Abstract
Polymer adsorption is a fundamental problem in statistical mechanics that has direct relevance to diverse disciplines ranging from biological lubrication to stability of colloidal suspensions. We combine experiments with computer simulations to investigate depletion induced adsorption of semi-flexible polymers onto a hard-wall. Three dimensional filament configurations of partially adsorbed F-actin polymers are visualized with total internal reflection fluorescence microscopy. This information is used to determine the location of the adsorption/desorption transition and extract the statistics of trains, tails and loops of partially adsorbed filament configurations. In contrast to long flexible filaments which primarily desorb by the formation of loops, the desorption of stiff, finite-sized filaments is largely driven by fluctuating filament tails. Simulations quantitatively reproduce our experimental data and allow us to extract universal laws that explain scaling of the adsorption-desorption transition with relevant microscopic parameters. Our results demonstrate how the adhesion strength, filament stiffness, length, as well as the configurational space accessible to the desorbed filament can be used to design the characteristics of filament adsorption and thus engineer properties of composite biopolymeric materials.
Highlights
In comparison to simple rigid molecules whose adsorption can be described by straightforward two-state models, the adsorption of complex molecules with internal degrees of freedom, such as polymeric chains, requires development of more intricate theories
The instantaneous 3D configurations of a partially adsorbed filament were extracted from Total Internal Reflection Fluorescence (TIRF) Microscopy images
At low depletant concentrations the vast majority of filaments are largely desorbed from the wall (Fig. 1b and c(i)). When such samples are viewed with TIRF microscopy, one occasionally observes short filament segments that briefly remain in the evanescent field
Summary
In comparison to simple rigid molecules whose adsorption can be described by straightforward two-state models, the adsorption of complex molecules with internal degrees of freedom, such as polymeric chains, requires development of more intricate theories. The complication arises because certain segments of an adsorbed filament can be surface bound while other segments within the same molecule remain desorbed. This qualitative change in behavior requires development of theoretical models of adsorption transition that can account for internal degrees of freedom of polymeric chains.[1,2,3,4,5,6,7,8,9,10,11,12] At a fundamental level the configurations of a partially adsorbed polymer can be described a Graduate Program in Biophysics and Structural Biology, Brandeis University, Waltham, MA 02454, USA.
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