Abstract
Here we report a link between the interfacial structure and adhesive property of homopolymer chains physically adsorbed (i.e., via physisorption) onto solids. Polyethylene oxide (PEO) was used as a model and two different chain conformations of the adsorbed polymer were created on silicon substrates via the well-established Guiselin's approach: "flattened chains" which lie flat on the solid and are densely packed, and "loosely adsorbed polymer chains" which form bridges jointing up nearby empty sites on the solid surface and cover the flattened chains. We investigated the adhesion properties of the two different adsorbed chains using a custom-built adhesion testing device. Bilayers of a thick PEO overlayer on top of the flattened chains or loosely adsorbed chains were subjected to the adhesion test. The results revealed that the flattened chains do not show any adhesion even with the chemically identical free polymer on top, while the loosely adsorbed chains exhibit adhesion. Neutron reflectivity experiments corroborated that the difference in the interfacial adhesion is not attributed to the interfacial brodening at the free polymer-adsorbed polymer interface. Instead, coarse-grained molecular dynamics simulation results suggest that the tail parts of the loosely adsorbed chains act as "connector molecules", bridging the free chains and substrate surface and improving the interfacial adhesion. These findings not only shed light on the structure-property relationship at the interface, but also provide a novel approach for developing sticking/anti-sticking technologies through precise control of the interfacial polymer nanostructures.
Original language | English |
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Pages (from-to) | 1108-1119 |
Number of pages | 12 |
Journal | Soft Matter |
Volume | 14 |
Issue number | 7 |
DOIs | |
State | Published - 2018 |
Funding
We thank Steve Bennett and Jean Jordan-Sweet for the XR measurements, Jonathan Sokolov for the contact angle experiments. We also acknowledge Alexei P. Sokolov for his critical reading of the manuscript. T. K. acknowledges partial financial support from NSF Grant (CMMI-1332499). This research used Beamline X9 of the National Synchrotron Light Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contracts No. DE-AC02-98CH10886. Computational aspects of this work were performed at the Center for Nanophase Materials Sciences (CNMS), a DOE Office of Science User Facility. This research used resources of the Oak Ridge Leadership Computing Facility (OLCF) at the Oak Ridge National Laboratory (ORNL), which is supported by the Office of Science of the U.S. DOE under Contract DEAC05-00OR22725. The computational work by B. G. S and J.-M. Y. C was partially supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.