Probing Gelation and Rheological Behavior of a Self-Assembled Molecular Gel

Molecular gels have been investigated over the last few decades; however, mechanical behavior of these self-assembled gels is not well understood, particularly how these materials fail at large strain. Here, we report the gelation and rheological behavior of a molecular gel formed by self-assembly of a low molecular weight gelator (LMWG), di-Fmoc-l-lysine, in 1-propanol/water mixture. Gels were prepared by solvent-triggered technique, and gelation was tracked using Fourier transform infrared (FTIR) spectroscopy and shear rheology. FTIR spectroscopy captures the formation of hydrogen bonding between the gelator molecules, and the change in IR spectra during the gelation process correlates with the gelation kinetics results captured by rheology. Self-assembly of gelator molecules leads to a fiber-like structure, and these long fibers topologically interact to form a gel-like material. Stretched-exponential function can capture the stress-relaxation data. Stress-relaxation time for these gels have been found to be long owing to long fiber dimensions, and the stretching exponent value of 1/3 indicates polydispersity in fiber dimensions. Cavitation rheology captures fracture-like behavior of these gels, and critical energy release rate has been estimated to be of the order 0.1 J/m². Our results provide new understanding of the rheological behavior of molecular gels and their structural origin

Molecular Insights into Gelation of Di-Fmoc‑l‑Lysine in Organic Solvent–Water Mixtures

Despite significant interest in molecular gels due to their intriguing structure formation through self-assembly and their stimuli-responsive behavior, our understanding of the gel formation mechanism of a low-molecular-weight gelator (LMWG) is incomplete. Here, we report a combined experimental and computational study on a LMWG, di-Fmoc-l-lysine, that has two aromatic moieties and multiple hydrogen bond donors and acceptors. Gelation in various organic solvent–water mixtures was obtained through the solvent-triggered technique. We show that an approach based on approximate cohesive energy density derived from density functional theory (DFT) calculations can capture the experimental solubility trend of LMWGs in different organic solvents. Furthermore, DFT calculations indicate parallel and helical structures to be the preferred structural motifs for gelator dimers. We believe that these motifs can potentially lead to fiber formation as observed with microscopy. Our work provides a relatively simple yet effective approach to quantify interactions between solvents and complex gelators that can help rationalize solubility and gelation behavior

Thermoresponsive nanoemulsion-based gel synthesized through a low-energy process

© 2019, The Author(s). Thermoresponsive nanoemulsions find utility in applications ranging from food to pharmaceuticals to consumer products. Prior systems have found limited translation to applications due to cytotoxicity of the compositions and/or difficulties in scaling-up the process. Here, we report a route to thermally gel an oil-in-water nanoemulsion using a small amount of FDA-approved amphiphilic triblock Pluronic copolymers which act as gelling agents. At ambient temperature the suspension displays liquid-like behavior, and quickly becomes an elastic gel at elevated temperatures. We propose a gelation mechanism triggered by synergistic action of thermally-induced adsorption of Pluronic copolymers onto the droplet interface and an increased micelle concentration in the aqueous solution. We demonstrate that the system’s properties can be tuned via many factors and report their rheological properties. The nanoemulsions are prepared using a low-energy process which offers an efficient route to scale-up. The nanoemulsion formulations are well-suited for use in cosmetics and pharmaceutical applications

Achieving High-Speed Retraction in a Stretchable Hydrogel

Many biological species apply the power amplification mechanism for locomotion, feeding, and protection. In power amplification, a biological system rapidly releases stored-energy by achieving a very high velocity over a short period of time, resulting in high power output. Such power amplification allows insects such as locust to jump and Mantis shrimp to kill prey by its appendage strike. Biological elastomeric polymers such as resilin play a vital role in the power amplification process because of their high stretchability and resilience. In synthetic materials, althoughcrosslinked rubbers display high stretchability and resilience, such is difficult to achieve in the water-containing systems such as in hydrogels, commonly considered materials for mimicking biological tissues. Here, we have used a simple free-radical polymerization of acrylic acid (AAc), methacrylamide (MAAm), and polypropylene glycol diacrylate (PPGDA) to obtain hydrogels. In these gels, the polymerized AAc and MAAm act as hydrophilic blocks and PPG as hydrophobic, and the gel structure resemble that of resilin consisting of hydrophilic and hydrophobic components. The bioinspired gels display very high stretchability, as high as eight times the original length, and greater than 90% resilience. In addition, the gel samples can reach a retraction velocity of 16 m/s with an acceleration of 4X10^3 m/s2. These values are similar or better than those observed in water containing biological systems, such as appendage strikes in Mantis shrimp, etc. To the best of our knowledge, such performance has not been reported in theliterature for any water containing networks

Development of an Ointment Formulation Using Hot-Melt Extrusion Technology

La radiación solar directa requiere la mediación del diseño para su uso como fuente de iluminación en condiciones de confort interior. En nuestro medio, en muy pocos, los diseños de control o filtro solar surgen del análisis de la geometría solar y clima luminoso local. El presente trabajo analiza el comportamiento de un caso de estudio de aulas, el cual posee ventanas y protecciones solares exteriores pero ineficientes para iluminación natural. Se proponen elementos para la redirección de la luz solar y se verifica su eficiencia para iluminar el aula con luz natural. Se comprobaron mediante simulación niveles mayores a 300 lux promedios y la ausencia de deslumbramiento por luz solar.Direct solar radiation requires the mediation of design to be used as a light source mainly to achieve associated indoor thermal comfort conditions. In our region, only few cases of solar control devices or sunshade for windows, are the result of solar geometry and local light climate analysis accompanying the design process. This paper shows a Classroom case study, whose windows and solar control devices are inefficient for natural lighting. Redesign of elements for redirecting sunlight were proposed, and their benefits and efficiency were verified, improving natural light in the classroom. Levels verified by simulation show averages above 300 lux and the lack of glare.Asociación Argentina de Energías Renovables y Medio Ambiente (ASADES