Biopolymer solutions preparation

A stock biopolymer solution containing 4,000 ppm biopolymer was prepared for each biopolymer following the procedure recommended by Pfizer Inc. [30]. All solutions were adjusted such that they contained about 5 g/L formaldehyde to inhibit bacterial degradation. The 4,000 ppm stock solutions were filtered using a Whatman number 1 filter paper and were stored in closed polyethylene containers to minimize oxygen uptake. 

W/W A number of researchers have prepared a new type of multiple emulsion termed OfWfW, based on the thermodynamic incompatibility of mixed biopolymer solutions. For example, oil-in-water-in-water (O/W/W) emulsions can be prepared by mixing an OAV emulsion with a W/W emulsion. 

Fig. 3.7 Schematic drawings demonstrating the main features of two-stage (A) and one-stage (B) procedures leading to a difference in the morphology of the fabricated materials. (A) Sol nanoparticles initially prepared in the first stage (1, see also Figure 3.3) can self-assemble into a three-dimensional network when they are in direct contact with each other. Forthis reason, a gel formed after cross-linking (sol-gel transition) has a smaller volume (2). (B) The initial stage (1) is represented by a solution of entangled biopolymer macromolecules. The...

Constmction of phase diagrams usually starts with the preparation of series of mixed solutions sufficiently differing in bulk biopolymer concentration. Some of them can be single-phase solutions, others biphasic systems. A true equilibrium between the phases is experimentally obtained by mixing or shaking the water-in-water emulsions under different time-temperature conditions. Separation of the phases by centrifuge provides information about both the number and the volume ratio of the system phases. The closer a system composition is to the critical point, the smaller the difference in density is between the phases and the more difficult their separation is by centrifugation. The amount of each biopolymer in each phase can be quantified by various techniques. Estimation of protein concentration by UV absorbance at 280 nm is widely used because of its simplicity and sensitivity. 

Multiwalled carbon nanotubes were solubilized in an aqueous solution of the biopolymer chitosan (CHIT) [56]. A 0.50 w/v % CHIT stock solution was prepared by dissolving ehitosan flakes in hot (80-90 °C) aqueous 0.05 M HCl. The solution was eooled at room temperature, and its pH adjusted to 3.5-5.0 using a concentrated NaOH solution. CNTs were solubilized in CHIT solutions (0.50-3.00 mg of CNT mL ) by ultrasonic agitation for 15 minutes. An aliquot of 30 pL of the eolloidal solution of CNT-CHIT was plaeed on the surface of GCE and dried for 2 hours at room temperature. 

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