A high-entropy GEL composition and method of producing thereof

Abstract

The present invention describes a high-entropy gel (HEG) composition derived from organic raw materials and method of producing thereof. Particularly, the composition comprises a high-entropy gel composition derived from organic materials, the composition comprising at least a semi-crystalline polymeric backbone and at least four different crystalline components in a non-equimolar ratio, wherein the at least four crystalline components interact with one another via reversible physical bonds of hydrogen bonds, ionic interactions and ion-dipole interactions hence forming a homogeneous, free-standing gel. The high-entropy gel composition provides enhanced ionic conductivity and high dielectric permittivity, thus enabling it to be used to fabricate self-healing sensors, for use in green electronics, soft robotics, environmental and healthcare industries. HEG is self- healing, reusable and biodegradable and can be used to make a tough packaging material, for example, to keep fruits and vegetables fresh.

Description

A HIGH-ENTROPY GEL COMPOSITION AND METHOD OF PRODUCING THEREOFRelated Application

[0001] The present invention claims priority to Singapore patent application no. 10202400186U filed on 23 January 2024. the disclosure of which is incorporated in its entirety.Field of Invention

[0002] Tire present invention relates to a high-entropy gel (HEGs) composition derived from organic raw materials. In particular, the invention relates to a composition, and a method of producing the composition.Background

[0003] Entropy is an important concept in thermodynamics, measuring the disorder in a system or, more precisely, the number of possible microscopic configurations of individual atoms or molecules of a system, i.e., microstates. High-entropy materials (HEMs), in terms of entropy, are a class of materials with a higher-than-usual degree of disorder in their microstructures. The high-entropy concept was first proposed in the field of metals in 2004 by Yeh et al. (2004), ,Adv . Eng. Mater. 2004, 6, 299-303 and the relevant materials would later become widely known as high-entropy alloys (HEAs). What interests researchers about HEAs is that the mixture of five or more elements in equal or near-equal atomic proportions could result in a single solid solution phase, which is unexpected given the established metallurgical theory. Since then, continuous development in HEMs expands the high-entropy concept outside of the field of metals, such as high-entropy ceramics (HECs), high-entropy polymers, and high-entropy composites.

[0004] HEMs have exceptional performances and multifunctionalities that surpass that of conventional materials. However, many HEMs focused on inorganic compounds. Bioderived organic raw materials are often too weak or stiff and would necessitate the incorporation of synthetic additives or catalysts to enhance their functional stability. The present invention provides a new class of HEMs, known as high-entropy gels (HEGs), aiming to enhance the capabilities of organic materials. Further, as organic materials arcinherently biodegradable, the HEGs provided can be fitted into a circular economy which seeks to reduce waste by keeping resources in a loop as long as possible.

[0005] Previous studies on HEAs and HECs mainly focused on configurational entropy of elements usually assembled in a single phase solid-solution or single crystalline form. According to the preceding method to achieve highest configurational entropy, the HEMs should adopt an equimolar distribution of species or close to it. However, such concept cannot be directly applied to HEGs. Gels, by definition, are a three-dimensional polymeric network capable of holding large proportion of fluids. The polymer used to form the pol mcric-nctwork usually has high molecular weights and will therefore have an extremely small hole, given that the liquid phase is made up of molecules of a much smaller molecular weight, equimolar distribution becomes practically unattainable . Besides, organic raw materials (made of organic compounds) have vastly different sizes and functional groups which have a huge impact on the bond formation and overall molecular arrangement. Hence, having an equimolar distribution might not guarantee full homogeneity'.

[0006] In view of the above, there is a need of technical solution to obtain the aforementioned HEGs based on organic material. HEGs hereinafter can be fabricated based on the following theories: (1) HEGs preferably comprises five or more components and there must not be a single dominant principal component. Tire number of components is set to preferably five, borrowing the concept from HEAs where there is sufficiently high entropy arising solely from the entropy of mixing; (2) HEGs preferably utilize at least one polymcnc backbone with functional groups capable of forming reversible physical or covalent bonds 'ith other components. A highly entropic system is one w'here the polymer chains can participate in favorable bonds and prevent phase separation or chain crystallization. The type of bond should be reversible to maximize chain mobility and thus increase conformational entropy; (3) HEGs preferably' comprise small molecules capable of forming reversible physical or covalent bonds with other components. By virtue of their small size, these molecules are highly mobile. With their ability to fonn reversible bonds, these small molecules can have high configurational, translational, rotational, and vibrational entropies; (4) HEGs preferably are self- standing, stable, amorphous, and homogeneous after fabrication. Self-standing is an important criterion given its feasibility' to be applied as a functional material. Stability is important as the material’s high entropystate ensures that it stays in the same state under external stimuli. Amorphousness and homogeneity are a mark of high entropy systems HEGs.Summary

[0007] The following presents a simplified summary to provide a basic understanding of the present invention. This summary is not an extensive overview of the present invention, and is not intended to identify key features of the invention. Rather, it is to present some of the inventive concepts of this invention in a generalised form as a prelude to the detailed description that is to follow.

