A fluorous sodium l-prolinate derivative as low molecular weight gelator for perfluorocarbons.

We report the first study dealing with the self-assembly of an α-amino acid derivative in perfluorocarbons. Rheology, microscopy, and spectroscopy studies reveal that the fluorous sodium l-prolinate derivative 1 self-assembles in perfluorocarbons to form a three-dimensional network of left-handed nano-helices resulting in solvent gelation. Singlet oxygen lifetime measured in a gel of perfluorodecalin is about 1000 times longer than in pure water.

Impact of saccharides on the drying kinetics of agarose gels measured by in-situ interferometry.

Agarose gels are viscoelastic soft solids that display a porous microstructure filled with water at 90% w/w or more. Despite an extensive use in food industry and microbiology, little is known about the drying kinetics of such squishy solids, which suffers from a lack of time-resolved local measurements. Moreover, only scattered empirical observations are available on the role of the gel composition on the drying kinetics. Here we study by in-situ interferometry the drying of agarose gels of various compositions cast in Petri dishes. The gel thinning is associated with the displacement of interference fringes that are analyzed using an efficient spatiotemporal filtering method, which allows us to assess local thinning rates as low as 10 nm/s with high accuracy. The gel thinning rate measured at the center of the dish appears as a robust observable to quantify the role of additives on the gel drying kinetics and compare the drying speed of agarose gels loaded with various non-gelling saccharides of increasing molecular weights. Our work shows that saccharides systematically decrease the agarose gel thinning rate up to a factor two, and exemplifies interferometry as a powerful tool to quantify the impact of additives on the drying kinetics of polymer gels.

Syneresis and delayed detachment in agar plates.

Biogels made of crosslinked polymers such as proteins or polysaccharides behave as porous soft solids and store large amounts of solvent. These gels undergo spontaneous aging, called syneresis, which consists of the shrinkage of the gel matrix and the progressive expulsion of solvent. As a result, a biogel originally casted in a container often loses contact with the container sidewalls, and the detachment time is difficult to anticipate a priori, since it may occur over variable time spans (from hours to days). Here we report on syneresis phenomena in agar plates, which consist of Petri dishes filled with a gel mainly composed of agar. Direct observations and speckle pattern correlation analysis allow us to rationalize the delayed detachment of the gel from the sidewall of the Petri dish. The detachment time t* is surprisingly not controlled by the mass loss as one would intuitively expect. Instead, t* is strongly correlated to the gel minimum thickness emin measured along the sidewall of the plate, and increases as a robust function of emin, independently of the prior mass-loss history. Time-resolved correlation spectroscopy atypically applied to such weakly diffusive media gives access to the local thinning rate of the gel. This technique also allows us to detect the gel micro-displacements that are triggered by water evaporation prior to the detachment, and even to anticipate the latter from a few hours. Our work provides observables to predict the detachment time of agar gels in dishes, and highlights the relevance of speckle pattern correlation analysis for the quantitative investigation of the syneresis dynamics in biopolymer gels.