Physical Gels Research Articles

Formulation and Evaluation of Physical Stability Natural Acne Gel Based on Aloevera Gel with Essential Oil Blend

This study aims to determine the formulation and evaluation of natural acne gel preparations made from aloe vera gel with a mixture of essential oils where the concentration of aloe vera gel can affect the stability of natural acne gel preparations. The use of herbal cosmetics is preferred because it comes from natural ingredients, is safe, can be used by all skin types, has various choices, is inexpensive, has low side effects, and does not pollute the environment. Organoleptic Test Process, pH Test, Adhesion Test, Spreadability Test, Stability Test (Cycling Test) for evaluation of natural acne gel preparations. The results showed that the higher the concentration of aloe vera gel, the higher the pH, dispersion, and stability. By paying attention to the data from each formula, it can be concluded that the most optimal preparation is the F3 preparation which shows the appropriate pH results, appropriate dispersion and homogeneous stability.

Phonon transport properties of particulate physical gels.

Particulate physical gels are sparse, low-density amorphous materials in which clusters of glasses are connected to form a heterogeneous network structure. This structure is characterized by two length scales, ξs and ξG: ξs measures the length of heterogeneities in the network structure and ξG is the size of glassy clusters. Accordingly, the vibrational states (eigenmodes) of such a material also exhibit a multiscale nature with two characteristic frequencies, ω* and ωG, which are associated with ξs and ξG, respectively: (i) phonon-like vibrations in the homogeneous medium at ω<ω*, (ii) phonon-like vibrations in the heterogeneous medium at ω*<ω<ωG, and (iii) disordered vibrations in the glassy clusters at ω > ωG. Here, we demonstrate that the multiscale characteristics seen in the static structures and vibrational states also extend to the phonon transport properties. Phonon transport exhibits two distinct crossovers at frequencies ω* and ωG (or at wavenumbers of ∼ξs -1 and ∼ξG -1). In particular, both transverse and longitudinal phonons cross over between Rayleigh scattering at ω<ω* and diffusive damping at ω>ω*. Remarkably, the Ioffe-Regel limit is located at the very low frequency of ω*. Thus, phonon transport is localized above ω*, even where phonon-like vibrational states persist. This markedly strong scattering behavior is caused by the sparse, porous structure of the gel.

Recombinant mussel protein Pvfp5β enhances cell adhesion of poly(vinyl alcohol)/k-carrageenan hydrogel scaffolds

Polymeric hydrogels are increasingly considered as scaffolds for tissue engineering due to their extraordinary resemblance with the extracellular matrix (ECM) of many tissues. As cell adhesion is a key factor in regulating important cell functions, hydrogel scaffolds are often functionalized or loaded with a variety of bioactive molecules that can promote adhesion. Interesting biomimetic approaches exploit the properties of mussel-inspired recombinant adhesive proteins. In this work, we prepared hydrogel scaffolds with a 50%w mixture of k-carrageenan (kC) and polyvinyl alcohol (PVA), by a two-step physical gelation process, and we coated them with Perna viridis foot protein-5β (Pvfp5β). The mechanical and morphological properties of hydrogels were investigated both after conditioning with typical cell culture media and also after coating with the Pvfp5β. The protein resulted strongly adsorbed onto the surface of the hydrogel and also able to penetrate in its interiors to a certain depth, mainly interacting with the kC component of the scaffold as resulted from the confocal analysis. Mouse embryonic fibroblasts NIH-3T3 were seeded on top of the hydrogels and cultured up to two weeks. The role of Pvfp5β in promoting cell adhesion, spreading and colonization of the scaffold was demonstrated.

Linear and non-linear rheological properties of water-ethanol hybrid pectin gels for aroma enhancement.

