Layer-by-layer films for tunable and rewritable control of contact electrification

Abstract

Charges generated by contact of solid surfaces (contact electrification) can be hazardous or useful depending on the circumstance. This paper describes a process to design a solid surface rationally to either induce or prevent charging during contact electrification; this process coats the surface with polyelectrolytes. It is observed experimentally that a surface coated with a layer of a polymer having multiple, covalently attached positive charges (a "polycation") develops a positive charge after contacting another surface; a surface coated with a layer of polymer having negative charges (a "polyanion") develops a negative charge. By coating the surface using layerby-layer (LBL) deposition, the tendency of the surface to charge either positively or negatively can be switched: adding a layer of polyelectrolyte with charge opposite to the charge on the surface switches the polarity of the surface. Through microcontact printing (µCP), the surface can be stamped to create a mosaic pattern of polycation and polyanion -and importantly, the fraction of the surface area covered with polycation and polyanion can be tuned by using stamps of different patterns. Using poly(diallyldimethylammonium chloride) (PDDA) as the polycation and poly(sodium 4-styrenesulfonate) (PSS) as the polyanion, it is found that for a surface with >75% PSS, the surface charges negatively; with <75% PSS, the surface charges positively. At ~75% PSS, the surface becomes non-charging. The patterns on the surface can, subsequently, be erased through coating the surface with a uniform layer of polyelectrolyte. After erasing, the surface is rewritable by depositing or patterning the surface with a desired polyelectrolyte.

Complete Prevention of Contact Electrification by Molecular Engineering

“…Our electrostatically homogeneous antistatic surface shows pronounced advantages over existing electrostatically heterogeneous antistatic surfaces. [24][25][26][27] Existing antistatic surfaces rely on careful control of the size and spatial distribution of patterns so as to achieve neutralization of the positive and negative charges (in Fig- ure 4C). In this case, the antistatic effect in localized areas may break down owing to the mismatch in the amount of positive and negative charges (in Figure 4C).…”

“…15,[20][21][22][23] These chemically heterogeneous coatings are spatially patterned with distinctive chemical components that tend to gain positive and negative charges, achieving a collective charge neutralization and electrostatic heterogeneity on the whole surface after contact electrification. [24][25][26][27] However, these electrostatically heterogeneous coatings are susceptible to several drawbacks. First, the patterns should be constructed using distinctive chemical components that possess strong charging capability to gain positive and negative charges.…”

Controlling Surface Charge Generated by Contact Electrification: Strategies and Applications

“…Hence, a surface covered with positively (or negatively) charged ionic molecules can gain a positive (or negative) charge after contact. A similar phenomenon has also been observed for layer‐by‐layer deposition of strong polyelectrolytes (e.g., poly(diallyldimethylammonium chloride) or poly(sodium 4‐styrenesulfonate)) . In general, many different types of coating (e.g., polymer grafting, dip coating, and many others) and methods for treating the surface (e.g., plasma or other chemical functionalization, such as oxidation or sulphonation) have been used for changing the amount and polarity of charge generated on surfaces …”

Extensional Rheological Measurements of Surfactant–Polymer Mixtures

“…Typically, NaCl tends to dissociate into Na + and Cl – ions in solution where Na + deposits on negatively charged polymer chains. 38 With increasing concentration, this increasing deposition progressively screens the charge present on the polymer chains. A complete screening of charges is expected at high NaCl concentration, which results in a significant loss of extensional resistance to break up.…”