Physical Gels Research Articles

Efficacy of sunscreen gel infused with giant tiger prawn (Penaeus monodon) head extract

Excessive sunlight exposure can lead to various minor skin disorders, including sunburn and the development of chronic skin malignancies. One effective preventive measure against these adverse effects is the use of sunscreen. Sunscreen can be derived from natural sources, such as the astaxanthin compound in giant tiger prawns (Penaeus monodon). This study aimed to formulate a sunscreen gel from giant tiger prawn head extract that meets good physical gel standards. Additionally, the study sought to determine the sun protection factor (SPF), erythema transmission level (%TE), and pigmentation transmission level (%TP) through in-vitro testing. The extraction process involved using coconut oil as a solvent using the maceration method. The resultant extract was then evaluated for SPF, %TE, and %TP values and subsequently formulated into gel variants with extract concentrations ranging from 1% to 10%. The findings of this investigation revealed that the giant tiger prawn head extract exhibited SPF, %TE, and %TP values of 8.0±0.11, 18.8±0.25%, and 21.7±0.73%, respectively, categorizing it as providing maximum protection, facilitating fast tanning, and acting as a sunblock. The gel formula containing 8% giant tiger prawn head extract demonstrated the highest sunscreen potential. In conclusion, this study highlights the promising potential of giant tiger prawn head extract as a natural sunscreen ingredient and identifies the optimal gel formula for effective sun protection.

3D Printing of Ceramics with Controllable Green‐Body Configuration Assisted by the Polyvinyl Alcohol‐Based Physical Gels

Additive manufacturing of ceramics has received intense attention. In particular, 3D‐printed ceramics with customized shapes are highly desirable in the chemical industry, aerospace, and biomedical engineering. Nevertheless, developing a simple and cost‐effective process that shapes dense ceramics to complex geometries remains challenging because of the high hardness and low ductility of ceramic materials. Extrusion‐based printing, such as direct ink writing (DIW), often requires supporting materials that pose additional difficulties during printing. Herein, a simple approach is developed to produce stretchable ceramic green bodies of zirconia and alumina for DIW. The ink is composed of polyvinyl alcohol (PVA) and an aqueous suspension of ceramic powders. Besides the colloidal network formed by the ceramic particles, PVA plays an important role in tuning the printability of the aqueous ink. Through a freeze‐thaw process, PVA crystallizes to form physical networks. This strategy provides highly stretchable hydrogel green bodies that can be reprogrammed to complex geometries difficult for common DIW printing. The subsequent drying, debinding, and sintering processes produce ceramics with dense structures and fine mechanical properties. In short, this work demonstrates an efficient method for the DIW of ceramic parts that can be reprogrammed to complex geometries.

Gel point investigation of liquid silicone rubber using rheological approaches

Liquid silicone rubber (LSR) is becoming increasingly popular due to its chemical, UV, and heat resistance as well as its excellent optical properties. However, there is currently a lack of research and understanding of the rheological properties of the material. During the processing of liquid silicone rubber, the material can assume different rheological states. In the present work, both the physical and the chemical gel behavior are investigated rheologically. For this purpose, measurements are carried out with a rotational rheometer and a high-pressure capillary rheometer. Depending on the temperature and pre-shear rate, times are given for the physical gel point, after which a significantly destroyed physical network is recovered. Investigations at higher temperatures, which lead to chemical crosslinking and, therefore, to a chemical gel point, resulted in a representation of the temperature-dependent chemical gel point. The presented results serve as a material database for reliable simulations.

Spinodal Decomposition, Nucleation Growth, and Arrested Macrophase Separation of Physical Gels of Atactic Poly(N-isopropylacrylamide) in Water

Spinodal Decomposition, Nucleation Growth, and Arrested Macrophase Separation of Physical Gels of Atactic Poly(<i>N</i>-isopropylacrylamide) in Water