[0008] The present invention seeks to provide a high-entropy gel (HEGs) composition using bio-derived organic materials. Hence, it follows that the HEGs is biodegradable and recyclable. Due to its vast application especially in the field of electronics, the issue in rampant problem of electronic waste can be resolved.

[0009] The present invention also provides HEGs with self-healing properties due to presence of strong, reversible physical interactions or bonds between components involved.

[0010] The present invention also provides HEGs with good mechanical properties due to its good balance between strong physical bond formation and quantity of components used. The HEGs remain a free-standing gel after being subjected to external stimuli stretching, physical stress, or fluctuations in temperature and humidity. Further, the HEGs is tunable to exhibit either high strength, high stretch ratio or both.

[0011] The present invention also provides HEGs with good electrical properties. The use of choline chloride (ChCl) in the HEGs provides enhanced ionic conductivity and boasted high dielectric permittivity. Therefore, the HEGs is suitable for application in tire field of green electronics, soft robotics, environmental technologies and healthcare technologies.

[0012] The present invention also provides transparent HEGs.

[0013] In line with the theories of forming high-entropy materials (HEMs), the starting materials (also the organic materials) used to form the HEGs comprises at least 5 different crystalline components, and the resultant gel obtained is free-standing, amorphous and therefore, entropic. In one embodiment, the HEGs comprises at least a semi-crystallinepolymeric backbone and at least four different cry stalline components in a non-equimolar ratio, wherein the at least four components interact with one another via reversible physical bonds of hydrogen bonds, ionic interactions and ion-dipole interactions hence forming a homogeneous, free-standing gel.

[0014] By way of example, the semi-crystalline polymeric backbone comprises sodium carboxymethyl cellulose.

[0015] By way of example, the at least four different crystalline components arc selected from citric acid, choline chloride, betaine, and / or urea.

[0016] In one embodiment, the HEGs comprises sodium carboxymethyl cellulose present in substantially 9 to 54 wt % of the composition, citric acid present in substantially 1 to 60 wt % of the composition, choline chloride present in substantially 0.5 to 39 wt % of the composition, betaine present in substantially 0.6 to 45 wt % of the composition, and urea present in substantially 0.4 to 34 wt % of the composition.

[0017] The present invention also provides a method for producing a high-entropy gel composition derived from organic materials, the method comprising the steps of: dissolving non-equimolar ratio of scmi-crysLalline sodium carboxymethyl cellulose, at least four different crystalline components, and a solvent to obtain a precursor mixture; stirring the precursor mixture until homogeneous; and removing water from the mixture in a gradual manner to obtain a continuous, free-standing gel where the components interact with one another via reversible, physical bonds of hydrogen bonds, ionic interactions and ion-dipole interactions to form a free-standing gel.

[0018] Preferably, the precursor mixture comprises sodium carboxymethyl cellulose present in substantially 9 to 54 wt % of the composition, citric acid present in substantially 1 to 60 wt % of the composition, choline chloride present in substantially 0.5 to 39 wt %, of the composition, betaine present in substantially 0.6 to 45 wt % of the composition, urea present in substantially 0.4 to 34 wt % of the composition and water.

[0019] By way of example, the stirring step is conducted at about 2000 rpm.

[0020] By way of example the step of removing water in a gradual manner is conducted at about substantially 55 °C to about 60 °C over 3 to 5 days.

[0021] Preferably, a packaging material is made according to the above HEG composition or method of production; this packaging material is seld-healing, tough, reusable and biodegradable. In addition, strain sensors, pressure sensors or wearable elastomeric actuators can also be made from the above HEG composition.Brief Description of the Drawings

[0022] This invention will be described by way of non-limiting embodiments of the present invention, with reference to the accompanying drawings, in which:

[0023] FIG. 1 illustrates a schematic diagram of an exemplary' HEG with components interact with each other via reversible physical bonds of hydrogen bonds, ionic interactions, and ion-dipole interactions.

[0024] FIG. 2 illustrates two FESEM images with the morphology images of the exemplary' HEG in the present invention (left) and the CMC backbone (right), with scale bar at 10 pm.

[0025] FIG. 3 illustrates a HEG of the present invention that is 45 pm in thickness has close to 100% transmittance over the entire visible spectrum, with inset scale bar of 2cm.

[0026] FIG. 4 illustrates sharps peaks of X-Ray Diffraction (XRD) pattern from MSG indicating its crystalline structure while the HEG is amorphous as evident by' the broad peak.

[0027] FIG. 5 illustrates X-Ray Diffraction (XRD) pattern of five components involved in the fabrication of the HEGs in the present invention.

