3 research outputs found
Layer-by-Layer Assembly of Amine-Reactive Multilayers Using an Azlactone-Functionalized Polymer and Small-Molecule Diamine Linkers
We report the reactive
layer-by-layer assembly of amine-reactive
polymer multilayers using an azlactone-functionalized polymer and
small-molecule diamine linkers. This approach yields cross-linked
polymer/linker-type films that can be further functionalized, after
fabrication, by treatment with functional primary amines, and provides
opportunities to incorporate other useful functionality that can be
difficult to introduce using other polyamine building blocks. Films
fabricated using poly(2-vinyl-4,4-dimethylazlactone) (PVDMA) and three
model nondegradable aliphatic diamine linkers yielded reactive thin
films that were stable upon incubation in physiologically relevant
media. By contrast, films fabricated using PVDMA and varying amounts
of the model disulfide-containing diamine linker cystamine were stable
in normal physiological media, but were unstable and eroded rapidly
upon exposure to chemical reducing agents. We demonstrate that this
approach can be used to fabricate functionalized polymer microcapsules
that degrade in reducing environments, and that rates of erosion,
extents of capsule swelling, and capsule degradation can be tuned
by control over the relative concentration of cystamine linker used
during fabrication. The polymer/linker approach used here expands
the range of properties and functions that can be designed into reactive
PVDMA-based coatings, including functionality that can degrade, erode,
and undergo triggered destruction in aqueous environments. We therefore
anticipate that these approaches will be useful for the functionalization,
patterning, and customization of coatings, membranes, capsules, and
interfaces of potential utility in biotechnical or biomedical contexts
and other areas where degradation and transience are desired. The
proof of concept strategies reported here are likely to be general,
and should prove useful for the design of amine-reactive coatings
containing other functional structures by judicious control of the
structures of the linkers used during assembly
Surfactant-Induced Ordering and Wetting Transitions of Droplets of Thermotropic Liquid Crystals “Caged” Inside Partially Filled Polymeric Capsules
We
report a study of the wetting and ordering of thermotropic liquid
crystal (LC) droplets that are trapped (or “caged”)
within micrometer-sized cationic polymeric microcapsules dispersed
in aqueous solutions of surfactants. When they were initially dispersed
in water, we observed caged, nearly spherical droplets of E7, a nematic
LC mixture, to occupy ∼40% of the interior volume of the polymeric
capsules [diameter of 6.7 ± 0.3 μm, formed via covalent
layer-by-layer assembly of branched polyethylenimine and poly(2-vinyl-4,4-dimethylazlactone)]
and to contact the interior surface of the capsule wall at an angle
of ∼157 ± 11°. The internal ordering of LC within
the droplets corresponded to the so-called bipolar configuration (distorted
by contact with the capsule walls). While the effects of dodecyltrimethylammonium
bromide (DTAB) and sodium dodecyl sulfate (SDS) on the internal ordering
of “free” LC droplets are similar, we observed the two
surfactants to trigger strikingly different wetting and configurational
transitions when LC droplets were caged within polymeric capsules.
Specifically, upon addition of SDS to the aqueous phase, we observed
the contact angles (θ) of caged LC on the interior surface of
the capsule to decrease, resulting in a progression of complex droplet
shapes, including lenses (θ ≈ 130 ± 10°), hemispheres
(θ ≈ 89 ± 5°), and concave hemispheres (θ
< 85°). The wetting transitions induced by SDS also resulted
in changes in the internal ordering of the LC to yield states topologically
equivalent to axial and radial configurations. Although topologically
equivalent to free droplets, the contributions that surface anchoring,
LC elasticity, and topological defects make to the free energy of
caged LC droplets differ from those of free droplets. Overall, these
results and others reported herein lead us to conclude that caged
LC droplets offer a platform for new designs of LC-droplet-based responsive
soft matter that cannot be realized in dispersions of free droplets