Effects of deacetylation degree of chitosan on the structure of aerogels

Chitosan aerogels, obtained by (supercritical) CO2 drying of hydrogels, are novel adsorbents because of their large surface area and high porosity. Intrinsic properties of chitosan such as molecular weight (MW) and degree of deacetylation (DDA) had large impacts on the characteristics of chitosan aerogels. Although there are a few studies about the effects of solely DDA or MW on aerogel structure, none of them has focused on the mutual effects. The study aims to investigate the combined effects of MW and DDA of chitosan on aerogel properties. Hydrogels were produced in beads form by physical gelation of the chitosan solutions (2 % w/v in acetic acid of 1 %, v/v) in an alkaline environment (NaOH, 4 N). Supercritical CO2 dried aerogels were examined with respect to the bulk density, diameter as well as pore characteristics, and surface area by Barrett-Joyner-Halenda (BJH) and Brunauer-Emmett-Teller (BET) methods, respectively. Morphologies of aerogels were also examined by Scanning Electron Microscopy (SEM) images and structural changes of aerogels were observed by Fourier Transform Infrared (FTIR) Spectroscopy. Additional to BET-BJH analysis, proton relaxation dispersion was measured by Fast Field Cycling NMR (FFC-NMR) to determine the pore volume of the aerogels. Compact structures were obtained for higher MW chitosan and lower MW chitosans with higher DDA increasing the aerogel diameters. All types of aerogels obtained by different chitosan characteristics (MW and DDA) showed a porous structure and the highest DDA with the lowest MW caused the minimum bulk density with the highest water absorption rate. Although different N2 adsorption-desorption profiles were obtained in terms of pore volumes; all aerogels had Type IV isotherms with Type H1 hysteresis curve. FFC-NMR experiments showed that the coherence length values were associated with the pore volumes and FFC-NMR experiments were found to be meaningful as supportive experiments for the characterization of aerogels.

Liquid state theory study of the phase behavior and macromolecular scale structure of model biomolecular condensates.

Biomolecular condensates can form through the liquid-liquid phase separation (LLPS) of proteins and RNAs in cells. However, other states of organization, including mesostructured network microstructures and physical gels, have been observed, the physical mechanism of which are not well understood. We use the Polymer Reference Interaction Site Model liquid state integral equation theory to study the equilibrium behavior of (generally aperiodic in sequence) biomolecular condensates based on a minimal sticker-spacer associating polymer model. The role of polymer packing fraction, sequence, and the strength and range of intermolecular interactions on macromolecular scale spatial organization and phase behavior is studied for typical sticker-spacer sequences. In addition to the prediction of conventional LLPS, a sequence-dependent strongly fluctuating polymeric microemulsion homogeneous state is predicted at high enough concentrations beyond the so-called Lifshitz-like point, which we suggest can be relevant to the dense phase of microstructured biomolecular condensates. New connections between local clustering and the formation of mesoscopic microdomains, the influence of attraction range, compressibility, and the role of spatial correlations across scales, are established. Our results are also germane to understanding the polymer physics of dense solutions of nonperiodic and unique sequence synthetic copolymers and provide a foundation to create new theories for how polymer diffusion and viscosity are modified in globally isotropic and homogeneous dense polymeric microemulsions.

Mechanically robust all-hydrogel supercapacitor having seamless interfaces among components by rapid phase transition of physical gels

In a flexible energy storage device, the interface between the components not only degrades the electrochemical performance but also makes it mechanically vulnerable. Therefore, interface engineering is important to ensure device performance. Here, we propose a design strategy for the fabrication of seamless energy storage device that maximizes the structural integrity between all-components. Utilizing a rapid phase transition characteristic of agarose, a seamless device composed of carbon cloth, agarose/activated carbon electrode, and agarose electrolyte were prepared. The seamless interface improved areal capacitance and lap-shear strength by 35% (166.6 mF/cm2) and 1000% (12 kPa), respectively, compared to that of the conventional sandwich-type supercapacitor. In addition, the impedance of the seamless device was measured as 80% of that of the sandwich device demonstrating a decrease of interfacial resistance. While the areal capacitance of the seamless device was maintained even after 100 bending cycles, the device failure by interfacial slip for the sandwich device was observed. Considering that flexible electronic devices are subjected to repeated mechanical deformations, the device fabrication strategy using phase changing materials proved to be very effective which can be applied to versatile applications.

Preparation and Properties of Physical Gel on Medical Titanium Alloy Surface.

