5 research outputs found
Salt-Responsive Bilayer Hydrogels with Pseudo-Double-Network Structure Actuated by Polyelectrolyte and Antipolyelectrolyte Effects
Development
of stimuli-responsive, shape-transformable materials
is fundamentally and practically important for smart actuators. Herein,
we design and synthesize a bilayer hydrogel by assembling a polycationic
(polyMETAC/HEAA) layer with polyelectrolyte effect and a polyzwitterionic
(polyVBIPS) layer with antipolyelectrolyte effect together. The bilayer
hydrogels adopt a pseudo-double-network structure, and both polyelectrolyte
and polyzwitterionic layers have salt-responsive swelling and shrinkage
properties, but in a completely opposite way. The resulting polyMETAC/HEAAâpolyVBIPS
bilayer hydrogels exhibit bidirectional bending in response to salt
solutions, salt concentrations, and counterion types. Such bidirectional
bending of this bilayer hydrogel is fully reversible and triggered
between salt solution and pure water multiple times. The bending orientation
and degree of the bilayer hydrogel is driven by the opposite volume
changes between the volume shrinking (swelling) of polyMETAC/HEAA
layer and the volume swelling (shrinking) of polyVBIPS layer. Such
cooperative, not competitive, salt-responsive swellingâshrinking
properties of the two layers are contributed to by the polyelectrolyte
and antipolyelectrolyte effects from the respective layers. Moreover,
an eight-arm gripper made of this bilayer hydrogel is fabricated and
demonstrates its ability to grasp an object in salt solution and release
the object in water. This work provides a new shape-regulated, stimuli-responsive
asymmetric hydrogel for actuator-based applications
Salt-Responsive Zwitterionic Polymer Brushes with Tunable Friction and Antifouling Properties
Development
of smart, multifunction materials is challenging but
important for many fundamental and industrial applications. Here,
we synthesized and characterized zwitterionic polyÂ(3-(1-(4-vinylÂbenzyl)-1<i>H</i>-imidazol-3-ium-3-yl)Âpropane-1-sulfonate) (polyVBIPS) brushes
as ion-responsive smart surfaces via the surface-initiated atom transfer
radical polymerization. PolyVBIPS brushes were carefully characterized
for their surface morphologies, compositions, wettability, and film
thicknesses by atomic force microscopy (AFM), X-ray photoelectron
spectroscopy (XPS), contact angle, and ellipsometer, respectively.
Salt-responsive, switching properties of polyVBIPS brushes on surface
hydration, friction, and antifouling properties were further examined
and compared both in water and in salt solutions with different salt
concentrations and counterion types. Collective data showed that polyVBIPS
brushes exhibited reversible surface wettability switching between
in water and saturated NaCl solution. PolyVBIPS brushes in water induced
the larger protein absorption, higher surface friction, and lower
surface hydration than those in salt solutions, exhibiting âanti-polyelectrolyte
effectâ salt responsive behaviors. At appropriate ionic conditions,
polyVBIPs brushes were able to switch to superlow fouling surfaces
(<0.3 ng/cm<sup>2</sup> protein adsorption) and superlow friction
surfaces (<i>u</i> ⌠10<sup>â3</sup>). The
relationship between brush structure and its salt-responsive performance
was also discussed. This work provides new zwitterionic surface-responsive
materials with controllable antifouling and friction capabilities
for multifunctional applications
Structural Dependence of Salt-Responsive Polyzwitterionic Brushes with an Anti-Polyelectrolyte Effect
Some
polyzwitterionic brushes exhibit a strong âanti-polyelectrolyte
effectâ and ionic specificity that make them versatile platforms
to build smart surfaces for many applications. However, the structureâproperty
relationship of zwitterionic polymer brushes still remains to be elucidated.
Herein, we aim to study the structure-dependent relationship between
different zwitterionic polymers and the anti-polyelectrolyte effect.