[0028] FIGs. 6a to 6c illustrate two-dimensional (2D) nuclear overhauser effect spectroscopy (NOESY) 1HNMR characterization of HEG. FIG. 6a illustrates 2D NOESY contour plot at high intensity and FIG. 6b illustrates the contour plot at low intensity. A set of cross-peaks between the ether (-OR), hydroxyl (-OH), and amine (-NH2) functional groups attributed to CMC (1.43 ppm), citric acid (3.67 ppm), and NADES (13.0 - 16.1 ppm) respectively, were detected in the NOESY contour plot (FIG. 6a). The ether groupdisplays a range of chemical shifts (0.56 - 1.67 ppm) conceivably caused by CMC chains entanglement, stacking, or variable chain lengths. FIG. 6c illustrates a contour plot of NOE intensity versus mixing time.

[0029] FIG. 7 illustrates four radar plots of the weight percentages of the components used in tire HEGs of the present invention. The composition may exist as HEGs, MSGs, and liquid-like gels (L series). O series refers to samples that exclude any one of the five components in its composition and the samples that we studied exist either as MSG or liquid-like gels. The physical form of these samples were studied at 80% humidity as it is considered it to be harsh as the compositions are hygroscopic in nature.

[0030] FIG. 8 illustrates optical photographs of LI (from L series), MSG1 (from MSGs), and HEG1 (from HEGs) at different humidity level (left hand side photographs). HEG1 was also subjected to freeze-drying to remove water from its composition (right hand side photographs).

[0031] FIG. 9 illustrates optical photographs of HEG1, 02, 03, 04, and 05 (based on Table 1 in FIG. 10). 02, 03, 04, and 05 were prepared using the same composition as HEG1, whilst selectively omitting one crystalline solid at a time, with scale bar of 1 cm.

[0032] FIG. 10 illustrates Tabic 1 with various lower entropy formulations that exclude one of the bioderived organic raw materials.

[0033] FIG. 11 illustrates Fourier Transform Infrared (FTIR) spectra of HEG3 precursor mixture, HEG3, pure CA, and HEG3 without CA.

[0034] FIG. 12 illustrates tensile performance of various HEGs. All the HEGs were tested in 50% humidity except for those labelled with 25% in the legend. HEGs displayed strain hardening behaviours and the high-entropy design imbued good elasticity yet maintained good toughness to an otherwise stiff and brittle CMC polymer.

[0035] FIG. 13 illustrates strain hardening behavior of human skin.

[0036] FIG. 14 illustrates optical photographs of some mechanical manipulation of HEG1 . HEG1 could be twisted and tied into a knot and then stretched without breaking. This shows that HEG possesses good mechanical behaviours.

[0037] FIG. 15 illustrates optical photographs of some mechanical manipulation of HEG1. HEG1 was utilized as the rope in a flywheel pull whistle to demonstrate its strainhardening behaviour.

[0038] FIG. 16 illustrates dielectric constant plotted against frequency for different HEGs. Most HEGs have the high dielectric constant in the order of 107at 1 Hz except for a sample which has less ChCl and urea. ChCl is an ionic species and is important in affecting the formation EDLC on the HEG-electrode interface.

[0039] FIG. 17 illustrates the electrical properties of HEG17, HEG1, HEG18, 02, 03, 04, and 05.

[0040] FIG. 18 illustrates ionic conductivity' of three HEG samples which kept all other components the same but changed the amount of ChCl. Hie sample with the highest ChCl content shows the best conductivity' at substantially 0.90 mS / cm. The conductivities were calculated after fitting the Nyquist plots with an equivalent circuit.

[0041] FIG. 19 illustrates Nyquist plots of HEG1, HEG17, and HEG18. The data was fitted with an equivalent circuit (inset). Here, it was expected that with higher ChCl content, HEG18 exhibited the greatest conductivity.

[0042] FIG. 20 illustrates dielectric constant at 100 Hz and conductivity of materials in existing literature. HEG outperforms the materials in these two metrics with the highest dielectric constant of substantially 4.52 x 107and ionic conductivity at substantially 61 mS / cm at 80% humidity.

[0043] FIG. 21a illustrates SEM images of the HEG venation pattern from the top view (left image) and cross-sectional view (centre image). A depth of 40 μm was achieved without any use of photolithography technique, at a scale bar of 250 pm. A transparent HEG held against the backdrop showing the leaf venation pattern (right image), at a scale bar of 1 cm. FIG. 21b illustrates benchmarking of leaf-patterned HEG against capacitance-based pressure sensors in literature. HEG has unparalleled sensitivity of substantially 59.2 kPa-1 when pitched against other microstructured and ionically conductive gels. FIG. 21c illustrates a capacitance-based pressure sensor made using HEG. Varying the pressure input to the sensor accurately controls a holographic display that was projected onto a HEGscreen. FIG. 2 Id illustrates a calibration pressure sensor was performed using a compressive testing machine and the onset of capacitance changes were set as the threshold values for inciting the change in the holographic display.