Whereas water-ethanol hybrid gels present an opportunity to realize aroma enhancement, translating hypothesis into practice is limited by poorly defined viscoelastic characteristics of those gels. In this work, the linear and non-linear rheological properties of water-ethanol hybrid pectin gels (WEPGs) were studied. Those WEPGs are physical gels in nature and the WEPG of 28.6% v/v ethanol differs basically from those of higher ethanol concentrations in the gel strength, resistance to deformation and non-linear properties. The retention of isopentyl acetate of WEPGs is dramatically improved by increasing the ethanol concentration to 33.3% v/v in the co-solvent system, but it is not further improved at 37.5% v/v. The cluster analysis reveals strong positive correlations between the isopentyl acetate release concentration and v 3/v 1 and absolute value of S/T ratio under 100% strain, suggesting the non-linear rheological responses of WEPGs have to be taken into account for which the enhancement of aroma is desired.

Nanofibrous, hierarchically porous poly(ether sulfone) xerogels templated from gel emulsions for removing organic vapors and particulate matters

Emulsion-templated method is an emerging technology for the fabrication of porous polymers, but the conventionally chemical crosslinking still restricts the popularization. Based on the physical gelation, emulsion-templated porous polymers (polyHIPEs) can be possible to break the bottleneck. This work reports gel emulsions and corresponding xerogels solidified by solvent-induced crystallization of the poly(ether sulfone) for removing organic vapors and particulate matters. Gel emulsions showed wide adaptability in the dispersed phase fraction (from 5% to 80%) and high stability over 5 months without change in appearance. Emulsion-templated xerogels were obtained from gel emulsions by atmospheric drying, which represents a facile method for the preparation of emulsion-templated porous polymers. The resulting xerogels exhibited controllable external shapes, low shrinkages, emulsion-templated voids, nanofibrous structures, hierarchically interconnecting pores, robust mechanical properties and the reshape ability, which are much more advantageous than conventional polyHIPEs. The xerogels exhibited high adsorption capacities to the organic solvent vapors from air (1.21 mL g−1 for toluene and 1.45 mL g−1 for chloroform), high reusability (without deterioration after five adsorption-desorption cycles) and enhanced adsorption rate imposed by emulsion-templated structures. Moreover, the xerogels captured a mass of particulate matters from air with high durability. The wide adaptability, facile preparation, unique morphology and high capacity and stability to capture solvent vapors and particulate matters enable the current xerogels to be excellent candidates for cleaning air.

Emulsion-templated, hydrophilic-oleophobic aerogels with flexibility, stretchability and recyclability

Hydrophilic-oleophobic porous materials, especially those fabricated from one-pot emulsion templating, are promising for removing water from oil-water mixtures, but the relatively dense covalent crosslinking makes the materials rigid and impossible for recycling, which hinders their real applications. Herein, we report the fabrication of hydrophilic-oleophobic aerogels with flexibility, stretchability and recyclability through high internal phase emulsion templating. The aerogels were formed through the interface-initiated condensation of perfluorooctyltriethoxysilane within the dispersed phase and the subsequent solidification of external aqueous phase through poly(vinyl alcohol) gelation. The resulting aerogels exhibited controllable external shapes, good flexibility, robust compression, high stretchability, and in-air hydrophilicity-oleophobicity. These features enabled the aerogels to remove water from not only free oil-water mixtures but also surfactant-stabilized water-in-oil emulsions through selective absorption, and the aerogels also showed good reusability. Since the aerogels were formed through physical gelation, they could be recycled and reshaped by dissolving in hot water, adding oil, and freeze drying. The as-recycled aerogels showed similar properties to that of the parent aerogels.

Chemically cross-linked gel storage for fuel to realize evaporation suppression

High-energy density liquid fuels are commonly used to operate combustors such as rockets, gas turbines, automotive engines, and boilers to make an energy transformation. To prevent a serious incident such as an explosion or a fire disaster, we have recognized practical issues of the liquid fuels that are safety and stability during transportation and storage, evaporation rate, and burning rate constant. In this experiment, ethanol is used as a liquid fuel and is retained on chemically cross-linked poly(N-isopropylacrylamide) (PNIPPAm) gel to use it as a polymeric gel storage for liquid fuels. In general, because the cross-linking structure of chemical gels is formed by covalent bonding, it is more stable than physical gels for a thermodynamic change such as temperature. The evaporation rate of the polymeric gel storage to suppress evaporating the ethanol is investigated. We finally demonstrate to obtain burning rate constants based on a changing mass of the polymeric gel storage during combustion. By demonstrating the polymeric gel storage combustion, we revealed existence of the d2 law in a droplet combustion.

