Vinyl addition polymers of substituted
norbornene (NB) monomers
possess very high glass-transition temperatures, making them useful
in diverse applications; however, until very recently, the lack of
an applicable living polymerization chemistry has precluded the synthesis
of such polymers with controlled architecture, or copolymers with
controlled sequence distribution. In the present work, block and random
copolymers of NB monomers bearing hydroxyhexafluoroisopropyl and n-butyl substituents (HFANB and BuNB) are synthesized via
living vinyl addition polymerization, using (η3-allyl)Pd(i-Pr3P)Cl activated by [Li(OEt2)2.5]B(C6F5)4 as the initiator.
Both series of polymers are cast into the selective skin layers of
thin film composite (TFC) membranes, and these organophilic membranes
are investigated for the concentration of n-butanol
from dilute aqueous solution via pervaporation. The block copolymers
show well-defined microphase-separated morphologies, both in bulk
and as the selective skin layers on TFC membranes, while the random
copolymers are homogeneous. Both block and random vinyl addition copolymers
are effective as n-butanol pervaporation membranes,
with the block copolymers showing a better flux-selectivity balance;
the optimal block copolymer, containing 19 wt % BuNB, showed
a process separation factor of 21 and a flux of 4300 g m–2 h–1 with a 1.00 wt % aqueous n-butanol feed, at a selective layer thickness of 1.3 μm. While
polyHFANB has much higher permeability and selectivity than polyBuNB,
incorporating BuNB units into the polymer (in either a block or random
sequence) limits the swelling of the polyHFANB and thereby improves
the n-butanol pervaporation selectivity. An analogous
block copolymer derived from ring-opening metathesis polymerization,
which shows much greater swelling than the vinyl addition polymers,
shows a correspondingly higher flux and lower selectivity.
We describe a method of fabrication of nanoporous flexible probes which work as artificial proboscises. The challenge of making probes with fast absorption rates and good retention capacity was addressed theoretically and experimentally. This work shows that the probe should possess two levels of pore hierarchy: nanopores are needed to enhance the capillary action and micrometer pores are required to speed up fluid transport. The model of controlled fluid absorption was verified in experiments. We also demonstrated that the artificial proboscises can be remotely controlled by electric or magnetic fields. Using an artificial proboscis, one can approach a drop of hazardous liquid, absorb it and safely deliver it to an analytical device. With these materials, the paradigm of a stationary microfluidic platform can be shifted to the flexible structures that would allow one to pack multiple microfluidic sensors into a single fiber.
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