Stimuli-Responsive Binary Mixed Polymer Brushes and Free-Standing Films by LbL-SIP

Abstract

We report a facile approach to preparing binary mixed polymer brushes and free-standing films by combining the layer-by-layer and surface-initiated polymerization (LbL-SIP) techniques. Specifically, the grafting of mixed polymer brushes of poly(n-isopropylacrylamide) and polystyrene (pNIPAM-pSt) onto LbL-macroinitiator-modified planar substrates is described. Atom transfer radical polymerization (ATRP) and free radical polymerization (FRP) techniques were employed for the syntheses of pNIPAM and pSt, respectively, yielding pNIPAM-pSt mixed polymer brushes. The composition of the two polymers was controlled by varying the number of macroinitiator layers deposited on the substrate (i.e., LbL layers = 4, 8, 12, 16, and 20); consequently, mixed brushes of different thicknesses and composition ratios were obtained. Moreover, the switching behavior of the LbL-mixed brush films as a function of solvent and temperature was demonstrated and evaluated by water contact angle and atomic force microscopy (AFM) experiments. It was found that both the solvent and temperature stimuli responses were a function of the mixed brush composition and thickness ratio where the dominant component played a larger role in the response behavior. Furthermore, the ability to obtain free-standing films was exploited. The LbL technique provided the macroinitiator density variation necessary for the preparation of stable free-standing mixed brush films. Specifically, the free-standing films exhibited the rigidity to withstand changes in the solvent and temperature environment and at the same time were flexible enough to respond accordingly to external stimuli.

Preparation and characterization of V-shaped PS-b-PEO brushes anchored on planar gold substrate through the trithiocarbonate junction group

“…Secondly, the mixed polymer brush is responsive to environmental stimuli, such as solvent atmosphere, and thus the surface composition and morphology of the mixed polymer brush is variable [12][13][14][15][16][17]. As a result, the surface properties of the mixed polymer brush can be tuned or switched by applying external stimuli [18][19][20][21][22][23][24][25][26][27][28][29]. Due to the interesting phase separation phenomena and the resulting smart properties of the mixed polymer brush, a substantial amount of theoretical [30][31][32][33][34][35][36][37][38][39][40][41][42] and experimental [43][44][45][46][47] work has been devoted to this field.…”

Effect of miscibility on migration of third component in star‐like co‐continuous and disperse‐within‐disperse mixed brushes

“…Polymer brushes, as a result of chains tethered onto a surface from one end, have different properties compared to bulk polymers . To obtain a combination of various characteristics for a surface‐grafted monolayer, polymer mixed brushes can be fabricated consisting of more than one type of polymer brush , . Because of their having various behaviours, these mixed‐brush structures are capable of introducing a wide range of morphologies in response to environmental stimuli, thereby representing an ample range of applications .…”

Free-Standing Macroinitiator Thin Film for Bifacial Polymer Chain Grafting

“…One limitation inherent to these kinds of films is having low‐density functional groups on the surface. Moreover, the success of the lift‐off process depends heavily on the mechanical strength of the film, which could be ensured by cross‐linking. However, cross‐linking further reduces the number of active sites available for interaction with the environment, and as a result, the sensitivity and functionality of the film is further lowered .…”

“…The stretching greatly prevents chain entanglement and, in effect, increases the density of functional group that can interact with the environment . Consequently, these polymer, commonly referred to as polymer brush, can respond quickly to small perturbations in its environment . Another advantage of surface grafting of polymer brush is the high degree of synthetic flexibility toward the introduction of a variety of functional groups, which is very challenging to achieve, for example, by spin casting …”

“…Our group has done several studies on the fabrication of intelligent surfaces by grafting polymer brushes on surfaces prefunctionalized by initiators . Homopolymer, block copolymer, and mixed polymer brushes were successfully grafted on the surface pre‐functionalized via LBL assembly of macroinitiators.…”