Key connection between gravitational instability in physical gels and granular media

We study gravitationally-driven (Rayleigh–Taylor-like) instability in physical gels as a model for the behavior of granular media falling under gravity; physical gels have a structural elasticity and may be fluidized, capturing both the solid and liquid properties of granular systems. Though ubiquitous in both industrial and natural contexts, the unique static and dynamic properties of granular media remain poorly understood. Under the action of a gravitational force, granular materials may flow while exhibiting heterogeneous rigidity, as seen during e.g., avalanches or landslides. Though the onset of this gravitational “instability” has been addressed, the mechanism behind its incidence is not yet understood. We find key quantitative similarities between Rayleigh–Taylor-like instability in physical gels and granular systems. In particular, we identify a common scaling law, showing that the instability is chiefly governed by the thickness of the flowable region.

Intelligent Paper-Free Sprayable Skin Mask Based on an In Situ Formed Janus Hydrogel of an Environmentally Friendly Polymer.

Traditional skin care masks usually use a piece of paper to hold the aqueous essences, which are not environmentally friendly and not easy to use. While a paper-free mask is desired, it is faced with a dilemma of moisture holding and rapid release of encapsulated bioactive substances. Herein, a paper-free sprayable skin mask is designed from an intelligent material-a thermogel which undergoes sol-gel-suspension transitions upon heating-to solve this dilemma. A synthesized block copolymer of poly(ethylene glycol) and poly(lactide-co-glycolide) with appropriate ratios can be dissolved in water, and thus easily mixed with a biological substance. The mixture is sprayable. After spraying, a Janus film is formed in situ with a physical gel on the outside and a suspension on the inside facing skin. Thus, both moisture holding and rapid release are achieved. Such a thermogel composed of biodegradable amphiphilic block copolymers loaded with nicotinamide as a skin mask is verified to reduce pigmentation on a 3D pigmented reconstructed epidermis model and further in a clinical study. This work might be stimulating for investigations and applications of biodegradable and intelligent soft matter in the fields of drug delivery and regenerative medicine.

Features of PABIGnx 3D Polymer Gel as an Ionising Radiation Dosimeter.

This work presents the features of the PABIGnx 3D polymer gel dosimeter. It consists of two cross-linkers: poly(ethylene glycol) diacrylate (PEGDA), as one biacrylic component, and N,N′-methylenebisacrylamide (MBA), which is another cross-linker often used in 3D dosimeters. Additionally, it contains oxygen scavenges of copper sulfate pentahydrate and ascorbic acid. All ingredients are embedded in a physical gel matrix of gelatine. Upon irradiation, the biacrylic cross-linking agents (PEGDA and MBA) undergo radical polymerisation and cross-linking, which is manifested by the appearance of the opacity of the intensity related to the absorbed dose. PABIGnx was irradiated with an oncological source of ionising radiation, and analysed by using a nuclear magnetic resonance (0.5 T). The following characteristics were obtained: (i) linear and dynamic dose-response of 0.5 to ~18 Gy and 40 Gy, respectively, (ii) dose sensitivity of 0.071 ± 0.001 Gy−1 s−1, (iii) integral 3D dose distribution for at least 24 days after irradiation, (iv) adequate batch-to-batch reproducibility, (v) dose-response independent of irradiation with 6 MV photons, 15 MV photons, 6 MV photons FFF of 0.0168–0.1094 Gy/s dose rates, and (vi) soft tissue equivalence. The study showed that the features of PABIGnx confirm its suitability for use in 3D radiotherapy dosimetry.

