric units that are covalently bonded in chains to form larger molecules. There are three main classes of biopolymers, cl ...

silk Silk is a natural protein fiber, some forms of which can be woven into textiles. The protein fiber of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the coc ...

, however the mechanism for solidification is thought to be inherent to many other biological materials.

Discovery and mechanism

Aquamelts were defined as a new class of polymeric material as a result of a comparison between the spinning feedstock of the Chinese silkworm (''

Bombyx mori The domestic silk moth (''Bombyx mori''), is an insect from the moth family Bombycidae. It is the closest relative of ''Bombyx mandarina'', the wild silk moth. The silkworm is the larva or caterpillar of a silk moth. It is an economically imp ...

'') and molten

high-density polyethylene High-density polyethylene (HDPE) or polyethylene high-density (PEHD) is a thermoplastic polymer produced from the monomer ethylene. It is sometimes called "alkathene" or "polythene" when used for HDPE pipes. With a high strength-to-density ratio, ...

(HDPE) using shear induced polarised light imaging (SIPLI). The current understanding of shear induced fibrillation requires

polymer chain A polymer (; Greek '' poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

s to undergo the following series of steps i) long-chain molecules are stretched, ii) and form persistent point nuclei, which iii) align under flow into rows and then iv) grow to create a crystalline fibrils. For these fibrils to remain, the temperature of the sample must be lowered to below the polymers melt point. This process is analogous to the fibrilogenesis of natural silk-polymers in which

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

align (refold), nucleate ( denature), and crystallize (aggregate). However, for silks, fibrils persist without the need for a drop in temperature. From a macromolecular perspective the two processes are thought to be similar due to a native protein's unique interaction with its closely bound water. Much like an individual polymer chain in a melt, a native protein and its closely bound water molecules may be considered not as a solution but as a single processable entity, a

nanocomposite Nanocomposite is a multiphase solid material where one of the phases has one, two or three dimensions of less than 100 nanometers (nm) or structures having nano-scale repeat distances between the different phases that make up the material. The id ...

termed an "aquamelt". The differences between a typical polymer and an aquamelt are highlighted by an aquamelt's ability to solidify in response to stress at environmental temperatures. This occurs when the stress applied is sufficient to separate the closely bound water from the protein, splitting the nanocomposite. This results in conformational changes to the protein and an increased probability to form hydrogen bonding between protein chains and subsequent solidification. Multiscale structures, i.e.,

fibrils Fibrils (from the Latin ''fibra'') are structural biological materials found in nearly all living organisms. Not to be confused with fibers or filaments, fibrils tend to have diameters ranging from 10-100 nanometers (whereas fibers are micro ...

foams Foams are materials formed by trapping pockets of gas in a liquid or solid. A bath sponge and the head on a glass of beer are examples of foams. In most foams, the volume of gas is large, with thin films of liquid or solid separating the reg ...

are the result of a combination of directional stress fields and the self-assembly properties of the aquamelt.

Potential uses

Aquamelts offer several advantages over current solutions to

synthetic polymer Some familiar household synthetic polymers include: Nylons in textiles and fabrics, Teflon in non-stick pans, Bakelite for electrical switches, polyvinyl chloride (PVC) in pipes, etc. The common PET bottles are made of a synthetic polymer, polye ...

production. Firstly they are naturally sourced, with no reliance on

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

for production and are

recyclable Recycling is the process of converting waste materials into new materials and objects. The recovery of energy from waste materials is often included in this concept. The recyclability of a material depends on its ability to reacquire the p ...

and

biodegradable Biodegradation is the breakdown of organic matter by microorganisms, such as bacteria and fungi. It is generally assumed to be a natural process, which differentiates it from composting. Composting is a human-driven process in which biodegradati ...

. Secondly they can be processed at

room temperature Colloquially, "room temperature" is a range of air temperatures that most people prefer for indoor settings. It feels comfortable to a person when they are wearing typical indoor clothing. Human comfort can extend beyond this range depending on ...

s and pressures resulting in only water as a by-product from the solidification process. Thirdly work calculations performed on silk and high-density polyethylene feedstocks revealed a tenfold difference in the amount of shear energy required in order to initiate solidification. When processing temperature is taken into account the difference in energy requirements to undergo solidification is a thousandfold less for aquamelts than synthetic polymers.

References

{{Reflist Polymers