Van der Waals interactions and microstructural changes in cellulose microfibrils dispersions

Abstract

Acetobacter xylinum bacteria can use as much as half the energy available to them spinning cellulose fibrils to create a biofilm. The material produced by these bacteria can be deagglomerized, after which the cellulose microfibrils are a good case study of semiflexible fiberlike colloidal particles, which have attracting interactions. The microfibrils were studied in mixtures of water and glycerol. By measuring the turbidity of microfibril suspensions, the dispersion relation for cellulose was determined, and found to match literature values reasonably well. The van der Waals free energy was calculated for parallel fibrils in mixtures of glycerol and water. The difference in aggregation caused by the stronger interaction in water and the weaker interaction in glycerol was studied. By means of transmission spectroscopy and confocal microscopy, microstructural changes due to van der Waals forces were studied. An increase in the turbidity of the samples was measured and attributed to aggregation of microfibrils. In images taken with a confocal microscope, a change of homogeneity of the network of fibrils was observed, when left untouched for several weeks. It was concluded it is likely the microfibrils were in fact aggregating due to van der Waals interactions over a period of several weeks.