Poly(tetrafluoroethylene) is Unique for Orienting Molecules

Abstract

A physical insight regarding poly(tetrafluoroethylene) (PTFE) is revealed herein. The driving force for the oriented growth of materials on aligned PTFE is investigated. The growth has been reported in numerous publications for a wide range of deposited materials on aligned PTFE layers since its discovery in 1991 because it is a promising method for preparing ordered molecular films. MD model simulations demonstrate herein that the shallow charged atomic grooves between adjacent PTFE chains trap typical two linear molecules, thus explaining the remarkable degrees of uniaxial orientation in their deposited thin films on the layers. Charge modifications to the model demonstrate for the first time that the negative charge of its fluorine atoms is crucial for the remarkable degrees. Hence, such an orientation is only possible with PTFE. Poly(tetrafluoroethylene) (PTFE) is regarded as the king of specialty plastic since its accidental discovery in 1938 by Plunkett.1 Currently, approximately 10 5 tons of PTFE is produced every year.2 Although this amount does account not for 1% of whole synthetic plastic, PTFE plays an irreplaceable role in various applications ranging from non-stick frying pans for kitchens to the chamber lining for corrosive uranium hexafluoride.2 Without PTFE, two atomic bombs would not have exploded in Japan. The outstanding character of PTFE is attributable to its robust CF bonds, which render PTFE extremely inert. 3The first author was specifically interested by a letter 4 and we have been keeping this first interest for over two decades. The oriented growth on PTFE was reported there and it is a promising method for preparing ordered molecular films; highly aligned PTFE thin layers are prepared by friction-transfer (FT) (or a rubbing procedure found later by us), 5 and the materials are merely deposited on the layers. Furthermore, linear molecules such as 1 (Figure 1) nanotubes, 25 and nanocomposites 26 ). For applying their thin films to molecular devices, such orientation is needed to enhance their functions such as carrier mobility 13,2729 and nonlinear optical properties. 7,12 Moreover, an intrinsic query has been nourishing our interest for so long. It remains unknown why this remarkable orientation takes place on extremely inert PTFE layers, e.g., nonsticking and poor wetting materials. An interesting question is: what happens between the orienting molecules and inert PTFE?Linear molecules orient along the atomic grooves between adjacent PTFE chains. We demonstrated previously through an MD simulation that the atomic grooves align some linear molecules including 1 (Figure 1) by trapping them along the grooves. 11The direction of linear molecules should be thus oriented in their early nuclei on which the growth further takes place somewhat epitaxially. Such grooves are shown in Figures 1a1c. However, it has been an open question whether the strong negative charge of F also contributes to trapping on the grooves or not. We report herein such a contribution for the first time.If this atomi...

Role of Molecular Chains Arrangement and Surface Energy State in the Low Ice Adhesion on Poly(tetrafluoroethylene)

“…The energy difference between the peak and the trough reaches 3.16 kcal/mol, about 2.4 times of that in the x direction, creating a large energy barrier for the movement of the ice layer, as shown in Figure b. It is noticed that the distance between two energy peaks is similar to the distance between molecular chains (5.4 nm) Figure c demonstrates the energy state distribution of water molecules on crystalline PTFE surfaces.…”

“…It is noticed that the distance between two energy peaks is similar to the distance between molecular chains (5.4 nm). 32 Figure 3c demonstrates the energy state distribution of water molecules on crystalline PTFE surfaces. The energy states of water molecules in molecular chains' gaps are significantly lower than that on another location, which proves that energy troughs appear in the molecular chains' gaps.…”

Fold Surfaces of Polymer Crystals Are Nucleation Sites: The Link between Polymer Decoration, Secondary Crystallization, and the Rigid Amorphous Fraction (RAF)

“…This variety underlines the relative ease with which mild interactions may induce orientation. Similar, mostly quasi- or graphoepitaxy-type substrate–deposit interactions are at play for friction-oriented PTFE films and different deposits, both organic or polymeric materials. − …”