Effect of Evaporation Rate on Meniscus Splitting with Formation of Vertical Polysaccharide Membranes

Abstract

method for performing macrospace partitioning. [19][20][21][22] The polymers deposit to bridge a millimeter-scale gap between two substrates and a membrane grows downward from the air-liquid interface. During the drying of viscous solutions, the poly mer condenses and integrates itself at the air-liquid interface, oriented by capillary force. This induces suppression of water evaporation and meniscus splitting or macrospace partitioning in a limited space. Comparing with a single meniscus curve, the split multiple meniscus curves have an advantage for compatibility between evaporation and polymer deposition on larger area of air-liquid interface to form a dried polysaccharide membrane in vertical. [6,19] Rather than observing fingering patterns, as is typical, we successfully immobilized the fluid pattern to a solid pattern and obtained multiple membranes with highly oriented polysaccharide microfibers. In addition, by introducing a crosslinker into the membrane, uniaxially swellable hydrogels were formed, which is expected for anisotropic DDSs. [21] We have used several kinds of liquid crystalline (LC) polysaccharides with molecular weights of >10 6 g mol −1 , such as sacran and xanthan gum. [23] Using these polymers, we have clarified the effects of main factors such as initial polymer concentration, temperature, and the dimensions of the cell where the viscous liquids are filled.In this study, the meniscus splitting was simply regulated by the rate of water evaporation from an LC polysaccharide solution. In principle, the evaporation rate is controlled not by the temperature but by the relative humidity around the air-liquid interface. The depth of the air-LC interface in a container having a 1 mm gap should strongly affect the local humidity at a constant temperature. Using this relationship, the evaporation rate can be controlled without the temperature affecting the polymeric behavior in the liquid. To clarify the necessary conditions for meniscus splitting and bridging the millimeterscale gap, the polymer adsorption on the substrates was studied as well. Focusing on the orientation of the adsorbed polymer, the ordered deposition process is discussed.A viscous solution of xanthan gum was poured into a topside-open cell (X-width, Y-thickness, Z-depth) = (20, 1, 50 mm) at ≈25 °C. The 1 wt% aqueous solution has an extremely high viscosity of ≈0.3 Pa s at 25 °C and ≈0.7 Pa s at 60 °C. [22] The sample was placed under atmospheric pressure in an oven with an air circulator and the relative humidity was constant at Evaporative self-assembly of polymeric colloids is among the most attractive strategies for the preparation of soft materials with submicrometer-scale ordered structures. In this study, meniscus splitting from an aqueous solution of liquid crystalline (LC) polysaccharide xanthan gum is verified under conditions of controlled evaporative rate in a limited space. Under fast evaporation rate with a steep gradient of humidity above the air-LC interface, the meniscus splitting is induced to bridge the gap an...

Convective meniscus splitting of polysaccharide microparticles on various surfaces

“…The viscous solution of XG was poured into a one-side-open cell of 15 mm × 1 mm × ~ 20 mm at ~ 25 °C. The 1.5-wt% aqueous solution has extremely high viscosity (~ 0.4 Pa s at 25 °C and ~ 0.6 Pa s at 40 °C at shear rate 10 s −1 ) 22 . The sample was placed under atmospheric pressure in an oven with an air circulator and the humidity was maintained at 24 ± 5% relative humidity (RH) at 40 °C as measured by a hygrometer.…”

“…Drying experiments. The drying condition for the aqueous solution was set according to our previous works 22 . After the XG was dissolved in pure water, the aqueous solutions were used within a few days.…”

“…In this study, meniscus splitting is examined by controlling the direction of the gravitational force and the substrate surface wettability. In our previous reports 11 , 19 – 22 , the demonstrated conditions for the meniscus splitting 11 were limited: the water evaporation direction was parallel to the direction of the gravitational forces, and the space was sandwiched in between the non-modified smooth surface of glass substrate. However, for the development of the splitting method, it is important to clarify and expand the possibility of the conditions.…”

“…This technique appears applicable to various types of viscous polymer solutions, among which liquid crystalline (LC) polysaccharides were chosen to orient the self-assembled structures on the evaporative interface 19 . The technique has been demonstrated using several LC polysaccharides having megamolecular weights, such as sacran (> 10 7 g/mol) and xanthan gum (XG; > 10 6 g/mol) 20 – 22 . XG can self-assemble as ~ 1-µm-diameter microparticles dispersed stably in an aqueous solution.…”

“…the development of the splitting method, it is important to clarify and expand the possibility of the conditions. Differing from previous reports 11,[19][20][21][22] , the phenomena is demonstrated under various effects from outer environments such as the gravitational forces and the substrate surface wettability to develop the phenomena into a fixed method. Actually, meniscus splitting occurs under many conditions, i.e., it is ultimately independent of gravitational forces and substrate wettability; therefore, ordered membranes can be designed under various conditions.…”