Discolouring 3D Gel Dosimeter for UV Dose Distribution Measurements.

This work reports on a new TBO–Pluronic F–127 three-dimensional (3D) gel dosimeter for UV light dose distribution measurements. The optimal gel composition was found to be 60 µM Toluidine Blue O (TBO), which acts as a UV-sensitive compound; 5% w/w hydrogen peroxide (H2O2), which is necessary for initiation of TBO photodegradation and 25% w/w poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (Pluronic F–127), which forms a physical gel matrix. The dosimeter becomes discoloured when exposed to UV radiation and a discolouration is the more intense, the higher the absorbed dose is. The samples after irradiation with UVA, UVB and UVC radiation were measured using UV-Vis spectrophotometry to obtain the basic dose–response characteristic of the dosimeter, including dose sensitivity, linear and dynamic dose range, threshold dose, stability over time and dose–response for fractioned and non-fractioned doses. Additionally, the TBO–Pluronic F–127 gel dosimeter was investigated for spatial stability and the ability to measure the dose distribution of UV radiation. The results obtained indicate that the TBO–Pluronic F–127 dosimeter is a promising UV sensor and 2D/3D UV dosimeter.

Ionic Conductivity Enhancement in UHMW PEO Gel Electrolytes Based on Room-Temperature Ionic Liquids and Deep Eutectic Solvents.

Physical gels made of poly(ethylene oxide) (PEO) and deep eutectic solvents urea-Li bis(trifluoromethanesulfonyl)imide (TFSI) and ethylene glycol/LiTFSI, or pyrrolidinium ionic liquid solutions PYR13TFSI-LiTFSI and PYR14TFSI-LiTFSI, are prepared by a fast, single-step process, which involves no auxiliary solvents or intermediates and is reproducible and scalable. The properties of these gels are studied as a function of the PEO content and its molecular weight and the nature of the liquid electrolyte. The gels prepared with a low concentration (1–5 wt %) of ultrahigh molecular weight (UHMW) PEO are tough, stretchable materials which resemble soft elastomers and are also self-healing and transparent. Their rheology shows the conventional behavior of physical polymer gels, so that the higher the molecular weight of PEO, the lower the polymer concentration needed to produce the gel. However, the ion conductivities and diffusivities of the gels are striking, in many cases being equal to or significantly higher than those of pure liquid electrolytes. This ion conductivity enhancement is the highest for the lowest PEO concentration with the highest molecular weight. This unprecedented molecular weight dependence of conductivity and diffusivity is the result of two combined effects: the liquid electrolyte chemical structure modification as a consequence of the addition of PEO and the development of elastic networks, where ion mobility and rheology are uncoupled when the PEO added is of UHMW.

Polydopamine-Coated Poly-Lactic Acid Aerogels as Scaffolds for Tissue Engineering Applications.

Poly-L-lactic acid (PLLA) aerogel-based scaffolds were obtained from physical PLLA gels containing cyclopentanone (CPO) or methyl benzoate (BzOMe) molecules. An innovative single step method of solvent extraction, using supercritical CO2, was used to achieve cylindrical monolithic aerogels. The pore distribution and size, analyzed by SEM microscopy, were found to be related to the crystalline forms present in the physical nodes that hold the gels together, the stable α’-form and the metastable co-crystalline ε-form, detected in the PLLA/BzOMe and PLLA/CPO aerogels, respectively. A higher mechanical compressive strength was found for the PLLA/CPO aerogels, which exhibit a more homogenous porosity. In vitro biocompatibility tests also indicated that monolithic PLLA/CPO aerogels exhibited greater cell viability than PLLA/BzOMe aerogels. An improved biocompatibility of PLLA/CPO monolithic aerogels was finally observed by coating the surface of the aerogels with polydopamine (PDA) obtained by the in situ polymerization of dopamine (DA). The synergistic effect of biodegradable polyester (PLLA) and the biomimetic interface (PDA) makes this new 3D porous scaffold, with porosity and mechanical properties that are tunable based on the solvent used in the preparation process, attractive for tissue engineering applications.