[0044] FIG. 22a illustrates biodegradation of HEG that was implanted into potting soil containing a seedling. The HEG biodegraded fully in the span of a 7-day window from visual inspection. The degradation products did not appear to exert any adverse effects on the growth of the seedling. FIG. 22b illustrates tire degree of biodegradation derived from biochemical oxygen demand (BOD) test of HEG indicates the cessation of microorganism aerobic activity by day 7 and that full biodegradation has been achieved. The recycled HEG2 sample retained the same tensile performance as the original sample. FIG. 22c illustrates cell viability' assessment that HEG maintained high biocompatibility at more than 91% across 3 days at different concentrations of 0.1%, 0.5%, and 1% of its precursor mixture Cell viability data was calculated from the optical density' (OD) values of MTT assay. FIG. 22d illustrates LIVE / DEAD fluorescent images of C2C12 mouse cell lines seeded with 0% (control) and 1% concentration of HEG precursor mixture over the span of 3 days, at a scale bar of 200 pm. FIG. 22e illustrates recycling of HEG can be achieved by dissolving in its precursor mixture. The precursor mixture was used to dissolve the HEG so as to keep the concentration of the recycled sample the same as the original. FIG. 22f illustrates a damaged HEG by virtue of its reversible physical bonds can self heal and reach 100% efficiency calculated from toughness values. FIG. 22g illustrates a FESEM image of a HEG sample that was cut and then allowed to heal for 1 day in 80% humidity. The sample was later washed with graduating ethanol to reveal the CMC backbone network The sclf-hcalcd sample showed reformation of CMC network with slight damage, at a scale bar of 25 pm. FIG. 22h illustrates mean squared displacement of each component in MD simulation systems MD1 and MD2. This study was done to show that water content helped with diffusion rate of the components in HEGs system. Overall, MD1 components have greater MSD which translates to a higher rate of diffusion. Interestingly, the MSD of CMC polymer in MD1 is at 3.542 which is more than twice of that in MD2 at 1.361 when time = 250 ps. Tire increased rate of diffusion in all components helps to elucidate the self-healing mechanism as the CMC polymer network diffuses and heals its damage with the aid of other smaller molecules with favorable reversible physical bonding.

[0045] FIG. 23 illustrates the HEG readily dissolves in 1 mol / dm3of NaOH in just 270 minutes.

[0046] FIG. 24 illustrates stress-stretch curves of various HEGs that were self-healed (dashed lines) as compared to pristine samples (solid lines).

[0047] FIG. 25 illustrates a table with number of molecules used in the atomistic modelling during molecular dynamics simulation. The number of molecules used in MD1 followed the mole ratio of the experimental formulation of HEG2 in a 50% humidity environment. Water content was determined experimentally by weighing HEG2 after it had been dried in oven for 2 days. MD2 adapted the formulation of MD 1 but with half the water content.

[0048] FIG. 26a illustrates the number of fruits that turned moldy or remained healthy after being kept in kraft paper cups where their openings were sealed with HEG, cling wrap, or not sealed for 6 days. This experiment was performed on fruits purchased from three different batches, totaling 15 fruits per group. HEG resulted in the lowest percentage of moldy fruits. FIG. 26b illustrates timelapse photographs of strawberries kept in cups sealed with HEG and cling wrap. Th e strawberry enclosed with HEG stayed healthy and showed no signs of tissue damage after 6 days. The strawberry enclosed with cling wrap showed brown lesion spots on day 2 and was infested with mold from day 4. FIG. 26c illustrates weight loss of strawberries over time in different conditions expressed in percentages of their initial weights. At room temperature, the strawberries enclosed with HEG can retain 10.6% higher in weight than those with no sealing at all. The strawberries enclosed with HEG at room temperature retain similar weight percentages with a slight difference of 2.2% as compared to those stored in 4°C refrigeration without sealing. This shows that HEG, even when used at room temperature, can achieve a similar fruit metabolism rate to that of refrigeration conditions. FIG. 26d illustrates T-peel tests of various adhesive materials on kraft paper. The peeling force per width of the HEG adhesive is nearly identical to that of Loctite 4011 super glue. A reused HEG adhesive achieved a high peeling force per width, similar to that of its original curve. The inset shows the T-peel process. FIG. 26e illustrates FESEM images, with scale bar at 100μ, show the paper fibers (false-colored) embedding and fusing into HEG. This elucidates the strong adhesive properties between HEG and paper materials. FIG. 26f illustrates, at a scale bar of 1cm, a piece of HEG showing no mold growth despite being stored at a high RH of 80% for 350 days. This is an excellent property for reusable food packaging. FIG. 26g illustrates, at ascale bar of 2cm, HEG used as a sustainable transportation sheet for a thorny durian without any signs of punctures. FIG. 26h illustrates microscope images, at a scale bar of 0.5mm, depict HEG resisting puncture from a durian thorn and is able to quickly and fully recover after retrieving the thorn. FIG. 26i illustrates, at a scale bar of 2cm, HEG can bear the heavy load of a watermelon which is 1086 times its mass.Detailed Description

[0049] One or more specific and alternative embodiments of the present invention will now be described with reference to the attached drawings. It shall be apparent to one skilled in the art, however, that this invention may be practised without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, common reference numerals or series of numerals will be used throughout the figures when referring to the same or similar features common to the figures.

