pH-responsive aqueous/LC interfaces using SGLCP-b-polyacrylic acid block copolymers

Abstract

Block copolymers that combine a side-group liquid crystalline polymer (SGLCP) block and a pH-responsive hydrophilic block, poly(acrylic acid) (PAA), are shown to confer pH-dependent anchoring of the director orientation at the aqueous/LC interface. The SGLCP block, poly-(4-cyanobiphenyl-4-oxyundecylacrylate), was chosen based on its ability to influence the director field of the 5CB (4-cyano-4 0 -pentylbiphenyl). At low pH the PAA block collapses and the inherent, planar alignment tendency of 5CB at a water interface prevails. As pH increases, the polyelectrolyte block becomes increasingly charged and expands, producing a change to homeotropic anchoring. The change in anchoring occurs as quickly as the buffer can be changed (within $2 s) and is reversible, with a response that is repeatable over as many cycles as were tested (approximately 20 cycles). The polymer-mediated anchoring persists for 6 days, indicating that the SGLCP block secures the self-assembled layer on the 5CB, even under conditions that cause repulsive interactions among the PAA blocks. Thus, SGLCP blocks can translate conformational changes of a responsive hydrophilic block into rapid, reversible changes in the director field.

Biosensor utilizing a liquid crystal/water interface functionalized with poly(4-cyanobiphenyl-4′-oxyundecylacrylate-b-((2-dimethyl amino) ethyl methacrylate))

“…A strong anionic polyelectrolyte such as salmon fish sperm DNA could be detected with this TEM PDMAEMA grid cell at a wide pH range below the pKa of PDMAEMA with a detection limit of 0.01 wt% because it contains negatively charged phosphate deoxyribose groups throughout its structure regardless of the pH. This simple and inexpensive set-up for non-specific biomaterial detection provides the basic groundwork for developing effective and selective biosensors through the introduction of specific binding groups such as aptamers, antibodies, single-stranded DNA, proteins, peptides, and aptamer-binding RNA into the cell [37].…”

“…The TEM grid cell and the flow chamber used in this study was prepared by the same procedure as reported elsewhere [37]. The glass slides were first cleaned using piranha solution (H 2 SO 4 and H 2 O 2 mixture (70/30, v/v)), which reacts violently with organic materials and should therefore be handled with extreme care and stored in closed containers.…”

“…An LC monomer, LC11, was prepared following a previously reported procedure [36,37]. LC11 monomers were synthesized through the etherification of 4-cyano-4 -hydroxybiphenyl (4.02 g, 20.62 mmol) and 11-bromo-1-undecanol (5.23 g, 20.80 mmol).…”

“…Since the polyelectrolyte-b-LCP can lead to micelle formation in the selected solvent (e.g. water), a facile strategy for incorporating the block copolymer into the LC molecules is to transfer the block copolymer monolayer, which was produced using a Langmuir Blodget (LB) trough, to the LC surface [33]. This method has advantages over the existing method of mixing receptor molecules with small LC molecules because the properties of monolayer can be easily controlled by adjusting the density of the receptor macromolecules per unit area [24].…”

Specific detection of avidin–biotin binding using liquid crystal droplets

“…CAUTION: Piranha solution is extremely corrosive and must be handled carefully. PAA-b-LCP was prepared using the same method reported previously [23]. The molecular weight was PAA(15k)-b-LCP(7k) with a M w /M n of 1.19; the number in parenthesis represents the number average molecular weight (M n ), which was calculated from the gel permeation chromatography (GPC) data of poly(tert-butyl acrylate) (PtBA)-b-LCP using 100% conversion.…”