Dynamics in Dialysis Process for Liquid Crystalline Gel Formation

Abstract

The processes of gelation and liquid crystalline formation in the dialysis of Curdlan solution have been observed under crossed nicols, and the calcium concentration and pH of the inner solution were traced. The results showed that the gelation and the liquid crystalline formation occurred simultaneously to form liquid crystalline gel (LCG), but the birefringence of the LCG increased even after the gelation, suggesting further ordering of the Curdlan molecules. On the basis of the calcium ion diffusion, a simple theory for the time development of the thickness of the LCG layer was developed. The experimental and theoretical results agree very well until an amorphous gel (AG) ring appears. The whole process was expressed by a master curve by reducing time and distance data for different radius dialysis tubes by those at the final state; a scaling behavior with respect to the dialysis tube radius was found. The experimental analysis for the calcium concentrations and the pH indicates that forming Curdlan LCG with high ordering of Curdlan molecules consists of two steps: the diffusion of calcium ions inducing the ordering of Curdlan molecules and yielding cross-links simultaneously, and the local relaxation of the Curdlan molecules increasing the ordering degree further.

Hydrogels with a macroscopic-scale liquid crystal structure by self-assembly of a semi-rigid polyion complex

“…The PBDT alignment in region I of the gel is further confirmed by small angle X-ray scattering measurements. 45 Our results show that the PBDT molecules align perpendicularly to the Ca 2 þ diffusion direction, which is opposite to the pattern reported for DNA and curdlan systems by Dobashi et al [51][52][53][54] However, we have noticed that their previous conclusion about the molecular orientation was not correct, and they have revised their conclusion in a recently published paper. 55 To track the diffusion-gelation process, we performed in situ observation of the entire gelation process under POM at different dialysis times (Figure 3a).…”

“…They have claimed that the biomacromolecules orient along the cationic ions diffusion paths to form a radial structure. [52][53][54] We have found that PBDT, which has properties similar to those of biomacromolecules, is also capable of forming macroscopic anisotropic physical gels via a dialysis process. 40,45 In this process, a 1 wt% solution of PBDT with a Mw of 2.1 Â 10 6 g mol À1 and a C LC * of 2 was poured into a mold that consists of a pair of parallel glass plates separated by a 1-mm thick silicone spacer (Figure 2a).…”

“…Reaction and diffusion compete with each other during this process, which forms intricate spatial or temporal structures. 51 Dobashi et al [52][53][54][55] have developed a method to synthesize physical LC hydrogels in a semi-permeable tube by dialyzing aqueous solutions of DNA or curdlan in a multivalent cation solution. The cationic ion diffusion induces molecular orientation and physical gelation of the semi-rigid biomacromolecules to form hydrogels with centimeter-scale anisotropic structures.…”

Hydrogels with self-assembling ordered structures and their functions

“…Regenerated cellulose hydrogel membranes are also strong enough to be used for dialysis in water. Dobashi and coworkers [25][26][27][28] successfully developed a facile dialysis method for fabricating physical biopolymer hydrogels with macroscopic ordered structures. Th ey immersed an aqueous solution of DNA or curdlan inside a semipermeable t ube in a multivalent cation solution, such as Ca 2+ and Co…”

Theoretical analysis for dialysis-induced chitosan gelation

“…The experimental data for the gel growth process induced by dialysis are analyzed by a theory based on the following assumptions [4]. (a) All hydroxide anions flowing into the inner chitosan solution are used up to neutralize the solution.…”