Medical titanium alloy Ti-6Al-4V (TC4) has been widely used in the medical field, especially in human tissue repair. However, TC4 has some shortcomings, which may cause problems with biocompatibility and mechanical compatibility in direct contact with the human body. To solve this problem, physical gels are formed on the surface of TC4, and the storage modulus of the formed physical gel matches that of the human soft tissue. 2-bromoisobutyryl bromide (BIBB) and dopamine (DA) were used to form initiators on the surface of hydroxylated medical titanium alloy. Different initiators were formed by changing the ratio of BIBB and DA, and the optimal one was selected for subsequent reactions. Under the action of the catalyst, L-lactide and D-lactide were ring-opened polymerized with hydroxyethyl methacrylate (HEMA), respectively, to form macromolecular monomers HEMA-PLLA29 and HEMA-PDLA29 with a polymerization degree of 29. The two macromolecular monomers were stereo-complexed by ultrasound to form HEMA-stereocomplex polylactic acid (HEMA-scPLA29). Based on two monomers, 2-(2-methoxyethoxy) ethyl methacrylate (MEO2MA) and oligo (ethylene oxide) methacrylate (OEGMA), and the physical crosslinking agent HEMA-scPLA29, physical gels are formed on the surface of TC4 attached to the initiator via Atom Transfer Radical Addition Reaction (ATRP) technology. The hydrogels on the surface of titanium alloy were characterized and analyzed by a series of instruments. The results showed that the storage modulus of physical glue was within the range of the energy storage modulus of human soft tissue, which was conducive to improving the mechanical compatibility of titanium alloy and human soft tissue.

Resilient and reprocessable physical gels based on crystalline olefin block copolymer elastomer and mineral oil toward optically transparent electronic packaging

Due to the urgent demand of high-performance electronic packaging materials, thermoplastic elastomer physical gels (TPEG) have emerged as a promising alternative to traditional hydrogels and crosslinked rubbers due to their good thermal stability and reprocessability. In this work, olefin block copolymer (OBC) elastomer was blended with soft-block selective mineral oil (MO) to tune the mechanical property and transparency. It was found that the MO molecules can disperse well within amorphous phase with effective filling ratio ranging from 9.85 wt% to 44.82 wt%. The hard segments pack into spherulites and gradually develop into segregated crystals of ∼800 nm with the increase of MO concentration. Interestingly, fast quenching induces breakout crystallization morphology while thermal annealing at 130 °C can result in confined crystallization morphology with increased domain spacing due to the selective distributed MO since the corrected crystallinity remains constant and the crystal structure maintains as orthogonal crystals. Due to the combined effect of weak mesophase separation and decreased crystal size, OBC gels has an increased transparency up to 80% in visible region. The extensibility and cyclic property of OBC-based TPEG were finely tuned along with high transparency and excellent dielectric insulation property. Furthermore, the OBC gels are highly stable over a wide temperature and can be recycled. Overall, our work highlights the potential of thermoplastic elastomer physical gels as a sustainable and high-performance alternative for transparent electronics packaging materials.

Structural and gelling properties of whey proteins influenced by various acids: Experimental and computational approaches

Five different acids, i.e., hydrochloric acid (HCl), acetic acid, lactic acid, γ-aminobutyric acid (GABA) and taurine were applied to investigated their effects on heat-induced gelation properties of whey protein isolate (WPI) at pH = 5.5. All WPI gels were found to have self-similar structures with the fractal dimension, df = 2.40. Those denatured WPI formed strong physical gels that were susceptible to shear and strain. Of all the acids, HCl, GABA and taurine significantly strengthened WPI gels. Moreover, denser packing of protein aggregates was observed from the gels with GABA and taurine. Besides experimental approaches, molecular dynamics (MD) simulations were also applied to investigate the effects of various acids on denaturation of β-lactoglobulin (β-LG). GABA and taurine were found to protect β-LG from denaturation and delayed the molecular heat-induced unfolding. Moreover, presence of HCl, GABA and taurine conserved the rigidity of unfolded β-LG and localized the residue –SH121, which was believed to result in promoted reaction-limited clustering aggregations (RLCA) of β-LG molecules and strengthened WPI gels. Further studies suggested that there was no strong binding or aggregation between cations (Na+) or anions/zwitterions and β-LG molecule. Therefore, the effects from various acids (anions/zwitterions) on β-LG and WPI were supposed to result from long-distanced electrostatic interactions and/or their effects on the protein hydration shells.