[0050] According to FIG. 1, the HEG in the present invention comprises at least a semicrystalline sodium carboxymethyl cellulose (CMC) backbone and crystalline citric acid, choline chloride, betaine, and urea in a non-equimolar ratio, wherein the at least four components interact with one another via reversible physical bonds of hydrogen bonds, ionic interactions and ion-dipole interactions hence forming a homogeneous, free-standing gel. The CMC serves as the gel network which synergistically interacts with the other four components. Strong yet reversible hydrogen bond, ionic interactions, and ion-dipole interactions exist between the components. The HEG obtained possesses high k, ionic conductivity, toughness, and is transparent due to its homogeneity (see FIG. 2). It is also aligned with a circular economy which greatly reduces waste.

[0051] According to FIGs. 3 and 4, the HEGs obtained exhibits a smooth morphology based on the SEM images. An energy-dispersive X-ray spectroscopy (EDX) mapping further indicates the homogeneous distribution of C, O, Na, N, and Cl elements within the HEG. Ultraviolet-visible (UV-Vis) spectroscopy in the visible wavelength demonstrates that high transparency in HEG with transmission values close to 100% enabled by its homogeneity' (shown in FIG. 2).

[0052] According to FIG. 5, a broad undulating peak between substantially 15° to 30° and a sharp peak at substantially 77.6° indicate that CMC has a semi-crystalline structure. Alsoaccording to FIG. 5, the other four components (betaine, citric acid, choline chloride, and urea) are crystalline solids as evident from their sharp peaks.

[0053] The HEG herein can be fabricated by dissolving non-equimolar ratio of the semicrystalline sodium carboxymethyl cellulose (CMC), crystalline betaine, citric acid, choline chloride, and urea, and a common solvent, such as water, to obtain a precursor mixture; followed by stirring the precursor mixture until homogeneous, and subsequently removing water from the mixture in a gradual manner to obtain a continuous, free-standing gel where the components interact with one another via reversible, physical bonds of hydrogen bonds, ionic interactions and ion-dipole interactions to form a free-standing gel.

[0054] According to the preferred embodiment, the HEG in the present invention can be fabricated by first dissolving sodium carboxymethyl cellulose (CMC), crystalline betaine, citric acid, choline chloride, and urea in water to obtain a homogeneous precursor mixture. The precursor mixture can be poured into a mold and the water can be subsequently removed in an oven at a moderate temperature of substantially 55 °C. At this temperature, evaporation of the water occurred gradually over time, leaving behind a free-standing gel. The abovementioned steps provide a gelation mechanism such that the HEG components interact with each other via strong reversible physical bonds of hydrogen bonds, ionic interactions, and ion-dipole interactions (as shown in FIG. 1). This is also corroborated by the high nuclear overhauser effect (NOE) intensities in the build-up curves at short mixing times of 5, 20, and 30 ms when performing a two-dimensional nuclear overhauser effect spectroscopy (2D NOESY HNMR) (FIGs. 6a to 6c). Such short mixing times were observed in the ether and amino groups which imply close inter-proton distances in the order of substantially, attributing to physical bonds such as hydrogen bonds, ionic interactions and ion-dipole interactions. It shall be understood that reversibility of bonds help maintain high mobility of components leading to a state of high entropy. Further, the components dissolved in water forms a liquid phase with relatively smaller molecules than a solid phase. Hence, favourable bonds between the smaller molecules and the CMC backbone help to maintain a homogenous system.

[0055] The composition of the present invention may present between HEG, mctastablc gel (MSG) and liquid-like gel phases (L series), based on different weight percentages of each component at 80 % humidity as shown in FIG. 7. O series refers to sample with composition that exclude any one of the components in the present invention. In onepreferred embodiment, non-equimolar ratio of the composition to form HEG (the HEG series) as a free-standing gel refers to sodium CMC present in substantially 9 to 54 wt % of the composition, citric acid (CA) present in substantially 1 to 60 wt % of the composition, choline chloride (ChCl) present in substantially 0.5 to 39 wt % of the composition, betaine present in substantially 0.6 to 45 wt % of the composition, and urea present in substantially 0.4 to 34 wt % of the composition. It was found that MSG formations are noticed in samples with higher weight percentages of CMC, CA and betaine, while L-senes are formed at higher weight percentages of ChCl and urea. Accordingly, it is evident that obtaining HEGs is not trivial and mixing the components together could form undcsircd crystals and liquid-like gels. There exists a delicate balance between the bond formation and quantity of components used.

[0056] Further, the HEG obtained according to the preferred embodiment remained a freestanding gel after being subjected to external stimuli stretching, physical stress, or fluctuations in temperature and humidity (as seen in FIG. 8). According to FIG. 8, HEG1 maintained a gel and did not form crystals. MSG1 were observed to have no changes in physical appearance as well LI became translucent at lower humidity. HEG1 was also subjected to freeze-drying to remove water from its composition (right hand side pictures). Noticeably, HEG1 curled up but there were no crystals formed, indicating that water does not play a dominant role in maintaining a high-entropy state in HEG1.