Study of NBT-Pluronic F-127 Gels as 1D UV Radiation Dosimeters for Measurement of Artificial Light Sources.

This work reports on radiochromic dosimeters for 1D UV light measurements. The dosimeter is composed of a 25% Pluronic F–127 that forms a physical gel matrix and nitro blue tetrazolium chloride (NBT) as a radiation-sensitive compound. This dosimeter was exposed to UVA, UVB and UVC radiation, and the radiochromic reactions were followed with reflectance spectrophotometry including changes in light reflectance and color coordinates in the CIELAB color system. The exposition of dosimeters to all UV radiation caused color changes from pale yellow to dark violet, and its intensity increased with increasing absorbed dose. The effects of NBT concentration and UV radiation type on the dose–response of the dosimeters were also examined. The results obtained reveal that the dosimeters are the least sensitive to irradiation with UVC and the most sensitive to irradiation with UVB (e.g., dosimeter with 2 g/dm3 of NBT was characterized by the following parameters: the threshold dose 0.1 J/cm2; the dose sensitivity −5.97 ± 0.69 cm2/J; the linear dose range 0.1–2.5 J/cm2; the dynamic dose range was equal to 0.1–3 J/cm2). The results obtained reveal that the NBT–Pluronic F–127 dosimeters can be potentially useful as 1D sensors for artificial UV radiation sources measurements.

Nanoporous-Crystalline Poly(2,6-dimethyl-1,4-phenylene)oxide Aerogels with Selectively Sulfonated Amorphous Phase for Fast VOC Sorption from Water.

This paper describes the preparation and characterization of poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) highly porous monolithic aerogels with a hydrophobic nanoporous–crystalline phase and a hydrophilic sulfonated amorphous phase. The sulfonated aerogels were obtained by the sulfonation of PPO physical gels, followed by the supercritical CO2 extraction of solvents. WAXD and FTIR analysis showed that the nanoporous–crystalline phase was preserved for a degree of sulfonation up to c.a. 35%, allowing a highly volatile organic compound (VOC) sorption capacity. The sulfonated PPO aerogels exhibited a high water sorption capacity, with a water uptake of up to 500 wt%, and faster VOC sorption kinetics from water with respect to unsulfonated aerogels.

Morphology and mechanical property of quenched poly(L-lactide)/N,N-dimethylacetamide gels

Mechanically tough poly(L-lactide) (PLLA)/N,N-dimethylacetamide (DMAc) gels by rapid quenching using liquid nitrogen (LN) were synthesized. PLLA/DMAc solution at 110 °C was cooled at room temperature (PLLA-RT), or quenched by LN before keeping at RT (PLLA-LN). PLLA-RT with the PLLA concentrations of 5, 8, and 11 wt% did not form gel, while PLLA-RT with 14 and 17 wt% could form brittle gel exhibiting coarse structures. In contrast, PLLA-LN could form stable gel regardless of the PLLA concentration. The storage modulus of the gel with the PLLA concentration of 17 wt% increased from 78.7 kPa (PLLA-RT) to 563.7 kPa (PLLA-LN) at the strain of 0.1%. From the structural analysis, PLLA-RT formed spherulites (100–200 μm in diameter), whereas PLLA-LN formed relatively uniform network structures with continuous microporous skeletons without spherulites. The structural changes significantly contributed to the formation of stable, re-moldable, biodegradable, and biocompatible physical gels with ecofriendly and enhanced mechanical properties.

Interfacial Charge Transfer Complexes in TiO2-Enediol Hybrids Synthesized by Sol-Gel.