Preparation and Characterization of Porous Cellulose Acetate Nanofiber Hydrogels.

The currently reported methods for preparing cellulose acetate hydrogels use chemical reagents as cross-linking agents, and the prepared ones are non-porous structured cellulose acetate hydrogels. Nonporous cellulose acetate hydrogels limit the range of applications, such as limiting cell attachment and nutrient delivery in tissue engineering. This research creatively proposed a facile method to prepare cellulose acetate hydrogels with porous structures. Water was added to the cellulose acetate-acetone solution as an anti-solvent to induce the phase separation of the cellulose acetate-acetone solution to obtain a physical gel with a network structure, where the cellulose acetate molecules undergo re-arrangement during the replacement of acetone by water to obtain hydrogels. The SEM and BET test results showed that the hydrogels are relatively porous. The maximum pore size of the cellulose acetate hydrogel is 380 nm, and the specific surface area reaches 62 m2/g. The porosity of the hydrogel is significantly higher than that of the cellulose acetate hydrogel reported in the previous literature. The XRD results show that the nanofibrous morphology of cellulose acetate hydrogels is caused by the deacetylation reaction of cellulose acetate.

Controllable Wetting Transitions on Photoswitchable Physical Gels.

Softness plays a key role in the deformation of soft elastic substrates at the three-phase contact line, and the acting forces lead to the formation of a wetting ridge due to elastocapillarity. The change in wetting ridge and surface profiles at different softness has a great impact on the droplet behavior in different phenomena. Commonly used materials to study soft wetting are swollen polymeric gels or polymer brushes. These materials offer no possibility to change the softness on demand. Therefore, adjustable surfaces with tunable softness are highly sought-after to achieve on-demand transition between wetting states on soft surfaces. Here, we present a photorheological physical soft gel with adjustable stiffness based on the spiropyran photoswitch that shows the formation of wetting ridges upon droplet deposition. The presented photoswitchable gels allow the creation of reversibly switchable softness patterns with microscale resolution using UV light-switching of the spiropyran molecule. Gels with varying softness are analyzed, showing a decrease in the wetting ridge height at higher gel stiffness. Furthermore, wetting ridges before and after photoswitching are visualized using confocal microscopy, showing the transition in the wetting properties from soft wetting to liquid/liquid wetting.

Fabrication of rice bran protein - sodium alginate - calcium double cross-linked foam template for oleogel preparation

In this study, a flexible double-crosslinked rice bran protein (RBP) foam template was developed for oleogel preparation based on Maillard reaction and physical gelation. The Maillard reaction of RBP and sodium alginate (SA) was optimized based on foaming properties of the conjugates. The best foaming capability and foam stability were observed when RBP (50 mg/mL) and SA (30 mg/mL) were mixed at a ratio of 2:1, under ultrasonication at 320 W for 45 min. The cryogel was prepared from RBP-SA foam under freeze drying. The pore structure, density and oil affinity of RBP-SA cryogels were significantly enhanced compared to those of the RBP cryogel, leading to better oil absorption and oil holding capacity of the resultant oleogels. Calcium ion was further introduced into the conjugates to prepare the double-crosslinked foam template (RBP-SA-Ca2+). The prepared cryogel exhibited improved flexibility and oil holding capacity with reduced storage modulus, yield stress and compressive strength. In conclusion, the chemical cross-linking mainly affected the oil absorption capacity and oil holding capacity of RBP cryogel and oleogel, while the physical cross-linking mainly affected the mechanical properties of RBP cryogel. This study provided further insights into preparation of foam-templated oleogel with tunable performance and practical application.