[0057] Further according to the preferred embodiment, the HEG composition is tested by emulating a lower entropy system where gels of the same composition were fabricated but selectively removing one crystalline component at a time, according to FIG. 10. According to FIG 9 and FIG. 10, the HEG of the present invention remained a gel while the four other gels had crystal formations. This proved that high-entropy design aided in suppressing crystal formation. The compositions encourage favorable bonds and interactions formed between all the components, leading to a high entropy blend of amorphous state. Such a state is both thermodynamically and kinetically more favorable than crystallization and thus the HEGs remain in this stable state.

[0058] FIG. 11 shows the Fourier transform infrared spectroscopy (FTIR) results of the precursor mixture and HEGs bear strong resemblance w ith minor differences at the 400 - 520 cm-1range. No C=O anhydride carbonyl peak was observed in the FTIR spectra whichindicates the absence of covalent bonds formed between citric acid (CA) and CMC via esterification. Here, it is proven that there is absence of covalent bonds due to crosslinking of CMC with CA in the HEGs. This is significant as the formation of reversible bonds greatly enhances the mobility of components, leading to lower entropy in the system.

[0059] Strain-hardening behavior of the HEGs is observed, as indicated by their pronounced J-shaped tensile curves (see FIG. 12). Depending on the specific application, HEGs can be tuned to exhibit either high strength or highest stretch ratio. According to the preferred embodiment based on FIG. 12, the highest strength achieved amongst the HEGs samples was substantially 17.8 MPa while the highest stretch ratio X = 4.22. The increase in strengths indicate that both betaine and CA play a crucial role in the strengthening of the gel polymer. An increase in stretch ratio but decrease in strength suggested that ChCl and urea function as plasticizers in the gel polymer. When mixed in a high-entropy state, all the components play an indispensable role helping the HEG to achieve a good strength and superior stretch ratio Fascinatingly, the same strain-hardening behavior is also observed in human tissues and skin (FIG. 13). Hence, the HEGs could potentially be used as wearable sensors or in-vivo devices where mechanical conformation to the host object is an important parameter.

[0060] Further, the HEG in the present invention can be twisted and stretched and even tied into a knot, an accomplishment since not many bio-derived materials can be manipulated like this (FIG. 14). Further, strain-hardening behavior of the HEGs can be shown by fabricating a flywheel pull whistle using HEGs as the rope (FIG. 15). HEG1 was utilized as the rope in a flywheel pull whistle to demonstrate its strain-hardening behaviour. The flywheel pull whistle was made by cutting 10 cm-long strips of HEG and adhering them to a container encasing a light-emitting diode (LED) device. It was primed by twirling the middle container a few rounds, causing the HEG1 strips to braid themselves. The flywheel pull whistle was given a gradual outward pull, causing the strips to be stretched from the toe to heel region. Gradually, the braids unraveled, causing the middle container to spin. Eventually, the HEG 1 strips entered the linear region and became taut at high tension.

[0061] In terms of electrical properties, the HEGs of the present invention boast high dielectric permittivity when measured from 1 Hz to 10 MHz (FIG. 16). This is due to the adsorption of ionic components to the HEG electrode interface, forming an electric doublelayer that acts as a capacitor. It was found that vary ing the amount of ChCl had the most significant impact on permittivity (FIG. 17). This is because ChCl is a charged group comprising of both quaternary ammonium cation and chlorine anion. Enhancing the weight percentage of ChCl incrementally from 1 1.2% to 20.1 %, and subsequently to 27.4%, correspondingly elevated the ionic conductivity from 0.057 mS / cm to 0.34 mS / cm and finally to 0.90 mS / cm (FIG. 18). The conductivities were calculated after fitting the Nyquist plots with an equivalent circuit (FIG. 19). Removing ChCl from HEG dramatically decreased the permittivity from 1.82 x 106to 4.01x 101 Upon benchmarking the HEG against existing materials and evaluating their dielectric permittivity at 100 Hz and conductivity levels, the HEG of the present invention outperforms others on this metric with a high dielectric constant of substantially' 4.52 x 107and an ionic conductivity at substantially 61 mS / cm (FIG. 20). Hence, the high-entropy design helped to significantly enhance the electrical performances of the organic materials.

[0062] In terms of application, the HEGs of the present invention is configured with embossed leaf venation pattern thereon, in which the embossment reaches a pattern height of 40 pm (FIG. 21a) The leaf patterned HEGs demonstrated superior sensitivity at substantially' 59.2 kPa-1when benchmarked against existing capacitive-based pressure sensors that were either microstructured or fabricated with ionically conductive gels (FIG. 21b). Further, the HEGs of the present invention is used to fabricate a capacitive-based pressure sensor which controls a holographic display' that is projected onto a transparent HEG screen (FIG. 21c). The seasons of the tree in the holographic display were programmed to change according to the capacitance values of the HEGs which were controlled by modulating the pressure applied to the sensor. The capacitance values were calibrated using a compression testing machine and used the onset of capacitance change as the reference values (FIG. 21d). By varying the amount of pressure, the holographic display can be controlled accurately. Further, the HEGs of the present invention can be used to make a strain sensor and a dielectric elastomer actuator (DEA).

