On the halt of spontaneous capillary flows in diverging open channels.

Due to their compactness and independence of exterior energy sources, capillary microsystems are increasingly used in many different scientific domains, from biotechnology to medicine and biology, chemistry, energy and space. Obtaining a capillary flow depends on channel geometry and contact angle. A general condition for the establishment of a spontaneous capillary flow in a uniform cross section channel has already been derived from Gibbs free energy. In this work, we consider spontaneous capillary flows (SCF) in diverging open rectangular channels and suspended channels, and we show that they do not flow indefinitely but stop at some location in the channel. In the case of linearly diverging open channels, we derive the expression that determines the location where the flow stops. The theoretical approach is verified by using the Surface Evolver numerical program and is checked by experiments. The approach is extended to sudden enlargements, and it is shown that the enlargements can act as stop and trigger valves.

Effect of different carboxylic acids in cyclodextrin functionalization of cellulose nanocrystals for prolonged release of carvacrol.

Current investigations deal with new surface functionalization strategy of nanocrystalline cellulose-based substrates to impart active molecule release properties. In this study, cellulose nanocrystals (CNC) were surface-functionalized with ß-cyclodextrin (ß-CD) using succinic acid (SA) and fumaric acid (FA) as bridging agents. The main objective of this surface modification performed only in aqueous media was to obtain new active materials able to release antibacterial molecules over a prolonged period of time. The reactions were conducted by immersing the CNC film into a solution composed of ß-CD, SA and FA, leading to CNC grafting. The materials were characterized by infrared spectroscopy (FT-IR), Quartz crystal microbalance-dissipation (QCM-D), AFM and phenolphthalein (PhP) was used to determine the efficiency of CNC grafting with ß-CD. The results indicated that ß-CD was successfully attached to the CNC backbone through the formation of ester bonds. Furthermore, carvacrol was entrapped by the attached ß-CD and a prolonged release was confirmed. In particular, CNC grafted to ß-CD in the presence of FA was selected as the best solution. The antibacterial activity and the controlled release were studied for this sample. Considerably longer bacterial activity against B. subtilis was observed for CNC grafted to ß-CD compared to CNC and CNC-FA, confirming the promising impact of the present strategy.