Advanced methodologies for the cleaning of works of art

AbstractCultural heritage assets constitute a fundamental socioeconomic resource, but the actual works of art need to be maintained, counteracting degradation processes, to transfer these benefits to future generations. In particular, the removal of soil, aged coatings, and vandalism/overpaints is one of the most needed interventions in art restoration. Traditional cleaning methodologies, based on classical solution and polymer chemistry, only grant limited control of the cleaning interventions, with the risk of affecting the original components of the artifacts, and often involving the use of toxic or non-environmentally friendly compounds. Alternatively, materials science, colloids, and soft matter have provided valuable and safe solutions in the last decades. This review provides a selection of the most recent and advanced methodologies for the wet cleaning of works of art, spanning from nanostructured cleaning fluids (microemulsions, surfactants swollen micelles) to physical and chemical gels. The new methodologies work on different physico-chemical mechanisms, such as processes for detaching/dewetting, to selectively remove the unwanted layers in sustainable and cost-effective interventions. The best performing systems, like microemulsions confined in “twin-chain” polyvinyl alcohol gels, have been assessed in the cleaning of masterpieces such as works by Pablo Picasso, Jackson Pollock and Roy Lichtenstein. Particular attention is dedicated to “green” chemistry systems, using low-toxicity solvents or bio-based/waste materials to build gel networks. Finally, current trends and future perspectives are given, showing that advanced systems for art cleaning link with transversal fields of crucial importance even beyond Cultural heritage conservation, e.g., detergency, tissue engineering, drug-delivery, food industry and cosmetics.

Chelating agents for the removal of calcareous deposits from archaeological ceramic materials. Compositional evaluation after immersion and physical gel application methods

The removal of calcareous deposits from archaeological ceramics is a very normal conservation-restoration treatment. Among the products used, chelating agents are quite common, including ethylenediaminetetraacetic acid salts (EDTA) (Berducou in La Conservation en archéologie: méthodes et pratique de la conservation-restauration des vestiges archéologiques, Masson, Paris, 1990; Buys and Oakley The conservation and restoration of ceramics, Butterworth-Heinemann, Oxford, 1993; Crisci et al. in Appl Phys A Mater Sci Process, 2010. https://doi.org/10.1155/2009/893528). Nevertheless, some studies have proved that they can cause damages on the ceramic pieces, regarding changes in their composition, such as dissolution of calcareous components and metallic oxides leaching (Gibson in Stud Conserv, 1971. https://doi.org/10.1155/2009/893528; Fernández and Seva Sautuola in Rev del Inst Prehist y Arqueol 9:471–982, 2003). As a consequence, their artistic values might also change. In spite of that, these products are nowadays still in use, meaning that the treatments might be changing the information that archaeological ceramics carry. However, from the 80 s onwards a more secure alternative to direct application methods based on thickening agents was developed. With the aim of analysing the degradation mechanisms that may take place after the cleaning treatments’ application, ceramic specimens with artificial calcareous deposits (Sáenz-Martínez et al. in Eur Phys J Plus 136:798, 2021) were treated with a low-concentrated solution of EDTA tetrasodium salt applied by immersion and thickened with xanthan gum powder (Vanzan® NF-C). Finally, the products from the cleaning treatments were neutralised, respectively, by immersion and by rinsing with deionized water. The composition of the ceramic samples was established before the growth of calcareous deposits and after the treatments, in order to determine their effectiveness and safety. According to the results, EDTA salt treatments, both by immersion and thickened, were effective regarding the removal of the calcareous deposits and did not modify the elemental and mineralogical original composition of the specimens (XRF, XRPD, TG-DSC). In addition, no gel residues were detected by FTIR-ATR.

Self-assembly of bent-core amphiphiles joining the ethylene-oxide/lithium ion tandem

The synthesis, supramolecular self-assembly and structural characterization of a new family of tetraethylene oxide (TEG)-based bent-core compounds and their 1/1 lithium-containing complexes are reported. TEG-based bent-core amphiphiles, even joining the TEG/Li+ tandem, are suitable building-blocks to achieve supramolecular nanostructures, in some cases showing chiral features from achiral molecules either in the mesophase or in solvents. The thermal and liquid crystal behavior of these materials studied by polarizing optical microscopy and X-ray diffraction confirmed that Li-based materials stabilized polar smectic C and helical nanofilament-type mesophases, in contrast to the non-liquid crystalline pure TEG-compounds. Alternatively, both the pure amphiphiles and the lithium-doped materials self-assemble into physical gels in non-polar solvents, displaying three-dimensional networks composed of long fibers with lamellar molecular organizations as shown by transmission electron microscopy and X-ray diffraction. Interestingly, biphenyl- and azobenzene-based bent core amphiphiles aggregate in solvent into chiral nanostructured morphologies with supramolecular trends comparable to their molecular arrangement in their liquid crystalline phases.