[0063] Tn terms of biodegradability', the HEG is mainly composed of bio-derived organic raw materials, hence it follows that HEG is biodegradable as well. According to FIG. 22a, HEG sample with a diameter of 20 mm was planted into soil already cultivating a black- eyed pea ( igna unguicidata) seedling to demonstrate its biodegradability. After seven days, the HEG was fully biodegraded. The seedling’s height was the same as the control.proving that the biodegradation products did not stifle its growth. The completeness of the biodegradation process was validated by a biochemical oxygen demand (BOD) test where the degree of biodegradation calculated by from the accumulated pressure drop caused by biodegradation of HEG against the theoretical oxygen demand stayed constant by day seven (FIG. 22b). Compared to filter paper, HEG biodegrades much faster. The fast biodegradation speed is due to the ease of biodegrading small-sized molecules which are held together by reversible physical bonds. The HEG can also be degraded-on -demand using common bases. It was found that in just 270 minutes, the HEG was fully dissolved in 1 mol / dm3of NaOH without any heating (FIG. 23). The lack of a heat source means that alkali hydrolysis did not take place and the complete dissolution supports that reversible bonds exist between the components. This attribute will be helpful for applications related to transient electronics.

[0064] In terms of biocompatibility, the HEG was studied by seeding HEG precursor mixtures at 0.1%, 0.5% and 1% concentrations to C2C12 cell lines (FIG. 22c). Over 72 hours, all samples maintained high cell viability of more than 95% calculated from their OD values. Live / dead fluorescent images show good cell proliferation for 1 % concentration (FIG. 22d). Beyond electronic devices and soft actuators, these versatile HEGs show promise for drug delivery', tissue engineering, agriculture, and food applications. Their high concentration and high variety of material loading capacity enables implantable, injectable or topical delivery of various drug cocktails for personalized therapeutics. This loading capability is also applicable to sustained nutrient and drug release in tissue engineering and fertilizers. In foods, they could fortify products with custom vitamin and mineral profiles through embedded active compounds. In summary, the HEGs’ adaptable encapsulation functionality supports a wide range of prospects across healthcare and biotechnology.

[0065] As the HEG relies on reversible physical bonds, it can be recycled by dissolving in its precursor mixture and re-casted into a film. The precursor mixture can be used to dissolve the HEGs in order to ensure that concentration of the recycled sample is kept the same as the pristine. Furthermore, the precursor mixture has a higher entropy than water which aids in the recycling of HEGs. We characterized the tensile performance of the recycled HEG and found that it had an ultimate tensile strength and a maximum strain nearly identical to the original sample (FIG. 22e).

[0066] In terms of self-healing, the self-healing efficiency of damaged samples were observed under two mild healing conditions: (1) free diffusion in 60% humidity and (2) in elevated temperature of 40 °C (FIG. 24). Notably, HEG3 that was left to heal in 60% humidity showed the best self-healing efficiency of 100% (Fig. 22f). This high self-healing efficiency was due to the reversible bonds present in HEG, high mobility of components from high-entropy design, and an increased rate of diffusion assisted by water absorption. SEM image of the self-healed CMC backbone further attested to the diffusion of CMC polymer chains (FIG. 22g), congruent to the well-established cracking healing theory . We also demonstrated that the self-healed HEG can withstand strain without breaking (FIG 14). We simulated different HEG systems with increased w ater content and observed that all components experienced a higher rate of diffusion as indicated by the increase in their mean square displacement (MSD) (FIG. 22h and FIG. 25). Unexpectedly, even a large molecule like CMC saw an increase in its MSD increased by substantially 158% when water content was doubled.

[0067] In terms of application, HEG can be used as a sustainable yet tough food packaging capable of keeping fruits fresh. We assessed the number of strawberries (Fragaria ananassa) that turned moldy via their morphological changes over 6 days under different conditions (in FIG. 26a). Specifically, strawberries were placed in kraft paper cups where the openings were sealed with HEG, cling wrap, or left unsealed. We found that strawberries scaled with HEG showed the best results with only 20% of the fruits turning moldy. This is in stark contrast with unsealed and cling wrap groups at 53% and 67%, respectively. Timclapsc photographs over 6 days show a strawberry enclosed by cling wrap with mold infection while a strawberry enclosed with HEG remains healthy (as seen in FIG. 26b). The weight loss of strawberries sealed with HEG or unsealed was studied at room temperature and 4°C refrigeration (FIG. 26c). By day 7, strawberries sealed with HEG retained 86.3% of their initial weights which is much higher than unsealed strawberries at 75.7% in room temperature. Remarkably, strawberries sealed with HEG at room temperature are only 2.2% lower in average percentage of initial weight than the unsealed strawberries stored in 4°C refrigeration. This suggests that HEG can be used in food transportation in remote areas where refrigeration is difficult to achieve and still maintains a good shclf-hfc.

