AFM observations of dimensional changes in individual cellulose aggregate fibrils under variable humidity environments

An algorithm was developed to rapidly analyze the height, width, and area of line scan data of step-shaped disconitunities acquired from atomic force microscope images. The effect of a number of AFM parameters (scan rate, dampening, and tip shape) on the quantitiative imaging of step features was discussed. The AFM scan rate and dampening were found to significantly affect the measured dimensions of step discontinunities. A geometric convolution of the step and the tip was shown to introduce an artifact in the images. Quantitiative imaging using AFM was shown to be very reporducible as five successive scans of a standard step height grating produced less than 3% variation in all measured parameters. A cellulose aggregate fibril (CAF) was also scanned under varying relative humdity conditions. Changes in the width of the CAF were weakly correlated with changes in the relative humdity, while changes in the height and area of the CAF were positively correlated with the relative humdity. The length of the CAF was found to be negatively correlated with the relative humdity, such that as the relative humidity increases the CAF becomes shorter. This finding has significant implications in paper dimensional stability and the application of cellulose micro and nano-fiber composites.