Metal oxide-organic hybrid semiconductors exhibit specific properties depending not only on their composition but also on the synthesis procedure, and particularly on the functionalization method, determining the interaction between the two components. Surface adsorption is the most common way to prepare organic-modified metal oxides. Here a simple sol–gel route is described as an alternative, finely controlled strategy to synthesize titanium oxide-based materials containing organic molecules coordinated to the metal. The effect of the molecular structure of the ligands on the surface properties of the hybrids is studied using three enediols able to form charge transfer complexes: catechol, dopamine, and ascorbic acid. For each system, the process conditions driving the transition from the sol to chemical, physical, or particulate gels are explored. The structural, optical, and photoelectrochemical characterization of the amorphous hybrid materials shows analogies and differences related to the organic component. In particular, electron paramagnetic resonance (EPR) spectroscopy at room temperature reveals the presence of organic radical species with different evolution and stability, and photocurrent measurements prove the effective photosensitization of TiO2 in the visible range induced by interfacial ligand-to-metal charge transfer.

Preparation of chemical-physical hybrid crosslinking double network gel composite incorporated SBS modified asphalt

ABSTRACT The chemical–physical hybrid cross-linked double network gel poly (acrylamide-co-acrylic acid)/Sodium alginate/Fe3+ (P(AM-co-AA)/SA/Fe3+, simplified as P-gel) was synthesised by free radical polymerisation combined with hydrogen bonding and ion coordination, which was in turn compounded with styrene–butadiene-styrene (SBS) to prepare P-gel gel/SBS modified asphalt. FT-IR, UV, XRD and SEM analyses confirmed the successful synthesis of P-gel. FM analysis revealed that the volume of P-gel increased after the long-term aging of asphalt. The physical, Dynamic Shear Rheometer (DSR), multi-stress creep recovery (MSCR), and time sweep tests showed that the addition of P-gel improved the road performance of the SBS modified asphalt. At a P-gel amount of 5%, the high-temperature performance grade (PG high temperature) of SBS modified asphalt improved from PG70 to PG76 and the recovery rate (64 oC) was increased by 17.08% and 41.13% at the stress of 0.1 and 3.2 kPa, respectively. The underlying mechanism behind these improvements in the mechanical properties of the composite modified asphalt was the different competitive relationship between the ‘softening’ effect of P-gel in asphalt and the ‘strengthening’ effect of the asphalt itself at different temperatures. This project provides an alternative strategy for preparing P-gel gel/SBS modified asphalt with enhanced mechanical properties for applications in the highway and construction industries.

A Review on Synthesis Methods of Phyllosilicate- and Graphene-Filled Composite Hydrogels

This review discusses, in brief, the various synthetic methods of two widely-used nanofillers; phyllosilicate and graphene. Both are 2D fillers introduced into hydrogel matrices to achieve mechanical robustness and water uptake behavior. Both the fillers are inserted by physical and chemical gelation methods where most of the chemical gelation, i.e., covalent approaches, results in better physical properties compared to their physical gels. Physical gels occur due to supramolecular assembly, van der Waals interactions, electrostatic interactions, hydrophobic associations, and H-bonding. For chemical gelation, in situ radical triggered gelation mostly occurs.

The preparation and properties of circularly polarized luminescent liquid crystal physical gels with self-supporting performance.

In recent years, great progress has been made in the preparation methods and performance regulation of host-guest doped CPL liquid crystal materials. However, there still exist some basic problems to be solved, such as complex packaging and unstable CPL properties. With the consideration of the above problems, in this study, we introduced gelators into the host-guest doped CPL liquid crystal materials to prepare CPL liquid crystal physical gels. The gelators can be assembled to form a nanofiber physical gel network, which limits the movement of the liquid crystals and enhances the stability of the CPL properties. Meanwhile, liquid crystal physical gels show self-supporting ability and the gel-sol phase transition temperature can reach 136 °C. The amplification of the glum value is achieved by self-assembly of chiral liquid crystals, and the glum value can reach -0.31. The phase structure changes with electric field and temperature, and the CPL properties can be regulated by changing the temperature and electric field. With the increasing applied voltage or the temperature, the glum value decreases. Therefore, we have successfully prepared a new type of CPL liquid crystal physical gels with self-supporting performance, stimulus response performance and large glum values.