To this end, a series of polyzwitterionic brushes with different cationic
moieties (e.g., imidazolium, ammonium, and pyridinium) in their monomeric
units and with different carbon spacer lengths (e.g., CSL = 1, 3,
and 4) between the cation and anion were designed and synthesized
to form polymer brushes via the surface-initiated atom transfer radical
polymerization. All zwitterionic brushes were carefully characterized
for their surface morphologies, compositions, wettability, and film
thicknesses by atomic force microscopy, contact angle measurement,
and ellipsometry, respectively. The salt-responsiveness of all zwitterionic
brushes to surface hydration and friction was further examined and
compared both in water and in salt solutions with different salt concentrations
and counterion types. The collective data showed that zwitterionic
brushes with different cationic moieties and shorter CSLs in salt
solution induced higher surface friction and lower surface hydration
than those in water, exhibiting strong anti-polyelectrolyte effect
salt-responsive behaviors. By tuning the CSLs, cationic moieties,
and salt concentrations and types, the surface wettability can be
changed from a highly hydrophobic surface (âŒ60°) to a
highly hydrophilic surface (âŒ9°), while interfacial friction
can be changed from ultrahigh friction (ÎŒ â 4.5) to superior
lubrication (ÎŒ â 10<sup>â3</sup>). This work provides
important structural insights into how subtle structural changes in
zwitterionic polymers can yield great changes in the salt-responsive
properties at the interface, which could be used for the development
of smart surfaces for different applications
Dual Salt- and Thermoresponsive Programmable Bilayer Hydrogel Actuators with Pseudo-Interpenetrating Double-Network Structures
Development of smart
soft actuators is highly important for fundamental research and industrial
applications but has proved to be extremely challenging. In this work,
we present a facile, one-pot, one-step method to prepare dual-responsive
bilayer hydrogels, consisting of a thermoresponsive polyÂ(<i>N</i>-isopropylacrylamide) (polyNIPAM) layer and a salt-responsive polyÂ(3-(1-(4-vinylbenzyl)-1<i>H</i>-imidazol-3-ium-3-yl)Âpropane-1-sulfonate) (polyVBIPS) layer.
Both polyNIPAM and polyVBIPS layers exhibit a completely opposite
swelling/shrinking behavior, where polyNIPAM shrinks (swells) but
polyVBIPS swells (shrinks) in salt solution (water) or at high (low)
temperatures. By tuning NIPAM:VBIPS ratios, the resulting polyNIPAM/polyVBIPS
bilayer hydrogels enable us to achieve fast and large-amplitude bidirectional
bending in response to temperatures, salt concentrations, and salt
types. Such bidirectional bending, bending orientation, and degree
can be reversibly, repeatedly, and precisely controlled by salt- or
temperature-induced cooperative swellingâshrinking properties
from both layers. Based on their fast, reversible, and bidirectional
bending behavior, we further design two conceptual hybrid hydrogel
actuators, serving as a six-arm gripper to capture, transport, and
release an object and an electrical circuit switch to turn on-and-off
a lamp. Different from the conventional two- or multistep methods
for preparation of bilayer hydrogels, our simple, one-pot, one-step
method and a new bilayer hydrogel system provide an innovative concept
to explore new hydrogel-based actuators through combining different
responsive materials that allow us to program different stimuli for
soft and intelligent materials applications
Dual Salt- and Thermoresponsive Programmable Bilayer Hydrogel Actuators with Pseudo-Interpenetrating Double-Network Structures
Development of smart
soft actuators is highly important for fundamental research and industrial
applications but has proved to be extremely challenging. In this work,
we present a facile, one-pot, one-step method to prepare dual-responsive
bilayer hydrogels, consisting of a thermoresponsive polyÂ(<i>N</i>-isopropylacrylamide) (polyNIPAM) layer and a salt-responsive polyÂ(3-(1-(4-vinylbenzyl)-1<i>H</i>-imidazol-3-ium-3-yl)Âpropane-1-sulfonate) (polyVBIPS) layer.
Both polyNIPAM and polyVBIPS layers exhibit a completely opposite
swelling/shrinking behavior, where polyNIPAM shrinks (swells) but
polyVBIPS swells (shrinks) in salt solution (water) or at high (low)
temperatures. By tuning NIPAM:VBIPS ratios, the resulting polyNIPAM/polyVBIPS
bilayer hydrogels enable us to achieve fast and large-amplitude bidirectional
bending in response to temperatures, salt concentrations, and salt
types. Such bidirectional bending, bending orientation, and degree
can be reversibly, repeatedly, and precisely controlled by salt- or
temperature-induced cooperative swellingâshrinking properties
from both layers. Based on their fast, reversible, and bidirectional
bending behavior, we further design two conceptual hybrid hydrogel
actuators, serving as a six-arm gripper to capture, transport, and
release an object and an electrical circuit switch to turn on-and-off
a lamp. Different from the conventional two- or multistep methods
for preparation of bilayer hydrogels, our simple, one-pot, one-step
method and a new bilayer hydrogel system provide an innovative concept
to explore new hydrogel-based actuators through combining different
responsive materials that allow us to program different stimuli for
soft and intelligent materials applications