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The force, f, required to slide a drop on a surface is shown to be a growing function of the time, t, that the drop waited resting on the surface prior to the commencement of sliding. In this first report on the resting time effect, we demonstrate the existence of this phenomenon in different systems, which suggests that this phenomenon is general. We show that d f/d t is never negative. The shorter the resting times, the higher d f/d t is. As the resting time increases, d f/d t decreases toward zero (plateau) as t --> infinity. The increase in the force, Delta f, due to the resting time effect (i.e., f( t --> infinity) - f( t --> 0)) correlates well with the vertical component of the liquid-vapor surface tension, and we attribute this phenomenon to the corrugation of the surface by the drop due to this unsatisfied normal component of Young's equation.

The force, f, required to slide a drop past a surface is often considered in the literature as linear with the drop width, w, so that f/w = const. Furthermore, according to the Dussan equation for the case that the advancing and receding contact angles are constant with drop size, one can further simplify the above proportionality to f/V(1/3) = const where V is the drop volume. We show, however, that experimentally f/V(1/3) is usually a decaying function of V (rather than constant). The retention force increases with the time the drop rested on the surface prior to sliding. We show that this rested-time effect is similar for different drop sizes, and thus the change of f/V(1/3) with V occurs irrespective of the rested-time effect which suggests that the two effects are induced by different physical phenomena. The time effect is induced by the unsatisfied normal component of the Young equation which slowly deforms the surface with time, while the size effect is induced by time independent properties. According to the Dussan equation, the change of f/V(1/3) with V is also expressed in contact angle variation. Our results, however, show that contact angle variation that is within the scatter suffices to explain the significant force variation. Thus, it is easier to predict contact angle variation based on force variation rather than predicting force variation based on contact angle variation. A decrease of f/V(1/3) with V appears more common in the system studied compared to an increase.

Simple and efficient methods are a key consideration for small molecule and polymer syntheses. Direct arylation polymerization (DArP) is of increasing interest for preparing conjugated polymers as an effective approach compared to conventional cross-coupling polymerizations. As DArP sees broader utilization, advancements are needed to access materials with improved properties and different monomer structures and to improve the scalability of conjugated polymer synthesis. Presented herein are considerations for developing new methods of conjugated polymer synthesis from small molecule transformations, exploring how DArP has successfully used this approach, and presenting how emerging polymerization methodologies are developing similarly. While it is common to adapt small molecule methods to polymerizations, we demonstrate the ways in which information gained from studying polymerizations can inform and inspire greater advancements in small molecule transformations. This circular approach to organic synthetic method development underlines the value of collaboration between small molecule and polymer-based synthetic research groups.