[0068] Owing to its J-curve mechanical behavior, HEG can conform well to kraft paper cups. We evaluated the seal integrity of HEG on sustainable materials such as kraft paper cups and cardboard from delivery parcels. HEG is an excellent adhesive to these materials as evidenced by the high peeling force per width of HEG which is remarkably close to that of Loctite 4011 super glue (as seen in FIG. 26d). HEG can achieve good adhesiveness without being tacky and sticky to the touch. FESEM images show that paper fibers are embedded and fused to HEG (as seen in FIG. 26e). This is due to the HEG conforming to the paper fibers when pressed. After heat-sealing, HEG dehydrates and stiffens, locking onto the fibers. Wc found that HEG adhesive can be reused by tearing off from the cup and removing the leftover paper residues before restarting the adhesion process. The reused adhesive has a peeling force over width result is highly comparable to its original curve (as seen in FIG. 26d). Towards their end-of-life, HEG and the paper material can both be biodegraded which conventional plastic containers are not able to do. HEG shows no signs of mold growth despite being stored at 80% RH for 350 days (as see in FIG. 26f).

[0069] In terms of application, HEG can be used as a tough and sustainable sheet to transport thorny fruits like durians without any punctures (as seen in FIG. 26g) The J- curve mechanical behavior enables HEG to deform and be locally strengthened, resisting puncture from the sharp durian thorns. Upon removal of the thorn, it can rapidly recover to its original state in just 2s (as seen in FIG. 26h). HEG sheets arc self-healing, reusable, and readily biodegraded unlike commercial single-use plastic bags. We further demonstrated HEG’s ability to bear heavy loads such as a watermelon with more than 1000 times the weight of the HEG (as seen in FIG. 26i). The superior toughness, together with its adhesive and mold-mitigating abilities, making HEG an excellent material for sustainable food packaging applications.

[0070] While specific embodiments have been described and illustrated, it is understood that many changes, modifications, variations and combinations of variations disclosed in the text description and drawings thereof could be made to the present invention without departing from the scope of the present invention. For example, the tough, self-healing, reusable and biodegradable HEG can also be used for making packaging material for industrial applications.

Claims

CLAIMS1. A high-entropy gel (HEG) composition derived from organic materials, the composition comprising at least a semi-crystalline polymeric backbone and at least four different crystalline components in a non-equimolar ratio, wherein the at least four crystalline components interact with one another via reversible physical bonds of hydrogen bonds, ionic interactions and ion-dipole interactions hence forming a homogeneous, freestanding gel.

2. The composition according to claim 1, wherein the semi-crystalline polymeric backbone comprises sodium carboxymethyl cellulose3. The composition according to claim 1 or 2, wherein the at least four different crystalline components are selected from citric acid, choline chloride, betaine, urea and / or water.

4. The composition according to claim 3 comprises sodium carboxymethyl cellulose present in substantially 9 to 54 wt % of the composition, citric acid present in substantially 1 to 60 wt % of the composition, choline chloride present in substantially 0.5 to 39 wt % of the composition, betaine present in substantially 0.6 to 45 wt % of the composition, and urea present in substantially 0.4 to 34 wt % of the composition.

5. A method for producing a high-entropy gel (HEG) composition derived from organic materials, the method comprising the steps of: dissolving non-equimolar ratio of semi-crystalline sodium carboxymethyl cellulose, at least four different crystalline components, and a solvent to obtain a precursor mixture; stirring the precursor mixture until homogeneous; and removing water from the mixture in a gradual manner to obtain a continuous, freestanding gel where the components interact w ith one another via reversible, physical bonds of hydrogen bonds, ionic interactions and ion-dipole interactions to form a free-standing gel.

6. The method according to claim 5, wherein the precursor mixture comprises sodium carboxymethyl cellulose present in substantially 9 to 54 wt % of the composition, citric acid present in substantially 1 to 60 wt % of the composition, choline chloride present insubstantially 0.5 to 39 wt %, of the composition, betaine present in substantially 0.6 to 45 wt % of the composition, urea present in substantially 0.4 to 34 wt % of the composition and water.

7. The method according to claim 5 or 6, wherein the stirring step is conducted at about 2000 rpm.

8. The method according to any one of claims 5 to 7, wherein the step of removing water in a gradual manner is conducted at about 55 °C to about 60 °C over 3 to 5 days.

9. A packaging material manufactured according to the HEG composition recited in claims 1-4 or produced according to claims 5-8, wherein the packaging material is self- healing, tough, bio-degradable and reusable.

10. A strain or pressure sensor made according to the HEG composition recited in claims 1-4 or produced according to claims 5-8.

11. A wearable elastomeric actuator made according to the HEG composition recited in claims 1 -4 or produced according to claims 5-8.

Images