Ultrafast gelation of hyaluronan hydrogels via alternate compression-decompression

High pressure-induced inter/intra-hydrogen bonds are strong enough to sustain microassemblies. Here, for the first time, we demonstrate a rapid route (several minutes) for dynamic pressure to enable effective gel formation from hyaluronic acid (HA). The HA hydrogels prepared in such an alternate compression-decompression procedure exhibit a layered structure and high yield of as-made gels. Compared to conventional freeze-thawed hydrogels, the gels via alternate compression-decompression (ACD) have an enhanced intermolecular interaction as well as improved mechanical properties. This method is fast, simple, and safe. Furthermore, the present results provide new ideas for obtaining physical gels and contribute to the development of HA-based materials that can be used in biomedical and agricultural applications.

Smart superabsorbent alginate/carboxymethyl chitosan composite hydrogel beads as efficient biosorbents for methylene blue dye removal

The presence of toxic dyes in the aqueous medium has threatened environmental safety, and thereby removing them from wastewater in an efficient way is highly desired. Herein, the efficient biosorbents were successfully fabricated via a facile physical gelation process of sodium alginate (SA) and carboxymethyl chitosan (CMCTS) in an acidic aqueous solution. The as-prepared hydrogel beads not only displayed water superabsorbent properties and pH-responsive swelling characters but also exhibited excellent methylene blue (MB) adsorption capacity removal efficiency with experimental maximum MB adsorption capacity of 2518 and 1005 mg g–1, which are comparable with most reported lignocellulosic and alginate-based hydrogels. The MB adsorption process fitted well in different kinetic and isotherm models and became more heterogeneous in concentrated MB solutions as verified by principal component analysis results. The adsorption mechanism was proposed, and the high dye absorbency was attributed to the strong electrostatic forces between adsorbents and adsorbates. Our current study provides a promising and sustainable composite hydrogels platform targeted to dye decontamination.

Microrheological study of PVA–borax physical gel: effects of charge screening

Microrheological study of PVA–borax physical gel: effects of charge screening

Physical Gels of Atactic Poly(N-isopropylacrylamide) in Water: Rheological Properties and As-Derived Spinodal Temperature

Aqueous solutions of atactic poly(N-isopropylacrylamide) (a-PNIPAM) undergo complex phase transitions at 20-33 °C. In this temperature range, the a-PNIPAM solution exhibits a phase behavior of lower critical solution temperature at the binodal temperature (Tb) and physical gel formation at the gel temperature (Tgel). On slow heating of the one-phase solution containing linear a-PNIPAM chains, branched chains are gradually developed to proceed with the physical gelation before phase separation considering that Tgel < Tb. Thus, the phase separation temperature determined from the conventional approaches, either by turbidity to derive the Tb or by scattering to derive the spindal temperature (Ts) from the Ornstein-Zernike analysis, is strictly the transition temperature associated with the a-PNIPAM hydrogel (or highly branched chains newly developed at elevated temperatures), rather than the initial a-PNIPAM solution prepared. Herein, the spinodal temperatures of a-PNIPAM hydrogels (Ts,gel) of various concentrations were determined from rheological measurements at a heating rate of 0.2 °C/min. Analyses of the temperature dependence of loss modulus G″ and storage modulus G' give rise to the Ts,gel, based on the Fredrickson-Larson-Ajji-Choplin mean field theory. In addition, the specific temperature (T1) above which the one-phase solution starts to dramatically form the aggregated structure (e.g., branched chains) was also derived from the onset temperature of G' increase; this is because as solution temperature approaches the spinodal point, the concentration fluctuations become significant, which is manifested with the elastic response to enhance G' at T > T1. Depending on the solution concentration, the measured Ts,gel is approximately 5-10 °C higher than the derived T1. On the other hand, Ts,gel is independent of solution concentration to be constant at 32.8 °C. A phase diagram of the a-PNIPAM/H2O mixture is thoroughly constructed together with the previous data of Tgel and Tb.