Supti Sadhukhan

Crack patterns in desiccating clay–polymer mixtures with varying composition

Crack patterns in desiccating clay suspensions are drastically altered by the addition of polymers. In this paper we report a systematic study of the effect of varying the composition of a clay-polymer composite on the formation of crack patterns. Experiments as well as computer simulations have been done. Details of the morphology and fractal dimension of the experimental patterns are observed and the simulation is done on a two-dimensional spring network model. We find a transition from a completely fragmented fractal pattern at high clay content to a continuous film at about 50% clay content. The results of the simulation are in good qualitative agreement with the experiments. The study is expected to be of importance for clay-polymer composites. These can be designed to give improved mechanical and electrical properties for practical applications.

Desiccation cracks on different substrates: simulation by a spring network model

Crack patterns formed due to desiccation of clay or similar materials show distinctive reproducible patterns. If one measures the cumulative area Acum covered by the cracks with widths ?Wmin, then Acum plotted against Wmin shows a typical reproducible shape. In a log?log plot, this curve has two roughly linear regions with different slopes. For a polypropylene (PP) substrate, there is a sharp change from a nearly horizontal line to a very steep line, whereas for a glass substrate, which is smoother, there is a gradual changeover between the two regions. We propose a simple one-dimensional spring chain model, in which reducing the natural length of the springs corresponds to the desiccation process. Springs may break, or slip against the substrate to accommodate strain beyond a specified threshold. The model successfully reproduces the successive stages of crack formation and behaviour of the cumulative area curve, as observed in experiments. The difference in the qualitative nature of the patterns on smooth and rougher substrates is also obtained.

Desiccation of a clay film: Cracking versus peeling

We report a simulation study on competition between cracking and peeling, in a layer of clay on desiccation and how this is affected by the rate of drying, as well as the roughness of the substrate. The system is based on a simple 2-dimensional spring model. A vertical section through the layer with finite thickness is represented by a rectangular array of nodes connected by linear springs on a square lattice. The effect of reduction of the natural length of the springs, which mimics the drying is studied. Varying the strength of adhesion between sample and substrate and the rate of penetration of the drying front produces an interesting phase diagram, showing cross-over from peeling to cracking behavior. Changes in the number and width of cracks on varying the layer thickness is observed to reproduce experimental reports.

Effect of Chemical Kinetics on Permeability of a Porous Rock Scaling by Concentration of Active Fluid

Pores and fractures in rocks are continuously being reshaped through different chemical and physical processes. Fluids filling the pore space and carrying different chemical species are responsible for these changes. In the present work, we study the effort of chemical kinetics on the reshaping of pore structure and thereby on permeability. A simulation study is carried on a two-dimentional random porous structure. The particles permeate with a constant Peclet number, and their diffusion is represented through a random walk. Changing the probability of interaction varies the strength of the chemical reaction between the fluid and the rock. This study is done for different concentrations for the active material in the fluid. A scaling law is found to exist between the changes in permeability with reaction rate.