Molecularly Capped Omniphobic Polydimethylsiloxane Brushes with Ultra‐Fast Contact Line Dynamics

Abstract

Droplet friction is common and significant in any field where liquids interact with solid surfaces. This study explores the molecular capping of surface‐tethered, liquid‐like polydimethylsiloxane (PDMS) brushes and its substantial effect on droplet friction and liquid repellency. By exchanging polymer chain terminal silanol groups for methyls using a single‐step vapor phase reaction, the contact line relaxation time is decreased by three orders of magnitude–from seconds to milliseconds. This leads to a substantial reduction in the static and kinetic friction of both high‐ and low‐surface tension fluids. Vertical droplet oscillatory imaging confirms the ultra‐fast contact line dynamics of capped PDMS brushes, which is corroborated by live contact angle monitoring during fluid flow. This study proposes that truly omniphobic surfaces should not only have very small contact angle hysteresis, but their contact line relaxation time should be significantly shorter than the timescale of their useful application, i.e., a Deborah number less than unity. Capped PDMS brushes that meet these criteria demonstrate complete suppression of the coffee ring effect, excellent anti‐fouling behavior, directional droplet transport, increased water harvesting performance, and transparency retention following the evaporation of non‐Newtonian fluids.

Maximizing Biochemical and Energy Recovery from Wastewater Using Vapor-Gap Membranes

“…The tighter regulation on these chemicals motivates the development of non-toxic low surface energy materials. Recent efforts have demonstrated a certain level of surface omniphobicity using non-fluorinated chemicals, albeit with less wetting resilience than long-chain fluorinated organosilanes. − Active research efforts on membrane distillation for desalination will certainly benefit omniphobic, fluorine-free VGM development.…”

All-atom molecular dynamics simulations of polymer and polyelectrolyte brushes

“…Since there is no net charge on the polymer chains, the chemical functional groups of the polymer chains play a vital role in determining the properties exhibited by such brushes. Some widely used uncharged polymer brushes are poly( N -isopropyl acrylamide) or PNIPAM, which is known for their thermos-responsive properties; 116 polyethylene oxide or PEO, known for their biocompatibility properties 117 as well as their ion-conducting properties (leveraged in fabricating solid polymer electrolytes 118 ); polypropylene oxide (PPO); 119 polydimethylsiloxane (PDMS); 120 etc. The chemical structures for the monomers of some of these different uncharged polymer chains have been provided in Fig.…”

Synthesis of Vinyl-Containing Polydimethylsiloxane in An Active Medium

“…Introducing ethyl substituents decreases the glass transition temperature [ 12 , 13 ], while polar substituents enhance dielectric permittivity and intermolecular interaction [ 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. Hydride functional groups in polysiloxane main chains may serve various purposes, including utilization in hydrophobicity, in polyadditional compositions as crosslinking agents [ 21 , 22 ], and alongside vinyl-containing polysiloxanes as matrices for polymeranalogical transformations [ 23 , 24 ]. Hydrothiolation, entailing the addition of thiols to substitutes containing unsaturated bonds, has gained substantial traction in polymer modification [ 14 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ].…”