Biocompatible nanoparticles have recently attracted significant attention due to increasing interest in their use for
biological sensing, cellular labeling and in vivo imaging. Semiconductor quantum dots (QDs) with good colloidal
stability as well as small hydrodynamic sizes are particularly useful within these applications. We have developed a
series of dihydrolipoic acid (DHLA) based surface ligands to enhance the colloidal stability and biocompatibility of
water soluble QDs. Modification of DHLA with poly(ethylene glycol) derivatives provided the QDs with extended
colloidal stability over a wide pH range and under high salt concentrations, which contrasts with the limited colloidal
stability provided by DHLA alone. Functionalization of the PEG termini enabled one to have easy access to the QD
surface and construct a variety of stable QD-biomolecules conjugates. A series of DHLA-based compact ligands with
zwitterionic character has also been explored to develop compact sized QDs without sacrificing the colloidal stability.
Despite their smaller sizes than the PEG analogs, the QDs coated with the zwitterionic ligands still have excellent
colloidal stability and minimize nonspecific interactions in biological environments. Recent studies of thiol-based
multidentate ligands and ligand exchange methods further improved the colloidal stability and fluorescence quantum
yields.
We investigate the influence of ionic liquids on the electromechanical performance of Ionic Polymer Conductor Network
Composite (IPCNC) bending actuators. Two imidazolium ionic liquids (ILs) with one cation, which is 1-ethyl-3-
methylimidazolium ([EMI+]), and two different anions, which are tetrafluoroborate ([BF4-]) and
trifluoromethanesulfonate ([Tf-]), are chosen for the study. By combining the time domain electric and
electromechanical responses, we developed a new model that describes the ion transports in IPCNC actuators. The time
constant of excess cation and anion migration in various composite electrodes are deduced: 6s and 25s in RuO2/Nafion;
7.9s and 36.3s in RuO2/Aquivion; 4.8s and 53s in Au/PAH, respectively. NMR is also applied to provide quantitative
measures of self-diffusion coefficients independently for IL anions and cations both in pure ILs and in ILs absorved into
ionomers. All the results indicate that the motion of cation, in the studied pure ionic liquids, polymer matrix and
conductor network composites, is faster than that of anion. Moreover, the CNC morphology is playing a crucial role in
determining the ion transport in the porous electrodes.
Traditional ionic polymer/conductor network composite (IPCNC) electromechanical actuators exhibit low actuation
speed and efficiency. In order to improve these parameters while still maintaining low voltage operation, we investigated
IPCNC with a range of composite layer (active layer) and middle ionomer layer (passive layer) thicknesses. We show
that it is the slow ion transport in the porous composite electrode layer that limits the actuation speed of IPCNCs. By
reducing the thickness of the composite electrode layers, both the actuation speed and efficiency can be improved.
Moreover, we show that the IPCNC actuator speed and efficiency are intimately related to the morphology of the
composite electrode layer and the conductor network composites fabricated by ionic self-assembled layer-by-layer
(LBL) exhibit higher strain response compared with that from the traditional IPCNC. For example, LBL composites
show very high intrinsic strain of about 7%. Detailed device analysis points out directions of further improvement of
these actuators.
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