Insulating materials
with a low dielectric constant and a low dielectric
loss are in high demand to meet requirements of the continuous miniaturization
of electronic devices and high speed information transmission. We
fabricated porous polyimide/reduced graphene oxide (PI/rGO) hybrid
films with an ultralow dielectric constant and a low dielectric loss
via a facile “blow-balloon” method. Poly(ethylene glycol)
(PEG) was used as a pore-forming agent by mixing with polyamide acid
carboxylate (PAAC) and GO in water. The ternary mixture of PAAC/GO/PEG
formed a hydrogel and dried naturally into a xerogel film. Porous
PI/rGO films were obtained by in situ thermal pyrolysis of PEG through
heating PAAC/GO/PEG hybrid films to 400 °C. The homogeneous porous
structure could be regulated easily by adjusting the mass ratio of
PEG to PAAC/GO. The porous structure inside the hybrid films prepared
by the hydrogel method provided the PI/rGO films with an ultralow
dielectric constant (κ) as low as 1.9 and a high ductility with
an average elongation at break above 38%. This porous PI/rGO film
with an ultralow κ value may be a promising candidate for next-generation
interlayer dielectrics.
A fluorescent and robust superhydrophobic coating based on a fluorinated polypyrene/silica hybrid film was prepared readily on the large-scale substrates.
Polyimide/inorganics
hybrid films fabricated by conventional approaches,
including an in situ polymerization method, the sol–gel process,
and a solution blending method, have a dramatic drop in malleability.
In this work, a hydrogel strategy for preparing ductile polyimide/reduced
graphene oxide (PI/rGO) nanohybrid films with internal porous structures
has been proposed. The hydrogel strategy involved two steps. The polyamide
acid carboxylate/GO (PAAC/GO) films were first prepared by tape casting,
followed by a gelation process of the PAAC/GO aqueous solution; the
PI/rGO films were then obtained after an imidization reaction of the
PAAC/GO films. Interestingly, in this strategy, the PAA chains tended
to self-assemble into microdomain crystalline structures assisted
by their interactions with water, as revealed by XRD and Raman spectroscopy.
The present PI/rGO films display more uniform microstructures, without
aggregation of the rGO nanosheets. Furthermore, they exhibited an
enhanced toughness property, with a high elongation at break of 37–55%.
In addition, their dielectric property is more stable and less frequency-dependent
due to the internal porous structure. This hydrogel strategy would
appear to be a promising candidate for fabricating hybrid PI–inorganic
composite materials, even other hybrid organic/inorganic composite
materials with specific features.
A polyvinylidene fluoride (PVDF) membrane was modified by a low temperature plasma treatment and grafted with cross-linked collagen. The crosslinker of collagen was glutaraldehyde. The effects of glutaraldehyde concentration, crosslinking time and crosslinking temperature on membrane properties and surface structure were investigated. The properties of the modified membrane were characterized by the contact angle and pure water flux. The surface structure of the membrane dyed with an acid dye was observed by a polarizing microscope. The modified membrane was further characterized concerning permeability and adsorption capacity. Bovine serum albumin (BSA) was used as a model protein. The cell culture ability of the membrane was examined by the methyl thiazolyl tetrazolium (MTT) method. The amount of grafted collagen on the membrane surface reached the maximum when collagen was cross-linked with 0.4 wt% glutaraldehyde for 1 h at 35 C. The BSA adsorption capacity and cell culture ability examination indicated that the PVDF membrane grafted with cross-linked collagen had good hydrophilicity and biocompatibility.
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